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us CLIVAR U.S. CLIVAR Spring 2007, Vol. 5, No. 1 VARIATIONS Leaving a Legacy The VAMOS Ocean-Cloud- by David M. Legler, Director Atmosphere-Land Study (VOCALS) ne the challenges of CL I- VAR is encouraging and Oguiding studies that not only investigate processes impor- tant for the understanding and prediction of climate changes, but provide a legacy that is more than Robert Wood, University of Washington; C. Roberto Mechoso, University of a collection of dense obser va tions California, Los Angeles; Christopher Bretherton, University of Washington; Barr ove r a limited region and time Huebert, University of Hawaii; Robert Weller, Woods Hole Oceanographic Institution period. The No rth American Monsoon Ex periment, NAME, and most persistent subtropical stratocu- took place nearly 3 ye ars ago OCALS is one of the princi- mulus deck in the world. The presence of and is now focusing on the syn- pal activities of the this cloud deck has a major impact upon thesis of its results, its legacy of W C R P / C L I VAR VA M O S the earth’s radiation budget. improved observa tional require- panel, and has links with the Several fundamental problems are ments and improve d forecasting VGEWEX Cloud System Study (GCSS) barriers to the understanding of SEP’s capabilities. As NAME winds group. The Southeast Pacific (SEP) cli- weather and climate: These problems down, advance planning for a mate is a tightly coupled system involv- include the serious difficulties in the new study, VOCALS, is underway. ing poorly understood interactions quantification of the indirect effect of VOCALS will explore the challeng- between clouds, aerosols, marine bound- aerosols upon cloud radiative properties ing ocean-atmosphere dynamics ary layer (MBL) processes, upper ocean (e.g. Lohmann and Feichter 2005). Also, of the southeast Pacific and will dynamics and thermodynamics, coastal coupled atmosphere-ocean general circu- consider both the physical as we ll currents and upwelling, large-scale subsi- lation models (CGCMs), have trouble- as biogeo chemical processes lead- dence, and regional diurnal circulations some systematic errors in the SEP, ing to changes in cloud formation (Fig. 1). This unique system is very notably (Fig. 2) too warm SSTs and too and upper ocean heat budgets in sparsely observed, yet its variations have little cloud cover (e.g. Mechoso et al. an attempt to improve coupled important impacts on the global climate. 1995). model simulations in this notori- There are also great economic impacts, ously difficult region. These are with the regional fisheries representing The principal program objectives of just a few of the studies currently almost one-fifth of the worldwide marine VOCALS are: 1) the improved under- in place or in planning stages. fish catch. standing and regional/global model repre- sentation of aerosol indirect effects over Consult the U.S. CL IVAR web The Andes Cordillera are barriers to the SEP; 2) the elimination of systematic pages for information on other zonal flow in the South Pacific, resulting errors in the region of coupled atmospher- studies. in strong winds parallel to the coasts of ic-ocean general circulation models, and Continued on Page Two Chile and Peru (Garreaud and Muñoz improved model simulations and predic- 2005), which drive intense coastal tions of the coupled climate in the SEP upwelling, bringing cold, deep, nutri- and global impacts of the system variabil- IN THIS ISSUE ent/biota rich waters to the ocean surface. ity. Program documents and information VOCALS...... 1 As a result, sea-surface temperatures can be found at www.eol.ucar.edu/proj- U.S. CLIVAR Drought WG...... 6 (SSTs) are colder along the Chilean and ects/vocals/. North American Monsoon Prediction...... 8 Peruvian coasts than at any comparable C a l e n d a r ...... 10 latitude. The cold SSTs, in combination The VOCALS Strategy Global Ocean Energy Cycle ...... 13 with warm and dry air aloft helped by VOCALS is organized into two tight- Western Boundary Current WG...... 16 orographic effects of the Andes (Richter ly coordinated components: 1) a Regional and Mechoso, 2006), support the largest Experiment (VOCALS-REx), and 2) a U.S. CLIMATE VARIABILITY AND PREDICTABILITY (CLIVAR) 1717 Pennsylvania Avenue, NW, Suite 250, Washington, DC 20006• www.usclivar.org USCL.Spring2007 4/11/07 12:13 PM Page 2

Continued from Page One U.S. CLIVAR A little ove r a year ago U.S. Modeling Program (VOCALS-Mod). There are no in-situ observations of these CL IVAR constituted some short- Extended observations (e.g. IMET surface clouds with which to test hypotheses con- term Working Groups that wo uld b u o y, satellites, cruises) will provide cerning their physics and chemistry. work collaboratively on focused important additional contextual datasets VOCALS observations will seek to quan- and pressing scientific challenges that help to link the field and the modeling tify the controls on cloud condensation and needs. The efforts of these components. The coordination through nuclei (CCN) formation and growth, in Working Groups can be found on VOCALS of observational and modeling concert with the IGBP’s Surface Ocean the U.S. CL IVAR we b site. The efforts will accelerate the rate at which Lower Atmosphere Study, SOLAS. Ocean Salinity Working Group is field data can be used to improve simula- finishing their written findings and b. Systematic biases in atmosphere-ocean tions and predictions of the tropical cli- the MJO Working Group efforts GCMs mate variability. VOCALS is primarily were highlighted at the recent CGCMs have difficulties in simulat- sponsored by NSF and NOAA with con- WGNE Systematic Biases wo rk- ing marine stratocumulus clouds (Ma et tributions from the Office of Naval shop. Two other Working Groups al. 1996; Kiehl and Gent 2004; Research (ONR), DOE, and international were recently initiated. Drought is Wittenberg et al. 2006). This is attributa- partners. a major focus of U.S. CLIVAR and ble, in part, to the inadequate representa- the Drought Working Group activ- VOCALS Scientific Issues tion of MBL processes (turbulence, driz- ities (d escribed in this article) will a . A e rosol-cloud-drizzle interactions in zle, mesoscale organization) in atmos- complement the DRICOMP funded the marine PBL pheric models, and to a poor representa- activities, which we re recently In addition to responding to large- tion of cloud microphysical processes solicited. Please check the respec- scale dynamics, cloud optical properties (i.e. aerosol processes, including their tive Working Group we b pages over the SEP are also impacted by atmos- transport from continental sources and for further information and how to pheric aerosols (Huneeus et al. 2006), their removal by drizzle). Studies using get involve d. with contributions from both natural and CGCMs (Ma et al. 1996, Gordon et al. 2000) demonstrate that the accurate pre- The recently released US anthropogenic sources. Cloud droplet effective radii are small off the coast of diction of the optical properties of low Ocean Research Priorities Plan clouds over the SEP is required in order to and Implementation Strategy Chile and Peru, implying enhanced cloud droplet concentration, particularly down- simulate the strong trade winds and the (http://ocean.ceq.gov/about/doc observed SST distribution. s/orpp12607.pdf) includes, as wind of major copper smelters whose one of its Ne ar Term Priorities, the combined sulfur emissions total 1.5 TgS The OGCM components of CGCMs -1 Atlantic Meridional Ove rturning yr , comparable to the entire sulfur emis- also have difficulties with coastal Circulation (MO C) . U.S. CL IVAR sions from large industrialized nations upwelling, and the offshore heat and and the agencies will be wo rking such as Mexico and Germany nutrient transport by the associated with the community to deve lop (Source:GEIA). Regional changes in sur- mesoscale eddy field (Penven et al. 2005, implementation plans for this ini- face and TOA radiation caused by the Colbo and Weller 2006). tiative. More information will fol- enhanced effective radii are as high as 10- Mean advection velocities in the -2 low in the nex t Variations and on 20 W m , with significant, but currently upper ocean in the SEP are weak (few cm the U.S. CL IVAR we b site. unknown, implications for the ocean heat s-1). The upper ocean, therefore accumu- budget. lates and expresses locally the influences The East Pacific Investigation of Climate (EPIC) field study Variations (Bretherton et al. 2004) found evi- Published three times per year U.S. CLIVAR Office dence that drizzle formation, 1717 Pennsylvania Ave., NW enhanced by the depletion of Suite 250, Washington, DC 20006 aerosols (Wood 2006) in the clean (202) 419-3471 [email protected] MBL, can drive remarkably rapid Staff: Dr. David M. Legler, Editor transitions which drastically reduce Cathy Stephens, cloud cover (Stevens et al. 2005). Assistant Editor and Staff Writer Although low clouds and the dynam- © 2007 U.S. CLIVAR ical and microphysical processes Permission to use any scientific material (text and fig - ures) published in this Newsletter should be obtained controlling their thickness and cover- from the respective authors. Reference to newsletter age are a cornerstone of the climate materials should appear as follows: AUTHORS, year. of the SEP, our knowledge of clouds Title, U.S. CLIVAR Newsletter, No. pp. (unpublished Figure 1. Key features of the SEP manuscript). in this region is so far limited to sur- This newsletter is supported through contributions to climate system. the U.S. CLIVAR Office by NASA, NOAA—Climate face and spaceborne remote sensing. Program Office, and NSF. Page 2 USCL.Spring2007 4/11/07 12:13 PM Page 3

VARIATIONS the characteristics of the sea surface tem- perature distribution across the SEP. The hypotheses and testing strategies are pre- sented in full in the VOCALS Scientific Program Overview (see www.eol.ucar.edu/projects/vocals/). b. Aerosol-cloud-drizzle theme A comprehensive suite of in-situ and remotely sensed cloud and boundary Figure 2. Annual mean sea-surface temperature biases in layer measurements will be performed CCSM3 1990 control run (Collins et al. 2006) using the aircraft platforms and the ships. Aircraft missions will focus upon under- of lateral fluxes associated with eddies nections. Previous work has provided standing the processes that control precip- (e.g. Penven et al. 2005), and vertical indications that features of tropical pre- itation, including the role of atmospheric mixing events associated with atmos- cipitation patterns are strongly influ- aerosols, their transport from the land to pheric forcing transients (Wijesekera enced by the SEP (Ma et al. 1996; Large the ocean, and their depletion by the and Gregg 1996). Mesoscale ocean and Danabasoglu 2006). The pro- clouds themselves. A key goal is to better eddies 50-200 km across can affect nounced annual cycle in the equatorial link aerosol microphysical variability S S T well offshore by fluxing cold cold tongue is also considered to origi- with the variability in the radiative prop- water from the coastal upwelling nate from the SEP (Mitchell and erties of the clouds by performing closure regions (Fig. 3). Eddies could also Wallace 1992). Atmospheric distur- studies that not only link cloud micro- impact the ocean-atmosphere flux of bances in the SEP with an asymmetric physics with aerosol microphysics, but dimethylsulfide (DMS), an important structure propagate westward in the also link the cloud optical properties precursor gas for cloud condensation form of Rossby waves (Xie 1996), and (measured with aircraft and satellite nuclei. Eddy heat flux divergence may oceanic disturbances similarly propa- remote sensing) to the underlying aerosol -2 account for roughly 40 W m net heat gate westward as Rossby waves and variability. SOLAS studies will seek to flux into the ocean over the remote SEP eddies (Chelton et al. 2006). However, relate this aerosol variability to the (Colbo and Weller 2006). Mesoscale the mechanisms of interaction are not marine sources and sinks of sulfur-con- eddies are poorly observed and under- well understood. taining gases and particles. stood, and are barely resolved in cou- c. Coupled ocean-atmosphere-land theme pled ocean-atmosphere climate models 4. VOCALS-REx (Canuto and Dubovikov 2005). a. Goals Observations at the IMET buoy (20°S, VOCALS-Rex will collect 85°W) show that another challenge for datasets required to address a OGCMs is vertical mixing at the base set of issues that are organized of the upper layer by near-inertial oscil- into two broad themes: (1) lations, which can entrain fluid from aerosol-cloud-drizzle interac- the cool, fresh intermediate water tions in the marine boundary below. layer (MBL) and the physico- VOCALS-Mod posits that allevia- chemical and spatiotemporal tion of the difficulties with the simula- properties of aerosols; (2) tion of stratocumulus and coastal chemical and physical cou- upwelling/ocean heat budget will result plings between the upper in major improvements in GCM per- ocean, the land, and the formance. These improvements include atmosphere. The overarching the alleviation/elimination of the dou- goal for work in the first ble-ITCZ biases that characterizes con- theme is a better understand- temporary CGCMs. There is evidence ing of processes that influence that this bias has a negative effect on cloud optical properties (cloud the CGCM performance in the predic- cover, thickness, and particle tion of ENSO and its remote impacts. size) over the SEP. The goal of c. Interactions between the SEP with the second theme refers to the remote climates roles that oceanic upwelling, mesoscale eddies and other Figure 3. SST and surface current variability There is consensus that climate associated with the mesoscale ocean eddy transient upper oceanic variability in the SEP can imprint a sig- field in a regional ocean model. nature in large-scale fields via telecon- processes play in determining Page 3 USCL.Spring2007 4/11/07 12:13 PM Page 4

U.S. CLIVAR A ship towing the SeaSoar platform will are used for climate change projection • Modeling biogeochemical processes: be used to conduct a survey of the and ENSO forecasting. VOCALS-Mod, VOCALS will accelerate the process by mesoscale eddy field at several distances therefore, provides the context for which a representation of the interactions from the coast. Detailed measurements of VOCALS and will directly benefit from between ocean biota and the climate sys- the microscale variability of the upper the observations collected in the field tem are included in climate models. ocean will be used to explore the connec- campaign. The principal objectives of • Development of a Multi-Scale tions between the ocean mixed layer and VOCALS-Mod are (1) improving the Simulation and Prediction (MUSSIP) the ocean beneath. Chilean and Peruvian understanding and simulation of diurnal, System: VOCALS-Mod will use a Multi- coastal components are expected to pro- seasonal, inter-annual, and inter-decadal Scale Simulation and Prediction (MUS- vide key data on the nature of the variability in the SEP; (2) improving the SIP) system based on a RAM coupled to upwelling and the initiation of the understanding and simulation of oceanic an eddy-resolving ROM embedded with- mesoscale eddies. Links between the budgets of heat, salinity, and nutrients in in a global climate model or forced by variability in oceanic upwelling and the the SEP and their feedbacks on the reanalysis data. biogenic production of important aerosol regional climate; (3) developing the capa- • Strategy: The VOCALS modeling precursor gases (e.g. DMS) will be bility for simulation of cloud optical vision is based on the concept of a multi- explored using DMS flux measurements. properties (coverage, thickness, and scale hierarchy of models reflecting the In addition, the role of the land at modi- droplet size) and the effect on these prop- multiscale nature of processes in the SEP fying the diurnal cycle (Garreaud and erties of aerosols emitted in the region; and the multiscale hierarchy of VOCALS Muñoz 2004) and synoptic variability of (4) elucidating the interactions between observations. VOCALS-Mod will coor- clouds and low level winds will be the SEP climate and remote climates. dinate activities carried out at operational explored. VOCALS-Mod will provide modeling centers (NCEP), research laboratories support for VOCALS-REx through real- An additional key V O C A L S - R E x (NCAR, GFDL) and universities, with time forecasts and data assimilation. The goal is to use the unparalleled combina- the goal of using VOCALS observational research methodology in VOCALS-Mod tion of cloud measurements and other datasets both to evaluate model perform- will be organized into several themes: observational datasets to critically evalu- ance and to inform physical parameteri- ate the accuracy of current and future • Downscaling to the V O C A L S - R e x zation development. Use of the opera- satellite cloud microphysical retrieval study region: Global reanalysis data will tional modeling systems will provide algorithms. be used as forcings for Regional insight into the time evolution of errors d. Strategy Atmospheric Models (RAMs) and and their dependency on the analysis VOCALS-REx will have an intense Regional Ocean Models (ROMs), the employed for initialization; use of observing period during October- output of which will provide invaluable research modeling systems will facilitate November 2008. The observational plat- regional context in which to interpret the realization of hypothesis-testing forms during the period will comprise VOCALS-REx field data. experiments. The collaborations estab- aircraft (chiefly the NSF C-130, the CIR- • Ocean mesoscale eddy structure and lished willl make available the hierarchy PAS Twin Otter, the DOE G-1, and possi- transports: High resolution ROMs will be of numerical models needed to address bly the UK BAe-146), research ships (the used in conjunction with the VOCALS- the broad range of space and time scales NOAA Ronald H Brown (RHB), and pos- REx oceanographic mesoscale survey of processes in the VOCALS region. sibly a second ship), a land site in Chile, and satellite data to determine the hori- The VOCALS Legacy zontal and vertical eddy structure, eddy and Peruvian and Chilean coastal cruises. VOCALS has been conceived with heat/freshwater/biota transports from the Figure 4 shows a map of the VOCALS- the overarching goal of improving large coastal upwelling region to the remote REx study region and platforms involved. scale coupled ocean-atmosphere model SEP, and interactions between the eddies, VOCALS-Rex activities have been care- simulations and predictions of the SEP the mixed layer and the deeper ocean. fully designed to complement and climate system. This will be achieved enhance a suite of enhanced long-term • Aerosol-cloud-drizzle-ocean interac- with a coordinated modeling and obser- observations in the SEP. These include tions: VOCALS-REx data will be used to vational program, in which datasets are an uninterrupted six year record from the constrain and refine parameterizations of identified, generated and shared through IMET instrumented surface buoy (85°W, aerosol scavenging, cloud fraction and a VOCALS-wide data archive. Datasets 20°S), annual buoy maintenance cruises cloud microphysical processes used in generated will be made available to the (in 2001 and then in 2003-2006), and participating AGCMs and RAMs. broad modeling community as soon as regionally-subsetted satellite data. • Diagnostic studies of the regional cli- quality control is completed. A multi- VOCALS-Mod mate system: RAMs, ROMs and scale simulation and prediction system • Goals: A principal goal of VOCALS Regional Ocean-Atmosphere Models will be developed. VOCALS will pave is to improve model simulations of key (ROAMs) will be used to investigate the the way for field campaigns in the stra- climate processes using the SEP as a test- coupling between the atmosphere, ocean tocumulus regions in the eastern tropical bed, particularly in coupled models that and land in the SEP region. Atlantic, which influence the western Page 4 USCL.Spring2007 4/11/07 12:13 PM Page 5

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Figure 4. VOCALS-REx study region and key plat- forms/components involved. The RHB will make station- ary measurements at 3 locations (20S and 75, 80, and 85W). Ideally, a second ship will make butterfly patterns with the SeaSoar platorm to survey ocean mesoscale variability. The C-130 will make cross-sectional meas- urements along 20S out to 85W, and conduct flights to study the sturcture of pockets of open cells (POCs). The other aircraft will work mainly in the near-coastal zone to examine aerosol, cloud and drizzle variability. The Chilean and Peruvian coastal components will involve coastal ship sampling of the upper ocean and marine boundary layer. The Chilean land site will be used to examine the chemical and physical properties of the air masses that are advected from Chile over the SEP.

African summer monsoon. In addition, Variability. Monthly Weather Review: 133, annual cycle in equatorial convection and sea VOCALS will provide education and 2246–2261. surface temperature. J. Climate, 5, 1140-1156. training for both U.S. and regional cli- GEIA: Global Emissions Inventory Penven, P., V. Echevin, J. Pasapera, F. mate scientists. A c t i v i t y, an integrating project of the Colas, and J. Tam, 2005: Average circulation, AIMES/IGBP programs. See http://geiacen- seasonal cycle, and mesoscale dynamics of the ter.org/ Peru Current System: a modeling approach. J. References Gordon C. T., A. Rosati, R. Gudgel, 2000: Geophys. Res., 110, 10.1029/2005JC002945. Bretherton, C. S., T. Uttal, C. W. Fairall, Tropical sensitivity of a coupled model to Richter, I., and C. R. Mechoso, 2006: S. Yuter, R. Weller, D. Baumgardner, K. specified ISCCP low clouds. J. Clim., 13, Orographic influences on the subtropical stra- Comstock, R. Wood, and G. Raga, 2004: The 2239-2260. tocumulus. J. Atmos. Sci., 63, 2585-2601. EPIC 2001 stratocumulus study. Bull. Amer. Huneeus, N., L. Gallardo, and J. A . Stevens, B., G. Vali, K. Comstock, R. Meteor. Soc., 85, 967-977. Rutllant, 2006: Offshore transport episodes of Wood, M. C. van Zanten, P. H. Austin, C. S. Canuto, V. M. and M. S. Dubovikov, anthropogenic sulfur in Northern Chile: Bretherton, and D. H. Lenschow, 2004: 2005: Modeling mesoscale eddies. Ocean Potential impact upon the stratocumulus cloud Pockets of open cells (POCs) and drizzle in Modeling, 8, 1-30. deck. Geophys. Res. Lett., 33, L19819, marine stratocumulus. Bull. A m e r. Meteor. Colbo, K. and R. A. Weller, 2006: The doi:10.1029/2006GL026921. Soc., 86, 51-57. variability and heat budget of the upper Kiehl, J. T., and P. R. Gent, 2004: The Wijesekera H.W, and M. C. Gregg, 1996: ocean under the Chile-Peru stratus. J. Community Climate System Model, version Surface layer response to weak winds, wester- Marine. Res., in press. 2. J. Climate., 17, 3666–3682. ly bursts, and rain squalls in the western Collins, W., and coauthors, 2006: The Large W. G., and G. Danabasoglu, 2006: Pacific Warm Pool. J. Geophys. Res., 101, Community Climate System Model Version Attribution and impacts of upper-ocean biases 977-997 3 (CCSM3). J. Climate, 19, 2122-2143. in CCSM3. J. Climate, 19, 2325–2346. Wittenberg, A. T., A. Rosati, N-C. Lau, Chelton, D. B., M. H. Freilich, J. M. Lohmann, U., and J. Feichter, 2005: and J. J. Ploshay, 2006: GFDL's CM2 Global Sienkiewicz and J. M. Von Ahn. 2006: On Global indirect aerosol effects: a review. Coupled Climate Models. Part III: Tropical the Use of QuikSCAT S c a t t e r o m e t e r Atmos. Chem. Phys. Disc., 5, 715-737. Pacific climate and ENSO. J. Clim., 19, 698- 722. Measurements of Surface Winds for Marine Ma, C.-C., C.R. Mechoso, A . W. Weather Prediction. Monthly We a t h e r Robertson and A. Arakawa, 1996: Peruvian Wood, R., 2006: The rate of loss of cloud Review, 134, 2055–2071. stratus clouds and the tropical Pacific circula- droplets by coalescence in warm clouds. R. Garreaud, R. D., and R. C. Muñoz, 2004: tion: A coupled ocean-atmosphere GCM Wood, J.Geophys. Res., 111, D21205, The diurnal cycle in circulation and cloudi- study. J. Cli¬mate, 9, 1635-1645. doi:10.1029/2006JD007553. ness over the subtropical southeast Pacific: Mechoso, C. R., and coauthors, 1995: Xie, S. -P., 1996: Westward propagation of A modeling study. J. Climate, 17. 1699- The seasonal cycle over the tropical Pacific in latitudinally asymmetry in a coupled ocean- 1710. cou¬pled ocean-atmosphere general circula- atmosphere model. J. Atmos. Sci., 53, 3236- Garreaud, R. D., and R. C. Muñoz, 2005: tion models. Mon. Wea. Rev., 123, 2825-283. 3250. The Low-Level Jet off the West Coast of Mitchell, T.P. and J.M. Wallace, 1992: The Subtropical South America: Structure and Page 5 USCL.Spring2007 4/11/07 12:13 PM Page 6

U.S. CLIVAR The U.S. CLIVAR Working Group on Long-term Drought

Dave Gutzler, University of New Mexico, co-chair Siegfried Schubert, NASA Goddard Space Flight Center, co-chair

.S. CLIVAR recently formed Drought Information System (NIDIS, ties about the relative roles of the differ- a Working Group to provide 2004) authorized by law in December ent ocean basins, the strength of the land- funding agencies and existing 2006. The vision for NIDIS is a dynamic atmosphere feedbacks, the role of deep scientific steering groups and accessible drought risk information soil moisture, the nature of long-term Uwith specific guidance on research needs system that provides users with the ability S S T v a r i a b i l i t y, the impact of global for improving prediction and monitoring to determine the potential impacts of change, as well as fundamental issues tools for long-term (multi-year) droughts drought, and the decision support tools about predictability of drought on multi- and to energize initial drought activities. needed to better prepare for and mitigate year time scales. Such droughts have tremendous societal the effects of drought. As the designated The primary objective of the U.S. and economic impacts on the United lead agency, NOAA is developing an CLIVAR Working Group is to facilitate States, and many other countries interagency implementation plan. NASA progress on the understanding and pre- throughout the world. Estimates of the is also engaged in planning for NIDIS as diction of long-term (multi-year) drought costs of drought to the United States part of an overall strategy to implement over North America and other drought- alone range from $6-$8 billion annually key aspects of the international Global prone regions of the world, including an with major droughts costing substantially Earth Observation System of Systems assessment of the impact of global more (e.g., $62B in 1988 according to (GEOSS) strategic plans. change on drought processes. The specif- NOAA). The Dust Bowl drought of the While NIDIS has a strong focus on the ic tasks of the Working Group will be to: 1930s, which at its maximum extent cov- U.S., it is clear that drought is a global 1) coordinate and encourage the analysis ered much of the continental U.S. (Fig. 1) phenomenon, both in terms of the forcing of observational data sets to reveal is ranked as one of the top 10 domestic elements and the potential commonality antecedent linkages of multi-year weather-related disasters of the 20th cen- of local processes that operate to make droughts; 2) propose a working defini- t u r y. Recent population increases in some regions more susceptible to drought tion of drought and related model predic- water-limited regions has increased vul- than others. As such, confidence in our tands of drought, 3) coordinate evalua- nerability to drought at the same time understanding of drought processes tions of existing relevant model simula- that climate change projections suggest (remote and local forcing, feedbacks, etc.) tions, 4) suggest new experiments (cou- that drought conditions may become will be significantly advanced by efforts pled and uncoupled) designed to address more extreme in the 21st Century, partic- to properly analyze and simulate regional some of the uncertainties mentioned ularly in the southwestern United States drought wherever it occurs. Recent stud- above, and to contribute to NIDIS-relat- (NRC, 2007). ies (e.g., Hoerling and Kumar 2003; ed drought risk assessment; 5) examine Several agencies including NOAA Schubert et al. 2004; Seager et al. 2005) the prospects for using land data assimi- and NASA are in the planning phase for suggest that such simulations are feasible lation products for operational monitor- implementing the National Integrated using current global models (Fig. 2). ing, assessment and hydrological appli- There are, however, still major uncertain- cations; and 6) organize an open work- shop in 2008 to present and discuss the working group results and consider results from the community. Figure 1. Spatial extent of the Dust As initial products, the Wo r k i n g Bowl drought of the Group is compiling a list of recent papers 1930s in August 1934. on drought research, and an inventory of Percentiles are for soil accessible data sets for observational moisture relative to the studies. These products (still under 85-year period 1915- development) can be obtained through 2003. From University the Working Group’s web page at of Washington Surface h t t p : / / w w w. u s c l i v a r. o rg / O rg a n i z a t i o n / d r Water Monitor, avail- able online at: ought-wg.html. The Working Group has http://www.hydro.washi also initiated discussion of a working ngton.edu/forecast/mo definition of drought (including onset nitor. and demise) for use by both the predic- tion/research and applications communi- ties. The goal of this effort will be to Page 6 USCL.Spring2007 4/11/07 12:13 PM Page 7

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bution activities funded by NOAA/CDEP, the attribution and pre- diction capabilities at various universi- ties and research institutes, and take advantage of the many long term cou- pled model runs that have been conduct- ed as part of the IPCC climate change assessment process. The upcoming DRI- COMP ( h t t p : / / w w w. u s c l i v a r. o r g / D R I C O M P - AO.html) model assessment research opportunity represents an important component of this effort. Additional activities of the Drought Working Group can be monitored on its web page: h t t p : / / w w w. u s c l i v a r. o rg / O rg a n i z a t i o n / d r ought-wg.html).

Figure 2. Time series of precipitation anomalies averaged over the U.S. Great Plains region (30°N to 50°N, 95°W to 105°W), from Schubert et al. (2004). A filter References has been applied to remove time scales shorter than about 6 years. The thin Hoerling, M.P. and A. Kumar, 2003: The black curves are the results from 14 ensemble members from C20C global model perfect ocean for drought. Science, 299, 691- runs. The green solid curve is the ensemble mean. The red curve is based on 699. observations. The maps show the simulated (left) and observed (right) precipita- IEOS, 2005: Strategic Plan for the U.S. tion anomalies averaged over the Dust Bowl period (1932 to 1938, units mm/day). Integrated Earth Observation System. The Interagency Working Group on Earth define drought in a way that is quantifi- (with its focus on large scale and ocean- Observations. NSTC Committee on able and verifiable for the purpose of atmosphere coupling), and GEWEX Environment and Natural Resources. Available online at: model prediction experiments, as well as (focusing on regional scales and land- http://iwgeo.ssc.nasa.gov/ for drought monitoring and early warn- atmosphere coupling). What is the role ing, and facilitating communication of the land (e.g., deep soil moisture, NIDIS, 2004: Creating a Drought Early Warning System for the 21st Century: The between the applications and snow, vegetation)? What is the role of National Integrated Drought Information modeling/research communities. the different ocean basins, including the System (NIDIS). A report of the National The working group will help coordi- impact of ENSO, the PDO, the AMO, Oceanic and Atmospheric A d m i n i s t r a t i o n nate key aspects of the long-term drought and longer term warming trends in the and the Western Governor’s A s s o c i a t i o n . Available onlin: http://www.westgov.org. research agenda outlined in the recent global oceans? To what extent can drought develop independently of NRC, 2007: Colorado River Basin Water drought workshop recommendations Management: Evaluating and Adjusting to (e.g. Schubert et al. 2005). It will interact ocean variability due to year-to-year Hydroclimatic Variability. Available online: with the developing NIDIS program to memory inherent to the land? h t t p : / / b o o k s . n a p . e d u / c a t a l o g . p h p ? r e c o r d _ i d = communicate current drought prediction The Working Group will recom- 11857 and attribution capabilities. The Working mend and promote a set of idealized Schubert S. D., M. J. Suarez, P. J. Pegion, Group will work with the NIDIS commu- experiments coordinated among differ- R. D. Koster, and J. T. Bacmeister. 2004: On nity and the relevant funding agencies to the cause of the 1930s Dust Bowl. Science, ent models to address some of the key 303, 1855–1859, doi: 10.11 2 6 / s c i - develop guidance on drought research issues outlined above (e.g., role of dif- ence.1095048. needs, based on assessments of predic- ferent ocean basins, deep soil moisture, ---, R. Koster, M. Hoerling, R. Seager, D. tion capabilities and input we will seek etc.). Specific details about the experi- L e t t e n m a i e r, A. Kumar, and D. Gutzler, concerning stakeholder-driven prediction ments and diagnostic analyses are 2005: Observational and Modeling priorities. It will advocate the coordina- beginning to be developed. T h e Requirements for Predicting Drought on tion of efforts among the agencies to Working Group will coordinate with Seasonal to Decadal Time Scales. Available online at: http://gmao.gsfc.nasa.gov/pubs/ advance drought prediction research in research institutes and universities ways that will maximize the utility for Seager, R., Y. Kushnir, C. Herweijer, N. active in drought research to ensure that Naik, and J. Velez, 2005: Modeling of tropi- NIDIS development. the relevant simulations are well docu- cal forcing of persistent droughts and pluvials The long-term drought problem can mented and accessible to the communi- over western North America: 1856-2000. J. be an important umbrella issue to bring ty. Climate, 18, 4068-4091. together the relevant research expertise New simulations will build upon of the International CLIVAR program the climate variability and change attri- Page 7 USCL.Spring2007 4/11/07 12:13 PM Page 8

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detail on NAME background informa- The Path to Improving tion and motivating science questions can be found in Higgins et al., 2006 and Predictions of the NAME-SWG, 2007). Central to the NAME research effort North American Monsoon is a list of science questions posed on the three tiers of the NAME study David J. Gochis, National Center for Atmospheric Research domain. These questions are aimed at R. Wayne Higgins, Climate Prediction Center/NOAA/NWS/NCEP improving the understanding and simu- lation of 1) warm season convective processes over complex terrain (Tier I), he North American Monsoon and Predictability (CLIVAR) and 2) the modes and drivers of intra-sea- System (NAMS) is considered Global Energy and Water Cycle sonal variability (Tier II) and, 3) the to be the principle organizing Experiment (GEWEX) research efforts. response of the NAMS to oceanic and structure for the warm season The underlying hypothesis of NAME is continental boundary conditions (Tier Tlimate of southwestern North America. that the structure and evolution of the III). The timeline for NAME activities Like its global, though often larg e r, NAMS provides a physical basis for (Fig. 1) encompasses planning, data col- counterparts in Asia, Australia, Africa determining the degree of predictability lection and principle research phases. A and South America, the NAMS exhibits warm season precipitation over much of progressive aspect of NAME has been marked seasonal reversals in land-ocean North America. A fundamental first step that modeling and data assimilation thermal contrasts, low and mid-tropos- towards improved prediction is the clear activities were engaged early in plan- pheric wind fields, atmospheric moisture documentation of the major elements of ning process in order to guide the obser- convergence patterns, atmospheric sta- the monsoon system and their variabili- vational strategy of a large Enhanced bility and, consequently, precipitation. ty within the context of the evolving Observing Period (EOP) or, field cam- The seasonal onset, intensity and decay Ocean-Atmosphere-Land (O-A-L) paign, which was conducted during the of summer rains drive a host of ecologi- annual cycle (Higgins and Gochis, summer of 2004. This coordination cal and societal dependencies ranging 2007). To achieve this NAME employs insured that the field data collected not from water resources to wildland fire a multi-scale (tiered) approach with only would serve as valuable data for threat to rangeland forage production to focused monitoring, diagnostic and conducting exploratory and diagnostic energy supply and demand to estuarine modeling activities in the core monsoon analysis, but would also directly address fisheries (cf Ray et al., 2007; Aragón and region, on the regional-scale and on the problematic modeling issues that had García, 2002; Gochis et al., 2006, continental-scale (Fig. 1). (Additional 2007a). However, also like its global arisen through numerous prior modeling counterparts, prediction skill of warm season rainfall on seasonal to interannu- Figure 1. Multi-tiered al timescales remains critically low. This research domain devel- lack of skill translates into a persistent oped for NAME. Important features of the vulnerability of the aforementioned monsoon climate are also dependencies. The 2006 summer mon- depicted. Digonal red soon, which brought persistent heavy lines indicate eastward rainfall to the U.S.-México border region (mid-latitude) and west- (Sonora, Chihuahua, Arizona and New ward (tropical) propagat- Mexico) and tens of millions of dollars ing transients known to in damages, served as a timely reminder imact monsoon behavior. of this vulnerability (cf FEMA, 2007, Wind vectors indicate the CLIMAS, 2006). mean 925hPa wind field from the NCEP/NCAR The NAME Program: reanalysis. Green shad- The North American Monsoon ing indicates merged Experiment (NAME) is a continental- satellite estimates and scale process study now in its seventh raingauge observatins of precipitation in millime- year that was conceived to directly ters. The timeline for address the issue of improving predic- NAME program, begin- tions of warm season precipitation in ning in 2000, is also North America. The NAME program is shown. (Adapted from jointly sponsored by Climate Variability Higgins et al., 2006) Page 8 USCL.Spring2007 4/11/07 12:13 PM Page 9

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studies. These issues included the struc- ture and evolution of regional moisture flux patterns over the Gulf of California Figure 2. Schematic of regional (GoC), air-sea interactions over the GoC circulation features of the North American Monsoon. Heavy and Eastern Pacific, the diurnal cycle of blue lines in plan view desig- precipitation, upscale organization and nate principle moisture path- propagation of convection, the influence ways. ‘H’ an d ‘L’ indicate clima- of low-and mid-latitude transients on pre- tological positions of hte upper- cipitation episodes and coupling between level monsoon anticyclone and the land-surface and the atmosphere. The hte low-level desert thermal NAME 2004 EOP was organized and low, respectively. Cross-section conducted by an international coalition of in top figure is approximated university and agency scientists, and fore- from heavy black dotted line on map. Cloud structures in grey casters from México, the U.S. and central shading approximate those America. More than 20 different types of structures diagnosed from vari- instrument platforms, including surface ous precipatation studies con- meteorological stations, radars, aircraft, ducted as part of NAME. research vessels, satellites, wind profilers, (Adaped from Johnson et al., rawinsondes, pibals, rain gauge networks, 2007, Higgins et al., 2006, soil moisture sensors and GPS integrated Nesbitt and Gochis, 2007). water vapor retrieval antennae were deployed within the Tier I and II regions in Figure 1. (Higgins and Gochis, 2007) The remainder of this article provides México, is considered to be the principle (Johnson et al., 2007; Zuidema et al., a brief overview of the key findings from driver of the NAMS. Peripherally, 2007; Williams et al., 2007). the 2004 EOP as well as a discussion on strong subsidence was found to persist C l i m a t o l o g i c a l l y, inverted troughs current activities aimed at improving pre- over the Gulf of California as a result of and other synoptic transients such as trop- dictions of warm season precipitation return flow from sea-breeze/terrain cir- ical easterly waves, and westerly mid-lat- over North America. Given the brevity of culation and from flow descending over itude troughs are critical features of the this summary only a few topics are high- the SMO (Johnson et al., 2007; Zuidema NAM (Douglas and Englehart, 2007). lighted. The summary provided below et al., 2007). Despite the enhanced Inverted troughs, propagating along the along with much of the work cited is con- observing network present during 2004, southern limb of the summertime sub- tained in a forthcoming special issue in significant uncertainty in the vertical tropical anticyclone, help advect moisture the Journal of Climate on NAME due to humidity structure over the complex ter- and provide dynamical support by means be published during the late-spring of rain exists due to lack of surface meteor- of large scale ascent and orographic lift in 2007, and in meeting reports from the ological and atmospheric observations. otherwise dry regions such as the central NAME SWG from 2005 and 2006 avail- Flow over the GoC and the western Mexican Plateau. In addition to having a able through the official NAME website coast of the Mexican mainland was typi- late onset, synoptic variability during (http://www.eol.ucar.edu/projects/name/) fied by nocturnal low level southeasterly 2004 summer monsoon was characterized flow and daytime low-level westerly by a reduced number of inverted troughs Key Findings from 2004 EOP: flow inland towards the SMO. Easterlies and nearly twice the climatological num- Regional circulation stru c t u res aro u n d tend to persist at middle and upper levels ber of midlatitude westerly troughs the Gulf of California (GoC): fostering a light to moderately sheared (Douglas and Englehart, 2007). T h e Owing to marked deficiencies in the environment over the principle convec- westerly troughs during 2004 were impli- pre-existing operational sounding net- tive region of the western slope of the cated in drier-than-normal conditions in work over the NAMS region, characteri- SMO. Divergence, vertical motion, Arizona and northern Sonora but wetter zation of the atmospheric circulation in heating and moistening profiles derived than normal conditions in eastern New the Gulf of California region was greatly from analyses of the special observations Mexico. On interannual timescales the enhanced during the 2004 NAME EOP. are all consistent with a convectively- dominance of a particular transient Time mean analyses of NAME 2004 dominated dynamical system (Johnson et regime significantly influences summer observations, conceptualized in Figure 2, al., 2007). Nevertheless, stratiform pre- rainfall patterns (Douglas and Englehart, show strong low-level convergence and cipitation structures were frequently 2007). upper-level divergence along the crest of observed during nighttime hours and are Characteristics of Precipitation: the Sierra Madre Occidental (SMO) assumed to play an important role in Forcing of the diurnal cycle of winds (Johnson et al., 2007). This direct circula- modifying the regional thermodynamic tion structure, centered over western structure over and around the GOC Page 9 USCL.Spring2007 4/11/07 12:13 PM Page 10

U.SU.S. CLI. CLIVVARAR Calendar of CLIVAR and CLIVAR-related meetings Further details are available on the U.S. CLIVAR and International CLIVAR web sites: www.usclivar.org and www.clivar.org

Variability of the American Monsoons NOAA Climate Observation Annual AMS Air-Sea Interaction Conference (VAMOS-10) Review 20-24 August 2007 2-5 April 2007 5-7 June 2007 Portland, Oregon Santiago, Chile Silver Spring, Maryland Attendance: Open Attendance: Invited Attendance: Open Contact: http://www.ametsoc.org Contact: http://www.clivar.org Contact: http://www.oco.noaa.gov Layered Ocean Model Meeting Int'l Oceanographic Data and Pacific Science Congress XXI 20-23 August 2007 Information Exchange (IODE) Symposium on Global Change, Asian Bergen, Norway 16-20 April 2007 Monsoon and Extreme Weather and Attendance: Open Trieste, Italy Climate Contact: www.clivar.org Attendance: Open 12-16 June 2007 Contact: http://www.iode.org Okinawa, Japan CLIVAR Working Group on Ocean Attendance: Open Model Development CLIVAR Indian Ocean Panel Meeting Contact: http://www.psc21.net 26-27 August 2007 23-25 April 2007 Bergen, Norway South Africa 12th Annual Community Climate Attendance: Invited Attendance: Invited System Model (CCSM) Workshop Contact: http://www.clivar.org Contact: http://www.clivar.org 18-21 June 2007 Breckinridge, CO 2nd International Conference on Seventh Workshop on Decadal Climate Attendance: Open Earth System Modeling Variability Contact: http://www.ccsm.ucar.edu 27-31 August 2007 30 April-3 May 2007 Hamburg, Germany Kona, Hawaii IEEE Oceans ‘07 Attendance: Open Attendance: Open 18-21 June 2007 Contact: http://www.mpimet.de/icesm Contact: http://www.decvar.org/work- Aberdeen, Scotland shops_conferences.php Attendance: Open CLIVAR SSG-15 Contact: http://www.oceans07ieeeab- 11-14 September 2007 Ocean Observataions Panel for erdeen.org/ Geneva, Switzerland Climate-12 Attendance: Invited 30 April-4 May 2007 IUGG 2007 Contact: http://www.clivar.org Melbourne, Australia 2-13 July 2007 Attendance: Invited Perugia, Italy AMS Conference on Satellite Contact: http://www.clivar.org Attendance: Open Meteorology and Oceanography and Contact: http://www.iugg2007perugia.it/ Ocean Vector Winds Science Team AGU Joint Assembly 24-28 September 2007 21-25 May 2007 U.S. CLIVAR Summit Amsterdam, Netherlands Acapulco, Mexico 23-25 July 2007 Attendance: Open Attendance:Open Annapolis, Maryland Contact: http://www.conferences.eumet- Contact: http:// www.agu.org Attendance: Invited sat.int Contact: www.usclivar.org WCRP Workshop on Seasonal PICES 16th Annual Meeting: The Prediction Application of Remotely Sensed Changing North Pacific: Previous pat- 4-8 June 2007 Observations in Data Assimilation terns, future projections and ecosys- Barcelona, Spain 23 July - 10 August 2007 tem impacts Attendance: Open College Park, Maryland 26 October - 5 November 2007 Contact: Attendance: Open Victoria, British Columbia http://www.wmo.ch/web/wcrp/AP_Seaso Contact:http://www.essic.umd.edu Attendance: Open nalPrediction.html Contact: http://www.pices.int/meetings

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VARIATIONS is supplied by land-sea contrasts and Ocean-Land-Atmosphere Coupling: These anomalies are largely established the heating of elevated terrain and these Onset of the 2004 monsoon was in response to antecedent cold-season circulations significantly influence the associated with the southeasterly advec- precipitation anomalies which vary diurnal cycle of precipitation. As a tion of warm water from the tropical greatly from year to year. This regional result, precipitation character (e.g. fre- East Pacific Ocean into the GoC forcing acts in concert or competition quency, intensity and duration) is often (Zuidema et al., 2007). Throughout the with large-scale teleconnective forcing related to variations in local (O~1-10 s u m m e r, oceanographic observations provided by remote and near shore sea km) and regional (O~10-100 km) ter- near the mouth of the GoC documented surface temperatures (Grantz et al., rain features, land-sea contrasts and that strong solar heating, ocean heat 2007, Gochis et al., 2007a). access to abundant atmospheric mois- advection and nighttime cloudiness over Towards Improving Predictions ture (Gebremichael et al., 2007; Gochis the Gulf provide a positive feedback Transferring this emerging under- et al., 2007b; Janowiak et al., 2007; resulting in net surface heating despite a Lang et al., 2007; Vivoni et al., 2007). standing of the NAMS into improved l a rge evaporation component. predictions of warm season precipitation Numerous studies now confirm a pre- Furthermore, periodic, strong advection cipitation climatology in which precip- will not be easy. Fundamental limita- of warm water from the southeast during tions still exist in the observing system itation forms most frequently and earli- atmospheric moisture surge events also est in the afternoon over the highest ter- over parts of México, in particular the appears to contribute to a surge-memory SMO, the intra-America Seas region, rain, albeit with comparatively light effect as the recently advected water intensity, and less frequently and later and the tropical oceans in general. Poor contributes to the latent and sensible treatment of convection in models and during the evening but with heavier fluxes within the Gulf region. intensities over the low elevation limited understanding of role of terres- Capturing the complex, transient behav- trial forcing will continue to inhibit coastal regions. While a large fraction ior of the GoC heat and moisture source of the regional precipitation climatol- rapid increases in seasonal and inter- will be essential for improving model annual forecast skill from dynamic mod- ogy is dominated by events whose simulations and highlights the impor- entire life cycles occur over the com- els. However, as part of NAME, tance of resolving the Gulf in free run- progress is being made on defining plex terrain of the SMO, a secondary, ning climate models. ‘disturbed’ regime is now recognized which observations are critical to Strong latitudinal and terrestrial gra- under which organized, propagating improving model initializations and dients in terrestrial hydrology and ecol- precipitation events move away from forecasts. Assimilation of NAME 2004 ogy are found throughout the monsoon topography (Lang et al., 2007). Radar special soundings into NCEP model- region. These variations act as a dynam- composite products collected during based data assimilation systems indi- ic assimilator of atmospheric processes 2004 also capture the complex interac- cates that impacts of the soundings are yet their influence as an atmospheric tions between the regional circulation, most pronounced at low levels in the driver (ie the nature of the land-atmos- the land-sea breeze and propagating atmosphere and mainly in the core mon- phere feedback) remains uncertain organized precipitation events over the soon region of northwestern México and (Vivoni et al., 2007; Watts et al., 2007; GoC. Notably, precipitation over the the southwestern U.S. where the sound- Zhu et al., 2007). During 2004, tower GoC is about 12 hours out of phase ing data were collected (Mo et al., flux and soil moisture measurements with precipitation occurring over the 2007). Enhanced sounding observa- were made in a variety of ecotones SMO (Lang et al., 2007; Zuidema et al., tions also had a significant and benefi- (transition areas between two adjacent 2007). Long-lived stratiform precipita- cial impact on depicting the structure of ecosystems). From a vegetation biome tion structures, characterized by strong the Gulf of California low-level jet. perspective tropical deciduous forests brightband signatures in radar and ver- However, additional data impact studies respond much more quickly and strong- tically-pointing profilers, are very sig- of the NAME 2004 enhanced observa- ly to precipitation than other semi-arid nificant and, at times, a dominant tions, such as sea surface temperatures, communities (Watts et al., 2007). mechanism for precipitation (Lang et rain gauge observations, and soil mois- Notably, the tropical deciduous forests al., 2007; Williams et al., 2007). ture measurements, on atmospheric exhibit slower decay of evapotranspira- Retrievals from NOAA wind profilers analyses are needed. These studies will, tion fluxes under moisture stress than and space-borne radar show a relative- over time, contribute to the development many other communities eff e c t i v e l y ly strong dependence on microphysical of an observing system design for the resulting in a ‘quick learning-long for- structures, in particular brightbanding NAMS which is key deliverable from g e t t i n g ’ b e h a v i o r. On seasonal and (Williams et al., 2007). Strong spatial the NAME program. interannual timescales antecedent land and temporal variations in cloud ther- Comparatively less progress has surface conditions across southwestern mal and microphysical characteristics been made in addressing NAME North America affect the timing of the present significant challenges in esti- research questions in Tiers II and III onset of monsoon precipitation by mod- mating precipitation from remote sens- compared to Tier I. While this is under- ulating the land-sea thermal contrast ing platforms (Nesbitt and Gochis, standable, given the focus of NAME (Grantz et al., 2007, Zhu et al., 2007). 2007). Page 11 USCL.Spring2007 4/11/07 12:13 PM Page 12

U.S. CLIVAR 2004, the research issues in Tiers II and cast products. One way NAME is (CIRMOUNT), 1, 16-19. III need to have greater priority in the addressing this issue is by developing Diaz, H.F., R. Villalba, G. Greenwood future in order to make progress on the NAME Forecast Forum which will and R.S. Bradley, 2006: The impact of cli- warm season precipitation forecasts. consolidate a variety of operational and mate change in the American Cordillera. experimental forecast products of mon- Eos, Transactions of the A m e r i c a n The 2004 monsoon highlighted the sig- Geophysical Union, 87(32), August, 2006, nificant dependence of monsoon precip- soon activity. This new effort will build p. 315. upon the success of the NAME Model itation, in many regions, on transient Douglas, A.V. and P.J. Englehart, 2007: synoptic features. For instance, mois- Assessment Project (NAMAP s e e A climatological perspective of transient ture surge activity appears to be Gutzler et al., 2006 for details), which synoptic features during NAME 2004. In enhanced during active phases of the has documented the attributes and press, J. Climate. Madden Julian Oscillation (Johnson et shortcomings of several leading global FEMA, 2007: New Mexico severe al., 2007; Lorenz and Hartmann, 2006). and regional models in the simulation of storms and flooding. Federal Emergency monsoon circulation and precipitation Management Agency (FEMA) Disaster Similarly, Mestas-Nunez et al. (2007) Information web page. Available online at: show that variability in the transport features. More detail on this effort will h t t p : / / w w w. f e m a . g o v / n e w s / e v e n t . f e m a ? i d = from the key moisture source region of be forthcoming in the coming months 6925 the intra-America Seas is linked to though interested parties are encour- Gebremichael, M., E.R. Vivoni, C.J. changes in summertime precipitation aged to contact the authors directly. Watts, and J.C. Rodriguez, 2007: Local- patterns over the central and eastern Another way for NAME to add value to scale spatio-temporal variability of North U.S. It has become clear that there are existing forecasts is by improving the American monsoon rainfall over complex terrain. In press, J. Climate. complex interactions between tropical application of dynamical and statistical- dynamical downscaling techniques in Gochis, D.J., L. Brito-Castillo, W. J . easterly waves, upper-level inverted Shuttleworth, 2006: Hydroclimatology of troughs, cold fronts, cut-off lows, open seasonal forecasts. While such the North American Monsoon region of troughs, and GoC moisture surges that approaches clearly can not correct for northwest México. J. Hydrology, 316, 53- are not well understood despite the fact erroneously forecasted climatic struc- 70. that they are critically important in the tures, they can serve to better transfer Gochis, D.J., L. Brito-Castillo, W. J . prediction of warm season precipitation. information captured in forecasted cli- Shuttleworth, 2007a: Correlations between sea-surface temperatures and warm season As NAME enters into its modeling mate modes to smaller scale, regional climate processes such as variable pre- streamflow in northwest México. In press, and prediction phase many significant Int’l. J. Climatol. cipitation characteristics across com- challenges remain. Some of these are Gochis, D.J., C.J. Watts, J. Garatuza- ‘grand challenge’ issues, such as the plex terrain. As has been the case from Payan, and J.C. Rodriguez, 2007b: Spatial representation of convection in models the beginning of NAME, it will be and temporal patterns of precipitation inten- or land-ocean-atmosphere coupling, that through a synthesis of multi-discipli- sity as observed by the NAME event rain gauge network from 2002 to 2004. In extend well beyond NAME. More nary activities that measured progress in improved understanding of the mon- press, J. Climate. importantly, in order to improve predic- G u t z l e r, D. S, H.-K. Kim, R. W. tions of warm season precipitation, soon system will be transferred into improved prediction capabilities. Higgins, et al., 2005: The North American NAME will need to engage a variety of monsoon Model Assessment Project strategies aimed at detecting critical (NAMAP): Integrating numerical modeling environmental processes that modulate into a field-based process study. Bull. References: Amer. Met. Soc, 86, 1423-1430. the warm season circulation and Aragón, E.A. and A. García, 2002: Lorenz, D.J. and D.L. Hartmann, 2006: improving the representation of these Postlarvae recruitment of blue shrimp The effect of the MJO on the North Litopenaeus stylirostris (Stimpson, 1871) in processes in empirical and dynamical American Monsoon. J. Climate, 19, 334- antiestuarin conditions due to anthropogenic prediction models. One way forward, as 343. activities. Hidrobiológica, 12(1), 37-46. mentioned previously, is to design and Higgins, R. W. and co-authors, 2006: CLIMAS, 2007: Southwest climate out- maintain a robust climate observing sys- The North American Monsoon Experiment look – August 2006. Online climate (NAME) 2004 Field Campaign and tem across the southern North American Outlook published by the Climate Modeling Strategy. Bull. A m e r. Meteor. cordillera, the GoC and the intra- Assessment for the Southwest (CLIMAS) Soc., 87, 79-94. America Seas regions. This need has project. Tucson, Arizona. Available online also been identified in the context of at: Higgins, R.W. and D.J Gochis, 2007: Synthesis of results from the North h t t p : / / w w w. i s p e . a r i z o n a . e d u / c l i m a s / f o r e - other climate variability and climate American Monsoon Experiment (NAME) casts/archive/aug2006/swoutlook.html change research efforts recently articu- process study. In press, J. Climate. Diamond, H.J. and M.R. Helfert, 2007: lated by Diaz et al. (2006) and Diamond Janowiak, J.E., V.J. Dagostaro, V. E . The U.S. Global Climate Observing System and Helfert (2007). Kousky and R.J. Joyce, 2007: An examina- (GCOS) Program: Plans for high elevation tion of precipitation in observations and Second, NAME must also engage GCOS surface network sites based on the model forecasts during NAME with benchmark U.S. Climate Reference efforts to provide added value to exist- emphasis on the diurnal cycle. In press, J. Network (CRN) System. Mountain Views, ing forecast methodologies in order to Climate. Newsletter of the Consortium for Integrated create more usable warm season fore- Climate Research in Western Mountains Johnson, R.H., P.E. Ciesielski, B.D. Page 12 USCL.Spring2007 4/11/07 12:13 PM Page 13

VARIATIONS McNoldy, P.J. Rogers and R.J. Taft, 2007: Multiscale variability of the flow during the Analyzing the Variations of the North American Monsoon Experiment. In press., J. Climate. Lang, T.J., D.A. Ahijevych, S.W. Global Ocean Energy Cycle Nesbitt, R.E. Carbone, S.A. Rutledge and R. Cifelli, 2007: Radar-observed characteris- William B. Rossow, NASA Goddard Institute for Space Studies tics of precipitating systems during NAME John J. Bates, NOAA National Climatic Data Center 2004. In press, J. Climate. Yuanchong Zhang, Columbia University Mestas-Nuñez, A., D.B. Enfield and C. Ken Knapp, NOAA National Climatic Data Center Zhang, 2007: Water vapor fluxes over the Intra-Americas Sea: Seasonal and interan- Ely Duenas, SSP, LLC at NASA GISS nual variability associated with rainfall. In Joy Romanski, Columbia University press, J. Climate. exchanges of energy and water to NAME Science Working Group, cited he Earth’s climate is an ener- 2007: North American Monsoon gy cycle that converts determine how they regulate and mod- Experiment Science and Implementation absorbed solar radiation into ulate the climate response to forcing. Plan. [Available online at heat and associated terrestrial For this purpose, the observations must h t t p : / / w w w. c p c . n c e p . n o a a . g o v / p r o d u c t s / m o Tradiation and into the circulations of the have a combination of high space-time nsoon/NAME.html.] atmosphere and ocean. A key exchange resolution and global, long-term cover- Nesbitt, S.W. and D.J. Gochis, 2007: age that can only be provided, in prac- Characteristics of convection along the of energy within the system, which also Sierra Madre Occidental observed during couples the circulations of the atmos- tice, by systematic satellite observa- NAME-2004: Implications for warm season phere and ocean, is between the surface tions. The former is required to resolve precipitation estimation in complex terrain. and the atmosphere, primarily through accurately the energy and water Manuscript in preparation. evaporation cooling of the surface and exchange variations at the weather- Ray, A.J., G.M. Garfin, M. Wilder, M. precipitation heating of the atmosphere, process-level and the latter is required Vasquez-Leon, M. Lenart and A.C. Comrie, forming a water cycle intimately linked to provide enough examples of the dif- 2007: Applications of monsoon research: ferent possible configurations of the Opportunities to inform decision making to the planetary energy cycle. Because and reduce regional vulnerability. In press, of Earth’s spherical shape, rapid rota- climate system to understand the range J. Climate. tion and elliptical orbit about the sun, of multi-variate, non-linear relation- Vivoni, E.R., H.A. Gutierrez-Jurado, the solar heating is neither uniform nor ships that are produced by the interac- C.A. Aragon, L.A. Mendez-Barrozo, A.J. constant. Because of the turbulent tions of the processes. Rinehart, R.L. Wycoff, J.C. Rodriguez, C.J. nature of the atmospheric and oceanic To describe the complete energy- Watts, J.D. Bolten, V. Lakshmi and T.J. Jackson, 2007 : Variation of hydrometeoro- motions that transport heat and water water cycle requires measurements of logical conditions along a topographic tran- with very different characteristic times the thermodynamic state of all the cli- sect in northwestern México during the scales, the response of the system is nei- mate components and the hydrody- North American monsoon. In press, J. ther steady nor in instantaneous bal- namic state of the atmosphere and Climate. ance. Although some statistics of the ocean, as well as all the properties of Watts, C.J., R.L. Scott, J. Garatuza- variations of energy and water them that affect the energy and water ayan, J.C. Rodriguez, J.H. Prueger, W.P. exchanges among the several climate Kustas and M. Douglas, 2007: Changes in exchanges. The state is described by vegetation condition and surface fluxes dur- system components may be static, the the 4-dimensional distribution of tem- ing NAME 2004. In press, J. Climate. e n e rgy-water cycle is fundamentally perature, humidity and winds in the Williams, C.R., A.B. White, K.S. Gage dynamic. atmosphere, of the temperature, salini- and F.M. Ralph, 2007: Vertical structure of Basic questions about the climate ty and currents in the ocean and the precipitation and related microphysics are: how variable is the climate with a temperature and “water content” of the observed by NOAA profilers and TRMM land and ice. To calculate the during NAME 2004. In press, J. Climate. “statistically steady” forcing (natural exchanges of energy requires determi- Zhu, C., T. Cavazos and D.P. variability) and how sensitive is the cli- Lettenmaier, 2007: Role of antecedent land mate to systematic changes in the forc- nation of the tendencies of the state surface conditions in warm season precipita- ing (climate change)? The latter is variables and their atmospheric and tion over northwestern México. In press, J. determined by numerous feedback oceanic transports which are functions Climate. processes that operate to alter the of spatial derivatives of these vari- Zuidema, P. C. Fairall, L.M. Hartten, exchanges of energy and water within ables. Additional properties that are J.E. Hare and D. Wolfe, 2007: On air-sea the system and with the outside but, in needed to calculate radiative interaction at the mouth of the Gulf of exchanges are the gas composition of California. In press, J. Climate. the truly dynamic climate system, the former is also influenced by these same the atmosphere (including the main processes. To learn the answers to these greenhouse gases), aerosols, clouds questions, therefore, we must observe and surface spectral albedo/emissivity. the varying relationships amongst the The main additional quantities to components of the climate system and determine the water cycle are precipi- diagnose the variations of their Page 13 USCL.Spring2007 4/11/07 12:13 PM Page 14

U.S. CLIVAR datasets (two different surface radiative flux products, ISCCP-FD and SRB [Stackhouse et al. 2001] and three dif- Figure 1. Comparison ferent surface turbulent flux products, of the decadal-scale GSSTF2, HOAPS [Grassl et al. 2000] anomaly in net surface and WHOI [Yu et al, 2004]), we can fluxes and the varia- tions of annual upper- estimate the mean meridional heat ocean heat content. transport of the global oceans (Figure 2), where the error bars indicate the spread of estimates obtained from these different data combinations (cf. Zhang and Rossow [1997]). The uncertainties are particularly significant in the south- ern oceans and are primarily caused by differences among the turbulent flux tation (rain and snow), evaporation, global mean heat content of the upper data products (cf. Chou et al. [2004]) water storage on the land as snow/ice ocean, diagnosed from buoy and satellite rather than the surface radiative flux and in the deep acquifer, as well as observations (Willis et al. [2004], updat- products (cf. Zhang et al. [2006]). water runoff from the land to the ocean. ed, private communication), compared Anomalies in the total (atmosphere The state of the ocean has been with the heat content variation inferred plus ocean) meridional energy trans- observed very sparsely for the past from the total surface energy fluxes, port over the past two decades inferred many decades but only recently have based on the GEWEX Surface Radiation from the ISCCP-FD reconstruction of these data been compiled to provide a Budget product (SRB, Stackhouse et al. top-of-atmosphere radiative fluxes, comprehensive description of the state [2001]) and the GSSTF2 turbulent flux- which agrees very well [Zhang et al. and circulation of the ocean. The World es [Chou et al. 2003]. Such a diagnostic 2004] with directly inferred anomalies Climate Research Program (WCRP) approach for the heat budget has been at lower latitudes from ERBE [Wong et was established, in part, to coordinate advocated by Pielke [2003]. Levitus et al. 2006]. The uncertainties in the sur- activities to develop a number of al. [2000] has compiled a longer record face fluxes currently preclude a defini- datasets that were missing for describ- of ocean heat content. Given the “large” tive separation of these features into ing the energy-water cycle [GARP uncertainties associated with these data separate atmospheric and oceanic con- 1975]. Among the first WCRP activities products, it is no wonder that these tributions, but the association with were projects to determine the thermo- results do not yet agree but the magni- ENSO events is clear, although vari- dynamic state of the world ocean (the tude of the differences is much smaller able. The higher latitude location of the World Ocean Circulation Experiment, than expected. Moreover, the surface transport anomalies in 1998/99, as con- WOCE) and to study the coupling flux products have known sources of trasted with generally lower latitude between the tropical oceans and global uncertainty that can be worked on to anomalies during other events, sug- atmosphere (Tropical Ocean Global improve them; in particular the surface gests the possibility that the former Atmosphere, TOGA). These studies are latent heat flux products based on satel- event was dominated by a change in continuing as part of the Climate lite microwave measurements appear to atmospheric heat transport while the Variations (CLIVAR) project. Several have an excessively strong increase earlier events were dominated by other projects, now collected under the (cooling) over this time period associat- changes in oceanic heat transport. If the Global Energy and Water Experiment ed with known problems of calibration. quality of these products can be (GEWEX), have produced a collection Using six different combination- improved by further evaluation and of cloud, precipitation, aerosol and radiative flux products that can provide important information about ocean- atmosphere exchanges of energy and water (Table 1, see Rossow et al. Figure 2. Mean merid- [2006]). A newer initiative under ional heat transport by GEWEX includes a project (SeaFlux) the global ocean to determine the turbulent fluxes of heat inferred from six differ- and water at the ocean surface [Curry et ent combinations of two radiative flux and al. 2004]. three turbulent flux As one illustration of analyses that products. can be done with this set of data prod- ucts, Figure 1 shows the decadal varia- tions (anomaly relative to 1993) of the Page 14 USCL.Spring2007 4/11/07 12:13 PM Page 15

VARIATIONS systematic re-processing, then this dif- NCDC. The online summary is now Schultz, S.R. Smith, P.J. Webster, G.A. Wick ference could be investigated further. available and the datasets are being and X. Zeng, 2004: SEAFLUX. Bull. Amer. Meteor. Soc., 85, 409-424. To stimulate more extensive analy- assembled for the server and should be available by the end of in 2007. This G A R P, 1975: The Physical Basis of ses of the variations of the global ener- Climate and Climate Modelling, Global gy-water cycle and the processes that collection could form the core of a larg- Atmospheric Research Program Publication influence them, as well as re-process- er climate dataset, if datasets are added Series, No. 16, pp. 265. ing of these products to improve thei by other components of the Wo r l d Grassl, H., V. Jost, R. Kumar, J. Schulz, r e l i a b i l i t y, the GEWEX Radiation Climate Research Program such as CLI- P. Bauer and P. Schluessel, 2000: T h e Panel is organizing a complete set, at VAR. H a m b u rg Ocean-Atmosphere Parameters and Fluxes from Satellite Data (HOAPS): A least one dataset for each of the compo- climatological atlas of satellite-derived air- nents of the energy-water cycle, in two References sea-interaction parameters over oceans. forms. The first is a summary of the Report No. 312, ISSN 0937-1060, Max Chou, S-H., E. Nelkin, J. Ardizzone, Planck Institute for Meteorology, Hamburg. datasets in the form of monthly mean R.M. Atlas and C-L. Shie, 2003: Surface tur- global maps, all in the same grid cover- bulent heat and momentum fluxes over glob- Levitus, S., J.I. Antonov, T.P. Boyer and ing the same time period, posted on and al oceans based on the Goddard satellite C. Stephens, 2000: Warming of the world downloadable from the GRP website: retrievals, version 2 (GSSTF2). J. Climate, ocean. Science, 287, 2225-2229. 16, 3256-3273. Pielke Sr., R., 2003: Heat storage within the ( h t t p : / / g r p . g i s s . n a s a . g o v / g e w e x d s e t s . h t Chou, S-H., E. Nelkin, J. Ardizzone and earth system. Bull. Amer. Meteor. Soc., 84, ml). The second is providing access to R.M. Atlas, 2004: A comparison of latent 331-335. the original versions of these datasets heat fluxes over global oceans for four flux Rossow, W.B., J.J. Bates, J. Romanski, (with a variety of map grids, sampling products. J. Climate, 17, 3973-3989. Y-C. Zhang, K. Knapp, E. Duenas, 2006: intervals and periods covered), starting Curry, J.A., A. Bentamy, M.A. Bourassa, Analyzing the variations of the global ener- with the four GRP products for radia- D. Bourras, M. Brunke, S. Castro, S. Chou, gy and water cycle. GEWEX NEWS, 16, 3- 5. tion, precipitation, clouds and aerosols, C.A. Clayson, W.J. Emery, L. Eymard, C.W. Fairall, M. Kubota, B. Lin, W. Perrie, R.R. on an active server to be hosted by Willis, J.K, D. Roemmich and B. R e e d e r, I.A. Renfrew, W.B. Rossow, J. Cornuelle, 2004: Interannual variability of upper ocean heat content, temperature and thermosteric expansion on global scales. J. Geophys. Res., 109, doi 10.1029/2003JC002260, (1-13). Wong, T., B.A. Wielicki and R.B. Lee III, 2006: Re-examination of the observed decadal variability of earth radiation budget using altitude-corrected ERBE/ERBS non- scanner WFOV data. J. Climate, (in press). Yu, L., R.A. Weller and B. Sun, 2004: Improving latent and sensible heat flux esti- mates for the Atlantic Ocean (1988-1999) by Table 1. Some available global, a synthesis approach. J. Climate, 17, 373- long-term datasets that can be 393. used to quantify variations of Zhang, Y-C., and W.B. Rossow, 1997: the global energy-water cycle. Estimating meridional energy transports by Most of these are being pro- the atmospheric and oceanic general circula- duced or studied in GEWEX activities; references and rele- tion using boundary flux data. J. Climate, vant web site addresses for 10, 2358-2373. these datasets can be found on Zhang, Y-C., W.B. Rossow, A.A. Lacis, the GEWEX Radiation Panel M.I. Mishchenko and V. Oinas, 2004: web site at Calculation of radiative fluxes from the sur- http://grp.giss.nasa.gov/gewexd face to top-of-atmosphere based on ISCCP sets.html). Additional products and other global datasets: Refinements of (not all mentioned below) are the radiative transfer model and the input being studied in CLIVAR activi- data. J. Geophys. Res., 109, doi ties. Asterisks indicate datasets 10.1029/2003JD004457, 1-27 + 1-25.. to be provided on the NCDC active server. Zhang, Y-C., W.B. Rossow and P.W. Stackhouse, 2006: Comparison of different global information sources used in surface radiative flux calculations: Radiative prop- erties of the near-surface atmosphere. J. Geophys. Res., 111, D13106, doi:10.1029/2005JD006873, (1-13).

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U.S. CLIVAR U.S. CLIVAR Western Boundary Current Working Group

- How does air-sea interaction compare in the n January 2007, the U.S. CLIVAR Western western North Atlantic and North Pacific? What Boundary Current Working Group began. A are the implications of the differences? primary objective of the working group is to I - What is the nature of atmosphere-ocean interac- encourage better understanding of the climate tion in western boundary current regions? On implications of the western boundary current what temporal and spatial scales does this occur? atmosphere-ocean interaction, which will in turn Is there predictability in the system? improve the decadal and longer timescale pre- - To what extent are coupled models getting the dictability of the climate system.This working interaction right? Can we identify specific group topic is timely because the Kuroshio problems in ocean or atmosphere models? Is there Extension System Study (KESS) and CLIVAR a "coupled" interaction? What numerical experi- Intermediate Mode Water Dynamic Experiment ments need to be done to test hypotheses? (CLIMODE) groups are just beginning their analy- - To what extent does air-sea interaction extend sis work, so the synthesis of those analyses could beyond the boundary layer and influence broader be shaped by encouraging joint group meetings. climate variability in both the atmosphere and In addition, high-resolution satellite observations ocean? What role do stratiform and convective (with lengthening data records) and more accu- clouds play in the atmospheric response? rate ocean and climate models are spurring Additional information regarding the increased interest in the midlatitude western Western Boundary Working Group can be found boundary current regions. at: http://www.usclivar.org/Organization/wbc- The working group will seek answers to the wg.html following science questions:

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