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Variations-V5N1.Pdf USCL.Spring2007 4/11/07 12:13 PM Page 1 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.
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