DOCSLIB.ORG

NOTES and CORRESPONDENCE Variability of Southern Hemisphere Cyclone and Anticyclone Behavior: Further Analysis

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

1APRIL 2003 NOTES AND CORRESPONDENCE 1075 NOTES AND CORRESPONDENCE Variability of Southern Hemisphere Cyclone and Anticyclone Behavior: Further Analysis ALEXANDRE BERNARDES PEZZA AND TEÂ RCIO AMBRIZZI Department of Atmospheric Sciences, Institute of Astronomy, Geophysics and Atmospheric Sciences, University of SaÄo Paulo, Sao Paulo, Brazil 27 December 2001 and 23 September 2002 ABSTRACT This paper presents some additional results on the use of an automatic scheme for tracking surface cyclones and anticyclones. The Southern Hemisphere (SH) total amount of synoptic tracks (every 12 h) was analyzed for the 1973±96 period using sea level pressure from the National Centers for Environmental Prediction±National Center for Atmospheric Research (NCEP±NCAR) reanalysis. Composites for seven El NinÄo (EN) and La NinÄa (LN) years were constructed in order to analyze the association between the hemispheric cyclone and anticyclone propagation and the phase of the El NinÄo±Southern Oscillation (ENSO) phenomenon. A climatological view of cyclone and anticyclone tracks and orphan centers superposed on the same map is presented and analyzed. A large area with overlapped cyclone and anticyclone tracks is seen between 308 and 608S, which is approximately the climatological position of the SH transient activity. To the north of 308S, the subtropical South Atlantic high is embedded in a region with just a few cyclone tracks. This feature is not evident for the Paci®c and the Indian Oceans' high. The subtropical cyclones dominate most of the west Paci®c and north of Australia. Orographic and heat lows are well spread over the tropical regions of South America and Africa. Finally, the storm track region appeared as a very marked feature around the Antarctic continent. In accordance with some previous studies, the total number of the SH cyclones and anticyclones during the austral winter season has shown an overall decline, particularly at the end of the 1970s. Nevertheless, a more complex behavior shows up when the weak systems are eliminated and the intense end of the spectrum is analyzed. For the anticyclone tracks above 1020 hPa, there is still some tendency toward an overall decline, but it is small and not statistically signi®cant. For the stronger anticyclones this tendency rapidly disappears. On the other hand, the cyclone tracks presented a different behavior, since the decreasing trend turned into a signi®cant increase for those stronger than 980 hPa. These results also emphasize how sensitive the tracking scheme is to capturing low and high pressure centers, and it presents another perspective for the interpretation of cyclone and anticyclone trends. The ENSO composites indicated a higher anticyclone concentration near the subtropical South Atlantic high during EN years, while in the subtropical South Paci®c high it occurs during LN years. On the other hand, the cyclone tracks showed a higher variability, with an excess of lows over the subtropical Paci®c, west of South America and southern Argentina during EN years and a more pronounced activity over the subtropical Atlantic and southeastern Australia during LN years. Nevertheless, the trends and the average of the total hemispheric number of cyclones and anticyclones are not signi®cantly affected by the ENSO phase. 1. Introduction ridges are one of the main causes of weather changes all over the subtropics and polar regions. Over the decades, operational meteorologists have In the past, the process of monitoring low and high been drawing synoptic charts with a particular concern pressure tracks on a climatic basis demanded a lot of for the precise location of cyclones and anticyclones operational time because of its manual nature. Nowa- near the surface. It is well known by experienced me- days, however, the situation is completely different due teorologists (e.g., Taljaard 1967) that these systems and to recent developments on automatic tracking schemes their movement associated with high-level troughs and like the ones described in Murray and Simmonds (1991a,b) and Sinclair (1994). Automatic procedures can be applied for ®nding and Corresponding author address: Dr. Alexandre Bernardes Pezza, tracking highs and lows from operational numerical Dept. of Atmospheric Sciences, University of SaÄo Paulo, Rua do MataÄo, 1226, CEP 05508-900, SaÄo Paulo SP, Brazil. analyses. The most important advantages are the pos- E-mail: [email protected] sibility of handling a large amount of information in a q 2003 American Meteorological Society Unauthenticated | Downloaded 10/02/21 07:59 PM UTC 1076 JOURNAL OF CLIMATE VOLUME 16 shorter time frame and generating results that can be h analyses seem to be suitable for climatological ap- easily compared between them, because most outputs plications. The area of study is the Southern Hemi- obtained from any automatic scheme are reproducible. sphere, and track analyses have been carried out during Furthermore, what constitutes a low or high pressure the SH wintertime, that is June±July±August (JJA). center is precisely speci®ed. Some authors have shown that there are arti®cial pres- Murray and Simmonds (1991a,b) developed one of sure trends in the NCEP±NCAR reanalysis over the the ®rst automatic procedures available nowadays to Southern Hemisphere (Hines et al. 2000; Simmonds and ®nd and track surface pressure systems. Jones and Sim- Keay 2000a). In fact, the SH has experienced a sub- monds (1993, 1994) analyzed the performance of such stantial increase in data coverage over the last few de- a tracking scheme with different datasets and concluded cades, which has affected the quality of the reanalysis that it is a very useful tool for meteorological appli- data (E. Kalnay 2000, personal communication). From cations. They were able to reproduce and complement our own compilations, it was observed that the period some previous results found in the literature. after 1975 experienced a reduction in the extratropical Nowadays, a large number of studies have applied sea level pressure up to 6 hPa in the border of the automatic schemes for tracking cyclones and anticy- Antarctic continent, in comparison to the period be- clones and con®rmed their reliability, adding a new tween 1950 and 1975. Bearing this in mind, only the global perspective for the signature of transient systems last available period was used, in which the coverage (e.g., Sinclair 1994, 1995, 1996; Sinclair et al. 1997; is much better than what it was before. Simmonds and Keay 2000a,b and references therein) The MS scheme was developed by Dr. Ross J. Murray and even tropical systems (Sinclair 2002). Indeed, in a and Dr. Ian Simmonds, from the University of Mel- recent work Sinclair (2002) showed the reliability of his bourne, Australia, in order to identify and track low and automatic scheme in capturing the transition of tropical high pressure centers on a sphere. The main principle cyclones into midlatitude systems over the southwest is that the center of a closed cyclone (anticyclone) is Paci®c. This is just an example of how developed and unequivocally identi®ed with its point of minimum physically consistent (and hence useful) the automatic (maximum) pressure; this is normally found within one schemes can be nowadays. grid space of the Laplacian maximum (minimum), de- In this work, a wintertime Southern Hemisphere (SH) pending on the degree of symmetry of the pressure sys- climatology of cyclone and anticyclone tracks created tem. A cyclone (anticyclone) is deemed to exist at any using the National Centers for Environmental Predic- point at which the pressure is lower (higher) than at any tion±National Center for Atmospheric Research of a small number of grid points (four or eight) sur- (NCEP±NCAR) reanalysis data applied to the Murray rounding it. The dimension problem related to the grid and Simmonds (hereafter MS) automatic scheme is pre- space was partially solved through the use of bicubic- sented for the 1973±96 period. A climatological map splines ®t. The pressure is approximated by a smoothly with the total synoptic tracks superposed was produced varying function, and the pressure Laplacian is used to in order to have a precise hemispheric signature for these ®nd the cyclones and anticyclones. systems. The total amount of tracks and orphan systems The array is ®rst scanned for the sites of ``possible'' were counted in order to analyze possible climatic lows (or highs) by comparing the values at neighboring trends. grid points. To allow for the possibility that a shallow Another perspective for the climatic trend shown by depression (ridge) may not be detected by a local min- Simmonds and Keay (2000b), particularly with relation imization (maximization) of gridpoint values, a less re- to their Fig. 6a will be discussed. Finally, some com- strictive scanning procedure has been implemented. posites of SST anomalies and cyclone and anticyclone This procedure seeks grid points at which the Laplacian track maps overlapping all synoptic trajectories were of the pressure shall be greater (or lower in the case of made for seven El NinÄo (EN) and La NinÄa (LN) years. an anticyclone) than at any of the eight surrounding Possible changes on the hemispheric high and low pres- points and greater than a speci®c threshold. In the case sure belts associated with the El NinÄo±Southern Oscil- of an open depression (ridge), in which no point of lation (ENSO) phase are discussed. minimum (maximum) pressure exists, it was decided that a suitable analog for it would be the in¯exion point in the pressure surface, that is, the point of the minimum 2. Data and methodology (maximum) pressure gradient. Finally, the lows and The MS automatic scheme was used to ®nd and track highs are checked for having the character of a mid- high and low pressure centers near the surface. Mean latitude storm. The method that was found to give good sea level pressure data from the NCEP±NCAR reanal- discrimination is one that requires a minimum average ysis (Kalnay et al.
Recommended publications
  • Air Masses and Fronts

    Air Masses and Fronts

    CHAPTER 4 AIR MASSES AND FRONTS Temperature, in the form of heating and cooling, contrasts and produces a homogeneous mass of air. The plays a key roll in our atmosphere’s circulation. energy supplied to Earth’s surface from the Sun is Heating and cooling is also the key in the formation of distributed to the air mass by convection, radiation, and various air masses. These air masses, because of conduction. temperature contrast, ultimately result in the formation Another condition necessary for air mass formation of frontal systems. The air masses and frontal systems, is equilibrium between ground and air. This is however, could not move significantly without the established by a combination of the following interplay of low-pressure systems (cyclones). processes: (1) turbulent-convective transport of heat Some regions of Earth have weak pressure upward into the higher levels of the air; (2) cooling of gradients at times that allow for little air movement. air by radiation loss of heat; and (3) transport of heat by Therefore, the air lying over these regions eventually evaporation and condensation processes. takes on the certain characteristics of temperature and The fastest and most effective process involved in moisture normal to that region. Ultimately, air masses establishing equilibrium is the turbulent-convective with these specific characteristics (warm, cold, moist, transport of heat upwards. The slowest and least or dry) develop. Because of the existence of cyclones effective process is radiation. and other factors aloft, these air masses are eventually subject to some movement that forces them together. During radiation and turbulent-convective When these air masses are forced together, fronts processes, evaporation and condensation contribute in develop between them.
  • Extreme Climatic Characteristics Near the Coastline of the Southeast Region of Brazil in the Last 40 Years

    Extreme Climatic Characteristics Near the Coastline of the Southeast Region of Brazil in the Last 40 Years

    Extreme Climatic Characteristics Near the Coastline of the Southeast Region of Brazil in the Last 40 Years Marilia Mitidieri Fernandes de Oliveira ( [email protected] ) Federal University of Rio de Janeiro: Universidade Federal do Rio de Janeiro Jorge Luiz Fernandes de Oliveira Fluminense Federal University Pedro José Farias Fernandes Fluminense Federal University, Physical Geography Laboratory (LAGEF), Eric Gilleland National, Center for Atmospheric Research (NCAR) Nelson Francisco Favilla Ebecken Federal University of Rio de Janeiro: Universidade Federal do Rio de Janeiro Research Article Keywords: ERA5 Reanalysis data, Non-parametric statistical tests, severe weather systems, subtropical cyclones Posted Date: June 7th, 2021 DOI: https://doi.org/10.21203/rs.3.rs-159473/v1 License: This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License 1 Extreme climatic characteristics near the coastline of the Southeast region of Brazil in the last 40 years Marilia Mitidieri Fernandes de Oliveira1, Jorge Luiz Fernandes de Oliveira2, Pedro José Farias Fernandes3, Eric Gilleland4, Nelson Francisco Favilla Ebecken1 1Federal University of Rio de Janeiro, Civil Engineering Postgraduate Program-COPPE/UFRJ, Center of Technology, Rio de Janeiro 21945-970, Brazil 2Fluminense Federal University, Geography Postgraduate Program, Department of Geography, Geoscience Institute, Niterói 24210-340, Brazil 3Fluminense Federal University, Physical Geography Laboratory (LAGEF), Department of Geography, Niterói 24210-340,
  • NOTES and CORRESPONDENCE Synoptic-Scale Controls of Summer

    NOTES and CORRESPONDENCE Synoptic-Scale Controls of Summer

    15 FEBRUARY 2006 NOTES AND CORRESPONDENCE 613 NOTES AND CORRESPONDENCE Synoptic-Scale Controls of Summer Precipitation in the Southeastern United States JEREMY E. DIEM Department of Anthropology and Geography, Georgia State University, Atlanta, Georgia (Manuscript received 15 October 2004, in final form 11 August 2005) ABSTRACT Past climatological research has not quantitatively defined the synoptic-scale circulation deviations re- sponsible for anomalous summer-season precipitation totals in the southeastern United States. Therefore, the objectives of this research were to determine the synoptic-scale controls of wet and dry multiday periods during the summer within a portion of the southeastern United States as well as to assess the linkages between synoptic-scale circulation and multidecadal variations in precipitation characteristics for the study domain. Daily precipitation data from 30 stations for June, July, and August from 1953 to 2002 were converted into 13-day totals. Using standardized principal components analysis (PCA), the study domain was divided into three precipitation regions (i.e., South, Northwest, and Northeast). Wet and dry periods for each region were composed of the top 56 and bottom 56 thirteen-day periods. Composite circulation maps for 500 and 850 mb revealed the following: wet periods were generally associated with an upper-level trough over the interior southeastern United States coincident with strong lower-tropospheric flow into the South- east from the Gulf of Mexico, and dry periods were characterized by ridges or anticyclones over the midwestern and southeastern United States coupled with weak lower-tropospheric flow. Many of the wet periods had surface fronts. Over the 50-yr period, increased precipitation was significantly correlated with increased occurrences of midtropospheric troughs over the study domain.
  • 1 Climatology of South American Seasonal Changes

    1 Climatology of South American Seasonal Changes

    Vol. 27 N° 1 y 2 (2002) 1-30 PROGRESS IN PAN AMERICAN CLIVAR RESEARCH: UNDERSTANDING THE SOUTH AMERICAN MONSOON Julia Nogués-Paegle 1 (1), Carlos R. Mechoso (2), Rong Fu (3), E. Hugo Berbery (4), Winston C. Chao (5), Tsing-Chang Chen (6), Kerry Cook (7), Alvaro F. Diaz (8), David Enfield (9), Rosana Ferreira (4), Alice M. Grimm (10), Vernon Kousky (11), Brant Liebmann (12), José Marengo (13), Kingste Mo (11), J. David Neelin (2), Jan Paegle (1), Andrew W. Robertson (14), Anji Seth (14), Carolina S. Vera (15), and Jiayu Zhou (16) (1) Department of Meteorology, University of Utah, USA, (2) Department of Atmospheric Sciences, University of California, Los Angeles, USA, (3) Georgia Institute of Technology; Earth & Atmospheric Sciences, USA (4) Department of Meteorology, University of Maryland, USA, (5) Laboratory for Atmospheres, NASA/Goddard Space Flight Center, USA, (6) Department of Geological and Atmospheric Sciences, Iowa State University, USA, (7) Department of Earth and Atmospheric Sciences, Cornell University, USA, (8) Instituto de Mecánica de Fluidos e Ingeniería Ambiental, Universidad de la República, Uruguay, (9) NOAA Atlantic Oceanographic Laboratory, USA, (10) Department of Physics, Federal University of Paraná, Brazil, (11) Climate Prediction Center/NCEP/NWS/NOAA, USA, (12) NOAA-CIRES Climate Diagnostics Center, USA, (13) Centro de Previsao do Tempo e Estudos de Clima, CPTEC, Brazil, (14) International Research Institute for Climate Prediction, Lamont Doherty Earth Observatory of Columbia University, USA, (15) CIMA/Departmento de Ciencias de la Atmósfera, University of Buenos Aires, Argentina, (16) Goddard Earth Sciences Technology Center, University of Maryland, USA. (Manuscript received 13 May 2002, in final form 20 January 2003) ABSTRACT A review of recent findings on the South American Monsoon System (SAMS) is presented.
  • El Niño and Health

    El Niño and Health

    World Health Organization Sustainable Development and Healthy Environments WHO/SDE/PHE/99.4 English only Dist. Limited El Niño and Health Protection of the Human Environment Task Force on Climate and Health Geneva 1999 EL NINO AND HEALTH PAGE i El Niño and Health R Sari Kovats Department of Epidemiology and Population Health London School of Hygiene and Tropical Medicine, United Kingdom Menno J Bouma Department of Infectious and Tropical Diseases London School of Hygiene and Tropical Medicine, United Kingdom Andy Haines Department of Primary Care and Population Sciences Royal Free and University College Medical School University College London United Kingdom CONTENTS ACKNOWLEDGEMENTS ................................................................................................. iii PREFACE ...........................................................................................................iv EXECUTIVE SUMMARY .....................................................................................................v 1. EL NIÑO SOUTHERN OSCILLATION......................................................................1 1.1 What is the El Niño Southern Oscillation? ...........................................................1 1.1.1 ENSO parameters................................................................................1 1.1.2 Frequency of El Niño............................................................................4 1.1.3 The El Niño of 1997/98 ........................................................................6 1.2 Long-term
  • Synoptic-Scale Controls of Fog and Low Clouds in the Namib Desert: Response to Reviewer 1

    Synoptic-Scale Controls of Fog and Low Clouds in the Namib Desert: Response to Reviewer 1

    Synoptic-scale controls of fog and low clouds in the Namib Desert: Response to Reviewer 1 Hendrik Andersen, Jan Cermak, Julia Fuchs, Peter Knippertz, Marco Gaetani, Julian Quinting, Sebastian Sippel, and Roland Vogt contact: [email protected] We would like to thank reviewer 1 for her/his careful review of the manuscript and her/his constructive criticism and valuable comments. Comments by the referee are colored in black, our replies or comments are colored in blue and italics. Using a 14-year period of reanalysis grids and backward trajectories, this study examines the impact of large-scale dynamics and thermodynamics on fog and low clouds (FLCs) over Namib. Specifically, the authors’ focus on two seasons when different FLC types are observed due to different synoptic-scale regimes. A main finding is that the mean sea level pressure (MSLP) field differs notably between clear and FLC days. To this end, the authors’ use a statistical model and MSLP fields to provide skillful prediction of FLCs up to one day in advance. A new conceptual model of the two different FLC regimes is developed to summarize findings and aid in future studies related to FLCs over Namib. In general, the scientific purpose is justified, the findings are important, and the paper is well-written; however, I do have concerns about some of the methods used. Overall, I think that the results are interesting and worthy of publication, and at this stage I suggest acceptance subject to major revisions. Major/general comments: 1. Use of MSLP, 2 m temperature, and 10 m winds to characterize synoptic-scale conditions This study relies on the assumption that near-surface (boundary layer) meteorological variables – specifically MSLP, 2 m temperature, and 10 m horizontal wind components – are representative of the large-scale dynamics.
  • Weather, Current and Routing Brief the Clipper 11/12 Round the World

    Weather, Current and Routing Brief the Clipper 11/12 Round the World

    Weather, Current and Routing Brief The Clipper 11/12 Round the World Race Prepared for the Race Skippers by Simon Rowell 27th April 2011 1. Leg One - Europe to Rio de Janeiro (early August to mid September) 4 1.1. The Route 4 1.2. The Weather 6 1.2.1. The Iberian Peninsula to the Canaries 6 1.2.2. The Canaries 10 1.2.3. The Canaries to the ITCZ, via the Cape Verdes 11 1.2.4. The ITCZ in the Atlantic 13 1.2.5. The ITCZ to Cabo Frio 16 1.3. Currents 18 1.3.1. The Iberian Peninsula to the Equator 18 1.3.2. The Equator to Rio 20 2. Leg 2 – Rio de Janeiro to Cape Town (mid September to mid October) 22 2.1. The Route 22 2.2. The Weather 22 2.3. Currents 27 3. Leg 3 – Cape Town to Western Australia (October to November) 29 3.1. The Route 29 3.2. The Weather 30 3.2.1. Southern Indian Ocean Fronts 34 3.3. Currents 35 3.3.1 Currents around the Aghulas Bank 35 3.3.2 Currents in the Southern Indian Ocean 37 4. Leg 4 –Western Australia to Wellington to Eastern Australia (mid November to December) 4.1. The Route 38 4.2. The Weather 39 4.2.1. Cape Leeuwin to Tasmania 39 4.2.2. Tasmania to Wellington and then to Gold Coast 43 4.3. Currents 47 5. Leg 5 – Gold Coast to Singapore to Qingdao (early January to end of February) 48 5.1.
  • North and South American Low-Level Jets

    North and South American Low-Level Jets

    American Low Level jetS A Scientific Prospectus and Implementation Plan North and South American Low-Level Jets Draft, March 2001 Prepared by Julia Nogues-Paegle and Jan Paegle (University of Utah, USA) with con- tributions from Michael Douglas (NOAA/NSSL, USA), Matilde Nicolini, Carolina Vera (University of Buenos Aires, Argentina), Jose Marengo (CPTEC, Brazil), Rene Garreaud (University of Chile, Chile), James Shuttleworth (University of Arizona, USA), C. Roberto Mechoso (UCLA, USA) and E. Hugo Berbery (University of Mary- land, USA). TABLE OF CONTENTS Executive Summary 5 1. What is the ALLS program? 6 2. Why the American Jets? 9 3. Science Objectives 11 3.1 Identify LLJ events and variability 11 3.1.1. North America 11 3.1.2. South America 14 3.2 Quantify LLJ contributions to the hydrological cycle 16 3.2.1. North America 16 3.2.2. South America 17 3.3 Determine plateau effects 19 3.3.1. North America 19 3.3.2. South America 19 3.4 Develop and validate theories on LLJ generation and variability 21 3.4.1. North America 21 3.4.2. South America 22 3.4.3 Local and remote influences on ALLS in relation 23 to droughts and floods 4. Implementation Plan 26 4.1 Numerical Modelling 26 4.2 Diagnostic Studies 29 4.3 Field Component of ALLS 30 4.3.1. Region of focus for the ALLS South American Field Program 32 4.3.2. Radiosonde network 33 4.3.3. Pilot balloon observations 35 4.3.4. Wind profiler observations 35 4.3.5.
  • Observational Study of Subtropical Highs

    Observational Study of Subtropical Highs

    Observational Study of Subtropical Highs Richard Grotjahn Dept. of Land, Air, and Water Resources University of California, Davis, U.S.A. Organization of Talk • There are 5 subtropical highs • Question: What season (or month) is each high strongest? • Question: What are other climatological aspects of the highs? • Question: What are some simple conceptual models? • Question: What remote processes seem linked to each high, and which leads? • Simple statistical analyses: means, variation, 1-pt correlations, composites will be shown • Apology: This is NOT a comprehensive survey of observational work by others. • Note: I will NOT discuss theories except to list them and state how they provide rationales for choosing certain remote variables. A Simple Fact about the Subtropical Highs On a ZONAL MEAN, they are strongest in winter. • NH SH Do individual subtropical highs have the same seasonal max? Not necessarily! Climatology: North Pacific High • On a long term monthly mean, the central pressure is greatest in SUMMER not winter. – Summer (July) • Shape is fairly consistent from year to year • location of the max SLP varies Climatology: North Atlantic High • On a long term monthly mean, the central pressure is greatest in SUMMER not winter. – Summer (July) – Secondary max in winter due to spill over from N. African cold high • Shape quite consistent from year to year • location of max SLP largest latitude variation North Atlantic High (1979-2004) 1031 Median 1030 1029 3rd Quartile 1028 1st Quartile 1027 Mean 1026 1025 1024 1023 1022 Central PresssureCentral (hPa) 1021 1020 1019 1018 J FMAMJ J ASOND Month Climatology: South Indian Ocean High • On a long term monthly mean, the central pressure is greatest in winter.
  • NWSI 10-2201, Dated February 5, 2004

    NWSI 10-2201, Dated February 5, 2004

    Department of Commerce • National Oceanic & Atmospheric Administration • National Weather Service NATIONAL WEATHER SERVICE INSTRUCTION 10-2201 January 6, 2010 Operations and Services Readiness, NWSPD 10-222 BACKUP OPERATIONSS NOTICE: This publication is available at: http://www.nws.noaa.gov/directives/ OPR: W/OS1 (K. Woodworth) Certified by: W/OS1 (C. Woods) Type of Issuance: Routine SUMMARY OF REVISIONS: This directive supersedes NWSI 10-2201, dated February 5, 2004. This directive includes the following changes: 1. Updated wording in section 2.2 to indicate that specific backup plan information for NWS Regions can be found in the associated regional supplements, applicable to NWSI 10-2201. Also changed “primary and secondary backup sites” to just “backup sites” 2. Added wording to section 2.7 to account for the possibility of additional local observational data being ingested through LDAD which can be used to initialize GFE gridded data. 3. Updated Appendix A for additional wording to account for “RVA” as a critical product issued by RFC’s during flooding situations. 4. Updated Appendix A to update wording for “coastal/lakeshore” WFO Critical products. 5. Updated Appendix A for removal of “Atlantic strike probabilities” from TPC critical products. 6. Updated Appendix A to add “Tropical cyclone wind speed probabilities (text only)”, “Tropical cyclone aviation advisory (ICAO)” and “Tropical weather outlook (text only)” to the list of TPC and CPHC/WFO Honolulu Critical Products. 7. Removed wording “WFO Guam” in Appendix A-2, due to the fact that they are no longer a Meteorological Watch Office (MWO) and updated Appendix A-4, and G-3,4 to change wording of “Tropical Cyclone Summaries” to “Tropical Cyclone Summaries - fixes for both north and south Pacific” for CPHC/WFO Honolulu.
  • Differences in Cyclogenesis and Extratropical Cyclone Tracks During Warm and Cool Analogs

    Differences in Cyclogenesis and Extratropical Cyclone Tracks During Warm and Cool Analogs

    Differences in Cyclogenesis and Extratropical Cyclone Tracks During Warm and Cool Analogs Jeffrey D. Auger1, Kirk Allen Maasch 2 1. Climate Change Institute, University of Maine. 2. School of Earth and Climate Sciences, University of Maine. Abstract: With the use of reanalysis datasets, warm and cool years will be found through variances in meteorological variables to find differences in cyclogenesis and extratropical cyclone tracks with the objective to find how warmer versus cooler years differ. This will be used to better understand the Medieval Climate Anomaly and Little Ice Age climates as well as the future environments. Proxy data has been used to show natural the LIA. It has been found that storminess variability in the atmosphere for the past one decreased during the MCA and increased during thousand years and beyond (Meeker and the LIA (Meeker and Mayewski 2002). It should Mayewski 2002). With the increase of follow that cool years will have an increase in anthropogenic forcing, the natural climate is storminess where warm years will show a increasingly becoming unpredictable. With the decrease. If this is the case, the future outlook of Medieval Climate Anomaly (MCA) and Little Ice an increase in warmer years may lead to a Age (LIA) being the most recent warm and cool decrease in storminess. analogs, respectively, more questions must be answered about these times to understand what may happen to the atmosphere and, furthermore, to the environment of the future. With the use of reanalysis datasets, recent warm and cool years will be used to build analogs to simulate the MCA and LIA.
  • Identification of Processes Driving Low-Level Westerlies in West

    Identification of Processes Driving Low-Level Westerlies in West

    1JUNE 2014 P O K A M E T A L . 4245 Identification of Processes Driving Low-Level Westerlies in West Equatorial Africa WILFRIED M. POKAM Department of Physics, Higher Teacher Training College, University of Yaounde 1, and Center for International Forestry Research, Central Africa Regional Office, Yaounde, Cameroon CAROLINE L. BAIN,ROBIN S. CHADWICK, AND RICHARD GRAHAM Met Office Hadley Centre, Exeter, United Kingdom DENIS JEAN SONWA Center for International Forestry Research, Central Africa Regional Office, Yaounde, Cameroon FRANCOIS MKANKAM KAMGA University of Mountain, Bangangte, Cameroon (Manuscript received 8 August 2013, in final form 16 January 2014) ABSTRACT This paper investigates and characterizes the control mechanisms of the low-level circulation over west equatorial Africa (WEA) using four reanalysis datasets. Emphasis is placed on the contribution of the di- vergent and rotational circulation to the total flow. Additional focus is made on analyzing the zonal wind component, in order to gain insight into the processes that control the variability of the low-level westerlies (LLW) in the region. The results suggest that the control mechanisms differ north and south of 68N. In the north, the LLW are primarily a rotational flow forming part of the cyclonic circulation driven primarily by the heat low of the West African monsoon system. This northern branch of the LLW is well developed from June to August and disappears in December–February. South of 68N, the seasonal variability of the LLW is controlled by the heating contrast between cooling associated with subsidence over the ocean and heating over land regions largely south of the equator, where ascent prevails.