DOCSLIB.ORG

Downloaded 10/07/21 04:00 PM UTC

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Downloaded 10/07/21 04:00 PM UTC 15 MAY 2007 S T E P HENS ET AL. 2191 Differences in Atmospheric Circulation between the Development of Weak and Strong Warm Events in the Southern Oscillation DAVID J. STEPHENS AND MICHAEL J. MEULENERS Department of Agriculture and Food WA, South Perth, Western Australia, Australia HARRY VAN LOON Colorado Research Associates/Northwest Research Associates, Boulder, Colorado MALCOLM H. LAMOND Lamond Weather Services, Karrinyup, Western Australia, Australia NICOLA P. TELCIK Yarra Valley Water, Mitcham, Victoria, Australia (Manuscript received 5 October 2005, in final form 7 September 2006) ABSTRACT In this study temporal and spatial aspects of El Niño (warm event) development are explored by com- paring composite sequences of sea level pressure (SLP), surface wind, and sea surface temperature (SST) anomalies leading into strong and weak events. El Niño strength is found to be related to the magnitude and spatial extent of large-scale SLP anomalies that move in a low-frequency mode. In association with this, it is also intricately linked to the amplitude and wavelength of the Rossby waves in the southern midlatitudes. The primary signature of the Southern Oscillation is a more pronounced standing wave of pressure anoma- lies between southeastern Australia and the central South Pacific leading into stronger events. A strong reversal in the strength of the annual cycle between these two regions causes a stronger (weaker) SLP gradient that drives southwesterly (northwesterly) wind stress forcing toward (away from) the western equatorial Pacific in austral winter–spring of year 0 (Ϫ1). Thus, pressure variations in the southwest Pacific preconditions the equatorial environment to a particular phase of ENSO and establishes the setting for greater tropical–extratropical interactions to occur in stronger events. Maximum warming in the Niño-3 region occurs between April and July (0) when a strong South Pacific trough most influences the trade winds at both ends of the Pacific. Cool SST anomalies that form to the east of high pressure anomalies over Indo–Australia assist an eastward propogation of high pressure into the Pacific midlatitudes and the demise of El Niño. Strong events have a more pronounced eastward propo- gation of SST and SLP anomalies and a much more noticeable enhancement of winter hemisphere Rossby waves from May–July (Ϫ1) to November–January (ϩ1). Weak events require an enhanced South Pacific trough to develop but have much less support from the North Pacific. They also appear more variable in their development and more difficult to predict with lead time. 1. Introduction ability (Latif et al. 1998; Fedorov and Philander 2000). However, the failure of operational forecasting models Recent theories and models of ENSO development to predict the rapid development, intensity, and abrupt have centered on equatorial ocean–atmosphere cou- termination of the intense 1997/98 El Niño (Ander- pling as sole explanators of Southern Oscillation vari- son and Davey 1998; Trenberth 1998; Barnston et al. 1999; Landsea and Knaff 2000) challenged this as- sumption. Subsequent analysis of the event provided Corresponding author address: Dr. David Stephens, Climate Risks and Opportunities Project, Dept. of Agriculture and Food support for the two main theories of the Southern Os- WA, Locked Bag No. 4, Bentley DC WA 6983, Australia. cillation. E-mail: [email protected] First, the Southern Osillation can be explained as a DOI: 10.1175/JCLI4131.1 © 2007 American Meteorological Society Unauthenticated | Downloaded 10/07/21 04:00 PM UTC JCLI4131 2192 JOURNAL OF CLIMATE VOLUME 20 weakly damped oscillator that needs to be triggered by Of critical importance to ENSO dynamics is the in- a random disturbance. Westerly wind bursts in the ference by van Loon (1984) that the quasi-permanent western equatorial Pacific appear necessary at the onset South Pacific trough in the surface westerlies weakens of El Niño as they are associated with 1) an eastward both the South Pacific high and associated trades dur- shift of warm water and convection, and 2) the genera- ing the important months between May, June, and July tion of oceanic Kelvin waves that warm the central and (MJJ, hereafter 3-month periods are denoted by the eastern Pacific through zonal advection and displace- first letter of each respective month). At this time, the ment of the thermocline. The timing and amplitude of trough and subtropical jet stream reach their farthest 1997 warming was attributed to exceptionally strong northward extent as part of the semiannual oscillation westerly wind events/Madden–Julian oscillation (MJO) (SAO) in trough positioning and intensity (van Loon activity, strong downwelling kelvin waves (McPhaden 1967; van Loon 1972; Hurrell et al. 1998). Over the year and Yu 1999; Picaut et al. 2002; Lengaigne et al. 2003), leading into El Niño, the South Pacific trough changes and a buildup of upper-ocean heat early in the year from a weakened to an enhanced state, that is, takes on (Meinen and McPhaden 2000; Sun 2003). MJO activity a more permanent feature (van Loon 1984). Associated was also proposed as a “triggering mechanism” that with this is a west-to-east pressure anomaly reversal or accelerated the ending of the event (Takayabu et al. “seesaw” in the southern midlatitudes (Berlage 1966; 1999; Straub et al. 2006). van Loon and Shea 1985, 1987) and other important However, the influence of the MJO on ENSO re- wind and SST anomalies (Trenberth 1976; Rasmusson mains a controversial topic (McPhaden 2004) as periods and Carpenter 1982; Harrison 1984; Harrison and Lar- of enhanced westerlies and MJO activity do not always kin 1996, 1998). Figure 1 sumarizes this process, which lead to El Niño (Chen and Wu 2000; Bergman et al. we shall call the “van Loon hypothesis.” 2001; Zhang and Gottschalck 2002; Jones et al. 2004; In austral winter/spring in the year before El Niño Levinson 2005). Of the 13 strongest MJO events since (year Ϫ1), the annual cycle is weak in the southern 1979, only the two events late in 1996 and early 1997 midlatitudes, with a strong trough pattern over the re- actually preceded an El Niño (Jones et al. 2004). Slingo gion of the Australian subtropical high, and a weak et al. (1999) found that the statistical relationship be- trough in the South Pacific (Fig. 1a). Northerly wind tween ENSO and MJO indices do not show that they anomalies between these two regions warm the Coral are causally related, and Bergman et al. (2001) specu- Sea and the southwest edge of the South Pacific con- lated that the MJO might be relevant to the timing and vergence zone (SPCZ) as it expands south in austral initial growth of El Niño rather than be responsible for spring (Ϫ1). Increased convection and lower pressures the event. over this warm water then coincide with anomalous Second, the Southern Oscillation can be viewed as a westerlies on the equatorward side of the northern lower-frequency self-sustaining mode of oscillation in SPCZ (Rasmusson and Carpenter 1982; Von Storch et the the tropical Pacific (Chen et al. 2004). Wang and al. 1988). At the southern end of the SPCZ, negative Weisberg (2000) found that off-equatorial SST and as- pressure anomalies continue to form over warm water sociated pressure anomalies in the subtropics played an and this is associated with an equatorward reposition- important role in the development and decay of the ing of the surface trough into the South Pacific (van 1997/98 El Niño. However, what went unnoticed was a Loon and Shea 1985; Fig. 1b). This whole process is major seesaw in pressure in the southern midlatitudes linked to the convective maximum in the annual cycle (van Loon and Shea 1985, 1987), and a large-scale gradually moving from southeast Asia into the Austra- propagating SLP signal noted in previous El Niño lian monsoon region (austral summer), and onto the events (Barnett 1985; Krishnamurti et al. 1986). southern end of the SPCZ (austral autumn; Meehl When Bjerknes (1966, 1969) linked maximum oce- 1987). anic warming in the eastern equatorial Pacific (El Niño) By austral winter in the El Niño year (year 0) the to the “Southern Oscillation” in pressure, the primary annual cycle is enhanced in the southern midlatitudes. cause for these events was attributed to an anomalous Stronger highs occur over Australia, and negative SLP weakening of the trade winds of the Southern Hemi- and upper-level height anomalies become established sphere and associated oceanic upwelling (Bjerknes in the central South Pacific along with an equatorward 1969). Since the South Pacific high dominates the equa- movement in the subtropical jet (Karoly 1989; Kiladis torial flow in the central and eastern Pacific to 10°N, and Mo 1998). The first result of this pattern is strong Bjerknes (1966) speculated that reasons for this warm- southerly wind anomalies to the east of an enhanced ing must be sought south of the equator. Australian high pressure. These southerlies converge Unauthenticated | Downloaded 10/07/21 04:00 PM UTC 15 MAY 2007 S T E P HENS ET AL. 2193 FIG. 1. Schematic diagram showing major weather systems and anomalies in the Southern Hemisphere in winter–spring in (a) the year before El Niño [year (Ϫ1)] and (b) during El Niño [year (0)]. The Walker Circulation (white) and westerly surface troughs (red curve) sit above surface anomalies measured at key stations represented by crosses [Alice Springs (A), Darwin (D), Easter Island (E), Mildura (M), Noumea (N), Rapa Island (R), Tahiti (T), Willis Island (W)]. The SPCZ is represented by parallel gray lines. Warm (red) and cold (green) SST anomalies are indicated, as are wind anomalies (black arrows). High and low SLP are indi- cated by “H” and “L” and anomalous pressures in the midlatitudes are dashed. with and intensify westerly wind anomalies in the equa- 2004; Thompson and Lorenz 2004; Anderson and Ma- torial western Pacific and appear to play a determining loney 2006).
Load more

Recommended publications
  • 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.
    [Show full text]
  • 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
    [Show full text]
  • 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.
    [Show full text]
  • 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.
    [Show full text]
  • 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.
    [Show full text]
  • Late Victorian Holocausts Late Victorian Holocausts El Niño Famines and the Making of the Third World
    Late Victorian Holocausts Late Victorian Holocausts El Niño Famines and the Making of the Third World MIKE DAVIS First published by Verso 2001 Copyright 2001 Mike Davis All rights reserved The moral rights of the author have been asserted Verso UK: 6 Meard Street, London W1V 3HR US: 20 Jay Street, Suite 1010, Brooklyn, NY 11201 Verso is the imprint of New Left Books eISBN 978-1-78168-061-2 British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress Designed and typeset by Steven Hiatt San Francisco, California Printed and bound in the USA by R. R. Donnelly & Sons Offended Lands … It is so much, so many tombs, so much martyrdom, so much galloping of beasts in the star! Nothing, not even victory will erase the terrible hollow of the blood: nothing, neither the sea, nor the passage of sand and time, nor the geranium flaming upon the grave. – Pablo Neruda (1937) Contents Acknowledgements Preface A Note on Definitions PART I The Great Drought, 1876–1878 1 Victoria’s Ghosts 2 ‘The Poor Eat Their Homes’ 3 Gunboats and Messiahs PART II El Niño and the New Imperialism, 1888–1902 4 The Government of Hell 5 Skeletons at the Feast 6 Millenarian Revolutions PART III Decyphering ENSO 7 The Mystery of the Monsoons 8 Climates of Hunger PART IV The Political Ecology of Famine 9 The Origins of the Third World 10 India: The Modernization of Poverty 11 China: Mandates Revoked 12 Brazil: Race and Capital in the Nordeste Glossary Notes Index Acknowledgements An ancient interest in climate history was rekindled during the week I spent as a fly on the wall at the June 1998 Chapman Conference, “Mechanism of Millennial-Scale Global Climate Change,” in Snowbird, Utah.
    [Show full text]
  • ENSO Teleconnections Oscar Vergara
    Ventilation of the oceanic circulation in the Southeast Pacific by mesoscale activity and Rossby waves at interannual to decadal timescales : ENSO teleconnections Oscar Vergara To cite this version: Oscar Vergara. Ventilation of the oceanic circulation in the Southeast Pacific by mesoscale activity and Rossby waves at interannual to decadal timescales : ENSO teleconnections. Ocean, Atmosphere. Université Paul Sabatier - Toulouse III, 2017. English. NNT : 2017TOU30356. tel-02059950v2 HAL Id: tel-02059950 https://tel.archives-ouvertes.fr/tel-02059950v2 Submitted on 1 Feb 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. THTHESEESE`` En vue de l’obtention du DOCTORAT DE L’UNIVERSITE´ DE TOULOUSE D´elivr´e par : l’Universit´eToulouse 3 Paul Sabatier (UT3 Paul Sabatier) Prt ´esen ´ee et soutenue le 07/04/2017 par : Oscar Vergara Ventilation de la circulation oc´eaniquedans le Pacifique Sud-Est par les ondes de Rossby et l’activit´em´eso-´echelle : t´el´econnexionsd’ENSO. JURY Monsieur Peter Brandt Professeur d’Universit´e Rapporteur Monsieur Thierry
    [Show full text]
  • Air-Sea Interaction in the Tropical Pacific Ocean
    AIR-SEA INTERACTION IN THE TROPICAL PACIFIC OCEAN ~..I. .. , , j '. ' . I : ', .,- , , by Lewis J. Allison, Joseph Sterunka, Robert J. Hohb, ...'... 1 . '\ :., I .. ,., Job92 Hunsen, Fredric A, Godshall, L ,*~ *. I. 1 f;*': .? , 1 ..\ ' .:. , and Cuddapuh Prubhukura ,. Goddard Spuce Flight Center Greenbelt, Md. 20771 NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. MAY 1972 TECH LIBRARY KAFB, NM 0 I33B 70 1. ReDort No. 2. Government Accession No. 3. Recipient's Catalog No. NASA TN D-6684 I 4. Title ond Subtitle 5. Report Dote May 1972 Air-Sea Interaction in the Tropical Pacific Ocean 6. Performing Organization Code __ 7. Author(5) Lewis J. Allison, Joseph Steranka, Robert .I.Holub, 8. Performing Organization Report No John Hansen, Fredric A. Godshall, Cuddapah Prabhakara G1042 9. Performing Organization Nome and Address 10. Work Unit No. Goddard Space Flight Center 11. Contract or Grant No. Greenbelt, Maryland 2077 1 13. Type of Report and Period Covered 2. Sponsoring Agency Nome and Address Technical Note National Aeronautics and Space Administration Washington, D.C. 20546 14. Sponsoring Agency Code - 5. Supplementary Notes 6. Abstract Charts of 3-month sea surface temperature (SST) anomaliesin the eastern tropical Pacific Ocean were produced for the period 1949 to 1970. The anomaliesalong the United States and South American west coasts and in the eastern tropical Pacific appeared to be oscillating in phase during this period. Similarly, the satellite-derivedcloudiness for each of four quadrants of the Pacific Ocean (130OE to 1OO"W, 30"N to 25"s) appeared to be oscillatingin phase. In addition, a global tropical cloudiness oscillation from 30"N to 30"s was noted from 1965 to 1970, by using J.
    [Show full text]
  • The South Pacific Convergence Zone As Depicted in Reanalysis and Satellite Products
    The South Pacific Convergence Zone as Depicted in Reanalysis and Satellite Products By Thomas Luke Harvey A thesis Submitted to Victoria University of Wellington In partial fulfilment of requirements for the degree of Master of Science in Physical Geography School of Geography, Environment and Earth Sciences Victoria University of Wellington 2018 I Abstract The South Pacific Convergence Zone (SPCZ) is the largest rainfall feature in the Southern Hemisphere, and is a critical component of the climate of Southwest Pacific Island nations. The small size and isolated nature of these islands leaves them vulnerable to short and long term changes in the position of the SPCZ. Its location and strength is strongly modulated by the El Niño-Southern Oscillation (ENSO) cycle and the Inter-decadal Pacific Oscillation (IPO), leading to large inter-annual and decadal variability in rainfall across the Southwest Pacific. Much of the analysis on the SPCZ has been restricted to the modern period, more specifically the “satellite era”, starting in 1979. Here, the representation of the SPCZ in the Twentieth Century Reanalysis (20CR) product, which reconstructs the three-dimensional state of the atmosphere based only on surface observations is discussed. The performance of two versions of the 20CR (versions 2 and 2c) in the satellite era is tested via inter-comparison with other reanalysis and observational satellite products, before using 20CR version 2c (20CRv2c) to perform extended analysis back to the early twentieth century. This study demonstrates that 20CR performs well in the satellite era, and is considered suitable for extended analysis. It is established that extra data added in the SPCZ region between 20CR versions 2 and 2c has improved the representation of the SPCZ during 1908-1958.
    [Show full text]
  • Hemispheric Atmospheric Variations and Oceanographic Impacts
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 98, NO. D7, PAGES 13,045-13,062, JULY 20, 1993 HemisphericAtmospheric Variations and Oceanographic Impacts Associated With KatabaticSurges Across the RossIce Shelf,Antarctica DAVIDH. BROMWICH,•'2JORGE F. CARRASCO,1'2'3ZHONG LILI, 1'2 AND REN-YOW TZENG' ByrdPolar R e•e,•rchCan t•r, OtubState Uaiv•rdt y, Columbus Numericalsimulations and surface-basedobservations show that katabaticwinds persistently converge towardand blow across the Siple Coast part of West Antarctica onto the Ross Ice Shelf. About 14% of the timeduring winter (April to August 1988), thermal infrared satellite images reveal the horizontal propagation ofthis negatively buoyant katabatic airstream for al•out 1000 km across the ice shelf to its northwestern edge, a trajectorythat nearly parallels the Transantarctic Mountains. This takes place when the pressure field supportssuch airflow, and is caused by synoptic scale cyclones that decay near and/or over Marie Byrd Land. Thenorthwestward propagation of thekatabatic winds is accompanied byother changes in thehemispheric longwave pattern. An upper level ridge develops over Wilkes Land, resulting inan enhancement ofthe split jetin thePacific Ocean. Then, more frequent and/or intensified synoptic scale cyclones are steered toward MarieByrd Land where they become nearly stationary to thenortheast of the climatological location. The resultingisobaric configuration accelerates the katabatic winds crossing Siple Coast and supports their horizontalpropagation across the Ross Ice Shelf. An immediateimpact ofthis katabatic airflow, that crosses fromthe ice shelf to the Ross Sea, is expansion of thepersistent polynya that is present just to theeast of Ross Island.This polynya is a conspicuousfeature on passive microwave images of Antarctic sea ice and plays a centralrole in the saltbudget of watermasses over the RossSea continental shelf.
    [Show full text]
  • CLIVAR/OOPC/Argo/GOOS/CPPS Workshop on the South Pacific
    CLIVAR/OOPC/Argo/GOOS/CPPS workshop on the South Pacific Concepción, Chile 11-14 October 2005 ICPO Publication Number 116 WCRP Informal report 8/2007 GOOS/OOPC Publication No. GOOS 164 Acknowledgements: Thanks to sponsors: WCRP, US CLIVAR, GOOS/OOPC and Argo. Special thanks also to the local organising committee and Monica Sorondo. The Centre for Oceanographic Research in the Eastern South Pacific (COPAS), and the Department of Geophysics (DGEO) of the Faculty of Physical Sciences and Mathematics, University of Concepción (UdeC) are acknowledged for hosting the workshop. A special thanks to working group chairs and to note takers for their support. Report of the CLIVAR/OOPC/Argo/GOOS/CPPS workshop on the South Pacific 2 11 – 14 October 2005 Concepción, Chile Table of Contents Executive Summary 5 List Of Recommendations And Actions 7 1 Introduction 8 2 Motivation, Scientific Background And Objectives Of The Workshop 8 3 Structure Of The Workshop 9 4 The Working Group Reports 9 4.1 Working Group 1: Basin-Scale Issues 9 4.2 Working Group 2: Regional Impacts 14 4.2.1 Scientific Issues 14 4.3 Working Group 3: South Pacific Observations 17 Appendix A: Organising Committee 19 Appendix B: Agenda 20 Appendix C: List Of Participants 24 Appendix D: Abstracts 30 Teleconnections Patterns In The South Pacific 30 Interdecadal Variability And El Niño Events Variations 31 Change Of The Eastern Australian Current Induced By An Upward Trend Of 32 The Southern Annular Mode Precipitation Events In Central Chile And Its Relation With The MJO 33 Surface Circulation
    [Show full text]
  • Variability of Southern Hemisphere Cyclone and Anticyclone Behavior: Further Analysis
    1 VARIABILITY OF SOUTHERN HEMISPHERE CYCLONE AND ANTICYCLONE BEHAVIOR: FURTHER ANALYSIS Alexandre Bernardes Pezza and Tércio Ambrizzi Department of Atmospheric Sciences Institute of Astronomy, Geophysics and Atmospheric Sciences University of São Paulo – São Paulo (Brazil) In press in the Journal of Climate Revised in September/2002. Corresponding authors address: Rua do Matão, 1226. CEP 05508-900. São Paulo, SP, Brazil Phone: (+55)(11)(96867162) Fax: (+55)(11)(61699240) e-mail: [email protected], [email protected] 2 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 hours) was analyzed for the 1973 –1996 period using sea level pressure from the National Center for Environmental Prediction (NCEP) Reanalysis. Composites for seven El Niño (EN) and La Niña (LN) years were constructed in order to analyze the association between the hemispheric cyclone and anticyclone propagation and the phase of the El Niño – Southern Oscillation phenomenon (ENSO). 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 30o and 60o S which is approximately the climatological position of the SH transient activity. To the north of 30o S, the Subtropical South Atlantic High is embedded in a region with just a few cyclone tracks. This feature is not evident for the Pacific and the Indian’s High. The subtropical cyclones dominate most of the west Pacific and north of Australia.
    [Show full text]