741 The Climatology of the Western Tropical Pacific: Analysis of the Radiosonde Data Base G.C. REID, K.S. GAGE and lR. McAFEE Aeronomy Laboratory National Oceanic and Atmospheric Administration Boulder, CO 80303 - U.S.A. INTRODUCTION Upper air data are available from several radiosonde stations in the western tropical Pacific at daily or twice-daily intervals for a periodof over 30 years, beginning in the early 1950s. Three of thesestations (ponape,Truk, and Majuro) lie within the TOGA COAREdomain,and several others (Koror, Yap, Guam, Eniwetok, and Pago Pago) are closely adjacent. Analysisof this data base is in principle capableof providing important information on the height and time structure of atmospheric variability over the wann pool region. As a preliminary study, we have used the temperature recordsfrom threeof these stations (Yap,Majuro,and Pago Pago), together with two moredistant stations(Wake Island and Curacao) to examine the development in time of the ENSO-related anomalies at 30 pressure levels from 1000 hPa to 15 hPa (about 28 km) during the 17-year period 1966-1982. The analysis is described in detail in Reid et al. (1989). THE RELATIONSHIP OF OCEANIC ANDATMOSPHERIC TEMPERATURE ANOMALIES The El Nino time seriesof SST anomalies used was that derived by Weare et a1. (1976) and updated by Weare (1986). It is the amplitude of the dominant interannual mode found in an EOF analysis of SSTs over a wideregion of the Pacific north of 2O oS, and the time series of monthly valuesis shownin Figure 1. The only pre-treatment of the time series was the removal of a weak: linear trend, shown in the figure. 71 72 73 74 75 76 77 78 79 80 81 82 YEAR 20 15 10 5 DC 0 -5 -10 -15 -20 66 67 68 69 70 Figure 1. Pacific SST anomaly time series (after Weare [1986]).
Upperair data are available from several radiosonde stations in the western tropical Pacificat daily or twice-daily intervals for a periodof over 30 years,beginning in the early 1950s. Threeofthesestations (ponape,Truk, and Majuro) lie within the TOGA COAREdomain,and several others(Koror, Yap, Guam, Eniwetok, and Pago Pago) are closely adjacent. Analysisof this data base isin principle capableof providing important information on the heightand time structure ofatmospheric variability over the wann pool region.
As a preliminary study, we haveused the temperature recordsfrom threeof these stations(Yap,Majuro,and Pago Pago), together with two moredistant stations(Wake Islandand Curacao)to examine the development in timeof the ENSO-related anomalies at 30 pressure levelsfrom 1000hPa to 15 hPa (about28 km) during the 17-year period 1966-1982. The analysis is described indetail in Reid et al. (1989).
THE RELATIONSHIP OF OCEANIC AND ATMOSPHERIC TEMPERATUREANOMALIES
The El Nino time seriesof SST anomalies used was that derived by Weare et a1. (1976) andupdated by Weare (1986). It is the amplitude of the dominant interannual mode foundin an EOFanalysis of SSTsover a wideregionof the Pacific northof 2OoS, and the time seriesof monthlyvaluesis shownin Figure 1. The only pre-treatment of the timeseries was the removalof a weak:linear trend, shownin the figure.
71 72 73 74 75 76 77 78 79 80 81 82YEAR
20
15
10
5
DC 0
-5
-10
-15
-2066 67 68 69 70
Figure 1. Pacific SST anomaly time series (afterWeare [1986]).
742
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Figure 2. Contourplot of cross-correlation coefficients betweentime seriesof Figure 1 andmonthly meanatmospheric temperature anomalies at Pago Pago.The ocean leads theatmosphere for positivelags.
743
The atmospheric temperature time seriesfor eachof the 5 stations and for each of the 30pressure levels (nearly 2 million individual measurements in all) werereducedto monthly means,and anomaly series wereformed by subtracting the 17-year meanfor each calendarmonth from theindividual values. Fairlypronounced trends were evidentat all levels, and were removed beforecarrying out the analysis. The trends and their significance are discussed below. .
For each station, the temperature anomalies at each pressure levelwere cross-correlatedwith the SST anomaly timeseriesfor lagsof ± 30 months (Positive lag meansSST leads theatmosphere). Figure 2 showsthe result for Pago Pago in the form of contoursof equalcross-correlation coefficient. Dark and lightshading indicate correlation significant at the 99% and95% levelsrespectively, taking autocorrelation in the individual time seriesinto account.
The mainfeatures are:(1) Strongpositivecorrelation in the main troposphere, from 850 hPa to 150 hPa, with the
atmosphere laggingthe oceanby about 2 months.(2) Strongnegative correlation between 100hPa and 60 hPa, with a similar lag.(3) A transition regionbetween 150hPa and the tropopause at about 100hPa.(4) A surface layer below 850 hPa, with little significant correlation.(5)Disappearance of the signalaboveabout40 hPa (22 km).
A generally similarpicture is seen at theother four stations, but with interesting differencesfrom stationto station, and witha systematic variation in lag.
Figure 3 shows the lag in the mid-troposphere as a function of longitudeof the station, andindicates that the signalappears to propagate slowlyoutwardfrom a center near 135°W, wherethelag would probably be close to zero (if therewere a station to observeit). The zonalpropagationspeedis about 0.8 metersper second, considerably less than typical wind speeds.
INTERPRETATION
The slow propagation speed, and the close similarity of the speedsin the troposphere andstratosphere, suggest that the mechanism is not simply the advection of air from a regionofenhanced convective activity. Two otherpossibilities are:(1) Enhancement of the large-scale tropospheric subsidence and stratospheric upwelling resultingfrom increased convective activity centered near 135°W. In thiscase, the tropospheric subsidencecan be considered as a signof an enhanced and displaced Walkercirculation accompanying El Ninoevents, while the stratospheric upwelling can be considered as a sign of an enhanced Hadleycirculation.(2) An increase in the extentof optically thickmesoscale cirrus sheetsin the upper troposphereresulting fromenhanced convective activity, leadingto radiative warming of the troposphere belowand radiative coolingof the stratosphere above.
Bothof these mechanisms may be contributing to theeffect, and someeffort is needed totry to devisewaysof estimating theirrelative effectiveness.
ATMOSPHERIC TEMPERATURE TRENDS
Significant trends werefound in the 1966-1982 atmospheric temperature anomaly timeseriesat all pressure levels. Figure4 shows the slopeof a least-squares straight-line fit to the trendat each of the five stationsfor several pressure levels. The station trendsall show similarcharacteristics - a warming belowthe 150hPa level,which continues into the lower stratosphereonly at the near-equatorial stations of Yap and Majuro. The other stationsshowa transition to acoolingtrend near the tropopause and at the base of the stratosphere, weakening with increasingheight and becoming irregular above about40 hPa.
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6
-Cl) 5Ir-Z 40~-o 3« 0.....J 2 W
1
120 140 160 180 160 140 120 100-E W-'"
LONGITUDE
80 60
Figure 3. Lag of m~imum correlation in the mid-troposphere as a function of station longitude forYap, Majuro,Wake Island, Pago Pago, and Curacao.The straight lines have slopesof0.8 meters per secondat the equator.
The variation with height is somewhat similar to the heightvariation of the correlationpatterns illustrated in Figure 2, and suggests that the trendsseen in the atmosphere may reflectawarming trend in the tropical Pacificduring the 1966-82 time period.The cause of such a warmingis a matterfor speculation.
CONCLUSIONS
(1)The signalsof tropospheric warming and stratospheric cooling that accompany El Ninoevents are clearlyevident in tropical radiosonde data, and appearto propagate both westwardandeastwardfrom a center near 135°W at a speedof about0.8 ms-I.
(2)The relative importance of dynamical (Walker and Hadleycirculations) and radiative(extensive cirrus sheets) effectsin producing the signal needs to be determined.
(3)Long-term trendsin atmospheric temperature over the period 1966to 1982areconsistent with an overallwarming of the tropical Pacific.
(4) Extension of the analysis to study(a) the characteristics of the signalat other tropical
745
and extratropicallocations, (b) the behavior of the signal at earlier times, before 1966, and (c) theexistence of a corresponding signal at intraseasonal frequencies, is being planned.
Figure 4. Slopes of the linear trend in temperature anomaly at the 5 stations during 1966-82.
746
REFERENCES
Reid,G.C.,K.S. Gage, and lR. McAfee, The thermal response of the tropical atmosphere tovariations in equatorial Pacific sea-surface temperature, J. Geophys. Res., in press, 1989.
Weare, RC., An extension of an El Ninoindex, Mon. Wea. Rev. 114,644-647, 1986.
Weare, RC., A.R. Navato, and R.E. Newell, Empirical orthogonal analysis of Pacificsea surfacetemperatures, J. Phys. Oceanogr. 6,671-678, 1976.
WESTERN PACIFIC INTERNATIONAL MEETING
AND WORKSHOP ON TOGA COARE
Noumea, New Caledonia
May 24-30, 1989
edited by
Joel Picaut *Roger Lukas **
Thierry Delcroix *
* ORSTOM, Noumea, New Caledonia** JIMAR, University of Hawaii, U.S.A.
INSTITUT FRANCAIS DE RECHERCHE SCIENTIFIQUEPOUR LE DtVELOPPEMENT EN COOPtRATlON
4. Presentations on related technology ....... ............ .. .. ..... ... ..... ... .. ...... .. . 405. National reports 406. Meeting of the International Ad Hoc Committee on TOGA COARE 40
APPENDIX: WORKSHOP RELATED PAPERS
Robert A. WeUer and David S. Hosom: Improved MeteorologicalMeasurements from Buoys and Ships for the World OceanCirculation Experiment ............. .. .... ............. .......... .. ........ ....... .... . ....... .... 45Peter H. Hildebrand: Flux Measurement using Aircraftand Radars 57-Waiter F. Dabberdt, Hale Cole, K. Gage, W. Ecklund and W.L. Smith:Determination of Boundary-Layer Fluxes with an IntegratedSounding System 81·
viii
MEETING COLLECTED PAPERS
WATER MASSES. SEA SURFACE TOPOGRAPHY. AND CIRCULATION
KJaus Wyrtki: Some Thoughts about the West Pacific Warm Pool.................. 99Jean Rene Donguy, Gary Meyers, and Eric Lindstrom: Comparison ofthe Results of two West Pacific Oceanographic Expeditions FOC (l971)and WEPOCS (1985-86) 111Dunxin Hu, and Maochang Cui: The Western Boundary Current in theFar Western Pacific Ocean 123Peter Hacker, Eric Firing, Roger Lukas, Philipp L. Richardson. andCurtis A. Collins: Observations of the Low-latitude Western BoundaryCirculation in the Pacific during WEPOCS ill ................ .. . . .. .. .. 135Stephen P. Murray, John Kindle, Dharma Arief, and Harley Hurlburt:Comparison of Observations and Numerical Model Results in the IndonesianThroughflow Region 145Christian Henin: Thermohaline Structure Variability along 165eEin the Western Tropical Pacific Ocean (January 1984 - January 1989) 155David J. Webb. and Brian A. King: Preliminary Results fromCharles Darwin Cruise 34A in the Western Equatorial Pacific 165Warren B. White, Nicholas Graham. and Chang-Kou Tai: Reflection ofAnnual Rossby Waves at The Maritime Western Boundary of the TropicalPacific ..... .......... ... .. .. .... .... ... .............................. ............ ........ ... .... .... .... 173William S. Kessler: Observations ofLong Rossby Waves in the NorthernTropical Pacific .......................... ..... .. .. ... . .. ... . ........... .. .. ......... .... . .. .. ... ... .. 185Eric Firing, and Jiang Songnian: Variable Currents in the WesternPacific Measured During the US/PRC Bilateral Air-Sea Interaction Programand WEPOCS 205John S. Godfrey, and A. Weaver: Why are there Such StrongSteric Height Gradients off Western Australia? 215John M. Toole, R.C. Millard, Z. Wang, and S. Po: Observationsof the Pacific North Equatorial Current Bifurcation at the Philippine Coast 223
EL NINO/SOUTHERN OSCILLATION 1986-87
Gary Meyers, Rick Bailey, Eric Lindstrom, and Helen PhiUips:Air/Sea Interaction in the Western Tropical Pacific Ocean during1982/83 and 1986/87 229Laury Miller, and Robert Cheney: GEOSAT Observations of SeaLevel in the Tropical Pacific and Indian Oceans during the 1986-87El Nino Event 247Thierry Delcroix, Gerard Elmn, and Joel Picaut: GEOSAT SeaLevel Anomalies in the Western Equatorial Pacific duringthe 1986-87 El Nino. Elucidated as Equatorial Kelvinand Rossby Waves 259Gerard Eldin. and Thierry Delcroix: Vertical Thermal StructureVariability along 165eE during the 1986-87 ENSO Event 269Michael J. McPhaden: On the Relationship between Winds andUpper Ocean Temperature Variability in the Western EquatorialPacific ..... ..... ...... ... .. .... ... ........................................... ..... .. .. .... .. .... ........ 283
i"'{
John S. Godfrey, K. Ridgway, Gary Meyers, and Rick Bailey:Sea Level and Thennal Response to the 1986-87 ENSO Event in theFar Western Pacific 291Joel Picaut, Bruno Camusat, Thierry Delcroix, MichaelJ. McPhaden, and Antonio J. Busalacchi: Surface Equatorial FlowAnomalies in the Pacific Ocean during the 1986-87 ENSO using GEOSATAltimeter Data 301
TIlEORETICAL AND MODELING STUDIES OF ENSOAND RELATED PROCESSES
Julian P. McCreary, Jr.: An Overview of Coupled Ocean-AtmosphereModels of El Nino and the Southern Oscillation 313Kensuke Takeuchi: On Wann RossbyWaves and their Relationsto ENSO Events 329Yves du Penhoat, and Mark A. Cane: Effect of Low Latitude WesternBoundary Gaps on the Reflection of Equatorial Motions 335Harley Hurlburt, John Kindle, E. Joseph Metzger, and Alan Wallcraft:Results from a Global Ocean Model in the Western Tropical Pacific 343John C. Kindle, Harley E. Hurlburt, and E. Joseph Metzger: On theSeasonal and Interannual Variability of the Pacific to Indian OceanThroughflow 355Antonio J. Busalacchi, Michael J. McPhaden, Joel Picaut, and ScottSpringer: Uncertainties in Tropical Pacific Ocean Simulations: TheSeasonal and Interannual Sea Level Response to Three Analyses of theSurface Wind Field 367Stephen E. Zebiak: Intraseasonal Variability - A Critical Componentof ENSO? 379Akimasa Sumi: Behavior of Convective Activity over the "Jovian-type"Aqua-Planet Experiments 389Ka-Ming Lau: Dynamics of Multi-Scale Interactions Relevant to ENSO 397Pecheng C. Chu and Roland W. Garwood, Jr.: Hydrological Effectson the Air-Ocean Coupled System 407Sam F. Iacobellis, and Richard CJ. Somerville: A one DimensionalCoupled Air-Sea Model for Diagnostic Studies during TOGA-COARE 419AlIan J. Clarke: On the Reflection and Transmission of Low FrequencyEnergy at the Irregular Western Pacific Ocean Boundary - a PreliminaryReport 423Roland W. Garwood, Jr., Pecheng C. Chu, Peter Muller, and NiklasSchneider: Equatorial Entrainment Zone: the Diurnal Cycle 435Peter R. Gent: A New Ocean GCM for Tropical Ocean and ENSO Studies 445Wasito Hadi, and Nuraini: The Steady State Response of IndonesianSea to a Steady Wind Field .......................................................... ............ 451Pedro Ripa: Instability Conditions and Energetics in the Equatorial Pacific 457Lewis M. Rothstein: Mixed Layer Modelling in the Western EquatorialPacific Ocean 465Neville R. Smith: An Oceanic Subsurface Thermal Analysis Scheme withObjective Quality Control 475Duane E. Stevens, Qi Hu, Graeme Stephens, and David Randall: Thehydrological Cycle of the Intraseasonal Oscillation , 485Peter J. Webster, Hai-Ru Chang, and Chidong Zhang: TransmissionCharacteristics of the Dynamic Response to Episodic Forcing in the WannPool Regions of the Tropical Oceans .. _ 493
x
MOMENWM, REAT, AND MOISlURE FLUXES BETWEENATMOSPHERE AND OCEAN
W. Timothy Liu: An Overview of Bulk Parametrization and RemoteSensing of Latent Heat Flux in the Tropical Ocean ...................................... 513E. Frank Bradley, Peter A. Coppin, and John S. Godfrey: Measurementsof Heat and Moisture Fluxes from the Western Tropical Pacific Ocean 523Richard W. Reynolds, and Ants Leetmaa: Evaluation of NMC'sOperational Surface Fluxes in the Tropical Pacific 535Stanley P. Hayes, Michael J. McPhaden, John M. Wallace, and JailPicaut: The Influence of Sea-Surface Temperature on Surface Wind in theEquatorial Pacific Ocean 543T.D. Keenan, and Richard E. Carbone: A Preliminary Morphology ofPrecipitation Systems In Tropical Northern Australia 549Phillip A. Arkin: Estimation of Large-Scale Oceanic Rainfall for TOOA 561Catherine Gautier, and Robert Frouin: Surface Radiation Processes inthe Tropical Pacific 571Thierry Delcroix, and Christian Henin: Mechanisms of SubsurfaceThermal Structure and Sea Surface Thermo-Haline Variabilities in the SouthWestern Tropical Pacific during 1979-85 - A Preliminary Report 581Greg. J. Holland, T.D. Keenan, and MJ. Manton: Observations from theMaritime Continent: Darwin, Australia 591Roger Lukas: Observations of Air-Sea Interactions in the Western PacificWarm Pool during WEPOCS 599M. Nunez, and K. Michael: Satellite Derivation of Ocean-Atmosphere HeatFluxes in a Tropical Environment ............................................................. 611
EMPIRICAL SlUDIES OF ENSO AND SHORT-TERM CLIMATE VARIABILITY
Klaus M. Weickmann: Convection and Circulation Anomalies over theOceanic Warm Pool during 1981-1982 623Claire Perigaud: Instability Waves in the Tropical Pacific Observed withGEOSAT 637Ryuichi Kawamura: Intraseasonal and Interannual Modes of Atmosphere;.Ocean System Over the Tropical Western Pacific 649David Gutzler, and Tamara M. Wood: Observed Structure of ConvectiveAnomalies 659Siri Jodha Khalsa: Remote Sensing of Atmospheric Thermodynamics inthe Tropics 665Bingrong Xu: Some Features of the Western Tropical Pacific: Surface WindField and its Influence on the Upper Ocean Thermal Structure 677,Bret A. Mullan: Influence of Southern Oscillation on New ZealandWeather 687Kenneth S. Gage, Ben Basley, Warner Ecklund, D.A. Carter, andJohn R.McAfee: Wind Profiler Related Research in the Tropical Pacific 699John Joseph Bates: Signature of a West Wind Convective Event inSSM/I Data 711David S. Gutzler: Seasonal and Interannual Variability of the Madden-Iulian Oscillation 723Marie-H~lene Radenac: Fine Structure Variability in the Equatorial WesternPacific Ocean 735George C. Reid, Kenneth S. Gage, and John R. McAfee: The Oimatologyof the Western Tropical Pacific: Analysis of the Radiosonde Data Base 741
xi
Chung-Hsiung Sui, and Ka-Ming Lau: Multi-Scale Processes in theEquatorial Western Pacific , 747Stephen E. Zebiak: Diagnostic Studies of Pacific Surface Winds 757
MISCELLANEOUS
Rick J. Bailey, Helene E. Phillips, and Gary Meyers: Relevance to TOGAof Systematic XBT Errors 775Jean Blanchot, Robert Le Borgne, Aubert Le Bouteiller, and MartineRodier: ENSO Events and Consequences on Nutrient, Planktonic Biomass,and Production in the Western Tropical Pacific Ocean 785Yves Dandonneau: Abnonnal Bloom of Phytoplankton around weN in theWestern Pacific during the 1982-83 ENSO 791Ceclle Dupouy: Sea Surface Chlorophyll Concentration in the South WesternTropical Pacific, as seen from NIMBUS Coastal Zone Color Scanner from1979 to 1984 (New Caledonia and Vanuatu) 803Michael Szabados, and Darren Wright: Field Evaluationof Real-Time XBT Systems 811Pierre Rual: For a Better XBT Bathy-Message: Onboard Quality Control,plus a New Data Reduction Method 823
