Free and forced tropical variability: role of the wind-evaporation-sea surface temperature (WES) feedback

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Title: Free and forced tropical variability: role of the wind-evaporation-sea surface temperature (WES) feedback
Author: Mahajan, Salil
Abstract: The Wind -Evaporation -Sea Surface Temperature (WES ) feedback is believedto play an important role in the tropics , where climate variability is governed byatmosphere -ocean coupled interactions . This dissertation reports on studies to distinctlyisolate the WES feedback mechanism over tropical oceans using a modiedversion of an NCAR -Community Climate Model (CCM3 ) thermodynamically coupledto a slab ocean model , where the WES feedback is deliberately suppressed inthe bulk aerodynamic formulation for surface heat uxes . A comparison of coupledintegrations using the modified WES -off CCM3 to those carried out using the standardCCM3 conclusively identifies the role of the WES feedback in enhancing theinter -annual variability over deep tropical oceans and the westward propagation ofthe equatorial annual cycle . An important role for near surface humidity in tropicalclimate variability in enhancing inter -annual variability and in sustaining the equatorialannual cycle is also suggested . Statistical analyses over the tropical Atlanticreveal that the free coupled meridional mode of the Atlantic Ocean is amplified in thepresence of the WES feedback . Similar analyses of coupled model integrations , whenforced with an articial El Ni ~no Southern Oscillation (ENSO ) -like SST cycle in tropicalPacific , reveal that only in the presence of the WES feedback is the meridionalmode the preferred mode of response of the Atlantic to ENSO forcings . It is also foundthat WES feedback reinforces the tendency of the ITCZ to stay north of the equator over the Atlantic during El -Nino events . Comparative studies between Last GlacialMaximum (LGM ) equivalent imposed northern hemispheric sea -ice experiments withthe WES -off model and the standard model indicate a dominant role for the WESfeedback in the southward shift of the ITCZ as indicated by paleo -climate records .However , it is found not to be the sole thermodynamic mechanism responsible for thepropagation of high latitude cold SST anomalies to the tropics , suggesting significantroles for other mechanisms in the tropical response to high latitude changes .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3107
Date: 2009-05-15

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Free and forced tropical variability: role of the wind-evaporation-sea surface temperature (WES) feedback. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -3107 .

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