Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Atmospheric & Oceanic Sciences

First Advisor

M. Joan Alexander

Second Advisor

Jeffrey B. Weiss

Third Advisor

O. Brian Toon

Fourth Advisor

Rajagopalan Balaji

Fifth Advisor

Julio T. Bacmeister

Abstract

Atmospheric equatorial waves play vital roles in tropical weather and climate. Tropical convective systems are often organized by waves, and at the same time convection itself generates a broad spectrum of waves propagating horizontally and vertically. Equatorial waves propagating into the stratosphere control the quasi-biennual oscillation (QBO) of equatorial stratospheric winds and are partially responsible for tropical upwelling as a part of the stratospheric Brewer-Dobson circulation. Waves in the tropical tropopause layer (TTL) affect dehydration of air entering the lower stratosphere by the formation of cirrus clouds, having significant radiative impacts on surface climate.

This thesis aims to provide an improved understanding of roles of equatorial waves on tropical convection and interaction processes between the troposphere and stratosphere. First, tropical precipitation characteristics associated with equatorial waves are studied using the TRMM satellite estimates and five reanalyses for the period of 2005-2007. Next, waves in the TTL are examined using temperatures in radiosondes and two reanalyses, ERA-interim and MERRA. Based on the results of variance difference between observations and reanalyses, we have developed a new wave parameterization scheme for simulations of the dehydration process in the TTL. We have found that, even though the mean temperature is the same, having stronger waves lowers cold point tropopause temperatures. This finding has led to an extended, comprehensive study of this relation using historical radiosonde data. Temperatures from 23-year observations of radiosondes in the western Pacific show that a broad spectrum of waves is responsible for lowering tropopause temperature. Moreover, the wave impact on the tropopause has decadal scale variations, suggesting changes in wave activity in the TTL have important implications for cirrus clouds and stratospheric water vapor. Lastly, aircraft measurements of meteorological fields and tracers have revealed that the tracer transport is highly correlated with a fine vertical wave structure in the TTL whose scale is unresolvable in current analysis and climate models due to limited vertical resolution.

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