Author

Casey Shoup

Date of Award

Spring 2020

Document Type

Open Access Thesis

Department

Marine Science

First Advisor

Subrahmanyam Bulusu

Abstract

The Madden-Julian Oscillation (MJO) is a highly air-sea coupled phenomenon and is the dominant mode of intraseasonal variability in the tropics. It is easily discernible in satellite-derived sea surface salinity (SSS), which varies as a direct result of MJO precipitation from the convectively active to suppressed phases. Negative (positive) SSS anomalies are associated with the active (suppressed) phase of the MJO. We find that all three available satellite salinity missions (ESA’s Soil Moisture Ocean Salinity (SMOS); NASA’s Aquarius/SAC-D, and NASA’s Soil Moisture Active Passive (SMAP)) are capable of capturing the MJO SSS signal and that the near-equatorial SSS response is enhanced when the combined active passive (CAP) processing algorithm is used..

Primary MJO events are those not preceded by MJO activity of sufficient strength and their initiation is also a focus of this study. These rare events are isolated and specific initiation mechanisms are debated; however, evidence exists for both the ocean and the atmosphere as potentially coupled triggering forces over the Indian Ocean. Intraseasonal signals of oceanic and atmospheric parameters were simultaneously examined in an attempt to bridge the connection of possible primary MJO triggers. The western and central Indian Ocean are shown to experience an increase in sea surface height (SSH) and absolute dynamic topography (ADT), sea surface temperature (SST), and ocean heat content (OHC) before peak atmospheric convection. SST warming destabilizes the lower troposphere. Lower-tropospheric moisture flux convergence (MFC) moistens the lower troposphere prior to MJO convection, which forces an increase in moist static energy (MSE) conducive to MJO convective growth. The moistening is coupled with mid- to upper-tropospheric cooling, which further destabilizes the atmosphere such that the effects of SST, SSH, OHC, MFC, and MSE synchronously precondition the Indian Ocean for MJO convection. MJO convection is shown to be favored (suppressed) under negative (positive) Indian Ocean Dipole (IOD) conditions across the eastern Indian Ocean. Similarly, MJO convection is favored (suppressed) over the central and eastern Pacific under El Niño (La Niña) conditions.

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