Air-sea interaction in tropical atmosphere: influence of ocean mixing on atmospheric processes

TL;DR

This study explores how ocean mixing influences atmospheric convection and Kelvin wave dynamics, revealing the ocean's role in modulating tropical weather patterns and the importance of diurnal cycles in wave propagation.

Contribution

It introduces a novel Kelvin wave database, analyzes wave initiation mechanisms, and demonstrates the ocean's impact on Kelvin wave behavior and atmospheric convection in the tropics.

Findings

Kelvin wave initiation is linked to high diurnal cycle and wind speed.

Maritime Continent acts as a filter for Kelvin wave propagation.

Kelvin waves are phase-locked with local diurnal convection cycles.

Abstract

One the major factors determining the development and evolution of atmospheric convection is the sea surface temperature and its variability. Results of this thesis show that state of atmospheric convection impacts the diurnal distribution of thermal energy in the upper ocean. Under calm and clear sky conditions a shallow warm layer of several meters depth develops on the surface of the ocean. This warm layer drives an anomalous flux from the ocean to the atmosphere. A novel Kelvin wave trajectory database based on satellite data is introduced in this study. The investigation of its data shows that substantial fraction of Kelvin waves is initiated as a result of interaction with another Kelvin wave. Two distinct categories are defined and analyzed: the two- and multiple Kelvin wave initiations, and a spin off initiation. Results show that primary forcing of such waves are high diurnal cycle and/or increased wind speed and latent heat flux at the ocean surface. Variability of the ocean surface and subsurface along Kelvin wave trajectories over Indian Ocean is investigated: wind speed and latent heat flux increase and a sea surface temperature anomaly decreases during a wave passage. It is also shown that Kelvin waves are longitude-diurnal cycle phase locked over the Maritime Continent. This cycle phase locking is such that it agrees with mean, local diurnal cycle of convection in the atmosphere. The strength of the longitude-diurnal cycle phase locking differs between non-blocked Kelvin waves, which make successful transition over the Maritime Continent, and blocked waves that terminate within it. The distance between the islands of Sumatra and Borneo agrees with the distance travelled by an average Kelvin wave in one day. This suggests that the Maritime Continent may act as a filter, favoring successful propagation waves, which are in phase with the local diurnal cycle of convection.