Water vapor budget of cold surge vortices

Tsay, Jenq-Dar
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The rainy season in Southeast Asia takes place during the northern winter. Cold surge vortices, which are initiated by cold surge events in East Asia, contribute over half the amount of precipitation in Southeast Asia and become the major source of rainfall. In this study, the water vapor budget analysis shows that the convergence of water vapor flux associated with cold surge vortices is generally strong. It not only transports the moisture into Southeast Asia, but also regulates the life cycle of a cold surge vortex. In addition, the interannual variation of the occurrence frequency of cold surge vortices can affect the total amount of the convergence of water vapor flux, which in turn results in the interannual variation of precipitation over Southeast Asia. Cold surge vortices can intensify the Southeast Asian high, the major circulation of the Asian winter monsoon, maintained by the Sverdrup balance. Results indicate that the maintenance of the anomalous circulation cannot be fully explained by the Sverdrup balance. The convergence of the eddy vorticity flux through the total transient flow contributed by cold surge vortex is required to maintain the anomalous circulation during cold surge vortex activity. The streamfunction budget analysis shows that the transient vorticity flux reinforces the vortex stretching effect to counter-balance the advection of planetary vorticity and helps to maintain the upper-level circulation anomalies.

Geological and atmospheric sciences, Meteorology