Isentropic analysis of polar cold air mass streams in the northern hemispheric winter

In the mass-weighted isentropic zonal mean (MIM), the meridional circulation reveals the
strong extratropical direct (ETD) circulation. Its complete lower boundary value formulation
allows us to analyze the angular momentum balance and energy conversions associated with
the ETD circulation. The ETD circulation indicates the generation of the polar cold air mass at
higher latitudes and “zonal mean” cold outbreaks at mid-latitudes.


The isentropic analysis is extended to geographical distributions of polar cold air mass, its
horizontal fluxes and its diabatic change below a designated potential temperature. In the NH
winter, the polar cold air mass below q=280K has two distinct main streams: the East Asian
stream and the North American stream. The EA stream grows over the northern part of the
Eurasian continent, flows eastward, turns down toward East Asia, and disappears over the
North Pacific Ocean. The NA stream grows over the Arctic Ocean, flows toward the eastern
coast of North America, and disappears over the North Atlantic Ocean. Concerning the EA
stream, an analysis is made of temporal variations of synoptic forcing to induce cold air
outbreaks.


Finally, the polar cold air mass amounts below q=280K is compared between the NH and SH
winters. The results are analyzed using a two box model composed of the genesis and loss
box. The difference in the polar cold air mass is attributed to the residence time in the
genesis.

About the presenter
Presenter(s): 
Dr. Toshiki Iwasaki

Affiliation or organization:

Where

Building:

Room: 
Main Seminar Room

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When
Date and time: 
Thursday, September 4, 2014 - 3:30pm