Barotropic Process Contributing to the Formation and Growth of Tropical Cyclone Nargis |
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Authors: | MAO Jiangyu and WU Guoxiong |
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Institution: | State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029,State Key Laboratory of Numerical Modeling for Atmospheric Sciences andGeophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029 |
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Abstract: | This study reveals the barotropic dynamics associated with the formation and
growth of tropical cyclone Nargis in 2008, during its formation stage. Strong equatorial
westerlies occurred over the southern Bay of Bengal in association with the arrival of an
intraseasonal westerly event during the period 22--24 April 2008. The westerlies, together
with strong tropical--subtropical easterlies, constituted a large-scale horizontal shear
flow, creating cyclonic vorticity and thereby promoting the incipient disturbance that eventually
evolved into Nargis. This basic zonal flow in the lower troposphere was barotropically unstable,
with the amplified disturbance gaining more kinetic energy from the easterly jet than from the
westerly jet during 25--26 April. This finding suggests that more attention should be paid to
the unstable easterly jet when monitoring and predicting the development of tropical cyclones.
Energetics analyses reveal that barotropic energy conversion by the meridional gradient of the
basic zonal flow was indeed an important energy source for the growth of Nargis. |
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Keywords: | tropical cyclone tropical--subtropical easterlies barotropic instability |
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