Diagnostic analysis of the evolution mechanism for a vortex over the Tibetan Plateau in June 2008 |
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| Authors: | Lun Li Renhe Zhang Min Wen |
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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,Graduate University of the Chinese Academy of Sciences, Beijing 100049,State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 100081,State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing 100081 |
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| Abstract: | Based on the final analyses data (FNL) of the Global Forecasting System of
the NCEP and the observational radiosonde data, the evolution mechanism of
an eastward-moving low-level vortex over the Tibetan Plateau in June 2008
was analyzed. The results show that the formation of the vortex was related
to the convergence between the northwesterly over the central Tibetan
Plateau from the westerly zone and the southerly from the Bay of Bengal at
500 hPa, and also to the divergence associated with the entrance region of
the upper westerly jet at 200 hPa. Their dynamic effects were favorable for
ascending motion and forming the vortex over the Tibetan Plateau.
Furthermore, the effect of the atmospheric heat source (Q1) is discussed
based on a transformed potential vorticity (PV) tendency equation. By
calculating the PV budgets, we showed that Q1 had a great influence on
the intensity and moving direction of the vortex. In t Q1 he developing stage of
the vortex, the heating of the vertically integrated was centered to
the east of the vortex center at 500 hPa, increasing PV
tendency to the east of the vortex. As a result, the vortex strengthened and
moved eastward through the vertically uneven distribution of Q1. In the
decaying stage, the horizontally uneven heating of Q1 at 500 hPa
weakened the vortex through causing the vortex tubes around the vortex to
slant and redistributing the vertical vorticity field. |
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| Keywords: | Tibetan Plateau low-level vortex atmospheric heat source PV tendency equation |
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