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CN 11-1768/O4

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Energy evolution characteristics of an eastward-moving convective cloud cluster producing heavy precipitation that originates from the Tibetan Plateau

1.Hubei Key Laboratory for Heavy Rain Monitoring and Warning Research,Institute of Heavy Rain,China Meteorological Administration;2.Institute of Atmospheric Physics,Chinese Academy of Sciences;3.Huangdao Sub-administration of Qingdao Meteorological Administration

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    Based on the Himawari-8 satellite TBB data from the Japan Meteorological Agency, the ERA5 reanalysis data from ECMWF and a new energy diagnostic method that uses temporal scale for scale separation, evolutionary characteristics of a convective cloud cluster (lasted 40 hours from 05:00 June 5th to 06:15 6th, 2016) that formed over the Tibetan Plateau (TP), moved eastward and induced heavy precipitation in downstream regions was investigated in this study. Main findings are listed as follows: the main influencing systems for the eastward-moving convective cloud cluster at different stages of its lifespan were different. Before moving out of the plateau, the cloud cluster was mainly affected by a plateau vortex and a short-wave trough. As the cloud cluster vacated the plateau, the plateau vortex dissipated, whereas the short-wave trough intensified with time, and finally the short-wave trough became the main influencing system of the cloud. The deep convection features of the eastward-moving cloud cluster were significant. The eastward-moving cloud cluster induced a series of precipitation from west to east, with the strongest precipitation occurred after it had moved out of the plateau and its convective barycenter lowered in height. The energetics characteristics of the eastward-moving convective cloud cluster experienced notable changes during its lifespan, and the associated precipitation characteristics were also significantly different. When the cloud cluster was over the TP (the first stage), the contribution from the background field was a dominant factor. The background filed provided energy for the evolution of eddy flow [by downscale kinetic energy (KE) cascade] which induced heavy precipitation directly. During the second stage, the precipitation-related latent heating was greatly enhanced, which significantly increased available potential energy (APE) of eddy flow. Under the influences of vertical motion, APE of eddy flow was released and converted to KE of eddy flow. This acted as a dominant factor for the sustainment of the precipitation-related eddy flow. When the cloud cluster moved out of the TP, the influence from background field on eddy flow enhanced again, however it was different from the direct influencing way that appeared at the first stage. In this stage, the influence from background environment favored the persistence of precipitation-related eddy flow indirectly. First, APE of the background filed transferred to APE of eddy flow through a downscale energy cascade. Then, a baroclinic energy conversion from APE of the eddy flow to its KE occurred. This acted as a dominant energy source for KE of eddy flow. Furthermore, in the third stage, a remarkable upscale energy cascade of KE was found, which reflected the feedback of eddy flow on its background field. However, the feedback intensity was not enough to affect evolution of the background field obviously.

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  • Received:September 18,2019
  • Revised:December 18,2019
  • Adopted:December 18,2019
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