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The relation of moist symmetric instability and upper‐level potential‐vorticity anomalies to the observed evolution of cloud heads
Author(s) -
Dixon R. S.,
Browning K. A.,
Shutts G. J.
Publication year - 2002
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1256/0035900021643719
Subject(s) - cyclogenesis , potential vorticity , baroclinity , geology , instability , vorticity , climatology , geostrophic wind , cyclone (programming language) , vortex , meteorology , atmospheric sciences , physics , mechanics , computer science , field programmable gate array , computer hardware
The cloud‐head phenomenon has been known for some time as a precursor of rapid cyclogenesis. Based upon satellite imagery, two stages of cloud‐head development are identified in this study that can be related to early and late stages of the associated cyclone. Weakly convex cloud heads emerge from the baroclinic zone at an early stage in cyclogenesis and strongly convex cloud heads develop in association with the rapid deepening of the cyclone. Trajectories are used to highlight the role of an upper‐level potential‐vorticity (PV) anomaly in the growth of the strongly convex cloud head and the main flow associated with the growth of the strongly convex cloud head is viewed using isentropic analysis. The possible role of moist symmetric instability in the development of both weakly and strongly convex cloud heads is discussed and a new diagnostic for measuring the vertically integrated extent of realizable symmetric (VRS) instability, based on the moist geostrophic PV, is introduced. © Royal Meteorological Society, 2002. G. J. Shutt's contribution is Crown copyright.