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On the Two‐Dimensional Steady Upshear‐Sloping Convection
Author(s) -
Xu Qin,
Chang LangPing
Publication year - 1987
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 - 10.1002/qj.49711347802
Subject(s) - squall line , outflow , inflow , hydraulic jump , inviscid flow , jump , convection , geology , mechanics , flow (mathematics) , atmospheric sciences , environmental science , meteorology , physics , quantum mechanics
A 2‐D inviscid steering‐level model due to M. W. Moncrieff is reexamined both analytically and numerically. It is found that the thermal effects on the distribution of energy and vorticity play opposite roles in determining the interface slope, with the former being dominant. By separating the two effects, a useful insight is obtained into how the interface is controlled by the internal flow regime. Consequently, a mixed jump and steering‐level model is proposed, in which the returning updraught and downdraught are separated by adjacent jump updraught and downdraught. By solving for the internal flow, upshear‐sloping convection is obtained in the mixed model. Numerical results indicate that the inferface slope increases towards the vertical, or even becomes downshear‐sloping, as (i) the jump outflow becomes shallow, (ii) the lifting condensation level (LCL) becomes low, and/or (iii) the Richardson number (proportional to the ratio between convective available potential energy and kinetic energy in the inflow) increases (except for the cases where the jump outflow is very deep and LCL is very high). These features are discussed in connection with the recent results of A. J. Thorpe et al. , and the observed differences between tropical propagating squall lines and mid‐latitude steering‐level‐type squall lines.