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Secondary initiation of multiple bands of cumulonimbus over southern Britain. II: Dynamics of secondary initiation
Author(s) -
Marsham J. H.,
Parker D. J.
Publication year - 2006
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/qj.05.152
Subject(s) - storm , convection , geology , convective storm detection , gravity wave , outflow , atmospheric sciences , meteorology , cold front , wavelength , climatology , wave propagation , physics , oceanography , quantum mechanics , optoelectronics
The Convective Storm Initiation Project (CSIP) pilot field programme took place in the summer of 2004 in southern England. During this field campaign a case of a cold‐pool outflow initiating an arc of convection downwind of the generating storm (the ‘primary storm’) was observed. Three further arcs were initiated further downwind of this first arc. These arcs all later gave significant rainfall over south‐east England. Results from the modelling studies described in this paper show that gravity waves, generated by the ‘primary storm’, may have been responsible for initiating the further three arcs of convective showers that were observed. The modelled primary storm generates waves with a range of vertical wavelengths. These are separated by dispersion, with the higher‐order modes (with the largest vertical wavelengths) travelling fastest (approximately 30 m s −1 ). The fastest two modes suppressed convection and later modes increased boundary‐layer depth and so initiated convection. The multiple peaks (from non‐hydrostatic effects) in the third mode may have been responsible for the two main arcs observed and the fourth mode may have been responsible for the third arc. The amplitude of the modelled waves at low levels was much larger downwind of the primary storm than upwind and only initiated convection there, which agrees with the observations of the arcs forming downwind of the primary storm. This asymmetry appears to be caused by the moving‐wave source and asymmetric wave trapping. Finally we discuss the implications for numerical weather prediction (NWP). Reducing the resolution of the model, and varying the magnitude of the wind speed used, shows that a non‐hydrostatic high‐resolution ( ≃1 km) NWP model should be able to capture such wave processes, if the generating storm is forecast or analysed correctly. Copyright © 2006 Royal Meteorological Society.