A Study of the 22 February 1993 TOGA COARE Squall Line: A Case Used for the GCSS Model Intercomparison

[摘要] Numerical experiments are performed to get a better understanding of the three-dimensional structure of a squall line system under an environmental wind that was observed on 22 February 1993, and used for the GCSS (GEWEX Cloud System Studies) model intercomparison (Redelsperger et al. 2000). The primary objective of this study is to clarify the effects of the observed environmental wind with directional shear on the squall line. More specifically, it is shown that the main features of the structure of the squall line under the observed wind can be explained more clearly by interpreting the wind as a superposition of a jet-type wind in the east-southeastward direction, and a wind with a low-level shear in the north-northeastward direction. For this purpose, numerical experiments are made not only with the use of the observed wind but also with a simplified wind mentioned above. In the latter case, two numerical experiments with, and without, the low-level north-northeastward shear are performed. These numerical experiments indicate that the low-level shear plays an important role on the observed location of enhanced convection at a leading edge, and that a stratiform cloud and pressure field are primarily explained by the jet-type wind. The properties of the squall lines obtained from the present model are also compared with those from the GCSS model intercomparison and other studies. A sensitivity of the properties of convective systems to different orientations of initial, roll-shaped buoyancy is also examined, with a focus on the role of the environmental wind as well as the selforganization mechanism of convection.

[学科分类] 大气科学