5:15 PM - 7:15 PM
[AAS03-P20] Numerical experiments of a back-building-type line-shaped convective system formed under various shear conditions
Keywords:Numerical simulation, Back-building, Line-shaped convective systems
The back-building type line-shaped convective systems (BB-LSCS) often cause heavy rainfall. In general, the generation mechanisms of BB-LSCS are many different and complex. Most studies investigating the formation process of BB-LSCS have been case studies, and there are few numerical studies under various ideal atmospheric conditions. In this study, we create several vertical shear patterns using a cloud-resolving atmospheric model to investigate the environment favorable for the evolution of BB-LSCSs. We also investigate the process of how convective cells organize and evolve into BB-LSCSs. Numerical simulations are conducted in a virtual environment with no terrain and uniform horizontal conditions using the JMA non-hydrostatic model (JMA-NHM). The horizontal resolution and the vertical layers are set to 500 m. The vertical layers are set to 50 layers. The initial wind profile is set with unidirectional shear (zonal wind only). The shear exists from the surface to the 3 km height, and the speed is constant above that. The maximum wind speed in the mid-level is created from 5 to 30 m/s at 5 m/s intervals. The experiments are also conducted in a very humid environment.
As a result, BB-LSCS develops best in environments with maximum zonal wind speeds of 20 m/s. This environment has a Bulk Richardson number close to 33, which is consistent with previous studies (e.g., Unuma and Takemi 2016). The BB-LSCS occurred behind the direction of movement of the preceding strong convective system. The preceding strong convective system causes the cold pool to expand at the low-level, and a localized low-level convergence area forms on the downwind side of the cold pool. Updraft is generated from this convergence area. The convergence area is found to contribute more to the convergence perpendicular to the BB-LSCS, rather than to the convergence between a low-level wind and a blow from the cold pool.
As a result, BB-LSCS develops best in environments with maximum zonal wind speeds of 20 m/s. This environment has a Bulk Richardson number close to 33, which is consistent with previous studies (e.g., Unuma and Takemi 2016). The BB-LSCS occurred behind the direction of movement of the preceding strong convective system. The preceding strong convective system causes the cold pool to expand at the low-level, and a localized low-level convergence area forms on the downwind side of the cold pool. Updraft is generated from this convergence area. The convergence area is found to contribute more to the convergence perpendicular to the BB-LSCS, rather than to the convergence between a low-level wind and a blow from the cold pool.