启动对流的初始扰动对热带飑线模拟的影响

在中尺度数值模拟及数值预报中，正确的对流启动是模拟或预报是否取得成功的关键。作者针对一次热带海洋飑线过程，利用一个风暴尺度云分辨数值模式进行数值模拟，采用不同的初始扰动触发与启动对流发展，重点讨论这些不同启动对流的初始扰动对飑线演变、生命史及其成熟结构等模拟的影响。结果表明，初始扰动的结构、形态分布及其与环境场的不同配置对具有深对流的飑线生命史存在重要影响，而对飑线的成熟结构影响较小。

Impacts of Initial Convection-Triggering Perturbations on Numerical Simulation of a Tropical Squall Line

Squall lines could be considered as self-organized convective systems,which develop through interaction between their own low-level cold pools and the environmental vertical shears.For the numerical simulations and forecasts,it is an initial-value problem in which the simulated convective systems are to be evaluated in a deterministic fashion.Even though squall lines are able to create their own forcings,the convection initialization plays an important role and remains an uncertain issue from both observational and modeling perspectives.In general,an initial and artificial temperature perturbation in a horizontally homogeneous environment is chosen for the triggering of these convective systems in the storm-scale numerical simulations.Although the choice of the initial perturbations is an important factor of successful simulations,the effects on the simulation of the nonphysical initiation set-up have been rarely discussed.In the present study,a well-documented tropical squall line observed during the TOGA-COARE on 22 February 1993 is simulated using a three-dimensional,non-hydrostatic and storm-scale numerical model ARPS,with different initial perturbation schemes triggering the convection in a horizontally homogeneous environment,to investigate the impacts of the different convection initiating on the mature structure,evolution and life cycle of the simulated tropical squall line.Observations revealed that the squall line studied here was characterized by a rapidly eastward propagating precipitation line which was about 100 km long and oriented perpendicular to the low-level vertical shear vector.It initially was highly linear and later evolved as a pronounced "bow-shaped" bulge.An up-shear tilting leading convective region with multiple updraft maximums was evident during its linear stage as well as its bow stage.The modeling results showed that the simulated squall lines using different convection-triggering perturbations could reproduce the main features of the observed ones.As a self-organized deep convection system,the mature structure and evolution of the squall line are mainly dominated by the environment field,however,the amplitude of initial convection-triggering perturbations has distinct impacts on the life cycle of the squall line.A relative weaker initial perturbation could lead to a later formation of the low-level cold pool,and then a slower development and longer life cycle of the squall line.Furthermore,the different structure,shape and configuration with environmental winds of initial perturbation result in the different evolution of the squall line.The warm and line type initial perturbation normal to the environmental low-level vertical wind shear vector is favorable to initiate convections and lead to the formation of cold pool,whose interaction with the low-level vertical shear supports a long-life tropical squall line.The deterministic adjustments of the environments on the mature structure of the tropical squall line are also discussed.It is suggested that the interaction between the low-level cold pool and the low-level vertical shear,and redistributing of precipitation substance by the up-level winds,etc.restricted the impact of initial perturbations on the development of conviction system,and conduce to the analogous features of squall line in its mature stage. Therefore,the predictability of such kind of convective systems could be ensured.