索马里低空急流的数值模拟

本文首先将5°×5°P—σ五层原始方程粗网格模式改进为2.5°×2.5°的细网格模式,进而设计了粗细网格的嵌套模式。用嵌套模式对索马里低空急流进行了数值模拟,其结果表明:模式的水平分辨率对急流的模拟效果影响很大,模拟的急流轴上最大风速为13米/秒,与急流实际强度较为接近。 我们用六月纬向平均风场作初值,进行了10天的数值积分。根据风速的时间变化将急流的演变分为形成、加强及维持三个阶段,对急流各个阶段的流场及结构特征作了详细讨论。索马里沿岸低空气流由南向北越赤道气流的上空500百帕和300百帕层正好相反,气流由北向南穿越赤道。还通过控制性试验讨论了索马里低空急流向北发展的情况。 

NUMERICAL SIMULATION OF THE SOMALI LOW-LEVEL JET

A nested numerical model is designed by constructing a 2.5 °(lat.)×2.5°(long.) fine grid model upon a 5°×5°P-σ 5-layer primitive equations ver-sion.Used to simulate the Somali low-level jet,the improved model shows great impact of its horizontal resolution on the jet simulation,which is 13m/s at maximum on the axis,close to the reality.Initializing with zonal mean for June,the wind field is put to a 10-day integration. With respect to the temporal fluctuations of the speed,the evolution of the jet is cut into three stages of generation,intensification and maintenance,which receive detailed discussion in terms of each of the flow fields and the compositional characteristics concerned. Just contrary to the low-level jet along the Somali coast,flows above it head south at both 500hPa and 300hPa levels. How the northward-going jet develops is also examined in a controlled test.