An Analytical Solution of Nocturnal Low Level Jets

Journal of the Meteorological Society of Japan. Ser. II

Hirotada KANEHISA¹  Sakie HIRA² 

[1] Meteorological College, Kashiwa, Japan;Climate Prediction Division, Japan Meteorological Agency, Tokyo, Japan

关键词: nocturnal low level jets;    inertial oscillation;    atmospheric boundary layer;   

DOI  :  10.2151/jmsj.2015-031

学科分类：大气科学

来源: Meteorological Society of Japan

【 摘 要 】

 In this study, an analytical solution of nocturnal low level jets (LLJs) is presented. The present model is an extension of Blackadar, who described the nocturnal LLJ as a result of an inertial oscillation. In the present model, the momentum equation in the daytime atmospheric boundary layer includes a term representing convective mixing in addition to mixing with a constant diffusion coefficient.  With the convective mixing, the daytime equilibrium wind velocity becomes vertically more uniform than the Ekman solution. In the nighttime atmospheric boundary layer, the convective mixing is assumed to be absent and the diffusion coefficient, which is assumed to be a constant, is smaller than that in the daytime. Without the convective mixing, the nighttime equilibrium wind velocity is the same as that of the Ekman solution. The analytical solution describes the temporal evolution of nighttime wind velocity as a damped inertial oscillation around the nighttime equilibrium wind velocity, starting from daytime equilibrium wind velocity.  By appropriately selecting the values of parameters in the analytical solution, some previously published results are reproduced. For example, the height of maximum wind speed decreases as time goes on. There exist backward inertial oscillations in addition to the well-known forward inertial oscillations. In the lower levels, the oscillations are rapidly damped.

【 授权许可】

Unknown