Some characteristics of atmospheric surface layer over a tropical inland region during southwest monsoon period

Abstract

A surface layer experiment conducted at a site in the northwest part of India is described. Micrometeorological data collected from the intense field experiment conducted at a tropical inland station, Ahmedabad (23°N, 72.5°E), India during southwest monsoon period by deploying tower-based instruments were analyzed using eddy correlation method to study the characteristics of atmospheric surface layer (ASL). The normalized standard deviation of vertical wind, temperature and specific humidity were studied using Monin Obukhov (MO) similarity relations. The normalized standard deviation of vertical wind velocity ( φ w) is found to be around 1.37 for near neutral condition and it is found to be proportional to ( z/ L) 1/3 for unstable condition and ( z/ L) 1 for stable conditions. The normalized standard deviation of temperature ( φ T) and humidity ( φ q) are studied as a function of z/ L and it showed ( z/ L) −1/3 dependence for unstable condition and ( z/ L) −1 dependence for stable condition. The value of φ T for near neutral condition is found to be around 6.5, which is high compared with the values reported from other field experiments. The drag coefficient showed a strong dependence on wind velocity at low wind conditions and it is found to obey a power law of wind speed irrespective of the various stability conditions.