Analysis of Weak Wind Stable Conditions from the Observations of the Land Surface Processes Experiment at Anand in India

The observations in weak wind stable conditions are scarce. The present study examines the observations from the Land Surface Processes Experiment (LASPEX) conducted at Anand, (Gujarat, India) during the year 1997–1998 to study the characteristics of surface layer under weak wind stable conditions. The observed surface fluxes are compared with those computed using Monin-Obukhov (M-O) similarity theory. The upper air observations and regional climatology are used to justify the persistence of weak wind conditions at Anand. The frequency of occurrence of weak wind stable conditions is observed to be around 67%. In 86% of the cases under weak wind conditions, bulk Richardson number (RiB) is found to be larger than 0.2. The magnitude of surface fluxes computed from M-O similarity theory is shown to be smaller in comparison to those based on the observations in weak wind stable conditions. Surface fluxes computed using the empirical relations for the eddy diffusivities and drag and heat exchange coefficients are found to be comparable with those based on M-O similarity theory however these fluxes are under-predicted in comparison to the observations. The traditional M-O similarity theory is not able to simulate the observed fluxes well in weak wind stable conditions at Anand.