Development of observation-based parameterizations of standard deviations of wind velocity fluctuations over an Indian region

The present study utilizes the turbulence observations over an Indian region, Ranchi, to study the diurnal and seasonal characteristics of mean and turbulent parameters in the atmospheric surface layer under different wind speed and stability regimes. Data for the year 2009 are chosen to compute mean and turbulent statistics using the eddy correlation technique and are studied within the framework of Monin–Obukhov similarity theory. The analysis of the observational behaviour of the standard deviation of wind velocity fluctuations (σi, i = u, v, w) normalized by friction velocity (u*) suggests that these parameters remain independent of stability of layer in near-neutral to moderately stable/unstable conditions. However, they are observed to increase following the classical 1/3 power law with increasing stability/instability in moderate to strong stable/unstable conditions. Further, an attempt has been made to develop possible parameterizations of these coefficients in terms of Monin–Obukhov stability parameter in low and moderate to strong wind regimes for four different seasons. The proposed observation-based functional forms the σi as functions of the stability exhibit different behaviours depending on the optimal values of unknown coefficients obtained for different seasons. However, within the limit of the uncertainty in the observed input parameters, the values of the season-dependent set of coefficients do not affect the overall statistical agreement between predicted and observed values of the normalized standard deviation of wind velocity fluctuations.