Coherent structures contributions in fluxes of momentum and heat at two tropical sites during pre-monsoon thunderstorm season

摘要

An attempt has been made to differentiate percentage contribution of coherent structures (CS) in the turbulent fluxes of heat and momentum during thunderstorm days (TD) and non-thunderstorm days (NTD) at two tropical sites. Premonsoon months (March to May) fast response data (10 Hz) of wind and temperature at Kharagpur (22?30'N, 87?20'E) for years 2007, 2009, and 2010, and at Ranchi (23?25'N, 85?26'E) for years 2008-2010 have been used. The contributions were calculated after decomposing the time series using wavelet technique by two methods: (1) the method of quadrant analysis for each scale, and (2) the method of zero-crossing. Contributions of CS in momentum flux are higher in TD than NTD, whereas for heat flux CS contribution is higher for NTD to that of TD at both sites; however, values are different at both sites and by each method as well. Significant percentages of contributions of CS to the total flux are noticed at both the sites.