On some aspects of objective analysis of humidity over indian region by the optimum interpolation method

Abstract

On the basis of a three year record of Radiosonde observations over Indian region, the autocorrelation function and structure function of the humidity mixing ratio (r) were computed for 850 hPa level. These are necessary for the construction of a suitable objective analysis scheme for humidity over Indian region using optimum interpolation method. The statistics were derived for the monsoon period (June through September) for 850 hPa level.

In order to model the humidity correlation for Indian region, two types of curves were fitted: (i) μ(ρ)=a exp (-bρ), (ii) μ(ρ)=A exp (-Bρ²) where μ is the autocorrelation function — a function of distance ρ-between two observing stations. It was found that the best description of humidity correlation function was given by Eq. (1). The value of ‘a’ gives a quantitative impression of the observation error. Further, the mean random errors were computed from structure functions, the weighting factors for the observing stations with respect to each grid point were calculated, and objective analyses were made for the humidity mixing ratio.