LAUSR

The effectiveness of the flux estimation techniques has been investigated over Umiam (25°40′32′′N, 91°54′06′′E, and altitude 1040 m above mean sea level), Shillong, in the Khasi hills located in north-east India. Primary dataset consists of sonic anemometer data recorded during January–February 2014 at 18 m and 30 m levels. Often, general planar fit (GPF) technique is used for long-term flux measurements using eddy covariance (EC). The three flux computation methods, namely double rotation (DR), GPF, and sector-wise planar fit (SPF) techniques have been compared in this investigation. SPF showed a reduction in the vertical wind (w) offset (b0, combination of instrument error and planar fit error) value compared to GPF. SPF minimized the planar-fit error in b0, while the instrument error was constant. The reduction of planar fit error has been seen in the computed sensible heat flux and momentum flux. Variations of 12–13% and 16–18% have been observed in the sensible heat flux and momentum flux in SPF compared to GPF. The effectiveness of SPF has been significant in the w-component estimation. An angle of attack (AA) which acts as a pivotal variable in the estimation of surface flux concentration varied between ± 6° in all atmospheric conditions. The standard deviations of horizontal and vertical velocity normalized by friction velocity (σu/u∗ and σw/u∗) as functions of atmospheric stability parameter (z/L) and obeyed a power-law relation during stable and unstable conditions. The variation in coefficients was in agreement with those estimated over flat and mountainous sites in the literature.