The influence of wind speed on surface layer stability and turbulent fluxes over southern Indian peninsula station

M N Patil, R T Waghmare, T Dharmaraj, G R Chinthalu, Devendraa Siingh, G S Meena
2016 Proceedings of the Indian Academy of Sciences, Earth and Planetary Sciences  
Surface to atmosphere exchange has received much attention in numerical weather prediction models. This exchange is defined by turbulent parameters such as frictional velocity, drag coefficient and heat fluxes, which have to be derived experimentally from high-frequency observations. High-frequency measurements of wind speed, air temperature and water vapour mixing ratio (eddy covariance measurements), were made during the Integrated Ground Observation Campaign (IGOC) of Cloud Aerosol
more » ... d Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) at Mahabubnagar, India (16 • 44 N, 77 • 59 E) in the south-west monsoon season. Using these observations, an attempt was made to investigate the behaviour of the turbulent parameters, mentioned above, with respect to wind speed. We found that the surface layer stability derived from the Monin-Obukhov length scale, is well depicted by the magnitude of wind speed, i.e., the atmospheric boundary layer was under unstable regime for wind speeds >4 m s −1 ; under stable regime for wind speeds <2 m s −1 and under neutral regime for wind speeds in the range of 2-3 m s −1 . All the three stability regimes were mixed for wind speeds 3-4 m s −1 . The drag coefficient shows scatter variation with wind speed in stable as well as unstable conditions. Arritt 1995), non-classical mesoscale phenomena and thunderstorm (Segal and Arritt 1992) . Over the Indian subcontinental stations, the steep decrease of C D (Kusuma et al. 1996; Krishnan and Kunhikrishnan 2002) as well as unsystematic (scatter) variations (Kusuma et al. 1996; Patil 2006) with wind speed was observed for low winds. Over the land region of Asia (20 • N-10 • S), the C DN (C D under neutral stability conditions) was ∼27.7 × 10 −3 , which is close to C DN over South America (C DN = 26.6 × 10 −3 ), but significantly higher than the regions of North America, Africa, Europe, Australia and the rest of Asia (Garratt 1977) . A study by Miao and Ji (1996) shows larger C D magnitude over the rough land surface than over the sea surface and found significant differences in the three typical underlying surfaces (urban, grassland and
doi:10.1007/s12040-016-0735-5 fatcat:nket7grpuzdrbku2xla2pseega