Surface layer structure for ten categories of land surfaces of the Indian region with instrumented Mini Boundary Layer Mast Network (MBLM-Net) establishment during PRWONAM

Abstract

Structure of the atmospheric surface layer on diurnal and seasonal time scales has been studied for ten categories of land surface patterns of the Indian region by making full-fledge measurements with the first of its kind network establishment of instrumented 15-m high Mini Boundary Layer Mast (MBLM-Net) during the PRWONAM programme. Land surface categories at 27 MBLM locations represented the complex, homogeneous, flat terrain with obstacles, urban, semi–arid, dry, complex hilly terrain, north-east moist region, monsoon trough region and the coastal.Box plots of air temperature, relative humidity, pressure, skin/soil temperatures and wind speed are constructed for 14 stations covering 10 land-surface categories. The mean air temperatures for 14 stations are in the ranges, 23.0–32.5 °C, 22.1–33.1 °C, 19.3–29.5 °C and 15.0–26.1 °C; the mean relative humidity in ranges, 43.1–91.4%, 54.1–92.1%, 69.2–87.2% and 54.1–85.9%; the mean skin temperature in ranges, 24–36.8 °C, 23.2–34.3 °C, 23.1–33.3 °C and 17.5–27.8 °C during the pre-monsoon, monsoon and post-monsoon and winter seasons respectively. The spread in air temperature is maximum (minimum) during the pre-monsoon (the monsoon) season. The minimum (maximum) in mean skin temperature decreased by 6.5 °C (9 °C) from the pre-monsoon season to winter season. Low wind speed (<4 m s−1), averaged over 14 stations, prevailed 95.0%, 86.7%, 97.2% and 98.1% of the time during the pre-monsoon, monsoon, post-monsoon and the winter seasons respectively.Diurnally for all the stations, peaks in mean temperature occurred during the pre-monsoon as clear sky days dominated during this season. Among all the stations and all the seasons, the air temperature curve during the monsoon season at Kodagu station is flat with low diurnal amplitude.Surface layer structure of nine Convective events at seven locations of durations 2 to 6 days are discussed. During the event at BIT, Ranchi with continuous rain for 4 days and peak rainfall of 20 mm h−1, maximum dip in pressure by ∼10 hPa, strong signature in soil temperature at depths up to 100 cm, drastic reduction in incoming SW radiative flux to < ∼100 W m−2 and the incoming LW radiative flux approaching near zero values, maximum dip in air temperature by ∼5° C, increase in relative humidity by ∼30% at its peak and in wind speed with the peak at ∼5.9 m s−1are observed.