Seasonal variation of mountain-valley wind circulation and surface layer parameters over the mountainous terrain of the northeastern region of India

Abstract

Mountainous topography and solar elevation angle have a significant influence on the wind circulation and energy exchange over a complex region. Here, the seasonal variation of mountain-valley wind circulation (MVWC) and surface layer parameters have been presented over a hilly station of northeastern India. For the study, quick-response sonic anemometer data have been utilized. The solar elevation angle varies from 85° to 43° in different seasons and controls the MVWC over the terrain. MVWC was dominated in winter (WN), pre-monsoon (PM), and post-monsoon (PMN) seasons, while the synoptic wind predominates the wind direction over the terrain in monsoon (MN). In WN and PM, nighttime heat transmission from the atmosphere to the ground was −10 to −20 W m−2, while the minimum in MN and PMN was −3 to −7 W m−2. The net seasonal daily mean sensible heat flux (H) values from the surface to the atmosphere were 42 W m−2, 58 W m−2, 35 W m−2, and 34 W m−2 in WN, PM, MN, and PMN. In MN, the average daytime temperature was 8 °C, 0.5 °C, and 3 °C higher and at night was 9.5 °C, 2 °C, and 4.5 °C higher than the WN, PM, and PMN. In WN, PM, and PMN, the momentum flux had a higher value of about 2 to 3 h after the maximum value in H was attained at the 6-m and 10-m levels. The daytime turbulence kinetic energy was higher by 99%, 56%, 72%, and 93% than the nighttime during WN, PM, MN, and PMN.