Perturbations of atmospheric surface layer characteristics during the annular solar eclipse on 26 December 2019 over a semi-arid region Anantapur in southern India

Abstract

The Annular Solar Eclipse (ASE) occurred on December 26, 2019, which was visible at most of the South Indian subcontinents with greater than 80% obscurity, particularly during the morning hours, and it played a crucial role in the atmospheric dynamics. For the first time, the ground-based measurements have used to investigate the fluctuations of air temperature, relative humidity, atmospheric pressure, wind speed and direction, UV-A radiation, and turbulence parameters on solar eclipse day over a semi-arid region, Anantapur, in Southern India. The Surface Layer (SL) meteorological parameters have abruptly changed on eclipse day (December 26, 2019) as compared to the control day (December 27, 2019). During eclipse day, the near-surface air temperature was significantly decreased (1.12 °C), and relative humidity increased (14.63%) after 60 min of the beginning of the eclipse, which mainly due to cooling the surface. The atmospheric pressure has reduced by 0.9 hPa during the eclipse period, and the winds speed also reduced to 0.92 ms−1 due to the stabilization of Atmospheric Boundary Layer (ABL) and cooling in the SL. The turbulence parameters, including those are Sensible Heat Flux (SHF), Momentum Flux (MF), and Turbulent Kinetic Energy (TKE) have also reduced from 99.37 to 0.91 Wm-2, 0.38 to 0.03 Nm−2, and 1.47 to 0.37 m2s-2, respectively during the eclipse day, which mainly due to eclipse cooling effect diminishing the turbulence in Atmospheric Surface Layer (ASL). The lowest values (0.18 ms−1) of friction velocity were observed during the eclipse day, and the Monin–Obukhov stability parameter showed a significant variation in the atmospheric from weakly unstable to neutral conditions during the eclipse day. The vertical wind speed showed downdrafts during the eclipse and even after the eclipse due to subsidence of air. The investigation revealed that the ABL dynamic process and turbulence processes are affected due to cut off of solar radiation and make the SL cooling.