The changes in near-surface ozone and precursors at two nearby tropical sites during annular solar eclipse of 15 January 2010

Abstract

Studies on the solar eclipse–induced changes in near-surface ozone and its precursors NOx and CO were carried out at two nearby tropical coastal locations, Thumba (very close to the sea) and the Centre for Earth Science Studies (CESS), which is 4.5 km off the Thumba coast and with varying topography, during the annular eclipse of 15 January 2010. The surface ozone decreased by 12 and 13 ppb (35% and 52%) over Thumba and CESS, with the time lag of 40 min and 25 min from the maximum phase of eclipse, respectively, and at CESS, post-eclipse recovery was faster compared to Thumba. No pronounced change was observed in NOx, but CO showed an enhancement toward the ending phase of the eclipse. The diurnal patterns of ozone and their differences at the two sites were strongly dependent on local meteorology, in particular, the mesoscale dynamics and topography. While the temperature decreased by 1.2°C at Thumba, the decrease was almost double (~2.1°C) at CESS. The early fall in temperature caused the early setting in of land-breeze (post-eclipse effect), which in turn triggered an early evening decrease in near-surface ozone compared to the control conditions. The present study points to the role of mesoscale meteorology/dynamics in controlling the evolution of solar eclipse–induced changes in ozone in a relatively clean environment. The chemical box model simulations reproduced these broad features: a percentage decrease and the time lag in surface ozone. The observation of total column ozone showed a decrease and fluctuations, after the eclipse maximum.