[1] Studies on the solar eclipse-induced changes in near-surface ozone and its precursors NO x 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 NO x , 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.

[1] Sedimentation of ice particles from cirrus clouds is one of the main processes responsible for dehydration of the upper troposphere. Multiyear-long-duration lidar observations of tropical cirrus over Thiruvananthapuram (8.5 N, 77 E) show the descending nature of these clouds throughout the year, with a mean frequency of occurrence of $20%. Majority of these descending cirrus occur near the base of tropical tropopause layer (TTL), while their frequency of occurrence and vertical extent of descent near the cold point tropopause are considerably less. On average, vertical displacement of the top and base of cirrus is almost similar. The most probable vertical displacement of cirrus is 1.5 -2.5 km with descent duration of 1-2 h. However, in >20% of the cases, the vertical displacement is >3 km and $40% of the descending cirrus layers last for 2-5 h. Around 95% of descending cirrus clouds have a settling speed <0.8 ms À1 . On average, the percentage of clouds that are thickening or thinning by >300 m during descent are almost equal ($23% each), while the thickening/thinning of the remaining 54% is <300 m. About 79% of these descending cirrus layers have cloud optical depth (COD) between 0.1 to 0.5. None of these clouds are of sub-visual type (COD <0.03). For the typical range of vertical displacements and CODs observed in the present study, the descending of cirrus clouds are estimated to decrease the longwave cloud radiative forcing at top of the atmosphere by 1 to 12.9 Wm À2 .

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Smoke plumes originating from vegetation fires engulf Southeast Asia and East Equatorial Indian Ocean (EEIO) during October‐November period in almost all the El Niño years. For the first time, observations of the vertical profiles of aerosol extinction coefficient using the Cloud Aerosol Lidar Pathfinder Satellite Observation (CALIPSO), along with the spatial distribution of aerosol optical depth (AOD) derived from NOAA‐18‐AVHRR provided an opportunity to study the 3‐dimensional structure of the plume that spread over an area of ∼1 million km2 (0.532 Wm−2 over a wide area and the mean aerosol radiative heating rate in the atmosphere estimated over Singapore is 1.2 K/day between 0.6–2 km. This led to an increase in the lower tropospheric stability in this location.