Abstract:Research work in the area of the Global Electric Circuit (GEC) has rapidly expanded in recent years mainly through observations of lightning from satellites and ground-based networks and observations of optical emissions between cloud and ionosphere. After reviewing this progress, we critically examine the role of various generators of the currents flowing in the lower and upper atmosphere and supplying currents to the GEC. The role of aerosols and cosmic rays in controlling the GEC and linkage between climate, solar-terrestrial relationships and the GEC has been briefly discussed. Some unsolved problems in this area are reported for future investigations.

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Many studies in recent times have suggested that long-term changes in Convective Available Potential Energy (CAPE) are associated with the changes in convective activity and atmospheric energy budget and, hence, the changes in CAPE could be used as a potential indicator of climate change. Here, we analyse daily radiosonde data of 32 stations over the Indian region from 1984 to 2008 (25 years), to study the climatology and long-term changes in CAPE, lower troposphere moisture content and upper tropospheric temperature. Using gridded daily rainfall data over this region, the relationship between average CAPE and average rainfall as well as the trends in CAPE and its effect on rainfall pattern are also examined during different seasons of this region. All the coastal and island stations, as well as some stations in the foothills of the Himalayas, show higher values of CAPE compared to other inland stations. This study clearly demonstrates that CAPE values have been systematically increasing over most parts of the Indian region during last 25 years. The increase in CAPE is found to be due to increase in low-level moisture content and decrease in upper level temperature over the last 25 years. The seasonal variations show that the CAPE is higher during the monsoon compared to pre-monsoon or post-monsoon seasons and it suggests that thermodynamic conditions favourable for high CAPE together with large-scale dynamics are necessary for organized monsoon convections over this region. In comparison with a large increase in the allIndia average of CAPE during monsoon season, which is about 38 J Kg −1 year −1 , the all-India summer monsoon rainfall increases about 1.3 mm year −1 . The systematic increasing trend in CAPE may be compensating for weakening of monsoon circulation and, thus, maintaining the monsoon rainfall over the Indian region.

Spatial and vertical distributions of aerosol radiative properties over Indian Continental Tropical Convergence Zone (CTCZ) up to 6 km altitude during the pre‐monsoon and monsoon seasons of 2008 have been measured and reported for the first time. Inter‐seasonal and intra‐seasonal comparisons of different aerosol properties below and above the boundary layer are carried out in and among different regions of CTCZ. During pre‐monsoon, aerosol layers were found to be present up to altitude as high as 6 km over the Indo‐Gangetic Plains and Himalayan foothills. A large increase in absorption coefficients (by two to five times) near the Himalayan foothills and coastal India than the background values may be attributed to extensive biomass burning as supported by fire counts data. During monsoon, the aerosols were mostly confined to lower troposphere. However, absorbing aerosols were found to rebuild much faster than scattering aerosols after rains. Heating rates were very high over urban city of Bareilly peaking around 2 km during the pre‐monsoon. The HR values over urban Kanpur during monsoon were comparable to Bareilly during pre‐monsoon. Negligible latitudinal gradient of heating rate from the Himalayan foothill to central India was observed during both the seasons.

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