[1] During an intense field campaign for generating a spatial composite of aerosol characteristics over peninsular India, collocated measurements of the mass concentration and size distribution of near-surface aerosols were made onboard instrumented vehicles along the road network during the dry, winter season (February-March) of 2004. The study regions covered coastal, industrial, urban, village, remote, semiarid, and vegetated forestlands. The results showed (1) comparatively high aerosol (mass) concentrations (exceeding 50 mg m À3 ), in general, along the coastal regions (east and west) and adjacent to urban locations, and (2) reduced mass concentration (<30 mg m À3) over the semiarid interior continental regions. Fine, accumulation-mode particles (<1 mm) contribute more than 50% to the total aerosol mass concentration in the coastal regions, which is more conspicuous along the east coast than the west coast, while the interior regions showed abundance (>50% of the total) of coarse-mode aerosols (>1 mm). The spatial composite of accumulation-mode share to the total aerosol mass concentration agreed very well with the monthly mean spatial composite of aerosol fine-mode fraction for February 2004, deduced from Moderate-Resolution Imaging Spectroradiometer data for the study region, while a point by point comparison yielded a linear association with a slope of 1.09 and correlation coefficient of 0.79 for 76 independent data pairs. Pockets of enhanced aerosol concentration were observed around the industrialized and urban centers along the coast as well as inland. Aerosol size distributions were parameterized using a power law. Spatial variation of the retrieved aerosol size index shows relatively high values (>4) along the coast compared to interior continental regions except at a few locations. Urban locations showed steeper size spectra than the remote locations.Citation: Moorthy, K. K., et al. (2005), Wintertime spatial characteristics of boundary layer aerosols over peninsular India,

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[1] The temperature dependencies of cirrus properties are studied using a dual polarization lidar and Mesosphere Stratosphere Troposphere (MST) radar at the tropical station Gadanki (13.5°N, 79.2°E). Cirrus clouds are generally observed in the altitude region 10 to 18 km, with midcloud temperature in the range À85°to À40°C. The cloud temperature decreases with increase in cloud altitude as expected. The mean cloud thickness is generally in the range 0.7 to 1.7 km. For temperatures in the range À75°to À50°C the cloud thickness is $1.7 km and shows a tendency to decrease at lower temperatures. The linear depolarization ratio (LDR) within the cloud shows a small increase with decrease in temperature. The cloud extinction and optical depth increases with increase in temperature. The temperature dependence of cirrus extinction/optical depth has been parameterized using different analytical forms such as exponential, linear, and polynomial, which shows that a second-order polynomial function is well suited for describing the temperature dependence of extinction coefficient/optical depth of tropical cirrus. The climate sensitivity factor derived based on the empirical relations shows an increase with decrease in cloud optical depth. The present study, however, indicates that the cirrus becomes radiatively significant when its optical depth exceeds a threshold value of 0.03.

Abstract. Aerosol distribution over the oceanic regions around the Indian subcontinent and its seasonal and interannual variabilities are studied using the aerosol optical depth (AOD) derived from NOAA-14 and NOAA-16 AVHRR data for the period

Using the MST radar observations at Gadanki (13.5°N, 79.2°E), a tropical station, the altitude of major convective outflow in the troposphere is identified and is considered to represent the convective tropopause. This is found to match well with the altitude of local minimum of potential temperature lapse rate obtained from simultaneous radiosonde observations. The convective tropopause altitudes are also compared with the cloud top altitudes obtained using satellite brightness temperature (BT) data and are found to match in the case of deep convection. The thickness of the tropical tropopause layer follows very closely the convective tropopause altitude and has little dependence on the cold point tropopause altitude. The thickness of the tropopause layer is found to shrink when convection reaches high altitudes. This occurs mainly during the monsoon months of July, September, and October.