Aerosol optical depth, ozone and water vapor measurements over Gadanki, a tropical station in peninsular India

This paper reports the results of a study related to the optical and physical characteristics of columnar aerosols and variation in total column ozone (TCO) and precipitable water content (PWC) over Gadanki (13.45°N, 79.18°E), a tropical station in peninsular India, for the first time, using MICROTOPS-II (Microprocessor-based Total Ozone Portable Spectrometer), comprising of both sun photometer and ozonometer. Results show wavelength dependence of AOD, having mean value of �0.4 (± 0.09) at 500 nm optical channel. Daily mean aerosol size spectra shows, most of the time, power-law distribution. However, its diurnal variations show significant changes in aerosol size spectra modulated by a combination of both power-law and bi-modal distributions. To characterize AOD, the Angstrom parameters (i.e., a and β) were used. The day-to-day variations in TCO were found to be in fair agreement with that derived from TOMS satellite data for all the experimental days, having mean observed value of ~253 (± 8) DU over the station. Interestingly, an inverse relationship between TCO and AOD or PWC was observed over the station, on some times of the day, which could be attributed to the mixing of significant fraction of ozone with aerosol and water vapor-rich air mass. However, a significant positive correlation was observed between AOD and PWC

Lidar Observations of aerosol layers just below the tropopause level during IFP-INDOEX

A lidar system has been used at Gadanki (13.5º, 79.2ºE) to study the characteristics of aerosol layer (cloud) occurring just below the tropical tropopause. The preliminary results of the lidar observations indicate that the cloud occurs ~ 2 km below the tropopause. The top and bottom edges of the cloud have propensity for ice crystal presence with liquid droplets/ vapours in-between. The clouds show temporal fluctuations (in their backscattering ratio) with temporal scales of the order of 30–90 min

Lidar observed characteristics of the tropical cirrus clouds

Using the polarization diversity lidar data collected during March 1998 to April 2001, the characteristics of the tropical cirrus clouds observed over Gadanki (13.5°N; 79.2°E) are presented in this paper. Out of 210 nights of observations during this period, cirrus clouds were observed over the lidar site on 170 nights. The cloud mean height is found to be in the range of 8-17 km with peak occurrence at 13-14 km, just below the tropopause. The cloud thickness has values ranging 0.6-4.2 km with maximum occurrence at 0.9-1.2 km. The scattering ratio and the linear depolarization ratio are in the ranges of 1.14-36 and 0.01-0.75 with peak occurrences seen at 1.14-2 and 0.01-0.05, respectively. The optical depth can be as high as 2, but values less than 0.1 account for most (>80%) of the clouds. The clouds with low optical depth occur most frequently during fall equinox and high optical depth during summer. The formations of thin and thick cirrus clouds are seen to be closely related to the minimum tropospheric temperature and cumulonimbus outflows, respectively

The influence of a south Asian dust storm on aerosol radiative forcing at a high-altitude station in central Himalayas

The impact of long-range transported dust aerosols, originating from the Thar Desert region, to a high-altitude station in the central Himalayas was studied with the help of micro-pulse lidar (MPL) observations. A drastic change in lidar back-scatter profile was observed on a dust day as compared with that on a pre– dust day. The back-scatter coefficient on a dust day revealed that the dust layer peaked at an altitude ∼1300 m above ground level (AGL) and extended up to ∼3000 m AGL, with maximum value ∼3 × 10–5 m–1 sr–1 . Aerosol Index (AI) and air mass back-trajectory analysis substantiate the transport of dust aerosols from the far-off Thar Desert region to the experimental site. A significant effect of dust aerosols was also observed over the station on the spectral aerosol optical depths (AODs), measured using a Microtops-II Sunphotometer. It showed signif- icantly different spectral behaviour of AOD on a dust day as compared with that on a pre-dust day. The Ångström exponent (α) showed a marked decrease from 0.42 to 0.04 from the pre-dust day to the dust day. The aerosol radiative forcing estimated using the Santa Barbara DISORT (discrete ordinate radiative transfer) atmospheric radiative transfer (SBDART) model, in conjunction with the opti- cal properties of aerosol and cloud (OPAC) model, showed values of about –30, –45 and +15 W m–2 , respectively, at top-of-atmosphere (TOA), surface and in the atmosphere on the dust day. The positive atmosphere forcing caused an estimated heating of the lower atmosphere by ∼0.4 K day–1

Thin aerosol clouds at tropopause level

Aerosol clouds about 2 km below the tropopause are studied using the data from lidar and MST radar at Gadanki. The cloud shows fluctuations with time scales as short as 1/2 h in the backscatter ratio. Depolarization factor indicates ice crystal formation when the cloud is strong. The MST radar wind data show strong turbulence below the cloud level indicating, probably, turbulent mixing/transport of water vapor from lower heights to cloud heights facilitating cloud formation

Thin aerosol clouds at tropopause level

245-248Aerosol clouds about 2 km below the tropopause are studied using the data from lidar and MST radar at Gadanki. The cloud shows fluctuations with time scales as short as 1/2 h in the backscatter ratio. Depolarization factor indicates ice crystal formation when the cloud is strong. The MST radar wind data show strong turbulence below the cloud level indicating, probably, turbulent mixing /transport of water vapour from lower heights to cloud heights facilitating cloud formation

Preliminary results of equatorial wave experiment conducted from 18 Jan. 1999 to 5 Mar. 1999 with lidar at Gadanki

231-234An experimental campaign has been conducted from 18 Jan. to 5 Mar. 1999 at Gadanki using MST radar and lidar to delineate the characteristics of equatorial waves. In this paper, the preliminary results from lidar data on temperature in the upper troposphere and mesosphere are presented. The characteristics of equatorial waves with periods in the range 9.4 days- 2.6 days in temperature are delineated

A study of equatorial wave characteristics using rockets, balloons, lidar and radar

A co-ordmated experimental campaign was conducted for 40 consecutive days from 21 February to 01 April 2000 using RH-200 rockets, balloons, Rayleigh lidar and MST radar, with the objective of delineating the equatorial waves and estimating momentum fluxes associated with them. Winds and temperatures in the troposphere, stratosphere and mesosphere over two low latitude stations Gadanki (13.5&#176;N, 79.2&#176;E) and SHAR (13.7&#176;N, 80.2&#176;E) were measured and were used for the study of equatorial waves and their interactions with the background mean flow in various atmospheric regions. The study shows the occurrence of a strong stratospheric cooling (<SUP>~</SUP>25 K) anomaly along with a zonal wind anomaly and this low-latitude event appears to be linked to high-latitude stratospheric warming event and followed by subsequent generation of short period (<SUP>~</SUP>5 days) oscillations lasting for a few cycles in the stratosphere. Slow and fast Kelvin waves and RG wave (<SUP>~</SUP>-17-day and <SUP>~</SUP>7.2-day and <SUP>~</SUP>4.2-day periods respectively) have been identified. The mean flow acceleration produced by the divergence of the momentum flux due to the observed Kelvin waves in the 35-60 km height region were compared with the zonal flow accelerations computed from the observed zonal winds. Contribution by the slow and fast Kelvin waves was found to be only <SUP>~</SUP>25 % of the observed acceleration during the evolution of the westerly phase of the semi-annual oscillation