Abstract. Atmospheric greenhouse gases (GHGs), such as carbon dioxide (CO 2 ) and methane (CH 4 ), are important climate forcing agents due to their significant impacts on the climate system. The present study brings out first continuous measurements of atmospheric GHGs using highprecision LGR-GGA over Shadnagar, a suburban site of Central India during the year 2014. The annual mean CO 2 and CH 4 over the study region are found to be 394 ± 2.92 and 1.92 ± 0.07 ppm (µ ± 1σ ) respectively. CO 2 and CH 4 show a significant seasonal variation during the study period with maximum (minimum) CO 2 observed during pre-monsoon (monsoon), while CH 4 recorded the maximum during postmonsoon and minimum during monsoon. Irrespective of the seasons, consistent diurnal variations of these gases are observed. Influences of prevailing meteorology (air temperature, wind speed, wind direction, and relative humidity) on GHGs have also been investigated. CO 2 and CH 4 show a strong positive correlation during winter, pre-monsoon, monsoon, and post-monsoon with correlation coefficients (R s ) equal to 0.80, 0.80, 0.61, and 0.72 respectively, indicating a common anthropogenic source for these gases. Analysis of this study reveals the major sources for CO 2 are soil respiration and anthropogenic emissions while vegetation acts as a main sink, whereas the major source and sink for CH 4 are vegetation and presence of hydroxyl (OH) radicals.

Atmospheric aerosols play an important role in the formation of warm clouds by acting as efficient cloud condensation nuclei (CCN) and their interactions are believed to cool the Earth-Atmosphere system (‘first indirect effect or Twomey effect’) in a highly uncertain manner compared to the other forcing agents. Here we demonstrate using long-term (2003–2016) satellite observations (NASA’s A-train satellite constellations) over the northern Indian Ocean, that enhanced aerosol loading (due to anthropogenic emissions) can reverse the first indirect effect significantly. In contrast to Twomey effect, a statistically significant increase in cloud effective radius (CER, µm) is observed with respect to an increase in aerosol loading for clouds having low liquid water path (LWP < 75 g m−2) and drier cloud tops. Probable physical mechanisms for this effect are the intense competition for available water vapour due to higher concentrations of anthropogenic aerosols and entrainment of dry air on cloud tops. For such clouds, cloud water content showed a negative response to cloud droplet number concentrations and the estimated intrinsic radiative effect suggest a warming at the Top of the Atmosphere. Although uncertainties exist in quantifying aerosol-cloud interactions (ACI) using satellite observations, present study indicates the physical existence of anti-Twomey effect over the northern Indian Ocean during south Asian outflow.

No abstract

In the present study we have attempted to characterize aerosols using their optical properties over a tropical urban location of Hyderabad, India. We have analyzed three years of in-situ data on aerosol absorption from Aethalometer and scattering from Nephelometer measurements. Satellite based absorption measurements from ozone monitoring instrument, absorbing aerosol index are also analyzed to investigate the role of long range transport of dust. Further, the CloudAerosol Lidar Pathfinder Satellite Observations (CALIPSO) data is used to study the vertical extent of aerosol particles as well as their sphericity using its particulate depolarization ratio. The study revealed that irrespective of seasonal variation, local anthropogenic fossil fuel aerosols form the predominant aerosol type over this site. Biomass/dust aerosols in their pure form are not present during the study period; however the spread of frequency distribution of scattering Angstrom exponent and absorption Angstrom exponent suggested their possible existence in mixed condition with local anthropogenic aerosols. The analysis of columnar aerosol absorption data during pre-monsoon period showed the dominance of UV absorbing dust aerosols in the study region. CALIPSO data analysis over study area showed that majority aerosols are confined within 2 km from the surface during winter while in pre-monsoon particles are distributed throughout the profile (~6 km) with extinction coefficient varying between 0.1-0.2 km -1 . As the season shift from winter to pre-monsoon a change in sphericity of particle is observed. Cluster mean trajectory analysis revealed that during premonsoon majority of air mass movements (~68%) are from western side passing through dust source region like Persian Gulf and Thar Desert before entering into Indian region. During post-monsoon (~70%) and winter (~65%), majority of the air masses are coming from north-west and north-east side of the study area where biomass burning is quite frequent during this period.

Dust storm events over the Arabian Sea (AS) have been detected using Moderate Resolution Imaging Spectroradiometer (MODIS) data. Shortwave Aerosol Radiative Forcing (SWARF) due to dust storm is estimated using synchronous observation of Clouds and Earth's Energy System (CERES) and MODIS aerosol optical depth (AOD). Study established a relationship between them as SWARF = −39.12 × AOD − 16.53 (0.4 ≤ AOD ≤ 4.0) with r 2 = 0.96. The developed relation can be used for quick, independent estimation of instantaneous SWARF for dust storm over the AS. The relationship can be used to explore the possible effect of dust on climate modulation in this region.