Assessment of Climate Change over the Indian Region : A Report of the Ministry of Earth Sciences (MoES), Government of India

We measured carbonaceous material and water-soluble ionic species in the fine fraction (D p < 1.3 μm) of aerosol samples collected on NCAR's C-130 aircraft during the intensive field phase (February-March 1999) of the Indian Ocean Experiment (INDOEX). Polluted layers were present over most of the study region north of the equator at altitudes up to 3.2 km. The estimated aerosol mass (sum of carbonaceous and soluble ionic aerosol components) of fine-mode particles in these layers was 15.3 ± 7.9 μg m -3 . The major components were particulate organic matter (POM, 35%), SO 2- 4 (34%), black carbon (BC, 14%), and NH4 (11%). The main difference between the composition of the marine boundary layer (MBL, 0 to ∼1.2 km), and the overlying residual continental boundary layer (1.2 to ∼3.2 km) was a higher abundance of SO 2- 4 relative to POM in the MBL, probably due to a faster conversion of SO 2 into SO 2- 4 in the MBL. Our results show that carbon is a major, and sometimes dominant, contributor to the aerosol mass and that its contribution increases with altitude. Low variability was observed in the optical properties of the aerosol in the two layers. Regression analysis of the absorption coefficient at 565 nm on BC mass (BC < 4.0 μg C m -3 ) yielded a specific absorption cross section of 8.1 ± 0.7 m 2 g -1 for the whole period. The unusually high fraction of BC and the good correlation between the absorption coefficient and BC suggest that BC was responsible for the strong light absorption observed for the polluted layers during INDOEX. High correlation between BC and total carbon (TC) (r 2 = 0.86) suggest that TC is predominantly of primary origin. Good correlations were also found between the scattering coefficient at 550 nm and the estimated aerosol mass for the fine fraction. These yielded a specific scattering cross section of 4.9 ± 0.4 m 2 g -1 . The observed BC/TC, BC/OC, SO 2- 4 /BC, and K + /BC ratios were fairly constant throughout the period. These ratios suggest that between 60 and 80% of the aerosol in the polluted layers during INDOEX originated from fossil fuel and between 20 and 40% from biofuel combustion.

Carbonaceous aerosols over the Indian Ocean during the Indian Ocean Experiment (INDOEX): Chemical characterization, optical properties, and probable sources : Indian Ocean Experiment (INDOEX)

[1] Coalescence of cloud droplets is essential for the production of small raindrops at a given vertical distance above the cloud base (Dp). The rate of droplet coalescence is determined mainly by droplet size, spectrum width and concentrations. The droplet condensational growth is determined by the number of activated CCN (Na) and height above cloud base. Here we show that when the droplet mean volume radius, rv, exceeds ∼13 μm, or when droplet effective radius (re) exceeds ∼14 μm, considerable precipitation mass (>0.03 g kg−1) is likely to be present in growing convective clouds. This is because the rate of droplet coalescence is proportional to ∼rv5 which practically implies the existence of a threshold rv above which efficient warm rain formation can occur, and also because the vertical profile of rv, even in diluted clouds, nearly follows the theoretical adiabatic condensational growth curve. The small observed deviations are mainly caused by deviations from purely inhomogeneous mixing which cause partial droplet evaporation. Consequently, Dp must theoretically change nearly linearly with Na. This is confirmed here observationally, where increasing Na by 100 per milligram (≈cm3 at cloud base) of air, resulted in an increase of ∼280 m in Dpfor both Israeli and Indian deep convective clouds. This means that in highly polluted clouds or where strong cloud-base updrafts occur, clouds have to grow well above the freezing level, even in tropical atmosphere, before precipitation forms either by warm or by mixed-phase processes.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2011JD016457

Linear relation between convective cloud drop number concentration and depth for rain initiation

While the demand for enhancing rainfall through cloud seeding is strong and persistent in the country, considerable uncertainty exists on the success of such an endeavour at a given location To understand the pathways of aerosol-cloud interaction through which this might be achieved, a national experiment named Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX) in two phases, was carried out The rationale of CAIPEEX, the strategy for conducting the experiment, data quality and potential for path-breaking science are described in this article Pending completion of quality control and calibration of the CAIPEEX phase-II data, here we present some initial results of CAIPEEX phase-I aimed at documenting the prevailing microphysical characteristics of aerosols and clouds and associated environmental conditions over different regions of the country and under different monsoon conditions with the help of an instrumented research aircraft First-time simultaneous observations of aerosol, cloud condensation nuclei (CCN) and cloud droplet number concentration (CDNC) over the Ganges Valley during monsoon season show very high concentrations (> 1000 cm-3) of CCN at elevated layers Observations of elevated layers with high aerosol concentration over the Gangetic valley extending up to 6 km and relatively less aerosol concentration in the boundary layer are also documented We also present evidence of strong cloud- aerosol interaction in the moist environments with an increase in the cloud droplet effective radius Our observations also show that pollution increases CDNC and the warm rain depth, and delays its initiation The critical effective radius for warm rain initiation is found to be between 10 and 12 I¼m in the polluted clouds and it is between 12 and 14 I¼m in cleaner monsoon clouds

The cloud aerosol interaction and precipitation enhancement experiment (CAIPEEX): Overview and preliminary results

[1] Aircraft measurements of cloud condensation nuclei (CCN) and microphysics of clouds at various altitudes were conducted over India during CAIPEEX (Cloud Aerosol Interaction and Precipitation Enhancement Experiment) phase I and II in 2009 and 2010 respectively. As expected, greater CCN concentrations gave rise to clouds with smaller drops with greater number concentrations (Nc). The cloud drop effective radius (re) increased with distance above cloud base (D). Warm rain became detectable, i.e., rain water content >0.01 g/Kg, at the tops of growing convective clouds when re exceeded 12 μm. The re is determined by the number of activated CCN, Nad, and D. The Nad can be approximated by the maximum measured values of Nc. Higher Nc resulted in greater D for reaching the re threshold for onset of warm rain, re*, denoted as D*. In extreme cases of highly polluted and moist air that formed the monsoon clouds over the Indo-Gangetic plains, D* exceeded 6 km, well above the 0°C isotherm level. The precipitation particles were initiated there as supercooled raindrops at a temperature of −8°C. Giant CCN reduced re* and D*, by initiating raindrops closer to cloud base. This effect was found mainly in dusty air masses over the Arabian Sea. Besides, the aerosol effect on D*, D* was found to decrease with increase in cloud water path.

/pdf/aerosol-control-on-depth-of-warm-rain-in-convective-clouds-ocd8johkh3.pdf

Aerosol control on depth of warm rain in convective clouds

A warm cloud modification experiment was carried out during the 11-summer monsoon (June - September) seasons (1973-74, 1976, 1979-86) using a double-area cross-over design with area randomization. An instrumented aircraft was used for the cloud physical measurements seeding. Finely pulverized salt (sodium chloride) particles were released into and the monsoon clouds (stratocumulus and cumulus) during aircraft penetrations into the clouds at a height of 200-300 m above the cloud base. The warm cloud responses to salt seeding were found to be critically dependent on the cloud physical characteristics e.g., vertical thickness and the liquid water content. When clouds having (i) vertical thickness > 1 km, and (ii) LWC > 0.5 g m^3 were seeded with salt particles (modal diameter 10 um, concentration 1 per liter of cloud air) produced increase in rainfall of 24 percent significant at 4 percent level. The cloud physical observations made in not-seeded (control) and seeded (target) clouds have apparently provided some useful evidence to illustrate the possibility that the hygroscopic particle seeding might accelerate the collision-coalescence process.

/pdf/11-year-warm-cloud-seeding-experiment-in-maharashtra-state-1che7l1ld0.pdf

11-Year Warm Cloud Seeding Experiment in Maharashtra State, India

The exact physical mechanism responsible for the generation of fair weather electric field is not clearly understood. Some of the recent remarkable observations showed evidence for the horizontal fields in the magnetosphere and ionosphere which penetrate at least into the stratosphere and perhaps into the troposphere. In the present paper a gravity wave feed back mechanism for the coupling of the troposphere and the ionosphere has been discussed. The physical mechanism proposed can offer an alternate explanation for the atmospheric electrical phenomena during fair and disturbed weather. Refs.

S. S. Kandalgaonkar

Papers

The cloud aerosol interaction and precipitation enhancement experiment (CAIPEEX): Overview and preliminary results

11-Year Warm Cloud Seeding Experiment in Maharashtra State, India

A New Mechanism for the Maintenance of Fair Weather Electric Field and Cloud Electrification