Cloud Aerosol Interaction And Precipitation Enhancement Experiment Research Articles

Cloud‐edge mixing: Direct numerical simulation and observations in Indian Monsoon clouds

AbstractA direct numerical simulation (DNS) with the decaying turbulence setup has been carried out to study cloud‐edge mixing and its impact on the droplet size distribution (DSD) applying thermodynamic conditions observed in monsoon convective clouds over Indian subcontinent during the Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX). Evaporation at the cloud‐edges initiates mixing at small scale and gradually introduces larger‐scale fluctuations of the temperature, moisture, and vertical velocity due to droplet evaporation. Our focus is on early evolution of simulated fields that show intriguing similarities to the CAIPEEX cloud observations. A strong dilution at the cloud edge, accompanied by significant spatial variations of the droplet concentration, mean radius, and spectral width, are found in both the DNS and in observations. In DNS, fluctuations of the mean radius and spectral width come from the impact of small‐scale turbulence on the motion and evaporation of inertial droplets. These fluctuations decrease with the increase of the volume over which DNS data are averaged, as one might expect. In cloud observations, these fluctuations also come from other processes, such as entrainment/mixing below the observation level, secondary CCN activation, or variations of CCN activation at the cloud base. Despite large differences in the spatial and temporal scales, the mixing diagram often used in entrainment/mixing studies with aircraft data is remarkably similar for both DNS and cloud observations. We argue that the similarity questions applicability of heuristic ideas based on mixing between two air parcels (that the mixing diagram is designed to properly represent) to the evolution of microphysical properties during turbulent mixing between a cloud and its environment.

The influence of wind speed on surface layer stability and turbulent fluxes over southern Indian peninsula station

Surface to atmosphere exchange has received much attention in numerical weather prediction models. This exchange is defined by turbulent parameters such as frictional velocity, drag coefficient and heat fluxes, which have to be derived experimentally from high-frequency observations. High-frequency measurements of wind speed, air temperature and water vapour mixing ratio (eddy covariance measurements), were made during the Integrated Ground Observation Campaign (IGOC) of Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) at Mahabubnagar, India (16∘44′N, 77∘59′E) in the south-west monsoon season. Using these observations, an attempt was made to investigate the behaviour of the turbulent parameters, mentioned above, with respect to wind speed. We found that the surface layer stability derived from the Monin–Obukhov length scale, is well depicted by the magnitude of wind speed, i.e., the atmospheric boundary layer was under unstable regime for wind speeds >4 m s−1; under stable regime for wind speeds <2 m s−1 and under neutral regime for wind speeds in the range of 2–3 m s−1. All the three stability regimes were mixed for wind speeds 3–4 m s−1. The drag coefficient shows scatter variation with wind speed in stable as well as unstable conditions.

Indirect forcing of black carbon on clouds over northeast India

Black carbon (BC) induced indirect radiative forcing and cloud albedo effect has been studied for the first time over northeast India. Measurements of BC and cloud microphysical parameters were carried out during Phase‐I of the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) over northeast India (Guwahati) in 2009. Liquid water path (LWP) in the cloud layers coherent with BC on different experimental days was found to be 206–327 g m−2 over the region. Black carbon aerosol indirect effect (BCIE) for fixed LWP is found to be 0.32–0.48 on different days of observations. The indirect forcing corresponding to this BCIE has been estimated using a radiative transfer model for fixed LWP by altering the derived BC‐AOD (aerosol optical depth from measured BC profiles) and cloud effective radius (Re) combinations. The estimated average BC‐induced indirect forcing (BCIF) was −24 to −37.1 W m−2 at the surface and +2.5 to +14.8 W m−2 at the top of the atmosphere (TOA). The average albedo due to BCIF at TOA was 0.49–0.61. BCIF is found to reduce the cloud reflection by 1.5–2% over the region. The sensitivities of cloud parameters to BCIF and the albedo effect are illustrated.

Atmospheric heating due to black carbon aerosol during the summer monsoon period over Ballia: A rural environment over Indo-Gangetic Plain

Black carbon (BC) aerosols are one of the most uncertain drivers of global climate change. The prevailing view is that BC mass concentrations are low in rural areas where industrialization and vehicular emissions are at a minimum. As part of a national research program called the “Ganga Basin Ground Based Experiment-2014 under the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) Phase-III” of Ministry of Earth Sciences, Government of India, the continuous measurements of BC and particulate matter (PM) mass concentrations, were conducted in a rural environment in the highly-polluted Indo-Gangetic Plain region during 16th June to 15th August (monsoon period), 2014. The mean mass concentration of BC was 4.03 (±0.85) μgm−3 with a daily variability between 2.4 and 5.64μgm−3, however, the mean mass PM concentrations [near ultrafine (PM1.0), fine (PM2.5) and inhalable (PM10)] were 29.1(±16.2), 34.7 (±19.9) and 43.7 (±28.3) μgm−3, respectively. The contribution of BC in PM1.0 was approximately 13%, which is one of the highest being recorded. Diurnally, the BC mass concentrations were highest (mean: 5.89μgm−3) between 20:00 to 22:00 local time (LT) due to the burning of biofuels/biomass such as wood, dung, straw and crop residue mixed with dung by the local residents for cooking purposes. The atmospheric direct radiative forcing values due to the composite and BC aerosols were determined to be +78.3, +44.9, and +45.0Wm−2 and +42.2, +35.4 and +34.3Wm−2 during the months of June, July and August, respectively. The corresponding atmospheric heating rates (AHR) for composite and BC aerosols were 2.21, 1.26 and 1.26; and 1.19, 0.99 and 0.96Kday−1 for the month of June, July and August, respectively, with a mean of 1.57 and 1.05Kday−1 which was 33% lower AHR (BC) than for the composite particles during the study period. This high AHR underscores the importance of absorbing aerosols such as BC contributed by residential cooking using biofuels in India. Our study demonstrates the need for immediate, effective regulations and policies that mitigate the emission of BC particles from domestic cooking in rural areas of India.

Aerosol-cloud associations over Gangetic Basin during a typical monsoon depression event using WRF-Chem simulation

To study aerosol-cloud interactions over the Gangetic Basin of India, the Weather Research and Forecasting model coupled with chemistry (WRF-Chem) has been applied to a typical monsoon depression event prevalent between the 23 and 29 August 2009. This event was sampled during the Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX) aircraft campaign, providing measurements of aerosol and cloud microphysical properties from two sorties. Comparison of the simulated meteorological, thermodynamical, and aerosol fields against satellite and in situ aircraft measurements illustrated that the westward propagation of the monsoon depression and the cloud, aerosol, and rainfall spatial distribution was simulated reasonably well using anthropogenic emission rates from Monitoring Atmospheric Composition and Climate project along with cityZEN projects (MACCity)+Intercontinental Chemical Transport Experiment Phase B anthropogenic emission rates. However,the magnitude of aerosol optical depth was underestimated by up to 50%. A simulation with aerosol emissions increased by a factor of 6 over the CAIPEEX campaign domain increased the simulated aerosol concentrations to values close to the observations, mainly within boundary layer. Comparison of the low-aerosol simulation and high-aerosol simulation for the two sorties illustrated that more anthropogenic aerosols increased the cloud condensing nuclei (CCN) and cloud droplet mass concentrations. The number of simulated cloud droplets increased while the cloud droplet effective radii decreased, highlighting the importance of CCN-cloud feedbacks over this region. The increase in simulated anthropogenic aerosols (including absorbing aerosols) also increased the temperature of air parcels below clouds and thus the convective available potential energy (CAPE). The increase in CAPE intensified the updraft and invigorated the cloud, inducing formation of deeper clouds with more ice-phase hydrometeors for both cases. These case studies provide evidence of aerosol-induced cloud invigoration over the Gangetic Basin.

Observational and simulated cloud microphysical features of rain formation in the mixed phase clouds observed during CAIPEEX

Cloud microphysical observations of rain formation in mixed phase monsoon clouds (from 10 to −9°C) using instrumented aircraft during Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) are presented. The drop size and particle size distributions are broader in the mixed phase region, indicating efficient growth of liquid as well as ice phase. Aircraft observations noticed higher ice particle concentrations in Hallet–Mossop zone (−3 to −8°C) with existence of smaller and larger cloud droplets, rimed needles columns, and graupel particles. Observations strongly suggested the active presence of Hallet–Mossop (1974) process in this cloud. The higher correlations found between slope and intercept parameters of exponential size distributions can be attributed to the efficient secondary ice production as well as to the aggregation growth of ice particles. Large Eddy Simulation (LES) of these clouds are compared with observed cloud microphysical properties, also illustrated the important role of Hallet–Mossop (HM) process and its link with warm rain and graupel formation. The raindrop freezing plays a crucial role in graupel formation in early stage of ice development. The observed mean values of microphysical parameters including liquid water content, ice water content, ice number concentrations, and reflectivity showed good agreement with model simulations. Primary ice nuclei have only a minor role in the total ice mass in these clouds.

Particle size distribution properties in mixed‐phase monsoon clouds from in situ measurements during CAIPEEX

AbstractA comprehensive analysis of particle size distributions measured in situ with airborne instrumentation during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) is presented. In situ airborne observations in the developing stage of continental convective clouds during premonsoon (PRE), transition, and monsoon (MON) period at temperatures from 25 to −22°C are used in the study. The PRE clouds have narrow drop size and particle size distributions compared to monsoon clouds and showed less development of size spectra with decrease in temperature. Overall, the PRE cases had much lower values of particle number concentrations and ice water content compared to MON cases, indicating large differences in the ice initiation and growth processes between these cloud regimes. This study provided compelling evidence that in addition to dynamics, aerosol and moisture are important for modulating ice microphysical processes in PRE and MON clouds through impacts on cloud drop size distribution. Significant differences are observed in the relationship of the slope and intercept parameters of the fitted particle size distributions (PSDs) with temperature in PRE and MON clouds. The intercept values are higher in MON clouds than PRE for exponential distribution which can be attributed to higher cloud particle number concentrations and ice water content in MON clouds. The PRE clouds tend to have larger values of dispersion of gamma size distributions than MON clouds, signifying narrower spectra. The relationships between PSDs parameters are presented and compared with previous observations.

Thermodynamical and cloud microphysical response during the transition from southwest to northeast monsoon

The thermodynamical and microphysical response during the transition from southwest to northeast monsoon season is studied. Unique mixed phase cloud observations from the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) and ground based observations from Integrated Ground Observation Campaign (IGOC), high resolution (3km) mesoscale forecasts with the nested Weather Research and Forecasting (WRF) model are used in the study. Convective available potential energy (CAPE), liquid water path (LWP) and precipitable water (PW) increased 3days before the onset and further enhanced with the onset of the northeast monsoon. A systematic decrease in lifting condensation level (LCL) height and increase in midlevel moisture before and during the onset period are observed, which resulted in increase in moist static energy in the midlayer for supporting deeper convection during the onset. Cloud microphysical response is noted with the mixed phase cloud observations of liquid water and ice water content. The model has simulated the mixed phase clouds in the area of detailed observations. Major cloud microphysical changes observed are (a) shallow warm clouds before the onset, (b) elevated supercooled liquid water content at the tops of clouds and (c) low ice water content during the onset period compared to subsequent periods after the onset with more ice water content.

Airborne and ground based CCN spectral characteristics: Inferences from CAIPEEX – 2011

Abstract A first time comprehensive study of Cloud Condensation Nuclei (CCN) and associated spectra from both airborne and ground campaigns of the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) conducted over the rain shadow region of Western Ghats during September and October 2011 is illustrated. Observations of CCN spectra during clean, polluted and highly polluted conditions indicated significant differences between airborne and ground observations. Vertical variation of CCN concentration is illustrated from airborne observations in the clean, polluted and highly polluted conditions with different air mass characteristics. The cloud base CCN number concentrations are three times less than that of the surface measurements at different supersaturations. Diurnal variations of the ground based CCN number concentration and activation diameter showed bimodality. Atmospheric mixing in the wet conditions is mainly through mechanical mixing. The dry conditions favored convective mixing and were dominated by more CCN than the wet conditions. New particle formation and growth events have been observed and were found more often on days with convective mixing. The average critical activation diameter (at 0.6% SS) observed at the ground is approximately 60 nm and availability of a large number of particles below this limit was due to the new particle formation. Observations give convincing evidence that the precipitable water and liquid water path is inversely proportional to surface CCN number concentration, and this relationship is largely dictated by the meteorological conditions.

Relationship Between the Momentum and Scalar Fluxes Close to the Ground During the Indian Post-monsoon Period

Results of a comprehensive study of the characteristics of turbulent transport very close to the ground using micrometeorological eddy-covariance measurements from the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) Integrated Ground Observational Campaign (IGOC) conducted in 2011 at a rural site over the Indian peninsular region are presented. The dataset used in the present study pertains to the morning hours when the convective boundary layer is at its growing phase. A new method, very similar to the traditional quadrant analysis, is introduced to investigate the relationship between the scalar and momentum flux transports by projecting the scalar and momentum flux contours onto the $$u-w$$ plane. Cospectral analysis is employed to study the scales of the transporting eddies; it was found that, during very unstable conditions, the scalar and momentum transports are poorly correlated with each other. However, for the near-neutral case, the correlation between the scalar and momentum transports becomes stronger, thus supporting the Reynolds analogy.

Deposition ice nuclei observations over the Indian region during CAIPEEX

A thermal gradient diffusion chamber (TGDC) designed to process the ice nuclei (IN) sample is illustrated with unique airborne observations. IN samples collected during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) have been analyzed using the TGDC. The TGDC is able to activate the IN by deposition mode over ice supersaturation of 6–24% and at a temperature range of −18.5 to −13.5C. These samples correspond to first observations at several vertical levels including the cloud layer and over several geographically distinct locations in India during the monsoon season. Vertical profile of IN concentration shows that at a given level, there is large spatial and temporal variation in IN concentration. Maximum IN concentrations are observed below 3km at all ice supersaturation. Highest IN concentrations are noted over inland continental regions. Spatial variation in IN concentration was observed in the range 0 to 5L−1 with an average of 1.12L−1 at highest ice supersaturation (20–25%) interval. Large variation in IN concentration at a single temperature is also observed. Our observation shows that there is a significant increase in IN concentrations with supersaturation over ice. Elemental chemical analysis of the collected aerosol samples by Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray Spectrometry (EDX) showed that copper, silica, aluminium and zinc are the most abundant elements.

Possible evidence of new particle formation and its impact on cloud microphysics from airborne measurements over Bay of Bengal

Airborne measurements conducted under a special mission over Bay of Bengal (BoB) during the CAIPEEX (Cloud Aerosol Interaction and Precipitation Enhancement EXperiment) in 2011 were analyzed in the present study. Research flights were carried out on 19 and 20 October, 2011 (referred as RF1 and RF2), in the region over BoB, which was influenced by a depression to evaluate the aerosol–cloud interactions over marine environment. The increased concentration of aitken/accumulation mode particles was observed at 500m above sea surface level over the ocean after the passage of the depression. The source of these particles and their subsequent growth during RF1 at about 200km from coastline has been attributed to (i) increased production of aerosols due to oxidation of dimethyl sulfide (DMS) because of upwelling of the deep ocean water during the depression and (ii) anthropogenic aerosols transported from inland. Moreover, measurements of accumulation and coarse mode particles with diameter ranging from 0.1 to 3μm and cloud droplets in the range 3 to 47μm show systematic growth associated with cloud microphysical/rain formation process. On the other hand, no such evidence of increasing particle concentration and growth has been observed at about 60km from coastline towards southeast during RF2. Evidently, the rain event observed during the night hours of 19 October caused the washout and scavenging of aerosols which contributed towards the decreased aerosol concentration observed near the coast.

Double blanket effect caused by two layers of black carbon aerosols escalates warming in the Brahmaputra River Valley

First ever 3-day aircraft observations of vertical profiles of Black Carbon (BC) were obtained during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) conducted on 30th August, 4th and 6th September 2009 over Guwahati (26°11′N, 91°44′E), the largest metropolitan city in the Brahmaputra River Valley (BRV) region. The results revealed that apart from the surface/near surface loading of BC due to anthropogenic processes causing a heating of 2 K/day, the large-scale Walker and Hadley atmospheric circulations associated with the Indian summer monsoon help in the formation of a second layer of black carbon in the upper atmosphere, which generates an upper atmospheric heating of ~2 K/day. Lofting of BC aerosols by these large-scale circulating atmospheric cells to the upper atmosphere (4–6 Km) could also be the reason for extreme climate change scenarios that are being witnessed in the BRV region.

Boundary layer aerosol characteristics at Mahabubnagar during CAIPEEX-IGOC: Modeling the optical and radiative properties

An Integrated Ground Observational Campaign (IGOC) was conducted at Mahabubnagar — a tropical rural station in the southern peninsular India, under the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) program during the period from July to November 2011. Measured chemical composition and carbonaceous aerosols from PM2.5 samples were used in an aerosol optical model to deduce crucial aerosol optical properties, which were then used in a radiative transfer model for radiative forcing estimations. The model derived aerosol optical depth (AOD at 500nm), varied from 0.13 to 0.76 (mean of 0.40±0.18) whereas Ångström exponent (AE) between 0.10 and 0.65 (mean of 0.33±0.17) suggests relative dominance of coarse particles over the station. On the other hand, single scattering albedo (SSA at 500nm) was found to vary from 0.78 to 0.92 (mean of 0.87±0.04) during the measurement period. The magnitude of absorption Ångström exponent (AAE), varied from 0.83 to 1.33 (mean of 1.10±0.15), suggests mixed type aerosols over the station. Aerosol direct radiative forcing was estimated and found to vary from −8.9 to −49.3Wm−2 (mean of −27.4±11.8Wm−2) at the surface and +9.7 to +44.5Wm−2 (mean of +21.3±9.4Wm−2) in the atmosphere during the course of measurements. The atmospheric forcing was observed to be ~30% higher during October (+29±9Wm−2) as compared to August (+21±7Wm−2) when the station is mostly influenced by continental polluted aerosols. The result suggests an additional atmospheric heating rate of 0.24Kday−1 during October, which may be crucial for various boundary layer processes in favorable atmospheric conditions.

Impact of elevated aerosol layer on the cloud macrophysical properties prior to monsoon onset

Atmospheric aerosols alter the radiation balance by absorption/scattering of solar radiation, and indirectly by modifying the cloud microphysical properties. Observations during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) provide a unique opportunity to investigate the aerosol–cloud interaction in a dry to wet transition phase prior to the onset of southwest monsoon. It is observed that aerosol loading increased over the central Indian region in spite of the increase in surface rainfall. This aerosol loading was observed mainly in the 2–5 km level above surface. The origin and influence of elevated aerosol layer have been investigated with the help of WRF-Chem simulations by conducting sensitivity experiments for dust emissions, modified based on the satellite observations. To enhance the dust emissions, the erodible fraction over the Thar Desert region is enhanced to an average factor of 1.7 based on TOMS aerosol index (AI) and USGS land use category, which contributed to enhanced dust emissions by a factor of 1.25 over the study region. This enhancement of dust emission from Thar Desert can result in an increased radiative heating due to elevated aerosol layers, which leads to an increase in the ice mixing ratio and ice water content in the regions of dry to wet transition. It is shown that even natural dust emissions (without changes in anthropogenic emissions) may also influence the spatial and temporal distribution of cloud and precipitation and the hydrological cycle.

Study of cloud microphysical properties over India during CAIPEEX using a mesoscale model with new cloud microphysical scheme—Part I

Incorporation of aerosol interaction in cloud microphysics is being the central issue now a day. In the present study, an improved and modified cloud microphysical scheme comprising bulk-formula two-moment mixed-phase cloud scheme has been incorporated with a regional model to study the cloud–aerosol interaction in the mixed-phase cloud system. The paper intends to sensitivity study as to what extent this new microphysical scheme can capture the observed cloud microphysical properties. The observed cloud microphysical hydrometeors are evaluated from MODIS (Moderate Resolution Imaging Spectrometer) and CAIPEEX (Cloud Aerosol Interaction and Precipitation Enhancement EXperiment) data set over the Indian peninsular region. Surface accumulated precipitation is collected from TRMM-3B42 data sets. One active convection (case study 1) and two suppressed convection events (case study 2 and case study 3) during Indian south west monsoon are simulated over three different locations of the Indian peninsular region with the help of a multi nested mesoscale model based on microphysical modification. The cloud microphysical properties such as cloud water path from satellite data retrieval and cloud drop number concentration, cloud droplet radius from CAIPEEX, are reproduced well by the modified microphysical scheme. The rainfall is also reasonably well simulated during active monsoon convection event (6th July, 2009) as well as suppressed monsoon convection events (15th June and 19th August, 2009). Moreover, another sensitivity experiment is done to include natural aerosols, like dust as a representation of heterogeneous ice nucleation. The inclusion of mineral dust effect as ice nuclei provides realistic cloud microphysical properties during present case studies successfully. So it is a worthy investigation of the role of different kinds of aerosols on the microphysics and precipitation processes.

Spectral width of premonsoon and monsoon clouds over Indo‐Gangetic valley

The combined effect of humidity and aerosol on cloud droplet spectral width (σ) in continental monsoon clouds is a topic of significant relevance for precipitation and radiation budgets over monsoon regions. The droplet spectral width in polluted, dry premonsoon conditions and moist monsoon conditions observed near the Himalayan Foothills region during Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX) is the focus of this study. Here σis small in premonsoon clouds developing from dry boundary layers. This is attributed to numerous aerosol particles and the absence/suppression of collision‐coalescence during premonsoon. For polluted and dry premonsoon clouds,σ is constant with height. In contrast to premonsoon clouds, σ in monsoon clouds increases with height irrespective of whether they are polluted or clean. The mean radius of polluted monsoon clouds is half that of clean monsoon clouds. In monsoon clouds, both mean radius and σ decreased with total cloud droplet number concentration (CDNC). The spectral widths of premonsoon clouds were independent of total droplet number concentrations, but both σ and mean radius decreased with small droplet (diameter &lt; 20 μm) number concentrations in the diluted part of the cloud. Observational evidence is provided for the formation of large droplets in the adiabatic regions of monsoon clouds. The number concentration of small droplets is found to decrease in the diluted cloud volumes that may be characterized by various spectral widths or mean droplet radii.

Aerosol effect on droplet spectral dispersion in warm continental cumuli

In situ aircraft measurements of cloud microphysical properties and aerosol during the 1st phase of the Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX‐I) over the Indian sub‐continent provided initial opportunities to investigate the dispersion effect and its implications for estimating aerosol indirect effects in continental cumuli. In contrast to earlier studies on continental shallow cumuli, it is found that not only the cloud droplet number concentration but also the relative dispersion increases with the aerosol number concentration in continental cumuli. The first aerosol indirect effect estimated from the relative changes in droplet concentration and effective radius with aerosol number concentration are 0.13 and 0.07, respectively. In‐depth analysis reveals that the dispersion effect could offset the cooling by enhanced droplet concentration by 39% in these continental cumuli. Adiabaticity analysis revealed aerosol indirect effect is lesser in subadiabatic clouds possibly due to inhomogeneous mixing processes. This study shows that adequate representation of the dispersion effect would help in accurately estimating the cloud albedo effect for continental cumuli and can reduce uncertainty in aerosol indirect effect estimates.

Aerosol control on depth of warm rain in convective clouds

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 &gt;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.

Vertical profiles of black carbon aerosols over the urban locations in South India

Vertical profiles of black carbon (BC) aerosol were determined from aircraft measurements under the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) program conducted by the Indian Institute of Tropical Meteorology, India during 2009 over Bangalore and Hyderabad in south India. BC mass loadings decreased approximately monotonically from 103 to 104ng/m3 at the surface to ~102ng/m3 at an altitude of about 7km; although layers at intermediate levels containing anomalously high BC loadings were frequently encountered that were attributed mainly to the convective transport from surface sources accompanied by changes in the local boundary layer and atmospheric stability. In addition, as evidenced from air mass back trajectories; long range transport from distant sources contributed to some anomalous spikes in BC concentration. The presence of BC in cloud forming regions of the free troposphere could have important implications for cloud microphysics and subsequent rainfall mechanism over this region. Apart from this, the effects on human health are equally important.