J. R. Kulkarni

Microphysics of Premonsoon and Monsoon Clouds as Seen from In Situ Measurements during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX)

AbstractAnalysis of the microphysical structure of deep convective clouds using in situ measurements during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) over the Indian peninsular region is presented. It is shown that droplet size distributions (DSDs) in highly polluted premonsoon clouds are substantially narrower than DSDs in less polluted monsoon clouds. High values of DSD dispersion (0.3–0.6) and its vertical variation in the transient and monsoon clouds are related largely to the existence of small cloud droplets with diameters less than 10 μm, which were found at nearly all levels. This finding indicates the existence of a continuous generation of the smallest droplets at different heights. In some cases this generation of small droplets leads to the formation of bimodal and even multimodal DSDs. The formation of bimodal DSDs is especially pronounced in monsoon clouds. Observational evidence is presented to suggest that in-cloud nucleation at elevated layers is a f...

Wavelet analysis of the association between the Southern Oscillation and the Indian summer monsoon

A new aspect of the monsoon-Southern Oscillation (SO) link has been investigated. All India Summer Monsoon Rainfall (AISMR) and Southern Oscillation Index (SOI) data (for August-September-October months) for the period 1871-1998 have been processed for wavelet analysis. Using the Haar wavelet function, the data are decomposed into seven dyadic scales corresponding to periods of 2, 4, 8, 16, 32, 64 and 128 years. The time frequency localization in the wavelet analysis was used to study the temporal variability of modes in AISMR and SOI. The 2 and 8 year modes in both are found to exhibit low frequency modulation. The 4 year mode in both showed large intermittency. The periods of high/low activities of 2, 4 and 8 year modes were associated with a large/low number of deficient AISMR years. The SOI derived from 2, 4 and 8 year modes in the ENSO years, is found to be related to AISMR variability, at 1 level of significance. The 2, 4 and 8 year modes in AISMR and SOI are found to be correlated at a 5 level of significance. There is a large temporal variability in the correlations of these modes. The occurrences of maxima and minima in these correlations followed a sequence, first in the 8 year mode, then in the 4 year mode and in the end, in the 2 year mode. The reasons for de-association between AISMR activity and SOI in the last 8 years of the present decade have been attributed to (i) the negative contributions by 128, 64, 32 and 16 year modes, (ii) the low activity of 4 and 8 year modes and (iii) the weak correlation between AISMR and SOI in 4 and 8 year modes during this period.

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.

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

[1] The combined effect of humidity and aerosol on cloud droplet spectral width (s) 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 s is 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, s is constant with height. In contrast to premonsoon clouds, s 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 s decreased with total cloud droplet number concentration (CDNC). The spectral widths of premonsoon clouds were independent of total droplet number concentrations, but both s and mean radius decreased with small droplet (diameter < 20 mm) 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.

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 10(3) to 10(4) ng/m(3) at the surface to ~10(2) ng/m(3) at an altitude of about 7 km; 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.

Variability of monsoon intracloud and intercloud microphysics over the Indian subcontinent

Intracloud/intercloud variability of microphysical quantities during different monsoon conditions has been studied for the first time over India using in situ observations of cloud microphysics collected during the Cloud-Aerosol Interaction and Precipitation Enhancement Experiment 2009. The observations for two inland locations (Hyderabad and Bareilly) for different phases of monsoon (preonset, onset, break, and active) have been used to investigate the entrainment and mixing processes which are defined with adiabatic fraction (ADFR)   ~ 0.59) with moderate concentration (  ~ 436 cm−3), an average re of 8 µm, and high value of factor k (0.774 ± 0.035). During break monsoon (Bareilly), clouds were diluted (  ≤ 0.2) having numerous (  > 1000 cm−3) smaller droplets (re ≤ 6 µm) and a low value of factor k (0.678 ± 0.064). The clouds had similar characteristics (  ~ 0.4 having lesser (  ~ 300 cm−3) droplets with re > 8 µm) over both stations during onset/active monsoon conditions. The investigation of the variability of intracloud and intercloud microphysics revealed positive correlation between factor k and N and no detectable correlation between factor k and N, respectively, and are sensitive to ADFR.

Comparative study of aircraft-and satellite-derived aerosol and cloud microphysical parameters during CAIPEEX-2009 over the Indian region

This article presents the spatial and vertical distribution of aerosols and cloud microphysical parameters from the combined data sets of aircraft and satellites. The aircraft-based Cloud Aerosol Interactions and Precipitation Enhancement Experiment (CAIPEEX) was conducted in India during May to September 2009. During the experimental period, 3 days were identified on which space-borne lidar (CALIPSO) and radar (CloudSat) were nearby/over passed the observational regions, which covered north, south central, and southern parts of the Indian subcontinent. The results obtained from these three cases are explored. Similar features of aerosol layering and water/ice cloud signatures are observed by both aircraft and CALIPSO. In addition, events where dust aerosols acting as ice nuclei and polluted aerosols increase the depth of warm rain initiation are observed. The CloudSat profiles of liquid water content, droplet number concentration, and effective radii are underestimated when compared with the corresponding aircraft profiles. The aircraft measurements are able to bring out fine variability in vertical distribution, which would be more useful for regional parameterization schemes and model evaluation.

Unprecedented hailstorms over north peninsular India during February–March 2014

Unprecedented, widespread, and devastating hailstorms occurred during February and March 2014 over north peninsular India (study area). A diagnostic study has been carried out to understand the causes for the same. Over the study area the atmosphere was convectively unstable due to the incursion of warm and moist air from Bay of Bengal and Arabian Sea which was overlaid by cold and dry midlatitude westerlies caused due to the unusual upper oceanic heat content of the Pacific Ocean. At the surface and lower levels, anticyclonic flow over the central India produced easterly winds and cyclonic circulation over Arabian Sea at 850 hPa level produced westerly winds over the peninsular India. Meeting of these winds caused convergence of moist air in the lower levels. The troughs in the upper level westerlies provided the divergence in the upper levels. As a consequence of this convergence/divergence structure, synoptic-scale slow rising motion occurred over the study region. This released the convective instability to cause deep and wide convection with cloud bases at ~1500 m above mean sea level and tops well above the freezing level. Release of latent heat of deposition of water vapor provided extra buoyancy and produced strong updrafts causing explosive growth of the clouds reaching to very high levels and formation of large hails in the clouds. This atmospheric setup was a result of combined effect of planetary and synoptic forcings which persisted for ~3 weeks.

Impact of global warming on the energetics of lower tropospheric ultra-long waves and the Indian summer monsoon

Analyses of 60 years (1949–2008) of monthly energetics of the zonal waves derived from NCEP/NCAR data indicate that ultra-long waves (waves 1 and 2) dominate the spectrum of lower tropospheric zonal waves during monsoon season (June–September). Westerlies over the Indian subcontinent are a source of energy to wave 1. Two oceanic anticyclones, one over Pacific and the other over Atlantic are sources of energy to wave 2. These two waves are inversely correlated. Climatology of the energetics of ultra-long waves for the two epochs 1949–1978 (CLP1) and 1979–2008 (CLP2) of 30 years indicates that the intensity of wave 1 has decreased by about 33% whereas the intensity of wave 2 has increased by about 27%. Northward transport of sensible heat during CLP1 changes to southward during CLP2. Larger generation of zonal mean Available Potential Energy (APE) during CLP2 indicates more heating. A larger conversion of kinetic energy (KE) of wave 1 into APE of wave 1 leads to weakening of wave 1 during CLP2. In case of wave 2, lower rate of conversion of KE to APE leads to stronger wave 2 during CLP2.