The program aims for understanding the water vapour, clouds, precipitation, energy balance and associated thermo-dynamical and feedback processes by using the remote sensing techniques. The remote sensing techniques make use of a sensors that can take the measurement of the objects or areas from a distance without coming into physical contact with the observed objects. Example of remote sensors are radar, lidar, satellite etc.
Radar is an acronym for RAdio Detection And Ranging. IITM has two mobile polarimetric radars operating at X-band (~9.53 GHz) and Ka-band (~35.23 GHz). Both are scanning radars. The polarization capability of radar gives better estimation of rainfall as compared to conventional radar systems. In addition, the shape and size of the hydrometeors can also be estimated.
The Western Ghats (WGs) located parallel to the west coast of India receives a huge amount of rainfall during the Indian summer monsoon (ISM) in which topography plays a huge role in it. To understand the dynamics and microphysics of monsoon precipitating clouds over the WGs, a High Altitude Cloud Physics Laboratory (HACPL) has been setup at Mahabaleshwar (17.92 oN, 73.6 oE, ~1.4 km AMSL) in 2012. The HACPL is a natural laboratory to understand the fundamental properties of clouds, as during the monsoon, the clouds can be at the surface level and can be examined with ground based monitoring system. To supplement HACPL in-situ measurements, the IITM’s, ground based, X- and Ka-band radars are deployed at Mandhardev (18.04 oN, 73.87 oE, ~1.3 km AMSL), hills of the Western Ghats. Both radar operates in volume of plane position indicator (PPI) and range height indicator (RHI) mode and are vital instruments to understand the 3-D cloud structures along with the dynamics and microphysics of monsoon precipitating clouds over the WGs. We also have interest to validate the numerical models by comparing with radar derived products.
The space based remote sensing payloads on satellites can an unique platform for monitoring the Earth’s atmosphere. This group focuses to use satellite data (e.g., A-Train, COSMIC, GPM, INSAT-3D, ISCCP, KALPANA, MODIS, SMMR-SSM/I, VHRR, TRMM, etc) to understand the spatial characteristics of the water vapour, clouds, precipitation, thermodynamics, tropical tropopause and associated dynamics. The dataset provide climatologies of the three-dimensional distribution of clouds and precipitation, their characteristics, their variabilities at various time and spatial scales and impact on atmospheric energetics. Also, utilisation of multi-satellite data for teleconnection studies of polar, mid and tropical varibailities in understanding the large-scale dynamical effects of clouds- and aerosol-precipitation interactions over the Asian domain, in particular, over India.
Cloud characteristics over the peninsular India during monsoon withdrawal and post withdrawal periods
Cloud characteristics over the rain-shadow region of the north central peninsular India has been studied using C-band radar data for the period 21 September–30 October 2011. The period covers withdrawal and post-withdrawal periods of monsoon 2011. Though the study has been carried out for one season, it has been shown that it is representative of climatic feature over the region. The cloud characteristics have been discussed in the context of large scale dynamical and thermodynamical conditions over the region using NCEP wind data and radiosonde data, respectively. The large scale dynamic and thermodynamical conditions were found favorable for occurrence of widespread and deep convection. The cloud top heights show tri-modal distribution with peaks at 2–3, 4–6 and 8–12 km which are associated with cumulus, congestus and cumulonimbus clouds, respectively. The tops of these three types of the clouds are found to be associated with the stable layers in the atmosphere. The frequency of congestus clouds was the highest. The cloud characteristics over the region differ from other tropical land and oceanic regions in respect of maximum height, mean duration and cumulative frequency distribution. Distribution of cloud top height and duration show deviation from lognormality in the lower ends. It indicates that the cloud growth mechanism is different than that observed over other tropical land and oceanic regions and also due to the large wind shear prevailed over the region. During the period, a large number of suitable clouds were found available for hygroscopic and glaciogenic cloud seeding.[Morwal S.B., Narkhedkar S.G., Padmakumari B., Maheskumar R.S., Kothawale D.R., Dani K.K., Burger R., Bruintjes R.T., Kulkarni J.R., Cloud characteristics over the rain-shadow region of North Central peninsular India during monsoon withdrawal and post-withdrawal periods, Climate Dynamics, 46, January 2016, DOI:10.1007/s00382-015-2595-0, 495-514]
Satellite observed large-scale cloud features over the Indo-Pacific: A manifestation of linkage between SAM and ISMR
Relationship between the Southern Annular Mode (SAM) and the India summer monsoon rainfall (ISMR) has been examined based on the data period 1949–2013. While the entire data period indicates a significant increasing trend in SAM, recent decades 1983–2013 indicate no trend. The relationship between the two strengthened considerably since 1983. Results reveal that the February–March SAM is significantly related with the subsequent ISMR. A positive (negative) SAM during February–March is favorable (unfavorable) for the ensuing summer monsoon rainfall over the Indian sub-continent. The delayed response is relayed through the central Pacific Ocean. We propose a hypothesis that states: when a negative (positive) phase of February–March SAM occurs, it gives rise to an anomalous meridional circulation in a longitudinally locked air–sea coupled system over the central Pacific that persists up to the subsequent boreal summer and propagates from the sub-polar latitudes to the equatorial latitudes inducing a warming (cooling) effect over the central equatorial Pacific region. In turn, this effect concomitantly weakens (strengthens) the monsoon rainfall over the Indian sub-continent. Thus, the February–March SAM could possibly serve as a new precursor to foreshadow the subsequent behavior of the Indian summer monsoon. [Prabhu Amita, Kripalani R.H., Preethi B., Pandithurai G., Potential role of the February–March Southern Annular Mode on the Indian summer monsoon rainfall: a new perspective, Climate Dynamics, 47, August 2016, DOI:10.1007/s00382-015-2894-5, 1161-1179]
Radar derived Meoscale Kinematics in terms of divergence profiles
Single Doppler analysis techniques known as velocity azimuth display (VAD) and volume velocity processing (VVP) are used to analyze kinematics of mesoscale flow such as horizontal wind and divergence using X-band Doppler weather radar observations, for selected cases of convective, stratiform, and shallow cloud systems near tropical Indian sites Pune (18.58°N, 73.92°E, above sea level (asl) 560 m) and Mandhardev (18.51°N, 73.85°E, asl 1297 m). The vertical profiles of horizontal wind estimated from radar VVP/VAD methods agree well with GPS radiosonde profiles, with the low-level jet at about 1.5 km during monsoon season well depicted in both. The vertical structure and temporal variability of divergence and reflectivity profiles are indicative of the dynamical and microphysical characteristics of shallow convective, deep convective, and stratiform cloud systems. In shallow convective systems, vertical development of reflectivity profiles is limited below 5 km. In deep convective systems, reflectivity values as large as 55 dBZ were observed above freezing level. The stratiform system shows the presence of a reflectivity bright band (~35 dBZ) near the melting level. The diagnosed vertical profiles of divergence in convective and stratiform systems are distinct. In shallow convective conditions, convergence was seen below 4 km with divergence above. Low-level convergence and upper level divergence are observed in deep convective profiles, while stratiform precipitation has midlevel convergence present between lower level and upper level divergence. The divergence profiles in stratiform precipitation exhibit intense shallow layers of “melting convergence” at 0°C level, near 4.5 km altitude, with a steep gradient on the both sides of the peak. The level of nondivergence in stratiform situations is lower than that in convective situations. These observed vertical structures of divergence are largely indicative of latent heating profiles in the atmosphere, an important ingredient of monsoon dynamics. [Deshpande S.M., Dhangar N., Das Subroto Kumar, Kalapureddy M.C.R., Chakravarty K., Sonbawne S., Konwar M., Mesoscale kinematics derived from X-band Doppler radar observations of convective versus stratiform precipitation and comparison with GPS radiosonde profiles, Journal of Geophysical Research, 120, November 2015, 11536–11551]
Project: Physics and Dynamics of Tropical Clouds
Project Director: Dr. G. Pandithurai, Scientist-F,
Sub-project: Radar & Satellite Meteorology