Physics and Dynamics of Tropical Clouds
(Chief Project Scientist: Dr. (Smt.) Thara Prabhakaran)
The research programs of IITM undertaken during its 11th Five Year Plan (2007-2012) consisted of development of systems and techniques for long range prediction of seasonal mean monsoon and extended range prediction of active/break spells. These involved assessing the component models, viz., models of atmosphere and ocean, coupling strategy, assessment of bias of the coupled model, data assimilation, development of forecast strategy, study of interaction between clouds and environment, etc. Basic research is crucial for improving any prediction capability. Keeping this in mind, stress has been given on strengthening of the Basic Research required for improving models for weather and climate forecast through observationalprograms under the project ‘Physics and Dynamics of Tropical Clouds’ of the 12th Five Year Plan.
Understanding convection is the goals of the monsoon meteorology. The monsoon rainfall is ultimately linked to the large scale convection. The deep convection over the Indian region is organized in to mesoscale convective systems, frequency of occurrence and morphology of which are in turn modulated by the synoptic scale systems. The large scale wind shear dictates the organization of the cloud system. The large scale circulation produces the cloud systems and microphysics works for the rainfall production from the clouds. Therefore, understanding the rainfall process involves understanding of the large scale environment and cloud processes and their interactions. This would help in developing the convective and microphysical parameterization schemes for the numerical models used for monsoon forecasting.
(Chief Deputy Project Scientist: Dr. Thara Prabhakaran)
Role of aerosol and cloud microphysics in the weather and climate systems has been gaining importance due to their impacts on the rainfall processes. It is known that the rainfall is the most important parameter to judge the impact of climate change due to anthropogenic emissions. Data of aerosol have been collected continuously using ground based and remote sensing instruments. For studying the cloud aerosol interaction, there is a need for simultaneous and in situ measurements of aerosol and cloud microphysics. This can be done only by airborne platforms. The scope and the extent of the subject will increase in future as these observations provide ways to improve representation of cloud processes in the models and understanding of weather modification. Many experiments using airborne platforms are being conducted in the world. In India, CAIPEEX is one such national experiment with two main objectives, viz., (1) to make progress in the aerosol and cloud microphysics observations suitable for the validation and development of physical parameterization schemes, and (2) to propose guidelines for cloud seeding.
A wealth of atmospheric, aerosol and cloud microphysics data will be generated through special cloud and aerosol observations over different parts of the country which will be useful to validate the convection and cloud microphysical schemes, and for improving the model physics. Also, it will beuseful in the fundamental research for years to come. In addition to the direct radiative effects of aerosol on climate, aerosol also influence, indirectly, through modifying cloud microphysics and dynamics in various cloud types. The ‘indirect effect’ of aerosol on climate has so far been poorly understood over Indian region from direct observations inside clouds and was not quantified due to lack of appropriate data. The program on large scale will provide valuable data for advancing our understanding and quantification of ‘indirect effect’ of aerosol on climate.
The program will address the impact of aerosols on the hydrological cycle by coordinated integrated observations of aerosol, cloud micro scale and macro scale characteristics, thermodynamic state of the atmosphere and numerical simulations. air pollution assessment and associated impacts over India (health, visibility, climate), hydrological and water resources studies, and enhancement of research infrastructure (human resources and technology). Monitoring of black carbon (BC), along with chemistry and composition, with the help of state of the art airborne and ground based instrumentation will be useful for the study of the role of BC aerosol through semi direct effect of modification of radiation balance for continental clouds over Indian region. The programme has the following objectives:
(Chief Deputy Project Scientist: Dr. G. Pandithurai)
The most important source of systematic errors in all weather and climate prediction model is related with inaccuracy in formulation (or parameterization) of clouds. The parameterization of convection in weather and climate models depends on our understanding of how small scale clouds interact with the large scale environments and how aerosol interact with the clouds. Therefore, during 11th Plan period, IITM has made studies of clouds and aerosol interaction as a major focused research area. For this purpose a special campaign mode national experiment called CAIPEEX has been launched to study the cloud-aerosol interactions. In this experiment hired instrumented air crafts were used. Since this is an expensive proposition and such measurements cannot be continued for long time. However, in order to get data on cloud microphysics under different large range of meteorological conditions and distributions, it is important to continue these measurements for a reasonably long time. On the other hand, if we could set up a cloud physics and aerosol measurements observatory at a high altitude station where cloud bases touch the ground, one could make cloud-microphysics measurements together with aerosol and meteorological measurements for many years and could thereby collect data spanning different conditions. Therefore, it is proposed to accelerate the experimental infrastructure by introducing uninterrupted observations and monitoring of critical atmospheric parameters and cloud parameters regularly at a high altitude station in Maharashtra viz., Mahabaleshwar along with supporting infrastructure at the IITM campus in Pune. It is proposed to establish state of art instrumentation facilities and necessary physical infrastructure at both the places.
The High Altitude Cloud Physics Laboratory (HACPL) originated from such a unique requirement, where clouds could be continuously monitored at a single location, where cloud base touches the ground. Observations on regular basis at the HACPL will provide continuous data for the study of cloud microphysics and interaction between clouds and aerosol and the process of precipitation and related dynamics. The impact of orography of Western Ghat on the precipitation dynamics will be addressed with continuous observations with radar at this site. The continuous and simultaneous observations at Mahabaleshwar will provide unique opportunity to study detailed interaction of the dynamics and microphysics over the region and explore the differences in their spatial characteristics. The observations will also be used along with other cloud physics observations in the physical parameterization development, testing etc and to establish cloud and precipitation climatology of the region. The programme has the following objectives:
(Chief Deputy Project Scientist: Dr. S.D. Pawar)
Development of observational facilities for thunderstorm monitoring and conducting mission- oriented experiments in different parts of India are required to understand the dynamical, thermo-dynamical structure and rain formation processes in thunderstorms.
In addition to surface observations, such efforts require measurements of microphysical and electrical variables on platforms like aircraft and balloon and simultaneous observations from Dual – Polarized Doppler Radar and Lightning Location Network. Observations of lightning using Lightning Location Network and satellite data will certainly help in the understanding of not only the geographical distribution of thunderstorms, but also their role and cause in different environments. Laboratory experiments simulating cloud conditions in some facilities such as wind tunnels, cold chambers, vertical free–fall tubes etc. need be conducted to study some phenomena in controlled conditions. The programme is being implemented with the following objectives: