Annual Report 2004-2005

Scientific Research

Atmospheric Sciences

The Programme Advisory Committee on Atmospheric Sciences (PAC-AS) was reconstituted and one meeting was organized during the year under report. 3 projects were recommended for support. In addition to this, 5 ongoing projects were also monitored through physical presentation by the concerned PIs. Some of the highlights of the achievements related to this programme are as below:

New Sanctioned Projects

Six new projects were sanctioned during this period viz. (1) Laboratory simulation of Cloud electrification under polluted conditions; ( 2) Development of soft computing model to forecast the occurrence of severe local storm; (3) Cloud and precipitation phenomena estimation by using different systems for propagation characteristics in microwave and millimeter wave frequency bands; (4) Studies on Indoor/ Outdoor Relation of Air Quality in Residential Homes Located in different environment; (5) A New Approach for Precision Measurement of Ionospheric Total Electron Content from dual frequency GPS Data; and (6) Size - Resolved Chemical speciation of Polycyclic Aromatic Hydrocarbons in Urban Atmosphere.

Research Highlights

• Consistency of different methods to monitor eddy diffusion coefficients and energy dissipation rates and their seasonal variabilities by Anwarul Uloom College, New Mallepally, Hyderabad

The turbulent parameters eddy dissipation rate and eddy diffusivity of the lower atmosphere (5 – 20) km have been derived using MST radar wind observations for a low latitude station Gadanki (13.5o N,79.2o E). An exclusive experiment was conducted by operating the radar continuously for 24 hours starting at 9.50 a.m. (local time) on 15th July, 2004 and ending at 9.40 a.m. of the next day with a time resolution of ~2.5 min and a height resolution of 150m. A study of vertical wind variance contour with simultaneous eddy dissipation rates revealed some interesting results. The wind disturbances are observed in the mid-troposphere at around 4-6 p.m. and slowly spread at higher altitudes. A layer of high turbulence is found in the lower stratosphere. It is possible that gravity waves generated in the lower troposphere due to topography and convection reach higher altitudes and once it crosses the critical level, it breaks into turbulence. A positive correlation has been observed between the wind variances in the troposphere and stratosphere suggesting a connection between the two.

• Modeling and Analysis of Boundary Layer Processes in Week Wind Conditions by IIT , Delhi

The proposed project is undertaken to gain an insight into the physics of weak wind atmospheric boundary layer. For this purpose, it was proposed to carry out modeling and analysis of boundary layer processes in weak wind stable conditions. Following are the major achievements:

(i) A good correlation is found between the surface wind measured at 10 m from tower and the geostrophic wind measured at 850 hPa from tethered balloon, in the classification of strong/weak winds.
(ii) It is shown that the linear functional forms of öm and öh are applicable as RiB < Prtã/â2, where Prt is the turbulent Prandtl number, â=4.7, ã=6.35 for linear profiles proposed by Businger et al. (1971) (J. Atmos. Sci 28,181-189)
(iii) z/L is also computed alternatively as a function of RiB, the readily available stability parameter from routine meteorological data. A comparison between the RiB computed from the inverse of the relation between z/L and RiB and RiB computed from observations shows a nonlinear behaviour for linear functional forms of öm and öh but a one-to-one correspondence for nonlinear functional forms proposed by Beljaars and Holtslag (1991) (J Applied Met, 30, 327-341).
(iv) The surface fluxes computed from nonlinear functional forms for öm and öh are found to be small but not negligible under weak wind stable conditions.

• Aerosol vertical profiling at select locations on the East Coast of India using a Micro Pulse LIDAR system by Andhra University, Visakhapatnam

Aerosol vertical profiles were obtained every day using the recently installed Micro Pulse LIDAR system and the data was analyzed for aerosol physical properties in conjunction with the data from the Multiwavelength Radiometer and Quartz crystal micro balance which reveal a distinct layered structure in the aerosol profiles. The data is being further investigated to derive various properties that characterize the coastal urban aerosol system as a consequence of the interaction of the industrial airmass with the marine airmass at this coastal urban location.

• Air quality Modeling of Vehicular Traffic in Delhi by IIT, Delhi

A detailed literature survey regarding the line source models developed earlier has been made. A trend analysis of ambient air quality with respect to various pollutants at different monitoring stations has been made to estimate the present status of air quality in Delhi. The mathematical formulation as analytical solution of advection diffusion equation in different wind conditions has been obtained. Extensive collection of emission factors and onsite air quality data has been acquired from CPCB. Models developed in the present study have been evaluated by comparing their concentration with observed data at different places in Delhi. A sensitivity analysis of models with different variables has also been made.

• Experimental and Theoretical Studies of Secondary Pollutants and Ozone for Chemical Forecasting by IITM, Pune

The main objective of this proposal is to develop a laboratory set-up at IITM, Pune under the DST project for continuous and field observations of surface ozone (O3) and its precursors like oxides of nitrogen (NOx), Carbon mono-oxide (CO) and Hydrocarbons (CH4-NMHCs) and stratospheric ozone and aerosols. Several interesting features related to diurnal, seasonal variations of these species are studied and compared with other Indian station data. It has been shown that despite the decreased emissions of NOx on weekends by about 10%, an increase in ozone concentration is noticed by 9% on weekends compared to weekdays. This phenomenon is termed as “Week-end Effect”.