• R Venkatesan

      Articles written in Journal of Earth System Science

    • Soil thermal properties at Kalpakkam in coastal South India

      K Anandakumar R Venkatesan Thara V Prabha

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      Time series of soil surface and subsurface temperatures, soil heat flux, net radiation, air temperature and wind speed were measured at two locations in Kalpakkam, coastal southeast India. The data were analysed to estimate soil thermal diffusivity, thermal conductivity, volumetric heat capacity and soil heat flux. This paper describes the results and discusses their implications.

    • Thermal internal boundary layer characteristics at a tropical coastal site as observed by a mini-SODAR under varying synoptic conditions

      Thara V Prabha R Venkatesan Erich Mursch-Radlgruber G Rengarajan N Jayanthi

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      Atmospheric boundary layer observations are conducted at a coastal site during a transition phase from winter to summer season over the Indian peninsula. Thermal Internal Boundary Layer (TIBL) characteristics in presence of an off-shore and a weakly influenced on-shore synoptic wind are examined with the help of measurements carried out with a mini-SODAR (SOund Detection And Ranging), tethered balloon, and tower-based micrometeorological measurements. Influence of the changing synoptic scale conditions on turbulent characteristics of TIBL is discussed.

      Mini-SODAR data showed the development and decay of sea and land breeze. It is seen that the characteristics of TIBL over the coastal land after sea breeze onset are similar to that of a shallow convective boundary layer (CBL) commonly found over plain land. Inside the TIBL, a maximum wind speed was noted close to the surface due to the penetration of sea breeze. In the off-shore case, a distinct sea breeze circulation was observed unlike in the case of on-shore flow. In the presence of weak on-shore case, a ‘minor sea’ breeze is noted before the establishment of sea breeze and a reduction in the momentum fluxes gives rise to decrease in the turbulence intensity. Updraft in the sea breeze front was stronger during weak synoptic conditions. Influence of synoptic changes on the sea breeze-land breeze circulation such as onset, strength and duration of the sea-land breeze are also examined.

    • Operational mesoscale atmospheric dispersion prediction using a parallel computing cluster

      C V Srinivas R Venkatesan N V Muralidharan Someshwar Das Hari Dass P Eswara Kumar

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      An operational atmospheric dispersion prediction system is implemented on a cluster supercomputer for Online Emergency Response at the Kalpakkam nuclear site. This numerical system constitutes a parallel version of a nested grid meso-scale meteorological model MM5 coupled to a random walk particle dispersion model FLEXPART. The system provides 48-hour forecast of the local weather and radioactive plume dispersion due to hypothetical airborne releases in a range of 100 km around the site. The parallel code was implemented on different cluster configurations like distributed and shared memory systems. A 16-node dual Xeon distributed memory gigabit ethernet cluster has been found sufficient for operational applications. The runtime of a triple nested domain MM5 is about 4 h for a 24 h forecast. The system had been operated continuously for a few months and results were ported on the IMSc home page.

      Initial and periodic boundary condition data for MM5 are provided by NCMRWF, New Delhi. An alternative source is found to be NCEP, USA. These two sources provide the input data to the operational models at different spatial and temporal resolutions using different assimilation methods. A comparative study on the results of forecast is presented using these two data sources for present operational use. Improvement is noticed in rainfall forecasts that used NCEP data, probably because of its high spatial and temporal resolution

    • A numerical study of sea breeze circulation observed at a tropical site Kalpakkam on the east coast of India, under different synoptic flow situations

      C V Srinivas R Venkatesan K M Somayaji A Bagavath Singh

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      A simulation study of the sea breeze circulation and thermal internal boundary layer (TIBL) characteristics has been carried out at the tropical site Kalpakkam on the east coast of India, for operational atmospheric dispersion prediction. The community based PSU/NCAR MM5 Meso-scale meteorological model is used for the study. Three cases on typical days in summer (24 May 2003), southwest (SW) monsoon (1 July 2001) winter season (2 February 2003) with different large-scale flow pattern are studied. The MM5 model is used with 3 nested domains with horizontal grid resolutions 18 km, 6 km and 2 km and 26 vertical levels. The model is integrated for 24 hours in the above cases with initial and boundary conditions taken from NCEP-FNL analyses data. Observations of 10 meteorological stations and coastal boundary layer experiments conducted at Kalpakkam are used for comparison and validation of the simulation. The characteristics of simulated sea breeze and TIBL at Kalpakkam are seen to vary in the above cases according to the prevailing large-scale winds and surface fluxes. The sea breeze circulation is seen to develop early with larger strength and inland propagation in the summer case under the influence of moderate synoptic wind and strong heating conditions than in the SW monsoon and winter cases. The horizontal and vertical extents of TIBL are found to be larger in the summer case than in other cases. Although model parameters agree in general with observations, all the fine features are not clearly captured and some slowness in model sea breeze development is also seen. The results indicate the need to improve i) the initial conditions by assimilation of available surface/upper air observations to reduce model bias and ii) surface net radiation parameterisation. The model could predict the essential features of the local circulation and further improvement is expected with better initial condition data and incorporation of more realistic surface data.

    • On the marine atmospheric boundary layer characteristics over Bay of Bengal and Arabian Sea during the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB)

      Denny P Alappattu D Bala Subrahamanyam P K Kunhikrishnan K M Somayaji G S Bhat R Venkatesan C B S Dutt A Bagavath Singh V K Soni A S Tripathi

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      Detailed measurements were carried out in the Marine Atmospheric Boundary Layer (MABL) during the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) which covered both Arabian Sea and Bay of Bengal during March to May 2006. In this paper, we present the meteorological observations made during this campaign. The latitudinal variation of the surface layer turbulent fluxes is also described in detail.

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