• D K Paul

      Articles written in Journal of Earth System Science

    • Sub-seasonal scale fluctuations of theITCZ over the Indo-Pacific region during the summer monsoon season. Part I: Features over the Indian region

      D R Sikka D K Paul V R Deshpande V R Mujumdar P V Puranik

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      Monex-79 andISMEX-73 data have been analysed to study the sub-seasonal scale fluctuation of near equatorial oceanic intertropical convergence zone (ITCZ) over the North Indian ocean during the summer monsoon of 1979 and 1973. The oceanicITCZ is characterised by a narrow shear zone between the equatorial westerlies and the tropical easterlies, associated with organised convective clouds. Synoptic analysis presented in this paper shows the steady northward propagation of the oceanicITCZ from its near equatorial position (5–10°N) to the continental position (20–25°N) during the onset and mid-season revivals of monsoon after breaks. The northward propagation is initiated by the strengthening of the equatorial westerlies which result in the intensification of the shear zone and the embedded disturbances. The establishment of the northward propagating mode near normal monsoon trough position over the continent characterises the active phase of monsoon. As the monsoon cycles from active to weak/break phase, the monsoon trough (continentalITCZ) dissipates near the foothills of the Himalayas and the oceanicITCZ gets emphasised once again near the equatorial region. The major phase changes in theITCZ occur at an interval of about 30–50 days which dominantly control the intra-seasonal fluctuation of the Indian summer monsoon. The paper also discusses the characteristic features of the oceanicITCZ during different phases of the monsoon.

    • Wind profiles in the boundary layer over Kharagpur associated with synoptic scale systems

      D K Paul S P Ghanekar B S Murthy K G Vernekar

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      Doppler sodar wind data for the boundary layer over Kharagpur obtained during MONTBLEX-1990 at a height interval of 30 m from surface up to 1500 m have been analysed for the periods when intense synoptic scale disturbances from north Bay of Bengal moved along the eastern end of the monsoon trough. The variation in the vertical wind profile in the lower boundary layer over Kharagpur during the passage of synoptic scale disturbances has been discussed in the paper. The analysis indicates that the mean winds over Kharagpur veered with height in the lower boundary layer near the surface suggesting divergence over Kharagpur when the system lay south/southwest of the station. No such veering has been noticed when the centre of the system lay very close to the station.

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