• H C Upadhyaya

      Articles written in Journal of Earth System Science

    • Adiabatic nonlinear normal mode initialization for a grid point global model

      H C Upadhyaya A Mokssit

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      The baroclinic primitive equation model used for short and medium range forecasting admits high frequency as well as desirable Rossby modes. These high frequency oscillations are excited by initial imbalances between the observed mass and wind fields. In this paper we determine and describe the normal modes of the linearized version of the general circulation model of Laboratoire de Meteorologie Dynamique, Paris. These normal modes are then used to initialize the model through Machenhauer’s nonlinear correction scheme. The adiabatic nonlinear normal mode initialization technique is shown to be superior to dynamic initialization in terms of elimination of high-frequency oscillations in the forecast. Normal modes of a particular model depend on the finite difference scheme chosen to approximate the governing system of model equations. The results presented correspond to enstrophy-conserving finite difference scheme.

    • On the problem of boundary conditions in isentropic coordinates

      H C Upadhyaya R Sadourny

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      The main advantages of constant potential enthalpy as a vertical coordinate are weaker horizontal velocity gradients in frontal regions and a higher vertical resolution. A disadvantage is the intersection of isentropes with the ground and folding of these surfaces. A numerical model is proposed to overcome the difficulties imposed by the intersection of isentropes with the ground. The model contains a physical and computational domain. The top and bottom surfaces of the computational domain are isentropes whereas the physical domain of the flow confined above by a free surface of constant pressure, and the bottom of this domain is the surface of the earth. In the present study the top surfaces of these two domains coincide (θT, PTare constants in space and time). The model was tested for the study of frontogenesis and cyclogenesis and integrated for 7 days. The results correspond to enstrophy-conserving finite difference scheme.

    • Response of an ocean general circulation model to wind and thermodynamic forcings

      A Chakraborty H C Upadhyaya O P Sharma

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      The stretched-coordinate ocean general circulation model has been designed to study the observed variability due to wind and thermodynamic forcings. The model domain extends from 60‡N to 60‡S and cyclically continuous in the longitudinal direction. The horizontal resolution is 5‡ x 5‡ and 9 discrete vertical levels. First a spin-up experiment has been done with ECMWF-AMIP 1979 January mean fields. The wind stress, ambient atmospheric temperature, evaporation and precipitation have been used in order to derive mechanical and thermodynamical surface forcings. Next, the experiment has been extended for another 30 years (3 cycles each of 10 year period) with varying surface boundary conditions (from January 1979 to December 1988 of ECMWF-AMIP monthly fields for each cycle) along with 120 years extended spin-up control run's results as initial conditions. The results presented here are for the last 10 years simulations. The preliminary results of this experiment show that the model is capable of simulating some of the general features and the pattern of interannual variability of the ocean.

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