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Dive into the research topics where H. S. Bedi is active.

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Featured researches published by H. S. Bedi.


Monthly Weather Review | 1988

Reduction of the Spinup Time for Evaporation and Precipitation in a Spectral Model

T. N. Krishnamurti; H. S. Bedi; William Heckley; Kevin Ingles

Abstract A dynamic relaxation technique is examined to update a spectral model. The technique consists of constraining selected time dependent model variables towards their predetermined space–time estimates, while the remaining variables evolve unconstrained. The scheme involves gradual assimilation of data and thus is essentially free from data insertion shocks generally associated with data assimilation schemes. The scheme can also be used to update the model variables consistent with the observed estimates of diabatic forcings. The spectral formulation is particularly suited to relax the current estimates of model variables towards their observed estimates scale-by-scale. The scheme has been applied to initialize model variables by relaxing vorticity, divergence and total mass (surface pressure) fields through one to three observation periods using an 11-layer model with T-42 spectral resolution. In addition, the moisture field and diabatic heating rates have been relaxed consistent with the observed ...


Meteorology and Atmospheric Physics | 1998

Organization of convection and monsoon forecasts

T. N. Krishnamurti; H. S. Bedi; Wei Han

SummaryIn this paper we address the issue of monsoon forecasts in relation to the organization of convection. Given a physical initialization procedure, within a data assimilation, it is possible to use the detailed distribution of rainfall from mesoconvective precipitating elements to define the initial state of a global model. If that is carried out using a very high resolution model then the initial state can carry within it an organization of convection within the resolvable scales. Then the impact of physical initialization on the maintenance and prediction of tropical weather such as the monsoon can be determined. Lacking such an initialization, one can expect the convectively driven energetics to be biased, and a slow degradation of the forecasts can follow. Several examples of forecasts at different resolutions are discussed here. The main findings of this study are that improved forecast results are obtained when physical initialization is invoked where the observed rain and the model resolution are comparable, i.e. the footprint of the highest resolutions rainfall estimates obtained from satellite based data sets (principally we use the SSM/I instrument over the oceans). At this resolution, we note that the model is able to carry an organization of convection in the initialization and in the forecasts through the medium-range time scale.We have compared our results of monsoon studies at a resolution T255 with those at resolution T62. The transform grid separation at the resolution T255 is approximately 50 km and at the resolution T62, it is approximately 200 km. We find that the model at the higher resolution (T255) performs better and has more realistic energy conversions for the convectively driven synoptic scale monsoon.An organization of convection, at the synoptic scales, is not seen in the forecasts at lower resolutions, T62, where the rainfall patterns are generally much broader and tend to be more zonal. Such organization appears more realistic at the resolution T255. Variances of the energy conversion, calculated in the two-dimensional spectral space, from physically initialized short range forecasts at the higher resolution are seen to be largest on the scales of the monsoon. Similar calculations for the reanalyzed fields at lower resolutions show the spectral distribution of variances to be biased towards local Hadley scale overturnings.


Meteorology and Atmospheric Physics | 1992

Recurvature dynamics of a typhoon

T. N. Krishnamurti; H. S. Bedi; K. S. Yap; D. Oosterhof; G. Rohaly

SummaryIn this paper we present some recent work on typhoon prediction with a high resolution global model. The emphasis of this paper is on typhoon recurvature. Here we include examples of successful typhoon recurvature track forecasts made from a very high resolution global spectral model. The main objective of this study however is to go beyond the forecasts, i.e. to interrogate the history tapes and to diagnose residue-free budgets of the divergence and vorticity. The premise of this paper is that the recurvature of the typhoons depends on both the usual advection of vorticity by the layer mean winds and the advection of divergence in the outflow layers of the storm.The region immediately outside the heavy rain area of the storm experiences large values of divergent outflows which contribute a significant advection of divergence. Through the Dines compensation this region must, in consort, experience an enhancement of low level convergence and of deep convection, thus contributing to the storm motion. We distinguish two facets of storm motion and recurvature, one based on the conventional steering that invokes the advection of vorticity by a vertical integrated flow, the other is the generation mechanism proposed here. During recurvature the storm appears to move in a direction which is influenced by the rotational and the divergent flow dynamics. Increased vertical resolution in the outflow layer is shown to resolve stronger amplitudes in the outflow layer divergence and thus to contribute to improved forecasts of recurvature. A number of processes seem to simultaneously evolve, these include the strong advection of divergence part of the wind, enhancement of cumulus convection over this region, an enhancement of lower tropospheric convergence, generation of vorticity of the lower troposphere and the attendant recurvature.


Monthly Weather Review | 1996

Partitioning of the Seasonal Simulation of a Monsoon Climate

T. N. Krishnamurti; H. S. Bedi; G. D. Rohaly; D. Oosterhof

Abstract The emphasis of this paper is on residue-free budgets of seasonal climate forecasts. It is possible to ask the following question: given a seasonal mean geopotential height simulation from a climate model, what is a breakdown of that contribution from different areas of the model physics and dynamics? In that context, the authors have examined the maintenance of a monsoonal 500-mb ridge, the eastward shift of the Tibetan anticyclone during an El Nin˜o year, and the Pacific-North American pattern. The salient results of this study include a substantial contribution from the advective nonlinear dynamics toward the maintenance (positive or negative) of the seasonal climate.


Advances in Atmospheric Sciences | 1993

Hurricane Forecasts in the FSU Models

T. N. Krishnamurti; H. S. Bedi; K. S. Yap; D. Oosterhof

A brief account of our studies on the hurricane forecast problem is presented here. This covers recent prediction results from the Florida State University (FSU) regional and global numerical weather prediction models. The re-gions covered are the Indian and the Pacific Oceans. The life cycle of the onset vortex (a hurricane) of the summer monsoon, typhoons over the western Pacific Ocean and tropical cyclones over the Bay of Bengal (Andhra Pradesh and the Bangladesh storms) are covered here. The essential elements in the storm formaton are the strong horizontal shear in the cyclogenetic areas, a lack of vertical shear and warn sea surface temperatures. The storm motion has a steering component largely described by the advection of vorticity by a vertically averaged layer mean wind, the recurvature of a storm appears to invoke physical processes via the advection of divergence by the divergent part of the wind especially in the outflow layers of the storm. Very high resolution global models seem to be able to handle the motion and structure during the entire life of typhoons quite reasonably. The scope for better diagnosis of the storms life cycle appears very promising in view of the realistic simulation of the life cycle.


Global and Planetary Change | 1995

Seasonal monsoon forecast for the years 1987 and 1988

T. N. Krishnamurti; H. S. Bedi; G. Rohaly; M. Fulakeza; D. Oosterhof; Kevin Ingles

Abstract The results of several seasonal integrations with an atmospheric global circulation model with prescribed “perfect” sea surface temperatures are presented. These experiments illustrate the results of seasonal simulations for the years 1987 and 1988. These were a dry and a wet monsson year, respectively, when compared to the average. The integrations cover the period from June 1 through August 31 for both years and were carried out at two horizontal resolutions, T42 and T106, of a global model containing two different parameterizations of surface hydrology. The seasonal differences of the motion fields, divergent circulations and rainfall distributions for these respective experiments are compared with the corresponding observed fields. The sensitivity of seasonal simulations to the initial state is explored with integrations starting on two successive dates. In these experiments we diagnose differences of the simulated time mean states from residue free budgets of the complete vorticity equation.


Monthly Weather Review | 1994

The formation of Hurricane Frederic of 1979

T. N. Krishnamurti; H. S. Bedi; D. Oosterhof; Vivek Hardiker

Abstract A high-resolution global model forecast of the formation of Hurricane Frederic of 1979 is analyzed by means of several diagnostic computations on the models output history. The formation is addressed from an analysis of limited-area energetics where the growth of eddy kinetic energy is examined. The question on internal versus external forcing during the formative stage of the hurricane is explored by means of the Kuo-Eliassen framework for the radial-vertical circulation of the hurricane. The intensity of the predicted hurricane is diagnosed from a detailed angular momentum budget following the three-dimensional motion of parcels arriving at the maximum wind belt. Overall, the successful simulation of the hurricane has enabled us to make such a detailed diagnosis of the predicted hurricane at a high resolution. The principal findings of this study are that a north-south-oriented beating function maintained a zonal easterly flow that supplied energy barotropically during the growth of an African...


Archive | 1994

Improved Precipitation Forecast Skill from the Use of Physical Initialization

T. N. Krishnamurti; G. Rohaly; H. S. Bedi

This study explores the impact of physical initialization on the numerical weather prediction of tropical rainfall An important finding of this study is related to the point correlations of the model-based rainfall at the initial time and at the end of a one day forecast which are significantly improved with the use of physical initialization within the tropics. Physical initialization refers to the use of a number of ‘reverse’ algorithms during an assimilation phase of the model forecast. The goal is to improve the definition of the initial state by the assimilation of proposed or currently available surface and satellite-based observations during a pre-integration phase of a forecast using a global spectral model.


Tellus A | 1993

Physical initialization using SSM/I rain rates

T. N. Krishnamurti; H. S. Bedi; Kevin Ingles


Tellus A | 1994

On the improvement of precipitation forecast skill from physical initialization

T. N. Krishnamurti; G. Rohaly; H. S. Bedi

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D. Oosterhof

Florida State University

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G. Rohaly

Florida State University

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Kevin Ingles

Florida State University

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K. S. Yap

Florida State University

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Jishan Xue

Florida State University

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M. Fulakeza

Florida State University

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Wei Han

Florida State University

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