• No results found

Performance and systematic errors in the short range prediction of Asian summer monsoon

N/A
N/A
Protected

Academic year: 2023

Share "Performance and systematic errors in the short range prediction of Asian summer monsoon"

Copied!
9
0
0

Loading.... (view fulltext now)

Full text

(1)

PERFORMANCE AND SYSTEMATIC ERRORS IN THE SHORT RANGE PREDICTION OF

ASIAN SUMMER MONSOON

silts "law

By

ALEXANDER JOHN

Center for Atmospheric Sciences

A THESIS SUBMITTED

IN FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

art O►

to the

INDIAN INSTITUTE OF TECHNOLOGY, DELHI

INDIA JULY, 1990

(2)

CERTIFICATE

This is to certify that the thesis entitled -PERFORMANCE AND SYSTEMATIC ERRORS IN THE SHORT RANGE PREDICTION OF ASIAN SUMMER MONSOON , being submitted by Alexander John for the award of the degree of DOCTOR OF PHILOSOPHY , is a record of the original bonafide research work carried out by him. He has worked under my guidance and supervision and has fulfilled the requirements for the submission of this thesis. The results presented in this thesis work have not been submitted in part or full to any other University or Institute for award of any degree/diploma.

zhz.,./VeL (U.C. MOHANT )

Principal Scientific Officer Centre for Atmospheric Sciences Indian Institute of Technology New Delhi.

(3)

, .

A

. EILI4 "

- A;

Ne'

(4)

ACKNOWLEDGMENTS

I express my deepest sense of gratitude to Dr. U.(

Mohanty for his most painstaking guidance, ceasele!

encouragement and invaluable help throughout this researc work.

I am extremely grateful to Dr. R.V. Madala, NRE Washington D.C. and Prof. S. Sethuraman, NCSU, USA fc constructive help and enlightening discussions during tA course of this work.

I am extremely thankful to Sqn. Ldr. Ajit Tyagi and Dr K.J. Ramesh for their suggestions and selfless help durir the course of this work.

All my friends have been a source of unceasing suppor for the completion of this work.

The students, faculty members and staff of Centre fo Atmospheric Sciences have actively helped me during th course of this work. I wish to express my cordial thanks t all of them in particular to Dr. Parashuram, Dr. V.B. Sari and Mr. K.V.J. Potty.

I acknowledge the CSIR for providing the researc fellowship in the initial stages of this work and Centre fo Atmospheric Sciences, IIT Delhi for providing the senio research assistantship to complete this research work.

Necessary data required for this work is very kindl provided by the European Centre for Medium Range Weathe Forecasts (ECMWF), Reading, UK. I am also grateful to th National Centre for Medium Range Weather Forecasting(NCMRWF New Delhi for providing the computer facilities.

(5)

ABSTRACT

It is well recognized that the accuracy of the numerica forecast in the tropics is at present substantially less tha that of mid-latitudes and useful tropical forecast can b produced only up to a period of 72 hours. A further limitation i forecast skill is exhibited when we consider the prediction of complex flow regime like the Asian summer monsoon. Thus a shor range numerical simulation/prediction of summer monsoon featurE is a challenging task in numerical weather prediction (NWP;

Considering the above limitation and computing constraints ar importance of regional features associated with summer monsoon, high resolution limited area model (LAM) is found to be essential tool to examine the performance and inherent systemat' errors in the short range numerical simulation/prediction (

Asian summer monsoon system.

The model used in this study is a three dimension.

hydrostatic, primitive equations of resolution 200 km., in sig coordinates with ten levels in the vertical. The mod incorporates physical processes such as planetary boundary laye dry and moist convective adjustment, deep cumulus convection a large scale precipitation. Performance of the LAM is found to sensitive to horizontal and vertical resolution. At the outset number of experiments are carried out to arrive at an optiu resolution appropriate to the physical processes incorporated the model. The complex monsoon circulation and the typic precipitation distribution over the Indian sub-continent largely attributed to mountains over the region. An attempt

(6)

made to provide a realistic representation of orographic feature!

in the model.

An important aspect of short range prediction with primitive equation model is to incorporate an appropriate anc efficient initialization scheme. A non-linear normal mod(

initialization based on vertical mode initialization approach adapted for the LAM. A number of experiments are carried out tc find the convergence of the scheme and its effectiveness tc suppress high frequency modes during the time integration of the model.

As the main rain bearing system of the monsoon season is depression, the prediction of its intensification, movement and associated rainfall is of great importance for the Indian region.

Five cases of monsoon depression developed during 1988 summer monsoon have been investigated in detail with the help of LAM and useful conclusion have been drawn.

In addition to the evaluation of the performance of the model, determination of systematic errors of the model is essential for judicious operational use of the NWP products and for diagnosis of the errors associated with inherent weakness in the formulation of the model. Systematic errors of the model for a representative month of monsoon , ie., July with a recent year (1988) analysis of European Centre for Medium Range Weather Forecast (ECMWF) have been carried out. The LAM systematic errors are compared with a state-of-art operational global model of ECMWF over the same region (Asian summer monsoon region) to find out the deficiencies of the LAM.

(7)

CONTENTS

ABSTRACT

CHAPTER-I INTRODUCTION

Page No.

1.1 Numerical Weather Prediction (NWP)

in the tropics 1

1.1.1 Numerical simulation of Asian Summer

monsoon 3

1.1.2 LAM for the simulation of monsoons 5 1.2 Influence of resolution and orography 7 1.3 Influence of initialization 9

1.4 Monsoon depressions 12

1.5 Systematic error studies 13 1.6 Objective of this study 16 CHAPTER-II MODEL DESCRIPTION AND SENSITIVITY

EXPERIMENTS

2.1 Introduction 19

2.2 Model description 22

2.2.1 Model dynamics 22

2.2.2 Horizontal discretization 26 2.2.3 Vertical discretization 28 2.2.4 Time integration scheme 36

2.2.5 Model physics 43

2.2.6 Boundary conditions 51

2.3 Resolution experiments 52

2.3.1 Brief description of experiments 54 2.3.2 Horizontal resolution 55 2.3.3 Vertical resolution 62

(8)

2.4 Orography experiments 68 2.4.1 Brief descriptions of topography

formulations 70

2.4.2 Results and discussions 73

2.5 Conclusions 86

CHAPTER-III APPLICATION OF A NON-LINEAR NORMAL MODE INITILIZATION TO A LIMITED AREA MODEL

3.1 Introduction 92

3.1.1 Nonlinear normal mode initialization

technique 95

3.2 Formulation of the vertical mode

initialization scheme 97 3.3 Experiments with the vertical mode

initialization scheme 105 3.4 Results and discussions 106

3.5 Conclusions 121

CHAPTER-IV MONSOON DEPRESSIONS : CASE STUDIES

4.1 Introduction 122

4.2 Monsoon depression of 1988 123

4.3 Discussion 126

4.3.1 Case 1 : Arabian Sea Deep Depression 126 4.3.2 Case 2 : Deep Depression over Bay 133 4.3.3 Case 3 : Bay Depression - 1 138 4.3.4 Case 4 : Bay Depression - 2 141 4.3.5 Case 5 : Depression over Land 150

4.4 Conclusions 156

CHAPTER-V SYSTEMATIC ERRORS OF A LIMITED AREA MODEL AND ITS COMPARISON WITH A GLOBAL MODEL OVER INDIA AND ITS NEIGHBOURHOOD

5.1 Introduction 158

(9)

5.2 Systematic errors in the analyses and

forecasts of the wind fields 161 5.2.1 Observational aspects 161 5.2.2 Errors in the analyses of the ECMWF

wind fields 163

5.2.3 Forecasts of the limited area model 167 5.2.4 Forecasts of the ECMWF model 173 5.3 Systematic errors in the analyses and

the forecasts of the temperature fields 182 5.4 Systematic errors in the analyses and

forecasts of the height fields 187

5.5 Conclusions 192

CHAPTER-VI CONCLUSIONS 194

REFERENCES 201

References

Related documents

Prediction of Indian summer monsoon rainfall using surface temperature and sea-level pressure cluster

This is to certify that the thesis entitled " Radiation and moisture initialization in short range weather prediction over India ", being submitted by B.Nandi for the award

Vertically integrated structure of the kinetic energy budget terms during the summer monsoon season shows a zone of flux divergence over the Bay of Bengal,adjoining peninsular

This is to certify that the thesis entitled "Modeling Short and Long Range Corticocortical Connections in the Visual Cortex and Study of Orientation Selectivity"

This is to certify that the thesis, entitled, "Characterisation of Short—Range TroposcPtter CommunicPtion Channels" being submitted by Suryp Prakpsh Uttpm for the award

This is to certify that the thesis entitled, “Computational Studies on Tertiary Structure Prediction of Small Proteins and Energetics of Folding”, being submitted by Miss

Figure 4: Different scenarios showing changes in the Southern Hemisphere high latitude, Southern Indian Ocean subtropics and Asian summer monsoon during (a)

Carmona et. In the theory of Random SchrOdinger Operators, one deals with a collection of random operators in a single fixed Hilbert Space. The assumption of strict