WINTER CIRCULATION CHARACTERISTICS AND LOCATION SPECIFIC FORECAST OVER
WESTERN HIMALAYAS
by A.P. Dimri
Centre for Atmospheric Sciences
Subm itted
in fu lfillm en t o f the requirements o f the degree o f
DOCTOR OF PHILOSOPHY
to the
Indian Institute of Technology, Delhi
H auz Khas, New Delhi - 110016, INDIA
M ay, 2003
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CERTIFICATE
This is to certify that the thesis entitled “ W in te r C irc u la tio n C h a ra c te ris tic s a n d L o c a tio n S pecific F o re c a s t o v e r W e s te rn H im a la y a s ” , being subm itted by A.P. D im ri for the aw ard o f the degree o f D o c to r o f P h ilo so p h y , is a record o f the original bonafide research w ork carried out by him . H e has w orked under our jo in t guidance and supervision and has fulfilled the requirem ents for the subm ission o f this thesis. T h e results presented in this thesis have not been subm itted by him in p art or full to any oth er U niversity or Institute for aw ard o f any degree or diplom a.
Professor
C entre for A tm ospheric Sciences Indian Institute o f Technology H auz Khas, New Delhi - 110016 IN D IA
(D r. L .S . R a th o re ) Scientist-G & A dviser
N ational C enter for M edium R ange W eather Forecasting M ausam B haw an C om plex
Lodhi R oad, N ew Delhi - 110003 IN D IA
Acknowledgements
I express my profound gratitude and indebtness to Prof. U.C. Mohanty fo r encouraging me to undertake this work and fo r guidance and support extended to me during the course o f the thesis work. He offered me genuine criticism in the work and gave numerous suggestions fo r improving the quality o f the work. I am unable to express, in words, the love, affection and deep understanding shown by him during the entire period o f my association with him.
I am extremely thankful to Dr. L.S. Rathore fo r providing necessary help, constant encouragement and supervision which enabled me to complete this work in the present form.
I am much influenced by his humbleness during my association with him.
I gratefully acknowledge my gratitude to my organization, the Snow and Avalanche Study Establishment (SASE), Defense Research and Development Organization (DRDO), Chandigarh fo r providing me an opportunity to work at CAS, IIT, Delhi. I profoundly thank Maj. Gen. (Retd.) S.S. Sharma, KC, VSM, Director (SASE) fo r the kind help extended to me in all possible ways during the course o f work. My thanks are also due to Mr. D.K. Prashar fo r unbending support he has extended to me.
I owe my deep sense o f appreciation to all the people at Directorate o f Personnel (DOP), DRDO - HQs, Delhi fo r helping in completing the present course at CAS, IIT, Delhi.
I express my sincere thanks to Prof. G. Jayaraman, Head, CAS, IIT, Delhi fo r making available necessary facilities in the centre. The help and support rendered by Prof. Dash, Dube, Sinha, Saran and Sharma is gratefully acknowledged.
My special thanks to Dr. V. Siddartha, Mr. J.S. Pandey, Mr. S.K. Reddy and Dr. M.C.
Pant, who took genuine interest in encouraging me to pursue/accomplish higher studies.
I thank Dr. M. Azadi fo r helping me to sort out my problems when I started working as a beginner. I acknowledge with thanks the considerable help provided by Mr. M. Mandal, Dr. R. Bhatla, Mr. P.V.S. Raju and Mr. Narender fo r data exploration and facilitating the subsequent computations. My thanks are also goes to Gp. Capt. O.P. Madan fo r helping me in all stages o f my research work.
I wish to thank to the personals o f the India Meteorological Department (IMD), National Center fo r Medium Range weather forecasting (NCMRWF), NCEP/NCAR fo r providing data and PSU/NCAR fo r providing the mesoscale model MM5 used extensively in present work.
I am extremely grateful to my colleagues Mr. G.R. Panesar and Mr. R.K. Garg fo r helping me during present course o f work.
I thank my family fo r their unwavering support and encouragement. I thank my
parents, Sri Jayanand and Smt Basu, fo r instilling the habit o f learning, learning and
learning in me. I thank my brother, Alok, fo r being all along with me. Finally, I am extremely
grateful to my wife, Shivani, who has shown all the patience, cooperation and understanding
during this period.
Abstract
T he set o f the present thesis w ork deals w ith the intricacies associated w ith prediction of w intertim e w eather over w estern H im alayas. This region is com prised o f com plex m ountain ranges having different altitudes and orientations. D ue to this highly variable altitude and orientation o f orographic barriers the prevailing w eather conditions over the region are very com plex. The foremost part o f this thesis deals w ith the circulation features, dynamics and energetics associated with wintertim e, D ecem ber, January, February and M arch (D JFM ), circulations over the western Himalayas. D ifferences in circulation features during excess and deficient years o f precipitation during w inter season over the western Himalayas have also been exam ined and tested with significance at 95% confidence level using Students t-test.
Large scale balances o f kinetic energy, vorticity, angular m om entum , heat and m oisture over the w estern H imalayas are studied. Forty years (1958-97) uninitialized daily reanalysis data o f the National C enter for Environm ental Prediction (N CEP), U SA , fo r w inter season is used to carry out this study. Differences in energetics associated w ith extrem e years o f precipitation have also been carried out. Surplus and deficient years o f seasonal (DJFM ) precipitation over the w estern Himalayas from 40 years o f N C E P data are identified using ± 20% departure from mean. The years 1965, 66, 67, 68, 69, 73 and 1991 are found to be surplus years and years 1962, 63, 71, 77 and 1985 are found to be deficient years.
Com posites o f these two categories are made and then anom alies are com puted using Students t-test.
W estern H imalayas is visited by m any synoptic w eather systems that produce large spatial and tem poral variability in weather and clim ate during winter. H im alayan region is a data sparse region due to inaccessible and difficult terrain. R em otely sensed w eather inform ation through w eather satellite is the m ain source o f initial data. Sim ulation studies o f the western disturbances (W D s) are expected to help in understanding the behavioral pattern
o f circulation fields and prediction o f precipitation. In the present study an attem pt is m ade to sim ulate five intense W D s cases over the w estern H im alayas using a regional m esoscale model M M 5V 2 and some im portant model sim ulated fields are com pared with verifying reanalysis. Precipitation and circulation features associated with the intense W D s are well sim ulated by the model. Forecast errors indicate that high resolution m eso-scale model could simulate the w eather associated with the W D s with reasonable accuracy.
Site and tim e specific prediction o f some o f the atm ospheric variables cannot be achieved by numerical model outputs only. Therefore, dynam ical statistical m odels are developed based on Perfect Prognostic M ethod (PPM ) concept for forecasting m axim um and m inim um tem peratures at three stations situated in the w estern H im alayas. R ealtim e observations and num erical analyses o r num erical model outputs are used for m odel developm ent during w inter season and tested with independent data. A nalysis data from the N CEP, U SA and station data o f some o f the stations o f the India M eteorological D epartm ent (IM D), India are used for the model developm ent. For evaluation of the perform ance o f the models with independent data sets as predictors, four sets o f experim ent are carried out with predictors selected from four different types of sources viz., reanalysis data o f NCEP, N ational Center for M edium Range W eather Forecasting (N CM RW F) operational analysis, T80 spectral model day 1 forecast and M M 5 day 1 forecast respectively.
Further, PPM is used to forecast Probability o f Precipitation (PoP) occurrence/non - occurrence and Q uantitative Precipitation Forecast (QPF). Analysis data o f the N CEP, USA and upper air and surface observations at three stations o f the IM D , India are used fo r the developm ent o f dynamical statistical models for w inter season, i.e., D JFM . It is found that by using numerical model outputs from M M 5 as predictors in dynamical statistical model based on PPM concept, definite im provem ents in PoP and Q PF are obtained as com pared to the direct numerical model outputs.
CONTENTS
Page No.
Acknowledgem ents i
A bstract ii-iii
List of Figures iv-ix
List o f Tables x-xi
CHAPTER 1: Introduction 1-16
1.1. Introduction 1
1.2. W estern D isturbance 4
1.3. D iagnostic and energetic aspects o f w intertim e circulations over w estern H im alayas 5
1.4. N um erical w eather prediction 6
1.5. Dynamical statistical w eather forecast 9
1.6. O bjective and scope of thesis 11
CHAPTER 2: Winter Circulation Characteristics 17-80
over Western Himalayas
2.1. Introduction 17
2.2. D ata 19
2.3. M ethodology 27
2.4. M ean w inter circulation characteristics 29
2.4.1. M ean circulation features 29
2.4.2. K inetic energy budget 32
2.4.3. V orticity budget 34
2.4.4. H eat and m oisture budget 37
2.4.5. A ngular m om entum budget 43
2.5. C ontrasting features associated with extrem e precipitation years 46
2.5.1. Surface fields 46
2.5.2. U pper air fields 52
2.5.3. K inetic energy budget 59
2.5.4. V orticity budget 65
2.5.5. H eat and m oisture budget 68
2.5.6. A ngular m om entum budget 74
2.6. Conclusions 75
CHAPTER 3: Simulation of mesoscale features associated with intense western 81-133 disturbances over western Himalayas using a mesoscale model
3.1. Introduction 81
3.2. D escription of the M esoscale M eteorological M odel (M M5) 83
3.2.1. Basic equations of M M 5 84
3.2.2. The M M 5 model horizontal and vertical grid 85
3.2.3. Terrain 90
3.2.4. Physical processes 93
3.2.4.1. Precipitation process 93
3.2.4.2. Cum ulus convection schem e 93
3.2.4.3. Radiation (shortw ave/longw ave) 94
3.2.4.4. Planetary boundary layer param eterization 95
3.3. D ata used and numerical experim ent 95
3.4. Synoptic situation 99
3.5. Results and discussion 102
3.5.1. W ind 102
3.5.2. G eopotential height 107
3.5.3. Tem perature and specific hum idity 111
3.5.4. M ean sea level pressure 111
3.5.5. Precipitation 115
3.5.6. Statistical skill score 117
3.5.7. Location specific prediction o f precipitation and tem perature 127
3.6. C onclusions 129
CHAPTER 4: Location Specific prediction of maximum and minimum 134-180 temperature over western Himalayas
4.1. Introduction 1 3 4
4.2. D ata and M ethodology 1 3 6
4.2.1. Selection and form atting the predictand 136
4.2.2. Predictor selection 1 3 7
4.2.2.1 Three source of predictors : classical, perfect prog & 139 model output statistics
4.3. Form ulation o f m axim um temperature forecast model 153
4.4. Form ulation o f m inim um temperature forecast model 161
4.5. Experim ents for validation o f m axim um and m inim um tem perature forecast m odels 163
4.5.1. Experim ent - 1 (Ex-1) 164
4.5.2. Experim ent - 2 (Ex-2) 164
4.5.3. Experim ent - 3 (Ex-3) 165
4.5.4. Experim ent - 4 (Ex-4) 165
4.6. Results and discussion 166
4.6.1. Perform ance o f m axim um tem perature forecast m odel 167 4.6.2. Perform ance o f m inim um tem perature forecast m odel 172
4.7. Conclusions 178
CHAPTER 5: Location specific prediction of probability of occurrence 181-203 and quantity of precipitation over western Himalayas
5.1. Introduction 181
5.2. D ata and analysis procedure 183
5.3. Form ulation o f probability of precipitation (PoP) forecast m odel 185 5.4. Form ulation o f quantitative precipitation forecast (QPF) m odel 188
5.5. Experim ent for validation of PoP and Q PF models 192
5.5.1. Experim ent - 1 (Ex-1) 192
5.5.2. Experim ent - 2 (Ex-2) 193
5.5.3. Experim ent - 3 (Ex-3) 193
5.5.4. Experim ent - 4 (Ex-4) 194
5.6. Results and discussion 194
5.6.1. Perform ance of probability o f precipitation (PoP) m odel 195 5.6.2. Perform ance of quantitative precipitation forecast (Q PF) m odel 199
5.7. C onclusions 202
CHAPTER 6: Summary 204-206
6.1. Sum m ary 204
6.2. Future studies 208
