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Proquest Dissertations INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy subm itted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6” x 9” black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. UMI' Bell & Howell Information and Learning 300 North Zeeb Road, Ann Artxar, Mi 48106-1346 USA 800-521-0600 PRECIPITATION OVER SOUTHERN AFRICA AND GLOBAL-SCALE ATMOSPHERIC CIRCULATION DURING BOREAL WINTER A Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Maurice J. McHugh ***** The Ohio State University 1999 Dissertation Committee; Approved By: Prof Jeffrey C. Rogers, Adviser Prof A John Amfield Prof J.S. Hobgood / ' AdvisW Prof E. Mosley-Thompson Department of Geography UMI Number: 99413 83 UMI Microform 9941383 Copyright 1999, by UMI Company. Ail rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 ABSTRACT Precipitation variability over Africa south of the equator is not very well understood and its variability has been poorly documented. Small populations, poor financial resources and relatively complicated meteorological conditions all contribute to our poor understanding of precipitation variability over these regions. The NCEP/NCAR reanalysis dataset, a new and unique dataset, is used to analyze the atmospheric circulation, and climatic conditions associated with precipitation variability over southeastern and southern Africa. Strong relationships are found between precipitation receipt and El Nino, and the North Atlantic Oscillation over both southeastern and southern Africa. Regional precipitation indices were constructed to summarize the precipitation receipt at stations significantly correlated to the North Atlantic Oscillation Index over both these regions. Regression analyses are used to estimate climatic conditions associated with atmospheric circulation and precipitation indices over southeastern and southern Africa. Decreased precipitation is recorded over eastern Africa, and increased precipitation over southern Africa during the positive phase of the North Atlantic Oscillation primarily due to near surface circulation anomalies. Conversely, increased precipitation is recorded over eastern Africa, and decreased precipitation over southern Africa during El Nino events, again. u principally due to near surface circulation anomalies. Upper level dynamics are examined in relation to precipitation variability; but it is shown that there is no consistent upper level support for near surface level dynamics associated with precipitation variability. Specific humidity, vertically integrated precipitable water and outgoing longwave radiation are also examined in relation to precipitation variability and while they are shown to be closely related to the anomalous atmospheric circulation, they are shown to have no consistent relationship act to precipitation variability. m DEDICATION To my parents Manus and Margaret McHugh IV ACKNOWLEDGMENTS I would firstly like to thank my advisor Professor JefiB'ey C. Rogers for his unlimited patience, support, advice and encouragement over the past few years. All members of my committee contributed greatly to my dissertation and to my studies at OSU. I would also like to acknowledge the assistance of Drs. Chung-Chieh Wang and Ken Yetzer for their assistance in computing and mapping. Dr. S.E. Nicholson, Department of Meteorology, Florida State University, kindly provided me with the Afiican lake level data. Many thanks also to Drs. Firooza Pavii, Mike Holtzclaw, Irene Casas and Jamie Rulli for their fiiendship, sage advice and assistance in times of need. Mr. J. Michael Straczynski and Mr. Michael Garibaldi also assisted greatly. I am indebted to my parents, my brothers Michael, Brian, Eoin, Liam, Fergal and Ronan, and my many fiiends who have supported me spiritually and emotionally during my studies, go raibh maith agat. Lastly thanks to my fiancé, Meaghan Conte for giving me hope, love and a great reason to finish. VITA April 15 1 9 7 1 ............................................................ Bom - Dublin, Ireland 1989-1992 ................................................................... Bachelor of Arts Degree (Honors) in Geography and Economics, University College Dublin, Ireland. 1992-1993 ................................................................... Master of Arts Degree (Honors) in Geography, University College Dublin, Ireland. 1995-1998 ................................................................... Graduate Research Associate in Geography at The Ohio State University, Columbus, Ohio. 1998-1999 ............................................................Graduate Teaching Associate in Geography at The Ohio State University, Columbus, Ohio. FIELD OF STUDY Major field: Geography PUBLICATIONS Rogers, J.C., C.-C. Wang, andM.J. McHugh, 1998: ‘Extreme persistent climate anomalies in the northwestern Atlantic: Role of decadal scale sea surface temperature anomalies’. GeophysicalResearch Letters, 25, 3971-3974. VI TABLE OF CONTENTS ABSTRACT..............................................................................................................................ii DEDICATION..................................................................................................................... iv ACKNOWLEDGMENTS....................................................................................................... v VITA ..................................................................................................................................... vi LIST OF FIGURES.................................................................................................................. x LIST OF TABLES ............................................................................................................ xxi LIST OF ABBREVIATIONS ............................................................................................xxiii CHAPTER 1 INTRODUCTION........................................................................................................1 LI Introduction ......................................................................................................1 1.2 Research outline...............................................................................................3 CHAPTER 2 LITERATURE REVIEW .......................................................................................... 6 2.1 Introduction ...................................................................................................... 6 2.2 Climate variability associated with the North Atlantic Oscillation ..............6 2.3 Interannual variability of precipitation over Africa ...................................... 22 CHAPTERS DATA AND METHODOLOGY............................................................................. 33 3.1 Introduction ................................................................................................33 3.2 General description of the NCEP/NCAR reanalysis dataset........................34 3.3 Precipitation d a ta........................................................................................... 40 3.4 Indices representing atmospheric teleconnections ...................................... 45 3.5 Data analysis ..................................................................................................48 3.5.1 Correlation........................................................................................ 48 3.5.2 Regression Analysis ............................................................................50 vu 3.5.3 Univariate and bivariate spectrum analysis and their relation to harmonic analysis ............................................................................. 53 CHAPTER 4 CLIMATOLOGY OF SOUTH AND SOUTHEASTERN AFRICA....................61 4.1 Introduction .....................................................................................................61 4.2 A climatology of south and southeastern Africa ............................................ 61 4.3 The Mean Airflow over Africa.........................................................................80 CHAPTER 5 RESULTS..................................................................................................................
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