THE UNIVERSITY OF NEW SOUTH WALES THE OBSERVATION AND MODELLING OF WINDS OVER SOUTH EASTERN AUSTRALIA KENNETH L. BATT A thesis submitted in fulfillment of the requirements for the degree of Master of Science (Mathematics), 2005 School of Mathematics, Faculty Of Science, University of New South Wales Sydney 2052, Australia PLEASE TYPE THE UNIVERSITY OF NEW SOUTH WALES Thesis/Project Report Sheet Surname or Family name: BATT First name: KENNETH LESLIE Abbreviation for degree as given in the University Calender: MSc School: MATHEMATICS Faculty: SCIENCE Title: THE OBSERVATION AND MODELLING OF WINDS OVER SOUTH EASTERN AUSTRALIA Abstract 350 words maximum: (PLEASE TYPE) This study uses a very high resolution numerical weather prediction (NWP) model to investigate the complex structure and behaviour of cold fronts along the New South Wales coast during the warmer months of the year, the complex interaction between the wind flow and coastlines and elevated areas as well as the lee-trough effect, particularly the way it affects waters off the east coast of Tasmania, The study also investigates the utility of the higher resolution NWP model to better predict wind fields compared to a lower resolution model. The University of New South Wales very high resolution model (HIRES), nested in the Australian Bureau of Meteorology's coarse NWP model (GASP), was run at various horizontal resolutions (from 15 to 25km) in order to investigate the above-mentioned features. It was found to have very good skill in resolving the features and was also found to be very accurate in the prediction of surface wind fields for various yacht race events out to at least four days ahead. It can be concluded that there is considerable skill in the ability of high-resolution NWP models such as HIRES, to predict the major features of the wind fields over the ocean out to several days ahead. Moreover, it was also able to more accurately simulate the complex structure of the summer-time cool change as it progressed along the NSW coast than the lower resolution model runs. The influence of coastlines, particularly ones with complex topographical features, on the wind flow was demonstrated to a limited extent throughout the study. Finally the following concepts were also verified as a result of the study: air flow takes the path of least resistance the shape of topography can help generate local turbulence the orientation of the wind flow to a mountain range is important in determining turbulent effects. under certain airflow and stability situations, standing wave activity and a lee trough can be observed in the lee of mountains, hills or even high coastal cliffs. Declaration relating to disposition of project report/thesis I am fully aware of the policy of the University relating to the retention and use of higher degree project reports and theses, namely that the University retains the copies submitted for examination and is free to allow them to be consulted or borrowed. Subject to the provisions of the Copyright Act 1968, the University may issue a project report or thesis in whole or in part, in photostat or microfilm or other copying medium. I also authorise the publication by University Microfilms of a 350 word abstract in Dissertation Abstracts International (applicable to doctorates only). …………………………………………………. …………………………………………………. …………………………………………………. Signature Witness Date The University recognises that there may be exceptional circumstances requiring restrictions on copying or conditions on use. Requests for restriction for a period of up to 2 years must be made in writing to the Registrar. Requests for a longer period of restrictions may be considered in exceptional circumstances if accompanied by a letter of support from the Supervisor or Head of School. Such requests must be submitted with the thesis/project report. FOR OFFICE USE ONLY Date of completion of requirements for Award: Registrar and Deputy Principal THIS SHEET IS TO BE GLUED TO THE INSIDE FRONT COVER OF THE THESIS DEDICATION To my adorable spouse Helen and our beautiful children Christie and Georgia who helped make this possible, my love and thanks forever. To my mother and late father who allowed a passion to blossom. 2 ACKNOWLEDGEMENTS Professor L. M. Leslie, for providing the opportunity, guidance and tools for this thesis. Professor J. Middleton for guidance and supervision. Mr R.P. Morison for technical assistance. Dr B. W. Buckley for guidance and motivation. Dr M. Speer for technical assistance. Dr L. Qi for technical assistance. Mr D. Williams for technical assistance. Ms Helen Smith for technical assistance. My family Helen, Christie and Georgia for allowing me the time to sail, research and write. The Bureau of Meteorology for allowing me to take up the opportunity and offer the time off to research and write this thesis. 3 SUPPORTING PUBLICATIONS Journals Batt, K.L. (1994). The Meteorology of the 1993 Sydney to Hobart Yacht Race. Offshore Yachting Feb/Mar 1994, Journal of the Cruising Yacht Club of Australia, Jamieson Publishing. Batt, K., and James, J. (1994). Weather dampens Sydney to Hobart yacht race. Mariners Weather Log, 38: 8-11. Batt, K.L. (1994). The 1993 Sydney to Hobart Yacht Race “Weather News” (in-house journal of the Australian Bureau of Meteorology). Buckley, B., and Batt, K. (1997). The Weather Factor-Sydney to Hobart Yacht Race 1996. Offshore Yachting Feb/Mar 1997, Journal of the Cruising Yacht Club of Australia, Jamieson Publishing. Batt, K.L., and Hainsworth, A. (2001). Tricky Tassie Coast. Offshore Yachting: December 2001, Journal of the Cruising Yacht Club of Australia, Jamieson Publishing. Batt, K.L., and Leslie L.M. (1998). Verification of output from a very high resolution numerical weather prediction model: the 1996 Sydney to Hobart yacht race. Meteorol. Appl. 5: 321-327 Batt, K.L., Morison R.P., and Speer, M.S. (2000). Direct verification of forecasts from a very high resolution numerical weather prediction (NWP) model. Meteorol Atmos Phys 74: 117- 127 Batt, K.L, Qi, L., and Morison, R.P. (2002).The Modeling and Observation of a Lee Trough event over Eastern Tasmania. Meteorol Atmos Phys 80: 177-187. 4 Conference Proceedings The Verification of Output from a High Resolution Numerical Weather Prediction Model: The 1996 Sydney to Hobart Yacht Race. Paper presented at AMOS-APOC Conference 1997, Macquarie University. A Modelling and Observational Study of Sea Breeze Regimes over the Greater Sydney Coastal Area. Paper presented at AMOS-APOC Conference 1997, Macquarie University. Verification of Output from a Very High Resolution Numerical Weather Prediction Model: The 1996 and 1997 Sydney to Hobart Yacht Races. Paper presented at Australian Atmospheres and Oceans ’98, 9-12 February, 1998 Victoria University, Wellington, New Zealand. Course Attendance Numerical Weather Modelling, MATH5295 UNSW 1996. 5 CONTENTS Chapter 1 Introduction 11 1.1 General and Aims 11 1.2 Data sources used in studies 15 Chapter 2 Theory 19 2.1 The greater accuracy of a very high resolution model over a lower resolution global model for the same domain. 19 2.2 The Summertime Cool Change over Southeast Australia 20 2.3 Coastal Wind Flows 27 2.4 Airflow in the vicinity of Complex Orography 31 Chapter 3 Description of the Model 35 Chapter 4 Verification of output from a very high resolution numerical weather prediction model: The 1996 Sydney to Hobart yacht race Overview 39 4.1 Introduction 40 4.2 The meteorological setting 42 4.3 Model performance 44 4.4 Discussion and verification of results 48 Figures 53 Chapter 5 Direct verification of forecasts from a very high resolution Numerical Weather Prediction (NWP) model. Overview 69 5.1 Introduction 70 5.2 The meteorological setting 71 5.3 Model performance 73 5.4 Discussion and verification of results 79 Figures 83 6 Chapter 6 The modelling and observation of a lee trough event over eastern Tasmania. Overview 97 6.1 Introduction 98 6.2 Theory 101 6.3 Synoptic and Mesoscale overview 104 6.4 Results 107 6.5 Discussion 109 Figures 111 Chapter 7 Concluding Remarks 126 References 130 Appendix 1 135 A1.1 Introduction 135 A1.2 A brief chronology of events 136 A1.3 Conclusion 144 7 List of Figures Chapter 2 Figure 2.1 Classic “textbook” picture of a cold front. Figure 2.2 Cold front with an associated frontal transition zone. Figure 2.3 A roll cloud over Botany Bay, NSW. Figure 2.4 Distorted shape of a summertime cold front as it moves along the NSW coast. Figure 2.5 A vertical cross-section of a front along the NSW coast. Figure 2.6 Topography and location map of Sydney Harbour, NSW. Figure 2.7 An idealized lee trough and mesoscale heat low event in Tasmania. Chapter 4 Figure 4.1 Map of southeastern Australia showing locations of places mentioned in this chapter. Figure 4.2 The HIRES model domain including topography. Contour interval is 100 m. Figure 4.3 Australian region mean sea level pressure analyses (4hPa spacing) at 1000 EDST for (a) 26 December 1996 and (b) 27 December 1996 and (c) 28 December 1996 and (d) 30 December 1996. Figure 4.4(a) HIRES model forecast winds for 1600 EDST on 26 December 1996 at 25 km resolution showing wind direction (arrows) and speed (indicated both by the length of the arrows and isotachs in knots). Observed wind velocity barb in standard meteorological format is also shown at the position of the yacht AMP Wild Oats, for comparison. Figure 4.4(b) Wind speed plot for Bellambi Point automatic weather station on 26 December 1996 (wind speed in knots, time in EDST) with the 25km horizontal resolution model forecast winds (smoothed black line) overlain. Figure 4.5(a) As in Figure 4.4(a) except at 15 km resolution.