Introducing Meteorology Other Titles in this Series Introducing Astronomy Introducing Geology ~ A Guide to the World of Rocks (Third Edition) Introducing Geomorphology Introducing Geophysics (forthcoming 2020) Introducing Metamorphism Introducing Mineralogy Introducing Natural Resources Introducing Oceanography Introducing Palaeontology ~ A Guide to Ancient Life Introducing Sea Level Change Introducing Sedimentology Introducing Stratigraphy Introducing Tectonics, Rock Structures and Mountain Belts Introducing the Planets and their Moons Introducing Volcanology ~ A Guide to Hot Rocks For further details of these and other Dunedin Earth and Environmental Sciences titles see www.dunedinacademicpress.co.uk Half-title frontispiece: A tornado-bearing storm supercell near Forgan, Oklahoma, on 17 May 2019. (Photo: Simon Lee.) Introducing Meteorology A Guide to Weather Second Edition Jon Shonk DUNEDIN EDINBURGH  LONDON First published in 2020 by Dunedin Academic Press Ltd Head Office: Hudson House, 8 Albany Street, Edinburgh EH1 3QB London Office: The Towers, 54 Vartry Road, London N15 6PU ISBNs 9781780460918 (Paperback) 9781780466439 (ePub) 9781780466446 (Amazon Kindle) 9781780466453 (PDF) © Jon Shonk 2020 The right of Jon Shonk to be identified as the author of this work has been asserted by him in accordance with sections 77 and 78 of the Copyright, Designs and Patents Act 1988 All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means or stored in any retrieval system of any nature without prior written permission, except for fair dealing under the Copyright, Designs and Patents Act 1988 or in accordance with the terms of a licence issued by the Copyright Licensing Society in respect of photocopying or reprographic reproduction. Full acknowledgement as to author, publisher and source must be given. Application for permission for any other use of copyright material should be made in writing to the publisher. British Library Cataloguing in Publication data A catalogue record for this book is available from the British Library Typeset by Makar Publishing Production, Edinburgh Printed in Poland by Hussar Books Contents Contents Acknowledgements and Figure Credits vii Preface ix 1 Watching the Weather 1 1.1 – The Influence of Weather ~ 1 § 1.2 – Weather Watchers ~ 4 2 From Seaweed to Supercomputers 7 2.1 – The Age of Seaweed ~ 7 § 2.2 – Early Meteorological Advances ~ 8 § 2.3 – The First Forecasts ~ 11 § 2.4 – Looking Up into the Atmosphere ~ 13 § 2.5 – Towards Modern Forecasting ~ 14 3 The Weather Station 16 3.1 – Surface Observations ~ 16 § 3.2 – Inside the Stevenson Screen ~ 17 § 3.3 – Outside the Stevenson Screen ~ 19 § 3.4 – Watching the Skies ~ 22 § 3.5 – Automatic Weather Stations ~ 25 4 Gauging the Atmosphere 27 4.1 – Measuring the Upper Air ~ 27 § 4.2 – Radar and Lidar ~ 29 § 4.3 – Observations from Space ~ 32 5 Anatomy of the Atmosphere 35 5.1 – Composition of the Atmosphere ~ 35 § 5.2 – Pressure, Temperature and Density ~ 37 § 5.3 – The Atmospheric Profile ~ 39 6 Water in the Atmosphere 42 6.1 – The Hydrological Cycle ~ 42 § 6.2 – Humidity and Moisture ~ 43 § 6.3 – Water Droplets and Rain ~ 44 § 6.4 – Ice Crystals and Snowflakes ~ 46 7 It All Starts with the Sun 49 7.1 – Our Local Star ~ 49 § 7.2 – The Earth in Equilibrium ~ 50 § 7.3 – The Effect of the Atmosphere ~ 51 § 7.4 – The Effect of Clouds ~ 53 8 Hot and Cold 58 8.1 – Surface Temperature ~ 58 § 8.2 – Adiabatic Ascent ~ 59 § 8.3 – Clouds, Fog, Dew and Frost ~ 60 § 8.4 – The Spherical Earth ~ 62 § 8.5 – Variation of Total Solar Irradiance ~ 64 § 8.6 – The Earth in Non-Equilibrium ~ 66 9 The Atmosphere in Motion 68 9.1 – Highs, Lows and Circulation of Air ~ 68 § 9.2 – The Coriolis Effect ~ 70 § 9.3 – Hadley Cells ~ 72 § 9.4 – Heat Transport in the Mid-Latitudes ~ 73 § 9.5 – The Global Circulation ~ 75 10 Mid-Latitude Weather Systems 77 10.1 – The Westerly Flow ~ 77 § 10.2 – Anticyclones and Air Masses ~ 78 § 10.3 – Low- Pressure Systems ~ 80 § 10.4 – Fronts and Conveyor Belts ~ 83 § 10.5 – When Storms Become Severe ~ 86 v vi Contents 11 Weather in the Tropics 88 11.1 – The Easterly Flow ~ 88 § 11.2 – Intertropical Convergence Zone and Monsoons ~ 89 § 11.3 – Tropical Depressions and Hurricanes ~ 91 § 11.4 – El Niño, La Niña and the Southern Oscillation ~ 95 12 Convective Systems, Tornadoes and Thunderstorms 98 12.1 – Unstable Conditions ~ 98 § 12.2 – Cumulonimbus, Thunder and Lightning ~ 99 § 12.3 – Organised Convective Systems ~ 102 § 12.4 – Supercells and Tornadoes ~ 103 13 Local Weather Effects 106 13.1 – Coastal Weather ~ 106 § 13.2 – Mountain Weather ~ 109 § 13.3 – Desert Weather ~ 112 § 13.4 – Urban Weather ~ 113 14 Forecasting the Weather 116 14.1 – Numerical Weather Prediction ~ 116 § 14.2 – The Initial Conditions ~ 117 § 14.3 – Running the Model ~ 119 § 14.4 – Global and Regional Models ~ 121 § 14.5 – Ensemble Forecasting ~ 118 15 The Forecaster’s Challenge 124 15.1 – Making a Weather Forecast ~ 124 § 15.2 – Forecasting Hazardous Weather ~ 126 § 15.3 – Users of Forecasts ~ 128 § 15.4 – When Forecasts Go Wrong ~ 129 16 The Changing Climate 131 16.1 – Past Records of Climate ~ 131 § 16.2 – Increasing Greenhouse Gas Concentrations ~ 134 § 16.3 – Climate Models ~ 135 § 16.4 – Simulating Past and Future Climate ~ 136 § 16.5 – Adaptation versus Mitigation ~ 139 Glossary 141 Further Reading 154 Acknowledgements Acknowledgements First, I wish to thank Ross Reynolds and Pete Inness for encouraging me to write the first edition of this book – their help and support throughout the writing process was invaluable, as has their willingness to check through various chapters of the manuscript. I also thank Keith Shine for his careful review of Chapter 16, Mike Stroud and Giles Harrison for permit- ting me to take photos and use data from the Atmospheric Observatory at the University of Reading, and David McLeod and Anne Morton at Dunedin Academic Press for their support and guidance. I must also thank all of the following for agreeing to look through a chapter or two: Lesley Allison, Laura Baker, Andy Barrett, Sylvia Bohnenstengel, Kirsty Hanley, Emma Irvine, Nick Klingaman, Keri Nicoll, Daniel Peake, Sam Ridout, Ali Rudd, Claire Ryder, Jane Shonk, Peter Shonk, Claire Thompson, Rob Thompson, Andy Turner and Curtis Wood. Finally, I thank all my friends and family for being supportive during preparation of both the first and second editions, especially my wife, Jess. This book is dedicated to the memory of David Grimes. Figure Credits Figures 0.1, 11.2: NASA Earth Observatory/NOAA. Figures 1.1, 1.2, 1.5, 2.1, 2.2, 3.7ABCGH, 7.4AB, 7.5, 7.7A, 8.5B, 12.1ABC, 13.5C, 15.5AD: © Jon Shonk. Figure 1.3: © Tina Dippe. Figures 1.4, 5.5, 6.5, 7.7BCD, 8.4AB, 13.5B: photographs Copyright © Stephen Burt. Figures 2.3ABCD, 3.2AB, 3.3, 3.4, 3.5AB, 3.6AB, 4.1, 4.2, 8.1, 10.9: courtesy of the Department of Meteorology, University of Reading. Figure 2.4: NOAA Photo Library/US Weather Bureau. Figures 2.5, 2.6: NOAA Photo Library. Figure 2.7: US Army Photo. Figures 3.1, 14.1, 15.1, 15.2: European Centre for Medium-Range Weather Forecasts (ECMWF). Figures 3.7DF: © Mike Blackburn. Figure 3.7E: © Peter Smith. Figure 3.8: NOAA (National Data Buoy Center). Figures 4.3, 4.4, 10.2, 15.3: © British Crown Copyright, Met Office. Figure 4.7ABC: ©2019, EUMETSAT. Figure 5.1: NASA Earth Observatory/JSC Gateway to Astronaut Photography of Earth. Figure 6.6: NOAA Photo Library/Wilson Bentley. vii viii Figure Credits Figure 7.8: adapted from Trenberth KE, Fasullo JT and Kiehl J (2009): Earth’s global energy budget. Bulletin of the American Meteorological Society 90: 311–324. Figure 8.5A: © Daniel Peake. Figure 8.5C: © Jonathan Beverley. Figures 8.7, 9.7AB: European Centre for Medium-Range Weather Forecasts (ECMWF); plots made using ERA-Interim data. Reference: Dee DP, Uppala SM, Simmons AJ, Berrisford P, Poli P, Kobayashi S and Co-authors (2011): The ERA-Interim reanalysis: configuration and performance of the data assimilation system. Quarterly Journal of the Royal Meteorological Society 137: 553–597. Figure 10.4: adapted from Bjerknes J and Solberg H (1922): Life Cycle of Cyclones and the Polar Front Theory of Atmospheric Circulation. Geofysiske Publikationer 1: 3–18. Figures 10.5, 13.4, 13.8: NASA Earth Observatory. Figure 10.11, 12.2, 13.2A: © Dundee Satellite Receiving Station. Figures 11.4, 13.2B: NASA Earth Observatory/NOAA/US Department of Defense. Figure 11.8: based on Halpert MS and Ropelewski CF (1992): Surface Temperature Patterns Associated with the Southern Oscillation. Journal of Climate 5, 577–593; Ropelewski CF and Halpert MS (1987): Global and Regional Scale Precipitation Patterns Associated with the El Niño–Southern Oscillation. Monthly Weather Review 115, 1,606–1,626. Figures 12.3, 12.6B: © Daniel Gregory. Figures 12.6A, Half-title Frontispiece: © Simon Lee. Figure 12.6C: © Beth Saunders. Figure 13.5A: © Claire Delsol. Figure 13.9: © Wagner Nogueira Neto. Figure 15.4: NASA Earth Observatory/USGS Earth Observing-1. Figures 15.5B: © Jane Shonk. Figure 15.5C: © Jane Shonk; courtesy of Jason James. Figure 16.1: data from the Climate Research Unit, University of East Anglia. Reference: Morice CP, Kennedy JJ, Rayner NA and Jones PD (2012): Quantifying uncertainties in global and regional temperature change using an ensemble of observational estimates: the HadCRUT4 dataset. Journal of Geophysical Research 117: D08101. Figure 16.2: National Science Foundation, photography by Heidi Roop. Figure 16.3: adapted from Petit JR, Jouzel J, Raynaud D, Barkov NI, Barnola JM, Basile I, Bender M, Chappellaz J, Davis J, Delaygue G, Delmotte M, Kotlyakov VM, Legrand M, Lipenkov V, Lorius C, Pépin L, Ritz C, Saltzman E and Stievenard M (1999): Climate and Atmospheric History of the Past 420,000 Years from the Vostok Ice Core, Antarctica. Nature 399, 429–436. Figure 16.4: Dr Pieter Tans (NOAA/ESRL) and Dr Ralph Keeling (Scripps Institution of Oceanography). Figure 16.5: from IPCC Fifth Assessment Report; Synthesis report, Figure 2.1 (page 59). Preface Preface Every time we step outdoors, or even look out of the window, we experience weather. Sometimes we are greeted by clear, blue skies; at other times we are faced with grey clouds. On some days, we feel the wind in our faces; on other days it can be completely calm. Some days are warm, some days are cold; some bring rain, some stay dry. Some even bring severe weather – heavy snowfall, freezing rain, tornadoes or dust storms. No two days of weather are the same, and the weather is always changing. Weather is the complex interaction of heat and water within the atmosphere. Its power source, the Sun, provides massive amounts of energy in the form of sunlight, which heats the Earth’s surface and sets the atmosphere in motion. We experience this motion as wind. Water in the atmosphere can exist in all three phases – solid ice, liquid water and water vapour – and as the air circulates, water in the atmosphere can switch between these three phases. Water vapour is invisible, but when it condenses to liquid or ice, it appears as cloud. These clouds can grow and bring rain, sleet, snow, hail, thunder and lightning. Since the dawn of time, mankind has watched the weather changing from day to day and year to year. Despite this, being able to forecast the changing weather is a skill that has eluded us until only very recently. The vast numbers of calculations required to produce a reliable weather forecast have only been possible since the advent of the supercomputer. Modern technology has played a vital part in the development of the science of meteorology, not just in terms of fore- casting, but also in improving our observations of the atmosphere, making meteorology perhaps one of the youngest of all the sciences. Nowadays, meteorology is a very accessible science. TV weather forecasts are screened many times a day and a wealth of weather information is now freely available over the internet. Mete- orologists also find themselves in the public eye a great deal more – every time they make a forecast, their science is put to public scrutiny. Their research is a constant, ongoing challenge to improve the ability to forecast the weather, not just through improving weather models, but also by improving understanding of the background science of meteorology, of how weather systems form and interact, and even improving techniques of observing the weather. Another area of increasing research is climate prediction: with rising global temperatures, attention is often turned to the climate scientist to understand how the future climate might vary. From a very early age, we are exposed to weather. For some of us, this sparks an enthusi- astic interest leading to a career in meteorology or climate science; others are encouraged to become dedicated amateur weather watchers. This book aims to provide a basic understanding of the science of meteorology for those keen to take it a little further. We begin by summaris- ing the history of meteorological observations and forecasting (Chapter 2), then we look into how the weather is observed using a combination of surface observations and remote sensing techniques (Chapters 3 and 4). The next chapters introduce the basic physical science behind ix