METEOROLOGICAL MONOGRAPHS EDITOR TECHNICAL EDITOR DoNALD R. JOHNSON HAROLD A. NAGEL University of Wisconsin, Madison American Meteorological Society ASSOCIATE EDITORS ROBERT C. BEARDSLEY JAMES R. HOLTON Woods Hole Oceanographic Institution University of Washington RICHARD E. ORVILLE JESSE J. 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See inside covers of at the beginning of certain paragraphs and underlined. the JOURNAL OF THE ATMOSPHERIC SciENCES. METEOROLOGICAL MONOGRAPHS VOLUME 23 JUNE 1990 NUMBER45 ATMOSPHERIC PROCESSES OVER COMPLEX TERRAIN Robert M. Banta, G. Berri, William Blumen, David J. Carruthers, G. A. Dalu, Dale R. Durran, Joseph Egger, J. R. Garratt, Steven R. Hanna, J. C. R. Hunt, Robert N. Meroney, W. Miller, William D. Neff, M. Nicolini, Jan Paegle, Roger A. Pielke, Ronald B. Smith, David G. Strimaitis, T. Vukicevic, C. David Whiteman Contributing Authors William Blumen Editor American Meteorological Society 45 Beacon Street, Boston, Massachusetts 02108 © Copyright 1990 by the American Meteorological Society. Permission to use figures, tables, and brief excerpts from this monograph in scientific and educational works is hereby granted provided the source is acknowledged. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. ISBN 978-1-935704-25-6 (eBook) DOl 10.1007/978-1-935704-25-6 ISSN 0065-9401 Library of Congress catalog card number 90-80548 Published by the American Meteorological Society 45 Beacon St., Boston, MA 02108 Richard E. Hallgren, Executive Director Kenneth C. Spengler, Executive Director Emeritus Evelyn Mazur, Assistant Executive Director Arlyn S. Powell, Jr., Publications Manager Jon Feld, Publications Production Manager Editorial services for this book were contributed by Pamela Jones. We wish to thank Keith Seitter and Linda Esche. TABLE OF CONTENTS Preface xii List of Contributors xiii Chapter 1. Mountain Meteorology -WILLIAM BLUMEN ......................................................... . ABSTRACT ..................................................................... . 1.1 Introduction ................................................................. . 1.2 Some historical footnotes ....................................................... . 1.2.1 Surface winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2.2 Observations and observers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2.3 The discovery of atmospheric waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3 Current directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Chapter 2. Observations of Thermally Developed Wind Systems in Mountainous Terrain -C. DAVID WHITEMAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1 Introduction to diurnal mountain winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1.1 Summary of recent field experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2 Along-valley wind systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2.1 Climatology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2.2 Basic physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.2.1 TOPOGRAPHIC AMPLIFICATION FACTOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.2.2 EQUATIONS FOR THE VALLEY WIND SYSTEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 2.2.3 Radiation and surface energy budgets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.2.3.1 RA.DIA TION BUDGET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.2.3.2 SURFACE ENERGY BUDGET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.2.4 Atmospheric budgets of mass, heat, momentum, and moisture . . . . . . . . . . . . . . . . . . . . . 21 2.2.4.1 CONSERVATION OF ATMOSPHERIC MASS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.2.4.2 THERMAL ENERGY BUDGET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.2.4.3 MOMENTUM BUDGET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.2.4.4 HUMIDITY BUDGET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.3 Slope wind systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.3.1 Simple slope flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.3.2 Slope flows on valley sidewalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.4 Morning transition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.5 Evening transition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.6 The diurnal cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 2.7 Other phenomena . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 2.7.1 Influence of external winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 2. 7.2 Maloja winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 2. 7.3 Jets at valley exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 2. 7.4 Antiw ind systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 2. 7.5 Tributary flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 2.8 Future research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 CONTENTS Chapter 3. Thermally Forced Flows: Theory -JOSEPH EGGER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.2 The problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.3 Circulation in a cavity with differentially heated sidewalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 3.4 Sloping boundaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 3.5 Circulation in valley cross-sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 3.6 Toward three-dimensional modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 3.7 Three-dimensional valley flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 3.8 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Chapter 4. Mountain Waves and Downslope Winds -DALE R. DURRAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 4.2 Fundamentals of internal gravity waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 4.3 Application to small-amplitude mountain waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 4.3.1 Sinusoidal ridges; constant wind speed and stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 4.3.2 Isolated mountain; constant wind speed and stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 4.3.3 Vertical variations in wind speed and stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 4.4 Downslope windstorms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 4.4.1 Three explanations for the production of severe downslope winds . . . . . . . . . . . . . . . . . . . 66 4.4.2 A comparison of the hydraulic and the vertically propagating wave theories . . . . . . . . . . . 69 4.4.3 A comparison of the hydraulic and the wave-breaking mechanisms . . . . . . . . . . . . . . . . . . 71 4.4.4 Forecasting downslope winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 4.4.5 Gustiness near the surface in downslope winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 4.5 Flow over isolated mountains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Chapter 5. Fluid Mechanics of Airflow over Hills: Turbulence, Fluxes, and Waves in the Boundary Layer -D. J. CARRUTHERS and J. C. R. HUNT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 5.1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 5.1.2 Classification off/ow regimes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 5. 1.2.1 STRATIFICATION EFFECTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 5.1.2.2 ROTATION EFFECTS................................................. 85 5.1.2.3 ROUGHNESS CHANGES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 5.2 Modeling of turbulent airflow over hills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 5.2.1 Linear analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 5.2.1.1 GENERAL EQUATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 5.2.1.2 INNER REGION SOLUTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 5.2.1.3 MIDDLE LAYER SOLUTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 5.2.1.4 UPPER LAYER SOLUTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 5.2.1.5 SURFACE ROUGHNESS EFFECTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 5.3 Effects of stratification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 5.3.1 Uniform stratification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 5.3.2 More complex stability profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 CONTENTS 5.3.3 Elevated inversion above neutral boundary layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 5.3.4 Strong stratification; large aspect ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 5.4 Turbulence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 5.5 Numerical models and flow over complex terrain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 5.5.1 Isolated hills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 5.5.2 Complex terrain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 5.6 Dispersion and deposition over complex terrain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 5.6.1 Overview and key processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 5.6.2 Localized sources near hills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 5.6.2.1 IDEALIZED HILL SHAPE [EPA-CTDM MODEL (PAINE ET AL. 1987)] . . . . . . . . . . . 98 5.6.2.2 FOURIER ANALYSIS OF HILL SHAPES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 5.6.3 Dispersion and deposition over terrain for well-mixed scalars . . . . . . . . . . . . . . . . . . . . . . 98 5.6.4 Temperature and humidity fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 5.7 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 APPENDIX: Why Can't Stably Stratified Air Rise over High Ground? -RONALD B. SMITH ......... 0 .......... 0 0 ......... 0 ........... 0................... 105 5.A.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 5.A.2 Combining the hydrostatic and Bernoulli equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 5.A.3 Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 5.A.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 Chapter 6. Rugged Terrain Effects on Diffusion -STEVEN R. HANNA and DAVID G. STRIMAITIS 109 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 6.1.1 Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 6.1.2 Overview of history of research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 6.2 Summary of EPA models and evaluations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 6.2.1 Model descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 6.2.2 Evaluations of regulatory models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 6.2.2.1 EPA EVALUATION AT LUKE MILL AND CINDER CONE BUTTE . . . . . . . . . . . . . . 113 6.2.2.2 EVALUATION OF COMPLEX I ANDRTDM AT WIDOWS CREEK . . . . . . . . . . . . 114 6.3 Theories and experiments regarding diffusion over slopes and valleys . . . . . . . . . . . . . . . . . . . . 114 6.3.1 Diffusion models for slope flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 6.3.2 Diffusion models for narrow valleys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 6.3.3 DOE ASCOT experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 6.4 EPA Complex Terrain Model Development (CTMD) Program . . . . . . . . . . . . . . . . . . . . . . . . . 121 6.4.1 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 6.4.2 Fluid modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 6.4.3 Field experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 6.4.3.1 CINDER CONE BUTTE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 6.4.3.2 HOGBACK RIDGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 6.4.3.3 TRACY POWER PLANT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 6.4.4 Assumptions contained in the Complex Terrain Dispersion Model (CTDM) . . . . . . . . . . 131 6.4.4.1 DISPERSION PARAMETERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 6.4.4.2 CONCENTRATION EQUATION FOR LIFT (FLOW ABOVE Hd) . . . . . . . . . . . . . . . . . . 133 6.4.4.3 CONCENTRATION EQUATION FOR WRAP (FLOW BELOW Hd) . . . . . . . . . . . . . . . . 135 6.4.5 Evaluation of CTDM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 CONTENTS 6.5 Mesoscale flow models that include diffusion algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 6.5.1 General principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 6.5.1.1 APPROACH I-LAGRANGIAN PARTICLE DIFFUSION . . . . . . . . . . . . . . . . . . . . . . . 138 6.5.1.2 APPROACH 2-USE OF DIFFUSION EQUATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 6.5.2 Evaluation of mesoscale grid-based diffusion models in rugged terrain . . . . . . . . . . . . . . . 141 6.6 Summary of findings and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Chapter 7. Fluid Dynamics of Flow over Hills/Mountains-Insights Obtained through Physical Modeling -ROBERT N. MERONEY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 7.1.1 Advantages and disadvantages off luid modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 7.1.2 Historical perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 7.2 Similarity considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 7.2.1 Similitude parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 7.2.2 Partial simulation of complex terrain flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 7.2.3 Performance envelopes for fluid modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 7 .2.3.1 NEUTRAL AIRFLOW MODELS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 7 .2.3.2 VALLEY DRAINAGE FLOWS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 7.2.3.3 VERIFICATION EVIDENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 7.3 Facilities for fluid modeling of complex terrain meteorology . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 7.3.1 Wind tunnels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 7.3.2 Drainage flow facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 7.3.3 Water channels and rotating tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 7.3.4 Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 7.4 Neutral flow over hills, ramps, and escarpments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 7.4.1 Idealized two-dimensional terrain flow studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 7 .4.1.1 EFFECTS OF RIDGE SHAPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3 7. 4.1.2 EFFECTS OF TURBULENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 5 7 .4.1.3 EFFECTS OF SURFACE ROUGHNESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 7.4.2 Idealized three-dimensional terrainflow studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 7.4.3 Field/laboratory comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 7. 4.3.1 RAKAIA RIVER GORGE, NEW ZEALAND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 7.4.3.2 GEBBIES PASS, BANKS PENINSULA, NEW ZEALAND . . . . . . . . . . . . . . . . . . . . . . . 158 7.4.3.3 KAHUKU POINT, OAHU, HAWAII . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 7.4.3.4 ASKERVEINHILLPROJECT, OUTER HEBRIDES, SCOTLAND . . . . . . . . . . . . . . . . . 159 7.4.4 Conclusions from neutral airflow terrain studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 7.5 Stratified flow over hills and ramps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 7.5.1 Idealized two-dimensional flow domains for waves and blocking . . . . . . . . . . . . . . . . . . . . 161 7.5.2 Downslope winds, valley flows induced by crosswinds . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 7.5.3 Idealized three-dimensional terrain studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 7.5.4 Field/laboratory comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 7.5.5 Conclusions from stratified airflow terrain studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 7.6 Drainage flow phenomena . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 7. 7 Diffusion phenomena in complex terrain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 7.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 CONTENTS Chapter 8. Remote Sensing of Atmospheric Processes over Complex Terrain -W. D. NEFF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 8.2 Remote sensing techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 8.2.1 Scattering mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 8.2.2 The role of turbulence microstructure in remote sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 8.2.2.1 STATICALLY UNSTABLE CONDITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 8.2.2.2 STATICALLY STABLE CONDITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 8.2.3 Sampling geometries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 8.2.3.1 FIXED-BEAM SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 8.2.3.2 SCANNING SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 8.2.4 Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 8.2.4.1 SODARS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 8.2.4.2 RADARS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 8.2.4.3 AEROSOL-MAPPING LIDARS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 8.2.4.4 DOPPLER LIDARS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 8.2.4.5 OPTICAL CROSSWIND SENSORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 8.3 Major complex terrain field studies using remote sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 8.3.1 Atmospheric Studies in Complex Terrain (ASCOT) Program . . . . . . . . . . . . . . . . . . . . . . 185 8.3.2 EPA Complex Terrain Model Development (CTMD) Program . . . . . . . . . . . . . . . . . . . . . 187 8.3.3 Urban and regional air quality studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 8.4 Application of remote and in-situ instrumentation to complex terrain studies-case studies . . 188 8.4.1 Sodar observations of simple drainage flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 8.4.2 Sodar observation of complex drainages and their interaction with ambient flows . . . . . . 191 8.4.2.1 THE ROLE OF DIFFERENTIAL ACCELERATION OF AIR MASSES IN ECHO CREATION 191 8.4.2.2 ENTRAINMENT BY THE EXTERNAL WIND-TURBULENCE AND INSTABILITY . . . . 193 8.4.3 Remote sensor observation ofwaves in complex terrain . . . . . . . . . . . . . . . . . . . . . . . . . . . 194 8.4.3.1 LONG-PERIOD OSCILLATIONS OBSERVED IN COMPLEX TERRAIN FLOWS . . . . . . . . 195 8.4.3.2 SCALE ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 8.4.3.3 SURFACE WIND ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 8.4.3.4 WAVES ASSOCIATED WITH FLOW OVER RIDGES AND MOUNTAINS . . . . . . . . . . . . 199 8.4.4 Volume flux in simple drainage flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 8.4.5 Main canyon mass fluxes and merging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 8.4.5.1 LIDAR DATA ANALYSIS AND CORRECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 8.4.5.2 VOLUME FLUX GROWTH AND THE ROLE OF TRIBUTARIES . . . . . . . . . . . . . . . . . . 205 8.4.5.3 THE MERGING OF DRAINAGE FLOWS FROM VALLEYS WITH DIFFERENT PHYSICAL CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 8.4.5.4 COMPARISON OF LIDAR OBSERVATIONS WITH OTHER MEASUREMENT METHODS IN COMPLEX TERRAIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 8.4.6 The role of remote and in-situ sensors in the study of elevated plumes during the 1984 CTMD experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 8.4.6.1 BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 8.4.6.2 LIDAR AEROSOL PLUME MAPPING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 8.4.6.3 COMPLEX TERRAIN PROCESSES AFFECTING PLUME TRANSPORT AND DISPERSION 209 8.4.6.4 INTERPRETATION OF ELEVATED PLUMES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 8.4. 7 Interpretation ofg round-based plumes during the 1980 ASCOT experiment . . . . . . . . . . 212 8.4.8 Remote-sensor observation of day/night transitions in complex terrain . . . . . . . . . . . . . . . 212 8.4.8.1 BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212 CONTENTS 8.40802 SODAR OBSERVATIONS OF NOCTURNAL INVERSION DESTRUCTION 0 0 0 .. o o o . . . 213 8.40803 LIDAR OBSERVATIONS OF MORNING FLOW REVERSALS . . . . . . . . . . . . . . . . . . . . 214 8.4.8.4 THE EVENING TRANSITION TO NOCTURNAL DRAINAGE IN A CONFINED VALLEY 215 8.4o8o5 THE EVENING TRANSITION AND THE EMERGENCE OF DRAINAGE FLOWS ONTO PLAINS ............................. 0... . . . . . . . . . . . . . . . . . . . . . . . . . . 216 805 The use of remote sensors in large-scale complex terrain flows ................. 0 . . . . . . . . 220 8.501 Large-scale drainage flows . 0.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 8.5.2 Denver Brown Cloud Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222 8o5o2.1 DOPPLER LIDAR OBSERVATIONS ...... o... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223 8050202 RASS OBSERVATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 806 Summary and future possibilities ...................................... 0 . 0 . . . . . . . . 226 Acknowledgments ................................................ 0 . . . . . . . . . . . . . . . . . 228 Chapter 9o The Role of Mountain Flows in Making Clouds -ROBERTMo BANTA 229 ABSTRACT ..................................... 0 ...... 0 . . . . . . . . . . . . . . . . . . . . . . . . . 229 901 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 9 02 Condensation and stability effects .................... 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 90201 Condensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 90202 Lifting profiles ............... 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 902.3 Stability effects on cloud forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 902.4 Interactional effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 903 Fog, stable clouds, and unstable snow clouds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236 9.301 Valley fog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236 9.302 Stable rain clouds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236 9030201 OROGRAPHIC STRATUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 9.3.2.1.1 Simple orographic flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 9.302.1.2 Microphysics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 9.30201.3 Blocking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 9.30201.4 Mountain-wave effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241 903.2.1.5 Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241 9.302.1.6 Other upslope flows ............................ 0 . . . . . . . . . . . . 242 9030202 INTERACTION WITH LARGER-SCALE PROCESSES ... 0 ............. 0........ 243 9.3.3 Stable snow clouds ...... 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244 9030301 OROGRAPHIC STRATUS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244 9030302 INTERACTION WITH LARGER-SCALE PROCESSES .................. o . o o . . . . 247 9.3.4 Unstable snow clouds .... 0 .................................... 0 . . . . . . . . . . . . 248 9.4 Unstable rain clouds . . . . . . . . . . . . . . . 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 9.4.1 Initiation mechanisms ... 0 ........... 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 9.401.1 DIRECT LIFTING TO THE LFC ....................... o . . . . . . . . . . . . . . . . . 250 9.40101.1 Potential instability release ............................ 0 . . . . . . 250 9.4.10102 Flashjlooding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 9.401.2 THERMALLY GENERA TED MOUNTAIN CIRCULATIONS .... o . . . . . . . . . . . . . . . . 254 9.4.1.2.1 Heat flux and soil moisture effects ................. 0 0 0... . . . . . . 256 9.401.2.2 Regional differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 9.4.1.2.3 Spatial and temporal distribution ................. 0 0 0... . . . . . . . 257 9.4.1.2.4 Isolated peaks and small ranges ......................... 0 0 0 0.. 258 9.4.1.205 Larger ranges of mountains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262