The Physics and Parameterization of Moist Atmospheric Convection

Transcription

1 The Physics and Parameterization of Moist Atmospheric Convection

2 NATO ASI Series Advanced Science Institutes Series A Series presenting the results of activities sponsored by the NATO Science Committee, which aims at the dissemination of advanced scientific and technological knowledge, with a view to strengthening links between scientific communities. The Series is published by an international board of publishers in conjunction with the NATO Scientific Affairs Division A Life Sciences B Physics C Mathematical and Physical Sciences D Behavioural and Social Sciences E Applied Sciences F Computer and Systems Sciences G Ecological Sciences H Cell Biology I Global Environmental Change Plenum Publishing Corporation London and New York Dordrecht, Boston and London Springer-Verlag Berlin, Heidelberg, New York, London, Paris and Tokyo PARTNERSHIP SUB-SERIES 1. Disarmament Technologies 2. Environment 3. High Technology 4. Science and Technology Polley 5. Computer Networking Springer-Verlag I The Partnership Sub-Series incorporates activities undertaken in collaboration with NATO's Cooperation Partners, the countries of the CIS and Central and Eastern Europe, in Priority Areas of concern to those countries. NATO.PCO.DATA BASE The electronic index to the NATO ASI Series provides full bibliographical references (with keywords and/or abstracts) to more lhan contributions from international scientists published in all sections of the NATO ASI Series. Access to the NATO-PCO-DATA BASE is possible in two ways: - via online FILE 128 (NATO-PCO-DATA BASE) hosted by ESRIN, Via Galileo Galilei, Frascati, Italy. - via CD-ROM "NATO-PCO-DATA BASE" with user-friendly retrieval software in English, French and German( WTV GmbH and DATAWARE Technologies Inc. 1989). The CD-ROM can be ordered through any member of the Board of Publishers or through NATO PCO, Overijse, Belgium. Series C: Mathematical and Physical Sciences-Vol. 505

3 The Physic~ and Parameterization of Moist Atmospheric Convection edited by Roger K. Smith University of Munich, Germany Springer-Science+Business Media, B.V.

4 Proceedings of the NATO Advanced Study Institute on The Physics and Parameterization of Moist Atmospheric Convection Kloster Seeon, Bavaria, Germany August 4-16, 1996 Co-Sponsored by the United States Office of Naval Research A C.I.P. Catalogue record for this book is available from the Library of Congress. ISBN ISBN (ebook) DOI / Printed an acid-free paper AII Rights Reserved 1997 Springer Science+Business Media Oordrecht Originally published by in 1997 No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without written permission from the.copyright owner.

5 CONTENTS Preface R.K. Smith Vll (a) MOIST CONVECTION Chapter I: Overview of atmospheric convection (K.A. Emanuel) Chapter 2: Thermodynamics of moist and cloudy air (R.K. Smith) 29 Chapter 3: The mesocale organization of deep convectionij-l. Redelsperger) 59 Chapter 4: Trade cumulus: observations and modelling (A.K. Betts) 99 Chapter 5: Convection in stratocumuius-topped atmospheric boundary layers (C.S. Bretherton) I27 Chapter 6: Discrete dry convective entities: I Review (B.R. Morton) I43 Chapter 7: Chapter 8: Discrete dry convective entities: II Thermals and deflected jets (B.R. Morton) Entrainment, detrainment and mixing in atmospheric convection (C.S. Bretherton) I75 2II Chapter 9: Momentum transport by organized convection (M. W. Moncrieft) 23I (b) PARAMETERIZATION OF MOIST CONVECTION Chapter 10: The Parameterization of deep convection (A.K. Betts) 255 Chapter II: The Arakawa-Schubert parameterization (D.A. Randall, P. Ding and D.-M. Pan) 28I Chapter 12: The mass flux approach to the parameterization of deep convection (D. Gregory) 297 (c) IMPLICATIONS OF CONVECTION FOR THE LARGE-SCALE FLOW Chapter 13: Equilibrium vs. activation control of large scale variations of tropical deep convection (B.E. Mapes) 321 Chapter 14: Quasi-equilibrium (D.A. Randall, D.-M. Pan P. Ding and D.G. Cripe) 359 Chapter 15: Boundary layer quasi-equilibrium (BLQ) (D.J. Raymond) 387 Chapter 16: Mutual adjustment of mass flux and stratification profiles (B.E. Mapes) 399

6 vi Chapter 17: Implications of convective quasi-equilibrium for the large scale flow (J.D. Neelin) 413 Chapter 18: The problem of convective moistening (K.A. Emanuel) 447 Chapter 19: Sensitivity of General Circulation Model perfonnance to convective parameterization (D. Gregory) 463 (d) SOME OBSERVATIONAL CONSIDERATIONS Chapter 20: Critical observations of convection - State of the art and a proposal (D.J. Raymond) 483

7 PREFACE The transport of heat, water and momentum by moist convection is of central importance in the atmospheric energy cycle and is fundamental to an understanding of the dynamics of the atmosphere, particular of the linkage between scales. It is especially important in the modelling of climate and the prediction of climate change where long model runs severely test the physical assumptions; and is of increasing importance in the study of pollutant transport in both the troposphere and lower stratosphere. However, the physical processes associated with moist convection and its interaction with the larger-scale flow are at best incompletely understood and their representation in atmospheric models still leaves much to be desired. There is an acute need to improve this situation in view of the enormous importance of a proper representation of moist convective processes in numerical prediction models on all scales and in climate models. This is particularly the case for weather prediction in the tropics; on time scales of more than a day or two at higher latitudes; in mesoscale models, including those concerned with the prediction of tropical cyclones; and in models that seek to represent the large-scale aspects of the tropical atmosphere, including the intraseasonal oscillation and the El Nino phenomenon. A comprehensive workshop on the cumulus parameterization problem was held on Key Biscayne, Florida in May 1991, a brief review of which was published by Emanuel and Raymond (1993)1. A monograph based on the state-of-art of the subject at about that time was produced by the American Meteorological Society with Emanuel and Raymond as co-editors2. The field of cumulus parameterization and the associated physics of convection has been moving rapidly since this last comprehensive summary of the field was put together. Major field programmes including The Azores Stratocumulus Experiment (ASTEX), The Tropical Experiment Mexico (TEXMEX) and The Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE) have added to our store of data on cloud processes, and new theoretical insights into the role of the boundary layer in governing deep convection and the stratocumulus break-up problem have been obtained. Accordingly the focus of the ASI was on the many new developments since the foregoing monograph was produced, although no attempt was made to ensure a complete review. This book is a collection of invited lectures given at an Advanced Study Institute funded by the North Atlantic Treaty Organization (NATO) with additional support provided by the United States Office of Naval Research (through its Marine 1 Emanuel K. A. and D. J. Raymond, 1992: Report from a workshop on cumulus parameterization, Key Biscayne, Florida, 3-5 May Bull. Amer. Meteor. Soc., 73, Emanuel K. A. and D. J. Raymond, 1993: The representation of cumulus convection in numerical models. Met. Monogr. 24, No. 46. American Meteorological Society, Boston, pp246. vii

8 viii Meteorology Program). The Institute sought to review our current understanding of moist atmospheric convection ranging from shallow trade-wind cumulus over the tropical oceans, to stratocumulus, and on to deep precipitating convection. Special interest was focused on the dynamical and radiative interaction between different types of convection and the large-scale environment in which it is embedded, and on ways to represent these complex interactions in numerical models. A range of cumulus parameterization schemes was covered and the advantages and limitations of particular schemes were discussed. Two new schemes based on the assumption of boundary-layer quasi-equilibrium were presented and their physical basis explained. It was noted that many parameterization schemes have been developed for conditions over the tropical oceans; however the effects of land surface conditions were given some prominence in the lectures also. Some questions that led to intensive debate were: What processes control where and when deep convection will occur? Is convection a result of low-level convergence, or is it a cause thereof? How can hypothesis pertaining to the interaction between deep convection and the large-scale flow be tested observationally? Definite answers to these and other questions remain elusive, but much progress was made in articulating the issues. There was much discussion about the issue of entrainment into clouds, a process which remains poorly understood, especially in the presence of vertical shear. The effects of convective momentum transport were addressed also and the boundaries of our current knowledge of this important subject were explored. The book is divided into four sections focusing on four broad themes: (a) covers the phenomenological aspects of moist convection; (b) discusses a range of cumulus parameterization schemes; (c) considers the implications of convection for the largescale flow and vice versa, and (d) concludes with a proposal for a future field experiment. It was impractical and unnecessary to avoid some overlap in the content of the lectures and, in the interest of their speedy publication, no attempt has been made to remove this overlap in the chapters of the book. The written version of each lecture was reviewed by at least one other lecturer. The organization of the ASI was a team effort and I wish to thank all those who helped so much in this including: the other members of the Scientific Organizing Committee, Martin Miller and Dave Raymond; Kerry Emanuel, who gave much advice and support; the Local Organizing Committee, Angie Hahn, Sarah Jones, Lars Schade, Wolfgang Ulrich, and several students from the University of Munich; and the friendly and helpful staff at Kloster Seeon. The magnificent facilities at Kloster Seeon contributed much to the success of the meeting.

9 A special thanks goes to all the lecturers for giving their time to participate in the ASI, for their efforts in preparing their lectures including the written versions, and for their help with the editing process. Thanks are due also to all the ASI participants for their involvement in the lectures, which led to stimulating discussions and made the ASI a particularly memorable event. The ASI would not have been possible without the generous financial support from the NATO Science Committee which is gratefully acknowledged. It was greatly enhanced by the financial support provided by the United States Office of Naval Research; this together with the personal support of Dr R. A. Abbey Jr. from this Office is gratefully acknowledged also. Finally I wish to thank Anna-Riitta Jii.rvinnen and Hilbert Wendt from the University of Munich who gave so much help in preparing the final manuscript of this book; Anna-Riitta typed Chapters 2, 6 and 7 and Hilbert, amongst other things, prepared many of the figures for these Chapters. ix Roger K. Smith Meteorological Institute University of Munich Munich, Germany Friday 22 August 1997