WORLD METEOROLOGICAL ORGANIZATION WORLD METEOROLOGICAL ORGANIZATION TECHNICAL NOTE No. 2 TECHNICAL NOTE No. 153 METHODS OF OABSERVATION AT SEA THE USE OF SATELLITE IMAGERY IN TROPICALPART I – SEA CYCLONE SURFACE TEMPERATURE ANALYSIS WMO-No.WMO-No. 26. 473 TP. 8 Secretariat of the World Meteorological Organization – Geneva – Switzerland THE USE OF SATELLITE IMAGERY IN TROPICAL CYCLONE ANALYSIS Satellite cloud pictures of the infamous tropical cyclone of November 1970 that devastated coastal areas of East Pakistan. Nearly 300000 people were killed (see Frank and Husain, 1971). The pictures are from the polar-orbiting satellite ITOS-I. Times are approximately 0900 GMT. On 7 November (top picture), a tropical depression was forming over the southern Bay of Bengal. On 9 November, the intensifying cyclone was centred near 15°N, 87°E, moving slowly north~north-eastward. By 11 November, hurricane strength had probably been attained. The cyclone moved inland on the following day, 12 November (not shown), riding the crest of a high tide and accompanied by a six-metre storm surge. Despite the destruction, which was caused mainly by the enormous storm surge, the cyclone was not extremely intense. Sustained winds may have reached 100 kt (51 m S-l), with estimated minimum central pressure between 950 and 960 mb WORLD METEOROLOGICAL ORGANIZATION TECHNICAL NOTE No. 153 THE USE OF SATELLITE IMAGERY IN TROPICAL CYCLONE ANALYSIS U. D. C. 551. 507.362.2: 551. 515.2 Secretariat of the W orId Meteorological Organization .. Geneva . Switzerland 1977 © 1977, World Meteorological Organization ISBN 92 - 63 -10473 - 5 NOTE The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the World Meteorological Organization concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. CONTENTS Page Foreword ..... , .. , ... ,,.,.,, ... ,,, .. ,,.,,.,,.,,.,,,.,,.,,.,,, .. , .. , .. ,, .. ,. VII Summary (English, French, Russian, Spanish) ,."."., .. ",."."."""."., ... ,..... IX Chapter 1 - Introduction, ,,., .. ,, .. ,.,,.',.,, ..... ,.,,,.,,,,,., .. ,,,.,,, ... , . , , 1 Chapter 2 - Data from geostationary satellites .,..,..,,.,,,,.,.,,.,,...,....,,.,.,,.,,, 3 Chapter 3 - Factors affecting satellite picture interpretation , .. ".,.,."."., .. "." .. , .. ,. 7 3.1 Picture resolution and quality ,,.,,.'.,,, .. , .. , .. ,,., .... ,,,,.,,,, .. ,, .. ,,,,, 7 3,2 Sun angle and viewing angle .,,.,,.,,.,,.,, .. ,.,,,.,,., .. ,,.,,,.,,,, .. ,,,,., 9 3.3 Accuracy ofgeographical gridding ., .,,.,,.,, .. ,.,,.,, .. ,,.',.,, ... ,,, .. , .. ,., 13 3.4 Regional differences in storm climatology .,,.,,,,.,,.,, .. ,.,,.,,,.,, 15 3.5 Visible versus infra-red data ~ . 15 3.6 Diurnal oscillations . 16 Chapter 4 - Theoretical and observational considerations ,.".", .. ,.".,."., .. ,., .. '",. 17 Chapter 5 - The analysis technique ... ,.,,., .. ,,.,,.,,.,,.,.,,.,.,,.,,.,,.,, .. ,,,., 20 5.1 General , .. ,'.',.,,.,.,,,,, .. ,,.,.,,,,.,,.',.,,,., .. ,,,,., 20 5,2 The analysis of cloud features .,.,,,,.,, .. ,,.,,.,,,,,,.,,.,,.,,.,,.,, .. ,.,,,. 24 5,2.1 Cloud features used to estimate current cyclone intensity, ,.,,.,,,,., .. , .. , .. ,,.,, 24 5.2.2 Cloud features used to estimate future cyclone intensity , ... ,."."",., .. "" .. " 26 5.2.3 Initial tropical cyclone development, ,,.,,.,,.,,.,,.,,,,, .. ,,,,,.,,.,,,,,. 30 5,2,4 Common tropical cyclone patterns, .,,.,,,.,,,,,,,.,,.,,.,,.,, ... ,,,.,,,. 30 VI CONTENTS Page 5.2.5 The superstorm . 31 5.3 Intensity change curves ofthe model . 32 5.4 The classification procedure . 32 5.5 The forecast procedure . 34 5.6 The use of anhnated cloud sequences . 34 5.7 The use ofinfra-red data . 35 Chapter 6 - Accuracy of the technique 42 6.1 Accuracy ofintensity estimates . 42 6.2 Accuracy ofposition estimates . 42 6.3 Comments on cyclone motion . 43 Annex I Summary and outline of the rules 44 Annex II Data from polar-orbiting satellites 63 Annex III - The subtropical, or semi-tropical, cyclone ................................... 66 Anuex N - Daily satellite picture sequeuces for individual tropical cyclones 73 Refereuces 82 FOREWORD The introduction of meteorological satellites has brought many advantages, not least ofwhich is the ability to detect tropical stenns over those ocean areas which previously had to be considered as data~sparse regions. Not only do satellites enable tropical storms to be detected but they also permit their subsequent movementsto be followed and their arrival at coastal areas to be more accurately predicted. In recent years, therefore, a great effort has been made in developing systematic techniques for the use of satellite cloud pictures for providing infonnation for both the analysis of tropical cyclones and the forecasting of their intensity. One of the aims of the WMO Tropical Cyclone Project has been the production of a text on the use of satellite imagery for tropical cyclone analysis. The present Technical Note is the outcome of this work. I am confident that it will be of considerable value to all those whose responsibilities entail the provision of forecasts and warnings oftropical cyclones. I should like to thank alI who have contributed to the preparation of this publication and, in particular, the three experts from the U.S.A., Mr. Carl O. Erickson, Dr. Jay S. Winston and Mr. Vernon F. Dvorak, on whom the main burden ofediting the publication fell. • l'c ~.,.• ...... ~ .. D. A. Davies Secretary-General SUMMARY The purpose of this Technical Note is to provide detailed guidance in the interpretation of images oftropical cyclones obtained from meteorological satellites. The technique itself is presented in Chapter 5. The general narrative discussion in that chapter includes both the major concepts of the technique and some details· of its application. Illustrations are included. Annex I gives a summary of the rules. Meteorologists already familiar with satellite pictures, and having some prior knowledge oftheir interpretation, will pro;'ably need to refer only to Annex I. Introductory and background information is presented in Chapters I to 4. Annexes II, III and IV contain auxiliary material. People who are unfamiliar with satellite pictures should fmd those chapters helpful. Essentially, the technique is a system for classifying tropical cyclones and disturbances based on certain cloud patterns and measurable cloud features. The classification is closely related to cyclone intensity. An empirical model of tropical cyclone development and decay provides guidance for this classification. The cloud features emphasized in the technique are, to some extent, the tangible manifestations of thermal and wind conditions known to be influential in tropical cyclone development or non-development. Therefore the method, though largely empiricaL is supported by both observation and theory. The technique is a somewhat different and more advanced method than that presented in Chapter IV of WMO Technical Note No. 124 (Anderson and Veltishchev, 1973). Practice with satellite pictures is considered indispensable to mastery of the technique. This manual can serve only as an introduction and a guide. Over large areas of the tropical oceans, the satellite is almost the only source ofmeteorological infonnation. For such areas, the full use of the technique should prove highly advantageous. For those tropical regions fortunate enough to be covered by both satellite pictures and other types of meteorological data, the technique should still be useful. It will serve as one diagnostic indicator among others that may be available. RESUME La presente Note technique a pour objet de donner des indications et des directives dOtaillees pour l'inter­ pretation des images de cyclones tropicaux obtenues au moyen de satellites meteorologiques. C'est dans Ie chapitre 5 que ron trouvera une description de la technique proprement dite, avec un expose de 8es principes essentiels et des precisions sur son application pratique. Cette description comporte des illustrations. L'Annexe I resume les diffe­ rerrtes regles aobserver; les meteorologistes qui ont deja pu se familiariser avec les images satellitaires et qui ont deja des notions de la fayon dont il convient de ~es interpreter n'auront d'ailleurs probablement besoin que de se referer acette annexe. Les chapitIes 1 a 4 contiennent une breve introduction ainsi que divers renseignements d'ordre general. Quant aux Annexes II, III et IV, elles contiennent des renseignements accessoires qui rendront tres certainement service aux lecteurs mains familiarises avec les images de satellites. La technique dOcrite dans la presente Note est en fait une methode de classification des cyclones et des perturbations tropicales fondee sur certaines configurations de TIuages et caracteristiques mesurables des nuages. Ce systeme de classification est etroit'ement fonction de l'intensite du cyclone. On trouvera aussi la description d'un modele empirique simulant la formation, Ie developpeplent et la disparition progressive d'un cyclone tropical, modele d'apres lequel il est possible de classer 1a perturbation dans telle ou telle categorie. Les caracteristiques de nuages sur lesquelles la technique est fondee sont, dans une certaine mesure, les manifestations concretes des conditions de temperature 'et de vent dont on sait qu'elles exercent une influence sur la fonnation d'un cyclone tropical. C'est pourquoi la methode