W O R L D M E T E O R O L O G I C A L O R G A N I Z A T I O N INSTRUMENTS AND OBSERVING METHODS R E P O R T No. 67 WMO SOLID PRECIPITATION MEASUREMENT INTERCOMPARISON FINAL REPORT by B.E. Goodison and P.Y.T. Louie (both Canada) and D. Yang (China) WMO/TD - No. 872 1998 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. This report has been produced without editorial revision by the WMO Secretariat. It is not an official WMO publication and its distribution in this form does not imply endorsement by the Organization of the ideas expressed. FOREWORD The WMO Solid Precipitation Measurement Intercomparison was started in the northern hemisphere winter of 1986/87. The field work was carried out in 13 Member countries for seven years. The Intercomparison was the result of Recommendation 17 of the ninth session of the Commission for Instruments and Methods of Observation (CIMO-IX). As in previous WMO intercomparisons of rain gauges, the main objective of this test was to assess national methods of measuring solid precipitation against methods whose accuracy and reliability were known. It included past and current procedures, automated systems and new methods of observation. The experiment was designed to determine especially wind related errors, and wetting and evaporative losses in national methods of measuring solid precipitation. The aim was to derive standard methods for adjusting solid precipitation measurements and to introduce a reference method of solid precipitation measurement for general use to calibrate any type of precipitation gauge. The report is a consolidation of data and information from the most challenging intercomparison organized by WMO so far to determine the in situ performance characteristics of instruments. Various types of national gauges were compared at 26 test sites in different climatic regions during at least 5 winter seasons against a commonly agreed reference design which was not previously used internationally. According to the goal of the test, the magnitude of the systematic errors in the measurement of solid precipitation is now clearly documented. This is very important for research in the field of climate change. Furthermore, methods for adjusting current and historical archive data have been derived which Members can test and, if needed, adapt to their own equipment and conditions. Although this intercomparison provides valuable information on how best to improve the measurements of not only solid precipitation but also of rain, one must continue to address the problem of determining the required algorithm for correcting data containing systematic errors to which all measurements may be subject. Specific attention should be given to identification of problems in measuring precipitation with automatic gauges. I should like to place on record the gratitude of CIMO to the managements, the national Project Leaders, the numerous scientists, and the operational staffs of all participating Members which were actively involved in this lntercomparison. The contributors came not only from the national services but also from other institutions that operated some of the test sites. I also should like to acknowledge the significant work done by the members of the International Organizing Committee (IOC) responsible for the preparation and proper conduct of the trial as well as for determining the best procedures for evaluation of the results and their presentation. Finally, I express my great appreciation to Dr. B.E. Goodison (Atmospheric Environment Service of Canada), the Chairman of the IOC and the Project Leader of the whole Intercomparison for his dedicated work and his efforts in bringing together all the national data needed for this report and for ensuring that they be evaluated and presented in the very clear manner that can be seen in this comprehensive report. In addition to this I would like to thank the staff of AES involved in this work for the significant support they provided in the evaluation of national test results and for the preparation of this report. I am confident that Members of WMO and others will find this report very useful, especially for improving the measurement of solid precipitation. It should contribute to the homogeneity of national data sets so that a better regional and global compatibility of the long-term data series might be achieved. (Dr. J. Kruus) President of the Commision for Instruments and Methods Observation (B L A N K P A G E) TABLE OF CONTENTS PAGE ACKNOWLEDGEMENTS EXECUTIVE SUMMARY i CHAPTER 1 BACKGROUND 1 1.1 INTRODUCTION 1 1.2 HISTORY OF PRECIPITATION MEASUREMENT INTERCOMPARISONS 1 1.3 HISTORY OF DFIR 5 1.4 THE WORKING NETWORK REFERENCE GAUGE 5 1.6 CONCLUSIONS 6 CHAPTER 2 METHODOLOGY 7 2.1 INTRODUCTION 7 2.2 ORGANIZATION OF THE INTERCOMPARISON 7 2.3 DATA COLLECTION AND OBSERVATION PROCEDURES 9 2.4 DATA ANALYSIS 12 CHAPTER 3 SUMMARY DESCRIPTION OF SITES, INSTRUMENTS 17 AND DATA ARCHIVE 3.1 SUMMARY OF SITE DESCRIPTIONS AND INSTRUMENTS 17 3.2 SUMMARY OF DATA ARCHIVE 17 CHAPTER 4 RESULTS AND DISCUSSION 25 4.1 INTRODUCTION 25 4.2 SITES AND DATA SOURCES 25 4.3 METHODS OF DATA ANALYSIS 25 4.4 RUSSIAN TRETYAKOV PRECIPITATION GAUGE 28 4.5 HELLMANN GAUGE 31 4.6 CANADIAN NIPHER SNOW GAUGE 34 4.7 NWS 8” STANDARD NON-RECORDING GAUGE 37 4.8 SUMMARY 39 4.9 DISCUSSION 46 PAGE CHAPTER 5 AUTOMATION OF WINTER PRECIPITATION 51 MEASUREMENTS 5.1 INTRODUCTION 51 5.2 CANADA 51 5.3 FINLAND 53 5.4 GERMANY 55 5.5 JAPAN 55 5.6 SUMMARY 57 CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS 58 6.1 CONCLUSIONS 58 6.2 RECOMMENDATIONS 59 CHAPTER 7 DEMONSTRATION AND IMPLEMENTATIONS OF THE 61 RESULTS 7.1 INTRODUCTION 61 7.2 CANADA: ADJUSTMENT OF PRECIPITATION ARCHIVE FOR THE 61 NORTHWEST TERRITORIES (NWT) 7.3 DENMARK: AN OPERATIONAL SYSTEM FOR CORRECTING 65 PRECIPITATION FOR THE AERODYNAMIC EFFECT 7.4 GERMANY: APPLICATION OF PRECIPITATION CORRECTION, 68 GERMAN METEOROLOGICAL SERVICE, BUSINESS UNIT HYDROMETEOROLOGY 7.5 NORWAY: OPERATIONAL CORRECTION OF MEASURED 70 PRECIPITATION 7.6 U.S.A.: APPLICATIONS OF THE WIND-BIAS ASSESSMENTS TO 73 PRECIPITATION DATA IN USA AND GLOBAL ARCHIVES REFERENCES 77 BIBLIOGRAPHY 83 GLOSSARY 87 ANNEXES ACKNOWLEDGEMENTS The WMO Solid Precipitation Measurement Intercomparison has been successfully completed through the contribution, dedication and commitment of many individuals and agencies. The Intercomparison was unique, with 16 countries participating at over 25 sites. The tireless work of participants who established and operated sites over a number of years, analyzed the data and contributed to writing reports and papers is gratefully acknowledged. The people who had direct contact with the Organizing Committee are listed below. In addition, there were numerous observers at the experimental sites whose dedication to acquiring quality data was essential for the success of the Intercomparison. Thanks is extended to the agencies which provided staff to work on this study and who funded the establishment and operation of sites. I extend special thanks to my own agency, the Atmospheric Environment Service, Canada, for its support of this Intercomparison, especially for the special funding required to establish the digital data base for the study. Thanks are due to John Metcalfe for overseeing the preparation of this data base. The support of the President, Executive and members of CIMO throughout this Intercomparison is acknowl- edged. We would not have succeeded without their on-going guidance, questions and suggestions. Thanks to my colleagues on the International Organizing Committee of the Intercomparison: Boris Sevruk, Valentin Golubev, and Thilo Günther for their on-going support. The preparation of the report has been a major undertaking; it would not have been possible without the dedicated work of Paul Louie and Daqing Yang. I trust that it meets Members' expectations. Finally, I wish to extend special thanks to the WMO Secretariat who made sure that we stayed on course and addressed the issues. Klaus Schulze, and his predecessor Stephan Klemm, ensured our meetings were focussed and relevant; they brought their own special expertise to the problems being discussed; they made sure that all countries’ concerns were considered. The Intercomparison would not have succeeded without their guidance. Thank you. Barry Goodison Chairman, International Organizing Committee WMO Solid Precipitation Measurement Intercomparison. List of Participants Canada India Russian Federation USA Barry Goodison N. Mohan Rao Valentin Golubev Roy Bates Paul Louie B. Bandyopadhyay A. Simonenko Timothy Pangburn John Metcalfe Virendra Kumar H. Greenan Ron Hopkinson Col K.C. Agarwal Slovakia George Leavesley Miland Lapin Larry Beaver China Germany Clayton Hanson Daqing Yang Thilo Günther Sweden Albert Rango Ersi Kang Bengt Dahlstrom Douglas Emerson Yafen Shi Japan David Legates Masanori Shiraki Switzerland P. Groisman Croatia Hiroyuki Ohno Boris Sevruk Janja Milkovic Kotaro Yokoyama Felix Blumer WMO Yasuhiro Kominami Vladislav Nešpor Klaus Schulze Denmark Satoshi Inoue Stephan Klemm Henning Madsen UK Flemming Vejen Norway J. Fullwood Peter Allerup Eirik Førland R. Johnson Finland Romania Esko Elomaa Violete Copaciu Reijo Hyvonen Bengt Tammelin Asko Tuominen S. Huovila (B L A N K P A G E) 102 EXECUTIVE SUMMARY Introduction In the spring of 1985, the International Workshop on Correction of Precipitation Measurement was held in Zurich, Switzerland. One of the conclusions was a recommendation to the WMO to organize a Solid Precipitation Measurement Intercomparison. Such a study would also complement the WMO Pit Gauge Intercomparison for liquid precipitation (Sevruk and Hamon, 1984). The WMO Solid Precipitation Measurement Intercomparison was initiated after approval by CIMO-IX in 1985.