WORLD METEOROLOGICAL ORGANIZATION GLOBAL ATMOSPHERE WATCH No. 162 WMO/GAW EXPERTS WORKSHOP ON A GLOBAL SURFACE-BASED NETWORK FOR LONG TERM OBSERVATIONS OF COLUMN AEROSOL OPTICAL PROPERTIES Davos, Switzerland, 8-10 March 2004 2005 WORLD METEOROLOGICAL ORGANIZATION GLOBAL ATMOSPHERE WATCH No. 162 WMO/GAW EXPERTS WORKSHOP ON A GLOBAL SURFACE-BASED NETWORK FOR LONG TERM OBSERVATIONS OF COLUMN AEROSOL OPTICAL PROPERTIES Hosted by the World Optical Depth Research and Calibration Centre (Davos, Switzerland, 8-10 March 2004) Edited by U. Baltensperger, L. Barrie and C. Wehrli WMO TD No. 1287 Foreword Suspended particulate matter in the atmosphere, commonly known as aerosol by the technical and scientific community, plays a role in climate change, air quality/human health, ozone depletion and the long-range transport and deposition of toxics and nutrients. Aerosols have many sources ranging from sea spray and mineral dust that are mechanically generated by wind at the Earth’s surface to sulphates, nitrates and organics produced primarily by chemical reaction of gases in the atmosphere producing non-volatile products that condense to form particles. In addition, semi-volatile substances such as certain herbicides and pesticides can simply condense on existing particles. Aerosols range in size from molecular clusters a few nm in diameter to dust and sea salt, which can be as large as tens of µm. The dynamics of aerosol production, transformation and removal that govern size distribution and composition are affected not only by clear air processes but also by interaction with clouds and precipitation. The complexity of aerosol processes in our environment is so great that it leads to large uncertainties in our quantitative understanding of their role in many of the major environmental issues listed above. For example, the last report of the Intergovernmental Panel on Climate Change (IPCC 2001) has identified atmospheric aerosols as the largest unknown in our understanding of climate forcing. At this stage of the early 21st century, a revolution is taking place in the approach to managing and utilizing global Earth observations. A single type of observational platform cannot, by itself, provide sufficient data to fulfil our current observational needs relative to climate and climate change. A combination of observations from surface-based (in situ and remote sensing), suborbital (aircraft and balloons), and satellites are needed. Further, the large gaps in existing global observing systems can only be filled, at least in part, by better coordination of the currently available variety of observations. One approach to better coordination is the global aerosol observing system. Thus, when the WMO Global Atmosphere Watch programme office in Geneva with the support of its Scientific Advisory Group for Aerosols approached us to support an international meeting to plan the development of a global surface-based observational network of aerosol optical depth, we endorsed the initiative with conviction. It provided an opportunity to give impetus to our organizations in supporting the World Optical Depth Research and Calibration Centre (WORCC, MeteoSwiss) and the global AERONET optical depth network (NASA). The workshop, held in March 2004 at WORCC in Davos, Switzerland, was attended by scientific researchers and instrument manufacturers from all parts of the world. This report is a big step toward a global AOD network coordinated by WMO. The network will be part of a global Earth observational system for aerosols that is firmly anchored in the quality assurance and calibration/validation activities proposed in this report. Gerhard Mueller Hal Maring MeteoSwiss NASA Headquarters Deputy Director Washington, DC Zurich, Switzerland USA i Table of contents Foreword........................................................................................................................................i Table of Contents..........................................................................................................................iii Editorial Note on Terminology Regarding Aerosol Optical Depth Measurement Community .........................................................................................................v Executive Summary......................................................................................................................vii Group Photo ..................................................................................................................................ix Strategies for Global Coverage and Application of Observations: Recommendations of Working Group I .....................................................................................................................1 Technical Coordination for Better Integration of a Global Network: Recommendations of Working Group II ...................................................................................................................7 EXPERT PRESENTATIONS......................................................................................................13 Introduction to GAW-CH (G. Müller)..............................................................................................15 IGACO and the Global Atmosphere Watch (GAW) (L. Barrie)..........................................................17 GAW’s SCIENTIFIC ADVISORY GROUP for AEROSOLS (U. Baltensperger) ..................................23 AEROSOL ROBOTIC NETWORK (AERONET) (B.N. Holben et al.) .....................................................26 BSRN Aerosol Optical Depth Activities (B. W. Forgan et al.)............................................................31 GAWPFR: A Network of Aerosol Optical Depth Observatioins with Precision Filter Radiometers (Ch. Wehrli) ............................................................................................................................36 Photons Summary (P. Goloub).....................................................................................................40 Aerosol Optical Depth Monitoring as Part of the Solar and Terrestrial Radiation Network (B. W. Forgan)............................................................................................................43 NOAA/SURFRAD and DOE/ARM AOT Measurements (J. Michalsky et al.)......................................49 AEROCAN Network Description and Associated Research Activities (A. Royer et al.) ..............54 Regular Observations of Column Aerosol Optical Properties in the Asian Part of Russia (S. M. Sakerin et al.) ......................................................................................61 AOD Measurements Of The German Weather Service- History, Status Quo, Some Results (M. Weller) ...............................................................................................................66 Aerosol Routine Observation Operated by the Japan Meteorological Agency (Tomoo OHNO) ......................................................................................70 Sunphotometry In The Netherlands And Suriname (W. Knap et al.)................................................72 Aerosol Optical Depth Measurements In Polar Regions (V. Vitale et al.) ..................................75 Temporal Variability of the Aerosol Optical Characteristics of the Atmosphere in the Russian Arctic (V. F. Radionov)......................................................................................................82 Experiences with and Current Status of AOD Measurements at the NOAA, Climate Monitoring and Diagnostics Laboratory (CMDL) and at its Baseline Observatories (E. G. Dutton) ....................................................................................................86 Acronym Soup MPL-NET, REALM, GLAS, CALIPSO (R. M. Hoff) ....................................................88 In Situ Aircraft Observations of Aerosol Optical Depths, Size Distributions and Radiative Properties (J. Haywood et al.) ...................................................................................................93 iii AEROCOM An Overview (M. Schulz et al.)...............................................................................................97 Real Time Measurements of Aerosol Optical Properties for Data Assimilation (B. McArthur et al.) ..........................................................................................................................................99 Overview of the Network for the Detection of Stratospheric Change (NDSC) (T. Deshler)....................................................................................................................... 105 Annex A: Agenda ...........................................................................................................................107 Annex B: List of Participants ..........................................................................................................111 Annex C: Network Discription Tables ...........................................................................................115 iv Editorial Note on Terminology Regarding Aerosol Optical Depth Measurement Community According to the AMS Glossary of Meteorology, optical thickness gives the line integral of extinction along any line of sight (e.g sunphotometer to the sun), while optical depth is optical thickness projected onto a vertical path. This definition is consistent with terminology used by the WMO Guide to Meteorological Instruments and Methods of Observation. In some contributed papers in this report,