Leonard A. Barrie
Chief , Environment Division, World Meteorological Organization
The need for predictive models and comprehensive long-term global measurements of greenhouse gases, ozone
(also a greenhouse gas), ultraviolet radiation, aerosols, reactive gases and precipitation is critical to answering
many of the outstanding questions in climate change, ozone depletion, and air quality issues. Measurements
are divisible into two types, namely, those originating from non-satellite (ground-based, aircraft, sondes) and
those from satellite instrumentation. The non-satellite observations are made by a host of different networks
operated by various agencies and organizations. For greenhouse gases and ozone, the Global Atmosphere
Watch (GAW) program operated by members of the World Meterological Organization (WMO) and its
partners takes a lead in defining measurement protocols, quality assurance, and data exchange. In some cases,
such as CO2, CH4, and total column ozone, the GAW family of stations constitute most of the global long-term
network; in other cases, such as ozonesonde measurements, CFCs, and aerosol optical depth, there is a
substantive contribution from networks operated by non-GAW members or partners. Satellite observations are
an emerging force in atmospheric chemistry. Despite challenges in retrieval accuracy, long-term continuity
between different satellite instruments, and vertical resolution, there are tremendous benefits to be gained from
greater global coverage offered by satellites. The greatest impact of these two types of observations will be
achieved by integrating satellite and non-satellite measurements into a global atmospheric chemistry observing
system using models with data assimilation, as depicted in Figure 1. Developing this system is a major
challenge to the measurement and modelling community.
A basic requirement for meeting this challenge is ensuring that the fundamentals of measurement (calibration,
standardization of measurement protocols, adequacy of coverage, quality assurance, timely reporting, data
archiving, data analysis) are in place. The GAW program is an important mechanism for making this happen
through its calibration, quality assurance, and data centers, and through the modelling community of World
Meterological Organization members. The current state of the integrated observational system is reviewed in
this presentation.