Assessment of the Marine Observing System (ASMOS): Final Report

The definition of user requirements for the marine observing system is not a simple process. When asked, users have a tendency to ask "what can you provide?" or reply "as much as possible". Sometimes there is not enough information or data at the outset to do more than guess at the requirement. There are also pragmatic considerations. The importance of well characterised user requirements is easy to demonstrate. Those observing programs that have clear user requirements, particularly when those requirements can be stated simply, have prospered in the developing Global Climate Observing System (GCOS). Examples are the Argo program of ocean profiling floats and the drifting buoy network for observing sea surface temperature (SST). The clear definition of user requirements, and in particular the point at which a particular component of the GCOS can be considered complete, has allowed funding agencies to target resources at these projects and to easily report back on the impact that their funding has had. Even more desirable is the ability to prove that the investment is reaping rewards, for example that the money spent on operational satellite programs can be demonstrated to have improved weather forecasting in a quantitative way. The assessment of observing system adequacy against user requirements is made easier when the contributing observing platforms sample regularly and predictably and the characteristics of the uncertainty in the components of the measurement system is known. Particularly difficult to assess are observing systems made up of a large number of observing platforms, where the characteristics of those observing platforms are variable and sometimes unknown, where details of the sampling is unpredictable, where the spatial and temporal characteristics of the observed field are poorly known and the signal to noise ratio is not particularly favourable. These are the characteristics of the marine surface meteorological observing system, currently made up of contributions from the JCOMM Voluntary Observing Ships (VOS) program managed by the Ship Observations Team (SOT, http://www.jcommops.org/sot/), a network of moored and drifting buoys co-ordinated by the Data Buoy Co-operation Panel (DBCP, http://www.dbcp.noaa.gov/) and satellite observations. This report will consider only the in situ component of the marine surface meteorological observing system. It should be remembered that the satellite observing system contributes substantially to observations of SST, winds, cloud and precipitation. All of the satellite-derived parameters require in situ ground truth for calibration, validation or bias correction. Surface air temperature, humidity and heat fluxes are examples of parameters which cannot be derived with usable accuracy from space-based platforms