GCOS GOOS WCRP/OOPC IX/3 

page 61 

Action: NWP centres and VOS operators should be reminded of the importance of collecting 

data in line with the GCOS Climate monitoring principles. The importance of VOS 

observations for the calculation of surface fluxes in regions away from flux reference sites 

should be stressed in revisions to the GCOS Draft Implementation Plan. 

Convergence of VOS and VOSClim  

Ideally all VOS observations would be of the quality aspired to by the VOSClim 

project. However, a significant minority of VOS observations are of poor quality and to some 

extent this undermines the usefulness of the remainder of the better quality observations. For 

example, SST observations from VOS are assimilated into SST analyses with a relatively low 

weight. This is partly because some VOS SST reports contain gross errors that could have a 

serious adverse effect on the analysis. Numerical Weather Prediction (NWP) centres therefore 

prefer to rely on SST reports from drifting buoys, which contain fewer gross errors but are 

prone to drift with time (potentially causing problems with large quantities of biased data in 

data sparse regions). VOS reports are therefore given a low priority by NWP centres and 

there is little incentive to improve the quality as little use is made of the reports. Demand from 

the NWP community is therefore shifting from VOS to alternative data sources. In the past 

the requirements of the NWP and climate researchers have to a large extent coincided, but 

more recently there have been moves by NWP centres to develop methods of targeting 

observations in  sensitive areas  for forecasting in order to reduce costs and improve forecasts. 

In addition new initiatives such as the Network of European Meteorological Services 

(EUMETNET) Composite Observing System (EUCOS) (http://www.eucos.net/) and its 

surface marine programme (E SURFMAR) are addressing their efforts to producing better 

quality NWP forecasts over Europe. As a consequence National Met Services are likely to re 

focus their VOS and buoy resources to meet the demands of NWP, possibly at the expense of 

climatological requirements7. The importance of VOS for climate is that ships provide a wide 

range of parameters from which the four components of the heat budget can be calculated 

(long and shortwave radiation, sensible and latent heat flux). Whilst some moored buoys 

provide similar information, typically alternative systems provide a subset of the information 

required for climate studies, concentrating on the variables most important for NWP, such as 

pressure and SST and possibly winds and air temperature. Limited automatic systems have 

been installed on VOS providing similar information to that obtained from a drifting buoy. 

The needs of the NWP and climate researchers for VOS data appear to be diverging. 

However, both communities would be well served by a smaller number of reliably high 

quality VOS providing a full range of meteorological variables. This would be supplemented 

for NWP by information from other systems such as the buoy network, satellites and 

radiosondes. The VOSClim project, although much smaller in size, provides a possible model 

for a future transition to make the VOS a high quality data system. Dialogue between the 

NWP and climate communities is limited, especially when one considers that many National 

Meteorological Agencies have both NWP and climate responsibility. Improving this dialogue 

7

The UK Met Office held a "User forum for observations" in May at which participants were invited to 

present their requirements and priorities for observations collected by the Met Office. We are now 

invited to submit our requirements for VOS sampling, and we urgently need to define requirements in 

terms of numbers of observations and target accuracies for basic meteorological variables rather than 

mean flux values. Until this is done our requirements cannot easily be incorporated into observing 

system design either by the Met Office or other Meteorological Agencies.

Action: OOPC should urgently convene a small taskgroup to define VOS sampling and accuracy 

requirements for basic meteorological variables to meet surface flux uncertainty targets. ????? to 

report by end July ??????