Advice on instrument monitoring by national weather services

by Leanne Avila — last modified Oct 01, 2015 08:51 AM Contributors: fsmith

Please see the **NWP SAF monitoring website** for a comprehensive list of websites with monitoring results from NWP centres and much further interesting information.

Discussion of satellite radiance monitoring at NWP centres

At the ATOVS workshop at ECMWF in 1999 agreement was reached on what should be monitored on external websites for ATOVS.

Mean and standard deviation of Observed - Background and bias corrected Observed - Bckground for the regions 90N-70N, 70N-20N, 20N-20S, 20S-70S, 70S-90S. Ideally monitoring would also be presented separately for sea, land and sea ice. Some centres might choose to monitor all data and data following quality control but some centers only monitor data after quality control. In the latter case what the monitoring looks like may depend very much on effect of the quality control. For example some recent data problems have not been visible in every centre's monitoring because in some centre's monitoring the bad data is already excluded whereas in another centre's monitoring it is still included. Therefore centres were urged to make it very clear what quality control and data selection they used in producing their monitoring reports. The length of time shown in monitoring plots varies from one month to two years. Again some centres offer a choice of a short and long time period plot. A minority of websites also included scan dependent bias plots. Some websites average data over 24 hours, others 6 hours and again some offer a choice.

The format of plots varies but the main problem in comparing them is taking account of the variations in paragraph above. Broadly speaking though it should be possible to achieve an "observation-forecast" standard deviation of difference for a tropospheric sounding channels after bias correction and appropriate quality control to under 0.15 K with negligible bias. Near surface and upper tropospheric and stratospheric sounding channels will fit much less well. Near surface channels fit will depend very much on choice of surface emissivity scheme and cloud detection and quality control, but will probably be of order 1 K standard deviation. Stratospheric channels will have a rising standard deviation of fit with increasing altitude, reaching several kelvin for channels peaking above 10 hPa. If any centres results are very far from these values it may be a cause for concern.

Channel selection for IASI monitoring at NWP centres

The NWP WG recommends that detailed NWP monitoring statistics for IASI radiances should be made publicly available on the monitoring websites for at least the following channels, in order to allow better intercomparison of monitoring results (see action DA/NWP-12 at ITSC-16 and recommendation DA/NWP-13 at ITSC-17). The list of channel and wavenumbers is as follows (the channels should be available in all the different channel selection sets disseminated in various parts of the world):

51 - 657.50 cm-1
92 - 667.75 cm-1
212 - 697.75 cm-1
246 - 706.25 cm-1
345 - 731.00 cm-1
347 - 731.50 cm-1
350 - 732.25 cm-1
381 - 740.00 cm-1
1509 - 1022.00 cm-1
1884 - 1115.75 cm-1
2239 - 1204.5 cm-1
2889 - 1367.00 cm-1
3029 - 1402.00 cm-1
3053 - 1408.00 cm-1
3582 - 1540.25 cm-1
5405 - 1996.00 cm-1
6985 - 2391.00 cm-1
6997 - 2394.00 cm-1

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Edited by Fiona Smith on Oct 01, 2015 08:51 AM