UK Met Office Correlative Analyses ---------------------------------- These data are sets of meteorological analyses on standard UARS pressure levels (from 1000 hPa to 0.316 hPa) on a 2.5 deg latitude by 3.75 deg longitude global grid. They are generated using the technique of data assimilation. The data assimilation system is a development of the scheme used at the UK Met Office for operational weather forecasting. These correlative analyses are based on operational meteorological observations (eg. radiosonde data and NOAA satellite temperature profiles), not UARS data. Further details are given by Swinbank and O'Neill (Monthly Weather Review, Vol 122, pp 686-702, 1994). Data Quality ------------ (applies to all versions) Temperature Pressure Est. RMS error Est. bias 1000 hPa 1.0K magnitude <0.3K tropopause 1.5K 100 hPa 1.0K magnitude <0.3K 10 hPa 1.0K magnitude <0.3K increasing to... 1hPa 2.0K magnitude <0.5K These are representative global-average errors, derived from the "Observation Processing Dataset" (or OPD), a dataset of observed and analysed values compiled as part of the assimilation process. Note that the figures do NOT take into account any bias in the original NOAA/NESDIS temperature retrievals. In general, the errors will be more than average at high latitudes and in winter. In particular, errors will be larger (perhaps 10-20K locally) during dynamically active periods such as stratospheric warmings. The errors will also be larger near the tropopause (200-300 hPa in mid-latitudes), as indicated in the table. Westerly and Southerly wind components Pressure Est. RMS error Est. bias 1000 hPa 6.0 m/s magnitude < 1 m/s tropopause 9.0 m/s 100 hPa 6.0 m/s magnitude < 1 m/s 10 hPa (8 m/s) 1 hPa (12 m/s) The wind errors in the troposphere are derived from OPD statistics for radiosondes, where available. The OPD gives very similar statistics for both westerly and southerly components. Since these errors are applicable to the two wind components independently, the RMS vector wind error will be approximately sqrt(2) times larger. The 10 hPa and 1 hPa figures (in brackets) are indicative estimates; they are consistent with differences found between the Met Office SSU analyses and the UARS correlative analyses. As with the temperature statistics these are global figures; errors will be larger in winter and dynamiclly active periods. Geopotential Height Pressure Est. RMS error Est. bias 1000 hPa (10 m) 100 hPa (20 m) 10 hPa (70 m) 1 hPa (100 m) These are rough estimates based on comparisons with our own SSU analyses and the NMC analyses. As with the temperature data, they do not take into account any systematic errors in the original NOAA/NESDIS satellite, which are used in all three sets of stratospheric analyses Vertical Velocity The vertical velocity is a diagnostic quantity produced from the numerical model used in the data assimilation system. This data is subject to considerable uncertainty, and should be used with caution. In our experience, the diagnostic appears to capture the broad-scale vertical circulation, but there are unrealistic features at smaller scales. Data Available -------------- Correlative analyses are available for 12 GMT daily from Oct 17th 1991 with a time lag of a 2-3 days. The near real-time assimilation data have version numbers V0001 or V0002; higher version numbers denote periods re-run at a later date. As a general rule, you should use the highest version number available. Most of the changes made to the assimilation system have not made large differences to the analyses. However, users should note the following significant changes:- 07-Dec-91 The original assimilation run has poor upper levels (p <~ 3 hPa), which was improved mainly by quality control changes (from 7 Dec to 16 Dec, use V0003 rather than V0001) 07-Jan-92 Polar filtering improved (V0006). 27-May-92 Polar filtering improved (V0001/2). This error gave very poor flow near the pole on a few occasions where there were strong winds at high latitudes. 26-Aug-92 Vertical velocities introduced. 22-Feb-93 Divergence damping increased. Gave less noisy temperatures at upper levels (p ~ 1hPa), with better fit to observations. As mentioned above, some periods have been re-run to overcome particular problems. Particular periods when you should avoid using versions V0001 or V0002 are:- 07-Dec-91 to 16-Dec-91 Use V0003 (see comments above) 07-Jan-92 to 11-Jan-92 Use V0006. Re-run due to particularly poor original run, as a results of cross-polar flow problem. Although re-run is improved, there are still large errors near the North Pole. 06-Sep-92 to 12-Sep-92 Use V0008. Problem in use of humidity data in Satellite soudings in original run. Use of the data --------------- The UK Meteorological Office retains the copyright and intellectual property rights of the data The Meteorological Office encourages the use of the data for bona fide research purposes but, if commercial use is to be made of the data, prior contact must be made with:- Branch Director (Sales) Meteorological Office Sutton House London Road Bracknell Berks RG12 2SY UK Phone: (+44) 344 85 6281 More information ---------------- For further details, please contact Richard Swinbank, or another member of the Middle Atmosphere Group at the UK Met Office. Richard Swinbank Meteorological Office London Road Bracknell Berks RG12 2SZ UK Phone: (+44) 344 85 4033 Internet: rswinbank@email.meto.govt.uk