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The Reading Assimilated Atmospheric Satellite Data - Version 1

• Brief model description

  The numerical forecast model which is the basis of the assimilation system is the HADAM3 version of the stratospheric configuration of the Unified Model (UM) [Cullen and Davies, 1991]. The tracer advection scheme used for the advection of ozone is a positive definite scheme based on the flux redistribution method of Roe [1985] with a superbee limiter [Cullen and Barnes, 1997].
  To approximate the atmospheric ozone photochemistry, the Cariolle [Cariolle and Deque, 1986] ozone photochemistry parameterisation was included in the UM.
  The radiation scheme in the HADAM3 configuration of the UM has been modified so the ozone used to calculate the radiative forcings are the assimilated ozone rather than climatology.

• Assimilation method

  The scheme used for the assimilation of the ozone data is the Analysis Correction (AC) method, which is described by Lorenc et al. [1991]. This scheme was used for real time meteorological analysis of the stratosphere at the Met Office from 1991 to 2000 as described by Swinbank and O'Neill [1994]. The analysis is performed by repeated insertion using a modified successive-correction scheme.

• Assimilated observational data sets

  UARS MLS profiles of ozone mixing ratios along track (version 4 'level 3AT' retrieved product) and UARS MLS temperature profiles.
  GOME Data Processor (GDP) version 2.7 operational level 2 total ozone column values, derived at the Deutschen Zentrum für Luft- und Raumfahrt (DLR).
  A full range of operational meteorological observational data was used in the assimilation in addition to the MLS and GOME observations. These are National Environmental Satellite Data and Information Service (NESDIS) temperature retrievals from the NOAA polar orbiters, radiosonde temperature, winds and relative humidity, aircraft temperature and winds, geostationary satellite cloud track winds and surface pressure observations.

• Recorded computed data (nature, unit)

  Ozone mass mixing ration (kg/kg).

• Spatial and temporal coverage of recorded data

  Global spatial coverage with lowermost model level at 1000 hPa and uppermost at 0.316 hPa.
  Temporal coverage from 10^th April to 30^th April 1997.

• Spatial and temporal resolution

  Arakawa B grid (nx = 96, ny = 73) with 2.5 deg resolution in latitude and 3.75 deg resolution in longitude.
  22 levels in the vertical corresponding to UARS vertical levels (approx. 6 UARS levels for every decade of pressure change) with approximately 1.6 km resolution in the stratosphere.
  Six-hourly temporal resolution.

• Validation procedure

  Analyses have been compared against independent observations (UARS HALOE profiles and TOMS total ozone measurements).
  Results:
  rms(HALOE - analysis) from 7% to 10% depending on the pressure level (lowest values are in the stratosphere)
  rms(TOMS - vertically integrated analysis) from 5% to 15% depending on latitude (highest values for latitudes South of 30 deg S, where there is a bias between GOME and TOMS).
  Quoted errors in HALOE and TOMS instruments: 5%.

• Data file format

  NetCDF (binary)

• Data volume, number of files

  83 files, 618 560 bytes each

• File names

  o3_qtgsyymmddhh.netcdf		where		yy = 97
  				mm = 04
  				dd = 10, 11, 12, ..., 29, 30
  				hh = 00, 06, 12, 18
  		from		yymmddhh = 97041006
  		to		yymmddhh = 97043018

• File contents

  3D ozone mass mixing ratio analysis at a given date and time (UTC). Date and time coding is given as o3_qtgs_yymmddhh.netcdf.
  
  Example: o3_qtgs_97042812.netcdf is O₃ analysis at 12 on 28 April 1997.

• References

  For a complete description of the work see:
  
  

  • Struthers, H., Brugge, R., Lahoz, W. A., O'Neill, A. and Swinbank, R., Assimilation of ozone profiles and total column measurements into a global general circulation model, submitted to J. Geoph. Res., 2002.
  
  Cited references:
  
  
  • Cariolle, D. and Deque, M., Southern Hemisphere Medium-Scale Waves and Total Ozone Disturbances in a Spectral General Circulation Model, J. Geophys. Res., 91, 10825-10846, 1986.
    
    
  • Cullen, M. J. P. and Barnes, R. T. H., A positive definite advection scheme, UM documentation paper N^o 11, Met Office, London Road, Bracknell, Berkshire, RG12 2SZ, UK, 1997.
    
    
  • Cullen, M. J. P. and Davies, T., Conservative split-explicit integration scheme with fourth-order horizontal advection, Q. J. R. Meteorol. Soc., 117, 993-1002, 1991.
    
    
  • Lorenc, A. C., Ballard, S. P., Bell, R. S., Ingleby, N. B., Andrews, P. L. F., Barker, D. M., Bray, J. R., Clayton, A. M., Dalby, T., Li, D., Payne, T. J. and Saunders, F. W., The Met Office Global 3-Dimensional Variational Data Assimilation Scheme, Q. J. R. Meteorol. Soc., 126, 2991-3011, 2000.
    
    
  • Roe, P. L., Large Scale Computations in Fluid Mechanics, Lectures in Applied Maths, 22, 162, 1985.
    
    
  • Swinbank, R. and O'Neill, A., A stratosphere-troposphere data assimilation system, Mon. Wea. Rev., 122, 686-702, 1994.
    
    

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