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TIGR
Thermodynamic Initial Guess Retrieval

Description of TIGR Available version of TIGR Ask for a TIGR databank

Description of TIGR

The Thermodynamic Initial Guess Retrieval (TIGR) data set, in its latest version, is a climatological library of about 2300 representative atmospheric situations selected by statistical methods from 80,000 radiosonde reports [Chédin et al., 1985; Achard, 1991; Chevallier et al., 1998]. Each situation is described by its temperature, water vapor and ozone profiles (40 levels from 1013 hPa to 0.05 hPa). The ozone profile is specified from the UGAMP ozone climatology [Li and Shine, 1995], taking into account the latitude, longitude and time of each situation archived in TIGR. For each atmospheric situation, a surface temperature is generated as the sum of the temperature of the atmosphere at the lowest level and a random number with zero mean and a standard deviation of 4K. Finally, the situations in TIGR are stratified by a hierarchical ascending classification into five airmass types (tropical, temperate -midlat1-, cold temperate and summer polar -midlat2-, Northern Hemisphere very cold polar -polar1-, winter polar -polar2-), depending of their virtual temperature profiles [Achard, 1991; Chédin et al., 1994].
Clear sky transmittances, brightness temperatures and Jacobians (partial derivatives of the brightness temperature with respect to temperature, gas concentration for H2O, O3, CO2, N2O CO, CH4, etc... surface temperature and emissivity, etc.) for all channels of the instrument considered (TOVS, AIRS, IASI, AMSU, etc.) are then computed for each situation archived using the fast line-by-line 4A model in its latest version 2000 [Scott et al., 2002]. For TOVS, for example, calculations are performed [Chédin et al., 1985] for 10 viewing angles, between 0°(nadir) and 60°(the maximum value for angular scanning), for 19 values of surface pressure (up to about 500 hPa) for elevated terrains, and for two surface types: land and sea. Over sea, the surface emissivity varies with frequency and viewing angle according to Masuda et al. [1988] and Matricardi and Saunders [1999]. A fixed emissivity of 0.98 is specified for all channels over land, except for the channels at 4.3 micron, for which the emissivity is 0.97. Minor gas concentrations have been given fixed values, close to the mean values observed during the lifetime of NOAA-10. These values are : 355 ppmv for CO2, 308 ppbv for N2O, 1.8 ppmv for CH4 and 100 ppbv for CO. These results are also stored within the TIGR dataset. It is worth pointing out that TIGR is not primarily sensitive to the relative quality of the radiosoundings sampled in it but only to their representativeness and plausibility. In fact, it is sensitive to the quality of the relationship between thermodynamic quantities and radiative quantities. For that reason, great attention has been paid to the validation of the 4A model.

Available version of TIGR

The current distributed version TIGR2000 is an heritage of two versions : TIGR 2 and TIGR 3. The current version is here.

• TIGR 2 : 1761 atmospheres
  • 322 tropical
  • 388 mid-latitude 1
  • 354 mid-latitude 2
  • 104 polar 1
  • 593 polar 2
• TIGR 3 : 2311 atmospheres
  For a better representation of the tropical region, the tropical airmass has been changed from 322 to 872 profiles with more humid profiles (content > 3cm).
  • 872 tropical
  • mid-latitude and polar same as TIGR 2
  
  
  Fig.1 Histograms (40 classes) of the water vapor content of the extended tropical class of TIGR (TIGR 3) (top) and in the preceding TIGR 2 tropical class (bottom).
• TIGR 2000 : 2311 atmospheres
  To have a better representativity of the variability of ozone profiles than in the TIGR 2 database, the multi-year three-dimensional UGAMP climatology is now used.
  The differences are shown in the figures below.
  

  differences in o3 mean profile	differences in stdv profile
  (click on any of the above figures to enlarge it.)

• In addition, the TIGR 2000 version includes modifications on the water vapor profiles in the upper part of the atmosphere. In previous versions, the water vapor profiles in the upper part of the atmosphere were extrapolated using a constant value of 2.5e-05 g/g. Due to the fact that the new generation of IR sounder (high spectral resolution) like AIRS or IASI are more sensitive to upper level water vapor, especially in the 6.3 microns band, a better characterization of this profile for pressures less than 100 mb turned out to be necessary. For that, use has been made of the Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS) measurements (ATMOS version 3.1 data file formats - FWI 2/15/00).
  NB: The distributed version of the TIGR 2000 dataset (see below) is labelled 'Tigr2000_v1.1.tar'.
  
  

  The differences are shown in the figures below.
  differences in mean water vapor profile	differences in standard deviation of the water vapor profile
  differences in mean water vapor profile (zoom in)	differences in standard deviation of the water vapor profile (zoom in)
  (click on any of the above figures to enlarge it.)

Ask for the TIGR databank

The TIGR Databank is available as a freeware product but only for academic use and to those wishing to use the code for scientific research.
For a purpose other than a research or academic use please, contact-us.

To obtain a copy of the latest release of the databank, please complete the Licence Agreement by way of the on-line registration form. The Licence Agreement must be printed, signed and either faxed to +33.1.69.33.52.18 or sent to :

Dr. Noelle.Scott
Laboratoire de Météorologie Dynamique
Analyse du Rayonnement Atmosphérique
Ecole Polytechnique
Route départementale 36
91128 PALAISEAU CEDEX
FRANCE

On receipt of the Licence Agreement, the TIGR Databank will be made available.

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