In an effort to facilitate studies of variations in the vertical structure of the atmosphere, a set of relevant parameters has been derived from soundings contained in IGRA. First released in 2008, the product was expanded to include a number of additional parameters in 2010-11. In addition to the reported temperatures and geopotential heights also available in IGRA proper, Version 2 of the IGRA-derived product contains the following variables:
- Virtual temperature, potential temperature, and virtual potential temperature at individual levels;
- Calculated geopotential heights at individual levels (to fill in missing heights in the original reports);
- Relative humidity, actual vapor pressure, and saturation vapor pressure at individual levels;
- Surface-to-500-hPa integrated column water vapor;
- Indicators of convective instability (convective available potential energy, convective inhibition, K Index, Lifted Index, Showalter Index, Total Totals Index);
- Pressure and height above the surface of the warmest temperature in the sounding, the top of the mixed layer, the lifting condensation level, the level of free convection, the level of neutral buoyancy, and the freezing level;
- Refractivity index at individual levels;
- Zonal and meridional wind components at individual levels; and
- Vertical gradients of temperature, potential temperature, relative humidity, and zonal and meridional wind components at individual levels.
The derived quantities are available at more than 1100 globally distributed stations. The records, which extend back as far as 1946, are updated daily and are available as station-by-station period-of-record files. It is hoped that these data will simplify the task of analyzing the observed characteristics of the planetary boundary layer, tropopause, and other atmospheric layers from a historical and large-scale perspective.