Table 1.
Improvements of GPT2 With Respect to GPT/GMF
| GPT/GMF | GPT2 | |
|---|---|---|
| NWM data | Monthly mean profiles from ERA-40 (23 pressure levels): 1999–2002 | Monthly mean profiles from ERA- Interim (37 levels): 2001–2010 |
| Representation | Spherical harmonics up to degree and order 9 at mean sea level | 5° grid at mean ETOPO5-based heights |
| Temporal variability | Mean and annual terms | Mean, annual, and semi-annual terms |
| Phase | Fixed to January 28 | Estimated |
| Temperature reduction | Constant lapse rate − 6.5°C/km assumed | Mean, annual, and semi-annual terms of temperature lapse rate estimated at every grid point |
| Pressure reduction | Exponential based on standard atmosphere | Exponential based on virtual temperature at each point |
| Output parameters | Pressure (p), temperature (T), mapping function coefficients (ah, aw) | p, T, lapse rate ( dT), water vapor pressure (e), ah, aw |