Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical. With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output where shown in the diagrams. At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.
Derivation of 2m Temperatures
Model output of 2m temperature is a diagnostic. It is not a direct output from the atmospheric model. Forecast screen level variables are not directly evaluated but are determined via knowledge of the the lowest model level temperature (at 10m) and the "skin" temperature of the underlying surface. In turn the skin temperature is determined via the land surface scheme HTESSEL, or the lake surface scheme FLake, or the sea-surface temperature (through NEMO).
Temperatures at 2m are then derived by interpolation between the forecast 10m temperature and the forecast surface skin temperature.
An urban tile incorporated into HTESSEL models the fluxes of heat, moisture and momentum allowing a more realistic representation the heat island effects of towns and cities. Tiles representing high and low vegetation incorporate the albedo effects of underlying snow cover.
FLake is currently not used directly in re-forecasts and consequently M-climate temperatures can be error prone over and adjacent to inland lakes, particularly if these are large (e.g. Lake Superior). This can affect Extreme Forecast Index(EFI) and Shift of Tails (SOT) values.
Users should assess the potential for deficiencies in low-level parameters and adjust as necessary.
Fig9.2-1: Values at the 2m level (e.g. temperature) are not taken from a model level as such but are computed via interpolation between skin temperature and the level of the lowest atmospheric model level (level 137). 2m dew point is derived from the humidity interpolated in a similar way. The nature of the interpolation profile used depends on other factors, such as wind speed.
Additional Sources of Information
(Note: In older material there may be references to issues that have subsequently been addressed)
- Read more on "Reducing surface temperature errors at coastlines".
- Read more on Bias in IFS.
(FUG Associated with Cy49r1)
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