reanalyses

However, despite these problems, reanalyses provide the best gridded, self-consistent datasets available for model evaluation.

Simulation of observed arctic climate with the ACIA designated models 2009

Neither of the two reanalyses should be considered as "truth" but their differences provide some information about the probable magnitude of errors in them.

Simulation of observed arctic climate with the ACIA designated models 2009

Observational data and reanalyses for model evaluation

Simulation of observed arctic climate with the ACIA designated models 2009

The ECMWF reanalysis is only available for the period since 1979; the difference between the ECMWF and NCEP/NCAR reanalyses shown in Fig. 4.2 was calculated for the overlapping interval (1979 – 1993).

Simulation of observed arctic climate with the ACIA designated models 2009

The differences between the NCEP/NCAR and ECMWF reanalyses over land follow the NCEP/NCAR minus CRU differences in most, but not all, respects.

Simulation of observed arctic climate with the ACIA designated models 2009

A good opportunity for model evaluation is provided by reanalyses employing numerical weather prediction models to convert irregularly spaced observational data into complete global, gridded, and temporally homogeneous data (presently available for periods of several decades).

Simulation of observed arctic climate with the ACIA designated models 2009

The quality of precipitation climatologies for high latitudes derived from reanalyses is lower than that for temperature (or, e.g., atmospheric pressure).

Simulation of observed arctic climate with the ACIA designated models 2009

It is worthwhile noting that direct point-to-point and time-step-to-time-step comparison of a climate GCM output against observations, reanalyses, or another climate model simulation is not methodologically correct.

Simulation of observed arctic climate with the ACIA designated models 2009

Seasonal and annual mean differences in surface air temperature (a) between the NCEP/NCAR reanalysis and the CRU dataset for the period 1961 to 1990 and (b) between the NCEP/NCAR and the ECMWF reanalyses for the period 1999 to 1993.

Simulation of observed arctic climate with the ACIA designated models 2009

This section examines Northern Hemisphere circulation using the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalyses for the period from 1952 to 2003 [4].

Arctic atmosphere 2009