April 2013 1

Jörg Trentmann, Uwe Pfeifroth,

Jennifer Lenhardt, Richard Müller

Deutscher Wetterdienst (DWD)

Evaluation of EURO4M Reanalysis

data using Satellite Data

April 2013 2

• Compare monthly means from reanalysis with gridded data

• So far, we used SMHI Reanalysis (1990 to 1995) (+ ERA-I for

comparison)

• Calculate spatial differences, distributions, correlations

• Compare Anomalies, trends….

• Cloud Fraction

• Surface Solar Radiation

• Precipitation

• Surface Albedo

• Integrated Water Vapor

General Concept

April 2013 3

• 6-hourly SMHI reanalysis data temporally averaged to monthly

means on the 0.2 deg rotated grid (SMHI, 1990 to 1995); for radiation +

precipitation the 24 h minus 12 h forecasted accumulation was used

• Regridding of all data sets (sat, reanalysis) to a common regular lon-

lat grid (conservative remapping); spatial resolution 0.2 or 0.5 deg

(determined by the lowest-resolution data set)

• Generation of one file with all available monthly means and the

corresponding differences

• Preparation of standardized figures for comparison

General Concept

April 2013 4

Cloud Fraction

Cloud Fraction; July 1994

SMHI

Sat

ERA-I

SMHI –

EURO4M

SMHI –

ERA-I

ERA-I-

EURO4M

April 2013 5

Cloud Fraction

Cloud Fraction; July (mean, 1990 – 1995)

SMHI Reanalysis SMHI – SatDaten

April 2013 6

Cloud Fraction

Cloud Fraction; January

SMHI Reanalysis SMHI – SatData

• SMHI Reanalysis underestimates cloud

fraction in the Mediterranean

• Overestimation in January along the

Norwegian Coast

April 2013 7

Cloud Fraction

Cloud Fraction; Comparison with SYNOP

SMHI ReanalysisEURO4M SatData

• SMHI Reanalysis fits perfectly with

SYNOP Cloud Fraction, satellite data

overestimates SYNOP

• Cloud Fraction is a tricky parameter for

comparison, because of different

definitions etc

April 2013 8

Solar Radiation

Surface Solar Radiation; July

SMHI – SatDaten

SMHI Reanalysis

April 2013 9

SMHI Reanalyse

ERA-I – SatDaten

Surface Solar Radiation; July

ERA-Interim

April 2013 10

Solar Radiation; Mean

SMHI Reanalysis

SMHI –

Sat-

Daten

ERA-Interim

ERA –

Sat-

Date

n

• SMHI Reanalysis overestimates surface

solar radiation

• ERA-I compares better with Satellite Data

• Interannual Variability captured by

Reanalyses

April 2013 11

SMHI – EURO4M DataSet

Precipitation, Mean

SMHI Reanalysis

ERA – EURO4M

DataSet

April 2013 12

Precipitation, July

SMHI Reanalysis SMHI – EURO4M DataSet

ERA – EURO4M

DataSet

• Reanalyses overestimate precipitation

• Interannual variability captured by

Reanalyses

April 2013 13

Conclusions

•SMHI reanalysis compares well with SYNOP cloud fraction; underestimates satellite-derived cloud fraction in the Mediterranean

•Satellite-derived Cloud Fraction not well suited for evaluation; different definitions, viewing geometries etc.

•Surface Solar Radiation overestimated in SMHI Reanalysis (ERA is doing better); clouds too thin, wrong timing??

•Year-to-year variability captured

•Too much precipitation in SMHI (and ERA-I) reanalysis, especially in mountainous regions, e.g. Alps

April 2013 14

Next Steps

•Assess the surface albedo and integrated water vapor

•Develop additional quality measures / metrics, e.g., for the ability of the reanalysis to quantify anomalies / trends etc.

•How to perform the evaluation in the “space of the user”? What means “good enough”?

•How to communicate the results to possible users of reanalysis data? What are the consequences of these results?

April 2013