april 2013 1 jörg trentmann, uwe pfeifroth, jennifer lenhardt, richard müller deutscher...
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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