Reanalyses – A sharing of juicy tidbits* and gory details**

Andrew Klekociuk, Australian Antarctic Division* a choice or pleasing bit of anything, as gossip.** to tell all the small details about something that is unpleasant or interesting in a shocking way.

Outline

• A Brief Introduction to Reanalyses

• Uses• Potential Issues• Resources

Reanalysis = Retrospective Analysis

• Observations taken over a long time period are combined objectively with a model forecast to form time-series of fields representing the state of the system.

• Observations:– Atmosphere: pressure, temperature, wind

humidity.– Ocean: pressure, temperature, currents, salinity.

Reanalysis = Retrospective Analysis

• Model is kept constant over entire time period (though quality, density and type of observations can change).

• Differs from ‘operation analysis’ where the model may change.

• Data assimilation fills gaps.• The best resource –

http://reanalyses.org/

Key Reanalyses

• Atmosphere – http://reanalysis.org/atmosphere/overview-current-reanalyses

– ECMWF (European Centre for Medium-Range Weather Forecasts)

– NCEP/NCAR (National Centers for Environmental Prediction, National Center for Atmospheric Research)

• Oceans – http://reanalysis.org/ocean/overview-current-reanalyses

– NCEP CFSR (Climate Forecast System Reanalysis)

Applications

• Climate Model Intercomparisons

ACCESS = Australian Community Climate and Earth System Simulator

Bias with respect to ERA-40, averaged over 1980-2000

Potential Issues• Data Assimilation/Filtering/Interpolation

Methods: 4-dimensional variational analysis (4D-var) vs other approaches.

– Treatment of uncertainties (Gaussian)

• http://earth.esa.int/dragon/D5_L1_Elbern.pdf

Potential Issues• What observational data are used?

ERA-Interim: Dee et al., QJRMS 2011, Fig 10

ERA-Interim Ozone Measurements

ERA-Interim: Dee et al., QJRMS 2011, Fig 15

Total Column Ozone

ERA-Interim Surface Pressure

ERA-Interim: Dee et al., QJRMS 2011, Fig 17

Surface Pressure

Other Reanalyses of Interest

• MACC (Monitoring Atmospheric Composition and Climate) http://www.gmes-atmosphere.eu/d/services/gac/reanalysis/macc

• 20th Century Reanalysis http://www.esrl.noaa.gov/psd/data/20thC_Rean

Useful Resources

• Downloading data – local servers (e.g. NCI) vs remote servers (e.g. http://apps.ecmwf.int/datasets)

• Data viewers (e.g. Panopoly for HDF, GRIB, NetCDF -

http://www.giss.nasa.gov/tools/panoply)

• Web-based Reanalysis Intercomparison Tools (WRIT) - http://reanalyses.org/atmosphere/writ

• NCO Tools http://nco.sourceforge.net

Useful Resources

• Climate Atlases – e.g. MERRA (Modern Era Retrospective-analyses for Research Applications) http://gmao.gsfc.nasa.gov/ref/merra/atlas/menu.php

• Climate Explorer http://climexp.knmi.nl

• Climate Data Library http://iridl.ldeo.columbia.edu

• Climate Reanalyser http://cci-reanalyzer.org

• Local Resources