1. 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.

2. Outline A Brief Introduction to Reanalyses Uses Potential Issues
Resources

3. 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.

4. 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 –

5. Key Reanalyses
Atmosphere –
ECMWF (European Centre for Medium-Range Weather Forecasts)
NCEP/NCAR (National Centers for Environmental Prediction, National Center for Atmospheric Research)
Oceans –
NCEP CFSR (Climate Forecast System Reanalysis)

6. Applications Climate Model Intercomparisons
Bias with respect to ERA-40, averaged over
ACCESS = Australian Community Climate and Earth System Simulator

7. Potential Issues
Data Assimilation/Filtering/Interpolation Methods: 4-dimensional variational analysis (4D-var) vs other approaches.
Treatment of uncertainties (Gaussian)

8. Potential Issues What observational data are used?
ERA-Interim: Dee et al., QJRMS 2011, Fig 10

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

10. Total Column Ozone

11. ERA-Interim Surface Pressure
(a) RMS departures and (b) daily counts for surface pressure observations (hPa) assimilated in ERA‐Interim and ERA‐40, for the Northern Hemisphere. Solid curves are 3‐month running averages, and lightly shaded dots show daily values. ERA‐Interim background departures are shown in red, analysis departures in blue, and background and analysis departures for ERA‐40 are shown in black. Gaps in 3‐monthly averages occur whenever data are missing for at least one day. (c, d) are as (a, b), but for the Southern Hemisphere.
ERA-Interim: Dee et al., QJRMS 2011, Fig 17

12. Other Reanalyses of Interest
MACC (Monitoring Atmospheric Composition and Climate)
20th Century Reanalysis

13. Useful Resources
Downloading data – local servers (e.g. NCI) vs remote servers (e.g.
Data viewers (e.g. Panopoly for HDF, GRIB, NetCDF -
Web-based Reanalysis Intercomparison Tools (WRIT) -
NCO Tools

14. Useful Resources
Climate Atlases – e.g. MERRA (Modern Era Retrospective-analyses for Research Applications)
Climate Explorer
Climate Data Library
Climate Reanalyser
Local Resources