Blocking index of the ERA40 re-analysis data

Topics

• Access
• Description
• Parameters
• Coverage, spatial and temporal resolution
• Data quality
• Contact person
• References
• Data citation and License

Access

UNRESTRICTED:

• Get blocking index data via FTP

RESTRICTED: This link to the data set is only available for a restricted user group.  The data set is only accessible in CEN/MPI net or accessible from external nets with a customer account.  Please contact ICDC if you would like to access this data from outside the network.

• Data access via file system: /data/icdc/climate_indices/blocking_index_era40

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Description

A blocking analysis was performed for the ERA40 re-analysis (Uppala, 2003) from the 500hPa geopotential in 6-hourly resolution with two different methods:

1. Blocking index employing the method of Tibaldi and Molteni (Tibaldi, 1990)

Every longitude (for ERA40: resolution T106, 320 values) is analysed separately. Three zonal bands of the following latitude ranges are relevant: 78.75+-3.75, 60+-3.75 and 41.25+-3.75 degrees. All data within these bands are considered, separately for the northern and the southern hemisphere. A longitude is considered blocked if the geopotential in a mid-latitude region (around 60 deg) is higher than in a corresponding region nearer to the equator (around 41.25 deg) as well as much higher than in a corresponding poleward region (around 78.75 deg, i.e. the gradient is above 10m/deglat). The single necessary modification to the original method is to the delta interval (Tibaldi, 1997) due to different data resolution. The analysis is done from 1.1.1958 00UTC to 31.12.2001 18UTC. This is not the whole ERA40 period, but only the completely available years.

2. Tibaldi-Molteni method with modifications (Schalge et al. 2011)

The Tibaldi-Molteni method was modified to reduce the results to synoptically
relevant blocking events.
The following modifications are realised:

1. Instead of fixed distances every combination of latitudes within the delta intervals is permitted.
2. Only regions with a geopotential of above the 70% percentile (for the whole latitude) in the mid latitude band at this time are taken into account.
3. Blocked regions separated by a zonal distance less than 10 deg are merged (the gap is closed by setting the originally unblocked regions to blocked and the GHG to 0.000001, GHG=geopotential height gradient)
4. Blocked regions with a zonal width of less than 20 deg are removed.
5. Events with a duration of less than 3 days are removed.

The columns of the provided ASCII data correspond to the longitudes (320 values, start: 0.0, increment 1.125), the rows to the time steps (64284 values, start: 1.1.1958 00UTC, increment 6 hours).

This was a CLISAP P2 project.

Last update of data set at ICDC:

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Parameters

Parameters of the blocking index data set

Name	Unit
Value GHGS	gpm/gradlat
Blocking yes (1) / no (0) Mask	-

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Coverage, spatial and temporal resolution

Period and temporal resolution:

• 1.1.1958 0:00 UTC to 31.12.2001 18:00 UTC
• Time step: 6h

Coverage and spatial resolution:

• Longitude from 0° to 360° (Resolution: 1.125°)
• Latitude from 56.75° to 63.75° (Resolution: zonal value)
• Height: 500hPa-Niveau

Format:

• NetCDF

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Data quality

Same quality as ERA-40 as this is only input data.

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Contact

Name:Silke Schubert
Institute: CEN / University of Hamburg
Email: silke.schubert (at) uni-hamburg.de

Annika Jahnke-Bornemann
ICDC / CEN / University of Hamburg
E-Mail: annika.jahnke-bornemann"AT"uni-hamburg.de

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References

Literature:

• Schalge, B., R. Blender, and K. Fraedrich, 2011: Blocking detection based on synoptic filters. Advances in Meteorology, ID 717812, 11 pages. doi:10.1155/2011/717812.
• Tibaldi S, Molteni F (1990) On the operational predictability of blocking. Tellus 42A : 343-365, doi:10.1034/j.1600-0870.1990.t01-2-00003.x
• Tibaldi S., F. D’Andrea, E. Tosi, E. Roeckner (1997) Climatology of Northern Hemisphere blocking in the ECHAM model. Climate Dynamics 13 : 649-666 (pdf, not barrier-free)
• Uppala, 2003: ERA40_PL00_6H (Pressure Level Data, 6 hourly). World Data Center for Climate. CERA-DB "ERA40_PL00_6H" http://cera-www.dkrz.de/WDCC/ui/Compact.jsp?acronym=ERA40_PL00_6H
• Uppala S. M., P. W. Kallberg, A. J. Simmons, U. Andraea et al. (2005) The ERA-40 Re-Analysis. Quarterly Journal of the Royal Meteorological Society 131, 612: 2961-3012

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Data citation, License, and Acknowledgments

Please cite the data as follows:

Silke Schubert (2011) "Blocking index from ERA-40 data" provided by ICDC, CEN , University of Hamburg.

and with the following acknowledgments:

Thanks to ICDC, CEN, University of Hamburg for data support.

License

The data was published under the Creative Commons Attribution 4.0 International License (CC-BY-4.0).

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