July 18, 2008

NCAR Distributes Premier Climate Reanalysis Dataset

BOULDER—The Japanese Meteorological Agency (JMA) and NCAR have partnered to distribute what scientists are calling the gold standard for climate studies. Two related products, the Japanese 25-year Reanalysis Project, JRA-25 for short, and the JMA Climate Data Assimilation System (JCDAS) are currently the most advanced reanalyses available to climate researchers.

A reanalysis is a comprehensive global, multi-decadal dataset generated by the latest numerical data assimilation techniques using various past observations. Reanalysis data have consistent technical quality over decades and provide vital context to many types of meteorological and climatological research and applications. NCAR holds the largest collection of reanalysis data in the world.

According to Dave Stepaniak, software engineer, "It's particularly rewarding when new reanalysis reproduces real events with improved accuracy. If you look at satellite images of Super Typhoon Sepat, which hit Taiwan in August of last year, you can see that the reanalysis shows the same track, with the same wind structure and outflow characteristics."

JRA-25 is the first long-term global atmospheric reanalysis undertaken in Asia. Covering 1979-2007, it provides a continuing estimate of what the climate was like during that period. Because of its accuracy, JRA-25 has become a reference data set.

JCDAS uses the same system as JRA-25, but the data assimilation cycle is extended to the present time, making it particularly useful. JRA-25 and JCDAS products will enable researchers to conduct climate diagnostics with a current, consistent and long-term set of data. JRA-25 and JCDAS show marked improvement over previous reanalyses in many areas, including precipitation and tropical cyclone analysis.

NCAR's Computational and Information Systems Laboratory (CISL) plays a key role in making both products available to the public for research and education as part of the CISL Research Data Archive (RDA).

Technical Details

Over 20 different products are available at a six-hourly temporal resolution and typically at both high and low spatial resolutions (approximately 1.125 and 2.5 degrees) in GRIB 1 format. In parallel, companion monthly mean products in netCDF are also available in the RDA. Details about the gridded parameter fields within each product, and the JMA model, assimilation system, and conventions, are readily available on the Web site.

The complete JRA-25/JCDAS collection, currently 10TB, can be accessed from the RDA Web server or the NCAR Mass Storage System. Registration and acceptance of the JMA prescribed data use policy is required and electronically logged as part of a user's first access session.

Click here or on image to view animation, [10 MB, .mpg]

Typhoon Sepat, 16 August 2007. Left: JCDAS mean sea level pressure and 1000 hPa winds at 2007-08-16 06:00:00 UTC (top panel), and convective precipitation (in mm day-1) also at 2007-08-16 06:00:00 UTC (lower panel). Right: NASA Terra-MODIS satellite image taken 2007-08-16 02:25:00 UTC, 3.5 hours prior to the JCDAS analysis in left image. Note strong correlation of significant convective rainband arcing over Luzon in the Philippines and eastward of Taiwan. At this stage Sepat's minimum central pressure has dipped to 910 hPa with eyewall winds exceedng 150 mph (although the eye is is not resolved in the JCDAS analysis where the resolution is 1.25° for fields interpolated to pressure levels). MPEG animation of JCDAS reanalysis of mean seal level pressure, 1000 hPa winds, and convective precipitation in region traversed by Typhoon Sepat, 2007-08-09 00:00:00 UTC to 2007-08-22 18:00:00 UTC. The disturbance leading to the eventual spin-up of Sepat begins at approximately 140°E, 15°N. Note the well developed southwesterly monsoon flow and low pressure system with significant precipitation moving north-northeast along the southeast coast of China, preceeding Sepat's appearance in the northernmost South China Sea by several days. (Other animations not shown: Sepat's track follows contours of maximum sea surface temperature. In addition, anticyclonoic equatorwards outflow is well-developed at 200 hPa while Sepat is between Luzon and Taiwan.) Terra-MODIS satellite image couresty of NASA's Earth Observatory. Further information may be found at Typhoon Sepat (2007) and links therein.