Introduction of new satellite data and adaptive tuning of satellite bias correction

Last update: 30th June 2009

The following changes will be introduced to JCDAS on 1st July 2009;

1. Introduction of new satellite data
   • Radiances from the Advanced Microwave Sounding Unit-A (AMSU-A) and the Mircowave Humidity Sounder (MHS) onboard NOAA-18
   • Radiances from AMSU-A and MHS onboard METOP-2
   • Precipitable water retrievals from the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) on board EOS-2
2. Introduction of adaptive tuning of satellite bias correction
   • In order to make bias correction coefficients adapt to drifting AMSU-A radiance observations, of which biases have shown downward trend in recent years, an adaptive bias correction scheme for satellite radiances will be introduced. In this scheme, bias estimation is performed every cycle (6 hourly), using observations of the latest three months.

The impact of the changes on the quality of the product has been tested in preliminary experiments. From the comparison between products of the operational JCDAS and of the exmeriments, the following changes in the quality of the product are anticipated;

• Global mean tropospheric thickness temperature rises 0.1 to 0.2 K (see Fig 1 and 2).
• Global mean precipitation increases 0.05 to 0.1 mm/day (see Fig 3, 4 and 5).

The primary cause of the changes is most likely to be the introduction of the adaptive bias correction scheme, which optimises bias estimates for AMSU-A radiance observations that have sensitivity to atmospheric temperature. When using the reanalysis product to monitor or study long term climatic trend or low freqency variability, please keep in mind that the quality of the reanalysis product could vary due to changes in the quality of satellite data.

Fig 1 Global monthly mean troposheric thickness temeprature anomalies (850 to 300 hPa)

Fig 2 Latitude-height cross sections of zonal mean temperature of the operational JCDAS (top), the preliminary experiment (middle) and difference between them (bottom) for July 2008 (left) and January 2009 (right). Full fields are shown in contour and anomalies in shade.

Fig 3 Global monthly mean precipitations

Fig 4 Differences between global monthly mean evapolation and precipitation

Fig 5 Global monthly mean total column diabatic heatings

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