Correction to the GEOS FP-IT System: Planned for June 13, 2019


NOTICE: The GMAO will make an adjustment to the GEOS FP-IT production stream, that will lead to small discontinuities in some fields. This adjustment is tentatively scheduled for June 13, 2019.

The adjustment corrects a problem in the GEOS FP-IT analyses that began on September 30, 2017, and has persisted until the present day. The impact is generally quite small and was discovered only recently. The following impacts have been detected:

  • A jump of approximately 0.5hPa in MSLP over the high latitudes of the southern hemisphere (30-70° S)
  • A corresponding cooling of several tenths of a Kelvin in the lower troposphere at these latitudes
  • Decreases of about 20-40% in cumulus mass flux and cloud liquid water in the middle tropical troposphere
  • A small decrease of about 1-2% in global low-cloud fraction by about 1-2%

Graphics illustrating some of these issues are shown below.

GMAO has run a corrected version of the GEOS-5.12.4 system that spans the entire period since September 30, 2017. This corrected system will be switched in to the forward production stream of GEOS FP-IT, beginning with the 00Z assimilation cycle on June 13, 2019 This change will be transparent to users. GMAO does not anticipate that most teams would want to reprocess their datasets for the sole reason of eliminating this problem with GEOS FP-IT. Note that the problem was discovered by GMAO’s evaluation team in monitoring the long time series of GEOS FP-IT data and there has been no report of adverse impacts from any of the users of the GEOS FP-IT dataset.

The problem itself was triggered by a corrupted input data stream on September 30, 2017, which led to a reaction in the observation bias correction which persisted over the 18 months since the first occurrence. Code changes that will prevent a recurrence of a reaction like this one have been implemented as a patch in the GEOS-5.12.4 code base.

GMAO apologizes for any inconvenience that this problem may have introduced.

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