NMOC Quarterly Summary July-September 2001

Summary of System Performance
Data Impact

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All impacts are now being calculated relative to the GASP T239 assimilation system, which replaced the T79 system in December 1998. On the basis of pre-implementation testing of the new system, the assigned background field errors for the new system are lower than in the old system, particularly so for upper winds in middle and high latitudes. As a consequence, one would expect tropical and subtropical upper air stations to figure now more prominently than before, among the higher impacts.

Mean sea level pressure observations

Buoys

The above ten buoys in the Southern Hemisphere had the greatest impacts on GASP analyses of sea level pressure on the basis of ensemble root-mean-square impacts for July to September 2001. The latitude and longitude columns show the buoy position at last report.

By contrast with the April to June quarter, the most influential buoys were in the eastern hemisphere.

Synops

The above ten synops in the Southern Hemisphere have had the greatest impacts upon GASP analyses, on the basis of ensemble statistics of root-mean-square impacts during July to September 2001. Only stations below 800 metres were considered, so that the impacts can all be taken as applying to sea level pressure.

Upper Winds

The above Australian upper air stations have had the greatest impacts upon GASP analyses at 500 hPa (left columns) and at 200 hPa (right columns) on the basis of ensemble statistics of root-mean-square vector impact during July to September 2001. Antarctic and island stations, and irregularly reporting stations, are excluded.

Port Hedland narrowly displaced Weipa as the top station at 200hPa, as happened in the same quarter of 2000. Nine of the ten stations appear at both levels.