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UPPER AIR SOUNDING NETWORK

Map of the upper air network proposed for the 2006 AMMA-NAMMA activities. Click on the map for a larger version.

A relatively dense pilot balloon network was deployed and operated in four countries (Senegal, Guinea, Mali and Mauritania) in West Africa to complement the NASA DC-8 aircraft measurements to study tropical cyclogenesis over West Africa and across the eastern Atlantic Ocean during the August - September 2006 period.

Why are conventional upper air measurements useful in west Africa?

Routine and accurate estimates of the lower to mid-tropospheric wind field from satellites remains difficult over West Africa in the presence of widespread convection; cloud motion vectors are often not reliable due to rapid cloud evolution and to uncertainties in level assignment, and surface wind fields cannot be obtained from satellite scatterometers such as from Quickscat.

Why did we attempt such a dense pilot balloon network over extreme West Africa?

Enhanced radiosonde observations, mostly in greater frequency of observations, will were planned for west Africa as part of AMMA, but these planned observations do not increase the spatial density of observations. To measure the intensity and other characteristics of AEW's crossing the west African coast during the DC-8 aircraft deployment, it was desirable to have all-weather in-situ sounding systems over west Africa, such as a network of radiosonde sites or wind profilers. Unfortunately, funding limitations and logistical considerations (lack of available sounding systems, gas generators, and radiosondes) prevented major upgrades to the radiosonde network over this region in time for NAMMA-06. To increase the density of wind soundings to improve the routine estimation of the wind field anomalies associated with the AEW's and to improve the accuracy of the calculated wave vorticity in the lower-mid troposphere we attempted to establish temporary pilot balloon sounding sites in a relatively tight network centered on Senegal and including parts of Guinea, Mali and Mauritania (see figure above).

The pilot balloon network was relatively dense because, due to cloudiness, not all soundings were expected to be made to high levels. A relatively dense network increases the chances that at least some balloons will be tracked to a high level.

When did this network operate?

Training begun in mid-July and continued through August 10th, with not all planned stations being established. A complete listing of the data available from the network will be available shortly.