An Introduction to SOWER/Pacific

The understanding on the atmospheric processes responsible for realizing the distributions and variations of the ozone and water vapor in the tropical stratosphere and troposphere is still inadequate to explain even the observed fundamental features of total ozone. The mechanism of mass exchange across the tropical tropopause is one of the key issues in the atmospheric dynamics in the tropics. The estimation of the chemical ozone depletion due to the biogenic halogen compounds in the tropical eastern Pacific is needed to quantify the tropospheric ozone budget since this region is characterized by strong upwelling that supports high biological activity and creates temperature inversion above the marine boundary layer. These are among the subjects Soundings of Ozone and Water in the Equatorial Region/Pacific Mission (SOWER/Pacific) is aimed to study by conducting coordinated, year-round ozone and water vapor soundings in the tropical Pacific. It is also intended to provide datasets suitable for validating the remote sensing data from satellites.

As is readily understood from the existence of the Walker circulation, extremely different climatic conditions prevail in the eastern, central and western Pacific. SOWER/Pacific is trying to shed light especially on the spatial structure of the ozone and water vapor profiles along the equator by maintaining observational stations representative of the three climatic regions in the tropical Pacific: San Cristobal in Galapagos Islands (0.90S, 89.62W), Christmas Island of Republic of Kiribati (2.00 N, 157.38 W), and Watukosek in Indonesia (7.57 S, 112.63 E). To fill the spatial gap between these stations, series of sonde launches from a cruising ship are also planed.

Due to the limited fund available, the initial effort has been to undertake spontaneous campaign observations under two extreme atmospheric conditions; the boreal winter (summer) when tropical tropopause is cold (warm) and high (low) reflecting the extratropical pumping activity in the Northern middle and high latitudes. The two periods also correspond to the local rainy season and dry season, respectively. What was unexpected, the record strong El Nino took place in 1997-1998 switching quickly to La Nina in the latter half of 1998. This talk will introduce the general scope of SOWER/Pacific and present some preliminary results obtained from campaign observations in March-April and September 1998 at Galapagos and in February 1999 at Galapagos and Christmas Island.