A study of the dynamics of the equatorial lower stratosphere by use of ultra-long-duration balloons 1. Planetary scales

In the late southern winter of 1998, Centre National d'Etudes Spatiales (CN ES), the French Space Agency, released six 10-m-diameter, superpressure bal loons from a location near Quito, Ecuador. Three balloons collapsed soon af ter launching, but the remaining three drifted westward for a few weeks at altitudes between 19 and 20 km. Two of those balloons crossed the Pacific O cean before falling above the "maritime continent," while the other complet ed a revolution around the Earth and crossed the Pacific for a second time before its final fall. Despite the small number and the relatively short du ration of the flights, the balloons provided a unique in situ data set for the lower equatorial stratosphere. This part 1 of a two-part paper describe s this data set and analyzes outstanding features in the planetary scales. Part 2 focuses on gravity-wave scale. It is argued that balloon trajectorie s over the Pacific are primarily determined by the westward drift during th e easterly phase of the equatorial quasi-biennial oscillation (QBO) and the meridional velocity field of a mixed Rossby-gravity (Yanai) wave with an a pparent period of 4 days and zonal wave number 4. This wave appears to have two episodes of amplification during the balloon flights. It is also argue d that the balloons show evidence of oscillations with periods between 2 an d 4 days and of a Kelvin wave with an apparent period close to 10 days and zonal wave number 1. In this way, the balloon behavior provided a pictorial view of air parcel trajectory in the equatorial lower stratosphere. It is stated that larger balloon campaigns can provide excellent in situ data set s for studies on the dynamics and composition of the middle atmosphere.