Author of report: Mike Douglas

Mission Number: 030111I

Type of Mission: LLJ

Start time of Mission(UTC): 2003/01/11 14:

End time of Mission(UTC): 2003/01/11 20:

Flight was called to both test aircraft operating procedures and to examine a weak to moderate low-level jet that was forecast to weaken over the next several days, making further flights unlikely. The basic plan was a "Z"-shaped pattern, with the initial leg extending about 105 degrees towards the ESE. After reaching the farthest point (corner of a restricted airspace near 198 min south, 58 38 min west, the aircraft turned WSW, flying to a point near Villamontes, Bolivia, before making its final leg to the ESE, the endpoint of which was near 22 40 min S, 59 W. The final leg back was somewhat contorted, to bypass rainshowers and to arrive close to the foothills south of Santa Cruz - to investigate possible topographic effects on the windflow around the "bend" in the eastern slopes of the Andes. Most of the flight involved porpoising between about 300 m above ground level (on average about 925 mb level) and 10,000 ft pressure altitude (= 694 mb pressure) at 1200 ft / min. About 28 porpoises were made on the 3 principal legs, with shorter and less regular porpoising being carried out on the return leg. Several slow spiral ascents to about 14,000 ft (about 575 mb) were made to sample higher parts of the LLJ. The strongest winds, of about 40 kts (from the NW) were found over Santa Cruz near 800 mb. These weakened to the SE and to the south, with southerly winds being found on the southernmost track. Satellite imagery suggests that we sampled a region of growing convection associated with a weak northward propagating feature resembling a cold front.