AN INTERCOMPARISON OF ISENTROPIC TRAJECTORIES OVER THE SOUTH-ATLANTIC

Citation
Ke. Pickering et al., AN INTERCOMPARISON OF ISENTROPIC TRAJECTORIES OVER THE SOUTH-ATLANTIC, Monthly weather review, 122(5), 1994, pp. 864-879
Citations number
28
Categorie Soggetti
Metereology & Atmospheric Sciences
Journal title
ISSN journal
00270644
Volume
122
Issue
5
Year of publication
1994
Pages
864 - 879
Database
ISI
SICI code
0027-0644(1994)122:5<864:AIOITO>2.0.ZU;2-N
Abstract
The authors have compared isentropic trajectories computed from meteor ological fields from different analysis centers. The analysis was perf ormed for the South Atlantic, where a springtime maximum in tropospher ic ozone has sparked considerable interest in the transport meteorolog y. Using the model of Schoeberl et al., isentropic forward trajectorie s were computed from an array of points over southern Africa and backw ard trajectories from an array of points over the South Atlantic. The model was run for an 8-day period in October 1989 with input taken fro m the twice-daily global gridded data fields from the National Meteoro logical Center (NMC) and from the European Centre for Medium-Range Wea ther Forecasts (ECMWF). There were large differences between the traje ctories based on the two fields in terms of travel distance, horizonta l separation, and vertical separation. Best comparisons for individual trajectories were found in the low-latitude easterlies, and the poore st comparisons were found in the westerlies and in the vicinity of the center of the South Atlantic subtropical anticyclone. Significant dif ferences in wind speeds between the two analyses also led to large tra jectory differences. Trajectories were also computed using once-daily NMC fields. The effect of this degradation of the data was small. Traj ectories computed from balanced winds computed from the NMC geopotenti al height and temperature fields showed the largest differences when c ompared with the ECMWF trajectories. The balanced wind fields should n ot be used in trajectory construction in the tropical lower tropospher e. It is difficult to make a definitive recommendation concerning whic h set of fields should be used in future transport analyses in this re gion due to the very large trajectory differences found in this analys is and the lack of any independent verification data. Any extensive an alysis of transport in this region should be done only in conjunction with considerable additional data collection.