The Global Aircraft Data Set (GADS) experiment has been collecting data from every (currently 48) British Airways (BA) 747-400 aircraft since 1 February 1995. Because of operational practice and the BA route structure, these data are generally independent of voice (AIREP) and automated (AMDAR) aircraft reports. Before thinning, we are receiving up to 9000 GADS reports per day. The UKMO did a recent tally and showed that these data represent a sixfold increase over AIREP and AMDAR data away from North America and Europe ( Table 1 at end). The current state of the problem of weak analyzed jet streams is illustrated by a strong wind case using GEOS-2 and NCEP analyses and GADS aircraft observations as shown in Figs. 1-3. Fig. 1 shows an enlarged image of NCEP Southwest Asia wind speeds at 200 mb for 00 UTC 14 January 1998. The maximum wind speed exceeds the maximum contour of 90 m/s near 30N, 65E. Fig. 2 shows the corresponding GEOS-2 Northern Hemisphere analyses for 00 UTC and 12 UTC on the same date. Small peak contours near 30N, 60E and 70E (unlabelled) of 100 m/s are present. Fig. 3 shows a comparison of the GADS aircraft observations to the analyses interpolated in time (to the jet stream traversal time of 04 UTC) and vertical coordinate (flight level 370, ~217 mb). Note that the NCEP and GEOS-2 analyses are similar and too weak compared to the peak aircraft wind by ~15 m/s. If the aircraft data were smoothed to analysis resolutions, an error of ~8 m/s would be present over a distance of ~400 km. References Rickard, G. and R. Lunnon, 1998: Upper air winds: prediction and verification in the context of commercial aircraft data. (UKMO Forecast Division, Technical Report No. 234). Rukhovets, L., J. Tenenbaum, and M. Geller, 1998: The Impact of Additional Aircraft Data on the Goddard Earth Observing System Analyses." Mon. Wea. Rev., 126, 2927-2941. Tenenbaum, J., 1991: Jet Stream Winds: Comparisons of Analyses with Independent Aircraft Data over Southwest Asia. Wea. and Forecasting, 6, 320-336. -----, 1996: Jet stream winds: comparisons of aircraft observations with analyses. Wea. and Forecasting, 11, 188-197. Table 1. A detailed tally for January and July 1997 of the non-ACARS automated aircraft data in the Met Office Data Base (MetDB) versus the data from the GADS mode C aircraft. (GADS mode C is triggered once every 128 sec at cruise altitudes.) From Rickard and Lunnon, 1998.
Figure Captions Fig. 1. NCEP analysis of wind speed at 200 mb for 00 UTC 14 January 1998. The maximum is in the upper 90's near 30N, 65E. Fig. 2. GEOS-2 analyses of wind speed at 200 mb for 00 and 12 UTC 14 January 1998. Contours of 100 m/s (unlabelled) exist near 30N, 60E and 70E. Fig. 3. Wind speed (m/s) versus longitude for GADS observations (small rectangles) and GEOS-2 and NCEP analyses (ovals) interpolated vertically (to FL 370, ~217 mb) and in time (to a jet traversal of ~04 UTC) from a London-Bangkok flight. |
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