Synoptic-scale weather systems observed during the FROST project via scatterometer winds

Using data obtained during January 1995—the third of three special observing periods associated with the Antarctic First Regional Observing Study of the Troposphere project—over a sector of the Southern Ocean (SO), this study investigates the capabilities of European Remote Sensing satellite (ERS) scatterometer winds to portray accurately synoptic-scale weather systems and comments upon their potential contribution to the forecasting process in this region. A sample population of cyclones was defined using satellite imagery and analyzed charts. The scatterometer successfully “captured” more than 60% of these systems that were existent over the open ocean. For manual analyses, the wind vectors proved extremely good for locating the positions of fronts, apparent as a marked turning in the wind direction, which coincided closely with frontal bands observed in contemporaneous satellite imagery. In most cases the wind vectors were also able to locate cyclone centers: their superior spatial resolution as compared with numerical analysis schemes revealed significant positional errors in the latter. This study demonstrates that typically each cyclone was captured twice by a scatterometer swath: such multitemporal data can provide information on the development of a system through changes in the strength of its associated winds. Those 40% of systems that were not captured generally had a duration of less than a day and in that time were never encompassed by the scatterometer swath, a limiting factor in the instrument’s effectiveness, as noted by other studies. However, this study reveals that the most significant problem in high southern latitudes appears to be missing data resulting from the use of the operationally mutually exclusive synthetic aperture radar instrument over coastal Antarctica. Additional limitations of scatterometer data for observing synoptic-scale systems are shown to be the maximum and minimum restrictions on the range of wind speeds that can be successfully derived and the granularity problems that are still existent in some ERS data. Nonetheless, scatterometer data have the potential to provide extremely important information for the forecasting process over the data-sparse SO, with the near-surface winds able to give an accurate reflection of the degree of activity of a weather system.

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