Application of ATS III Photographs for Determination of Dust and Cloud Velocities over the Northern Tropical Atlantic

Abstract

July 14, 1969 was selected from BOMEX Period IV as the day of detailed analysis of cloud velocity fi elds over the northern tropical Atlantic Ocean. A total of 375 low-cloud velocities were obtained between ITCZ and 34N and 70 velocities between ITCZ and the equator. These velocities are found to be very useful in understanding circulation pa tterns over a vast region of water where little synoptic data is availa ble.Over 170 high-cloud velocities were computed mostly in the area of cloud clusters. It was found that a field of high-cloud divergence existed over practica lly each of la rge cloud clusters in the ITCZ a nd an easterly wave a ppearing on this day. Motion of dust clouds from Sahara was a lso computed by using an accelerated movie technique. It is concluded that ATS III picture sequences can be a nalyzed independently from conventional synoptic and/ or network da ta so that the computed velocities of clouds, dust, a nd propagating waves can be used as supplementary data to past a nd future tropical experiments.

Assessment of the African airborne dust mass over the western Mediterranean Sea using Meteosat data

“…Satellite observations offer an opportunity to make spatial extrapolations of local ground measurements, meteorological satellites being of particular interest for long term and large scale studies. It was recognized early on that remote sensing techniques could be used to detect desert dust clouds [Fujita, 1970;Prospero et al, 1970;Shenk and Curran, 1974], and satellite data have often been used for qualitative investigations of movements and source areas of individual dust plumes [e.g., Oliva et al, 1983;lwasaka et al, 1983;Legrand et al, 1985; Coudd-Gaussen et al, 1897; Bergametti et al, 1989b], or for long-term assessment of frequencies and source regions of dust conditions have already been published elsewhere Bergarnetti et al, 1989a;Dulac et al, 1989]. We shall focus here on the late June-early July 1985 period, during which a transport of dust particles from Africa was recorded [Bergametti et al, 1989b].…”

Tropical Circulation Systems and Monsoons

“…A possible implication of a change of thermal wind across a borderline between the two regions in the development of a tropical disturbance will be discussed in a later part of this chapter. Fujita (1971) used cloud motion vectors at low and high levels from satellite cloud imagery around 15 GCT on 14 July 1969 to construct streamlines to demonstrate the presence of easterly waves and their associated cloud systems over the tropical north Atlantic.…”