The eclipse occurs while southern Africa is in the midst of its winter dry season. Fine sunny weather dominates the sky in mid June (the second sunniest region of the globe at this time) and the eclipse seeker who ventures to the most favorable parts of the shadow track has excellent prospects for success.
The interior of southern Africa is a vast plateau lying about 1000 m above sea level with a cool and pleasant winter climate. Surrounding this plateau is a jumble of hilly and mountainous terrain ending abruptly in a narrow coastal belt that hugs the Atlantic Ocean on one side and the Indian Ocean on the other. On the Atlantic side of the African continent the cool Benguela current bathes the coast of Angola with 13 degree temperatures, moderating the heat and cloudiness. On the eastern side the wide Equatorial Current of the South Indian Ocean meets the African coast near the Tanzania-Mozambique border. This warm 20° current then turns southward to flow through the Mozambique Channel west of Madagascar.
Over Zimbabwe, the mountain barrier that separates the broad coastal lowlands of Mozambique from the plateau is known as the Eastern Highlands. Reaching an altitude of more than 2000 m, the Highlands block the flow of moist easterly trade winds from the Indian Ocean and the Mozambique Channel. Further north, between Malawi and Mozambique, the Mlanje Mountains serve the same function.
The eastern mountain barrier is broken in two places. To the south, between Zimbabwe and South Africa, the Limpopo River valley provides weather systems with convenient passage into Botswana and eventually to southern Zambia near Victoria Falls (Figure 10). Further north, the Zambezi River provides an opening to the interior along the Mozambique-Zimbabwe border, occasionally bringing cloudy skies as far inland as Lusaka in Zambia. This second entrance to the continent is of most importance to eclipse watchers because the track of the shadow runs more-or-less along the course of the Zambezi through Zimbabwe and Mozambique.
Over Madagascar the terrain is more dramatic. A prominent mountain ridge extends the length of the island, ascending over 2500 m in some places. On the sharply rising eastern side the prevailing easterly trade winds are forced to rise upward, depositing much of their moisture on the slopes. Once across the divide however, the descending airflow is rapidly dried, bringing semi-arid conditions to the southwest corner of the island where the eclipse track comes ashore.
The eclipse track crosses the African continent just to the north of a semi-permanent high pressure belt that circles the globe at about 30° south latitude (Figure 10). In June this anticyclonic zone straddles the southern tip of South Africa, with one center in the Indian Ocean off Madagascar and another in the Atlantic to the west of Namibia. These high pressure centers represent the polar side of the southern Hadley circulation, a zone of notably sunny skies and limited precipitation. Only the Sahara Desert can claim less cloud cover in the month of June than the western parts of the African eclipse track.
The Intertropical Convergence Zone (ICZ) is Earth's "weather equator" and is formed by the gentle collision of air flows from the northern and southern hemispheres. It is a region of heavy cloudiness, high relative humidity and considerable precipitation, but at this time of year, in the southern winter, it tends to be found well away from the eclipse track, on the other side of the equator at about 20° north (Figure 11). Occasionally the tropical air associated with the ICZ will make an excursion into western Angola, but for the most part it stays well away from the eclipse track during the southern hemisphere's winter.
The oceans on each side of the continent are other more obvious moisture sources. On the Atlantic side, only small amounts of cloud and fog occasionally drift onto the Angolan shores. The story is not the same in the east however, where low level cloud and light precipitation are frequent visitors to the Mozambique lowlands and the slopes of the Eastern Highlands of Zimbabwe. Still other cloudiness comes with the passage of weak frontal systems, though these are modest in size in comparison with the continent-straddling weather systems of Europe and North America. The fronts arrive from the south, temporarily breaking through the anticyclonic belt, and bringing a notable change in the weather when they reach the mountainous parts of Zimbabwe and Mozambique.
Much of the region of the eclipse track has an annual precipitation in excess of 1000 mm, divided between a summer wet season and a winter dry. The dry season begins abruptly in May and by the time of the eclipse, is in full sway. June precipitation amounts to only a few millimeters in many locations, and in much of Zambia and Angola, is less than one millimeter. The dry season, when it arrives, does so with great authority.
Adapted from NASA TP 1999-209484 "Total Solar Eclipse of 2001 June 21". Permission is freely granted to reproduce this information and data when accompanied by an acknowledgment of the source:
"From Total Solar Eclipse of 2001 June 21 by Fred Espenak and Jay Anderson, NASA"
WebMaster: Fred Espenak
Planetary Systems Branch - Code 693
NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771 USA