S17-42-47 (50 mm)
Flight 41G; 36 N. 21E, 11:43:49 GMT, 8 Oct 1984
The entire southern part of Europe, the Mediterranean Sea, and northern Africa were exceptionally windy during the Challenger's Flight 41G. As the shuttle passed over the Adriatic and then the lonian Sea, the crew observed what appeared to be an impressive ocean front with internal waves in the sea off the southwest coast of Greece (see picture above). The front and internal wave train seemed to have refracted around the island of Zakinthos to head onto the shore. One curious feature was the occurrence of lines of cumulus atop the internal waves that lag well behind the front.
A closer look (see picture on page 67) showed that the ocean feature was actually the impact on the sea surface caused by the leading edge of a bora (a gust front). The katabatic wind had spread down the Adriatic Sea, probably increasing in speed through the venturi of the Strait of Otranto. Just as the Challenger crossed in its descending orbit, the leading edge of the bora was indeed bending around Zakinthos Island. The internal waves, rather than being in the water, were formed in the atmosphere at the temperature inversion, creating the convection for cumulus cloud lines on the wave crests.
Ship wakes crossing the gust front were readily visible to the crew, as well as the square track left by a ship that had apparently sailed offshore to dump refuse or clean its tanks.
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