Gold Coast Propeller Cumulus Clyve Herbert
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Photographic sequence showing what appears to be a propeller driven congesting cumulus street with the tail rotating horizontally. Photos - C Herbert (ASWA Archive) |
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| A trip to the Gold Coast in
February introduced me to the delights of warm sea water. For the most part the
Victorian coastline, near to where I live (Ocean Grove), sea water temperatures rarely
exceed 18C in mid-summer. Needless to say, I was delighted with the 24C water
temperature at Burleigh Heads, and apparently this was 2C below the average! Ocean
temperatures off Queensland being below normal for most of the summer ('99-'00) may have
been responsible for the quasi-stationary ridge that persisted offshore (named 'quidge').
Despite the presence of relatively high pressure, bands of congesting cumulus
persistently moved in across the Gold Coast coastline. The photographic sequence shows a relatively low vertical extent cumulus street moving northwest along the coastline (Burleigh Heads). Always looking for something unusual, I zeroed in on a tail formation on the eastern side of the cumulus street. I was stunned to see this area rotating horizontally. The rotation persisted for almost 10 minutes, continuously turning over and over, and occasionally showing breaking wave formations (refer photographs and diagram above). An explanation for this phenomenon is difficult. Clues to the existence of this rotation may be:- the rotation was occurring near to the condensation level, also the top part of the cumulus street (see above), was showing subsidence. There was also a fresh easterly seabreeze while the cumulus moved from the southeast to the northwest. The presence of a boundary layer may also have had some influence. Surface air temperatures were approximately 27C, dew point was 19C. The cumulus street itself produced a small droplet light shower. I would appreciate your comments on the information contained in this article. |
