observations and photographs of noctilucent clouds and aurorae
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Weather – M
arch 2011, Vol. 66, No. 3
LettersThe demise of Airmet
Gordon Currie is not alone in his nostalgic memories of Airmet broadcasts and their somewhat mournful interval signal.
I first came across them in early 1947, and soon realised that there were sufficient sta-tion reports to allow the compilation of one’s own synoptic charts. To someone with a keen interest in weather it was exciting to be able to follow developing situations hour by hour, and record them on paper if desired. It was the immediacy of this that appealed in days long before home com-puters. I still have memo pads with daily records of 1947, and was intrigued at the time to find that the pressure situation (a high over Scandinavia) which generated the heat waves of August was similar to that associated with the very severe winter ear-lier that same year.
The closure of Airmet, with only four days notice, provoked some lively correspondence in successive editions of Weather in 1950, which I still have. There was even a letter from the Air Ministry (MacBride, 1950) to the Copenhagen Broadcasting Convention, who presumably were responsible for the alloca-tion of wavelengths, as well as a petition (Weather editors, 1950) – all to no avail. No place could be found for this service, nor ever anything like it in the way of continuous live voice transmission as distinct from the current automated Volmet-type stations on airband radio. I wonder whether the (eventual) advent of digital radio could facilitate the inaugura-tion of what Mr Currie calls a continuous straight-talking broad casting service which might meet present day needs.
ReferencesCurrie G. 2010. This used to be Airmet . . . Weather 65: 253–254.MacBride LM. 1950. Airmet. Weather 5: 261.Weather editors. 1950. Airmet petition. Weather 5: 403–405.
Reg W. SelfeBenfleet, Essex
DOI: 10.1002/wea.729
Observations and photographs of noctilucent clouds and aurorae
During his talk at the recent 1st National Amateur Observers Symposium, George Anderson, Weather’s Photo Editor, showed an image of noctilucent clouds (NLC) and they have been featured recently on the cover of Weather (August 2009) and in a Weather image in September 2009 (Burt, 2009).
It is perhaps appropriate to point out that any observations of NLC and of aurorae are of great scientific interest. The Aurora Section of the British Astronomical Association col-lects observations from Canada, the United States, Iceland, the British Isles and other European countries. The current network includes astronomical societies, individual amateur and professional observers (includ-ing meteorologists) and ships’ officers. There is close co-operation with the Royal New Zealand Astronomical Society, which collects southern- hemisphere observations.
Even casual photographs are of consider-able value. Those of aurorae may be submit-ted to the Section Director, Dr David Gavine at 29 Coilles dene Crescent, Edinburgh, EH15 2JJ (Tel: 0131 657 2338, email: [email protected] or via [email protected]). Those of NLC should be sent to the NLC Coordinator, Ken Kennedy at 80 Torridon Road, Broughty Ferry, Dundee, DD5 3JH (Tel: 01382 776320, email: [email protected]).
Detailed methods of visual and photo-graphic observations of both phenomena may be found on the Section’s web pages: http://www.britastro.org/aurora/, and the Section is always happy to advise potential observers or photographers.
ReferenceBurt S. 2009. Noctilucent clouds. Weather 64: 238.
Storm Dunlop
East Wittering, Chichester
DOI: 10.1002/wea.751
A thunderstorm in northern Nigeria
Joan Kenworthy’s letter (2010) brings back a West African memory. In February 1955, I was serving as touring Assistant District Officer in the southern Katsina Province of the then British Protectorate of Northern Nigeria. On the 15th, the usual seasonal change took place from the cool dry season to the hot dry season. The Harmattan ceased to blow dust southwards from the Sahara, the sky cleared and the temperature shot up 15 degC or more, all in one day. However, the usual symptoms were supplemented in mid-morning by a short-lived high-level thunderstorm. What might have caused this; where did the moisture come from?
ReferenceKenworthy J. 2010. The occurrence of east-erly waves in West Africa. Weather 65: 310.
ADG WebbCorsham, Wiltshire
A response from Jim GalvinIt seems that in February 1955 the Harmattan rather suddenly brought warmer air, heated strongly under sunny skies. This is likely to have generated some very high-based con-vective cloud that grew to become cumu-lonimbus with a base possibly around 4000m and top near 12 000m. It is relatively common to see lines of high-based deep convection over the Sahel (see e.g. http://rapidfire.sci.gsfc.nasa.gov/ realtime/single.php?T100461030).
Although the Harmattan has very low humidity, it is not moisture-free. When air in the upper troposphere is sufficiently cold, deep convection may produce precipitation. If the precipitation began as hail, it could have reached the ground (some of it as rain). In addition, above the Harmattan tropo-spheric winds are usually westerly or south-westerly over northern Nigeria in winter, north-west of the upper-tropospheric high centred over the northern Indian Ocean. These winds may bring moist air from the humid tropics, allowing the cloud to grow.
DOI: 10.1002/wea.770