The dogs of weather

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  • Two Norfolk Terriers take shelter from the rain during a world record dog walking attempt at the Royal Highland Centre in Edinburgh on 11 May. Photo: David Cheskin/PA Archive/Press Association Images.

    The Dog Star, Sirius A, with its white dwarf companion, Sirius B, from a Hubble Space Telescope image. NASA/ESA/H. Bond (STScI)/M. Barstow (University of Leicester).

    Roman carved white marble dog with a brown patina from the the Walters Art Gallery, Baltimore, USA.

    Sun dogs, or parhelia, either side of the sun over Minnesota, USA, on 22 January 2005.

    A Pomeranian sheltering under an Afghan Hound at Crufts dog show 2001. Photo: Johnny Green/PA Archive/Press Association Images.

  • The dogs of weather
    22.06.2012 07:04

     

    Our canine pals crop up occasionally in meteorology.

    The “dog days”, for example, refer to what are supposed to be the hottest and most languid days of summer in July and August – certainly not June this year.

    They were named in Greek and Roman society because at that time of year in that age Sirius, the Dog Star, used to rise at about the same time as the sun. The faulty assumption was that it added to the heat of the sun, and in an attempt to assuage the most torrid conditions, Romans used to sacrifice a dog. Specifically, a brown dog.

    Because of precession, at this point in the 21st century Sirius no longer rises at the same time but the phrase has stuck around to describe those sultry days when only Noël Coward’s “mad dogs and Englishmen” – there’s another allusion – go out in the midday sun.

    A “sun dog” is a very different thing to the Dog Star. Also known as a “mock sun”, or more properly a parhelion, it is a burst of light seen on either one side or both sides of the sun when it shines through a layer of cirrus or cirrostratus cloud and its light is refracted. Often it can be seen as the brightest part of a very wide halo around the sun.

    A rather strange belief, possibly originating in North America, is that dogs attract lightning. Well, of course they do not, and thay are only as likely to be hit as any creature. Less so, perhaps, because herd animals, via “step potential” are more likely to succumb to a lightning bolt.

    When lightning hits the earth’s surface, it causes the ground’s electric potential to rise hugely at that point. Further away the ground potential remains neutral, so a large “gradient” is created between the electrified and non-electrified areas.

    If a creature – or indeed human - is standing with one foot closer to the strike than another, then there will be a difference in potential between the two, which can set up an electrical current sufficient to stop the heart. 

    The greater the distance between the feet, the larger the potential difference and the stronger the current, so larger animals are at greater risk.

    During thunderstorms, animals are in the habit of huddling together, which makes things worse; if their bodies are touching then the step potential becomes even greater. Groups of elephants in Africa and herds of alpaca in the Andes have been found struck down in this way.

    Finally, and rather aptly, we come to the well-worn “raining cats and dogs”, a phrase which has an uncertain etymology.

    Odin, the Norse god of storms, was associated with dogs but that does not account for the feline half of the saying. The French word “catadoupe” means cascade or waterfall, and it is somewhat plausible that a corruption gets us to “cats and dogs” but it is a bit of a stretch.

    More likely, perhaps, is the inevitable upshot of the noisome state of British cities in the 18th and 19th centuries during heavy rain. With inadequate drainage the detritus of the gutters would be washed down the roads by flooding rain, and dead dogs and cats are likely to have figured largely.

    Jonathan Swift lit upon this unpleasantness in his poem “A Description of a City Shower”:

     “Now from all parts the swelling kennels flow

    Threat'ning with deluge this devoted town.…

    … Drown’d puppies, stinking sprats, all drench’d in mud,

    Dead cats and turnip-tops come tumbling down the flood”.