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John Titterton wrote:

> British reference books all appear to define the term as:
> The wind is said to back when it changes direction anticlockwise.
> (Note that there is no reference to the different hemispheres)
>
> US reference books all appear to define the term as:
> A change in wind direction in reverse of the normal pattern, or
> counterclockwise in the Northern Hemisphere and clockwise in the
> Southern Hemisphere.
>
> Who is correct? What is the correct definition?


I doubt that the British/US difference is anything more than a chance
selection of over-simplified British books and more professional
American ones. Growing up in England, I learnt that a wind "veers" when
it changes "with the Sun" and "backs" when it changes "against the Sun".
In the Northern Hemisphere, of course, "with the Sun" is synonymous with
"clockwise" and it is sometimes used in that sense globally. (Right-hand
laid rope has sometimes been said to be laid "with the Sun", for
example.) However, where astronomical phenomena or anything affected by
the Corriolis force are concerned, I would understand "with the Sun" to
mean anti-clockwise once you pass south of the Line.

In short, I would suggest that what John sees as the US meaning is both
correct and universal -- even if books written for a local, Northern
Hemisphere audience are often oversimplified. (Blame it on the arrogance
of the majority.)


Which means that I am surprised by Vic Fraenckel's:

> FWIW: In the '60s when I was a meteorologist for the US Air Force, backing
> referred to the the change of wind direction against the compass and veering
> with the compass, i.e.  wind at 150 deg veered to 180  deg and backed to 120
> degrees.

If the USAF uses "veer" for a clockwise wind shift even if the Southern
Hemisphere, does the USN follow the same usage? And, if so, how does
that relate to John's observation that US textbooks state that the sense
of the rotation changes across the Equator?


Trevor Kenchington


--
Trevor J. Kenchington PhD                         Gadus@iStar.ca
Gadus Associates,                                 Office(902) 889-9250
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