Monday, 7 December 2015

On lines and slopes

I keep hearing, on weather reports, '... isobars close together, so high winds...'. And this reminds me of my short membership of the Meteorology Club
<autobiographical_note>
In 1964-65 – spanning the end of the Lower VI and the beginning of the Upper VI [the UCCA season, during which 17-18 year-olds created a cv that might interest a university admissions officer –  UCCA being the forerunner of UCAS] of the founder cum chairman cum <you-name-it> Edmund Nickless; we lesser mortals, in short trousers, were just UCCA-fodder.
</autobiographical_note>
One of the few things that stayed with me from that short-lived enthusiasm was the mnemonic "Winds blow from high to low" – a jingle that leads me to  reflect on a metaphor that will mean nothing to millennials (as I gather young whipper-snappers are called nowadays). Poor, deprived, benighted souls; for them, physical maps with contour lines have had their rightful place usurped by the Google Maps Satellite view and various other 3-D displays – available at the touch of a mouse/stylus/finger (in ascending order of hi-techeryO tempora, as I have said before,  O mores the pity.

For them, isobars will just be squiggly lines on weather maps, as long as they remain meaningful to a few grey-beards. Then they'll just be dropped, I shouldn't wonder, and replaced by some other graphic device with a vague meaning something to do with the roughness of the weather.

Chixculub, 261km-162m
(Is God metric? – that anagram
can't be just blind chance.)
But they're quite like inverted contours*. A depression is marked by isobars that indicate lower pressure as they approach a centre, not unlike the contour lines on a physical map that shows The Devil‘s Punchbowl or, on a larger scale, the Chixculub Crater.

In contrast. a mountain is the analogue of an anti-cyclone, with lines marking progressively higher altitudes as they approach a peak. When contours are closer on a physical map, the slope in the Real World is steeper. A marble dropped at one level will quickly roll down to ground that could be marked by a contour line that indicates a lower level; the steeper the descent, the quicker the marble.
<digression>
In my school we sliced half a potato into smaller and smaller discs, and traced round them to reveal, on our exercise books, the shape of the potato (reduced to two dimensions); magic. But where is the lowly potato in today's geography classes? Maybe geography teachers still use this trick – but they were brought up with physical maps. What will happen when they retire?
</digression>
Similarly, with isobars, winds blow from high to low. Air in a place marked by an isobar flows "down the hill" to a spot marked by a lower-value isobar. But that's not the whole story:  presumably because of the Earth's spin, winds blow around a pressure system. My mnemonic works only in the Northern hemisphere (but, like Newton's physics, it works for me): imagine yourself writing a capital L  –  that's for low pressure; your mental pen travels anti-clockwise, down the upright and along the "foot".
<digression>
And that's another thing. What was the word for clockwise before clocks were invented? Counter-widdershins?                                                                                      </digression>
For an anti-cyclone you have to take a lower-case (and a rather florid one); you produce it with two strokes, starting the upright at the base-line and moving clockwise up to the curly top. There, with a rather strained manuscript , you have your memory aid for wind direction round a high-pressure system. (This trick will only work if as well as living in the Northern Hemisphere you remember the phenomenon of hand-writing.)

Enough of this metaphor. Time for DIY.

b

PS: And here's a crossword clue:

Potential victims surrounding island race - quite attractive. (6)

Update 2015.12.06.18:15 –  Added this footnote:
*Now I come to think of it, they could be called isoheights; but that would risk confusion with "isohyets" which are already A Thing.

And here‘s another clue:

Marx in reprint at the helm of a chat-show. (5)

Update 2016.01.11.17:15 – Crossword answers: PRETTY and OPRAH (respectively). I thought Oprah was pretty neat, until I saw that I was coming late to the party.


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