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From: George Huxtable (no email)
Date: Fri Jun 16 2006 - 11:46:54 EDT
Alex wrote-
| Indeed the sign and magnitude of the error I observed
| look like an error produced by "positive dip".
Do we agree, then, that the observed problem is that the actual dip is
reduced to zero, or indeed slightly the other way, from its usual
"book" value? We have to be careful about naming it "positive" or
otherwise. Usually, dip is usually a value that you have to subtract
off a sextant observation, so is that "positive" or "negative"?
"Normal" and "reversed" might be a better choice of words.
| But I suppose that the physical conditions you are
| talking about were not present in Kielerforde on that day.
| The water was very cool (and always is) here.
| I mean most people do not dare to swim in Kiel till the beginning of
| August:-)
| But the air was hot, at least that was what I felt:-)
|
| So I suppose the gradient of temperature could not be "inverted"
| on that day, that is the air was cooler near the water and
| hotter above. As I understand from your message
| this is the "normal gradient", not inverted.
There can be misunderstandings here, also. Normally, with increasing
height, the air temperature falls. So that is a negative temperature
gradient. On the other hand, because that gradient is usually
negative, it's often referred to by meteoroligists and others in terms
of a "lapse rate", the rate at which the temperature FALLS with
increasing height, and that lapse rate then usually has a positive
value. I don't know a good way to cut through that confusion. I am
hypothesising that an inversion happened at Keil, in which the air
temperature varied in the opposite way to the usual. That is, warm air
above was cooled by contact with the cooler sea surface below. Every
word that Alex has offered reinforces that picture. Just a quarter of
a degree Centigrate less, for the air at the surface of the fjord,
compared with the air a couple of metres above it, would be enough to
annul the dip. Alex is describing an effect which appears to be of
that order, and perhaps a bit greater in magnitude.
| The dip correction was taken from the almanach tables,
| and it was -2.2, -2.8 and -3.5 at the three places of various
elevation
| where the observations were made.
| The observations on the highest place were such as if there was
| no dip.
|
| So I am looking for another explanation.
I don't think that's necessary. We have a sufficient explanation, in
my view.
===========================
By the way, when I wrote, in a previous mailing,
| So, according to Young,
| there's no limit to the gradient in such inversions, and "... rates
| exceeding a degree a meter are common. An inversion gradient of 20
| degrees per metre has been measured directly ..."
I would not like to give the impression that such extreme values
occurred at the sea surface. I simply don't know where such large
gradients were measured; Young was quoting observed values to show the
physical possibility and stability of high inverted gradients, without
stating where.
George.
contact George Huxtable at
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK..
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