On 12/11/12 20:32, Len Wood wrote:
On Nov 12, 7:21 pm, "Ian
wrote:
"Weatherlawyer" wrote in message

...





Why does the weather flow west to east?
I've been looking at Karman and Bernoulli and all that stuff to get
some idea why the weather dissipates the way it does overland.
To me it just appears vortex shedding and fairly simple convergence/
divergence/convergence/divergence at the west/eastern shores of the
continents.
It goes round and round, eventually ending up at either pole as per
von Karman principles. But (assuming upper levels rotate in the same
direction) there is no real explanation to the direction.
I ruled out Coriolis Effect for two reasons:
1. It is not a force and the west winds are absolute forces, nothing
else but.
2. If it were a phenomenon, Newton would have found it first.
You'd think the heat source would push air eastwards. The fact that it
does happen in some latitudes "occasionally" is immaterial as this
"occasionally" business seems to rely on total calm -which could
actually be seen as proof that the winds aught to be travelling east
to west in ideal conditions.
Which obviously means something is pushing it the other way.

What?

Weather flows west to east, ultimately, because the atmosphere is warmer in
lower latitudes than in higher. As a result of this, the atmosphere in low
latitudes is in an expanded state so that, at height, there is more air
above a given level at low latitudes than at high. This means that, again
at height, pressure is higher at low latitudes. So the bulk of the
atmosphere moves from west to east (low pressure on its left), carrying the
surface features with it.
In the southern hemisphere two reversals, latitude and Coriolis, cancel out,
so that there too, surface features generally move from west to east.
There are parts of the world (eg the south coast of Arabia) where it is
actually warmer on the poleward side in summer (only) due to the fierce heat
of the interior, and there, disturbances move from east to west with an
easterly jet.

Ian Bingham,
Inchmarlo, Aberdeenshire.- Hide quoted text -

- Show quoted text -

This has all become rather mid- latitude biased. With weather being
embedded in the westerly propagating atmospheric waves.

What about the easterly waves in low latitudes? The ones that spawn
those rather intensive weather features called hurricanes?

Len
Wembury, SW Devon

That is due to the African Easterly Jet, which occurs because the Sahara
is hotter than the equator, reversing the N/S temperature gradient in
this region. The vertical lapse rate in the Sahara is greater on average
than at the equator so at some height above sea level (around 700 mb I
think) the N/S temperature gradient reverses so the jet reaches a peak
at this altitude then gets weaker higher up.