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On Sun, 13 Jan 2008 14:25:29 +1100, "Landy" wrote:


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I live on the western edge of Australia, with the Indian ocean 10 km
to the west, and the vast desert interior of Australia a few hundred
kilometers to the east.
I've been watching dew point temperature refreshed every 10 minutes on
the weather bureau's website, and I'm wondering what happens to a
moist sea breeze when it blows over the interior, and then returns
much drier. It hasn't dropped any rain, but yet it somehow dries.
If it cools below the dew point (even frost point) overnight, would it
not regain that frost/dew when the land warms up? Or would there be a
time lag, so you would get dried masses of air, that have not had the
opportunity to recapture the dew/frost and then later masses carrying
this evaporated precipitation?
Does the desert act as a dessicant at all?
Perhaps some of the dew/frost (is this called precipitation?) is lost
to lower soil profiles?
Just now, we have an easterly wind that appears to be getting
increasingly humid (specific) and I'm guessing that this actual air
has either not gone over much desert, or has not dropped below the dew
point overnight and is merely a returnimg sea breeze with all of
yesterday afternoon's ocean-derived moisture.
Anyone have any opinions on this? jack

I would imagine you're not getting the same air back - or at least it has
mixed with "continental" air that has much lower humidity. In fact, after
thinking about it, it's hard to how it would not mix with other air.
cheers
Bill

Thanks Bill, I agree, but my question was more to a simple easterly
gale overnight and morning (and we have thousands of miles of desert
out there) and a sea breeze (gale) in the afternoon. No rain has
occurred, but the desert wind is much much drier than the sea breeze.
Or are you saying that the reason that winds off the desert are dry is
because they MUST have dropped their moisture as precipitation
somewhere? I'm just asking the question whether deserts can have some
drying effect by way of being a dessicant or some other non-rain
moisture loss. jack

Jack,
No - I'm just saying that because the high-humidity air that blew in from
the sea mixed with very low-humidity air in the desert, the resulting
humidity of the mixed air that blows back out will be lower. It's a matter
of mixing ratios. I guess the absolute moisture loss (of the air that blows
back) has been to the desert air - it doesn't have to have precipitated. I
think if you did humidty measurements inland in the deserts on evenings
following the sea breezes versus days without, you would see the difference.
I hope this makes sense.
cheers
Bill