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(meteorobs) FWD from Wayne Re: Reading Water Vapor Satellite Images
------- Forwarded Message
From: wayne.t.hally@tekdot com (Wayne T. Hally)
Subject: Re: Reading Water Vapor Satellite Images
Date: Fri, 2 Aug 1996 13:50:51 LOCAL
Gentlemen, I'm forwarding this here for our perusal. No articles axplaining the
water vapor image have yet appeared in the weather journals I subscribe to, but
Mr Brewster's explaination seems pretty knowledgeable and rational to me
WXVANE, Meteorology, and Meteor-ology are my hobbies
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In article <4tom9n$ein@frazier.backbone.uoknordot edu>
kbrews@stratus.gcn.uoknordot edu (Keith Brewster) writes:>From:
kbrews@stratus.gcn.uoknordot edu (Keith Brewster)>Subject: Re: Reading Water
Vapor Satellite Images>Date: 31 Jul 1996 22:21:43 GMT
>In article <1996Jul31.092954.123224@kuhub.ccdot ukansdot edu>,
paul@kuhub.ccdot ukansdot edu
>(Craig Paul) writes:
>|> In article <4tleld$m91@Nntp1.mcsdot net>, radam@cttdot com (Mike Rada) writes:
>|> > Hello:
>|> >
>|> > I would greately appreciate it if anyone could, in general terms,
>|> > describe how to read a water-vapor enhanced satellite image such as
>|> > the one found at:
>|> > http://apollo.lsc.vscdot edu/gopher-data/Pictures/wxgifs.sat/h2ovapor.gif
>|> >
>|> > I.E., what do the dark vs. light areas mean, what to look for when
>|> > forecasting dry vs. wet weather patterns, etc.
>|>
>|> Areas that aren't black have some water vapor in the atmosphere. The
>|> more white the pixel, the more water vapor there is there, generally.
>|> This will vary according to whether high clouds are very thick.
>This is a common fallacy, and I cringe whenever I see it propagated
>(I do alot of cringing at TWC). The appearance of the water
>vapor channel image has little to do with the total amount of water
>vapor at any location. Like most satellite images, it is
>an indication of _temperature_, in this case, it is roughly
>the temperature of the first mm of water vapor in the atmosphere
>integrating from the top. The warmer the temperature, the
>darker the color. It is an indicator of upper-level vertical
>velocity and a tracer of upper level moisture transport.
>Since the capacity to hold moisture increases strongly
>toward the surface, there can be a lot of activity moisture present
>below that first mm that is not depicted in the water vapor
>channel images.
>|> The WVap images generally match the wind streamlines at 500 hPa (mb).
>|> Vort maxes USUALLY show up dark, as do upper level jet streams. Where
>|> there's subsidence there also tends to be dark areas in the water
>|> vapor images.
>Yes, dark areas are usually associated with subsidence aloft, that
>is air and water vapor is brought downward increasing temperature.
>Short waves are often marked by the contrast between
>upward motion (and sometimes clouds), appearing white, and
>the dark downdraft region. Since QG theory tells us there
>is a cross-over between vertical velocity at the core of the
>jet, yes the jet axis can roughly be inferred.
>-Keith
>---------------------------
>Keith Brewster
>kbrewster@uoknordot edu
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