[NLRS] Skew - T data for over Lake Superior

[Baker, Donn B]

After our trip last fall, I did some looking for data myself.  I did get
some info from the Houghton, MI area from a retired Michigan Tech professor
(W8LTL !).  He also said that the path from Houghton to Thunder Bay on 2m
has enhancement from ducting A LOT.  I don't have any of that here, but
hopefully, its where I can find it at home.

There are WX buoys in Superior, plus C-MAN stations; see the link:
<http://www.ndbc.noaa.gov/Maps/WestGL.shtml>   There is nothing for vertical
profile, however.

The "over-the-water" ducting stuff is well known and documented around the
world.  I'd even heard of it, but always associated with warm water.  Lake
Superior is NOT warm water, so I never thought the mechanism would work.
Oh, well.  Another cherished belief proven wrong.

One interesting thing in the stuff I found was that the depth of the layer
was corelated with wind speed.  Calm days produce a thinner layer than windy
days.  (Of course, TOO windy, and the layer is ripped apart.)  This would
suggest to me that the ducting is triggered by moisture content... i.e., the
more moist the air, the greater the refraction coefficient.  Low wind days
mean that evaporation is limited because the duct "seals" the surface,
reducing evaporation.  With wind to stir things up, there is more
evaporation possible, so the duct gets thicker.

73 Donn
WA2VOI/0



-----Original Message-----
From: jcplatt1@mmm.com [mailto:jcplatt1@mmm.com]
Sent: Monday, February 10, 2003 9:55 AM
To: nlrs@mailman.qth.net
Subject: [NLRS] Skew - T data for over Lake Superior



I was taking with Bob,W0AUS, at our club breakfast last Sat. regarding 10
GHz propagation over the Great Lakes and my thoughts once again turned
toward "ducting" over that large body of pretty darn cold water and what is
going on.    We know that the 10 GHz group has shown on at least several
occasions that height above the lake is detrimental to making the path and
that being located close to the water was important.   This would suggest
some type of duct effect, or maybe a boundary layer.

We do know that a refraction layer is created when you have warmer drier
air over colder moist air and that the required duct thickness for
propagation decreases with increasing frequency.   So, is Lake Superior
with its very cold water capable of cooling the air right above it and
providing moisture to that same air mass ?   Given that the lake is pretty
fixed in its physical characteristics, but the weather above it fluctuates,
are there better weather days to look for any ducts over the lake, like
perhaps a warm dry day with little or no wind ?     A humid day may be bad
for duct forming in this case as it may neutralize any boundary.

So, here is my question, is anyone aware of temperature & dew point data,
or studies, for the summertime over the Great Lakes, preferably just the
lowest 200 feet or so, with vertical resolution (data points) of 10's of
feet ?    Best data would include air pressure, air temperature, and dew
point for each vertical data point (just like the sounding balloons that
the NWS puts up twice a day).

73, Jon
W0ZQ

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