Re: In Search of Dip Anomaly
From: Bruce J. Pennino
Date: 2013 Dec 28, 12:44 -0500
Hello Greg and Everyone:
Really interesting data, and because of it
I did a bit of "Searching" in my theodolite measurements
from the shore. I also went back and looked at
the paper prepared by WJ Peters (Dip Measurements etc). First, I
sometimes have trouble with the phrasing that Peters used. He said,or seems to
say, " Horizon never raised more than 2.4 minutes nor depressed more than
2.0 ." I herewith quote: "Values of + 2.0 ' occur quite
frequently, that is, about 1' above the average refraction at sea. The maximum
depression, -2.0', occurs once in 10 years and was observed August 11,1914 in
latitude 71 * N, longitude 5* W.... position on the northern edge of the Gulf
Stream, and not far from the ice floes of Greenland Sea in a region where
atmospheric conditions are subject to marked changes. Negative values are more
rare than positive". Negative refers to a lowering of the horizon. Also,
Peters states that near shore and ocean areas subject to warm breezes over
cold water, etc, were not included in his data set.
Looking at my 40 odd measurements, I have 7
values of clearly anomalous dip between 0.9 and 1.6 minutes of arc.
These values consider the value obtained by
0.97sqrt H (ft) as normal, so my values are higher or lower by 0.9 -1.6 minutes,
not much to get excited about. FIVE of these latter 7 points are
looking onto Long Island Sound and Cape Cod Bay, both subject to warm winds
from land or cold waters rushing in from the Race, or some odd unusual
wind/water conditions. Once I fully realized the problem with these
measurements, I tried to measure more dip data facing the Atlantic Ocean (but
still near shore and somewhat subject to local anomalies). If I were to
do additional measurements, I guess I would try to pick windy days
with onshore(maybe along shore) winds. But probably depends on how much
colder or warmer the air and water temperature are.On windy days less
stratification?
Greg, it seems you really picked a good day
and site for anomalies. When the Santa Ana winds blow, you've got to
find someone with a theodolite to set up with you.
Very best regards,
Bruce
----- Original Message -----
Sent: Thursday, December 26, 2013 10:10
PM
Subject: [NavList] In Search of Dip
Anomaly
For two days now Santa Ana winds have been blowing here in Southern
California. I have been waiting for these exact conditions of hot air over
cold water to see if dip anomaly is present.. To check for this a series of
sextant observations were made using the natural horizon which were then
compared to a series of sextant observations using an artificial horizon.
Intercepts using the natural horizon all fell between 3 and 4 NM from GPS.
Intercepts using the artificial horizon all fell between 0 and 1 NM from GPS.
It appears that 3 minutes of arc of anomalous dip is present. When prevailing
conditions return then another series of observations will be made to see if
the natural horizon intercepts and the artificial horizon intercepts are in
better agreement.
http://en.wikipedia.org/wiki/Santa_Ana_winds
Greg Rudzinski
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