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    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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