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    Re: The taxonomy of refraction
    From: John Huth
    Date: 2011 Apr 1, 05:18 -0400
    Marcel  - 

    It makes a lot of sense.   The shift in water temperature on either side of that island/peninsula is dramatic, particularly that time of year.   So, although we don't know for sure, it seems like it's a good explanation to me (much better than rewriting the laws of optics).

    Best,

    John H. 

    On Thu, Mar 31, 2011 at 3:47 PM, Marcel Tschudin <marcel.e.tschudin---.com> wrote:
    John,

    When I saw the high resolution SST data from JPL I couldn't resist to zoom-in to the area where you took the photos of the inferior mirage and for which we haven't been able before to explain the corresponding atmospheric condition. It's thanks to those high resolution data that we know now the possible origin of the cold air over the bay and also the possible reason why you haven't been able to notice it at your place.

    Marcel




    On Thu, Mar 31, 2011 at 8:00 PM, Apache Runner <apacherunner---.com> wrote:
    Marcel - 

    That sounds roughly correct to me.   I do know that the air on the ocean side of Monomoy Island (that peninsula you see) is much colder.   I've kayaked on that side of the island and the temperature difference is astonishing.   So, it certainly seems like a cogent explanation.

    Good detective work!

    John H. 


    On Thu, Mar 31, 2011 at 12:08 PM, Marcel Tschudin <marcel.e.tschudin---.com> wrote:
    After a second thought: It looks like the SST-data sent in my at last mail may actually at last be able to explain the atmospheric conditions for the inferior mirage, this together with the attached meteorological data for Chatham at 41.7N, 70.0W for the same day of Aug. 10, 2010:
    - In the bay south of Chatham, and the island south of it with the light house, the sea has a SST of about 23C to 24C.
    - East and South-East of the bay the SST is considerably colder, between about 16C to 19C.
    - Air coming from East or South-East is likely to have cooled at the cold sea surface.
    - The meteorological data for Chatham show that during the afternoon the wind turned from South-West to East and may then thus have covered the warm sea in the bay area with cold air.
    - The temperature records at Chatham indicate that some cooling took place when the wind started to come from east. The SSTs east of Chatham were however generally not quite as cold than further south. In addition, the meteorological station which is about 2 km from the coast may also be somewhat protected.

    May be John can tell us to what extend this scenario agrees with what he remembers when taking the photos.

    Marcel



    On Thu, Mar 31, 2011 at 3:58 PM, Marcel Tschudin <marcel.e.tschudin---.com> wrote:
    In January an abnormal refraction phenomenon near the horizon has been discussed here under the above subject. In this context I provided some links to atmospheric data which may help to understand the conditions which led to the phenomenon. One such source related to the Sea Surface Temperature (SST) where I wrote: "The best I could find so far for your area is here http://www7320.nrlssc.navy.mil/global_nlom32/ ...".

    I previously had access to data with higher resolutions than those provided under the mentioned navy-mil-link but which - for some reason - were not any more available at that time. It looks to me like a concentration process has been going on for providing world-wide data of the seas. I recently have been advised to use now the following Web-based-tools for accessing (analysed) data:
    - For "recent" historical data: http://ourocean.jpl.nasa.gov/ and
    - for "older" historical data: http://data.ncof.co.uk:8080/ncWMS/godiva2.html
    The JPL-data have a higher resolution than NCOF-data but the JPL-data are at the moment only available for the last two or three years. The data sets are updated on a daily base.

    These sources may eventually be useful when investigating some abnormal refraction phenomenon. However, in the case of John's photo of the light house it unfortunately can not explain the reason for the inferior mirage. The sea was about as warm as John mentioned and the air had about the same temperature or was even slightly warmer. I attach here a screenshot of the JPL-data for August10, 2010 showing the SSTs in the area where John took the photos from the light house.

    Marcel






    --
    Keeping up with the grind





       
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