Giant Towers over the Olympic Mountains

During the past week I received a startling picture from Andrew Laszlo, a doctoral candidate in the UW Physics Dept.   Andrew had been hiking in the North Cascades and took the following picture of the Olympic Mountains at 11:25 AM, December 8th.  Huge towers, resembling mesa, loomed high in the sky, well above the usual position of the Olympic peaks.

Had the mountains grown suddenly?  Rapid uplift?   A photoshop moment?

No, this was a wonderful example of a superior mirage, when the atmosphere acts as a weird lens that causes objects to appear bigger and higher than they should be.  Let's investigate.

First, the facts.  The following map shows the location of Andrew when he took the picture.  He reported being at 6900 ft at the time.

Light can be bent in strange ways when there are very large changes of temperature in the vertical.  We can get an idea of the temperature structure at the time from reports from planes taking off and landing at Seattle;  some are equipped with weather sensors.   Courtesy of UW's Mark Albright here are the temperatures from an aircraft taking off from Sea-Tac Airport at 11:36 AM (1936 UTC) Dec. 8.

If you look closely you will see a strong inversion between  5722 ft and 6932 ft (from -11.1 to -7.7C), an inversion right below Andrew's location when he took the picture.  Confirmation of the inversion came from the radiosonde sounding at Quillayute, on the WA coast.  The sounding was for approximately 4 AM

Temperature is in red. You see how the temperature warmed abruptly below around 780 hPa pressure (about 6900 ft). 

When you have cold air below, with warmer air above, separated by a sharp inversion, the abrupt change in atmospheric density that results can produce a lens effect that makes object loom upwards.   As noted above, this is called a superior mirage, and is illustrated in the two schematics below.

This phenomenon is also known as the Fata Morgana, named after the illusions produced byKing Arrthur's enchantress half sister. 

 Finally, I should note that others have observed this phenomenon before around the Olympics.   Here is a picture of the Olympic Mts. I found taken from Vesper Peak in the North Cascades on Dec. 3, 2011.  The picture was taken around 12:30 PM at around 6200 ft.

Picture courtesy of Steph Abegg

What did the radiosonde sounding look like at Quillayute that afternoon?  Here is it (for 4 PM).   850 hPa is about 5000 ft and the two black lines are temperature (right one) and dew point.  Another strong inversion below the photographer's location!  Further support of the inversion causing the superior mirage of the Olympics when viewed from altitude in the North Cascades.

2014 Washington Weather Calendar
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Then consider the 2014 Washington Weather Calendar!  You can order online (about $15. plus shipping) here.  A few dollars  goes to the UW Chapter of the American Meteorological Society for each calender.  A fine holiday gift for the weather lover.

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