Thunderhead magic from far out at sea

To the editor:

On June 19, I encountered an ocean light phenomenon off Little Compton that I haven’t seen in the 60 years I’ve been staring out at the ocean in these parts.

It was a flashing band of white light at the ocean horizon.  Very thin in elevation, and parallel to the horizon, and right at it, in a broad arc of the horizon — perhaps 30-40 degrees.  It looked like someone was turning a fluorescent light on and off. Occurred perhaps on average once every 10 seconds.  No obvious rhythm to it. Flashing continued for perhaps 15 minutes.  Not a hallucination.  My wife first observed it and I confirmed it.  Google of no help.

This observation occurred from the cliffs of Little Compton above and west of Town Beach at sunset — opposite the setting sun but at an angle to it, toward Massachusetts.  The sun was setting behind my right shoulder.  Looking southeast toward Martha’s Vineyard, albeit at a great distance, it continued along the horizon south of that.  The phenomenon occurred largely over open ocean.  Clouds — negligible.  Visibility — near unlimited.  Height of eyeballs above sea level — perhaps 50 feet.  Time — 6:30 p.m.-ish.

I contacted Tom Champoux at the American Meteorological Society in Boston about my stumper.  He graciously passed it on to Executive Director Keith Seitter.

Seitter initially replied:

“I cannot be sure, but the only guess I have is that they were seeing thunderstorms at a great distance away.  I checked the satellite loop from last evening.  The front that caused rain and showers [along] the south coast earlier in the day yesterday moved slowly southward and triggered a pretty massive thunderstorm complex on the order of 100 km to the southeast of RI.  At that distance, the tops of the thunderstorms would be a thin line at about the horizon, so when lightning flashes lit them up, all you would see was that thin band of the anvil tops being lit up.  Despite the distance, the air behind the front is quite clear, with low humidity, allowing great visibility.”

Then, the next day, Seitter added:

“I looked at this a little more carefully, and the thunderstorm complex was even further offshore than my first guess (probably a couple hundred km).  That actually makes it more likely that they were just seeing the top layers of the thunderstorm anvils near the horizon, but also reinforces why this would only be visible in a case like this when the air behind the front was really clear to allow high visibility.”Thanks to our Boston meteorological neighbors for their sage thoughts.

Cheers,

Joel Garreau

Little Compton

 

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