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From: (FMims)
Newsgroups: sci.environment
Date: 29 Nov 1995 20:11:46 -0500

Since late September colorful twilights having durations exceeding 45-50
minutes have been observed in Texas, New Mexico, Arkansas and
elsewhere. The twilight tonight (29 November) at Seguin, Texas (29.6N
97.9W) exceeded 50 minutes.

Twilights with these durations imply the presence of aerosols in the
stratosphere. Although the most likely source for such aerosols is a
volcanic eruption, no known recent volcano eruptions have reached the
stratosphere. This does not rule out a volcanic source since some
eruptions are unobserved or unreported. Some e-correspondents have
suggested that the aerosols might be of meteoric origin. 

Stratospheric aerosols have very important significance to ozone
abundance and in climate modeling. Therefore it is important to
document as many possible observations of the current event as
possible. Please send reports of dates and locations of twilights
exceeding 30 minutes to the Sun Photometer Atmospheric Network at

Twilight duration is the time between sunset (or sunrise) and twilight
glow set (or rise). If you see an unusually long, colorful twilight but
don't know the time of sunset (or sunrise) send time twilight sets (or
rises) and your location.  We can then calculate the twilight duration. 

Thanks to all those who have sent reports thus far.

Forrest M. Mims III
Sun Photometer Atmospheric Network (SPAN)

Subject: Re: Japenese volcano vs us weather?
From: (FMims) 
Date: Oct 24 1995
Newsgroups: sci.geo.meteorology

Thanks for the response from (Gerard J. Gonthier) re.
volcano twilights, who wrote in part:

>Ok.  I'll give it a shot.  Define twilight set for consistency.

Duration of volcano twilight is time between sunset and the setting of the
colored glow. Typically the sunset will be followed by an ordinary looking
twilight. About 15-20 minutes later, there will be a large arc of orange
under a larger arc of lighter color. The time you want is when the orange
touched the horizon. Don't worry if you're a few minutes off since the
formula for aerosol stratum height (given by Meinel in "Sunsets and
Evening Skies") is approximate.

I look forward to seeing your reports--which I hope you will also post on
this newsgroup.

Forrest M. Mims III
Sun Photometer Atmospheric Network (SPAN)
Phone: 210-372-0548
Fax: 210-372-2284

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