Wednesday, December 12, 2012

Darkest Before the Dawn

It has been very, very dark around here lately.  


 In fact, the measurements of solar radiation on top of the atmospheric sciences building showed that today was the 6th darkest day since the beginning of the year, with Sunday being the fourth darkest (thanks to Mark Albright for supplying these numbers).  Here is the total daily radiation in megajoules per day per square meter (megajoules is an amount of energy) for the darkest days of the year:

19 Nov 2012 0.47 
23 Nov 2012  0.49
4 Jan 2012    0.76
9 Dec 2012    0.79
15 Jan 2012   0.93
11 Dec 2012   0.94
22 Jan 2012   0.99


In mid-summer we often get above 20, and occasionally above 30.  Yes, we can get 20-30 times more radiation in summer than during this dark days.  No wonder we feel better then.


But I have some very good news for those with Seasonal Affective Disorder (SAD) or the need to wear sunglasses... sunset is no longer moving earlier and today sunset actually occurred slightly later than yesterday.

Here are the sunrise/sunset table for Seattle. Sunset has bottomed out at 4:18 PM and WILL BE 4:19 by Sunday.  A reason to rejoice.  Now the day is still getting shorter and will continue to do so until December 21st, so don't get too excited. 


Does the sun look any bigger to you during December?   Did you know we are closest to the sun during midwinter?  The table shows our distance to the sun; you can see we are getting closer and closer!  If that weren't true our winters would be even cooler.  We are actually farther from the sun during summer.

The shortest day of the year and the earliest sunset do not coincide because the day is not exactly 24 h and the earth's orbit around the sun is not circular.  But those details belong in an astronomy blog.

Super dark days like today start with weak winter sun and add to it a deep, multilevel cloud deck.   Here is the visible satellite picture for this afternoon at 1 PM Tuesday--you can see the thick frontal cloud band that messed up our day.


More good news: today will be a bit brighter, with no major system in our area.  At least the darkness and clouds keeps the influx of Californians down to a reasonable level.  Let them think we are the land of darkness, rain, and vampires.

15 comments:

jamesdeanreeves said...

"Does the sun look any bigger to you during December?" - That's not funny, Dr. Mass! I don't believe we've seen the sun since November! ;^)

Tom said...

Does that mean southern hemisphere winters are on average colder than northern hemisphere winters?

Restless_one said...

Tom, there's a lot more variables than just the sun's radiation. Say the fact that the North Ice caps sit over water and aren't as large as the Antarctic ice Caps. Then factor in the larger amount of water in the Southern Hemi and the effect this has on cooling/warming as well as wind. Then factor in local phenomena. In closing, you can't really make a generalization. I'd guess it's colder, but more based on the mass of ice, which I assume is more of a factor of the huge land mass.
But I repeatedly heard the argument that the solar radiation is more "intense" while in NZ due to this proximity(and the thinner Ozone layer).

Mulva said...

As many commented on December 3rd -- it's not that it rains too much here, it's that it's gets really grey and very dark for a sustained amount of time. If we had one *very cold* (like in 30s) day and it was matched with bright sunshine once every 10 days in the winter, I'd be perfectly fine.

Eric said...

Thanks Cliff, I have often wondered if the solstice and the earliest sunset coincided or not.

Mai Pai said...

When will sunrise start getting earlier? I can barely get out of bed in the morning.

Westside guy said...

Cliff, what is this "sun" of which you speak? I don't believe I'm familiar with that term.

MidWest Bill said...

How can I get that chart for Springfield, Il?

TIA.

TomP said...

Cliff I'd love to learn more about the aggregate darkness of days in Seattle. Do you have more information you can point us toward?

Rob said...

Are we going to see snow at all this year?

Mariana said...

MidWest Bill, try http://aa.usno.navy.mil/data/docs/RS_OneYear.php
The output is not as user friendly and complete as Cliff's, but it'll do the job in terms of sunrise/sunset times.

Rod said...

Midwest Bill,

Try this in your browser:

http://www.timeanddate.com/worldclock/astronomy.html?month=12&year=2012&obj=sun&afl=-11&day=1&n=893

Mike said...

Can't resist:

http://youtu.be/09tb8luF82c

Amber said...

I noticed this past week that our Christmas lights (which are set to turn on at 'dusk' and off 6 hours later) would be off when I got up at 7am, then on again around 7:20am for about 5 minutes before turning off again due to 'dawn'.

Indeed, darkest before dawn.

Barbara Biddle said...

Hey Cliff--Being the L/C and the weather enthusiast that he was, Bill would have loved this column. Barbara