The FAA webcam image below shows the scene a few minutes after solar noon, with the sun just 5 degrees above the theoretical horizon.
Thursday, November 7, 2013
Ineffective Sunshine
The sun is shining brilliantly in Arctic Village today, but the temperature is holding steady at around -17 °F after an earlier low of -26 °F. With light winds, this suggests a near balance between absorbed incoming solar radiation and emitted outgoing longwave radiation.
The FAA webcam image below shows the scene a few minutes after solar noon, with the sun just 5 degrees above the theoretical horizon.
The FAA webcam image below shows the scene a few minutes after solar noon, with the sun just 5 degrees above the theoretical horizon.
Subscribe to:
Post Comments (Atom)
I suppose it depends upon the latitude, solar input, surface color, surrounding air temp, and wind velocity, but midday temps in the teens on a clear calm day still allow for some surface heating and minor snow melting on dark surfaces facing the sun. That'll soon end.
ReplyDeleteAnother surface temp modifier are clouds...the high thin ones. I recall their prevalence during the PDO warm cycle years ago and wondered if and how much they affected the unusually warm surface temps in mid-winter we had at that time.
We had some more today in Fairbanks associated with the incoming weather systems to the WSW.
Gary
Gary,
DeleteYour remark about the PDO is very interesting - I wouldn't be surprised at all if the wintertime connection between PDO and temperature were partly mediated by cloud cover variations. As you note, even thin high clouds can make a significant difference, as they are a radiation source. I haven't come across this idea before in relation to the PDO, but perhaps it has been considered in the literature.
Well Richard I didn't take notes or photos from later 1976 and for the following 20 some years the PDO was considered warm.
DeleteAt that time nobody I encountered even knew what the driver of the warm winters were. Beamish, Hare, Mantua, Zhang among others didn't publish their theories until the early-mid '90's. And then only because of the unusual response of ocean reared fishery production.
All I recall was when it was first starting in the mid-later '70's to get warm in winter there were typically at least high level wisps of clouds...thin to scattered I suppose. Heavier layers at lower levels did occur concurrently as well. Clear skies still meant cold and that still happened.
I doubt any have bothered to implicate the potentially PDO-driven radiational restriction via clouds as a contributor to unusual surface temps. Surely warm air advection occurred simultaneously to some degree so why bother?
My take on that event.
Gary
Well as usual I blindly stepped in it (not talking about the dog's yard) by poo-pooing (pun) above the lack of studies regarding the PDO and "Cloud Radiational Forcing". Did a search, and without getting into the Greenhouse debate, it seems there's inferred causality by some authors. It'll take some time to read further.
DeleteGary
Example describing Cloud Radiational Forcing:
Deletehttp://earthobservatory.nasa.gov/Features/Clouds/clouds.php
Gary
Here in Anchorage, the solar angle bottoms out at 5.2° above the horizon at solar noon on the winter solstice (refraction makes the apparent angle closer to 10°). On the very lowest solar angle days that are cloud free, we have a spike in temperatures for about 2 hours. That implies a solar angle under 3°- 4° provides little to no heating.
ReplyDeleteMy "Theory" is that the PDO and other surface temp modifiers exclusive of Solar input affect a surface temp increase via high clouds among other factors.
ReplyDeleteI'd like to read about the assumed/documented effects of 10-20K AGL cloud layers on insolation/outsolation (is that a word?).
If there's a link I'll read. TU.
Gary
Gary, here is an oldie, but a goodie. http://journals.ametsoc.org/doi/pdf/10.1175/1520-0469%281945%29002%3C0154%3AIIRTCA%3E2.0.CO%3B2
DeleteThanks Brian for the link. Nothing inherently bad about old sources. Looks like a good read.
DeleteI was also pondering Richard's reference to outgoing long wave radiation via my latter post above so will pursue that aspect soon.
Clouds vs clear do have an effect during the winter perhaps as drivers for the inversions Rick nicely documents above.
Gary