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Headshot of Emily Lakdawalla

A rare clear day in Alaska

Posted By Emily Lakdawalla

12-07-2013 6:00 CDT

Topics: pretty pictures, Earth, Earth observing missions

NASA recently shared a gloriously detailed image of an unusual clear day in Alaska as seen from the Terra satellite, one of the pair that provides the United States with regular, frequent, detailed satellite photos of areas all over Earth. Terra and its sister Aqua help us with land use monitoring and disaster response because of their reliable, repeatable photo coverage. But they can't see through clouds, and when you're talking about Alaska, that severely limits what we can see. Well, on June 17, it was a rare clear day, and you can see the relatively undeveloped Arctic state in all its forested, mountained, snow-capped, running-river glory. Check out the meandering river channels, and the plumes of sediment where they empty into the ocean. Look at the decaying sea ice next to the coast, and the funny blebs of ice on the land near the northern coastline. You can tell where the land slopes more steeply and where it's more level by the shapes of the rivers -- they're straight on regional slopes, windy and curvy on flat floodplains. Enjoy the creamy turquoise color of lakes fed by glacial streams choked with "rock flour" ground from the bedrock by the slow motion of mountain glaciers. So cool.

Rare cloud-free view of Alaska from Terra MODIS

Image: NASA/Jeff Schmaltz, LANCE MODIS Rapid Response Team, NASA GSFC. Caption: Adam Voiland

Rare cloud-free view of Alaska from Terra MODIS
On most days, relentless rivers of clouds wash over Alaska, obscuring most of the state's 10,690 kilometers of coastline and 1,518,000 square kilometers of land. The south coast of Alaska even has the dubious distinction of being the cloudiest region of the United States, with some locations averaging more than 340 cloudy days per year. That was certainly not the case on June 17, 2013, the date that the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite acquired this rare, nearly cloud-free view of the state. The absence of clouds exposed a striking tapestry of water, ice, land, forests, and even wildfires.
 
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Read more blog entries about: pretty pictures, Earth, Earth observing missions

Comments:

UKahan: 07/13/2013 01:16 CDT

Emily, I saw this picture on the NASA website when it was featured there. The blurb below the picture says that this cloudless state was caused by a high-pressure region over Alaska (at the time of imaging), which they also imply was behind the unusually high temperatures recorded at the time. Can someone explain this? I thought high pressure regions meant calmer, and more pleasant weather in general. There are no inbound winds, and the whole reason you have a high pressure in the first place is because the solar flux is lower than it is in the neighbouring areas. If anything, it ought to be cooler than usual. Meteorology is a complex beast, sensitive to hand-waving arguments that don't use numbers, and especially sensitive with respect to the direction of causality, but I'd also like to know how a high-pressure region leads to cloudlessness. I understand water vapour condenses with altitude, but I always figured that it was because the temperature lapse rate outpaces the pressure drop.

Samer Hariri: 07/13/2013 11:09 CDT

Very beautiful, thanks for sharing :)

Samer Hariri: 07/13/2013 11:21 CDT

UKahan , a high pressure system means the atmosphere is pushed closer to the ground so the molecules in that region of atmosphere are compressed, thus increasing temperature which in turn warms up the area and prevents condensation thus no clouds. Of course with no clouds the sun warms up the area even more during the day, which adds to the temperature. Hope this helps!

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