Minchumina Follow-Up

Yesterday I posted what I thought was a bit of a mystery regarding solar radiation and temperature data from the Lake Minchumina RAWS, but within just a few minutes reader Gary pointed to a possible solution: increasing shade from vegetation that may have grown up right next to the RAWS instruments.  Here's a 2004 photo from the Western Regional Climate Center website (click to enlarge):

As Gary noted, the photo faces approximately east, so the tree growing up on the right side appears to be roughly southwest of what look like the thermometer and pyranometer in the middle of the arm.  Obviously if this and other vegetation hasn't been controlled in the 10+ years since the photo was taken, then it may have provided increasing amounts of shade over the instruments in recent years; and this would explain the reduction in both solar radiation and warm bias.

Interestingly the hourly solar radiation data support the idea that shading has developed from objects to the south and southwest.  The chart below shows the mean hourly solar radiation (units of langleys) during May on a kind of polar plot; the distance away from the center indicates the radiation amount in each hour, and the angle from the vertical corresponds to the average position (azimuth) of the sun in that hour.  So over the course of the day the solar radiation starts small in the east, increases as the sun moves towards the south, and decreases as the sun goes west.  The blue line shows the averages for 2009-2013 and the red line is for 2015-2017.

The plot makes clear that the reduction in sunshine is fairly small in the morning until about 11am in May, but then it appears that the shading effect is pronounced by around 1-3pm, when the sun is just west of south.  This is nicely consistent with the apparent location of vegetation in the photo.

The charts below show similar results for June, July, and August.  Interestingly the month of June is the only month in which there appears to be no shading from the southeast, i.e. around 9am-noon, and this makes sense if we consider that the sun rises highest in the sky near the solstice; so whatever vegetation has grown up to the southeast, it's apparently not yet high enough to cause shading in June.

In conclusion, I think the problem is just about solved - it looks like the Minchumina radiation data have been seriously affected by shading in recent years, and this has also altered the temperature bias relative to the nearby airport thermometer.  Final confirmation will await a site visit: anyone want to take a field trip?

Gina Puffin Feeder

Here's a link to a website I just learned about yesterday: the GINA Puffin Feeder site. GINA is a group at UAF that is involved with capturing and distributing Alaska and high latitude imagery from a wide variety of sources.  I've used GINA's Swath Viewer for some years, but yesterday I saw a presentation on the GINA Puffin Feeder website that is distributing imagery from the new VIIRS polar orbiter satellite. It has a variety of interesting images, including true color, landform and a low light visible channel.

Here's the low light visible image taken at 4am Friday. This is unprocessed by me; this is as-is on the website. Look at that detail! The bright swirl on the upper left hand side of the image is aurora, and the lights of Prudhoe Bay, Anchorage and Fairbanks are all clearly visible.

Wickersham Dome Weather Station

Big news for Fairbanks area weather buffs: a new automated weather on Wickersham Dome came online yesterday.  It is located near the White Mountains National Recreation area Wickersham Dome Trailhead at Mile 28 Elliott Highway. This is about 20 miles northwest of Fox. The station is at an elevation of 2230' MSL. This is a bit below treeline, and the anemometer is about level with the tops of the tallest trees around it. This is a great place for a weather station and should provide useful temperature and wind information in the winter, plus rainfall data in the warm season. This area gets a lot of convection, and this station fills a big hole in the rain gauge network north of Fairbanks. You can find the data from the Wickersham Dome weather station here and here.

Created by RT with Google Maps

To the right is a map I ginned up showing the locations of real-time reporting weather stations at higher elevations (vaguely) north and west of Fairbanks. I have NOT included any of the CWOP or Weather Underground personal weather stations, as the data availability and quality are highly variable. At the link for this map you can find additional information on the specific sites as well as the weather stations at elevation east of Fairbanks. 

New Webcam

Yahoo! The FAA's webcam high atop Ester Dome, northwest of UAF, is finally online. Here's the southeast view from 418pm ADT Wednesday. There are also views looking north, southwest and west. You can plainly see Chena Ridge and the Tanana River.

Temperature Differences

Measuring the temperature of the air seems like a simple thing, but in fact getting an accurate measure is actually not so trivial. For meteorological/cimatological purposes we of course want to keep the sensor out of the sun (because we're interested in the temperature of the air, not the temperature of the thermometer). This is done by enclosing the thermometer (or temperature sensor) in some kind of enclosure. But you want to keep the air moving through the enclosure, otherwise the mere fact that there is an enclosure will impact the temperature of the air inside.

So, there are basically two approaches used. First, have a fan move air from outside the enclosure across the thermometer and then out, or design you enclosure so that air can move freely through. The fan approach is termed aspirated, the second is termed passive. Usually there is not not much difference, but conditions this week, with brilliant sunshine, a still solid snow cover and not much wind are producing small but consistent differences. The graphic above shows the high temperatures on Wednesday. As you would expect, aspirated sensors run a little bit cooler.

More Cold

Scott Bachmeier sent a link to this false color infrared image from early Friday morning (I've reoriented the original image to be longitudinally centered over Alaska):

The purple colors are radiance derived temperatures -50C (-58F) and lower. Over mainland Alaska any temperatures this cold are surface temperatures. These are a bit lower than the surface observations. The difference comes from several different sources, the most of significant of which are satellite calibration and the fact that "surface observations", i.e. METARS, cooperative obs, etc are from thermometers exposed above the surface. Nominal exposure 1.5 to 2 meters above the ground, though some are routinely higher (SNOTEL, RWIS). The presence of the mid-winter snowpack makes the actual thermometer exposure something like 0.5 meters lower in most places north of the Alaska Range.
Skies cleared by mid-morning over Fairbanks. By Noon temperatures have been down to 41 below at the Airport and 42 below at Fort Wainwright and Goldstream Valley.

New Barrow Webcam

The long awaited FAA webcam at Barrow is now online. This does not have a coastline view like the UAF Sea Ice program does, but should be more reliable. Here's the view looking east across the runway noon Tuesday.

It was NOT 97 degrees at Northway in July

Okay, I guess have have to say this: It was NOT 97 degrees at Northway in July.

There is a news story going around about record highs in all 50 states in July, including 97F at Northway on July 11th. 97F would be an all-time record high for Northway.

Except that the high temperature on July 11th at Northway was 77F.

The 97F high temperature was encoded in an observation, but the temperature sensor was bused (probably the aspirator fan failed). The FAA observers did correct the daily max temp after the original observation went out to the world.

Other high temps that day were in the upper Tanana Valley region were in the upper 70s and lower 80s.

Moral of the story is the same as always: constant vigilance.

FAA WebCam at Central

New FAA Webcam at Central came online last week. Here's the north-looking cam Tuesday afternoon. Nice view.

Problems with Interior Temps

Problems with manual obs on Friday: Fort Yukon 104F (FYRA2 RAWS had 86F) and 92F at Chandalar Lake, and 84F at 11am. I don't think so.

The problem at Fort Yukon has been ongoing for months: the AWOS has been out of commission since the comms lines were back-hoed over the winter, and the FAA contractor appears to have a thermometer in the window that gets evening sun. On May 27th Fort Yukon reported a temp of 102F. The RAWS is on the airport grounds, and looks reasonable.