Figure 1: A snow pit near the headwaters of Imnavait Creek. The researcher is whisking the pit face to accentuate the layers (P. Martin photo).

To help interpret the snow pit, we use a variety of tricks to delineate and accentuate the layers. For example, using brushes, we whisk the pit face (Fig. 1). This sweeps away material from the weaker layers, making the harder wind slabs stand out in bolder relief. Another way is to back cut the pit, allowing sunlight to shine through the snow, essentially the same effect as if we were looking at a section of the snow on a light table (Fig. 2). Both the brushing and the light tend to highlight the grain differences between layers, and these differences arise from differences in snow metamorphism. Surprisingly little of the layer texture is due to the nature of the initial snowfall. A third, newer method to expose the layers, is to photograph the pit face using a near-infrared camera, which is very sensitive to variations in light reflection due to grain size differences. Unfortunately, this method requires post-processing, so it does not have the immediacy of the other methods.

Figure 2: The backside (sunny side) of the snow pit has been cut away to allow light to pass through the snow layers.

There are dozens of types of snow layers in nature (not to be confused with snowflakes, of which there are many as well): new snow layers, recent snow layers, fine-grained layers, melt clusters, ice layers, grauple. And there is hoar: surface hoar and depth hoar. It turns out these latter are both very common in the Arctic, and in a moment I will explain why, but first a disclaimer: this type of hoar is quite different from the other type, more commonly found in gangster movies etc. The

Figure 3: Frost feathers (also known as frost flowers) on a freshwater ice surface.

Figure 4: Depth hoar from the base of the snow pack (J. Holmgren photo). The sharp edge in the foreground was facing downward during growth.

The reason why the Arctic snow pack has such a high percentage of depth hoar and frequent surface hoar formation is simply because it is cold. It will come as no surprise that this is a cold place in winter, and even when spring is arriving (as it is now), it can still be extremely cold at night. Cold air creates temperature gradients. The snow surface will be perhaps -30°C, while the base of the snow will be -10°C. Heat moves from warm to cold, and moisture follows the same gradient, so moisture in the form of water molecules are constantly moving upward from the relatively warm ground surface below the snow through the porous snow pack, condensing on the lower sides of crystals, causing them to grow (and have razor-sharp edges), and sublimating from the tops of the grains, making the tops rounded. In the case of the surface hoar, on a cold, clear night the snow surface cools by long wave radiation, and soon is the coldest surface around. Any moisture migrating upward from below, or downward from above, condenses out as surface hoar. All three types of crystals are ornate, with sharp edges and well-defined facets because they grow in very moist environments. The supply of moisture for growth is not the limiting factor: instead the crystal kinetics control the growth (a good topic for another blog. The end result is beautiful crystals in all there cases.

These are the hoars….surface hoar, depth hoar, hoar frost. While they can be found in many snowy locations, they can be found in their prime in the Arctic.

Figure 5: A field of barchans (horn-shaped snow dunes) march down a hill into a creek in Western Alaska.

(Click on image below for animation)

Figure 6: Time lapse of a barchan moving past our webcam. Note the horns pointing downwind (A. Gelvin images).

Figure 7: A field of unusually large (and hard) sastrugi.

Figure 8: The end result of the snow pit with lots of depth hoar and a thick, hard wind slab right in the middle.

We are not the only ones in the Arctic thinking about wind slabs. Large animals like this muskox (Fig. 9) and caribou have to work down through these hard slabs to get at their food. A hard wind slab can make that effort too taxing, so they are excellent at finding where the slabs are thin or non-existent…..better even than Arctic snow scientists at doing so. But more on this process (called cratering) tomorrow.

Figure 9: A muskox has been doing some serious cratering in the snow.

Ptarmigan gather in the willows (C. Polashenski)

Figure 1: My four companions at Atigun Pass (from left: Simon, Philip, Art and Chris).

We five are the advance team for a campaign to measure the snow cover of the North Slope of Alaska. The snow cover (Fig. 2) here lasts 8 months of the year, and it is important for several reasons. First, somewhere between 50% and 80% of the run-off in the rivers in this part of Alaska come from snow melt alone. Second, the snow is an effective insulator that keeps the ground from freezing even more deeply during the winter than it does now. Without the snow the permafrost here might be thicker, the summer thawing active layer thinner, and the plant life less verdant. Third, the snow is a wonderful reflector of solar energy (it has a high albedo, reflecting about 85% of the light that hits it), which effectively keeps Northern Alaska cooler in the winter and early spring than it might otherwise be. If it seems like these last two are contradictory, you are right. There is a fine balance between the insulation effect and the solar reflecting effect of snow, and this balance plays a critical role not only in the climate of the Arctic, but also of the entire planet. So in short, in a place like Northern Alaska, snow matters, and we had come to measure its properties.

Figure 2: Snow blankets the slopes of an unnamed mountain south of Atigun Pass. Notice the drifts. (C. Polashenski photo).

Many other methods of measuring snow depth have been tried: Mono-pulse and FM-CW radars on sleds and helicopters, passive and active microwave transmitter/receivers on sleds, aircraft and satellites, gamma-ray detectors on aircraft, and even satellite borne gravimeters. To date there have been some successes, but really no operational quality methods have emerged that work for all types of snow, and the problem has been especially acute for snow that tends to be thin (<100 cm in general) like the snow of the North Slope of Alaska. However, the recent development of scanning LiDAR (Light Detection And Ranging) equipment may be the game-changer. Mounted on an aircraft looking downward, one of these scanning devices can create a swath map of the snow surface with near centimeter precision. If a second map of the exact same area is acquired when there is no snow, the two surfaces can be differenced to produce a snow depth map. DGPS (Differential Global Positioning Systems) make this precise co-registration possible. In principle, all this could be done with sufficient accuracy to produce useful and reliable snow maps, but is it possible in practice? That’s why we were driving North on Easter Sunday. And this snow depth problem is not simply academic. The State of Alaska and the Federal Government manage thousands of square kilometers of land on the North Slope and have to make decision where and when oil, gas and mining companies can be allowed to transit over the tundra. Open the tundra too soon with too little snow cover and the tundra will be damaged; open it too late and the companies may not be able to effectively explore for or develop strategic deposits (Fig. 3).

Figure 3: An oil rig near Prudhoe Bay, Alaska.

We have been preparing for the campaign for months, and had been packing for days. In addition to our advance team, 7 more people will be coming in at the end of this week to help make the thousands of ground-based measurements we will need to check the accuracy of the airborne LiDAR products. The aircraft will be coming a week from now.

Today, we are driving two rigs north pulling snowmobile trailers. Our pickup and the SUV were packed full, and on the trailers were three snowmobiles, four plastic sleds, and a special sled for a ground-based LiDAR (more on this later too). Everything was covered over because we were expecting a muddy trip. We left Fairbanks at 8:30 AM. From Fairbanks, the first part of the trip (245 km) is through the spruce- and birch-covered hills of the Yukon Tanana uplands along the Elliot Highway. Next it follows the Dalton Highway, which runs through the Brooks Range at Atigun Pass (Fig. 4). The latter is also know as the Haul Road, as it was built in order to haul materials north during the building of the Trans-Alaska Pipeline. The Dalton is steeper than normal highways, much of it is dirt (or used to be), and it is mainly transited by truckers headed to the oilfields of Prudhoe Bay. For those who watch Ice Road Truckers (Season 3), it details the tribulations of the truckers along this stretch of road… and exaggerates them considerably. Personally, I think I have driven over Atigun Pass more than 40 times in winter, and while it requires care, it is more beautiful than dangerous.

Figure 4: Looking north from Atigun Pass. Art and Philip are in the truck and trailer in front of us. (C. Polashenski photo).

Figure 5: The bridge over the Yukon River (note the semi headed south…the main traffic on the road. (C. Polashenski photo).

The trip started to get more exciting as the Brooks Range came into view. We always gas up at Coldfoot (Fig. 6), which to me marks the south edge of this great mountain range. Coldfoot was founded in around 1902 as a gold mining town. Legend has it that miners who had penetrated this far got “cold feet” and turned back south, fearing the on-coming winter and slow starvation. Many years later, the famous Iditarod musher Dick Mackie founded the truck stop/café/tourist attraction that still exists today. Lots of visitors come through here in the summer because it is a jumping off place for trips into the Brooks Range. Not far away is the other old gold mining town of Wiseman, made famous by the writings of Bob Marshall (Fig. 7). Marshall came into the country

Figure 6: Coldfoot Camp.

Figure 7: Bob Marshall (4th from left)

From Coldfoot we wound through the Brooks Range following the Koyukuk River drainage toward its head, passing Sukapak (Fig.8) and Snowden Mountain and climbing up on to the Chandalar Shelf. Here the wildlife became spectacular….hundreds of caribou (Fig. 9) grazing near the road, ptarmigan in full white winter plumage (Fig. 10) enjoying the sunny day out on the tundra, and even some Dall sheep. From the Shelf, we continued climbing up to the Pass at 4739’ (1444 m). When I was a student first

Figure 8: Sukapak Mountain (C. Polashenski photo).

~ Matthew

Tomorrow: Setting up a control network on the Arctic Tundra.

Figure 9: Caribou near the road (C. Polashenski photo).

Figure 10: Ptarmigan enjoying a sunny day on the tundra (C. Polashenski photo).

Figure 11: The long road North (C. Polashenski photo).

Figure 12:Not only gangsta’s have spinners!

Art working on the Gradient Tower

Returning from a day of slogging

Matthew stands in the fog and snow.

~ Matthew Sturm

Brooks Range

Toolik Lake

Musk Ox

~ Chris Hiemstra

Overview of the Barrow SnowNet site

Soggy Crew

Winter can be harsh on electronic equipment several miles out on the tundra. Cables that are supple and bendable in 40°F weather will snap like Styrofoam when it is -40°F. Tasks like tightening a bolt that can be done in mere seconds in daylight with warm bare hands can be almost impossible in the dark in the narrow beam of a headlight where the cold wind renders fingers un-useable in minutes. Not surprisingly, we have generally found it best to perform a thorough renovation of our instruments in summer. But that means getting wet, and a long slog over the tundra carrying heavy batteries and other equipment.

Chipping Ice

This year the big surprise was the solid-state snow water equivalent gauge (SSSWE). This gauge, which consists of nine aluminum panels, each 3 by 3 feet, weighs the snow that covers it in winter. Beneath the aluminum plates is a plywood and insulation base designed to keep the tundra from thawing and having the whole affair go out of level. However, this year, the insulation and a cold spring resulted in the formation of segregation ice, a common feature in permafrost, but a bad thing under a SSSWE. Segregation ice forms when ground water migrates to a freezing front. Typically this freezing front is at the bottom of the active layer, but in our case it was at the bottom og the insulation. At the freezing front, a layer of black ice forms and thickens. In our case, it seems to have grown several inches thick over the past 2 years, heaving up the SSSWE. The solution to the problem was to pick-axe the ice to pieces and then shovel up the ice cubes and mud.

Barge and Welcome Sign

We weren’t the only ones in Barrow hurrying to get ready for winter in August. Barges were coming in with the annual supplies for the town, as well as staging equipment for a major drilling campaign this winter. It has been in the news that Shell Oil will be drilling for oil and gas in the Chukchi Sea off of Barrow in the future, but this is a different campaign. Gas fields have been known, and utilized by Barrow, since the late 1940s. Gas from a series of wells out on the tundra south of town supply the fuel for heating and electrical generation. But with growth has come higher demands for fuel. The existing gas wells are no longer sufficient to supply the need. This winter several more wells will be drilled. This is an enormous undertaking requiring tons of gear, most of which has been coming in from Prudhoe Bay. We were told that 30 barge-loads would be needed before all the required equipment is on the beach at Barrow.

Snow fence tower

We finished our maintenance work by reconstructing the towers we have near the Cakeater snow fence. This fence creates a drift that can be almost 15 feet deep. The towers hold sonic sounders that measure the snow depth as the drift builds up. Each tower is guyed out using ¼” steel cable. The weight of the snow on these cables during the winter can ( and has) snapped the welds on the towers. As long as the towers are encased in snow, they are fine and won’t fall down, but once the snow melts (in late-July) the towers become wobbly and unstable. We have to re-cable them and re-level them so they are vertical. The area where this thick drift sits for 10 months of the year is a bad place for plants. They get crushed by the weight of the snow, flooded by the snow melt, and deprived of sunlight for much of the summer. Almost nothing can grow under those conditions….just some water-tolerant mosses. The end product after 20 years of enormous winter drifts is a mucky bog and ponds next to the fence.

Snow on the ground still in late June…..new snow in late-August: winter is long in Barrow. No wonder we are thinking about winter in August.

Matthew Sturm