Archive for July, 2013
We’ve made it to the middle of the melt season 2013. It’s been a roller coaster for Greenland climate in 2013.
The year started out with an astonishing low albedo from a snow drought that made huge melt possible. Yet this was punctuated by the return of snow late April and prolonged low temperatures as the North Atlantic Oscillation (NAO) shifted from persistent negative that had been causing west Greenland temperatures to be abnormally warm while Copenhagen thad its coldest late winter and early spring in decades. The dipole in temperatures between NW Europe and W Greenland has been recognized for more than a century and called the “seesaw” in temperature (van Loon and Rogers, 1978).
Like in 2012, melt came on strong by early June but was shut down again by abnormally low temperatures, accompanied by additional snowfalls [1, Ruth Mottram, Danish Meteorological Institute, personal communication] in some areas, that lasted until mid July. The key difference between 2013 and the previous 6 summers (2007-2012) is the absence of a persistent negative NAO that drove south air over Greenland, heating it while promoting clear skies that maximized the impact of surface darkening through the albedo feedback (Box et al. 2012). With this much of a delayed start, the albedo feedback has not had enough time to produce strong melt. Given now that we are at the mid point of the melt season, it is too late now for 2013 to produce melting anywhere nearly as large as we saw in 2012.
The NASA MODIS data indicate that the 2013 Greenland mid melt season (mid-July) albedo is at its lowest in 4 years; behind 2009, 2010, 2011, and 2012.
The 2013 June ice sheet is more reflective across the southern third than the average of the recent decade. This may also be partly a consequence of the late season snowfall which was concentrated in the south eastern quarter (Ruth Mottram, DMI). Across the northern 2/3 of the ice sheet, the difference is below average, though not as far below average as in previous years, especially 2010, 2012.
But the bigger story seems to be the preliminary July 2013 average (the first 20 days of the month) where much of the lower elevation ablation area is more reflective than the recent decade (2000-2011). This is slowing down accumulated melt. Meanwhile, the upper elevations (inland) have below average reflectivity. Why are the upper elevations (inland) somewhat below normal reflectivity? While Dark Snow project was successful in gathering surface reflectivity samples from southwest Greenland this 8th and 9th July, the samples were not from where the high July albedo anomaly is. Were it anyway North American fire smoke contributing to the reduced ice reflectivity, it could be a.) lower than normal snowfall at the upper elevations over the year . Could the albedo of 2013 literally be reflecting the ice of 2012 buried less than 1 m below the surface? The albedo signal can originate from some 10s of cm below the surface. According to DMI’s HIRLAM model estimates, there is less than 1 m of snow accumulation over much of the higher elevations. Then again, the fire factor may also be at play. We’ll be looking into this with Dark Snow project.
-  Ruth Mottram, Danish Meteorological Institute (DMI), personal communication. The DMI High Resolution Limited Area Model (HIRLAM) simulates snowfall in southeast and east Greenland. The cumulative surface mass balance indicated net mass accumulation. HIRLAM is initialized by observations from satellites, weather balloons, aircraft, ground stations, buoys, etc.
- Box, J. E., Fettweis, X., Stroeve, J. C., Tedesco, M., Hall, D. K., and Steffen, K.: Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers, The Cryosphere, 6, 821-839, doi:10.5194/tc-6-821-2012, 2012. open access
- van Loon, Harry, Jeffery C. Rogers, 1978: The Seesaw in Winter Temperatures between Greenland and Northern Europe. Part I: General Description. Mon. Wea. Rev., 106, 296–310. doi: http://dx.doi.org/10.1175/1520-0493(1978)106<0296:TSIWTB>2.0.CO;2
On the lower limit of this 4 July NASA CALIPSO laser scan, between latitude 42.60 N, longitude -68.93 W, evident is a rising smoke plume. The plume seeds cloud formation toward Greenland, reaching the southwest of the island.
The orange areas are smoke aerosols.
On 12 July, when Dark Snow scientist McKenzie Skiles, after camping, was picked up along Greenland’s longest road for a ride back to town, without prompt the driver remarked on haze in the sky from Canadian fires. McKenzie Skiles “It was the first thing he said after I got in the car, as if apologizing for the haze in the air (which was noticeable).”
hazy Kangerlussuaq, West Greenland. Photo McKenzie Skiles
9 July, 2013, we gathered snow and ice core samples from the surface and down through the 2012 melt layer, and we left only footprints. We’ll eventually see how much soot the laboratory and field spectral reflectance measurements tell us is there.
In my new position, Professor of Glaciology at the Geological Survey of Denmark and Greenland (GEUS), I’ve started to gather momentum working with a fine group of people to establish for the first time, a Greenland ice sheet total mass balance product that estimates what the GRACE satellite measures and posting the estimate on-line 2-3 months ahead of the GRACE processing.
Our new “Nowcast” of Greenland ice sheet mass balance has as little as 24 h delay from realtime.
The product exploits the fact that on average, 90% of the time, when monthly all ice sheet reflectivity (also called “albedo”) goes up, the rate of total ice sheet mass change goes down and visa versa.
The Nowcast only works in the sunlit period from mid April to mid September.
So, now as we’re mid-melt season (6 July), we finally have some interesting news…delay of the 2013 melt season due to relatively northerly air flow along west Greenland has led to the lowest elevations of the ice sheet having an above average reflectivity due primarily to more persistent snowcover (snow patches) and secondarily due to summer snowfall in some areas. According to the empirical relationship, the rate of ice melt water loss from the ice sheet to the surrounding seas has declined and now approaches the average of the 2003-2009 period.
People involved with what I like to call the “GRACE-cast” include: GEUS glaciology post-doc William Colgan; Danish Meteorological Institute (DMI) ice climatologists Dr. Peter Langer and Dr. Ruth Mottram, and Danish Tecnhical University (DTU) geodesists Dr. Valentina Barletta and Dr. Rene Forsberg.
A delayed melting at low elevations and probably some summer snowfall blanketing the Greenland ice sheet ablation area with (highly reflective) fresh snow have resulted in an important slow down of Greenland melting. This pattern is in contrast to this time last year (in 2012) when record melting was emerging.