The image above shows springtime melting of Arctic sea ice extent over the month of April 2020. As usual the process of declining ice extent follows a LIFO pattern: Last In First Out. That is, the marginal seas are the last to freeze and the first to melt. Thus at the top of the image, the Pacific basins of Bering and Okohtsk seas show a steady decline in ice. Meanwhile at bottom left, Baffin Bay ice retreats from south to north. Note center left Hudson Bay loses very little ice during the month. The central mass of Arctic ice is intact with some fluctuations back and forth bottom right, as patches of water appear in Barents and Kara Seas.
The graph below shows the ice extent retreating during April compared to some other years and the 13 year average (2007 to 2019 inclusive).
Note that the MASIE NH ice extent 13 year average loses about 1.2M km2 during April, down to 13.5M km2. MASIE 2019 started much lower and lost ice at a similar rate, ending nearly 800k km2 below average. This year started in the middle of the other tracks, the most interesting thing being the wide divergence between SII and MASIE reports for April, with a sawtooth pattern alternating loses and gains. The two indices were close in the beginning, but the gap grew to 600k km2 before narrowing at the end. I inquired whether NIC had experienced any measurement issues, but their response indicated nothing remarkable. It is notable that MASIE is the low estimate of the two.
|Region||2020121||Day 121 Average||2020-Ave.||2019121||2020-2019|
The table shows where the ice is distributed compared to average. Baffin Bay has the largest deficit to average followed by Bering and Okhotsk. Greenland Sea and Barents Sea are in surplus, offsetting small deficits in Kara, Laptev and Hudson Bay.
Footnote: Interesting comments recently by Dr. Judah Cohen at his blog regarding the Arctic fluctuations this winter and spring. Excerpts with my bolds.
As I sit here in home, enduring a second day of cloudy, wet, relatively cold and windy weather from a storm passing to our south and had this been winter would have brought a crippling snowstorm. And this storm or pattern isn’t unique. It seems that every few days here in the Northeastern US we get a rainstorm that had it been winter would have produced a snowstorm, though even these late season storms are bringing snow to the higher elevations of the Northeast. I find myself asking (and I realize that I am not unique asking this question) – where was this pattern in winter?
I reflexively look to the PV for answers. The winter was characterized by a stronger than normal stratospheric PV that was hostile to meridional (north to south), large amplitude flow and high latitude blocking that is so favorable for sustained cold air outbreaks and snowstorms. Instead the strong PV supported fast zonal flow of the Jet Stream that was displaced to the north that favored overall mild temperatures and rainfall across the US except for higher elevations and near the Canadian border. Similarly, an even milder and snowless pattern persisted across Europe all winter.
Then once winter was over, high pressure/blocking returned to the North Atlantic sector that excited the vertical transfer of energy from the troposphere to the stratosphere and has weakened the stratospheric PV. This increase in vertical energy transfer has decelerated a hyperactive PV and it does appear that the weakening of the PV will actually overshoot the typical weakening resulting in stronger easterly winds in the polar stratosphere than the climatological average (see Figure i). Easterly winds in the polar stratosphere are the telltale sign of the Final Warming (where the stratospheric PV disappears until the fall).
Illustration by Eleanor Lutz shows Earth’s seasonal climate changes. If played in full screen, the four corners present views from top, bottom and sides. It is a visual representation of scientific datasets measuring Arctic ice extents.