As the photo shows, back in February 2017 you didn’t have to go looking for ice, it came after you. A convoy including icebreakers was trapped by ice in Chukchi, reported in Siberian Times and posted here as Arctic Ice Takes Revenge.

Now we are two weeks into April and about a month into the Arctic melt season. The hunt is on to see how ice extent reacts to the sun, warmer water and weather.

Firstly the graph shows that both this year and last have dipped below 14M km2, 400k km2 below average but still ahead of 2007. Day 104 refers to April 14.

As noted before, the heart of the Arctic is still frozen solid, with changes in extent occurring mainly in the marginal seas that usually melt out by September. Comparing the last two weeks in the Atlantic side, we can see almost no change overall, with an unexpected small increase in Barents Sea.

On the Pacific side is where the deficit to average appears in the melting of both Bering and Okhotsk Seas.

The table compares 2017 regional extents to average and to 2007.

Clearly, Barents is down slightly to average but more than offset by surpluses in Baffin and Greenland. The 2017 differences from average and from 2007 arise from Bering and Okhotsk in the Pacific.

Summary

Despite what you may hear from alarmist sources, there is plenty of Arctic Ice if you know where to look for it.

MASIE ice extents reported March 8 through 31, 2017.

This time of year the heart of the Arctic is frozen solid, and the only changes occur in the marginal seas.  Above shows the Atlantic basins, especially Kara, Barents, Greenland Sea and Baffin Bay.  All of them seesawed during the month, with some fall off at the end, especially noticeable in Gulf of St. Lawrence (counted with Baffin Bay).

Meanwhile on the Pacific side, Bering fluctuated, while Okhotsk lost extent steadily toward month end.

Context

The monthly ice extent average for March provides indication of any year’s annual maximum, prior to melting down to the September annual minimum. Sometimes a lower March extent yields a lower September extent, but not always: 2012 had both the highest maximum and lowest minimum in the last 11 years. That was the year of the Great Arctic Cyclone, and an outlier in the record.

Looking at the 11-year averages in the MASIE data set, the pattern in round numbers is:
Maximum: 15.0 M km2
Minimum: 4.8 M km2
Loss: 10.2 M km2
Loss: 68.0 % of maximum

So about 2/3 of the maximum extent is lost, varying from 66 to 70%. Obviously, all the factors affecting ice extents are in play: (Water, Wind and Weather) with the September outcome uncertain, but likely to be in the range observed.

March 2017 in Comparison

As has been reported, ice formation this year has been sluggish compared to other years. The graph below shows March 2017 compared with the 11 year average, and with 2006 and 2016, as well as SII (Sea Ice Index).

This March started below average, lost sllghtly until the third week, then recovered some before dropping off at the end. 2006 dropped off more rapidly than 2017, while 2016 ended near average. SII showed lower extents all month but drew close at the end.

The Table below shows Day 90 extents across the Arctic Seas compared to averages and 2006, the lowest recent year.

The marginal seas in the Atlantic and Pacific make the 2017 deficits to average: especially Barents, Kara, Bering and Okhotsk. Those seas usually lose all their ice by September. 2017 Surpluses in Greenland Sea and Baffin Bay are smaller, but make most of the difference with 2006.

2017 Outlook

March this year averaged 14.509 M Km2 compared to the 11 year average of 14.986 M km2, a deficit of 478k km2 or 3.2% down. That suggests that a typical melt later this year would result in a minimum of about 4.5 or 4.6 M km2, slightly down from the 11 year average of 4.8M km2.

Sea Ice Index (SII) typically shows less ice than MASIE, and SII reports a 2017 March average ice extent of 14.273 M km2 compared to SII 11 year March average of 14.842, a drop of 569k km2 or 3.8%.  Folks relying on SII may be expecting a lower September minimum, perhaps even breaking the present plateau of ice extents since 2007.  That remains to be seen.

An early-spring sunset over the icy Chukchi Sea near Barrow (Utqiaġvik), Alaska, documented during the OASIS field project (Ocean_Atmosphere_Sea Ice_Snowpack) on March 22, 2009. Image credit: UCAR, photo by Carlye Calvin.

An earlier post Arctic Ice Factors discussed how ice extent varies in the Arctic primarily due to the three Ws: Water, Wind and Weather. There are other posts on the details of Water and Wind linked below at the end, but this post looks at some ordinary and repeating Weather events in the Arctic that influence ice formation. An interesting new study prompted this essay, but first some background on heat exchange observations in the Arctic.

Ice Station SHEBA near the beginning of the drift on 28 October 1997. The Canadian Coast Guard Icebreaker Des Groseilliers served as a base of operations for the field experiment. The huts housed scientific equipment and logistical supplies.

One project in particular has provided comprehensive empirical data on the energy interface between Arctic Sea Ice and the atmosphere.  The SHEBA project collected heat exchange data on site in the Arctic as described in this article SHEBA: The Surface Heat Budget of the Arctic Ocean by Donald K. Perovich and John Weatherly, U.S. Army Engineer Research and Development Center, Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire; and Richard C. Moritz, Polar Science Center, University of Washington, Seattle.

Overview

The combination of the importance of the Arctic sea ice cover to climate and the uncertainties of how to treat the sea ice cover led directly to SHEBA: the Surface Heat Budget of the Arctic Ocean. SHEBA is a large, interdisciplinary project that was developed through several workshops and reports. SHEBA was governed by two broad goals: understand the ice–albedo and cloud–radiation feedback mechanisms and use that understanding to improve the treatment of the Arctic in large-scale climate models. The SHEBA project was sponsored _jointly by the National Science Foundation’s Office of Polar Programs Arctic System Science program and the Office of Naval Research’s High Latitude Dynamics program.

Ice Station SHEBA

On 2 October 1997, the Canadian Coast Guard icebreaker Des Groseilliers stopped in the middle of an ice floe in the Arctic Ocean, beginning the year-long drift of Ice Station SHEBA. For the next 12 months, until 11 October 1998, Ice Station SHEBA drifted with the pack ice from 75°N, 142°W to 80°N, 162°W. At any given time, there were 20–50 researchers at Ice Station SHEBA. During the year over 200 researchers participated in the field campaign, spending anywhere from just a few days to the entire year. Conducting a year-long sea ice experiment provided daunting scientific and logistic challenges: low temperatures, high winds, ice breakup, demanding instruments, and polar bears.

There was an intense measurement program designed to obtain a complete, integrated time series of every possible variable defining the state of the “SHEBA column” over an entire annual cycle. This column is an imaginary cylinder stretching from the top of the atmosphere through the ice into the upper ocean. Observations included longwave and shortwave radiative fluxes; the turbulent fluxes of latent and sensible heat; cloud height, thickness, phase, and properties; energy exchange in the boundary layers of the atmosphere and ocean; snow depth and ice thickness; and upper ocean salinity, temperature, and currents. This year-long, integrated data set provides a test bed for exploring the feedback mechanisms and for model development.

The full set of observations is available in a report entitled Reconciling different observational data sets from Surface Heat Budget of the Arctic Ocean (SHEBA) for model validation purposes

All the detailed measurements are in the report, and the takeaway findings are summarized in Figure 8 below.

Figure 8. (a) Main components of the Surface Heat Budget of the Arctic Ocean (SHEBA) surface energy budget at the Pittsburgh site. (b) Sensible and latent heat fluxes (calculated using bulk formulations). The dashed line indicates the beginning of the summer (1 April), and the dotted line marks the onset of surface melt (29 May). Fluxes are smoothed using a 7 day running mean.

Figure 8a shows how the conductive heat flux in winter (October –March) is controlled by the net longwave radiation. The net longwave radiation has large variability. It is generally high for clear sky conditions, and low for cloudy sky, and constitutes a heat loss from the surface throughout the whole year. The net shortwave radiation (Figure 8a) is steadily growing in spring and early summer with a sudden increase in mid-June when the snow cover starts disappearing and the albedo drops to a lower value. When the surface temperature is at the melting point, the energy surplus is used for melting. This heat flux becomes the major counterbalance of the net solar flux during summer (April –September).

The sensible heat flux (Figure 8b) is usually small except in winter during clear sky conditions when the air temperature is relatively higher than the surface and the wind speed is higher [see Walsh and Chapman, 1998] (see Figure 1). In general, the surface is colder than the overlying air and the sensible heat is downward. During the winter,the sensible heat flux and the net longwave radiation are generally anticorrelated (Figures 8a – 8b). That is, the heat loss from the surface to the atmosphere during clear sky conditions leads to a positive temperature gradient in the air and results in a downward sensible heat flux. The coupling between these two fluxes is discussed in more detail by Makshtas et al. [1999]. The latent heat flux (Figure 8b) is close to zero except after the onset of the melt season when it has several peaks indicating moisture transport from the surface to the atmosphere. Figure 8a shows most components of the surface energy budget together, and the residual from all fluxes.

The Effects of Polar Weather Intrusions

With this background understanding of the winter heat flux over Arctic ice, let us consider the implications of the recent study.

An interesting paper analyzes intrusive weather and estimates the connection between such events and ice extents in the Arctic. The paper is:  The role of moist intrusions in winter Arctic warming and sea ice decline in Journal of Climate 29(12):160314091706008 · March 2016 by Cian Woods and Rodrigo Caballero, Department of Meteorology, and Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden

FIG. 1. Region with ONDJ SIC > 90% and trend < 2% decade-1 (gray shading). Numbered black dots show the location of the radiosonde stations: 1) Barrow, 2) Resolute, 3) Eureka, 4) Alert, 5) Ny-Ålesund, 6) Bjørnøya (Bear Island), 7) Polargmo (Heiss Island), and 8) Dikson Island. Solid black lines show the Barents Sea box (75°–80°N, 20°–80°E). Dotted lines indicate the 70° and 80°N latitude lines.

Abstract:

This paper examines the trajectories followed by intense intrusions of moist air into the Arctic polar region during autumn and winter and their impact on local temperature and sea ice concentration. It is found that the vertical structure of the warming associated with moist intrusions is bottom amplified, corresponding to a transition of local conditions from a ‘‘cold clear’’ state with a strong inversion to a ‘‘warm opaque’’ state with a weaker inversion. In the marginal sea ice zone of the Barents Sea, the passage of an intrusion also causes a retreat of the ice margin, which persists for many days after the intrusion has passed. The authors find that there is a positive trend in the number of intrusion events crossing 708N during December and January that can explain roughly 45% of the surface air temperature and 30% of the sea ice concentration trends observed in the Barents Sea during the past two decades.

An injection event is defined as a vertically integrated northward moisture flux across 708N in excess of 200 Tg day21 deg21 that is sustained for at least 1.5 days and occupies a contiguous zonal extent of at least 98 at all times.

The case study in Fig. 2 shows that the passage of an intrusion can induce local warming of over 20 K in the central Arctic. Here, we examine the typical thermodynamic impact of intrusions, focusing on the fully ice-covered interior of the Arctic basin—specifically, the region where monthly climatological SIC exceeds 90% and shows negligible trend across the data record. This region is shaded gray in Fig. 1.

FIG. 2. Case study of an intrusion event beginning over northern Norway at 1800 UTC on 27 December 1999. Each panel shows a snapshot at a time relative to the beginning of the event as indicated in the lower-right corner. Gray lines show centroid trajectories with gray dots at 1-day intervals. Shading shows surface air temperature anomaly from a 6-hourly, smoothed seasonal cycle, arrows show 10-m wind, and the heavy black line shows the 15% SIC contour. As a reference, the dashed black line shows the 15% SIC contour 5 days before the beginning of the event. Dotted line is the 70°N latitude line. Thin black lines in the +5 days panel show the Barents Sea box.

An example intrusion event is shown in Fig. 2. The injection occurs over the northern tip of Norway and lasts for 1.75 days, yielding seven centroid trajectories. As the injection event progresses, its centroid shifts slowly eastward, giving some zonal spread in centroid trajectories. The flow field during the event features a large-scale dipole straddling the North Pole, with cyclonic circulation over the Atlantic/North American sector and an anticyclone over Eurasia. The trajectories reflect this structure, heading toward the North Pole after injection and then curving cyclonically to exit the Arctic over North America. The intrusion event is associated with large surface air temperature anomalies in the central Arctic and a retreat of the sea ice margin in the Barents Sea, topics we discuss in detail in sections 4 and 5 below.

To focus on intrusions that reach deep into the Arctic basin, events in which fewer than 40% of the trajectory ensemble members reaches 808N over 5 days are discarded. This leaves us with a final dataset of 359 intrusion events from 1990 to 2012, or ;16 per ONDJ season.

It is clear from Fig. 3 that by far the largest fraction of intrusions enters the Arctic through the Atlantic sector, with smaller numbers entering over the Labrador Sea and Greenland and from the Pacific. Interestingly, intrusions entering via the Atlantic and the Barents/Kara sector typically turn cyclonically toward North America—just as in the case study above—while those entering to the east of the Kara Sea typically turn anticyclonically and exit over Siberia. This suggests that moist intrusions into the Arctic are typically associated with cyclonic anomalies over eastern North America and anticyclonic anomalies over western Siberia, consistent with previous work.

Summary

FIG. 5. (top) Humidity and (bottom) temperature profiles (left) in the ice-covered Arctic Ocean during ONDJ and (right) in the Barents Sea box during DJ. Solid lines show climatologies over the respective regions and seasons (representative of typical conditions in the absence of an intrusion event), and dashed lines show profiles at the time of maximum surface warming during a composite intrusion event (representative of conditions at the peak of the event).

A key feature of the warming trend in the Arctic is that it is bottom amplified (i.e., that it is in fact a trend toward a weakening of the climatological temperature inversion that prevails in ice-covered regions of the Arctic basin in winter). This feature has previously been mostly attributed to increased upward turbulent heat flux due to sea ice loss (Serreze et al. 2009; Screen and Simmonds 2010a,b).

Our results suggest a more nuanced view. The passage of an intrusion affects local conditions by inducing a transition from a “cold clear” state with a strong inversion to a “warm opaque” state with a much weaker inversion, in agreement with recent modeling work (Pithan et al. 2014; Cronin and Tziperman 2015). This yields an overall bottom-amplified local temperature perturbation, owing largely to surface heating by increased downwelling longwave radiation.

An increase in the frequency of intrusions can therefore drive bottom-amplified warming trend even in the absence of sea ice loss. In addition, the intrusions themselves drive sea ice retreat in the marginal zone and thus promote the upward turbulent fluxes that help produce bottom-amplified warming.

Our results agree with other recent work showing a strong impact of poleward moisture flux on Arctic sea ice variability and trends (D.-S. R. Park et al. 2015; H.-S. Park et al. 2015a,b). Since most of the moisture flux into the Arctic occurs in a small number of extreme events (Woods et al. 2013; Liu and Barnes 2015), it is natural to take an event-based approach as we do here, which allows us to study the structure of the intrusion events and their link to dynamical processes in the Arctic region and at lower latitudes.

Predicted surface air temperature trends (Fig. 9f) are greatest in the Barents Sea area extending into the central Arctic in agreement with observations (Fig. 9k), with the average trend predicted in the Barents Sea box approximately 45% of that observed. This localization of the trends arises both because intrusion counts have risen most rapidly in that region (Fig. 8b) and because individual intrusions have the greatest impact in that region (Fig. 9a). The predicted trend has a peak amplitude of about 3 K decade-1, about half of the observed value. For SIC the predicted trend (Fig. 9g) again coincides spatially with the observed trend (Fig. 9l) and peaks at about 10% decade, or about 1/3 the observed value at the same location, with the average predicted trend in the Barents Sea box being approximately 30% of that observed.

PS:

Current wind patterns over Barents and the Atlantic gateway to the Arctic can viewed at nullschool:
https://earth.nullschool.net/#current/wind/surface/level/orthographic=-6.21,74.48,522/loc=33.553,72.930

Footnote:

Arctic Sea Ice: Self-Oscillating System

Arctic Shifts between Cyclonic and Anticyclonic Wind Regimes The Great Arctic Ice Exchange

Drift ice in Okhotsk Sea at sunrise.

Previous posts have noted that in March, all the Arctic seas are locked in ice, the exceptions being Bering and Okhotsk in the Pacific, and Barents and Baffin Bay in the Atlantic. And the seesaw continues, shown in the images below.  Firstly on the Atlantic side, featuring Baffin Bay and Kara, Barents, Greenland Seas.

And on the Pacific side, the only action is in Bering and Okhotsk Seas.

The overall NH extents are down from the 11-year average, and it is mostly due to deficits in the usual places: Barents, Bering and Okhotsk, somewhat offset by a surplus in Baffin. All of them melt out in September, and Bering and Okhotsk basins are effectively outside of the Arctic ocean per se.

As reported previously, 2017 peaked early, rising close to the average on day 53 in February, then losing extent and never achieving the 15M km2 threshold.  14.8 M km2 proved to be the 2017 peak daily ice extent.  2016 also lost extent throughout March, though higher than the current year, and will likely end with a higher monthly average.  2006 and 2017 are virtually tied at this point, though 2017 will likely end up higher on the month.  SII shows about 300km2 less extent for the month, but drawing closer lately.

The Table below presents the ice extents reported by MASIE for day 80 in the years 2017, 2006 and the 11-year average (2006 through 2016).

The 2017 deficit to average is largely due to Okhotsk and Bering declining early, along with Barents and Kara.  A surplus in Baffin somewhat offsets these, especially in comparison with 2006.

To summarize, central Arctic seas are locked in ice, while extents have started to decline in the peripheral basins.  As of day 80, extents in 2017 are 4% below average and tied with 2006.

For ice extent in the Arctic, the bar is set at 15M km2. The average in the last 11 years occurs on day 73 at 15.07M before descending. Most years are able to clear 15M, except for 2006, 2007 and 2015 who topped out below that height.

Yesterday, March 2, 2016 cleared 15M, but will not reach that level again. 2016 will now drop down to 14.6M, rise to day 84 average of 14.9M, then start the descent into spring and summer. Typically, Arctic ice extent loses 67 to 70% of the March maximum by mid September, before recovering the ice in building toward the next March.

As reported previously, 2017 rose to the average in February, then lost extent for two days and is now increasing again.  The next two weeks will be interesting. The average year in the last eleven gained about 20k km2 from now to mid March. But the variability ranged from 2015 losing 350K while 2010 gained 300k km2. What will the ice do this year?  Where will 2017 rank in the annual Arctic Ice High Jump competition?

Drift ice in Okhotsk Sea at sunrise.

As reported previously, Arctic ice extents are solid in most seas, but continue to fluctuate at the margins. In the latter part of February 2017 there was a great leap upward for nine days, nearly reaching average and surpassing 2016, before falling back after day 53. The surplus over 2006 is now 500k km2. SII reports about 360k km2 less extent than MASIE.

The Atlantic upward leap and back in Barents and Baffin.

Note both Barents and Baffin pulled back slightly.

The Pacific shifting up and down in Bering and Okhotsk.

Note that Okhotsk continued to gain while Bering pulled back since day 53.

While the seesaws are tilting back and forth on the margins, the bulk of the Arctic is frozen solid. And with limited places where more extent can be added, the pace of overall growth has slowed.

The table below shows ice extents in the seas comprising the Arctic, comparing 2017 day 058 with the same day average over the last 11 years and with 2006.

The table shows that 2017 ice extent exceeds 2006 by about 500k km2 at this date. Surpluses are sizeable in Barents, Baffin and Okhotsk, with only the Baltic showing a deficit.  Baffin and Okhotsk are now average, and the 300k km2 deficit to average comes from Bering in the Pacific, and Barents and Greenland Seas on the Atlantic side

The big picture compares this day in 2017 with 2006.  Not much change overall, but a slight increase of 500k km2.

Drift ice in Okhotsk Sea at sunrise.

As reported previously, Arctic ice extents are solid in most seas, but continue to fluctuate at the margins. In the latter part of February 2017 there was a great leap upward for nine days, nearly reaching average and surpassing 2016, before falling back after day 53. The surplus over 2006 is now 500k km2. SII reports about 360k km2 less extent than MASIE.

The Atlantic upward leap and back in Barents and Baffin.

Note both Barents and Baffin pulled back slightly.

The Pacific shifting up and down in Bering and Okhotsk.

Note that Okhotsk continued to gain while Bering pulled back since day 53.

While the seesaws are tilting back and forth on the margins, the bulk of the Arctic is frozen solid. And with limited places where more extent can be added, the pace of overall growth has slowed.

The table below shows ice extents in the seas comprising the Arctic, comparing 2017 day 058 with the same day average over the last 11 years and with 2006.

The table shows that 2017 ice extent exceeds 2006 by about 500k km2 at this date. Surpluses are sizeable in Barents, Baffin and Okhotsk, with only the Baltic showing a deficit.  Baffin and Okhotsk are now average, and the 300k km2 deficit to average comes from Bering in the Pacific, and Barents and Greenland Seas on the Atlantic side

The next two weeks will be interesting. The average year in the last eleven gained about 100k km2 from now to mid March. But the variability ranged from 2015 losing 300K while other years gained 400k km2. What will the ice do this year?

The big picture compares this day in 2017 with 2006.  Not much change overall, but a slight increase of 500k km2.

Mid February is about a month away from the annual maximum Arctic ice extent, and measurements continue to seesaw in the two dynamic places where freezing and drifting cause gains and losses in sea ice. In each region, the gains and losses teeter-totter between two basins.

Here is the Atlantic seesaw with Barents and Baffin.

And here is the Pacific seesaw with Bering and Okhotsk.

While the seesaws are tilting back and forth on the margins, the bulk of the Arctic is frozen solid. And with limited places where more extent can be added, the pace of overall growth has slowed.

The graph shows that 2017 and 2006 are virtually tied at this date. It shows both years are below average by about 450k km2, and SII adds a further deficit by showing 2017 averaging in February ~400k km2 lower than MASIE.

The table below shows ice extents in the seas comprising the Arctic, comparing day 044 2017 with the same day average over the last 11 years and with 2006.

The table indicates some differences in locations of ice surpluses and deficits. Bering Sea has been the largest deficit this year, while Barents is now matching it by losing ~100k in the last week. Greenland Sea is also down slightly compared to average and to 2006. Baffin Bay is the largest surplus to average and to 2006. Okhotsk lost more than 200k km2 in recent days, but still exceeds 2006 by 115k.

The second half of February will be interesting. The average year in the last eleven gained about 200k km2 from now to month end. But the variability ranged from 2006 losing 170K to 2012 gaining 590k km2. What will the ice do this year?

The polar bears have a Valentine Day’s wish for Arctic Ice.

And Arctic Ice loves them back, returning every year so the bears can roam and hunt for seals.

Footnote:

Seesaw accurately describes Arctic ice in another sense:  The ice we see now is not the same ice we saw previously.  It is better to think of the Arctic as an ice blender than as an ice cap, explained in the post The Great Arctic Ice Exchange.

In just the last week, the progression of ice extents in Barents Sea is impressive.  The first image from MASIE is January 27, 2017.  h/t Pethefin

Then a week later on February 3 we see that Svalbard is almost enclosed.

In that one week Arctic ice gained 240k km2 up to 14.3 M km2, including Barents Sea adding 145k km2.  Thanks to MASIE we can see Arctic ice growing before our eyes.

One Week in Barents Sea shows Svalbard under siege.

MASIE: “high-resolution, accurate charts of ice conditions”
Walt Meier, NSIDC, October 2015 article in Annals of Glaciology.

Update February 4, 2017 Below

The home page for MASIE (here) invites visitors to show their interest in the dataset and analysis tools since continued funding is not assured. The page says:
NSIDC has received support to develop MASIE but not to maintain MASIE. We are actively seeking support to maintain the Web site and products over the long term. If you find MASIE helpful, please let us know with a quick message to NSIDC User Services.

For the reasons below, I hope people will go there and express their support.

1. MASIE is Rigorous.

Note on Sea Ice Resolution:

Northern Hemisphere Spatial Coverage (left) SH Spatial Coverage (right)

Sea Ice Index (SII) from NOAA is based on 25 km cells and 15% ice coverage. That means if a grid cell 25X25, or 625 km2 is estimated to have at least 15% ice, then 625 km2 is added to the total extent. In the mapping details, grid cells vary between 382 to 664 km2 with latitudes.  And the satellites’ Field of View (FOV) is actually an ellipsoid ranging from 486 to 3330 km2 depending on the channel and frequency.  More info is here.

MASIE is based on 4 km cells and 40% ice coverage. Thus, for MASIE estimates, if a grid cell is deemed to have at least 40% ice, then 16 km2 is added to the total extent.

The significantly higher resolution in MASIE means that any error in detecting ice cover at the threshold level affects only 16 km2 in the MASIE total, compared to at least 600 km2 variation in SII.  A few dozen SII cells falling below the 15% threshold is reported as a sizable loss of ice in the Arctic.

2. MASIE is Reliable.

MASIE is an operational ice product developed from multiple sources to provide the most accurate possible description of Arctic ice for the sake of ships operating in the region.

Operational analyses combine a variety of remote-sensing inputs and other sources via manual integration to create high-resolution, accurate charts of ice conditions in support of navigation and operational forecast models. One such product is the daily Multisensor Analyzed Sea Ice Extent (MASIE). The higher spatial resolution along with multiple input data and manual analysis potentially provide more precise mapping of the ice edge than passive microwave estimates.  From Meier et al., link below.

Some people have latched onto a line from the NSIDC background page:
Use the Sea Ice Index when comparing trends in sea ice over time or when consistency is important. Even then, the monthly, not the daily, Sea Ice Index views should be used to look at trends in sea ice. The Sea Ice Index documentation explains how linear regression is used to say something about trends in ice extent, and what the limitations of that method are. Use MASIE when you want the most accurate view possible of Arctic-wide ice on a given day or through the week.

That statement was not updated to reflect recent developments:
“In June 2014, we decided to make the MASIE product available back to 2006. This was done in response to user requests, and because the IMS product output, upon which MASIE is based, appeared to be reasonably consistent.”

The fact that MASIE employs human judgment is discomforting to climatologists as a potential source of error, so Meier and others prefer that the analysis be done by computer algorithms. Yet, as we shall see, the computer programs are themselves human inventions and when applied uncritically by machines produce errors of their own.

3. MASIE serves as Calibration for satellite products.

The NSIDC Background cites as support a study by Partington et al (2003).  Reading that study, one finds that the authors preferred the MASIE data and said this:

“Passive microwave sensors from the U.S. Defense Meteorological Satellite Program have long provided a key source of information on Arctic-wide sea ice conditions, but suffer from some known deficiencies, notably a tendency to underestimate ice concentrations in summer. With the recent release of digital and quality controlled ice charts extending back to 1972 from the U.S. National Ice Center (NIC), there is now an alternative record of late twentieth century Northern Hemisphere sea ice conditions to compare with the valuable, but imperfect, passive microwave sea ice record.”

“This analysis has been based on ice chart data rather than the more commonly analyzed passive microwave derived ice concentrations. Differences between the NIC ice chart sea ice record and the passive microwave sea ice record are highly significant despite the fact that the NIC charts are semi-dependent on the passive microwave data, and it is worth noting these differences. . .In summer, the difference between the two sources of data rises to a maximum of 23% peaking in early August, equivalent to ice coverage the size of Greenland.” (my bold)  For clarity: the ice chart data show higher extents than passive microwave data.

The differences are even greater for Canadian regions.

“More than 1380 regional Canadian weekly sea-ice charts for four Canadian regions and 839 hemispheric U.S. weekly sea-ice charts from 1979 to 1996 are compared with passive microwave sea-ice concentration estimates using the National Aeronautics and Space Administration (NASA) Team algorithm. Compared with the Canadian regional ice charts, the NASA Team algorithm underestimates the total ice-covered area by 20.4% to 33.5% during ice melt in the summer and by 7.6% to 43.5% during ice growth in the late fall.”

From: The Use of Operational Ice Charts for Evaluating Passive Microwave Ice Concentration Data, Agnew and Howell  http://www.tandfonline.com/doi/pdf/10.3137/ao.410405

More recently Walter Meier, who is in charge of SII, and several colleagues compared SII and MASIE and published their findings October 2015 (here).  The purpose of the analysis was stated thus:
Our comparison is not meant to be an extensive validation of either product, but to illustrate as guidance for future use how the two products behave in different regimes.

The abstract concludes:
Comparisons indicate that MASIE shows higher Arctic-wide extent values throughout most of the year, largely because of the limitations of passive microwave sensors in some conditions (e.g. surface melt). However, during some parts of the year, MASIE tends to indicate less ice than estimated by passive microwave sensors. These comparisons yield a better understanding of operational and research sea-ice data products; this in turn has important implications for their use in climate and weather models.

A more extensive comparison of MASIE from NIC and SII from NOAA is here.

4. MASIE continues a long history of Arctic Ice Charts.

Naval authorities have for centuries prepared ice charts for the safety of ships operating in the Arctic.  There are Russian, Danish, Norwegian, and Canadian charts, in addition to MASIE, the US version.  These estimates rely on multiple sources of data, including the NASA reports.  Charts are made with no climate ax to grind, only to get accurate locations and extents of Arctic ice each day.

Figure 16-3: Time series of April sea-ice extent in Nordic Sea (1864-1998) given by 2-year running mean and second-order polynomial curves. Top: Nordic Sea; middle: eastern area; bottom: western area (after Vinje, 2000). IPCC Third Assessment Report

Since these long-term records show a quasi-60 year cycle in ice extents, it is vital to have a modern dataset based on the same methodology, albeit with sophisticated modern tools.

Summary

Measuring anything in the Arctic is difficult, and especially sea ice that is constantly moving around.  It is a good thing to have independent measures using different methodologies, since any estimate is prone to error.

Please take the time to express your appreciation for NIC’s contribution and your support for their products at MASIE  home page.

Update February 4, 2017

In the comments Neven said MASIE was unusable because it was biased low before 2010 and high afterward.  I have looked into that and he is mistaken.  Below is the pattern that is observed most months.  March is the annual maximum and coming up soon.

As the graph shows, the two datasets were aligned through 2010, and then SII began underestimating ice extent, resulting in a negative 11-year trend.  MASIE shows the same fluctuations, but with higher extents and a slightly positive trend for March extents.  The satellite sensors have a hard time with mixed ice/water conditions (well-documented).

More on the two datasets NOAA has been Losing Arctic Ice