Given the fluctuations in daily sea ice measurements, climatology typically relies on monthly averages. November daily extents are now fully reported and the 2017 November monthly results can be compared with years of the previous decade. MASIE showed 2017 reached 9.7M km2, 0.2M below the 9.9M October 10 year average. SII was slightly lower at 9.5M for the month. The 10 year average for SII is about 200k km2 lower than MASIE, with a similar differential appearing in 2017. In either case, one can easily see the Arctic ice extents have not declined in the last decade. MASIE shows 2017 matching 2007, higher than 2012 by 200k km2, and 844k km2 more than 2016.
Sea Ice Index statistics are from recently released SIIv.3.0, as reported in Sea Ice Index Updates to v.3.0.
The graph below shows November comparisons through day 334 (Nov. 30).
Note that 2017 in both MASIE and SII tracked the 10 year average, slightly lower throughout. SII is now about 240k km2 less than MASIE. 2012 grew strongly to approach the 10 year average, recovering after being decimated by the August Great Arctic Cyclone. 2007 lags behind, and the lackluster 2016 recovery is also evident.
The narrative from activist ice watchers is along these lines: 2017 minimum was not especially low, but it is very thin. “The Arctic is on thin ice.” They are basing that notion on PIOMAS, a model-based estimate of ice volumes, combining extents with estimated thickness. That technology is not mature, with only a decade or so of remote sensing. The image below from AARI shows widespread thick ice at end of November 2017.
The formation of ice this year does shows solid concentrations in the central Arctic. Watch the November refreezing of Arctic marginal seas from the center outward.
At the top, open water in Chukchi is shrinking while neighboring Beaufort and East Siberian seas freeze completely. On the left, Hudson Bay starts with fast ice on the western shore, now growing extent strongly. On the right, Kara ice cover is 90% complete.
The table shows ice extents in the regions for 2017, 10 year averages and 2016 for day 334. Decadal averages refer to 2007 through 2016 inclusive.
NH extent is close to average with the only large deficit in Chukchi. Most seas are nearly average with a large surplus in Hudson offsetting Chukchi. Both seas are now refreezing strongly.
Earlier observations showed that Arctic ice extents were low in the 1940s, grew thereafter up to a peak in 1977, before declining. That decline was gentle until 1994 which started a decade of multi-year ice loss through the Fram Strait. There was also a major earthquake under the north pole in that period. In any case, the effects and the decline ceased in 2007, 30 years after the previous peak. Now we have a plateau in ice extents, which could be the precursor of a growing phase of the quasi-60 year Arctic ice oscillation.
Background on MASIE Data Sources
MASIE reports are generated by National Ice Center from the Interactive Multisensor Snow and Ice Mapping System (IMS). From the documentation, the multiple sources feeding IMS are:
Platform(s) AQUA, DMSP, DMSP 5D-3/F17, GOES-10, GOES-11, GOES-13, GOES-9, METEOSAT, MSG, MTSAT-1R, MTSAT-2, NOAA-14, NOAA-15, NOAA-16, NOAA-17, NOAA-18, NOAA-N, RADARSAT-2, SUOMI-NPP, TERRA
Sensor(s): AMSU-A, ATMS, AVHRR, GOES I-M IMAGER, MODIS, MTSAT 1R Imager, MTSAT 2 Imager, MVIRI, SAR, SEVIRI, SSM/I, SSMIS, VIIRS
Summary: IMS Daily Northern Hemisphere Snow and Ice Analysis
The National Oceanic and Atmospheric Administration / National Environmental Satellite, Data, and Information Service (NOAA/NESDIS) has an extensive history of monitoring snow and ice coverage.Accurate monitoring of global snow/ice cover is a key component in the study of climate and global change as well as daily weather forecasting.
The Polar and Geostationary Operational Environmental Satellite programs (POES/GOES) operated by NESDIS provide invaluable visible and infrared spectral data in support of these efforts. Clear-sky imagery from both the POES and the GOES sensors show snow/ice boundaries very well; however, the visible and infrared techniques may suffer from persistent cloud cover near the snowline, making observations difficult (Ramsay, 1995). The microwave products (DMSP and AMSR-E) are unobstructed by clouds and thus can be used as another observational platform in most regions. Synthetic Aperture Radar (SAR) imagery also provides all-weather, near daily capacities to discriminate sea and lake ice. With several other derived snow/ice products of varying accuracy, such as those from NCEP and the NWS NOHRSC, it is highly desirable for analysts to be able to interactively compare and contrast the products so that a more accurate composite map can be produced.
The Satellite Analysis Branch (SAB) of NESDIS first began generating Northern Hemisphere Weekly Snow and Ice Cover analysis charts derived from the visible satellite imagery in November, 1966. The spatial and temporal resolutions of the analysis (190 km and 7 days, respectively) remained unchanged for the product’s 33-year lifespan.
As a result of increasing customer needs and expectations, it was decided that an efficient, interactive workstation application should be constructed which would enable SAB to produce snow/ice analyses at a higher resolution and on a daily basis (~25 km / 1024 x 1024 grid and once per day) using a consolidated array of new as well as existing satellite and surface imagery products. The Daily Northern Hemisphere Snow and Ice Cover chart has been produced since February, 1997 by SAB meteorologists on the IMS.
Another large resolution improvement began in early 2004, when improved technology allowed the SAB to begin creation of a daily ~4 km (6144×6144) grid. At this time, both the ~4 km and ~24 km products are available from NSIDC with a slight delay. Near real-time gridded data is available in ASCII format by request.
In March 2008, the product was migrated from SAB to the National Ice Center (NIC) of NESDIS. The production system and methodology was preserved during the migration. Improved access to DMSP, SAR, and modeled data sources is expected as a short-term from the migration, with longer term plans of twice daily production, GRIB2 output format, a Southern Hemisphere analysis, and an expanded suite of integrated snow and ice variable on horizon.
Some people unhappy with the higher amounts of ice extent shown by MASIE continue to claim that Sea Ice Index is the only dataset that can be used. This is false in fact and in logic. Why should anyone accept that the highest quality picture of ice day to day has no shelf life, that one year’s charts can not be compared with another year? Researchers do this, including Walt Meier in charge of Sea Ice Index. That said, I understand his interest in directing people to use his product rather than one he does not control. As I have said before:
MASIE is rigorous, reliable, serves as calibration for satellite products, and continues the long and honorable tradition of naval ice charting using modern technologies. More on this at my post Support MASIE Arctic Ice Dataset
via Science Matters
December 1, 2017 at 10:33AM