Data Description

Yearly maps of early melt (earliest observed melt conditions), melt (melt conditions observed from this point until freeze), early freeze (earliest observed freeze conditions), and freeze (freeze conditions observed from this point on) for the surface of sea ice derived from SSM/I data. Reference:

Markus, T., J. C. Stroeve, and J. Miller (2009), Recent changes in Arctic sea ice melt onset, freezeup, and melt season length, J. Geophys. Res., 114, C12024, doi:10.1029/2009JC005436

Product Updated, 7/2/2015

In early October 2011, the AMSR-E instrument developed a fault and further data was unavailable on the archive. The previous source data for this routine, SSM/I F13, stopped providing data at the end of 2007 and at that time the routine had been adapted to AMSR-E and maps were processed from 2003 through 2010. The routine has now been adapted to use SSM/IS F17 as a data source for microwave brightness temperatures with the version “701s”, and the 2011 maps were processed.

In February 2014, we investigated anomalous behavior of the routine in coastal areas on the early freeze and freeze maps. We discovered that the bias correction used for F17 was misreporting ice concentration values during the melt period, and that was resulting in the poor freeze-up values. The bias was adjusted and the datset was reprocessed for 2007 on with version "702s".

In the figures below, trends in melt onset day of year, freeze onset day of year, and melt season length in days are shown for the three source data revisions of this algorithm. Blue is the original SMMR - SSM/I dataset (1979 – 2007), black is the AMSR-E dataset (2003 – 2010), and red is the SSM/IS F17 dataset (2008 – 2011).

The following figure shows average melt / freeze onset in day of year and average melt duration in days for the entire Arctic. The solid line is "early", the first indication that melt/freeze conditions are occurring. The dashed line where melt / freeze conditions persist until the next freeze / melt season occurs. In the third panel, the solid line is the difference between early freeze and melt and the dashed line is the difference between freeze and early melt. Those two values give information on how long the melt season is.



Data Format

Readme for melt / freeze products

4 files:

YYYY - year
VVVV - version, current set is 528s for SMMR/SSMI through F13, and 702s for SSMIS F17.

Integer arrays, 304 x 448, big endian (unix and mac don't need to byteswap). Values are the day of year where the event described in the filename occurs.

Data Flags:

land and the "hole" in the coverage over the pole
open water
valid data

All negative values represent pixels where melt or freeze could not be determined; the different negative values correspond to different criteria in the algorithm. The earliest melt possible due to the algorithm is day 75.

Updated on 7/02/2015

Removed the AMSR-E products from this distribution in favor of SSM/I / SMMR trend only, since AMSR-E stopped providing data. Updated 2007+ to improved bias adjustment, version 702s.

Contact info:

README last updated 7/02/2015

Data Files

  • melt_update_2015.tar - tar, 37.62 MB: Last Updated: July 2, 2015 Artic sea ice melt/freeze datafiles (tar'ed)
  • - zip, 3.47 MB: Last Updated: July 2, 2015 Artic sea ice melt/freeze datafiles (zipped)