Close

Service Interruption

The NSIDC Web site and data services are currently having intermittent problems and may be unavailable. We are working to restore these services as soon as possible and apologize for any inconvenience this may cause. Please contact NSIDC User Services for assistance.

NASA Distributed Active Archive Center (DAAC) at NSIDC

Sea Ice Trends and Climatologies from SMMR and SSM/I-SSMIS

Data from Defense Meteorological Satellite Program (DMSP) Sensors

Ice Persistence

Monthly climatologies of ice persistence are intended for users interested in persistence of ice over a particular month during the time series, which includes January 1979 through current processing. Ice persistence fields provide information on how frequently ice occurs in a region during a given month over the time period of the data. The ice extent climatologies are derived each month from monthly-averaged sea ice concentrations using the NASA Team Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data.

Individual ocean pixels containing a minimum of 15 percent ice cover are summed throughout the time series. The maximum ice persistence value is 100 percent. Each pixel represents the percentage of years for which ice was present.

Data Access

Data are available via FTP.

Data Format

Data are stored in two-byte integer format. For the Northern Hemisphere, the grid size is 304 x 448 pixels; and for the Southern Hemisphere, the grid size is 316 x 332 pixels. Land is set to a value of 254 and coastlines to a value of 253. Corresponding PNG images of ice persistence are also provided in the browse directory on the FTP site.

File Naming Convention

Ice extent climatologies are computed for each month and are named according to the following convention, and as described in Table 1:

persistence.mmm.yyyy1-yyyy2.h

where:

Table 1. File Naming Convention Description
Variable Description
persistence Identifies this as an ice persistence data file
mmm 3-character month
yyyy1 4-digit year of the first year for which data was available
yyyy2 4-digit year of the last year for which data was available
h Hemisphere (n: Northern, s: Southern)