The Arctic PASSION Polar Monthly Mean IST data set (AP-MMIST) is a combined surface temperature product covering open ocean, marginal ice zone and closed sea ice areas, represented by Sea Surface Temperatures (SST), Marginal Ice Zone Temperatures (MIZT) and sea Ice Surface Temperatures (IST). Beside ocean and sea ice the data set also includes surface temperatures from the Greenland and Antarctic ice sheets. AP-MMIST has been jointly developed and produced by Arctic PASSION WP-1 and the Sea Ice Thematic Assembly Centre (Sea Ice TAC) under the Copernicus Climate Change Service (C3S - service contract: 2022/C3S2_312b_MOi_SC1). The AP-MMIST is a monthly averaged temperature product based on the C3S daily IST CDR and ICDR level 3 data. The daily mean C3S IST data set is a resampled and averaged daily mean IST product using Global Area Coverage - Advanced Very High-Resolution Radiometer (AVHRR) IST level 2 data as input. The level 2 and 3 CDR and ICDR data records are described in Algorithm Theoretical Baseline Document (Eastwood et al., 2023). The surface temperature retrieval algorithm used to produce the basic level 2 product is a traditional split window algorithm using two Thermal InfraRed (TIR) channels to compensate for atmosphere and angular emissivity dependency. This is described in the Algorithm Theoretical Baseline Document (Eastwood et al., 2023). The level 1 TIR input data set is the full data record from the AVHRR on-board NOAA satellite platforms since 1982, as well as AVHRR records on-board Metop satellites since 2006. The product output format is NetCDF with standard attributes, following CF convention to the degree possible. The monthly data are divided into 2 monthly files, one for each hemisphere, SH and NH.

AP-MMIST - Variables:ST: Monthly Mean Surface temperature (Integrated ocean, sea ice and marginal ice zone surface temperature and Greenland and Antarctic ice sheets)STmax: The maximum pixel value within the given monthSTmin: The minimum pixel value within the given monthCounts: Number of daily temperatures that a given MMIST pixel value is based on.Temporal coverage: 1982-2024Geographical coverage: Pole-wards of 50 N and 50 SSpatial resolution: 0.25 degree'sProjection: Regular geographical gridProduct type: Level 3 (Fixed projection with data gaps)_________NetCDF file example of the AP-MMIST data set: netcdf \202410-DMI_MET-L3S_GHRSST-STskin-AVHRR_nh_SST_IST-MM_ICDR-v1.1-fv1.0{ dimensions: time = 1 ; lat = 160 ; lon = 1440 ; variables: int64 time(time) ; time:standard_name = time ; time:long_name = First time of period. ; time:units = days since 1970-01-01 ; time:calendar = proleptic_gregorian ; float lat(lat) ; lat:units = degrees_north ; lat:long_name = Latitude ; float lon(lon) ; lon:units = degrees_east ; lon:long_name = Longitude ; float surface_temperature(time, lat, lon) ; surface_temperature:_FillValue = NaNf ; surface_temperature:standard_name = surface_temperature ; surface_temperature:long_name = Monthly mean sea and ice surface temperature ; surface_temperature:units = K ; int64 N(time, lat, lon) ; N:long_name = Number of daily mean values applied in monthly mean value ; N:units = 1 ; N:standard_name = number_of_observations ; N:ancillary_variables = surface_temperature ; float t2m(time, lat, lon) ; t2m:_FillValue = NaNf ; t2m:standard_name = air_temperature ; t2m:long_name = Daily mean 2m air temperatures from ERA Interim reanalysis ; t2m:units = K ; float surface_temperature_min(time, lat, lon) ; surface_temperature_min:_FillValue = NaNf ; surface_temperature_min:standard_name = surface_temperature ; surface_temperature_min:long_name = Monthly minimum surface temperature ; surface_temperature_min:units = K ; float surface_temperature_max(time, lat, lon) ; surface_temperature_max:_FillValue = NaNf ; surface_temperature_max:standard_name = surface_temperature ; surface_temperature_max:long_name = Monthly maximum surface temperature ; surface_temperature_max:units = K ; float sea_ice_fraction(time, lat, lon) ; sea_ice_fraction:_FillValue = NaNf ; sea_ice_fraction:standard_name = sea_ice_area_fraction ; sea_ice_fraction:long_name = Monthly mean sea ice fraction from OSI-430-a ; sea_ice_fraction:units = 1 ; ubyte surface_type(time, lat, lon) ; surface_type:units = 1 ; surface_type:long_name = icecap=1, water=2, bedrock=3, ETOP01_waterOSISAF_land=4, sea_ice=5 ; // global attributes: :title = C3S, Monthly Mean Ice and Sea Surface Temperatures (MMIST) ; :institution = Danish Meteorological Institute (DMI) ; :source = Satellite Observations ; :activity_type = Space borne instrument(s) ; :start_date = 2024-10-31T23:59Z ; :product_status = Operational ; :abstract = The C3S Monthly Mean Ice and sea Surface Temperatures (MMIST) product is based on the original work from DMI and MET on the combined Polar ocean and ice surface temperature product, originally named \the Arctic and Antarctic Surface Temperature from thermal Infrared satellite sensors\, AASTI. The MMIST provides monthly mean, minimum and maximum snow and ice skin temperatures pole-wards of 50 degrees North and South in the period from January 1982 and on-wards. Surface temperatures are calculated from thermal infrared brightness temperature measurements (Tb) from the Global Area Coverage - Advanced Very High Resolution Radiometer (GAC - AVHRR) data. The underlying AASTI algorithm is a commonly known split window algorithm that conceptually is applied for numerous land, sea and ice retrieval systems. In addition to the IST retrieval, the MMIST also contains Sea Surface Temperatures (SST) that are seamlessly estimated through Marginal Ice Zone temperatures that are interpolated from IST and SST temperatures. ; :spatial_resolution_latitude = 0.25 ; :spatial_resolution_longitude = 0.25 ; :area = Arctic ; :southernmost_latitude = 50 ; :northernmost_latitude = 90 ; :references = DMI ; :institution_reference = http://www.dmi.dk/ ; :contact = gd@dmi.dk ; :software_version = C3S, Monthly Mean Ice and sea Surface Temperature version 1.00; C3S-MMISTv1.00 ; :comments = The monthly mean ice and ocean temperature product is calculated from all available daily mean values of the C3S daily Ice Surface Temperature CDR version 1.0 and ICDR version 1.1, covering January 1982 to June 2019 and July 2019 - onwards, respectively. The Number of daily values applied for each monthly mean pixel estimate is given in the N-variable. ; :acknowledgement = This work is funded and carried out by the Sea Ice Tac (C3S2_312b) of Copernicus Climate Change Service (C3S) and by the European Union\'s Horizon 2020 research and innovation programme through the project Arctic PASSION under grant agreement No. 101003472. ; :DOI = ; :grid = regular geographic grid ; :input_data = AASTI daily means ICDR v1.1 ; :Conventions = CF-1.6 ; }