A data-assimilative reanalyses of ocean and sea ice in the Arctic are composed of 3D daily and monthly mean fields of temperature, salinity, sea surface height, zonal velocity, meridional velocity, sea ice concentration, sea ice thickness and sea ice velocity. It was generated from TOPAZ4 which is driven by the forcing of ERA-Interim reanalysis during the years of 1991-2018. The files named as TP4a_002-003_daily_yyyy.tgz in which the daily state using netCDF format covers the Arctic ocean (>58N) by the grids with a spatial resolution of 12.5x12.5 km and 40 levels on vertical (0, 2, 4, 6, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 125, 150, 175, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1200, 1400, 1600, 1800, 2000, 2500, 3000, 3500, 4000).

TOPAZ4 is a coupled ocean and sea ice data assimilation system for the North Atlantic and the Arctic that is based on the HYCOM ocean model and the ensemble Kalman filter data assimilation method using 100 dynamical members. The native ocean model uses 28 hybrid z-isopycnal layers, and the top layer has a minimum thickness of 3 m. The horizontal resolution in the model is 12–16 km, which is eddy permitting from the Equator to the Nordic Seas but is still far from being eddy resolving in the Arctic. The concerned daily outputs on the model native grids are also included in this dataset whose name takes the format of TP4DAILY_yyyy.tar.gz. These daily files are binary format with the suffix .a. The .b files are ACSII and list the related fields in the concerned .a files. The matlab script of loada.m is a function how to load one field from the input .a file, which needs the supports from the model grid information from reginal.*.?.