This dataset contains v3.0 of the Daily Snow Water Equivalent (SWE) product from the ESA Climate Change Initiative (CCI) Snow project, at 0.1 degree resolution.

Snow water equivalent (SWE) indicates the amount of accumulated snow on land surfaces, in other words the amount of water contained within the snowpack. The SWE product time series covers the period from 1979/01 to 2022/12. Northern Hemisphere SWE products are available at daily temporal resolution with alpine areas masked.

The product is based on data from the Scanning Multichannel Microwave Radiometer (SMMR) operated on National Aeronautics and Space Administration’s (NASA) Nimbus-7 satellite, the Special Sensor Microwave / Imager (SSM/I) and the Special Sensor Microwave Imager / Sounder (SSMI/S) carried onboard the Defense Meteorological Satellite Program (DMSP) 5D- and F-series satellites. The satellite bands provide spatial resolutions between 15 and 69 km. The retrieval methodology combines satellite passive microwave radiometer (PMR) measurements with ground-based synoptic weather station observations by Bayesian non-linear iterative assimilation. A background snow-depth field from re-gridded surface snow-depth observations and a passive microwave emission model are required components of the retrieval scheme.

The dataset is aimed to serve the needs of users working on climate research and monitoring activities, including the detection of variability and trends, climate modelling, and aspects of hydrology and meteorology.

The Finnish Meteorological Institute is responsible for the SWE product development and generation.

For the period from 1979 to May 1987, the products are available every second day. From October 1987 till December 2022, the products are available daily. Products are only generated for the Northern Hemisphere winter seasons, usually from beginning of October till the middle of May. A limited number of SWE products are available for days in June and September; products are not available for the months July and August as there is usually no snow information reported on synoptic weather stations, which is required as input for the SWE retrieval. Because of known limitations in alpine terrain, a complex-terrain mask is applied based on the sub-grid variability in elevation determined from a high-resolution digital elevation model. All land ice and large lakes are also masked; retrievals are not produced for coastal regions of Greenland.

Passive microwave radiometer data are obtained from the recalibrated enhanced resolution CETB ESDR dataset (MEaSUREs Calibrated Enhanced-Resolution Passive Microwave Daily EASE-Grid 2.0 Brightness Temperature (CETB) Earth System Data Record (ESDR) https://nsidc.org/pmesdr/data-sets/). Spatially and temporally varying snow density fields are implemented into the SWE retrieval, dry snow detection algorithm has been updated and snow masking in post-production has been improved. The time series has been extended from snow_cci version 2 by two years with data from 2020 to 2022 added.

The ESA CCI phased product development framework allowed for a systematic analysis of these changes in the snow density parameterization, snow dry detection and snow masking that occurred between v2 and v3 using a series of step-wise developmental datasets. In comparison with in-situ snow courses, the correlation and RMSE of v3 improved 0.014 and 0.6 mm, respectively, relative to v2. The timing of peak snow mass is shifted two weeks later compared to v1 and reduction in peak snow mass presented in v2 is removed in v3.

This dataset has been deprecated due to data errors in the v3.0 product.