European Space Administration Snow Climate Change Initiative (Snow_cci): Snow Water Equivalent (SWE) level 3C daily global climate research data package (CRDP) (1979 – 2020), version 2.0

This dataset contains v2.0 of the Daily Snow Water Equivalent (SWE) product from the European Space Administration (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 2020/05. Northern Hemisphere SWE products are available at daily temporal resolution with alpine areas masked. 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 modeling, and aspects of hydrology and meteorology. The Finnish Meteorological Institute is responsible for the SWE product development and generation. This version 2 dataset has some notable differences compared to the v1 data. In v2, 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/), the grid spacing is reduced from 25 kilometers (km) to 12.5 km, and spatially and temporally varying snow density fields are used to adjust SWE retrievals in post processing. The output grid spacing is reduced from 0.25-degree to 0.10-degree WGS84 latitude / longitude to be compatible with other Snow_cci products. The time series has been extended by two years with data from 2018 to 2020 added. The ESA CCI phased product development framework allowed for a systematic analysis of these changes to the input data and snow density parameterization that occurred between v1 and v2 using a series of step-wise developmental datasets. In comparison with in-situ snow courses, the correlation and Root Mean Squared Error (RMSE) of v2 improved 18 percent (%) (0.1) and 12% (5 millimeters (mm)), respectively, relative to v1. The timing of peak snow mass is shifted two weeks later and a temporal discontinuity in the monthly northern hemisphere snow mass time series associated with the shift from the Special Sensor Microwave/Imager (SSM/I) and the Special Sensor Microwave Imager/Sounder (SSMIS) in 2009 is removed in v2. Luojus, K.; Moisander, M.; Pulliainen, J.; Takala, M.; Lemmetyinen, J.; Derksen, C.; Mortimer, C.; Schwaizer, G.; Nagler, T.; Venäläinen, P. (2022): ESA Snow Climate Change Initiative (Snow_cci): Snow Water Equivalent (SWE) level 3C daily global climate research data package (CRDP) (1979 – 2020), version 2.0. NERC EDS Centre for Environmental Data Analysis, 17 March 2022. doi:10.5285/4647cc9ad3c044439d6c643208d3c494. https://dx.doi.org/10.5285/4647cc9ad3c044439d6c643208d3c494