2.2 SP data
The SP data was derived by using the snow cover phenology data of the
northern middle and high latitudes (2001–2014) (Chen et al.,2016). That original data is an improved merge of five widely used snow
datasets, including the reanalyzed dataset of daily snow depths
published by the Canada Meteorological Center, the binary daily snow
cover mask dataset derived from both the interactive multi-sensor snow
and ice mapping system and the Northern Hemisphere weekly snow cover and
sea ice extent, the 8-day Level 3 snow cover fraction product derived
from the moderate resolution imaging spectroradiometer satellite MODIS
data, and the snow water equivalent data derived from the near-real-time
ice and snow extent dataset (Chen et al., 2016). Chen et
al. (2016) employed a multi-data method in developing the combined snow
cover phenology matrix (with the geo-grids unified into 0.5°×0.5°) that
can integrate snow cover phenology information derived from multiple
sources of snow observations. The snow cover accumulation season was
defined to be from the November of the last year to the February of any
given year, and the snow melting season is from the March to June of any
given year (Chen et al., 2016). The snow-onset SP date was
defined as the beginning date of the first five consecutive days on
which snow is observed to cover the ground surface in its accumulation
season, and the snow-end SP date was defined as the beginning date of
the last five consecutive days when snow cover can still be noticed in
its melting season (Chen et al., 2016). Specifically for the
derivations of the snow-onset and -end SP datasets required in this
study, the NH-related terrestrial area was simply segmented out by
restricting the latitude to be larger than 45° in the Northern
Hemisphere.