Add NSIDC (National Snow and Ice Data Center)

• source: https://nsidc.org/data/docs/noaa/g02202_ice_conc_cdr/

• reference: Meier, W., F. Fetterer, M. Savoie, S. Mallory, R. Duerr, and J. Stroeve. 2013, updated 2015. NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration, Version 2. Boulder, Colorado USA: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N55M63M1 data:

• From the 00README.txt:

ftp sidads.colorado.edu
# (login as anonymous, and use your e-mail address as password)
cd /pub/DATASETS/NOAA/G02202_v2/north/monthly/.
# (or "south" for Antarctica)
get 2007.tar

This command will generate a tar file on your local disk containing everything under the directory 2007.

There's also daily data. Just use /pub/DATASETS/NOAA/G02202_v2/north/monthly/. But let's check sizes firs.