We investigate the variation of sea surface salinity (SSS) retrieved in the Hudson Bay from L-band microwave measurements of SMAP and SMOS for open water seasons 2015-2017. We analyzed the differences between three SSS products (SMAP from JPL and RSS, and SMOS from BEC), and assessed in the context of seasonal and inter-annual variation of the freshwater contents, considering river runoffs, sea ice changes, and surface forcing (P-E). We found SMAP JPL (V4.2) shows reasonable responses to the freshwater inputs which is dominated by the sea ice change particularly early in the melting season. This result demonstrates the potential of currently available L-band missions in monitoring cryospheric changes; also underscore urgent needs of in situ salinity measurements in the region to improve retrieval algorithms.

Sea surface salinity (SSS) plays a critical role in the water cycle. In the Arctic Ocean, SSS responses to river discharge, sea ice melting/freezing and drifting, surface freshwater forcing (precipitation and evaporation), and ocean transport through open straits from/to Pacific and Atlantic oceans. However, in situ SSS data in the Arctic Ocean are very sparse. The L-band microwave radiometer on board of NASA SMAP mission provides salinity measurements since April 2015, at 40 km resolution with global ocean coverage in ~3 days. With improved land/ice correction and RFI detection, SMAP SSS are retrieved in ice-free regions near the river mouth and ice edge. The collocated SMAP SSS and in situ salinity data collected by AXCTD from Ocean Melting Greenland (OMG) 2016 field campaign along Greenland coast show reasonable agreement in revealing the freshening signature, which is not seen in ocean model output. During the open water season (August), SMAP SSS were retrieved in Chukchi Sea (2015), in Prudhoe Bay and East Siberian Sea (2016), and in Kara Sea in both years. The SSS contrast between the two years is consistent with sea ice concentration observations. Variability of SSS in Kara Sea is correlated positively with adjacent river discharges but negatively with the salinity of water transported from Atlantic Ocean.

The two-coloring number of graphs, which was originally introduced in the study of the game chromatic number, also gives an upper bound on the degenerate chromatic number as introduced by Borodin. It is proved that the two-coloring number of any planar graph is at most nine. As a consequence, the degenerate list chromatic number of any planar graph is at most nine. It is also shown that the degenerate diagonal chromatic number is at most 11 and the degenerate diagonal list chromatic number is at most 12 for all planar graphs.