Arctic warming by cloud radiation enhanced by moist air intrusion observed at Ny-Alesund, Svalbard

At Ny-Alesund, Svalbard, Arctic, two distinct states were seen in downward longwave radiation (LD) during winter 2015/16. After the cold state with the temperature around -10 to -20 degrees C, a warm state with plus temperature appeared and LD increased from about 170 to 320-330 W m(-2). This abrupt and large increase of LD was due to the change of cloud condition, from clear to overcast, which was examined from the cloud radar data taken during GRENE Arctic Research Project. However, only the cloud change could not explain this large change of LD. During the warm state, the atmospheric circulation patterns changed, distortion of tropospheric polar vortex appeared with a high pressure ridge (blocking high), and strong cyclone and intrusion of warm and moist air from the Atlantic Ocean together with longwave radiation from clouds influenced the warming at Svalbard. Thus, the discussions of two Arctic winter states in LD was much effective than those in net longwave. This intrusion of warm-moist air from the lower latitude was one of the major processes contributing to the Arctic amplification, just as also proposed using GCM by Yoshimori et al. (2017). The paper provided the actual observational evidence of this warming process.