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The Norwegian young sea ICE (N-ICE2015) expedition was designed to investigate the atmosphere-snow-ice-ocean interactions in the young and thin sea ice regime north of Svalbard. Radiosondes were launched twice daily during the expedition from January to June 2015. Here we use these upper air measurements to study the multiple cyclonic events observed during N-ICE2015 with respect to changes in the vertical thermodynamic structure, moisture content, and boundary layer characteristics. We provide statistics of temperature inversion characteristics, static stability, and boundary layer extent. During winter, when radiative cooling is most effective, we find the strongest impact of synoptic cyclones. Changes to thermodynamic characteristics of the boundary layer are associated with transitions between the radiatively “clear” and “opaque” atmospheric states. In spring, radiative fluxes warm the surface leading to lifted temperature inversions and a statically unstable boundary layer. Further, we compare the N-ICE2015 static stability distributions to corresponding profiles from ERA-Interim reanalysis, from the closest land station in the Arctic North Atlantic sector, Ny-Alesund, and to soundings from the SHEBA expedition (1997/1998). We find similar stability characteristics for N-ICE2015 and SHEBA throughout the troposphere, despite differences in location, sea ice thickness, and snow cover. For Ny-Alesund, we observe similar characteristics above 1000 m, while the topography and ice-free fjord surrounding Ny-Alesund generate great differences below. The long-term radiosonde record (1993–2014) from Ny-Alesund indicates that during the N-ICE2015 spring period, temperatures were close to the climatological mean, while the lowest 3000 m were 1–3∘C warmer than the climatology during winter.

[1] This study investigates the relationship between tropical cyclone (TC)–induced heavy rainfall over East Asia (EA) and large-scale climate variability during June–October for the period of 1961–2005. An empirical orthogonal function analysis is applied to the seasonal-total TC-induced heavy rainfall obtained in meteorological stations over EA. The first leading mode shows a dipole pattern between South China (SC) and Northeast Asia (NEA; i.e., Southeast-East China, Taiwan, and Japan). This dipole pattern is found to be associated with the two modes of sea surface temperature (SST) variations over the Pacific: one in the tropical Pacific, and the other spanning from EA to the North Pacific Ocean. The former is located in the NINO4 region, while the latter is characterized by the North Pacific center of the Pacific Decadal Oscillation (PDO). The dipole mode is generally well explained by the combined NINO4 and PDO impacts on TC tracks. During positive NINO4, cyclonic steering flows appear over inshore Southeast China, which increases recurving TCs. Meanwhile, the midlatitude North Pacific SST warming during negative PDO is overlaid by the barotropic anticyclone. The anomalous steering easterlies along 20°–40°N related to the anticyclone increase TC occurrence toward Southeast-East China and Taiwan. Furthermore, the precipitable water greatly increases in the midlatitude ocean during negative PDO years, which may help to enhance the rainfall amount while TCs approach Japan. To sum up, in a climatological sense, the first mode of TC-induced heavy rainfall over EA can be interpreted by the combined variations of negative (positive) PDO with positive (negative) NINO4.

This study demonstrates that absorbed solar radiation (ASR) at the top of the atmosphere in early summer (May–July) plays a precursory role in determining the Arctic sea ice concentration (SIC) in late summer (August–October). The monthly ASR anomalies are obtained over the Arctic Ocean (65°N–90°N) from the Clouds and the Earth's Radiant Energy System during 2000–2013. The ASR changes primarily with cloud variation. We found that the ASR anomaly in early summer is significantly correlated with the SIC anomaly in late summer (correlation coefficient, r ≈ −0.8 with a lag of 1 to 4 months). The region exhibiting high (low) ASR anomalies and low (high) SIC anomalies varies yearly. The possible reason is that the solar heat input to ice is most effectively affected by the cloud shielding effect under the maximum TOA solar radiation in June and amplified by the ice-albedo feedback. This intimate delayed ASR-SIC relationship is not represented in most of current climate models. Rather, the models tend to over-emphasize internal sea ice processes in summer.