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Seasonal and interannual variabilities of sea-ice area in the Southern Ocean were examined using daily sea-ice concentration and ice velocity products for 2003–2019, derived from Advanced Microwave Scanning Radiometer for EOS (AMSR-E) and AMSR2 data. This study quantified the contributions to changes in the sea-ice area due to sea-ice transport and local processes, including ice formation/melting and ice deformation. Regional differences in the processes of seasonal advance and retreat of sea ice were elucidated. In most regions, sea-ice area increases mainly due to new ice formation in the marginal ice zone during autumn and winter. However, in the Amundsen–Bellingshausen seas, ice melting occurs in the marginal ice zone, even during winter, and expansion of the ice cover is attributable mainly to off-ice transport. With regard to interannual variability, the maximum ice area for each year is highly correlated with increase of ice area attributable to the ice formation in the marginal ice zone. Revealed processes that controls sea-ice changes could help improve our understanding of the sea-ice response to climate change.

Accurate description of sea ice velocity is necessary for improving the reproduction and prediction of high-latitude climate in modeling studies. In order to improve the simulated sea ice velocity field based on satellite-derived daily data, a set of sea ice dynamic parameters of the ocean–sea ice model was optimized with a Green’s function method, which uses linear combination of forward sensitivity operators for these parameters. An improved sea ice velocity field with 15–20% error reduction was obtained for both simulations with and without the data constraint of sea ice concentration. Moreover, dependencies of the sea ice dynamic parameters on background conditions were examined and linear dependency coefficients were also optimized by extending the above method. The sea ice velocity field was further improved for both free-drift and high-pressure regions with mean error reduction of about 25%. This resulted in decreases of surface salinities in the marginal ice zones, making them closer to observations. While the parameter adjustments as constants tended mainly to compensate influences of biases in surface forcing, the obtained dependencies were generally consistent with previous observational and theoretical studies and thus improved parameterizations of air–ice–ocean momentum exchange and ice pressure which are widely used in OGCMs. The enhanced ocean–sea ice initialization and parameterizations would be useful for operational seasonal prediction and climate prediction studies.

Superconductivity at interfaces has been investigated since the first demonstration of electric-field-tunable superconductivity in ultrathin films in 1960(1). So far, research on interface superconductivity has focused on materials that are known to be superconductors in bulk. Here, we show that electrostatic carrier doping can induce superconductivity in KTaO(3), a material in which superconductivity has not been observed before. Taking advantage of the large capacitance of the self-organized electric double layer that forms at the interface between an ionic liquid and KTaO(3) (ref. 12), we achieve a charge carrier density that is an order of magnitude larger than the density that can be achieved with conventional chemical doping. Superconductivity emerges in KTaO(3) at 50 mK for two-dimensional carrier densities in the range 2.3 × 10(14) to 3.7 × 10(14) cm(-2). The present result clearly shows that electrostatic carrier doping can lead to new states of matter at nanoscale interfaces.

This paper examines the mechanism controlling the short time-scale variation of sea ice cover over the Southern Ocean. Sea ice concentration and ice velocity datasets derived from images of the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imager (SSM/I) are employed to reveal this mechanism. The contribution of both dynamic and thermodynamic processes to the change in ice edge location is examined by comparing the meridional velocity of ice edge displacement and sea ice drift. In the winter expansion phase, the thermodynamic process of new ice production off the ice edge plays an important role in daily advances of ice cover, whereas daily retreats are mostly due to southward ice drift. On the other hand, both advance and retreat of ice edges in the spring contraction phase are mostly caused by the dynamic process of the ice drift. Based on the above mechanism and the linear relation between the degree of ice production at the ice edge and northward wind speed, the seasonal advance of ice cover can be roughly reproduced using the meridional velocity of ice drift at the ice edge.

Theories predict that spontaneous magnetization occurs in the superconducting B phase in UPt3 because of broken time-reversal symmetry. The strength of the spontaneous magnetization depends on whether it comes from spin degeneracy or orbital degeneracy. We measured the internal field due to the spontaneous magnetization on the supercondicting transition to the B phase for a UPt3 sample in the magnetic fields very close to zero, using a SQUID magnetometer. The upper limit of the spontaneous internal field was 0.007 gauss. This result seems to favor the theory of the orbital degeneracy.

The195Pt Knight shift of the high quality single crystal UPt3 measured down toT=28 mK have revealed no change acrossTc regardless of the applied field directions and of the superconducting multiphases. An estimation of the spin part from theT linear specific heat has ensured no variation of the dominant spin part of the measured Knight shift belowTc as well as its estimation by the subtraction of the Van Vleck part from theT dependence of the Knight shift in the highT region reported in the previous paper. It is reinforced that UPt3 is the odd-parity superconductor with equal spin pairing and the pinning of the order parameter does not take place, suggesting the spin-orbit coupling for the pairing interaction to be not so strong.

The thermal expansion of the single crystal of UPt3 has been measured at temperatures down to 1 mK by a capacitance dilatometer. We have first observed a large thermal expansion anomaly aroundT a =17 mK. It corresponds to the specific heat anomaly observed in 1992. Furthermore, the expansion coefficients depend onT −2 at the temperature aboveT a , andT 2 at that belowT a respectively.