Description: Author(s): Y. Segal, K. F. Garrity, C. A. F. Vaz, J. D. Hoffman, F. J. Walker, S. Ismail-Beigi, and C. H. Ahn The transport and magnetic properties of correlated La 0.53 Sr 0.47 MnO 3 ultrathin films, grown epitaxially on SrTiO 3 , show a sharp cusp at the structural transition temperature of the substrate. Using a combination of experiment and first principles theory we show that the cusp is a result of evanescen... [Phys. Rev. Lett. 107, 105501] Published Tue Aug 30, 2011

Description: Sea ice concentrations, derived from passive microwave satellite sensor measurements, provide today reliable ice information on global scal. The current operational Special Sensor Microwave/ Imager (SSM/ I ) operating as part of the U. S. Defence Meteorological Satellite Program ( DMSP ), was first launched in june 1987 into a polar orbit. Due to the different emissivities of water and different ice types it is possible to obtain ice concentrations and ice fractions using suitable algorithms. During the winter time, when the overlying snow on sea ice is dry, concentrations can be retrieved to an accuracy of +/- 7%. In the summer, when surface melt is predominant, melt features appear on the ice in form of puddles or melt holes. The extent of melt features depends very much on the host ice type. In general the ice can be calssified as first year ice or old ice.The amount of water accumulated in melt features could be as high as 90% on first year ice and possibly up to 50% on old ice can lead to significant algorithm retrieval errors of ice concentrations. In order to obtain accurate melt feature concentrations a line scan camera mounted on a helicopter can provide areal coverage. Preliminary analysis of the camera data indicates that water, ice, puddles and refrozen puddles could be quantitatively separated. On 7 an 8 August 1990, based on two line scan camera flights, the ice concentration was 67% with 14% melt puddles and 40% ice concentrations with 52% melt puddles, respectively.The rest open water. The SSM/ I ice concentration for the same locations wer 46% and 35% respectively. The SSM/I ice concentrations can be compared directly to the line scan camera values. The difference in ice concentrations observed of 21 and 5% respectively can be explained due to differences in areal coverage by the two sensors. The line scan camera covered only about 6% of the gridpoint area covered by the SSM/I which consist of an area of 625 Km2 , based on these measurements, the actual SSM/I ice concentration should be 86% and 65% respectively. The method of using a line scan camera shows great promise of providing a correction to the SSM/I algorithm under summer conditions. With further experiments the camera measurements will also provide a better understanding of the melt feature life cycle on old ice.

Description: Sea ice melt processes during the Arctic summer affect the sea-air-interactions dramatically. The determination of puddles and quantification their morphology, size distribution and life cycle provides important information to the study of physical processes of sea ice, heat budget, total ice concentration etc.During the summer cruise of ARK IX/2 and 3 of the RV "POLARSTERN" in June and July 1993, a helicopter survey of sea ice for different times and locations was carried out using a Line Scan Camera (LSC) with a reselution of 2 m^2. An area between 78°N-82°N and 2°E-14°W was covered.Indication of the appearance of free water within the snow pack is usually observed in the surface layers first. This occurred on day 146 (26 May) ranging in the amount of free water present between 0.5 and 2.5%. The first melt puddles on first year ice (FY) were visually observed on June 13 day 164. The subsequent indication of the general onset of melt occurred on 17 June (Julian day 168) in the polynya region as observed on the SSM/I ice charts. This continues for about a week (Julian day 175) until the free water has increased to 6-10% within the surface layer. This period of significant free water production through melt processes coincides with a sharp increase in the melt puddles coverage, based on visual observations from the helicopter, going from 3% (Julian day 164) to 10-80% melt water on FY ice (Julian day 185-190) and 30-40% melt puddles on old ice for the same period. About 10-15 days after the brightness temperature reaches nearly black body behaviour, the maximum melt puddles coverage is reached. The refreezing period started at the end of July. The minimum of puddles concentration was detected between 80°N and 81°N. No other geographical correlation was found.Size of the puddles was between 2 m2 to more than 1 km2 and the depth was between a few centimeters to full thickness of the ice floe (thaw hole). The maximum frequency of the puddles size distribution was by a 1000 m2 category at the beginning, then shifted to 1 km2 in the middle, and finally to 100 m2 at the end of the campaign.The average depth of the snow at the beginning of ARK IX/2 varied significantly over old ice (OI) as compared to first-year ice. The mean depth during the first 10 days (Julian day 144 - 154) was 38.1 - 21.8 cm over OI and 14.6 - 8.1 cm over FY ice. The maximum-minimum range over OI varied between 62-8 cm and 26-6 cm for FY ice. By Julian day 180 the snow over FY ice had disappeared, while the snow over old ice reached that state around day 188.The comparison between SSMI and LSC ice date shows, that SSMI derived total ice concentration was higher than that from LSC but lower than the sum of both fractional concentrations of puddles and ice derived from LSC. This is what should be expected and means, that the SSMI derived ice concentrations should be corrected due to the melt features.Using the LSC provides useful ice data on small scale (resolution about 2 m2 ), which could be used for better understanding the physical processes of the sea ice.

Description: Melt-water ponds on sea ice in the Northeast Water Polynya (77-82°N, 1-18°W) were mapped using a Line Scan Camera (LSC) mounted on a helicopter. Passive microwave satellite data from the Special Sensor Microwave/Imager (SSM/I) were employed to analyse the temporal trend of radiances of shorefast ice for 1993 and sea ice during sixteen flights of the LSC (June-July). A simple, linear algorithm tailored to accomodate the summer ice regime, was developed. The LSC measurements of ice (50.9±12.5%), water and melt-water pond fractions compared very well with the SSM/I derived mean ice concentrations (50.9±12.8%). The comparison resulted in a correlation coefficient of 0.953. Combining the LSC melt-water pond fraction data with other data available from the literature provided the basis to construct a second degree polynomial function of a melt-water empirical model to correct the under estimation of SSM/I derived sea ice concentration due to the effect of melt-water ponds.