On the Frequency of Lake-Effect Snowfall in the Catskill Mountains.

Meltwater from snow that falls in the Catskill/Delaware Watershed in the Catskill Mountains in south-central New York contributes to reservoirs that supply drinking water to approximately nine million people in and near New York City (NYC). Using the Interactive Multisensor Snow and Ice Mapping System (IMS) 4km snow maps from the National Oceanic and Atmospheric Administration's National Ice Center, we identified and tracked 28 lake-effect (LE) storms that deposited snow in the Catskill Mountains from 2004-2017. These storms, that generally originated from Lake Ontario, but sometimes from Lake Erie, represent an underestimate of the number of LE storms that contribute snowfall to the total Catskills snowpack because snowstorms are not visible on the IMS maps when they travel over already-snow-covered terrain. Using satellite, meteorological (including NEXRAD and National Weather Service Cooperative Observer Program), and reanalysis data we identify conditions that contributed to the LE snowstorms and map snow-cover extent (SCE) following the storms when possible. IMS 4km maps tend to overestimate SCE compared to MODerate-resolution Imaging Spectroradiometer (MODIS) and Landsat. Though the total amount of snow from each LE snow event that contributes snow to the Catskills is often small, there are a large number of events in some years that, together, add up to a great deal of snow. Changes that are predicted in LE snowfall events could impact the distribution of rain vs. snow in the Catskills which may affect future reservoir operations in the NYC Water Supply System and winter recreation in the Catskills.

A Multilayer Surface Temperature, Surface Albedo and Water Vapor Product of Greenland from MODIS.

A multilayer, daily ice-surface temperature (IST)-albedo-water vapor product of Greenland, extending from March 2000 through December 2016, has been developed using standard MODerate-resolution Imaging Spectroradiometer (MODIS) data products from the Terra satellite. To meet the needs of the ice sheet modeling community, this new Earth Science Data Record (ESDR) is provided in a polar stereographic projection in NetCDF format, and includes the existing standard MODIS Collection-6.1 IST and derived melt maps, and Collection 6 snow albedo and water vapor maps, along with ancillary data, and is provided at a spatial resolution of ~0.78 km. This ESDR enables relationships between IST, surface melt, albedo and water vapor to be evaluated easily. We show examples of the components of the ESDR and describe some uses of the ESDR such as for comparison with skin temperature, albedo and water vapor output from Modern Era Retrospective-analysis for Research and Applications, Version 2 (MERRA-2). Additionally we show validation of the MODIS IST using in situ and aircraft data, and validation of MERRA-2 skin temperature maps using MODIS IST and in situ data. The ESDR has been assigned a DOI and will be available through the National Snow and Ice Data Center by the summer of 2018.

Greenland ice sheet melt from MODIS and associated atmospheric variability.

Daily June-July melt fraction variations over the Greenland ice sheet (GIS) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) (2000-2013) are associated with atmospheric blocking forming an omega-shape ridge over the GIS at 500 hPa height. Blocking activity with a range of time scales, from synoptic waves breaking poleward (<5 days) to full-fledged blocks (≥5 days), brings warm subtropical air masses over the GIS controlling daily surface temperatures and melt. The temperature anomaly of these subtropical air mass intrusions is also important for melting. Based on the years with the greatest melt (2002 and 2012) during the MODIS era, the area-average temperature anomaly of 2 standard deviations above the 14 year June-July mean results in a melt fraction of 40% or more. Though the summer of 2007 had the most blocking days, atmospheric temperature anomalies were too small to instigate extreme melting. KEY POINTS: Short-term atmospheric blocking over Greenland contributes to melt episodesAssociated temperature anomalies are equally important for the meltDuration and strength of blocking events contribute to surface melt intensity.

History effects and phase diagram near the lower critical point in YBa2Cu3O7 single crystals.

Using a sensitive torque magnetometer we have studied magnetization curves for untwinned overdoped YBa2Cu3O7 single crystals in fields of up to 28 T. We demonstrate the existence of history effects below the lower critical point and provide a full demarcation of the Bragg-glass phase. A pronounced symmetry is observed in the behavior of the phase lines, irreversible magnetization, and value of the magnetization jump near both critical points.