University of Maryland, Baltimore County

About: University of Maryland, Baltimore County is a education organization based out in Baltimore, Maryland, United States. It is known for research contribution in the topics: Population & Aerosol. The organization has 8749 authors who have published 20843 publications receiving 795706 citations. The organization is also known as: UMBC.

Atmospheric and oceanic climate forcing of the exceptional Greenland ice sheet surface melt in summer 2012

Abstract: The NASA announcement of record surface melting of the Greenland ice sheet in July 2012 led us to examine the atmospheric and oceanic climatic anomalies that are likely to have contributed to these exceptional conditions and also to ask the question of how unusual these anomalies were compared to available records. Our analysis allows us to assess the relative contributions of these two key influences to both the extreme melt event and ongoing climate change. In 2012, as in recent warm summers since 2007, a blocking high pressure feature, associated with negative NAO conditions, was present in the mid-troposphere over Greenland for much of the summer. This circulation pattern advected relatively warm southerly winds over the western flank of the ice sheet, forming a heat dome' over Greenland that led to the widespread surface melting. Both sea-surface temperature and sea-ice cover anomalies seem to have played a minimal role in this record melt, relative to atmospheric circulation. Two representative coastal climatological station averages and several individual stations in south, west and north-west Greenland set new surface air temperature records for May, June, July and the whole (JJA) summer. The unusually warm summer 2012 conditions extended to the top of the ice sheet at Summit, where our reanalysed (1994-2012) DMI Summit weather station summer (JJA) temperature series set new record high mean and extreme temperatures in 2012; 3-hourly instantaneous 2-m temperatures reached an exceptional value of 2.2 degrees C at Summit on 11 July 2012. These conditions translated into the record observed ice-sheet wide melt during summer 2012. However, 2012 seems not to be climatically representative of future average' summers projected this century.

Flood hydrology and geomorphic effectiveness in the central Appalachians

Abstract: This paper compares hydrologic records and geomorphic effects of several historic floods in the central Appalachian region of the eastern United States. The most recent of these, occurring in November 1985, was the largest ever recorded in West Virginia, with peak discharges exceeding the estimated 500-year discharge at eight of eleven stations in the South Branch Potomac River and Cheat River basins. Geomorphic effects on valley floors included some of the most severe and widespread floodplain erosion ever documented and exceeded anything seen in previous floods, even though comparable or greater rainfall and unit discharge have been observed several times in the region over the past 50 years. Comparison of discharge-drainage area plots suggests that the intensity and spatial scale of the November 1985 flood were optimal for erosion of valley floors along the three forks of the South Branch Potomac River. However, when a larger geographic area is considered, rainfall totals and discharge-drainage area relationships are insufficient predictors of geomorphic effectiveness for valley floors at drainage areas of 250 to 2500 km2. Unit stream power was calculated for the largest recorded flood discharge at 46 stations in the central Appalachians. Maximum values of unit stream power are developed in bedrock canyons, where the boundaries are resistant to erosion and the flow cross-section cannot adjust its width to accommodate extreme discharges. The largest value was 2570 W m−2; record discharge at most stations was associated with unit stream power values less than 300 W m−2, but more stations exceeded this value in the November 1985 flood than in the other floods that were analysed. Unit stream power at indirect discharge measurement sites near areas experiencing severe erosion in this and other central Appalachian floods generally exceeded 300 W m−2; reach-average values of 200-500 W m−2 were calculated for valleys where erosion damage was most widespread. Despite these general trends, unit stream power is not a reliable predictor of geomorphic change for individual sites. Improved understanding of flood impacts will require more detailed investigation of interactions between local site characteristics and patterns of flood flow over the valley floor.

Maximizing the bandwidth of supercontinuum generation in As_2Se_3 chalcogenide fibers

Abstract: We describe in detail a procedure for maximizing the bandwidth of supercontinuum generation in As2Se3 chalcogenide fibers and the physics behind this procedure. First, we determine the key parameters that govern the design. Second, we find the conditions for the fiber to be endlessly single-mode; the fiber should be endlessly single-mode to maintain high nonlinearity and low coupling loss. We find that supercontinuum generation in As2Se3 fibers proceeds in two stages — an initial stage that is dominated by four-wave mixing and a later stage that is dominated by the Raman-induced soliton self-frequency shift. Third, we determine the conditions to maximize the Stokes wavelength that is generated by four-wave mixing in the initial stage. Finally, we put all these pieces together to maximize the bandwidth. We show that it is possible to generate an optical bandwidth of more than 4 μm with an input pump wavelength of 2.5 μm using an As2Se3 fiber with an air-hole-diameter-to-pitch ratio of 0.4 and a pitch of 3 μm. Obtaining this bandwidth requires a careful choice of the fiber’s waveguide parameters and the pulse’s peak power and duration, which determine respectively the fiber’s dispersion and nonlinearity.