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Huntsville, AL, United States

Winebarger A.R.,NASA | Warren H.P.,U.S. Navy | Schmelz J.T.,University of Memphis | Cirtain J.,NASA | And 3 more authors.
Astrophysical Journal Letters | Year: 2012

Observing high-temperature, low emission measure plasma is key to unlocking the coronal heating problem. With current instrumentation, a combination of EUV spectral data from Hinode Extreme-ultraviolet Imaging Spectrometer (EIS; sensitive to temperatures up to 4MK) and broadband filter data from Hinode X-ray Telescope (XRT; sensitive to higher temperatures) is typically used to diagnose the temperature structure of the observed plasma. In this Letter, we demonstrate that a "blind spot" exists in temperature-emission measure space for combined Hinode EIS and XRT observations. For a typical active region core with significant emission at 3-4MK, Hinode EIS and XRT are insensitive to plasma with temperatures greater than ∼6 MK and emission measures less than ∼1027 cm-5. We then demonstrate that the temperature and emission measure limits of this blind spot depend upon the temperature distribution of the plasma along the line of sight by considering a hypothetical emission measure distribution sharply peaked at 1MK. For this emission measure distribution, we find that EIS and XRT are insensitive to plasma with emission measures less than ∼1026 cm-5. We suggest that a spatially and spectrally resolved 6-24 Å spectrum would improve the sensitivity to these high-temperature, low emission measure plasma. © 2012 The American Astronomical Society. All rights reserved. Source


Regnier S.,University of Central Lancashire | Alexander C.E.,University of Central Lancashire | Walsh R.W.,University of Central Lancashire | Winebarger A.R.,NASA | And 11 more authors.
Astrophysical Journal | Year: 2014

Observing the Sun at high time and spatial scales is a step toward understanding the finest and fundamental scales of heating events in the solar corona. The high-resolution coronal (Hi-C) instrument has provided the highest spatial and temporal resolution images of the solar corona in the EUV wavelength range to date. Hi-C observed an active region on 2012 July 11 that exhibits several interesting features in the EUV line at 193 Å. One of them is the existence of short, small brightenings "sparkling" at the edge of the active region; we call these EUV bright dots (EBDs). Individual EBDs have a characteristic duration of 25 s with a characteristic length of 680 km. These brightenings are not fully resolved by the SDO/AIA instrument at the same wavelength; however, they can be identified with respect to the Hi-C location of the EBDs. In addition, EBDs are seen in other chromospheric/coronal channels of SDO/AIA, which suggests a temperature between 0.5 and 1.5 MK. Based on their frequency in the Hi-C time series, we define four different categories of EBDs: single peak, double peak, long duration, and bursty. Based on a potential field extrapolation from an SDO/HMI magnetogram, the EBDs appear at the footpoints of large-scale, trans-equatorial coronal loops. The Hi-C observations provide the first evidence of small-scale EUV heating events at the base of these coronal loops, which have a free magnetic energy of the order of 1026 erg. © 2014. The American Astronomical Society. All rights reserved. Source


Choi J.,University of Alabama in Huntsville | Hu Q.,Center for Space Plasma and Aeronomic Research
Proceedings of the International Astronautical Congress, IAC | Year: 2012

Our Sun, as a variable star, plays a dominant role in controlling the Solar-Terrestrial environment. It is constantly emitting highly ionized material (plasma) mostly composed of protons and electrons (so-called "solar wind"), carrying along solar magnetic field. Transient structures, often originating from explosive events on the Sun, propagate in the solar wind and impact on near-Earth space environment, generating various adverse effects. These effects include spacecraft malfunction, disruption of communication and navigation systems, radiation hazard to astronauts and passengers on polar flights, and power outage on the ground. One particular type of such structures, the interplanetary shock waves, driven by masses ejected from the Sun, is well observed and studied. We report our analysis of the set of interplanetary shock waves observed by the spacecraft Advanced Composition Explorer (ACE) between the year 1998 and 2004. We report on their properties characterizing their geometries and strengths etc. In particular, we examine the properties of turbulence associated with interplanetary shocks that have implications for energetic particle effect. We will further relate these shocks with geomagnetic storms and develop a preliminary tool for shock identification from real-time ACE solar wind data for the purpose of Space Weather forecasting. Source


Li Z.-H.,NASA | Li Z.-H.,Center for Space Plasma and Aeronomic Research | Driese S.G.,Baylor University | Cheng H.,Xian Jiaotong University | Cheng H.,University of Minnesota
Sedimentology | Year: 2014

The suitability of speleothems for interpreting palaeoclimate is typically determined by using either the Hendy Test, overlapping analysis or long-term cave environment monitoring. However, in many cases, these methods are not applicable, because a speleothem lacks clearly traceable layers for the Hendy Test, it is difficult to obtain an overlapping speleothem nearby, or long-term cave monitoring is impractical. The authors propose a multiple cave deposit approach to assess the suitability of speleothems for palaeoclimate study. Speleothems collected from two sites within Raccoon Mountain Cave, Tennessee (USA) exhibit remarkable spatial variation (δ13C: -10·3‰ to -2·2‰) over a relatively short distance (ca 260 m). Drip water δ18O values exhibit a seasonal precipitation signal at Site 1 and an annual signal at Site 2. Combining field observations, water isotope analysis and trace-element data, the authors propose that the speleothem formation at Site 1 and Site 2 tapped distinct sources of CO2: (i) CO2 derived from overlying soils for Site 1; and (ii) limestone dissolved inorganic carbon induced by ground water dissolution for Site 2. Using fresh cave deposits (modern speleothem) δ13C (100% C3 vegetation) as an analogue, a simple model was developed to estimate land surface vegetation for speleothems. The speleothem formation temperature estimated using fresh cave deposit δ18O values generally reflects the mean annual temperature in this region. This study indicates that spatial variations in carbon isotopes could be caused by different carbon sources dominating in different parts of the cave, which should be taken into consideration by researchers when using speleothem δ13C values to reconstruct temporal palaeo-vegetation changes. This study demonstrates a practical sampling strategy for verifying suitability of speleothems for palaeo-vegetation and palaeo-temperature reconstructions by analysing multiple cave deposits, especially for cases in which the Hendy Test, parallel sampling and long-term monitoring of cave environment are not feasible. © 2013 International Association of Sedimentologists. Source


Teunissen van Manen J.L.,University of Tennessee at Knoxville | Muller L.I.,University of Tennessee at Knoxville | Li Z.-H.,University of Tennessee at Knoxville | Li Z.-H.,Center for Space Plasma and Aeronomic Research | And 2 more authors.
Isotopes in Environmental and Health Studies | Year: 2014

We measured stable carbon and nitrogen isotope ratios in 117 hair samples from American black bears (Ursus americanus) in Great Smoky Mountains National Park, Tennessee, during 1980-2001 from live-trapped bears. We also collected hair from bears with known diets to compare with the wild bears. We hypothesized that biological factors (age, mass, and sex), food availability (hard mast and wild hogs (Sus scrofa)), and nuisance status would influence food selection by black bears and changes in their feeding history would be measureable using stable isotopes. We developed a set of a priori models using nine variables to examine changes in black bear stable isotope values. We found no support for changes in δ13C values associated with any of the nine variables we analyzed. Bears had enriched 15N in years with low white oak mast production and depleted 15N when white oak mast was abundant. Subadults had enriched 15N compared with adults and older adults. Variation in δ15N increased from 1980-1991 to 1992-2000 when hard mast production had greater fluctuations. Bears in a better physical condition appeared more likely to access foods with higher protein content. In years of low white oak acorn production, larger bears and subadults likely turned to alternative food sources. The long-term variation detected in this study was important in identifying which bears were potentially more susceptible to changes in availability of hard mast. © 2014 © 2014 Taylor & Francis. Source

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