High Angular Resolution Studies of Coronal Structures with SOHO     

Margarita Karovska  Brian Wood  John W. Cook  James Chen  Russ Howard 《Astrophysics and Space Science》2000,273(1-4):7-15

Since January 1996, the Solar and Heliospheric Observatory (SOHO)has been providing unprecedented views of the extended solar coronato heliocentric distances of up to 32 solar radii. During the past threeyears we carried out studies of the morphology and dynamical evolutionof various structures in the solar corona using two instruments on boardSOHO: the Large Angle Spectrometric Coronagraph (LASCO) and the ExtremeUltraviolet Imaging Telescope (EIT). We have applied advanced image resolutionenhancement techniques to explore in detail the characteristics of thesmall-scale structures and/or the low contrast structures in the solarcorona. We describe here the results from these high-angular resolutionstudies, including of the kinematics of several Coronal Mass Ejections andpolar jets.  相似文献   

Spring recharge and groundwater flow patterns in flysch aquifer in the Po(l)onina Wetli(n)ska Massif in the Carpathian Mountains     

Karolina MOSTOWIK  Damian KRZYCZMAN  Eliza PACZKOWSKA  Bartomiej RZONCA  Janusz SIWEK  Patryk WACAWCZYK 《山地科学学报》2021,(4):819-833

Flysch-type aquifers in the Eastern Carpathians usually feed periodic and low-discharge springs.However,in some areas,such as in the upper part of the Po(l)onin...  相似文献   

The constancy of galactic cosmic rays as recorded by cosmogenic nuclides in iron meteorites     

Thomas Smith  David L. Cook  Silke Merchel  Stefan Pavetich  Georg Rugel  Andreas Scharf  Ingo Leya 《Meteoritics & planetary science》2019,54(12):2951-2976

We measured the He, Ne, and Ar isotopic concentrations and the ¹⁰Be, ²⁶Al, ³⁶Cl, and ⁴¹Ca concentrations in 56 iron meteorites of groups IIIAB, IIAB, IVA, IC, IIA, IIB, and one ungrouped. From ⁴¹Ca and ³⁶Cl data, we calculated terrestrial ages indistinguishable from zero for six samples, indicating recent falls, up to 562 ± 86 ka. Three of the studied meteorites are falls. The data for the other 47 irons confirm that terrestrial ages for iron meteorites can be as long as a few hundred thousand years even in relatively humid conditions. The ³⁶Cl‐³⁶Ar cosmic ray exposure (CRE) ages range from 4.3 ± 0.4 Ma to 652 ± 99 Ma. By including literature data, we established a consistent and reliable CRE age database for 67 iron meteorites. The high quality of the CRE ages enables us to study structures in the CRE age histogram more reliably. At first sight, the CRE age histogram shows peaks at about 400 and 630 Ma. After correction for pairing, the updated CRE age histogram comprises 41 individual samples and shows no indications of temporal periodicity, especially not if one considers each iron meteorite group separately. Our study contradicts the hypothesis of periodic GCR intensity variations (Shaviv 2002, 2003), confirming other studies indicating that there are no periodic structures in the CRE age histogram (e.g., Rahmstorf et al. 2004; Jahnke 2005). The data contradict the hypothesis that periodic GCR intensity variations might have triggered periodic Earth climate changes. The ³⁶Cl‐³⁶Ar CRE ages are on average 40% lower than the ⁴¹K‐K CRE ages (e.g., Voshage 1967). This offset can either be due to an offset in the ⁴¹K‐K dating system or due to a significantly lower GCR intensity in the time interval 195–656 Ma compared to the recent past. A 40% lower GCR intensity, however, would have increased the Earth temperature by up to 2 °C, which seems unrealistic and leaves an ill‐defined ⁴¹K‐K CRE age system the most likely explanation. Finally, we present new ²⁶Al/²¹Ne and ¹⁰Be/²¹Ne production rate ratios of 0.32 ± 0.01 and 0.44 ± 0.03, respectively.  相似文献   

Creating an isotopically similar Earth–Moon system with correct angular momentum from a giant impact     

Bryant M. Wyatt  Jonathan M. Petz  William J. Sumpter  Ty R. Turner  Edward L. Smith  Baylor G. Fain  Taylor J. Hutyra  Scott A. Cook  John H. Gresham  Michael F. Hibbs  Shaukat N. Goderya 《Journal of Astrophysics and Astronomy》2018,39(2):26

The giant impact hypothesis is the dominant theory explaining the formation of our Moon. However, the inability to produce an isotopically similar Earth–Moon system with correct angular momentum has cast a shadow on its validity. Computer-generated impacts have been successful in producing virtual systems that possess many of the observed physical properties. However, addressing the isotopic similarities between the Earth and Moon coupled with correct angular momentum has proven to be challenging. Equilibration and evection resonance have been proposed as means of reconciling the models. In the summer of 2013, the Royal Society called a meeting solely to discuss the formation of the Moon. In this meeting, evection resonance and equilibration were both questioned as viable means of removing the deficiencies from giant impact models. The main concerns were that models were multi-staged and too complex. We present here initial impact conditions that produce an isotopically similar Earth–Moon system with correct angular momentum. This is done in a single-staged simulation. The initial parameters are straightforward and the results evolve solely from the impact. This was accomplished by colliding two roughly half-Earth-sized impactors, rotating in approximately the same plane in a high-energy, off-centered impact, where both impactors spin into the collision.  相似文献   

Azimuthal impact directions from oblique impact crater morphology     

D. Wallis †  M. J. Burchell  A. C. Cook  C. J. Solomon  N. McBride 《Monthly notices of the Royal Astronomical Society》2005,359(3):1137-1149

Planetary impact craters have a high degree of radial symmetry. This hampers efforts to identify the azimuthal impact direction for most craters – the radially symmetric component of an impact crater swamps any asymmetries that may be present. We demonstrate how the asymmetric component can be isolated and the direction of the asymmetries quantified using a two-dimensional eigenfunction expansion over a circular domain. The complex coefficients of expansion describe the magnitude and phase (angular alignment) of each term. From the analysis of hypervelocity impact craters formed in the laboratory, with impact angles ranging from 0° to 50° from the surface normal, we show that asymmetries which reveal the impact direction are still present at just 10° from the surface normal, and that the phase of one complex coefficient of expansion, c ₁₁, indicates the impact direction. Analysis of the lunar crater Hadley shows bilateral symmetry in the radially asymmetric component, which may be due to oblique impact. The 31-km lunar ray crater Kepler has morphological features that indicate the azimuthal impact direction. Coefficient c ₁₁ gives an azimuthal impact direction similar to that expected from the morphology, although post-impact gravitational collapse and slumping obscure the result to some degree. Ray craters may provide a means of testing the method for smaller 'simple' craters when data are available.  相似文献   

Paleolimnology of McNearney lake: an acidic lake in northern Michigan     

Robert B. Cook  Russell G. Kreis Jr.  John C. Kingston  Keith E. Camburn  Stephen A. Norton  Myron J. Mitchell  Brian Fry  Linda C. K. Shane 《Journal of Paleolimnology》1990,3(1):13-34

McNearney Lake is an acidic (pH=4.4) lake in the Upper Peninsula of Michigan with low acid neutralizing capacity (ANC=-38 eq L^-1) and high SO _inf4 ^sup2- and aluminium concentrations. Oligotrophy is indicated by high Secchi transparency and by low chlorophyll a, total phosphorus, and total nitrogen concentrations. The lake water is currently acidic because base cations are supplied to the lake water at a low rate and because SO _inf4 ^sup2- from atmospheric deposition was not appreciably retained by the lake sediments or watershed and was present in the water column.This interdisciplinary paleolimnological study indicates that McNearney Lake is naturally acidic and has been so since at least 4000 years B.P., as determined from inferred-pH techniques based on contemporary diatom-pH relationships. Predicted pH values ranged from 4.7 to 5.0 over the 4000-year stratigraphy. Considerable shifts in species composition and abundance were observed in diatom stratigraphy, but present-day distributions indicate that all abundant taxa most frequently occur under acidic conditions, suggesting that factors other than pH are responsible for the shifts. The diatom-inferred pH technique as applied to McNearney Lake has too large an uncertainly and is not sensitive enough to determine the subtle recent changes in lakewater pH expected from changes in atmospheric deposition because: (1) McNearney Lake has the lowest pH in the contemporary diatom data set in the region and confidence intervals for pH predictions increase at the extremes of regressions; (2) other factors in addition to pH may be responsible for the diatom species distribution in the lake and in the entire northern Great Lakes region; (3) McNearney Lake has a well-buffered pH as a consequence of its low pH and high aluminium concentrations and is not expected to exhibit a large pH change as a result of changes in atmospheric deposition; and (4) atmospheric deposition in the region is modest and would not cause a pH shift large enough to be discernable in McNearney Lake.Elevated atmospheric deposition is indicated in recent sediments by Pb, V, and polycyclic aromatic hydrocarbon accumulation rates and to a lesser extent by those of Cu and Zn; however, these accumulation rates are substantially lower than those observed for acidified lakes in the northeastern United States. Although atmospheric loadings of materials associated with fossil fuel combustion have recently increased to McNearney Lake and apparently are continuing, the present study of the diatom subfossil record does not indicate a distinct, recent acidification (pH decrease).Order of the first two authors is alphabetical  相似文献   

Anisotropy of magnetic susceptibility studies in Tertiary ridge-parallel dykes (Iceland), Tertiary margin-normal Aishihik dykes (Yukon), and Proterozoic Kenora–Kabetogama composite dykes (Minnesota and Ontario)     

John P. Craddock  Bryan C. Kennedy  Avery L. Cook  Melissa S. Pawlisch  Stephen T. Johnston  Mike Jackson 《Tectonophysics》2008,448(1-4):115-124

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On predicting the response of forests in eastern North America to future climatic change     

Edward R. Cook  Julie Cole 《Climatic change》1991,19(3):271-282

Our ability to accurately predict the response of forests in eastern North America to future climatic change is limited by our knowledge of how different tree species respond to climate. When the climatic response of eastern hemlock is modeled across its range, we find that the assumed climatic response used in simulation models is not sufficient to explain how this species is presently responding to climate. This is also the case for red spruce growing in the northern Appalachian Mountains. Consequently, simulations of future change to forests that include eastern hemlock and red spruce may need to be improved. We suspect that similar findings will be made when other tree species are studied in detail using tree-ring analysis. If so, our present understanding of how individual tree species respond to climate may not be adequate for accurately predicting future changes to these forests. Tree-ring analysis can increase our understanding of how climate affects tree growth in eastern North America and, hence, provide the knowledge necessary to produce more accurate predictions.  相似文献   

An Appreciation: Teresa Emily Jeffries          下载免费PDF全文

Jennifer M. Cook 《Geostandards and Geoanalytical Research》2016,40(4):455-456

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Sedimentological records of the C.E. 1707 Hōei Nankai Trough tsunami in the Bungo Channel,southwestern Japan     

Hannah E. Baranes  Jonathan D. Woodruff  Davin J. Wallace  Kinuyo Kanamaru  Timothy L. Cook 《Natural Hazards》2016,84(2):1185-1205

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