Electron densities above a polar coronal hole based on improved Si IX density diagnostics

Using new close-coupling excitation rates for the C-like ion Siix, density-diagnostic ratios based on Siix lines have been re-evaluated and applied to a sequence of CDS observations taken above a polar coronal hole. The derived electron densities are in excellent agreement with previous values of N_eestimated from the N-like ion Siviii for another coronal hole. The confirmed trend is for a fall-off of one order of magnitude within the first 0.3 Rabove the limb. These densities are well fitted with an analytic formula for the density profile out to at least 8 R, by which stage the electron density has fallen to 4×10³ cm^–3, from 1.5×10⁸ cm^–3at 1.0 R.     

A comparison of theoretical Fe xii emission line strengths with EUV observations of a solar active region

New theoretical electron-density-sensitive Fe xii emission line ratios $$R_1 = I(3s^2 3p^3 {}^4S_{3/2} - 3s3p^4 {}^4P_{5/2} )/I(3s^2 3p^3 {}^2P_{3/2} - 3s3p^4 D_{5/2} )$$ and $$R_2 = I(3s^2 3p^3 {}^2P_{3/2} - 3s3p^4 {}^2D_{5/2} )/I(3s^2 3p^3 {}^4S_{3/2} - 3s3p^2 P_{3/2} )$$ are derived using R-matrix electron impact excitation rate calculations. We have identified the Fexii \(3s^2 3p^3 {}^4S_{3/2} - 3s3p^4 {}^4P_{5/2} ,{\text{ }}3s^2 3p^3 {}^2P_{3/2} - 3s^3 3p^4 {}^2D_{5/2} ,{\text{ }}3s^2 3p^3 S_{3/2} - 3s^2 3p^3 P_{3/2} \) and \(3s^2 3p^3 {}^4S_{3/2} - 3s^2 3p^3 {}^2P_{1/2}\) transitions in an active region spectrum obtained with the Harvard S-055 spectrometer on board Skylab at wavelengths of 364.0, 382.8, 1241.7, and 1349.4 Å, respectively. Electron densities determined from the observed values of R ₁ (log N _e ? 11.0) and R ₂(log N _e ? 11.4) are significantly larger than the typical active region measurements, but are similar to those derived from some active region spectra observed with the Skylab 2082A instrument, which provides observational support for the atomic data adopted in the line ratio calculations, and also for the identification of the Fe xii transitions in the S-055 spectrum. However the observed value of R ₃ = I(1349.4 Å)/I(1241.7 Å) is approximately a factor of two larger than one would expect from theory which, considering that the 1349.4 Å line lies at the edge of the S-055 wavelength coverage, may reflect errors in the instrument efficiency curve. Another possibility is that the 1349.4 Å transition is blended, probably with Si ii 1350.1 Å.     

Coronal response of Bi-directional Jets

EUV bi-directional jets are a prominent class of phenomena characterizing the solar transition region. Using simultaneously obtained SUMER observations in the chromospheric Si ii 1251.16 Å and C i 1251.17 Å, transition region N v 1238.8 Å and coronal Mg x 625 Å lines we show an example of a bi-directional jet observed in the chromospheric and the transition region lines but not showing any detectable signature in the coronal line. The phenomenon, however, was also clearly detected by the TRACE imager with the 171 Å filter. This discrepancy is explained here with a non-Maxwellian electron distribution which makes a significant fraction of the plasma in the TRACE 171 Å pass-band to be derived from temperatures around ≈ 300 000 K, as opposed to ≈ 800 000 K. This could have implications for other phenomena observed in the TRACE pass-bands, including the transition region ‘moss’ and the 3- and 5-min oscillations.     

Nonhydrostatic,mesobeta-scale,real-data simulations with the Penn State University/National Center for Atmospheric Research mesoscale model

Summary The Penn State University/National Center for Atmospheric Research (PSU/NCAR) mesoscale model is a widely used research tool that has been applied in a wide variety of real-data, mesoalpha-scale applications. Recently a nonhydrostatic version of this model has been developed by Dudhia (1993). It is the purpose of this paper to illustrate the capabilities of this modeling system by describing four examples of mesobeta-scale simulations: two of the cases involve maritime processes and two deal with continental weather events. All utilize fully three-dimensional sets of initial conditions that are based on real data, both standard data and from special measurements programs. One case employs the model in a data-assimilation configuration, wherein Newtonian relaxation terms are used in the equations to assimilate data from a variety of platforms. This example of nonhydrostatic four-dimensional data assimilation (FDDA) is performed for the purpose of generating a dynamically consistent four-dimensional data-set, however the same procedure can be used for model initialization. The first case, described in section 2, involves the simulation of a coastal front that forms offshore near the western edge of the Gulf Stream. In the second case, described in section 3, the model is used in the FDDA mode to define the mesobeta-scale windfield over the complex terrain of the region around Grand Canyon, Arizona. In sections 4 and 5 will be described the mesobeta-scale structure of cold fronts, one within a marine cyclone, and another near the Rocky Mountains.With 21 FiguresNCAR is sponsored by the National Science Foundation.     

近10年新疆积雪面积时空变化研究

区域尺度积雪信息的时空监测对确定雪灾的影响范围及灾情等级划分具有重要意义。本文利用近10年的MODIS积雪产品,按月最大面积的规则合成;分析了新疆积雪覆盖面积的时空变化特征,结果表明:时间上,新疆积雪面积有减少的趋势。空间上,近10年新疆积雪季节内永久性积雪覆盖区域主要分布在阿勒泰山脉、天山北麓及沿昆仑山脉西南部。其中天山及阿尔泰山之间的河谷及盆地的草原积雪面积波动主导了新疆整体积雪总面积的波动。     

Geology and the war on the Western Front, 1914–1918

The First World War started a hundred years ago this year. On 4 August 2014 the United Kingdom marked the anniversary of involvement in this war with a remembrance event at Mons, and over the next four years there will be new museums and exhibitions, services and events, conferences and colloquia world‐wide. The aim of this collective recognition of a major event in world history is to pick over the impact and effects, innovations and consequences of a war that claimed the lives of at least 16 million people and left the world with geopolitical issues that still reverberate today. One of its notable innovations was the use of geology in warfare. As is well known, compared with the open war fought against the Russians on the eastern front, the war in the west very quickly became positional, with opposing trench lines locked into a position that would dictate the war's approach. And with trench warfare, came the need to understand the geology of the land over which the men were fighting.     

Application of 4D-Variational data assimilation to the California Current System

The Incremental Strong constraint 4D-Variational (IS4DVAR) data assimilation system of the Regional Ocean Model System (ROMS) is used to study the controllability of a realistic, high resolution configuration of the California Current System. The configuration and results of assimilating both satellite-derived surface observations along with in situ data are presented. Results show consequent improvements in many characteristics of the model circulation, and some of the strengths of the adjoint method for data assimilation are highlighted. General issues of the sensitivity of the results to the configuration of ROMS-IS4DVAR are also discussed.     

Melt inclusions from the deep Slave lithosphere: implications for the origin and evolution of mantle-derived carbonatite and kimberlite

Melt inclusions in clinopyroxenes from lherzolitic xenoliths from the deep lithospheric mantle beneath the Slave Craton (Lac de Gras area, Canada) reveal multiple origins for carbonatitic melts. One type of inclusions consists of a series of silicate–carbonate–silicate concentric layers, interpreted to have unmixed under disequilibrium conditions during rapid ascent to the surface. Bulk major- and trace-element compositions are typical of Group 1 kimberlites and quantitative nuclear microprobe imaging of the globules reveals fractionation of related elements (e.g. F–Br, Nb–Ta) between the silicate and carbonate components. The globules probably formed by partial melting of carbonated peridotite, consistent with results of melting experiments and some models for the generation of kimberlite magmas. They provide evidence for a genetic relationship between some carbonate-rich magmas and ultramafic silicate magmas, and for the possibility of unmixing processes of these melts during their evolution.

The second inclusion type comprises carbonate-rich globules interpreted as samples of Mg-carbonatite melt that quenched on ascent to the surface. Bulk major- and trace-element compositions indicate that the melts were derived from a carbonate-rich source and oxygen, carbon, and strontium isotope data are consistent with the involvement of recycled crustal material and suggest that some mantle-derived carbonatites are unrelated to kimberlites.     

Origins of Xenolithic Eclogites and Pyroxenites from the Central Slave Craton, Canada

Major- and trace-element and Sr–Nd–Hf isotopic compositionsof garnet and clinopyroxene in kimberlite-borne eclogite andpyroxenite xenoliths were used to establish their origins andevolution in the subcontinental lithospheric mantle beneaththe central Slave Craton, Canada. The majority of eclogitescan be assigned to three groups (high-Mg, high-Ca or low-Mgeclogites) that have distinct trace-element patterns. Althoughpost-formation metasomatism involving high field strength element(HFSE) and light rare earth element (LREE) addition has partiallyobscured the primary compositional features of the high-Mg andhigh-Ca eclogites, trace-element features, such as unfractionatedmiddle REE (MREE) to heavy REE (HREE) patterns suggestive ofgarnet-free residues and low Zr/Sm consistent with plagioclaseaccumulation, could indicate a subduction origin from a broadlygabbroic protolith. In this scenario, the low REE and smallpositive Eu anomalies of the high-Mg eclogites suggest moreprimitive, plagioclase-rich protoliths, whereas the high-Caeclogites are proposed to have more evolved protoliths withhigher (normative) clinopyroxene/plagioclase ratios plus trappedmelt, consistent with their lower Mg-numbers, higher REE andabsence of Eu anomalies. In contrast, the subchondritic Zr/Hfand positive slope in the HREE of the low-Mg eclogites are similarto Archaean second-stage melts and point to a previously depletedsource for their precursors. Low ratios of fluid-mobile to lessfluid-mobile elements and of LREE to HREE are consistent withdehydration and partial melt loss for some eclogites. The trace-elementcharacteristics of the different eclogite types translate intolower _Nd for high-Mg eclogites than for low-Mg eclogites. Withinthe low-Mg group, samples that show evidence for metasomaticenrichment in LREE and HFSE have lower _Nd and _Hf than a samplethat was apparently not enriched, pointing to long-term evolutionat their respective parent–daughter ratios. Garnet andclinopyroxene in pyroxenites show different major-element relationshipsfrom those in eclogites, such as an opposite CaO–Na₂Otrend and the presence of a CaO–Cr₂O₃ trend, independentof whether or not opx is part of the assemblage. Therefore,these two rock types are probably not related by fractionationprocesses. The presence of opx in about half of the samplesprecludes direct crystallization from eclogite-derived melts.They probably formed from hybridized melts that reacted withthe peridotitic mantle. KEY WORDS: eclogites; pyroxenite xenoliths; mantle xenoliths; eclogite trace elements; eclogite Sr isotopes; eclogite Hf isotopes; eclogite Nd isotopes