Evidence that auroral zone electric fields act in opposition to superrotation of the upper atmosphere     

Michael C. Kelley 《Planetary and Space Science》1976,24(4):355-357

The average auroral zone electric field pattern has been studied to determine whether such fields can, as has been suggested, drive the super-rotation of the upper atmosphere. It is shown that the local time averaged meridional electric field is small and, in fact, poleward, which would tend to drive a prevailing westerly wind. When averaged only over the dayside, where ion drag should be most important due to the higher ion density, the poleward average is even more pronounced. Thus at high latitudes ion drag acts to drive a prevailing neutral wind to the west. Model calculations indicate that without including electric fields the prevailing wind at mid-latitudes should be to the west, due to higher ion drag on the dayside. Including the present results will increase ion drag on the dayside and further enhance this effect. These results thus suggest that at middle and high latitudes the upper atmosphere does not superrotate.  相似文献   

Radar Observations of Asteroid 3908 Nyx     

Lance A.M. BennerSteven J. Ostro  R.Scott HudsonKeith D. Rosema  Raymond F. JurgensDonald K. Yeomans  Donald B. CampbellJohn F. Chandler  Irwin I. Shapiro 《Icarus》2002,158(2):379-388

We report Doppler-only (cw) radar observations of basaltic near-Earth asteroid 3908 Nyx obtained at Arecibo and Goldstone in September and October of 1988. The circular polarization ratio of 0.75±0.03 exceeds ∼90% of those reported among radar-detected near-Earth asteroids and it implies an extremely rough near-surface at centimeter-to-decimeter spatial scales. Echo power spectra over narrow longitudinal intervals show a central dip indicative of at least one significant concavity. Inversion of cw spectra yields two statistically indistinguishable shape models that have similar shapes and dimensions but pole directions that differ by ∼100°. We adopt one as our working model and explore its implications. It has an effective diameter of 1.0±0.15 km and radar and visual geometric albedos of 0.15±0.075 and 0.16^+0.08_−0.05. The visual albedo supports the interpretation by D. P. Cruikshank et al. (1991, Icarus89, 1-13) that Nyx has a thermal inertia consistent with that of bare rock. The model is irregular, modestly asymmetric, and topographically rugged.  相似文献   

Microwave Remote Sensing of the Temperature and Distribution of Sulfur Compounds in the Lower Atmosphere of Venus     

Jon M. JenkinsMarc A. Kolodner  Bryan J. ButlerShady H. Suleiman  Paul G. Steffes 《Icarus》2002,158(2):312-328

A multi-wavelength radio frequency observation of Venus was performed on April 5, 1996, with the Very Large Array to investigate potential variations in the vertical and horizontal distribution of temperature and the sulfur compounds sulfur dioxide (SO₂) and sulfuric acid vapor (H₂SO₄(g)) in the atmosphere of the planet. Brightness temperature maps were produced which feature significantly darkened polar regions compared to the brighter low-latitude regions at both observed frequencies. This is the first time such polar features have been seen unambiguously in radio wavelength observations of Venus. The limb-darkening displayed in the maps helps to constrain the vertical profile of H₂SO₄(g), temperature, and to some degree SO₂. The maps were interpreted by applying a retrieval algorithm to produce vertical profiles of temperature and abundance of H₂SO₄(g) given an assumed sub-cloud abundance of SO₂. The results indicate a substantially higher abundance of H₂SO₄(g) at high latitudes (above 45°) than in the low-latitude regions. The retrieved temperature profiles are up to 25 K warmer than the profile obtained by the Pioneer Venus sounder probe at altitudes below 40 km (depending on location and assumed SO₂ abundance). For 150 ppm of SO₂, it is more consistent with the temperature profile obtained by Mariner 5, extrapolated to the surface via a dry adiabat. The profiles obtained for H₂SO₄(g) at high latitudes are consistent with those derived from the Magellan radio occultation experiments, peaking at around 8 ppm at an altitude of 46 km and decaying rapidly away from that altitude. At low latitudes, no significant H₂SO₄(g) is observed, regardless of the assumed SO₂ content. This is well below that measured by Mariner 10 (Lipa and Tyler 1979, Icarus39, 192-208), which peaked at ∼14 ppm near 47 km. Our results favor ≤100 ppm of SO₂ at low latitudes and ≤50 ppm in polar regions. The low-latitude value is statistically consistent with the results of Bézard et al. (1983, Geophs. Res. Lett.20, 1587-1590), who found that a sub-cloud SO₂ abundance of 130±40 ppm best matched their observations in the near-IR. The retrieved temperature profile and higher abundance of H₂SO₄(g) in polar regions are consistent with a strong equatorial-to-polar, cloud-level flow due to a Hadley cell in the atmosphere of Venus.  相似文献   

垂直上升管中气液两相流电导波动信号的混沌特性分析   总被引：11，自引：0，他引：11       下载免费PDF全文

金宁德  郑桂波  胡凌云 《地球物理学报》2006,49(5):1552-1560

首先以Lorenz混沌方程产生的非线性时间序列为例，讨论了在不同时间序列长度下各种延迟时间算法对噪声的适用性.研究发现，采用C_C算法计算延迟时间的鲁棒性强.在此基础上，给出了垂直上升管中气水两相流电导波动信号混沌表征结果，发现在较低水相表观速度时，随着气相表观速度增加，泡状流及混状流动力学特性变得愈加复杂，而段塞流动力学特性受液相表观速度影响较大；在较高水相表观速度时，随着气相表观速度增加，当流型从泡状流向段塞流转变时，气液两相流动力学特性变得相对简单.但是，由于受液相湍流作用影响，段塞流的动力学特性表现出了涨落现象，呈现不稳定性，当流型从段塞流向混状流转变时，气液两相流动力学特性则变得愈加复杂.研究结果表明：基于电导波动信号的混沌分析可以较好地表征气液两相流流型变化，是理解流型转变机理及其动力学演变特性的有用工具.  相似文献   

Application of neural approaches to one-step daily flow forecasting in Portuguese watersheds     

《Journal of Hydrology》2007,332(1-2):1-15

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Fractal characteristics of the ground-observed ULF emissions in relation to geomagnetic and seismic activities     

《Journal of Atmospheric and Solar》2007,69(15):1833-1841

Results of fractal analysis of ultra-low-frequency (ULF) emissions registered at a low-latitude observatory, Guam (geomagnetic coordinates Φ_m=9°N, Λ_m=225°), and at a high-latitude drifting station, North Pole-30 (Φ_m=75°N, Λ_m=172°), are presented. The first set of data covers a long period of observations (20 months) including the strong (Ms=8) Guam earthquake of 8 August 1993. The second set of data covers a short period of observations (21 days) in April 1989 during the preparation phase of the big magnetic storm of 25 April 1989. Definite peculiarities in the behavior of ULF emission scaling (fractal) characteristics have been found, which are discussed on the basis of the self-organized criticality concept. The principal common peculiarity for magnetosphere–ionosphere and lithosphere systems is detection of flicker noise (β∼1, D₀∼2) in a certain frequency range on the preparation phase of strong magnetospheric and seismic events.  相似文献   

CURRENT LITERATURE SURVEY     

《Journal of African Earth Sciences》2011,59(5):857-859

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Variability of GPS derived water vapor and comparison with MODIS data over the Indo-Gangetic plains     

《Physics and Chemistry of the Earth》2013

The water vapor is one of the important constituents of the atmosphere that affects the thermodynamics of the atmosphere and has direct impact on the weather conditions. The total column atmospheric water vapor, obtained from Global Positioning System (GPS) and Moderate Resolution Imaging Spectroradiometer (MODIS), is found to be very dynamic over the Indo-Gangetic (IG) plains. In this paper, we present an analysis of GPS data recently deployed (as of May 2007) on the campus of Banaras Hindu University, Varanasi (latitude 25°15′N, longitude 82°59′E). Further, we have compared the variability of water vapor from Kanpur GPS, AERONET and MODIS water vapor data for the year 2007. The monthly variability of water vapor shows characteristic features and dynamics of water vapor between two closely spaced GPS stations, found to be controlled by monsoon dynamics and wind pattern.  相似文献   

On the observations of unique low latitude whistler-triggered VLF/ELF emissions     

《Physics and Chemistry of the Earth》2013

A detailed analysis of the VLF/ELF wave data obtained during a whistler campaign under All India Coordinated Program of Ionosphere Thermosphere Studies (AICPITS) at our low latitude Indian ground station Jammu (geomag. lat. = 22° 26′ N, L = 1.17) has yielded two types of unusual and unique whistler-triggered VLF/ELF emissions. These include (1) whistler-triggered hook emissions and (2) whistler-triggered long enduring discrete chorus riser emissions in VLF/ELF frequency range during night time. Such types of whistler-triggered emissions have not been reported earlier from any of the ground observations at low latitudes. In the present study, the observed characteristics of these emissions are described and interpreted. Dispersion analysis of these emissions show that the whistlers as well as emissions have propagated along a higher geomagnetic field line path with L-values lying ∼L = 4, suggesting that these triggered emissions are to be regarded as mid-latitude emissions. These waves could have propagated along the geomagnetic field lines either in a ducted mode or in a pro-longitudinal (PL) mode. The measured intensity of the triggered emissions is almost equal to that of the source waves and does not vary throughout the period of observation on that day. It is speculated that these emissions may have been generated through a process of resonant interaction of the whistler waves with energetic electrons. Parameters related to this interaction are computed for different values of L and wave amplitude. The proposed mechanism explains some aspects of the dynamic spectra.  相似文献   

Litho-stratigraphic effect on Variscan fluid flow within the Prague synform,Barrandian: Evidence based on C,O, Sr isotopes and fluid inclusions     

《Marine and Petroleum Geology》2012,36(1):128-138

The Palaeozoic sedimentary sequence of the Prague synform (Ordovician–Devonian) in the centre of the Bohemian massif underwent Variscan deformation and thermal overprint events. Variscan veins widespread throughout the sedimentary strata have precipitated from syntectonic aqueous and hydrocarbon-rich fluids. Homogenization temperatures of aqueous inclusions increased from 70 up to 226 °C in the Cambrian rocks underlying the Prague synform. Seawater, modified due to intensive water–rock interaction, was the main fluid component. Fluid flow was limited and restricted to the lithostratigraphic compartments forming a rock-buffered system. Stable isotopic modelling (C, O) and final interpretations of the confined hydrostratigraphic fluid migration was supported by the ⁸⁷Sr/⁸⁶Sr ratio in veins and wall rocks. Siliciclastic Cambrian and Ordovician rocks and the associated intersecting veins yielded similar isotopic signatures, and consequently the fluid migration is restricted to layer- and formation-scales. Gradually downwards increasing fluid temperature and compositional changes reflect burial at oil-window conditions. An open fluid system could be expected in proximity of major faults of the Prague syncline and at the top of the sedimentary sequence.  相似文献