中国大陆地区GNSS ZTD对超强东部型厄尔尼诺事件的响应     

于腾丽  王勇  黄靖  杨军  占伟 《大地测量与地球动力学》2022,42(10):1015-1019

利用CMONOC提供的GNSS连续观测数据分析天顶对流层延迟（ZTD）代替水汽的可行性,并利用快速傅里叶变换（FFT）和小波变换(WT)开展GNSS ZTD对超强东部型厄尔尼诺事件的响应分析。结果表明,超强东部型厄尔尼诺事件会增加中国大陆地区水汽含量,在热带及亚热带地区响应更为显著;同时该事件会影响GNSS ZTD 的显著变化周期,使9个月的变化周期减弱,0.8~3个月内的变化周期增强。  相似文献   

2021年滦州M_S4.3地震和2015年昌黎M_S4.2地震震源参数及构造意义研究     

李赫  董一兵  王熠熙 《大地测量与地球动力学》2022,42(12):1281-1287

基于京津冀地震台网观测资料,利用CAP方法反演滦州M_S4.3地震、昌黎M_S4.2地震及其M_S3.3余震的震源机制,并利用近震深度震相获得更为准确的震源深度,结合双差定位法获得2个地震序列的震源分布结果,对发震构造及成因关联开展分析研究。结果显示：1）滦州M_S4.3地震的节面Ⅰ走向、倾角、滑动角分别为211°、85°、168°,节面Ⅱ分别为302°、78°、5°,震源错动类型为走滑型,震源深度为8 km,地震序列的震源分布呈NNE向,短轴剖面显示断层面倾角近垂直,认为其发震断层面为节面Ⅰ;昌黎M_S4.2地震及M_S3.3余震的节面Ⅰ分别为189°、68°、161°及190°、61°、170°,节面Ⅱ分别为286°、72°、23°及285°、81°、29°,震源错动类型同为走滑型,震源深度为10.5 km,地震序列的震源分布呈NNE向,短轴剖面显示断层面倾角近垂直,认为其发震断层面为节面Ⅰ;2）基于滦州M_S4.3地震、昌黎M_S4.2地震及滦州M_S7.1地震的震源参数结果,结合区域地质构造等资料分析认为,3次地震的发震构造不是上地壳先存断裂,而可能与震源区的深部构造背景密切相关,即壳内包体现象是孕育这些地震的共同基础。  相似文献   

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κ���  ��һ��  �ս��� 《大地测量与地球动力学》2014,34(5):17-20

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ML3.7?????????????????93°?????????????????????С??????????????????????????????????2???????￡????????????????????????????????????????????????????????????????4??2??28??ML3.8?????????λ?????????????????????????????????????????????????????????￡????????????  相似文献   

Point pattern analysis of north polar crescentic dunes, Mars: A geography of dune self-organization     

Mark A. Bishop 《Icarus》2007,191(1):151-157

The geographic signature of dune distribution and self-organization as measured by the R-statistic offers a viewpoint on the geography of crescentic eolian systems and proposes an index from which to determine the degree of self-organization across a variety of spatial scales. Fields of simple dunes (dome, barchan, barchan-seif) are comparatively less regular in distribution than are those fields, or part thereof, that consist of compound (barchanoid) morphologies whose patterns are more highly regular.  相似文献   

The shielding effect of small-scale martian surface geometry on ultraviolet flux   总被引：2，自引：0，他引：2  

J.E. Moores  P.H. Smith  R. Tanner  A.C. Schuerger  K.J. Venkateswaran 《Icarus》2007,192(2):417-433

The atmosphere of Mars does little to attenuate incoming ultraviolet (UV) radiation. Large amounts of UV radiation sterilize the hardiest of terrestrial organisms within minutes, and chemically alter the soil such that organic molecules at or near the surface are rapidly destroyed. Thus the survival of any putative martian life near the surface depends to a large extent on how much UV radiation it receives. Variations in small-scale geometry of the surface such as pits, trenches, flat faces and overhangs can have a significant effect on the incident UV flux and may create “safe havens” for organisms and organic molecules. In order to examine this effect, a 1-D radiative transfer sky model with 836 meshed points (plus the Sun) was developed which includes both diffuse and direct components of the surface irradiance. This model derives the variation of UV flux with latitude and an object's Geometric Shielding Ratio (a ratio which describes the geometry of each situation). The best protection is offered by overhangs with flux reduced to a factor of 1.8±0.2×10⁻⁵ of the unprotected value, a reduction which does not vary significantly by latitude. Pits and cracks are less effective with a reduction in UV flux of only up to 4.5±0.5×10⁻³ for the modeled scenarios; however, they are more effective for the same geometric shielding ratio than overhangs at high latitudes due to the low height of the Sun in the sky. Lastly, polar faces of rocks have the least effective shielding geometry with at most a 1.1±0.1×10⁻¹ reduction in UV flux. Polar faces of rocks are most effective at mid latitudes where the Sun is never directly overhead, as at tropical latitudes, and never exposes the back of the rock, as at polar latitudes. In the most favorable cases, UV flux is sufficiently reduced such that organic in-fall could accumulate beneath overhanging surfaces and in pits and cracks. As well, hardy terrestrial microorganisms such as Bacillus pumilus could persist for up to 100 sols on the outer surfaces of typical spacecraft or several tens of martian years in the most shielded surface niches.  相似文献   

Tidal pattern instabilities on multi-moon planets     

Joanna Furno 《Icarus》2007,189(1):246-255

The equilibrium tide-generating forces in the lunar orbital plane of a planet of radius R are calculated for the case of N moons of mass Mi orbiting the planet at instantaneous polar coordinates (Di, αi). For the case of a single moon, there are only two high tides. For the case of two moons, it is found that there can exist a critical lunar orbital distance at which two high tides become unstable with respect to formation of three high tides. Bifurcation diagrams are presented which depict how the angular positions of the high and low tides on the planet vary with the lunar distances and lunar separation angle. Tidal stability diagrams, which illustrate the stability regions for various tidal patterns as a function of lunar distances and lunar separation angle, are presented for various values of D₂/D₁ and M₂/M₁. Generally speaking, the aforementioned tidal instability, and hence the propensity for formation of three high tides on a two-moon planet, exists over a significant range of lunar distances and separation angles provided that M₂/M₁∼³(D₂/D₁). For the case of N>2 moons, the tidal stability diagram becomes more complex, revealing a diversity of potential tidal patterns.  相似文献   

Assimilation of thermal emission spectrometer atmospheric data during the Mars Global Surveyor aerobraking period     

Stephen R. Lewis  Peter L. Read  Barney J. Conrath  John C. Pearl  Michael D. Smith 《Icarus》2007,192(2):327-347

The Thermal Emission Spectrometer aboard the Mars Global Surveyor spacecraft has produced an extensive atmospheric data set, beginning during aerobraking and continuing throughout the extended scientific mapping phase. Temperature profiles for the atmosphere below about 40 km, surface temperatures and total dust and water ice opacities, can be retrieved from infrared spectra in nadir viewing mode. This paper describes assimilation of nadir retrievals from the spacecraft aerobraking period, L_S=190°–260°, northern hemisphere autumn to winter, into a Mars general circulation model. The assimilation scheme is able to combine information from temperature and dust optical depth retrievals, making use of a model forecast containing information from the assimilation of earlier observations, to obtain a global, time-dependent analysis. Given sufficient temperature retrievals, the assimilation procedure indicates errors in the a priori dust distribution assumptions even when lacking dust observations; in this case there are relatively cold regions above the poles compared to a model which assumes a horizontally-uniform dust distribution. One major reason for using assimilation techniques is in order to investigate the transient wave behavior on Mars. Whilst the data from the 2-h spacecraft mapping orbit phase is much more suitable for assimilation, even the longer (45–24 h) period aerobraking orbit data contain useful information about the three-dimensional synoptic-scale martian circulation which the assimilation procedure can reconstruct in a consistent way. Assimilations from the period of the Noachis regional dust storm demonstrate that the combined assimilation of temperature and dust retrievals has a beneficial impact on the atmospheric analysis.  相似文献   

The effects of vigorous mixing in a convective model of zonal flow on the ice giants     

Jonathan Aurnou  Moritz Heimpel 《Icarus》2007,190(1):110-126

Previous studies have used models of three-dimensional (3D) Boussinesq convection in a rotating spherical shell to explain the zonal flows on the gas giants, Jupiter and Saturn. In this paper we demonstrate that this approach can also generate flow patterns similar to those observed on the ice giants, Uranus and Neptune. The equatorial jets of Uranus and Neptune are often assumed to result from baroclinic cloud layer processes and have been simulated with shallow layer models. Here we show that vigorous, 3D convection in a spherical shell can produce the retrograde (westward) equatorial flows that occur on the ice giants as well as the prograde (eastward) equatorial flows of the gas giants. In our models, the direction of the equatorial jet depends on the ratio of buoyancy to Coriolis forces in the system. In cases where Coriolis forces dominate buoyancy, cylindrical Reynolds stresses drive prograde equatorial jets. However, as buoyancy forces approach and exceed Coriolis forces, the cylindrical nature of the flow is lost and 3D mixing homogenizes the fluid's angular momentum; the equatorial jet reverses direction, while strong prograde jets form in the polar regions. Although the results suggest that conditions involving strong atmospheric mixing are responsible for generating the zonal flows on the ice giants, our present models require roughly 100 and 10 times the internal heat fluxes observed on Uranus and Neptune, respectively.  相似文献   

Towards a new standard model for black hole accretion     

Zdenka Kuncic  Geoffrey V. Bicknell 《Astrophysics and Space Science》2007,311(1-3):127-135

We briefly review recent developments in black hole accretion disk theory, emphasizing the vital role played by magnetohydrodynamic (MHD) stresses in transporting angular momentum. The apparent universality of accretion-related outflow phenomena is a strong indicator that large-scale MHD torques facilitate vertical transport of angular momentum. This leads to an enhanced overall rate of angular momentum transport and allows accretion of matter to proceed at an interesting rate. Furthermore, we argue that when vertical transport is important, the radial structure of the accretion disk is modified at small radii and this affects the disk emission spectrum. We present a simple model demonstrating how energetic, magnetically-driven outflows modify the emergent disk emission spectrum with respect to that predicted by standard accretion disk theory. A comparison of the predicted spectra against observations of quasar spectral energy distributions suggests that mass accretion rates inferred using the standard disk model may be severely underestimated.  相似文献   

Valley formation on martian volcanoes in the Hesperian: Evidence for melting of summit snowpack, caldera lake formation, drainage and erosion on Ceraunius Tholus     

Caleb I. Fassett 《Icarus》2007,189(1):118-135

Ceraunius Tholus, a Hesperian-aged volcano in the Tharsis region, is characterized by small radial valleys on its flanks, and several larger valleys originating near its summit caldera. All of these large valleys drain from near the lowest present portion of the caldera rim and down the flanks of the volcano. The largest valley debauches into Rahe Crater (an oblique impact crater), forming a depositional fan. Recent study of climate change on Mars suggests that many low-latitude regions (especially large volcanic edifices) were periodically the sites of snow accumulation, likely triggered by variations in spin orbital parameters. We apply a conductive heat flow model to Ceraunius Tholus that suggests that following magmatic intrusion, sufficient heating would be available to cause basal melting of any accumulated summit snowpack and produce sufficient meltwater to cause the radial valleys. The geometry of the volcano summit caldera suggests that meltwater would also accumulate in a volumetrically significant caldera lake. Analysis of the morphology and volumes of the largest valley, as well as depositional features at its base, suggest that fluvial erosion due to drainage of this summit caldera lake formed the large valleys, in a manner analogous to how valleys were formed catastrophically from a lake in Aniakchak caldera in Alaska. Moreover, the event which carved the largest valley on Ceraunius Tholus appears to have led to the formation of a temporary lake within Rahe Crater, at its base. The more abundant, small valleys on the flanks are interpreted to form by radial drainage of melted ice or snow from the outside of the caldera rim. Comparison of Ceraunius Tholus with the volcano-capping Icelandic ice sheet Myrdalsjokull provides insight into the detailed mechanisms of summit heating, ice-cap accumulation and melting, and meltwater drainage. These observations further underline the importance of a combination of circumstances (i.e., climate change to produce summit snowpack and an active period of magmatism to produce melting) to form the valley systems on some martian volcanoes and not on others.  相似文献