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1.
Anna Belehaki Ivan Kutiev Bodo Reinisch Norbert Jakowski Pencho Marinov Ivan Galkin Chris Mayer Ioanna Tsagouri Themistocles Herekakis 《Acta Geophysica》2010,58(3):432-452
The purpose of this paper is to evaluate the performance of the TSMP-assisted Digisonde (TaD) topside profiling technique.
We present systematic comparisons between electron density profiles and TEC parameters extracted from TaD model with (a) CHAMP-derived TEC parameters, (b) CHAMP reconstructed profiles, (c) ground based GPSderived TEC parameters, and (d) profiles reconstructed from RPI/IMAGE plasmagrams. In all cases, TaD follows the general trend of plasmaspheric
observations derived from the above datasets. Especially during storm cases, TaD shows remarkable agreement with the variations
of the ground based GPS-derived TEC parameters. Overall, the comparison results shows that TaD method can be adopted by EURIPOS to provide the electron density
distribution up to plasmaspheric heights in real-time. 相似文献
2.
The numerical global self-consistent model of the Earth’s thermosphere, ionosphere and protonosphere (GSM TIP), which makes
it possible to calculate all the main parameters of the near-Earth plasma, is used to calculate the total electron content
(TEC). Calculations have been performed along the radiosignal propagation trajectory between a surface receiving point and a GPS
satellite. The TEC value calculated from the satellite data have been compared with such a “true model” TEC value for magnetically quiet conditions of the spring equinox and moderate solar activity. The relative errors in determining
the satellite data-based TEC for two European (Troms have been calculated. It has been indicated that an increase in the number of satellites not always
results in an increase in accuracy of the TEC value measured on satellites. 相似文献
3.
In this paper we present specific features of TEC (total electron content of the ionosphere) behavior as possible precursors of Kythira (Southern Greece) earthquake of January
8, 2006 (M6.8). For this purpose, we used both the TEC data of GPS-IGS stations nearest to the epicenter, and TEC maps over Europe. The favorable circumstance for this analysis was the quiet geomagnetic situation during the period prior
to the earthquake. One day before the earthquake, a characteristic anomaly was found out as the day-time significant increase
of TEC at the nearest stations, up to the value of 50% relative to the background condition. To estimate the spatial dimensions
of seismo-ionospheric anomaly, the differential mapping method was used. The ionosphere modification as a cloud-like increase
of electron concentration situated in the immediate vicinity of the forthcoming earthquake epicenter has been revealed. The
amplitude of modification reached the value of 50% relative to the non-disturbed condition and was in existence from 10:00
till 22:00 UT. The area of significant TEC enhancement had a size of about 4000 km in longitude and 1500 km in latitude. 相似文献
4.
5.
On the treatment of uncertainties in the development of fragility functions for earthquake loss estimation of building portfolios 
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下载免费PDF全文 State‐of‐the‐art methods for the assessment of building fragility consider the structural capacity and seismic demand variability in the estimation of the probability of exceeding different damage states. However, questions remain regarding the appropriate treatment of such sources of uncertainty from a statistical significance perspective. In this study, material, geometrical and mechanical properties of a number of building classes are simulated by means of a Monte Carlo sampling process in which the statistical distribution of the aforementioned parameters is taken into consideration. Record selection is performed in accordance with hazard‐consistent distributions of a comprehensive set of intensity measures, and issues related with sufficiency, efficiency, predictability and scaling robustness are addressed. Based on the appraised minimum number of ground motion records required to achieve statistically meaningful estimates of response variability conditioned on different levels of seismic intensity, the concept of conditional fragility functions is presented. These functions translate the probability of exceeding a set of damage states as a function of a secondary sufficient intensity measure, when records are selected and scaled for a particular level of primary seismic intensity parameter. It is demonstrated that this process allows a hazard‐consistent and statistically meaningful representation of uncertainty and correlation in the estimation of intensity‐dependent damage exceedance probabilities. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
6.
A self-consistent method for day-time F2-region modelling was applied to the analysis of Millstone Hill incoherent scatter observations during the storm period of March 16-22, 1990. The method allows us to calculate in a self-consistent way neutral composition, temperature and meridional wind as well as the ionized species height distribution. Theoretically calculated Ne(h) profiles fit the observed daytime ones with great accuracy in the whole range of heights above 150 km for both quiet and disturbed days. The overall increase in Tex by 270 K from March 16 to March 22 reflects the increase of solar activity level during the period in question. A 30% decrease in [O] and a twofold increase in [A^] are calculated for the disturbed day of March 22 relative to quiet time prestorm conditions. Only a small reaction to the first geomagnetic disturbance on March 18 and the initial phase of the second storm on March 20 was found in [O] and [N2] variations. The meridional neutral wind inferred from plasma vertical drift clearly demonstrates the dependence on the geomagnetic activity level being more equatorward on disturbed days. Small positive F2-layer storm effects on March 18 and 20 are totally attributed to the decrease in the northward neutral wind but not to changes in neutral composition. A moderate (by a factor of 1.5) O/ N2 ratio decrease relative to the MSIS-83 model prediction is required to describe the observed NmF2 decrease on the most disturbed day of March 22, but virtually no change of this ratio is needed for March 21. 相似文献
7.
In a related study developed by the authors, building fragility is represented by intensity‐specific distributions of damage exceedance probability of various damage states. The contribution of the latter has been demonstrated in the context of loss estimation of building portfolios, where it is shown that the proposed concept of conditional fragility functions provides the link between seismic intensity and the uncertainty in damage exceedance probabilities. In the present study, this methodology is extended to the definition of building vulnerability, whereby vulnerability functions are characterized by hazard‐consistent distributions of damage ratio per level of primary seismic intensity parameter—Sa(T1). The latter is further included in a loss assessment framework, in which the impact of variability and spatial correlation of damage ratio in the probabilistic evaluation of seismic loss is accounted for, using test‐bed portfolios of 2, 5, and 8‐story precode reinforced concrete buildings located in the district of Lisbon, Portugal. This methodology is evaluated in comparison with current state‐of‐the‐art methods of vulnerability and loss calculation, highlighting the discrepancies that can arise in loss estimates when the variability and spatial distributions of damage ratio, influenced by ground motion properties other than the considered primary intensity measure, are not taken into account. 相似文献
8.
Ljiljana R. Cander 《Acta Geophysica》2007,55(3):410-423
The spatial variations of the ionospheric F2-layer vertical incidence critical frequency (foF2) and GPS-derived vertical total electron content (vTEC) under geomagnetically quiet and disturbed days are examined using measurements from the latitudinal and longitudinal chains
of ionospheric stations and GPS receivers over the European area. Plots produced for January 2005 are used to discuss temporal
structures in terms of the prevailing solar-terrestrial conditions. Then the line trends procedure has been applied to simultaneous
data collected from a limited number of measuring stations during quiet monthly median ionospheric conditions as well as during
the storm period of 16–23 January 2005. The procedure is explained involving an application of the least squares method to
define latitudinal and longitudinal dependence of foF2 and vTEC at different locations. Examples of coefficients of determination thereby produced show that the linear regression equations
are very helpful in predicting longitudinal and latitudinal vTEC and foF2 variations during the quiet as well as disturbed ionospheric conditions. 相似文献
9.
Although climate has been shown to have a considerable influence on alpine forest dynamics, many fine‐scale processes contribute to observable forest patterns. Disturbances created by burrowing mammals may provide conifer seedlings with refuge in previously inhospitable environments and may result in conifer invasion that is not directly associated with climate change. In Olympic National Park, Washington, USA, Olympic marmot (Marmota olympus) populations have declined. Abandoned marmot burrows, which may provide ideal sites for conifer establishment, now dot the alpine landscape. Similarly, in Glacier National Park, Montana, USA, pocket gophers (Thomomys talpoides) have disturbed large areas of alpine meadows at treeline. Field and laboratory analysis of gopher eskers and spoil mounds of abandoned marmot burrows illustrated that such sites are less compacted than soils in adjacent, undisturbed locations. Additionally, disturbed soils contained higher amounts of phosphorus and lower amounts of potassium and organic matter. Soils disturbed by gophers were cooler at the surface and warmer at depth than undisturbed soils, whereas marmot‐disturbed soils were warmer at the surface and cooler at depth. Experimental seed germination of subalpine fir (Abies lasiocarpa) was higher on mammal‐disturbed soils, and this was statistically significant for marmot‐disturbed soils. These findings suggest that fossorial mammal disturbances have the potential to affect conifer germination and establishment. Furthermore, this research initiates the dialogue for future research on the distinct morphological and behavioral influences of different fossorial mammals as zoogeomorphic agents and ecosystem engineers. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
10.
AbstractSoil water content (θ) and saturated hydraulic conductivity (Ks) vary in space. The objective of this study was to examine the effects of initial soil water content (θi) and Ks variability on runoff simulations using the LImburg Soil Erosion Model (LISEM) in a small watershed in the Chinese Loess Plateau, based on model parameters derived from intensive measurements. The results showed that the total discharge (TD) and peak discharge (PD) were underestimated when the variability of θi and Ks was partially considered or completely ignored compared with those when the variability was fully considered. Time to peak (TP) was less affected by the spatial variability compared to TD and PD. Except for TP in some cases, significant differences were found in all hydrological variables (TD, PD and TP) between the cases in which spatial variability of θi or Ks was fully considered and those in which spatial variability was partially considered or completely ignored. Furthermore, runoff simulations were affected more strongly by Ks variability than by θi variability. The degree of spatial variability influences on runoff simulations was related to the rainfall pattern and θi. Greater rainfall depth and instantaneous rainfall intensity corresponded to a smaller influence of the spatial variability. Stronger effects of the θi variability on runoff simulation were found in wetter soils, while stronger effects of the Ks variability were found in drier soils. For accurate runoff simulation, the θi variability can be completely ignored in cases of a 1-h duration storm with a return period greater than 10 years, while Ks variability should be fully considered even in the case of a 1-h duration storm with a return period of 20 years.
Editor D. Koutsoyiannis; Associate editor A. Fiori 相似文献
11.
M. G. Deminov G. F. Deminova G. A. Zherebtsov O. M. Pirog N. M. Polekh 《Geomagnetism and Aeronomy》2011,51(3):348-355
Results of statistical analysis of the properties of variability of F2-layer maximum parameters (critical frequency foF2 and the height hmF2) in quiet midlatitude ionosphere under low solar activity in the daytime (1000–1500 LT) and nighttime (2200–0300 LT) hours
are presented on the basis of Irkutsk station data for 2007–2008. It is found that the distribution density of δfoF2 could be presented as consisting of two distinctly different normal laws of this distribution, one of which corresponds
to weak (|δfoF2| < 10%) fluctuations in foF2 and the other corresponds to strong (30% > |δfoF2| > 10%) fluctuations. Weak fluctuations in foF2 to a substantial degree are related to ionospheric variability at times less of than 1–3 h and determine the δfoF2 variability in the daytime hours. Strong fluctuations in foF2 are mainly related to day-to-day variability of the ionosphere at a fixed local time, the variability increasing by approximately
a factor of 3 during the transition from day to night and determining the δfoF2 variability in the nighttime hours. The distribution density of ΔhmF2 is close to the normal distribution law. An interpretation of the different character of the distribution densities of δfoF2 and ΔhmF2 is given. 相似文献
12.
Ground-based ionosonde and magnetic-field observations on the equatorial station Huancayo, ESRO4 neutral-composition measurements, and theoretical model calculations were used to analyze disturbed E×B vertical plasma drift during the phase of solar minimum in 1973. Vertical drifts calculated for disturbed days do not show the systematic decrease often mentioned in publications, and demonstrate strong dependence on IMF-Bz changes. It is confirmed with the help of our drift calculations that Bz turnings to a northward direction result in a decrease (up to reversal) of normal Sq (eastward during daytime and westward at nighttime) in the zonal component of electric field. Southward Bz excursions enhance normal Ey both in daytime and nighttime hours. Model predictions of Ey’s reaction to IMF-Bz changes are discussed. 相似文献
13.
A series of numerical studies on the behaviour of magnetic fields and motions in a spherical body of an electrically conducting incompressible fluid have been carried out. The magnetic field was assumed to be maintained by a given electromotive force inside the body and to continue as a potential field in outer space. In view of the motion an external forcing was taken into account, and boundary conditions were considered which correspond to a stress-free surface. The stability of several steady states has been studied as well as the evolutions starting from unstable states. In this paper a configuration with a poloidal magnetic field and a differential rotation, both symmetric about the same axis, is considered. This configuration is stable only for sufficiently small Hartmann numbers but evolves, if disturbed, in the case of larger Hartmann numbers toward a non-axisymmetric state. In this case the well-known symmetrization effect of differential rotation in magnetic fields is destroyed. 相似文献
14.
Two-Dimensional Probabilistic Infiltration Analysis in a Hillslope Using First-Order Moment Approach
A first-order moment analysis method is introduced to evaluate the pore-water pressure variability within a hillslope due to spatial variability in saturated hydraulic conductivity (Ks) during rainfall. The influences of the variance of the natural logarithm of Ks(ln Ks), spatial structure anisotropy of ln Ks, and normalized vertical infiltration flux (q) on the evaluations of the pore-water pressure uncertainty are investigated. Results indicate different responses of pressure head variability in the unsaturated region and the saturated region. In the unsaturated region, a larger variance of ln Ks, a higher spatial structure anisotropy, and a smaller q lead to a larger variability in pressure head, while in the saturated region, the variability in pressure head increases with the increase of variance of ln Ks, the decrease of spatial structure anisotropy, or the increase of q. These variables have great impacts on the range of fluctuation of the phreatic surface within the hillslope. The influences of these three variables on the variance of pressure head within the saturated region are greater than those within the unsaturated region, and the variance of ln Ks has the greatest impact. These results yield useful insight into the effects of heterogeneity on pressure head and uncertainty associated with predicted flow field. 相似文献
15.
The existence of a disturbed region in front of a coronal mass ejection (CME) has been proved; its variation with increasing
CME velocity has been investigated. It has been shown that a plasma density discontinuity, which can be interpreted as a shock
wave, is formed in front of the disturbed region at CME velocities that are about or above the local Alfvén velocity. Within
the experimental error, the observed shock-front width is estimated to be about the mean free path for proton-proton collisions
at distances R < 15−20 R
⊙ from the center of the Sun; i.e., the energy dissipation mechanism in the front is conceivably collisional at these distances. 相似文献
16.
Shear flow instability is studied in the Earth’s magnetotail by treating plasma as compressible. A dispersion relation is derived from the linearized MHD equations using the oscillating boundary conditions at the inner central plasma sheet/outer central plasma sheet (OCPS) interface and OCPS/plasma-sheet boundary layer (PSBL) interface, whereas the surface-mode boundary condition is used at the PSBL/lobe interface. The growth rates and the real frequencies are obtained numerically for near-Earth (\midX\mid\sim10-15 RE) and far-Earth (\midX\mid\sim100 RE) magnetotail parameters. The periods and wavelengths of excited modes depend sensitively on the value of plasma-sheet half thickness, L, which is taken as L=5 RE for quiet time and L=1 RE for disturbed time. The plasma-sheet region is found to be stable for constant plasma flows unless MA3>1.25, where MA3 is the Alfvén Mach number in PSBL. For near-Earth magnetotail, the excited oscillations have periods of 2–20 min (quiet time) and 0.5-4 min (disturbed time) with typical transverse wavelengths of 2–30 RE and 0.5-6.5 RE, respectively; whereas for distant magnetotail, the analysis predicts the oscillation periods of \sim8-80 min for quiet periods and 2–16 min for disturbed periods. 相似文献
17.
《水文科学杂志》2012,57(1):87-101
ABSTRACTThe coefficient of determination R2 and Pearson correlation coefficient ρ = R are standard metrics in hydrology for the evaluation of the goodness of fit between model simulations and observations, and as measures of the degree of dependence of one variable upon another. We show that the standard product moment estimator of ρ, termed r, while well-behaved for bivariate normal data, is upward biased and highly variable for bivariate non-normal data. We introduce three alternative estimators of ρ which are nearly unbiased and exhibit much less variability than r for non-normal data. We also document remarkable upward bias and tremendous increases in variability associated with r using both synthetic data and daily streamflow simulations from 905 calibrated rainfall–runoff models. We show that estimators of ρ = R accounting for skewness are needed for daily streamflow series because they exhibit high variability and skewness compared to, for example, monthly/annual series, where r should perform well. 相似文献
18.
Dana A. Lapides Christine D. Leclerc Hana Moidu David N. Dralle W. Jesse Hahm 《水文研究》2021,35(3):e14079
Stream networks expand and contract through time, impacting chemical export, aquatic habitat, and water quality. Although recent advances improve prediction of the extent of the wetted channel network (L ) based on discharge at the catchment outlet (Q ), controls on the temporal variability of L remain poorly understood and unquantified. Here we develop a quantitative, conceptual framework to explore how flow regime and stream network hydraulic scaling factors co-determine the relative temporal variability in L (denoted here as the total wetted channel drainage density). Network hydraulic scaling determines how much L changes for a change in Q , while the flow regime describes how Q changes in time. We compiled datasets of co-located dynamic stream extent mapping and discharge to analyze all globally available empirical data using the presented framework. We found that although variability in L is universally damped relative to variability in Q (i.e., streamflow is relatively more variable in time than network extent), the relationship is elastic, meaning that for a given increase in the variability in Q , headwater catchments will experience greater-than-proportional increases in the variability of L . Thus, under anticipated climatic shifts towards more volatile precipitation, relative variability in headwater stream network extents can be expected to increase even more than the relative variability of discharge itself. Comparison between network extents inferred from the L -Q relationship and blue lines on USGS topographic maps shows widespread underestimation of the wetted channel network by the blue line network. 相似文献
19.
It is shown in a joint analysis of ionospheric vertical sounding data at the arctic Heiss Island and antarctic Vostok stations and the geomagnetic PC index, which characterizes the geoefficient component of the interplanetary magnetic field, that, during a disturbed geomagnetic period when PC > 2 in years of solar activity (SA) maxima in the winter season, positive phases of ionospheric disturbances are predominantly observed. In the nighttime hours, an increase in the critical foF2 frequencies by a factor of 2–3 can occur. In a disturbed geomagnetic period at the PC > 1.5 level in the summer season, negative phases of ionospheric disturbances are mainly observed. In years of maximum and moderate SA, the decrease in foF2, as compared to their median values, happens at night (∼30%). In years of low SA, the decrease value is much lower. At a substantial decrease in the PC index level, in the region of the geomagnetic pole at the Vostok station, in some cases, a substantial increase in the electron density level in the F region occurs with a delay of 0.5 h. At the same time, a significant correlation (r = −0.57) is observed between variations in the PC index and foF2. 相似文献
20.
《Journal of Atmospheric and Solar》2008,70(1):169-183
We study the cosmic ray modulation during different solar cycles and polarity states of the heliosphere. We determine (a) time lag between the cosmic ray intensity and the solar variability, (b) area of the cosmic ray intensity versus solar activity modulation loops and (c) dependence of the cosmic ray intensity on the solar variability, during different solar activity cycles and polarity states of the heliosphere. We find differences during odd and even solar cycles. Differences during positive and negative polarity periods are also found. Consequences and implications of the observed differences during (i) odd and even cycles, and (ii) opposite polarity states (A<0 and A>0) are discussed in the light of the modulation models, including drift effects. 相似文献