共查询到20条相似文献,搜索用时 15 毫秒
1.
K. G. Ivanov 《Geomagnetism and Aeronomy》2010,50(3):285-297
The dynamics of the large-scale open field and solar activity at the second stage of the MHD process, including the origination
and disappearance of the four-sector structure during the decline phase of cycle 23 (the stage when the blocking field is
displaced from the main zone of active longitudes), has been considered. Extremely fast changes in the scales of one of new
sectors (from an extremely small sector (“singularity”) to a usual sector that originated after the uniform expansion (“explosion”)
of singularity with a “kick” into the zone of active longitudes, westward motion of the MHD disturbance front in the direction
of solar rotation, and formation of an active quasi-rigidly corotating sector boundary responsible for the heliospheric storm
of November 2004) have been detected in the field dynamics. It has been indicated that a very powerful group of sunspots AR
10656 (which disappeared after the explosion) with an area of up to 1540 ppmh (part per million hemisphere), a considerable
deficit of the external energy release, and zero geoeffectiveness in spite of the closeness to the Earth helioprojection existed
within singularity. It has been assumed that the energy escaped from this group with effort owing to the interaction between
coronal ejections and narrow sector walls (singularity), and a considerable part of the energy was released in the outer layers
of the convective zone, as a result of which singularity exploded and this explosion was accompanied by the above effects
in the large-scale field and solar activity. 相似文献
2.
Boundary layer characteristics and turbulent exchange mechanisms in highly complex terrain 总被引:2,自引:0,他引:2
Mathias W. Rotach Marco Andretta Pierluigi Calanca Andreas P. Weigel Alexandra Weiss 《Acta Geophysica》2008,56(1):194-219
The Mesoscale Alpine Programme’s Riviera project investigated the turbulence structure and related exchange processes in an
Alpine valley by combining a detailed experimental campaign with high-resolution numerical modelling. The present contribution
reviews published material on the Riviera Valley’s boundary layer structure and discusses new material on the near-surface
turbulence structure. The general conclusion of the project is that despite the large spatial variability of turbulence characteristics
and the crucial influence of topography at all scales, the physical processes can accurately be understood and modelled. Nevertheless,
many of the “text book characteristics” like the interaction between the valley and slope wind systems or the erosion of the
nocturnal valley inversion need reconsideration, at least for small non-ideal valleys like the Riviera Valley. The project
has identified new areas of research such as post-processing methods for turbulence variables in complex terrain and new approaches
for the surface energy balance when advection is non-negligible. The exchange of moisture and heat between the valley atmosphere
and the free troposphere is dominated by local “secondary” circulations due to the curvature of the valley axis. Because many
curved valleys exist, and operational models still have rather poor resolution, parameterization of these processes may be
required. 相似文献
3.
Influence of the surface roughness, geostrophic wind speed and initial stable stratification on surface layer scales, namely the friction velocity, temperature scale and the Monin-Obukhov length, and on non-dimensional profiles has been studied in quasi-stationary PIAPBLM (Prague Institute of Atmospheric Physics Boundary Layer Model) runs. Modifications of the stability functions, of the non-local mixing length concept, and of surface layer parametrization have improved the model results. With the ground temperature kept constant in time, the boundary layer is subjected to a turbulent cooling induced by surface roughness and to a counteracting turbulent heat transfer directed downwards. If the wind speed is lower, a rather mixed layer develops capped by a more stable layer. The estimated Monin-Obukhov length then slightly increases and the non-dimensional gradients overpredict the empirical values even more. 相似文献
4.
Estimation of orographically induced wave drag in the stable boundary layer during the CASES-99 experimental campaign 总被引:1,自引:0,他引:1
This paper addresses the quantification of gravity wave drag due to small hills in the stable boundary layer. A single column
atmospheric model is used to forecast wind and temperature profiles in the boundary layer. Next, these profiles are used to
calculate vertical profiles of gravity wave drag. Climatology of wave drag magnitude and “wave drag events” is presented for
the CASES-99 experimental campaign. It is found that gravity wave drag events occur for several relatively calm nights, and
that the wave drag is then of equivalent magnitude as the turbulent drag. We also illustrate that wave drag events modify
the wind speed sufficiently to substantially change the surface sensible heat flux. 相似文献
5.
杨智娴 《地震学报(英文版)》1999,12(6):659-666
IntroductionTaiwanlocatedinthecollisionboundalbetweentheEurasianandthePhilippineSeaplatesisoneofhighseismicityregionsintheworld.HundredsofearthquakeswithM25occurredperyearandmorethan40withM27since1900.Amongtheseevents,shalloweventswithdepthofseveraltensofkilometersandintermediate-deepeventswithdepthof100-200kinexistwhichrepresentsacharacterofthesubductionzone.ThemagnitudesofTaiwaneventslistedinthecatalogofChineseearthquakesaretakenfromsomehistoricaldocumentsandGutenbergandRichter'sworks(19… 相似文献
6.
D. N. Osokina 《Izvestiya Physics of the Solid Earth》2010,46(5):419-432
In the work 2D and 3D fields of stresses of several scale levels close to the off of the main fault (vertical strike-slip
fault) in conditions of compression are mathematically calculated and investigated. The solution is found for the elastic
task for a 2D “horizontal” field; a 3D field of stresses is obtained by the imposition of a “vertical” unaxis compression.
It is shown that the surroundings of the fault are subdivided into three (not two, as is usually considered) regions of types
of predictable secondary fractures: “extension,” “strike-slip fault,” and “compression.” In regions close to the off of the
main fault, three different microregions occur. The type of destruction in these microregions depends on the parameters of
the outer load. Natural and model data of second order fractures that are compared with the calculated data are examined and
generalized. The performed investigation is important for the determination of the genesis of secondary fractures, located
close to the main fault. The calculated parageneses of secondary fractures may be used for the estimation of the stress tensor
type of the regional field. 相似文献
7.
Introduction In the years when the reliable data could not be obtained and in the analysis of strain property and magnitude in history, the intensity, property and activity pattern of strain field were mainly inferred on the bases of geometric characters of surface traces and behaviors (especially the faults) as well as the characteristics of petrology (XIE, et al, 1993; Molnar, Tapponnier, 1975, 1977; Tapponnier, Molnar, 1977; FU, et al, 2000). However, they are the averaged results accumu… 相似文献
8.
Pioneer organisms after F-F mass extinction in Dushan region, Guizhou Province, and their significance in establishing new ecosystem 总被引:1,自引:0,他引:1
After bio-mass extinction, the ecosystems in most areas were damaged seriously and may become an “ecologically barren area” lacking or even without ecosystems. To know what the pioneer organisms would be and their development, and to trace the es- tablishment process of the ecosystems are of great importance for the study of the biological evolution and recovery in aftermath. As one of the “big five” mass extinctions in the geological history, the Late Devonian Frasnian-Famennian (F-F) e… 相似文献
9.
Using ground temperature data from meteorological stations as well as earthquake, ground tilt and precipitation data, the
spatial-temporal distribution of “Underground Hot Vortex” (UHV) in China was analyzed in detail. The results show that concerning
an “Underground Hot Vortex” cell, its life-span is 3–8 seasons, 1.5 years on average; the mean horizontal scale is 600 km
and its characteristic velocity is about 400 km/a; UHV is likely to appear in some areas where the crustal movement is intense
and the absolute value of vertical deformation rate is relatively high; its activity could hardly be detected in the area
where the crust is stable and the vertical deformation is weak; most of “Underground Hot Vortex Groups” originate from the
edge of Indian Plate, then migrate eastwards with a leaping-frog style. 5–10 years are needed for their arrival in the eastern
border of China. Their horizontal migrating velocity is 200–500 km/a which is nearly equal to the characteristic velocity
of a single UHV.
Project sponsored by the National Climbing Project and Key Project of the Chinese Academy of Sciences. 相似文献
10.
R. Signer F. v. Beust Ulrich A. Corti 《Aquatic Sciences - Research Across Boundaries》1951,13(1):31-35
Summary The investigation with an electron-microscope of the scales of the fresh water fish,Leuciscus rutilus L., showed that their ventral “smooth” surface scems to be formed like a corrugated plate with a distance between the ridges
of 1–2 μ. The dorsal “rough” side of the scales shows a very fine roughness. It is interrupted by pointed combs of the same
structure in a regular distance of 16–27 μ. The thickness of these combs is of about 1 μ at their base, their height of about
5–10 μ. It seems probable that the surface of scales is partially covered with laminas of hyalodentine or guanine.
13. Mitteilung siehe diese Zeitschrift,13, 29–30 (1951). 相似文献
13. Mitteilung siehe diese Zeitschrift,13, 29–30 (1951). 相似文献
11.
The discrete scale spectrum of the convective flows observed on the Sun has not yet received a convincing explanation. Here, an attempt is made to find conditions for the coexistence of convective flows on various scales in a horizontal fluid layer heated from below, where the thermal diffusivity varies with temperature in such a way that the static temperature difference across a thin sublayer near the upper surface of the layer is many times larger than the temperature variation across the remainder of the layer. The equations of two-dimensional thermal convection are solved numerically in an extended Boussinesq approximation, which admits thermal-diffusivity variations. The no-slip conditions are assumed at the lower boundary of the layer; either no-slip or free-slip conditions, at the upper boundary. In the former case, stable large-scale rolls develop, which experience small deformations under the action of small structures concentrated near the horizontal boundaries. In the latter case, the flow structure is highly variable, different flow scales dominate at different heights, the number of large rolls is not constant, and a sort of intermittency occurs: the enhancement of the small-scale flow component is frequently accompanied by the weakening of the large-scale one, and vice versa. The scale-splitting effects revealed here should manifest themselves in one way or another in the structure of solar convection. 相似文献
12.
Gerhard Neumann 《Ocean Dynamics》1951,4(1-2):6-13
Zusammenfassung Aus Windprofilmessungen in feststehenden H?hen über den Wellenk?mmen lassen sich keine zuverl?ssigen Schlüsse über die effektive
Schubkraft des Windes an der Meeresoberfl?che ziehen. Der Grund liegt im wesentlichen in der verschiedenartigen vertikalen
Windgeschwindigkeitsverteilung über Wellenbergen und Wellent?lern und in der Tatsache, da? die Windprofilmessungen im wesentlichen
nur das Windprofil über den Bergen widerspiegeln. Der Versuch, die Windprofilmessungen zu „reduzieren“, ist mit zu gro?en
Fehlern behaftet, zeigt aber qualitativ eine systematische Erh?hung der aus Windmessungen berechneten Reibungsfaktoren an.
Damit kann der Anschlu? an die aus Windstaubeobachtungen ermittelten Reibungsfaktoren gewonnen werden, so da? der vermeintliche
„Sprung“ von einer „glatten“ zu einer „rauhen“ Grenzfl?che verschwindet, und eine „kritische Windgeschwindigkeit“, die diesen
Sprung angeben soll, gar nicht existiert.
On the problem of the “critical wind velocity” at the air — sea boundary surface
Summary From the measurements of wind profiles at fixed heights above the wave crests no reliable conclusions can be drawn with regard to the wind's effective shearing force at the sea surface. This is essentially due to the diversified vertical distribution of the wind speed above the waves' crests and troughs as well as to the fact that when measuring wind profiles above the waves it is mainly the profiles above the wave crests that are obtained. Attempts to “reduce” wind profiles have proved to be subject to considerable errors; however, they show qualitatively a systematic increase of the frictional factors as computed from wind measurements. This links up with the frictional factors ascertained from observations of the wind effect so that the supposed “leap” from a “smooth” to a “rough” boundary surface and the “critical wind speed” corresponding to this leap do not exist at all.相似文献
13.
A new modified magnitude scale M
S
(20R) is elaborated. It permits us to extend the teleseismic magnitude scale M
S
(20) to the regional epicenter distances. The data set used in this study contains digital records at 12 seismic stations
of 392 earthquakes that occured in the northwest Pacific Ocean in the period of 1993–2008. The new scale is based on amplitudes
of surface waves of a narrow range of the periods (16–25 s) close to the period of 20 s, for distances of 80–3000 km. The
digital Butterworth filter is used for processing. On the basis of the found regional features concerning distance dependence
for seismic wave attenuation, all the stations of the region have been subdivided into two groups, namely, “continental” and
“island-arc.” For each group of stations, its own calibration function is proposed. Individual station corrections are used
to compensate for the local features. 相似文献
14.
Jitka Hájková 《Studia Geophysica et Geodaetica》2011,55(3):515-528
A mathematical model used for determination of a local geoid model by combining airborne gravity disturbances and the Earth
Gravitational Model 2008 (EGM08) is shortly reviewed. The precision of the estimated local geoid model of Taiwan is tested
by its comparison with the “real” geoid at Global Satellite Navigation Systems (GNSS)/levelling points. The same comparison
at GNSS/levelling points is done for the geoid evaluated only by using EGM08. Conclusions concerning a rate of improvement
of the “global” geoid from EGM08 using the “local” geoid from airborne gravity data are presented. 相似文献
15.
Properties of wave velocity for two types of granitoids at high pressure and temperature and their geological meaning 总被引:1,自引:0,他引:1
Shufeng Yang Hanlin Chen Jishuang Jiang Guoqiang Zhu Hongshen Xie Wei Hou Yueming Zhang Huigang Xu 《中国科学D辑(英文版)》1997,40(5):470-476
The wave velocity for two types of granitoids was measured using the analytic method of full-wave vibration at high pressure
and high temperature. The laws of velocity changes for them differ with the pressure boost and temperature rise, and the velocity
change of S-type is more violent than that of I-type. The “softening point” of compressional wave velocity (V μ) is also revealed
during the measurement for two types of granitoids imitating the pressure and temperature at a certain depth. But the depth
of “softening”, Vp after “softening” and the percentage of Vp’s drop around the “sofrening point” for two types of granitoids are obviously different. The depth of “softening” is 15 km
approximately and Vp after “softening” is 5.62 km/s for S-type granitoid. But for I-type granitoid the depth of “softening” is 26 km approximately
and Vp after “softening” is 6. 08 km/s. Through careful analysis of rock slices after the experiment, it was found that the “softening”
of elastic-wave velocity is caused by the partial melting of granite. Combined with the results of geophysical prospecting,
these results suggest that the low-velocity layers developing in the interior of Earth crust are related to thc partial melting
of different types of granitoids. The formation of the low-velocity layer in the upper-middle Earth crust is closely related
to the development of S-type granitoid, but that in the lower Earth crust is closely related to the development of I-type
granitoid. 相似文献
16.
Aditya R. Kartadikaria Yasumasa Miyazawa Kazuo Nadaoka Atsushi Watanabe 《Ocean Dynamics》2012,62(1):31-44
An eddy-resolving Indo-Pacific ocean circulation model was applied to highlight the behavior of eddies throughout the Indonesian
seas. The complexity of the topography and coastline at the entrance of the Makassar Strait induce an eddy-type throughflow,
instead of a straightforward flow. A sill and a narrow passage in the Makassar strait creates a barrier and impedes the continuation
of eddies from the Pacific ocean, but the existence of a steep deep basin (>500 m depth) between the Java and Flores seas
indicates a possible area for eddies. Based on our numerical results, we described the presence of a unique eddy structure
north of Lombok Island, which we designated the “Lombok Eddy” and verified it by performing a drifter release field experiment
and reviewing monthly mean climatology data from the World Ocean Atlas 2001 and XBT PX2 track data. NCEP/NCAR reanalysis,
satellite observation data, and mixed layer depth analysis were also used to confirm these processes. By analyzing numerical
simulation results and available temperature datasets, two additional eddies were found. All eddies form primarily due to
eastward local winds correlated with seasonal monsoon winds during the austral summer. These eddies vary synchronously at
an interannual time scale. Together, they are referred to as the Lombok Eddy Train (LET), which affects the surface layer
down to a depth of 60 m, and the intensity of the eddy system is strongly affected by mixed layer depth variability from December
to February. 相似文献
17.
Luan-Sheng Su 《地震学报(英文版)》1995,8(1):51-56
Based on the observations of many years, it has been found that “small earthquake modulation windows” exist in the situation
of some special geological structures, which respond sensitively to the variations of regional stress fields and the activities
of earthquake swarms greater than moderate strong magnitude, and can supply some precursory information. More than two “small
earthquake modulation windows” can also provide a general orientation of the first main earthquake of a earthquake cluster.
Compared with “seismic window” based on frequency it is no doubt that the “modulation-window” has an unique characteristic
of applicational significance to medium-term earthquake prediction with a time scale of two or three years.
The English version is improved by Prof. Xin-Ling QIN, Institute of Geophysics, SSB, China. 相似文献
18.
本文利用高分辨率中尺度WRF模式,通过改变边界层参数化方案进行多组试验,评估该模式对美国北部森林地区边界层结构的模拟能力,同时比较了五种不同边界层参数化方案模拟得出的边界层热力和动力结构.结果表明:除个别方案外,配合不同边界层方案的WRF模式都能成功模拟出白天对流边界层强湍流混合特征和夜间稳定边界层内强逆温、逆湿和低空急流等热力和动力结构.非局地YSU、ACM2方案在白天表现出强的湍流混合和卷夹,相比于局地MYJ、UW方案,模拟的对流边界层温度更高、湿度更低、混合层高度更高、感热通量更大,更接近实际观测,这表明在不稳定层结下考虑非局地大涡输送更为合理,但局地方案在风速和风向的预报上存在一定优势.TEMF方案得到的白天局地湍流混合强度为所有方案中最弱,混合层难以发展,无法体现对流边界层内气象要素垂直分布均匀的特点.对于夜间稳定边界层的模拟,不同参数化方案之间的差异较小,但是YSU方案在一定程度上高估了机械湍流,导致局地湍流混合偏强,从而影响了其对稳定边界层的模拟能力. 相似文献
19.
Effects of shear in the convective boundary layer: analysis of the turbulent kinetic energy budget 总被引:1,自引:0,他引:1
Effects of convective and mechanical turbulence at the entrainment zone are studied through the use of systematic Large-Eddy
Simulation (LES) experiments. Five LES experiments with different shear characteristics in the quasi-steady barotropic boundary
layer were conducted by increasing the value of the constant geostrophic wind by 5 m s-1 until the geostrophic wind was equal to 20 m s-1. The main result of this sensitivity analysis is that the convective boundary layer deepens with increasing wind speed due
to the enhancement of the entrainment heat flux by the presence of shear.
Regarding the evolution of the turbulence kinetic energy (TKE) budget for the studied cases, the following conclusions are
drawn: (i) dissipation increases with shear, (ii) the transport and pressure terms decrease with increasing shear and can
become a destruction term at the entrainment zone, and (iii) the time tendency of TKE remains small in all analyzed cases.
Convective and local scaling arguments are applied to parameterize the TKE budget terms. Depending on the physical properties
of each TKE budget contribution, two types of scaling parameters have been identified. For the processes influenced by mixed-layer
properties, boundary layer depth and convective velocity have been used as scaling variables. On the contrary, if the physical
processes are restricted to the entrainment zone, the inversion layer depth, the modulus of the horizontal velocity jump and
the momentum fluxes at the inversion appear to be the natural choices for scaling these processes. A good fit of the TKE budget
terms is obtained with the scaling, especially for shear contribution. 相似文献
20.
E. S. Sarachik 《Pure and Applied Geophysics》1985,123(2):261-271
It is suggested that the gross mean vertical structure of the undisturbed tropical atmosphere may be understood in terms of convective boundary layers driven in different ways and on different time scales by the evaporation of water from the sea surface. The mixed layer on a short time scale is driven partly by the buoyancy produced by the light weight of the water vapor; the trade cumulus layer on an intermediate time scale by the buoyancy (but not heating) produced by the condensation of the water vapor in shallow trade cumulus clouds; and the troposphere itself on a long time scale by the buoyancyand heating produced by the condensation of the water vapor in the deep cumulonimbus clouds.May 1985This paper was issued as a Harvard University report in 1974. For this version only Section 5 has been rewritten. There has been sufficient interest in this work over the years to warrant making it more widely available through the open literature.Contribution No. 783 from NOAA/Pacific Marine Environmental Laboratory 相似文献