长江中游夏季降水场预报技术研究

经SVD分析,截取足够多的预报场和因子场时间系数,使其相互关系代表两场的大尺度联系,预报场时间系数与其奇异向量线性组合估计场能反映原场主要特征.借助最优化技术,选择合理的系数,建立预测公式,由因子场时间系数预测预报场时间系数,同时订正预报场时间系数心a₁ a₂ a_N本身的误差和反演过程中分析误差造成的场格点趋势预测的误差.最后将预测的预报场时间系数和对应奇异向量反演为整个场的预报.预报过程重点考虑可预报的大尺度变化,滤去不可预报的小扰动,依据两场主要耦合关系,预测预报场未来的主要变化.     

The specific features of geophysical fields in the fault zones

Instrumental measurements of geophysical fields in several regions of the Earth’s crust with a complex structure and tectonics are analyzed. The observed geophysical fields include the electric field in the boundary layer of the atmosphere and in the subsurface crust, the ground magnetic field, and the fields formed by microseismic vibrations and natural radon emanation. It is shown that the fault zones are characterized by noticeably higher (compared to the middle segments of crustal blocks) variations in the geophysical fields, a stronger response to the faint external impacts in the form of lunisolar tides, and baric variations in the atmosphere, as well as by higher intensity relaxation processes. Energy transformations between the geophysical fields of different origins are observed predominantly in the fault regions.     

On the connection between the atmospheric electric field measured at the surface and the ionospheric electric field in the Central Antarctica

Regular measurements of the atmospheric electric field made at Vostok Station (φ=78.45°S; λ=106.87°E, elevation 3500 m) in Antarctica demonstrate that extremely intense electric fields (1000–5000 V/m) can be observed during snow storms. Usually the measured value of the atmospheric electric field at Vostok is about 100–250 V/m during periods with “fair weather” conditions. Actual relation between near-surface electric fields and ionospheric electric fields remain to be a controversial problem. Some people claimed that these intense electric fields produced by snowstorms or appearing before strong earthquakes can re-distribute electric potential in the ionosphere at the heights up to 300 km. We investigated interrelation between the atmospheric and ionospheric electric fields by both experimental and theoretical methods. Our conclusion is that increased near-surface atmospheric electric fields do not contribute notably to distribution of ionospheric electric potential.     

Comparison of data and derived quantities for the middle atmosphere of the Southern Hemisphere

Before data from satellites can be used with confidence in dynamical studies of the middle atmosphere an assessment of their reliability is necessary. To this end, independently analysed data from different instruments may be compared. In this paper, this is done for the Southern Hemisphere as a prelude to the dynamical studies of the middle atmosphere being fostered by the MASH project of the Middle Atmosphere Program. Data from two infrared radiometers are used: a limb scanner (LIMS) and a nadir sounder (SSU). While there is usually qualitative agreement between basic fields (temperatures, winds), substantial quantitative differences are found, with more pronounced differences in fields of Eliassen-Palm flux divergence and Ertel's potential vorticity.The fidelity of the base-level analysis to which satellite data are tied is important for calculating quantities of relevance to dynamical theory. In the Southern Hemisphere, conventional data are sparse and, through the analysis procedure, this introduces errors into derived fields for the middle atmosphere. The impact of using base-level analyses from different sources is assessed. Large discrepancies are found in fields computed by differentiation.Several techniques are suggested whereby the reliability of fields derived from satellite data may be gauged.     

Fast dynamo action in the Ponomarenko dynamo

Abstract

An analysis of small-scale magnetic fields shows that the Ponomarenko dynamo is a fast dynamo; the maximum growth rate remains of order unity in the limit of large magnetic Reynolds number. Magnetic fields are regenerated by a “stretch-diffuse” mechanism. General smooth axisymmetric velocity fields are also analysed; these give slow dynamo action by the same mechanism.     

Interpretation of MHD-sounding data from the Kola Peninsula by the electromagnetic migration method

The electromagnetic migration method, based on principles analogous to those of seismic migration, is developed.The concept of migrated fields is based on the Stratton-Chu type integrals, written in reverse time for the observed electromagnetic fields. Four types of migrated fields, which form a system of migration transformations of the transient electromagnetic field, are introduced.Study of the properties of the migrated fields by means of theoretical and model examples makes it possible to determine the optimal parameters of the migration procedure in which the anomalous field sources are localized by means of migration transformation.Information about the experiment using the MHD-generator (experiment ‘Chibini’) carried out on the Kola Peninsula to study the geoelectrical structure of the Earth's crust and upper mantle is included. The electromagnetic migration method for the interpretation of MHD-sounding data recorded on the Kola Peninsula, along a profile crossing the mineral-rich region of the Imandra-Varzuga structure, permits us to determine the location of a conducting zone at the depth of 10 km in the Earth's crust.     

On the use of Empirical Orthogonal Function (EOF) analysis in the simulation of random fields

In several fields of Geophysics, such as Hydrology, Meteorology or Oceanography, it is often useful to generate random fields, displaying the same variabilitity as the observed variables. Usually, these synthetic data are used as forcing fields into numerical models, to test the sensitivity of their outputs to the variability of the inputs. Examples can be found in subsurface or surface Hydrology and in Meteorology with General Circulation Models (GCM). Different techniques have already been proposed, often based on the spectral representation of the random process, with, usually, assumptions of stationarity. This paper suggests that Empirical Orthogonal Function (EOF) analysis, which leads to the decomposition of the covariance kernel on the set of its eigen-functions, is a possible answer to this problem. The convergence and accuracy of the method are shown to depend mainly on the number of EOFs retained in the expansion of the covariance kemel. This result is confirmed by a comparison with the turning band method and a matrix technique. Furthermore, a synthetic example of non-homogencous fields shows the interest of EOF analysis in the direct simulation of such fields.     

Investigation of the stochastic properties of anomalous geophysical potential fields defined at points of the surface of an ellipsoid

Summary Using a general model, constructed for random fields defined on a Lyapunov surface, the stochastic properties of fields defined at points of the surface of a tri-axial rotational ellipsoid are investigated within the correlation theory of these fields.     

Analyses of the warm season rainfall climatology of the northeastern US using regional climate model simulations and radar rainfall fields

We examine the warm season (April-September) rainfall climatology of the northeastern US through analyses of high-resolution radar rainfall fields from the Hydro-NEXRAD system and regional climate model simulations using the weather research and forecasting (WRF) model. Analyses center on the 5-year period from 2003 to 2007 and the study area includes the New York-New Jersey metropolitan region covered by radar rainfall fields from the Fort Dix, NJ WSR-88D. The objective of this study is to develop and test tools for examining rainfall climatology, with a special focus on heavy rainfall. An additional emphasis is on rainfall climatology in regions of complex terrain, like the northeastern US, which is characterized by land-water boundaries, large heterogeneity in land use and cover, and mountainous terrain in the western portion of the region. We develop a 5-year record of warm season radar rainfall fields for the study region using the Hydro-NEXRAD system. We perform regional downscaling simulations for the 5-year study period using the WRF model. Radar rainfall fields are used to characterize the interannual, seasonal and diurnal variation of rainfall over the study region and to examine spatial heterogeneity of rainfall. Regional climate model simulations are characterized by a wet bias in the rainfall fields, with the largest bias in the high-elevation regions of the model domain. We show that model simulations capture broad features of the interannual, seasonal, and diurnal variation of rainfall. Model simulations do not capture spatial gradients in radar rainfall fields around the New York metropolitan region and land-water boundaries to the east. The model climatology of convective available potential energy (CAPE) is used to interpret the regional distribution of warm season rainfall and the seasonal and diurnal variability of rainfall. We use hydrologic and meteorological observations from July 2007 to examine the interactions of land surface processes and rainfall from a regional perspective.     

An efficient multivariate random field generator using the fast Fourier transform

It is often convenient to use synthetically generated random fields to study the hydrologic effects of spatial heterogeneity. Although there are many ways to produce such fields, spectral techniques are particularly attractive because they are fast and conceptually straightforward. This paper describes a spectral algorithm for generating sets of random fields which are correlated with one another. The algorithm is based on a discrete version of the Fourier-Stieltjes representation for multidimensional random fields. The Fourier increment used in this representation depends on a random phase angle process and a complex-valued spectral factor matrix which can be readily derived from a specified set of cross-spectral densities (or cross-covariances). The inverse Fourier transform of the Fourier increment is a complex random field with real and imaginary parts which each have the desired coveriance structure. Our complex-valued spectral formulation provides an especially convenient way to generate a set of random fields which all depend on a single underlying (independent) field, provided that the fields in question can be related by space-invariant linear transformations. We illustrate this by generating multi-dimensional mass conservative groundwater velocity fields which can be used to simulate solute transport through heterogeneous anisotropic porous media.     

Influence of plate tectonics on the locations of geothermal fields

A number of geothermal fields explored so far in the circum-Pacific area occur along spreading ridges and subduction zones in areas of young tectonism and volcanism. A preliminary analysis, however, suggests that these geothermal fields are not situated along entire segments of plate boundaries but only at certain locations. In convergent zones these locations are (i) near the ends of plate boundary segments or (ii) in transverse zones that divide plates into several blocks 100–1000 km long. The locations of geothermal fields therefore appear to be influenced by plate geometry and correspond to lateral breaks in the continuity of the underthrusting plate.     

Two types of lava fields and the mechanism of their generation

Two types of lava fields, elongate and compact, are generated by two types of discrete lava flows that are designated as wide and narrow in this paper. The width of a wide flow considerably exceeds its thickness, the converse being true for a narrow one. Wide flows produce relatively narrow elongate lava fields, while narrow ones give rise to wider and compact lava fields of relatively smaller area and greater thickness, which is related to peculiarities in their dynamics causing branching and greater heat losses in such flows. Exact analytical formulas have been derived to relate the rate of lava in a flow to the flow geometry and lava rheology for idealized models of both flow types; a combination of these yields the approximate relationships for actual flows. We have found conditions for the generation of narrow flows showing strongly nonlinear behavior, which produces the peculiar features of the lava fields they create. Examples of lava fields generated by narrow flows from lateral vents on Klyuchevskoi Volcano are given. The conditions for their generation are more closely fulfilled in the upper part of the volcano’s cone. It is hypothesized that such an arrangement of lava fields may facilitate slope instabilities and enhance the likelihood of major landslides.     

Geophysical evidence on the structure of the Taupo Volcanic Zone and its hydrothermal circulation

The Taupo Volcanic Zone (TVZ) of New Zealand is characterised by extensive volcanism and by high rates of magma production. Associated with this volcanism are numerous high-temperature (> 250 °C) geothermal systems through which the natural heat output of 4200 ± 500 MW is channelled. Outside the geothermal fields the heat flow is negligible. The average heat flux from the central 6000 km² of the TVZ, which contains most of the geothermal fields, is 700 mW/m³. This heat flux appears to be more concentrated along the eastern margin of the TVZ.Schlumberger resistivity measurements (AB/2 of 500 m and 1000 m) have identified 17 distinct geothermal fields with natural heat outputs greater than 20 MW. An additional six, low-heat-output geothermal fields also occur, and may represent formerly more active systems now in decline. Two extinct fields have also been identified. The average spacing between fields is 10–15 km. The distribution of geothermal fields does not appear to be directly associated with individual volcanic features except for the geothermal system that occurs within Lake Taupo and which occupies the vent of the 1800 yr.B.P. Taupo eruption. The positions of the geothermal fields do not appear to have varied for at least the last 200,000 years. These data are consistent with a model of large-scale convection occurring throughout the TVZ, in which the geothermal fields represent the upper portion of the rising, high-temperature, convective plumes. The majority of the recharge to the convection system is provided by the downward movement of cold meteoric water between the fields which suppresses the heat flow in these regions.Gravity measurements indicate that to a depth of about 2.5 km the upper layers of the TVZ consist of low-density pyroclastic infill. A seismic refraction interface with velocity change from 3.2 km/s to 5.5 km/s occurs at a similar depth. The cross-sectional area of the convection plumes (identified electrically) appears to increase at depths of 1–2 km, consistent with a decrease in permeability at the depth at which the velocity and density increase.The seismicity is dominated by swarm activity which accounts for about half of all earthquakes and is highly variable in both space and time. The small number of seismic events (and swarms) that have well determined depths show a cut off of seismicity at depths of 7–9 km. The depth of the transition from brittle to ductile behaviour of the rocks is identified with the transition from a regime where heat is transported by (hydrothermal) convection and pore pressures are near-hydrostatic to a regime where heat transport is dominantly conductive and pore pressures are lithostatic. Within the convective region, temperatures are moderated by the circulation of water so that the depth of the transition from convective to conductive heat transfer can be linked to the bottom of the seismogenic zone. Rocks must become ductile within about 1 km of the bottom of the overlying convective zone.Seismic refraction studies suggest that the crust beneath the TVZ is highly thinned with a seismic velocity of about 7.5 km/ s, typical of the upper mantle, occurring at depth of 15 km. Seismological studies indicate the upper mantle is highly attenuating beneath the TVZ. Conductive heat transfer between the bottom of the convective system, at about 8 km, and the base of the material with crustal velocities, at 15 km, is not able to provide all the heat that is discharged at the surface. Repeated intrusion from the mantle may provide the additional heat transport required.     

淀山湖风浪场的数值模拟

对淀山湖的风场和风浪场进行了观测,根据所观测的风场利用SWAN模型计算了湖区的风浪场.通过将计算的波高和观测值进行比较,说明计算结果的变化趋势和观测结果的变化趋势相吻合;观测结果的波动幅度较大,而计算结果比较平滑.总体说来,基于SWAN模型所计算的波高可信、可靠.在此基础上,利用SWAN模型较为系统地计算了不同水位和不...     

Observing,Modeling, and Interpreting Magnetic Fields of the Solid Earth

Many Earth system processes generate magnetic fields, either primary magnetic fields or in response to other magnetic fields. The largest of these magnetic fields is due to the dynamo in the Earth’s core, and can be approximated by a geocentric axial dipole that has decayed by nearly 10% during the last 150 years. This is an order of magnitude faster than its natural decay time, a reflection of the growth of patches of reverse flux at the core–mantle boundary. The velocity of the North magnetic pole reached some 40 km/yr in 2001. This velocity is the highest recorded so far in the last two centuries. The second largest magnetic field in the solid Earth is caused by induced and remanent magnetization within the crust. Controlled in part by the thermo-mechanical properties of the crust, these fields contain signatures of tectonic processes currently active, and those active in the distant past. Recent work has included an estimate of the surface heat flux under the Antarctic ice cap. In order to understand the recent changes in the Earth’s magnetic field, new high-quality measurements are needed to continue those being made by Ørsted (launched in 1999), CHAMP and the Ørsted-2 experiment onboard SAC-C (both launched in 2000). The present paper is motivated by the advent of space surveys of the geomagnetic field, and illustrates how our way of observing, modeling, and interpreting the Earth’s magnetic field has changed in recent years due to the new magnetic satellite measurements.     

On the occurrence and characteristics of intense low-altitude electric fields observed by Freja

High-resolution measurements by the double probe electric field instrument on the Freja satellite are presented. The observations show that extremely intense (up to 1 V m⁻¹) and fine-structured (<1 km) electric fields exist at auroral latitudes within the altitude regime explored by Freja (up to 1700 km). The intense field events typically occur within the early morning sector of the auroral oval (01-07 MLT) during times of geomagnetic activity. In contrast to the observations within the auroral acceleration region characterized by intense converging electric fields associated with electron precipitation, upward ion beams and upward field-aligned currents, the intense electric fields observed by Freja are often found to be diverging and located within regions of downward field-aligned currents outside the electron aurora. Moreover, the intense fields are observed in conjunction with precipitating and transversely energized ions of energies 0.5-1 keV and may play an important role in the ion heating. The observations suggest that the intense electric field events are associated with small-scale low-conductivity ionospheric regions void of auroral emissions such as east-west aligned dark filaments or vortex streets of black auroral curls located between or adjacent to auroral arcs within the morningside diffuse auroral region. We suggest that these intense fields also exist at ionospheric altitudes although no such observations have yet been made. This is possible since the height-integrated conductivity associated with the dark filaments may be as low as 0.1 S or less. In addition, Freja electric field data collected outside the auroral region are discussed with particular emphasis on subauroral electric fields which are observed within the 19–01 MLT sector between the equatorward edge of the auroral oval and the inner edge of the ring current.     

Modeling of deep magnetovariation soundings on the rotating earth

Induced magnetic fields in the Earth arise due to two phenomena: induction generated by the time-variable exciting field and the motional induction caused by movement of the conductive planet in the outer magnetic fields. The comparison of both approaches on the spherical Earth has been analyzed in the present work for two sources in the ionosphere and magnetosphere. For this aim, both sources with their natural sizes and positions have been modeled analytically to obtain the fields on the layered sphere at the middle latitudes. The conditions when the steady ring current field is not influenced by the Earth’s rotation have been established theoretically. The synthetic diurnal magnetograms were used for the deep sounding by the magnetovariation spatial gradient method and the result was compared with the one obtained on the nonrotating sphere. Sounding results using both approaches were found different above the 2D inhomogeneous mantle. The precessions of the magnetospheric belt current pole for daily sampling frequency were presented using several geomagnetic observatory data in the northern hemisphere.     

Generation of Magnetic Fields During the Protogalactic Collapse

Large-scale galactic magnetic fields are probably caused by some magnetic field amplification mechanism starting from a seed field. This seed field is still enigmatic. In this contribution it is shown that macroscopic sheared relative velocities of the charged and neutral components of a protogalactic partially ionized plasma generate magnetic fields during the protogalactic collapse. Plasma-neutral gas fluid simulations are performed in order to illustrate this magnetic field-self generation mechanism.     

Cauchy integral analogues for the separation and continuation of electromagnetic fields within conducting matter

The main results in the theory of the interpretation of geopotential fields are generalized to the case of arbitrary variable electromagnetic fields by means of elaborating electrodynamic analogues for the integral of the Cauchy type.The generalized Kertz method for separating a variable electromagnetic field into parts related to the sources located in different regions of space is elaborated on the basis of this technique. The generalized Kertz method allows the selection of external and internal, normal and anomalous parts of the geomagnetic field, as well as the separation of geomagnetic anomalies into the surface and deep components caused by conductivity inhomogeneities in the Earth's crust and upper mantle.The theory of analytical continuation of variable electromagnetic fields in a conducting medium is also developed in the present work using the technique of analogues for the integral of the Cauchy type. It is shown that analytical continuation of a field downwards permits the determination of the location and form of deep geoelectric inhomogeneities according to the configuration of the isolines of flux functions for magnetic and electric fields.     

Effects of geomagnetic activity on the mesospheric electric fields

The results of three series of rocket measurements of mesospheric electric fields carried out under different geomagnetic conditions at polar and high middle latitudes are analysed. The measurements show a clear dependence of the vertical electric fields on geomagnetic activity at polar and high middle latitudes. The vertical electric fields in the lower mesosphere increase with the increase of geomagnetic indexes K_p and K_p. The simultaneous increase of the vertical electric field strength and ion conductivity was observed in the mesosphere during geomagnetic disturbances. This striking phenomenon was displayed most clearly during the solar proton events of October, 1989 accompanied by very strong geomagnetic storm (K_p = 8+). A possible mechanism of generation of the vertical electric fields in the mesosphere caused by gravitational sedimentation of charged aerosol particles is discussed. Simultaneous existence in the mesosphere of both the negative and positive multiply charged aerosol particles of different sizes is assumed for explanation of the observed V/m vertical electric fields and their behaviour under geomagnetically disturbed conditions.Paper Presented at the Second IAGA/ICMA (IAMAS) Workshop on Solar Activity Forcing of the Middle Atmosphere, Prague, August 1997