基于双金属球三维电场探空仪的一次雷暴云内电荷结构观测研究

本文自主研制性能稳定的双金属球三维电场探空仪,并结合气象探空仪等构建了雷暴电场-气象综合探空系统,实现了雷暴云内三维电场及温度、湿度的同步测量.2019年夏季对华北平原地区雷暴开展穿云观测,并结合地面大气电场、雷达回波、变分多普勒雷达分析系统(VDRAS)反演的动力场等资料进行综合研究,首次给出该地区雷暴云内的电场和电荷结构分布特征.对2019年8月7日发生的一次中尺度对流系统电场探空发现,在雷暴减弱阶段,其弱回波区内存在5个极性交替的电荷区：4.4~5.6 km之间的上部正电荷区(0℃附近)、3.6~4.4 km之间的中部负电荷区和1.0~3.6 km之间的下部正电荷区,此外在1 km下方有一个负极性电荷区,雷暴云顶附近5.7~6.9 km之间为一个弱负极性屏蔽电荷区.其中,中部负电荷区和下部正电荷区由多个不同强度、不同厚度的电荷层构成.此外,电场探空系统在中部负电荷区高度范围内经历的上升—下沉—再次上升的往返探空数据表明,雷暴云内动力环境复杂,电荷结构分布相似但又有所差异,反映了实际雷暴云内电荷分布的时空不均匀性和复杂性.

     

The role of moisture fluctuations in unsaturated transport

Within the framework of stochastic theory and the spectral perturbation techniques, three-dimensional dispersion in partially saturated soils with a finite correlation scale of log-hydraulic conductivity is analyzed. The effects of spatial variability of the moisture distribution parameter on the asymptotic spreading behavior of a unsaturated solute plume are assessed. This is accomplished by comparing two asymptotic macrodispersivities and two variance of solute concentration, obtained for a constant moisture content and spatially varied moisture, respectively.     

Observations on the flow structures and transport in a simulated warm-core ring in the Gulf of Mexico

This study presents several new observations from the study of a numerically simulated warm-core ring (WCR) in the Gulf of Mexico based on the ECCO2 global ocean simulation. Using Lagrangian coherent structures (LCS) techniques to investigate this flow reveals a pattern of transversely intersecting LCS in the mixed layer of the WCR which experiences consistent stretching behavior over a large region of space and time. A detailed analysis of this flow region leads to an analytical model of the velocity field which captures the essential elements that generate the transversely intersecting LCS. The model parameters are determined from the simulated WCR and the resulting LCS show excellent agreement with those observed in the WCR. The three-dimensional transport behavior that creates these structures relies on the small radial outflow that is present in the mixed layer and is not seen below the pycnocline, leading to a sharp change in the character of the LCS at the bottom of the mixed layer. The flow behavior revealed by the LCS limits fluid exchange between the WCR and the surrounding ocean, contributing to the long life of WCRs. Further study of these structures and their associated transport behavior may lead to further insights into the development and persistence of such geophysical vortices as well as their transport behavior.     

The role of wind direction in eolian transport on a narrow sandy beach

Comparison of eolian transport during five high-velocity wind events over a 29 day period on a narrow estuarine beach in Delaware Bay, New Jersey, USA, reveals the temporal variability of transport, due to changes in direction of wind approach. Mean wind speed measured 6 m above the dune crest for the five events ranged from 8·5 to 15·9 ms^?1. Mean wind direction was oblique to the shoreline (63° from shore-normal) during one event but was within 14° of shore-normal during the other events. Eolian transport is greatest during low tide and rising tide, when the beach source area is widest and when drying of surface sediments occurs. The quantity of sediment caught in a vertical trap for the five events varied from a total of 0·07 to 113·73 kgm^?1. Differences in temperature, relative humidity and moisture and salt content of surficial sediments were slight. Mean grain sizes ranged from 0·33 to 0·58 mm, causing slight differences in threshold shear velocity, but shear velocities exceeded the threshold required for transport during all events. Beach width, measured normal to the shoreline, varied from 15·5 to 18·0 m; beach slope differed by 0·5°. The oblique wind during one event created a source width nearly double the width during other days. Beach slope, measured in the direction of the wind, was less than half as steep as the slope measured normal to the shoreline. The amount of sand trapped during the oblique wind was over 20 times greater than any other event, even those with higher shear velocities. The ability of the beach surface to supply grains to the air stream is limited on narrow beaches, but increased source width, due to oblique wind approach, can partially overcome limitations of surface conditions on the beach.     

Detailed PSC formation in a two-dimensional chemical transport model of the stratosphere

A new two-dimensional zonal model of the stratosphere, based on a formulation in an isentropic framework, with complete chemistry has been coupled with a high resolution detailed microphysical model for polar stratospheric clouds (PSCs). The 2D model chemistry includes all presently known heterogeneous processes on sulfate aerosols and PSCs. The coupling of these two models, with inherently different time scales, is discussed. It is demonstrated that in order to obtain a realistic interrelationship between NO_y and N₂O an accurate simulation of the sedimentation by PSC particles is necessary. A good agreement of model PSC presence and observations is found for the Antarctic polar winter without the need to impose additional artificial temperature variations in the model. The calculated occurrence of polar stratospheric clouds and resulting heterogeneous chemistry during the Antarctic winter are discussed. Sensitivity of the polar stratospheric chemical composition and cloud formation for different perturbations is investigated by studying the effects of transport across the polar vortex boundary and heterogeneous processing by an enhanced sulfate aerosol load. The importance of including sedimentation for all cases is also discussed.     

The role of water-vapour photodissociation on the formation of a deep minimum in mesopause ozone

A one-dimensional atmospheric photochemical model with an altitude grid of about 1.5 km was used to examine the structure of the global mean vertical ozone profile and its night-time-to-daytime variation in the upper atmosphere. Two distinct ozone layers are predicted, separated by a sharp drop in the ozone concentration near the mesopause. This naturally occurring mesopause ozone deep minimum is primarily produced by the rapid increase in the destruction of water vapour, and hence increase in HO_x, at altitudes between 80 and 85 km, a region where water-vapour photodissociation by ultraviolet radiation of the solar Lyman-alpha line is significant, and where the supply of water vapour is maintained by methane oxidation even for very dry conditions at the tropospheric-stratospheric exchange region. The model indicates that the depth of the mesopause ozone minimum is limited by the efficiency with which inactive molecular hydrogen is produced, either by the conversion of atomic hydrogen to molecular hydrogen via one of the reaction channels of H with HO₂, or by Lyman-alpha photodissociation of water vapour via the channel that leads to the production of molecular hydrogen. The ozone concentration rapidly recovers above 85 km due to the rapid increase in O produced by the photodissociation of O₂ by absorption of ultraviolet solar radiation in the Schumann-Runge bands and continuum. Above 90 km, there is a decrease in ozone due to photolysis as the production of ozone through the three-body recombination of O₂ and O becomes slower with decreasing pressure. The model also predicts two peaks in the night-time/daytime ozone ratio, one near 75 km and the other near 110 km, plus a strong peak in the night-time/daytime ratio of OH near 110 km. Recent observational evidence supports the predictions of the model.     

The role of the gravitational potential of the lithosphere in the formation of a global stress field

The global stress field appearing in the Earth’s lithosphere under the action of forces caused by the difference of gravitational potential is calculated. An original algorithm is proposed and the operational Earth Stresses program code is developed. The data on the topography, thickness, and density of the Earth’s crust and the upper mantle, as well as the gravitational anomalies and thermal conditions in the lithosphere were taken into account in the calculations. A comparison of the calculation results and the observed data makes it possible to conclude that the action of the forces of the difference of the gravitational potential alone is sufficient to explain the features of the first order of the stress field in the Earth’s lithosphere.     

沿海地区一次多单体雷暴电荷结构时空演变

利用闪电放电辐射源三维时空分布测量,分析了山东低海拔地区一次多单体雷暴过程的电荷结构演变以及与回波强度的关系.结果表明对流云区电荷结构是典型的上正下负电偶极结构,且随着雷暴发展正负电荷层强度增大,高度抬升.负电荷区处在40 dBz以上的强回波区域中,正电荷层处在约40 dBz区域中.层状云区也有类似结构,只是强度弱,高度低.观测到的四层电荷结构是出现在对流区消散阶段,此时,由于云体不同部位的不同消散程度,电荷结构发生断裂,云体前部正负电荷区下沉,云体中部正负电荷区高度变化不大,但负电荷区域变薄,呈现出四层电荷结构.从本例结果说明,雷暴优势起电机制通常能形成电偶极或三极性结构,多极结构可能不是起电形成.本文还分析了一次负地闪传输过程,和宏观电荷结构很好吻合,说明利用三维定位系统观测,可以较好地描述雷暴宏观电荷结构.     

The role of playas in pedogenic gypsum crust formation in the Central Namib Desert: a theoretical model

The formation of Namibia's extensive pedogenic gypsum crusts (CaSO₄·2H₂O) is interpreted in a new light. It is suggested that gypsum primarily precipitates at isolated points of evaporitic concentration, such as inland playas, and that deflation of evaporitic‐rich gypsum dust from these playas contributes to the formation of pedogenic gypsum duricrusts on the coastal gravel plains of the Namib Desert surrounding these playas. This study establishes the nature, extent and distribution of playas in the Central Namib Desert and provides evidence for playa gypsum deflation and gravel plain deposition. Remote sensing shows the distribution of playas, captures ongoing deflation and provides evidence of gypsum deflation. It is proposed that, following primary marine aerosol deposition, both inland playas and coastal sabkhas generate gypsum which through the process of playa deflation and gravel plain redeposition contributes to the extensive pedogenic crusts found in the Namib Desert region. Copyright © 2001 John Wiley & Sons, Ltd.     

湍流相干结构在中蒙中区一次沙尘暴起沙中的作用

起沙机制是沙尘暴天气研究中一个重要问题.本文基于中蒙中区一次沙尘暴天气过程,通过提取沙尘源地涡动相关数据中的湍流相干结构（Coherent structure,简称为CS）,研究了CS在起沙中的作用.结果发现：（1）起沙期间存在CS,其典型特征表现为上扬—下扫循环,即暖空气的辐合上升与冷空气的辐散下沉相伴;（2）起沙期间,CS具有频次高、持续时间短、间歇性适中、连发频繁、速度切变大、水平尺度远大于垂直尺度和尺度变化比较大的特点;（3）CS是重要的起沙机制,它可起动粒径在0.1~156 μm之间的各种沙粒,起动最多的是粒径低于8 μm的粉粒与粘粒,但CS不是唯一的起沙机制;（4）CS的上扬与下扫两过程均可引起起沙,区别在于前者通过暖空气的上升将沙粒向上空输送,后者则是将上空高速冷空气拖带下来引起地表沙粒的起动;（5）CS起沙分为单起式和连发配合式两种形式.单起式是单发CS产生的起沙形式,连发配合式是连发的CS产生的跃移—上扬的配合起沙形式.其中,连发配合式为主要形式;（6）下扫过程对起沙的贡献是上扬过程的1.8~15倍,上扬过程可将下扫过程中起动沙粒的1/3左右向上输送到空中;（7）一般情况下,CS对起沙具有稳定的贡献,其贡献率为51%,当临界起沙风速大于13 m·s^-1时,其贡献急剧降低.     

On the similarity in the formation mechanism of the fracture structure of a rock massif

Local segments of the Earth’s crust reside at the mechanical nonequilibrium and continuously obtain and dissipate mechanical energy. The energy exchange between the structural elements of a geophysical medium determines its state, especially if the medium is fragmented into blocks. The stationary state of a rock differs from its static equilibrium by the fact that the mechanical energy is conserved because the energy input is equal to the energy dissipation. From this point of view, the cracks, the faults, and the block structure are not simply the manifestations of rock destruction, but rather the mode of existence of a medium with large irreversible deformations. Then, the fracture structure, whose formation is actually a response of a rock to large irreversible deformation, becomes, in terms of physics, the characteristic of the state of a geophysical medium; for example, it allows one to assess the parameters of the deformation processes during the period of formation of the fracture structure. The present paper addresses the identification of the features of the fracture structure in geological objects of different scales.     

湍流相干结构在中蒙中区一次沙尘暴起沙中的作用

起沙机制是沙尘暴天气研究中一个重要问题.本文基于中蒙中区一次沙尘暴天气过程,通过提取沙尘源地涡动相关数据中的湍流相干结构（Coherent structure,简称为CS）,研究了CS在起沙中的作用.结果发现：（1）起沙期间存在CS,其典型特征表现为上扬—下扫循环,即暖空气的辐合上升与冷空气的辐散下沉相伴;（2）起沙期间,CS具有频次高、持续时间短、间歇性适中、连发频繁、速度切变大、水平尺度远大于垂直尺度和尺度变化比较大的特点;（3）CS是重要的起沙机制,它可起动粒径在0.1~156 μm之间的各种沙粒,起动最多的是粒径低于8 μm的粉粒与粘粒,但CS不是唯一的起沙机制;（4）CS的上扬与下扫两过程均可引起起沙,区别在于前者通过暖空气的上升将沙粒向上空输送,后者则是将上空高速冷空气拖带下来引起地表沙粒的起动;（5）CS起沙分为单起式和连发配合式两种形式.单起式是单发CS产生的起沙形式,连发配合式是连发的CS产生的跃移—上扬的配合起沙形式.其中,连发配合式为主要形式;（6）下扫过程对起沙的贡献是上扬过程的1.8~15倍,上扬过程可将下扫过程中起动沙粒的1/3左右向上输送到空中;（7）一般情况下,CS对起沙具有稳定的贡献,其贡献率为51%,当临界起沙风速大于13 m·s^-1时,其贡献急剧降低.

     

Modeling the formation of undulations of the coastline: The role of tides

An idealized model is developed and analyzed to investigate the relevance of tidal motion for the emergence of undulations of a sandy coastline. The model describes feedbacks between tidal and steady flow on the inner shelf, sand transport in the nearshore zone and an irregular coastline. It is demonstrated that an initially straight coastline can become unstable with respect to perturbations with a rhythmic structure in the alongshore direction. The mechanism causing the growth of these perturbations is explained in terms of vorticity concepts. The relative importance of tide-related and wave-driven sediment fluxes in generating undulations of the coastline is investigated for the Dutch coast. Using parameter values that are appropriate for the Dutch coast it is found that tides can render a straight coastline unstable. The model predicts a fastest growing mode (FGM) with a wavelength that is in the order of the observed length of barrier islands. The mode grows on a time scale of 50 yr and it migrates 200 m per year. The wavelength of the FGM decreases with increasing amplitude of the tidal currents. This result is consistent with data of tides, waves and the lengths of barrier islands that are located along the Dutch and German Wadden coast.     

对流输运在TOI断裂形成等离子体云块中的作用研究

极盖等离子体云块是极区电离层常见特征之一,其形成演化过程是当前重要研究课题.光电离高密度等离子体在对流输送作用下从日侧穿过极隙,通过极盖到达夜侧,已成为共识.日侧磁场重联作用下的极区对流输运过程,在舌状等离子体结构（TOI）"断裂"形成极盖等离子体云块中发挥重要作用.利用极区全域GPS/TEC观测数据,结合SuperDARN雷达实测的对流速度,对等离子体云块形成过程进行案例研究,重点分析两种TOI断裂形成等离子体云块的发生机制.研究结果显示,等离子体对流输运过程在TOI断裂形成等离子体云块过程中发挥关键性作用,对流形态或局部对流速度矢量急剧变化都可能导致TOI结构不稳定,使TOI结构断裂形成等离子体云块.     

The role of vibrationally excited nitrogen in the formation of the mid-latitude negative ionospheric storms

Millstone Hill ionospheric storm time measurements of the electron density and temperature during the ionospheric storms (15-16 June 1965; 29–30 September 1969 and 17–18 August 1970) are compared with model results. The model of the Earth’s ionosphere and plasmasphere includes interhemispheric coupling, the H⁺, O⁺(⁴S), O⁺(²D), O⁺(²P), NO⁺, O⁺₂ and N⁺₂ ions, electrons, photoelectrons, the electron and ion temperature, vibrationally excited N₂ and the components of thermospheric wind.In order to model the electron temperature at the time of the 16 June 1965 negative storm, the heating rate of the electron gas by photoelectrons in the energy balance equation was multiplied by the factors 5–30 at he altitude above 700 km for the period 4.50-12.00 LT, 16 June 1965. The [O]/[N₂] MSIS-86 decrease and vibrationally excited N₂ effects are enough to account for the electron density depressions at Millstone Hill during the three storms. The factor of 2 (for 27–30 September 1969 magnetic storm) and the & actor 2.7 (for 16–18 August 1970 magnetic storm) reduction in the daytime peak density due to enhanced vibrationally excited N₂ is brought about by the increase in the O⁺+N₂ rate factor.     

The role of the water/soil distribution coefficient in the watershed transport of environmental radionuclides

The concept of the distribution coefficient is invoked to rationalize the observed dependence of the watershed residence time of a radionuclide on its nature. A mathematical model is presented to show that this residence time is proportional to the dimensionless field distribution coefficient of the radionuclide. The proportionality constant, β, is defined as the ratio of the volume of rain-impacted soil in the watershed and the annual volume of rainfall in the watershed or expressed as the ratio between the water penetration depth in soil and the annual thickness of water above the soil surface. An empirical evaluation of β supports our assumption of its constancy in a given watershed. The described model may be very useful in deciphering the impact of atmospherically delivered pollutants on watershed quality. Expressions are also derived to estimate the value of soil erosion constant using naturally occurring radionuclides.     

对流输运在TOI断裂形成等离子体云块中的作用研究

极盖等离子体云块是极区电离层常见特征之一,其形成演化过程是当前重要研究课题.光电离高密度等离子体在对流输送作用下从日侧穿过极隙,通过极盖到达夜侧,已成为共识.日侧磁场重联作用下的极区对流输运过程,在舌状等离子体结构（TOI）"断裂"形成极盖等离子体云块中发挥重要作用.利用极区全域GPS/TEC观测数据,结合SuperDARN雷达实测的对流速度,对等离子体云块形成过程进行案例研究,重点分析两种TOI断裂形成等离子体云块的发生机制.研究结果显示,等离子体对流输运过程在TOI断裂形成等离子体云块过程中发挥关键性作用,对流形态或局部对流速度矢量急剧变化都可能导致TOI结构不稳定,使TOI结构断裂形成等离子体云块.     

Magma transport and reservoir formation by a system of propagating cracks

A system of propagating cracks may explain magma transport and the evolution of a volcano. This paper considers only a basaltic magma. The system is controlled by two boundary conditions: the stress field, and the production rate of the magma-filled cracks in the mantle. Numerical solutions of crack propagation for various stress conditions, with a constant production rate high enough to coalesce isolated cracks, were performed, and the results applied to different tectonic conditions. For the hydrostatic stress conditions, most magma-filled cracks beneath a polygenetic volcano become trapped either in the lower crust, because there the density difference between magma and the host rocks () becomes suddenly small, compared with that in the mantle, or trapped in the upper crust, because there is near to zero. Magma traps composed of such cracks may grow into magma reservoirs if the production rate of cracks in the mantle is large. If horizontal stress with a vertical gradient is superimposed on the hydrostatic condition in the crust, that is, tensile stress which increases upward or compressional stress which increases downward, magmafilled cracks, even if the density of magma is higher than that of the crust, may ascend directly without trapping. When the crust undergoes relative tension, magma-filled cracks may become trapped. Then, the lower part of the trap may grow into a magma reservoir, while the upper part may become filled with dikes. When the production rate of cracks is small, an initial magma-filled crack can rise directly to the surface only when the stress with a gradient is superimposed as mentioned above, or when the average density in a crack decreases, owing to, for example, vesiculation of volatile components.     

The role of suspended sediments and phytoplankton in the partitioning and transport of silver in estuaries

Silver sorbs readily at low salinities to both phytoplankton and suspended sediments. As salinity increases, the degree of sorption decreases. Nearly 80% of silver sorbed to suspended sediments at low salinities will desorb at higher salinities, but desorption does not occur when silver is associated with phytoplankton. Thus, silver incorporation onto/into cellular material will increase the retention of silver within the estuary, reducing its rate of transport.     

On the dynamic mechanism of formation of rift valleys

A dynamic mechanism that accounts for the sinking of a lithospheric plate near an accretion zone in the vicinity of a passive rift is revealed. It is shown that the influence of the underlying “cold” mantle can be described in terms of a concentrated vertical force applied to the rift axis. At a moderate spreading rate, the value of this force is an order of magnitude smaller than the characteristic values of forces acting in the plate tectonics. The average viscosity coefficient of the cold upper mantle is estimated at ～10²¹ P. The concentrated force at the rift axis produces a characteristic topography of the rift valley type of mid-ocean ridges.