M.P. Poland,T.J. Takahashi,and C.M. Landowski (eds): Characteristics of Hawaiian Volcanoes     

John P. Lockwood 《Bulletin of Volcanology》2016,78(3):16

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A Multispacecraft Analysis of a Small-Scale Transient Entrained by Solar Wind Streams     

A. P. Rouillard  N. P. Savani  J. A. Davies  B. Lavraud  R. J. Forsyth  S. K. Morley  A. Opitz  N. R. Sheeley  L. F. Burlaga  J.-A. Sauvaud  K. D. C. Simunac  J. G. Luhmann  A. B. Galvin  S. R. Crothers  C. J. Davis  R. A. Harrison  M. Lockwood  C. J. Eyles  D. Bewsher  D. S. Brown 《Solar physics》2009,256(1-2):307-326

The images taken by the Heliospheric Imagers (HIs), part of the SECCHI imaging package onboard the pair of STEREO spacecraft, provide information on the radial and latitudinal evolution of the plasma compressed inside corotating interaction regions (CIRs). A plasma density wave imaged by the HI instrument onboard STEREO-B was found to propagate towards STEREO-A, enabling a comparison between simultaneous remote-sensing and in situ observations of its structure to be performed. In situ measurements made by STEREO-A show that the plasma density wave is associated with the passage of a CIR. The magnetic field compressed after the CIR stream interface (SI) is found to have a planar distribution. Minimum variance analysis of the magnetic field vectors shows that the SI is inclined at 54° to the orbital plane of the STEREO-A spacecraft. This inclination of the CIR SI is comparable to the inclination of the associated plasma density wave observed by HI. A small-scale magnetic cloud with a flux rope topology and radial extent of 0.08 AU is also embedded prior to the SI. The pitch-angle distribution of suprathermal electrons measured by the STEREO-A SWEA instrument shows that an open magnetic field topology in the cloud replaced the heliospheric current sheet locally. These observations confirm that HI observes CIRs in difference images when a small-scale transient is caught up in the compression region.  相似文献   

An analysis of the accuracy of magnetopause reconnection rate variations deduced from cusp ion dispersion characteristics     

M. Lockwood  C. J. Davis 《Annales Geophysicae》1996,14(2):149-161

We present an analysis of the accuracy of the method introduced by Lockwood et al. (1994) for the determination of the magnetopause reconnection rate from the dispersion of precipitating ions in the ionospheric cusp region. Tests are made by applying the method to synthesised data. The simulated cusp ion precipitation data are produced by an analytic model of the evolution of newly-opened field lines, along which magnetosheath ions are firstly injected across the magnetopause and then dispersed as they propagate into the ionosphere. The rate at which these newly opened field lines are generated by reconnection can be varied. The derived reconnection rate estimates are then compared with the input variation to the model and the accuracy of the method assessed. Results are presented for steady-state reconnection, for continuous reconnection showing a sine-wave variation in rate and for reconnection which only occurs in square wave pulses. It is found that the method always yields the total flux reconnected (per unit length of the open-closed field-line boundary) to within an accuracy of better than 5%, but that pulses tend to be smoothed so that the peak reconnection rate within the pulse is underestimated and the pulse length is overestimated. This smoothing is reduced if the separation between energy channels of the instrument is reduced; however this also acts to increase the experimental uncertainty in the estimates, an effect which can be countered by improving the time resolution of the observations. The limited time resolution of the data is shown to set a minimum reconnection rate below which the method gives spurious short-period oscillations about the true value. Various examples of reconnection rate variations derived from cusp observations are discussed in the light of this analysis.  相似文献   

The Evolution of the Sun's Open Magnetic Flux – I. A Single Bipole     

Mackay  D.H.  Priest  E.R.  Lockwood  M. 《Solar physics》2002,207(2):291-308

In this paper the origin and evolution of the Sun's open magnetic flux are considered for single magnetic bipoles as they are transported across the Sun. The effects of magnetic flux transport on the radial field at the surface of the Sun are modeled numerically by developing earlier work by Wang, Sheeley, and Lean (2000). The paper considers how the initial tilt of the bipole axis () and its latitude of emergence affect the variation and magnitude of the surface and open magnetic flux. The amount of open magnetic flux is estimated by constructing potential coronal fields. It is found that the open flux may evolve independently from the surface field for certain ranges of the tilt angle. For a given tilt angle, the lower the latitude of emergence, the higher the magnitude of the surface and open flux at the end of the simulation. In addition, three types of behavior are found for the open flux depending on the initial tilt angle of the bipole axis. When the tilt is such that ge2° the open flux is independent of the surface flux and initially increases before decaying away. In contrast, for tilt angles in the range –16°<<2° the open flux follows the surface flux and continually decays. Finally, for le–16° the open flux first decays and then increases in magnitude towards a second maximum before decaying away. This behavior of the open flux can be explained in terms of two competing effects produced by differential rotation. Firstly, differential rotation may increase or decrease the open flux by rotating the centers of each polarity of the bipole at different rates when the axis has tilt. Secondly, it decreases the open flux by increasing the length of the polarity inversion line where flux cancellation occurs. The results suggest that, in order to reproduce a realistic model of the Sun's open magnetic flux over a solar cycle, it is important to have accurate input data on the latitude of emergence of bipoles along with the variation of their tilt angles as the cycle progresses.  相似文献   

Energy and pitch-angle dispersions of LLBL/cusp ions seen at middle altitudes: predictions by the open magnetosphere model     

M. Lockwood 《Annales Geophysicae》1997,15(12):1501-1514

Numerical simulations are presented of the ion distribution functions seen by middle-altitude spacecraft in the low-latitude boundary layer (LLBL) and cusp regions when reconnection is, or has recently been, taking place at the equatorial magnetopause. From the evolution of the distribution function with time elapsed since the field line was opened, both the observed energy/observation-time and pitch-angle/energy dispersions are well reproduced. Distribution functions showing a mixture of magnetosheath and magnetospheric ions, often thought to be a signature of the LLBL, are found on newly opened field lines as a natural consequence of the magnetopause effects on the ions and their flight times. In addition, it is shown that the extent of the source region of the magnetosheath ions that are detected by a satellite is a function of the sensitivity of the ion instrument . If the instrument one-count level is high (and/or solar-wind densities are low), the cusp ion precipitation detected comes from a localised region of the mid-latitude magnetopause (around the magnetic cusp), even though the reconnection takes place at the equatorial magnetopause. However, if the instrument sensitivity is high enough, then ions injected from a large segment of the dayside magnetosphere (in the relevant hemisphere) will be detected in the cusp. Ion precipitation classed as LLBL is shown to arise from the low-latitude magnetopause, irrespective of the instrument sensitivity. Adoption of threshold flux definitions has the same effect as instrument sensitivity in artificially restricting the apparent source region.  相似文献   

Macroscale modelling of the hydrosphere edited by W. B. Wilkinson,International Association of Hydrological Sciences,Publication No. 214, IAHS Press,Wallingford, 1993. No. of pages: viii + 193. Price: £33.34. ISBN 0-947571-63-9     

J. G. Lockwood 《地球表面变化过程与地形》1995,20(8):776-776

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Microprocessor systems as an aid to estuarine studies in the laboratory     

A.P.M. Lockwood  N.W. Jenkinson  S.R.L. Bolt  M.E. Dawson  A.C. Jensen 《Estuarine, Coastal and Shelf Science》1982,15(2):199-206

Three systems are outlined which indicate the potential of microprocessor systems as control devices in the generation of specifically varying environmental mental conditions. The use of an RCA 1802 Cosmac microprocessor to generate salinity cycles, tidal cycles and temperature cycles is described.  相似文献   

The use of the von Bertalanffy growth equation to describe the seasonal growth of fish   总被引：1，自引：0，他引：1  

Lockwood  Stephen J. 《ICES Journal of Marine Science》1974,35(2):175-179

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The self-organising of youth volunteers during the Rena oil spill in New Zealand     

Sarah Lockwood  C Kay Weaver  Debashish Munshi  Mary Simpson 《新西兰海洋与淡水研究杂志》2016,50(1):28-41

ABSTRACT

This study explores the communication and organising of youth volunteers during a crisis, focusing on how they conceived, framed, and executed self-organising efforts during the 2011 Rena oil spill in New Zealand. It offers insights into the intersections of self-organising, youth volunteering and crisis events which have not been researched before. The study addresses two core research questions: 1. how was ‘volunteering’ conceptualised by youth volunteers involved in the Rena crisis; and 2. how did these volunteers communicate and self-organise during this crisis? The findings indicate that self-organising emerged out of a resistance towards structured responses and as a reaction to the inability of the official volunteer response to meet the needs of the community. Self-organised efforts were particularly attractive among youth volunteers because they offered flexibility, required minimal administrative processes, and fostered an environment of innovation and creativity. The volunteers’ youthful energy and technological aptitude additionally drove their self-organised responses. The study identifies the considerable challenges that crisis officials faced in utilising youth volunteers despite the significant advantages of self-organising.  相似文献   

极区电离层对IMF Bz 4次快速转向的响应——EISCAT/ESR雷达观测          下载免费PDF全文

蔡红涛  马淑英  I.W.McCrea  J.A.Davis  M.Lockwood  S.E.Milan 《地球物理学报》2009,52(7)

利用EISCAT VHF和EISCAT Svalbard(ESR)雷达观测数据,对2003年2月12日IMF Bz分量4次快速方向转换期间,极区电离层,尤其是极尖/极隙区的响应特征进行了分析研究.随着IMF Bz方向的多次快速变化,地面雷达观测到极尖/极隙区所在位置随着开放-闭合磁力线边界在纬度方向上来回移动.在此期间,极区电离层等离子体水平对流多次反向,表现出与IMF Bz分量强的负相关性.进一步分析表明:极区磁层-电离层系统在日侧对IMF极性变化的平均响应时间约为3 min.  相似文献