Palaeomagnetic directions and pole positions — XV. Pole numbers 15/1 to 15/232     

M. W. McElhinny  J. A. Cowley 《Geophysical Journal International》1978,52(2):259-276

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Wave-particle interactions in a magnetic neutral sheet     

C. Robertson  S.W.H. Cowley  J.W. Dungey 《Planetary and Space Science》1981,29(4):399-403

The effect of an electrostatic wave on the motion of particles in a magnetic neutral sheet is studied. The first-order perturbation of the distribution function is conveniently obtained by a method in which the changes in the zero-order constants of the motion are calculated. Simple analytic approximation is possible in certain regions of velocity space, but it is shown that in general numerical calculation is required. Some sample numerical results are presented and the conditions for waveparticle resonance discussed.  相似文献   

Palaeomagnetic directions and pole positions—XIV. Pole numbers 14/1 to 14/574     

M. W. McElhinny  J. A. Cowley 《Geophysical Journal International》1977,49(2):313-356

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Choice chamber experiments to test the attraction of postflexion Rhabdosargus holubi larvae to water of estuarine and riverine origin     

Nicola C. James  Paul D. Cowley  Alan K. Whitfield  Horst Kaiser 《Estuarine, Coastal and Shelf Science》2008

Although the recruitment of larvae and juveniles of marine fishes into estuaries has been well documented, little is known about the factors governing the immigration of estuary-associated marine fishes into estuaries. Fishes have a well-developed sense of smell and it has been suggested by several workers that olfactory cues of freshwater or estuarine origin serve as stimuli, attracting larvae and juveniles of estuary-associated species into estuaries. Attraction of postflexion Rhabdosargus holubi larvae to estuary and river water from the Kowie estuarine system, South Africa, was measured using a rectangular choice chamber. In experiments, conducted during peak recruitment periods, larvae selected estuary and river water with a significantly higher frequency than sea water. This study, the first to assess the possible role of olfaction in the recruitment process of an estuary-associated marine fish species, demonstrates that larvae are able to recognise water from different origins, probably based on odour.  相似文献   

Interpretation of magnetic field perturbations in the earth's magnetopause boundary layers     

S.W.H. Cowley  D.J. Southwood  M.A. Saunders 《Planetary and Space Science》1983,31(11):1237-1258

Studies of the boundary layers in the vicinity of the Earth's dayside magnetopause are important in determining the nature of the processes which couple the magnetosphere to the flowing solar wind, thereby driving magnetospheric convection. In this paper we examine theoretically the magnetic field and plasma properties expected in the boundary regions for various models involving either diffusion or reconnection at the boundary. For diffusion models the transport of magnetosheath momentum across the magnetopause will result in field shears on either side of the boundary, the field rotations being in opposite senses on either side relative to the undisturbed fields. The directions of these rotations depend upon location at the magnetopause relative to the momentum transfer region and to the noon meridian. In reconnection models the effect of the tension of the open boundary layer field lines must be taken into account in addition to the magnetosheath flow, but on the super-Alfvénic flanks of the magnetosphere the latter still dominates, so that qualitatively similar effects will occur in the two models. More detailed, quantitative or statistical studies are then required to distinguish the two models in this regime. In the sub-Alfvénic dayside region, however, open field tension effects will dominate in reconnection models such that boundary layer field and plasma properties will then be determined mainly by the magnetosheath magnetic field configuration. In particular the East-West flow in the magnetospheric boundary layer will be controlled largely by the East-West field in the magnetosheath, leading to flow reversals across the magnetopause in some quadrants of the magnetopause. This behaviour is directly related to the Svalgaard-Mansurov effect and is a signature unique to reconnection models. The boundary layer fields are also expected to tilt towards the field on the opposite side of the boundary in these models on the dayside. “Toward” tilting can also occur in this regime in diffusion models, but “away” tilting, a signature unique to dayside diffusion, should also occur equally frequently. Finally, we briefly discuss previously published high-resolution ISEE 1 and 2 data from the boundary regions in the light of our results. We find that “toward” tilting generally occurs in boundary region crossings previously identified as being reconnection-associated and we present some examples in which the above unique reconnection signature has been observed. During impulsive FTE-like events, however, the field may tilt in either direction, possibly as a result of field line twists, thus complicating our simple picture in this case. We also show that the “reverse draping” observations presented by Hones et al. (1982) approximately satisfy the open magnetopause stress balance conditions.  相似文献   

On the distribution of B_y in the geomagnetic tail     

S.W.H. Cowley 《Planetary and Space Science》1979,27(6):769-793

The distribution of B_y in the geomagnetic tail associated with a net cross-tail magnetic flux, recently experimentally discovered, is here investigated within the framework of two-dimensional but non-planar field adiabatic time-independent equilbria. It is found that the flux distribution is controlled by the pressure anisotropy of the plasma, B_y being enhanced at the current sheet centre relative to that in the lobes for P_∥>P_⊥ and vice-versa for P_⊥>P_∥. For P_⊥>P_∥ a broad region of depressed field strength is found across the centre plane of the current sheet, terminated at its outer boundaries by spikes in the perpendicular current, across which B_y and B_x are “switched on” and rapidly increase towards their values in the low-β lobes. For P_∥>P_⊥ a thin high-current density layer forms at the sheet centre if the marginal firehose condition is approached, across which the B_x field reverses by rotation at nearly constant magnitude about the z-axis. The field magnitude in this thin layer depends upon the pressure anisotropy, such that the plasma remains just firehose stable within it, and may approach an appreciable fraction of the lobe field strength even for moderate anisotropies. Such structures have been observed in the geomagnetic tail, but do not appear to be a common feature of the quiet-time plasmasheet, where the field strength at the centre plane can reach small values with little obvious enhancement of B_y. In terms of the present model these observations require that either P_⊥>P_∥ in the quiet-time tail or that the plasma is within one or two per cent of isotropy if P_∥>P_⊥. These results then indicate that the production of plasma pressure anisotropy during adiabatic inward transport towards the Earth, which is generally expected to lead to P_∥>P_⊥ and its destruction by either macroscopic or microscopic processes, requires further study.  相似文献   

A note on adiabatic solutions of the one-dimensional current sheet problem     

S.W.H. Cowley  R. Pellat 《Planetary and Space Science》1979,27(3):265-271

It has recently been shown that adiabatic solutions of the one-dimensional current sheet problem exist provided that magnetically trapped particles are included in the model together with the current-carrying untrapped “beam” particles. We show here that a formulation of the problem in terms of particle velocity and pitch angle is advantageous, and we derive some general properties of the solutions. In particular it is shown that there is, in general, no discontinuity in the value of the particle distribution function ? across the boundary in velocity space between “beam” and trapped particles, but that there will be a discontinuity in the gradients of ?. An example is given in which the beam population is of bi-Maxwellian form at the outer boundary of the current sheet.  相似文献   

The motion of lithium test ions in the quiet time nightside magnetosphere: Conservation of magnetic moment and longitudinal invariants     

S.C. Chapman  S.W.H. Cowley 《Planetary and Space Science》1985,33(6):685-709

One of the active experiments to be performed as part of the AMPTE mission involves the release of lithium ions in the geomagnetic tail and their subsequent detection after Earthward convection into the nightside outer ring current region. In a previous paper, the guiding centre trajectories of ions were integrated in a simple two-dimensional model of the quiet time nightside magnetosphere in order to estimate their properties on arrival in the ring current region. In this paper, the validity of the guiding centre approximation is investigated, using full trajectory integrations in a simplified one-dimensional field model. In particular, it is shown to be valid for the lithium ion trajectories in the simple two-dimensional model field over the observed range of quiet time magnetotail field values. Analytical approximations for the properties of ions as they first cross the tail centre plane, and approximate longitudinal invariants of the subsequent Earthward motion are then derived. Finally, by comparison of these with the numerical results it is demonstrated that the speeds and pitch angles of the ions arriving in the ring current region can be predicted analytically to a reasonable approximation, and hence can be simply calculated for any given model of the quiet time geomagnetic tail.  相似文献   

AXIOM: Advanced X‐ray imaging of the magnetosheath     

S. Sembay  G. Branduardi‐Raymont  J.P. Eastwood  D.G. Sibeck  A. Abbey  P. Brown  J.A. Carter  C.M. Carr  C. Forsyth  D. Kataria  S. Kemble  S. Milan  C.J. Owen  A.M. Read  L. Peacocke  C.S. Arridge  A.J. Coates  M.R. Collier  S.W.H. Cowley  A.N. Fazakerley  G. Fraser  G.H. Jones  R. Lallement  M. Lester  F.S. Porter  T. Yeoman 《Astronomische Nachrichten》2012,333(4):388-392

AXIOM (Advanced X‐ray Imaging Of the Magnetosphere) is a concept mission which aims to explain how the Earth's magnetosphere responds to the changing impact of the solar wind using a unique method never attempted before; performing wide‐field soft X‐ray imaging and spectroscopy of the magnetosheath, magnetopause and bow shock at high spatial and temporal resolution. Global imaging of these regions is possible because of the solar wind charge exchange (SWCX) process which produces elevated soft X‐ray emission from the interaction of high charge‐state solar wind ions with primarily neutral hydrogen in the Earth's exosphere and near‐interplanetary space (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Geomorphological control on boulder transport and coastal erosion before,during and after an extreme extra‐tropical cyclone          下载免费PDF全文

Larissa A. Naylor  Wayne J. Stephenson  Helen C. M. Smith  Oliver Way  James Mendelssohn  Andrew Cowley 《地球表面变化过程与地形》2016,41(5):685-700

Extreme wave events in coastal zones are principal drivers of geomorphic change. Evidence of boulder entrainment and erosional impact during storms is increasing. However, there is currently poor time coupling between pre‐ and post‐storm measurements of coastal boulder deposits. Importantly there are no data reporting shore platform erosion, boulder entrainment and/or boulder transport during storm events – rock coast dynamics during storm events are currently unexplored. Here, we use high‐resolution (daily) field data to measure and characterize coastal boulder transport before, during and after the extreme Northeast Atlantic extra‐tropical cyclone Johanna in March 2008. Forty‐eight limestone fine‐medium boulders (n = 46) and coarse cobbles (n = 2) were tracked daily over a 0.1 km² intertidal area during this multi‐day storm. Boulders were repeatedly entrained, transported and deposited, and in some cases broken down (n = 1) or quarried (n = 3), during the most intense days of the storm. Eighty‐one percent (n = 39) of boulders were located at both the start and end of the storm. Of these, 92% were entrained where entrainment patterns were closely aligned to wave parameters. These data firmly demonstrate rock coasts are dynamic and vulnerable under storm conditions. No statistically significant relationship was found between boulder size (mass) and net transport distance. Graphical analyses suggest that boulder size limits the maximum longshore transport distance but that for the majority of boulders lying under this threshold, other factors influence transport distance. Paired analysis of 20 similar sized and shaped boulders in different morphogenic zones demonstrates that geomorphological control affects entrainment and transport distance – where net transport distances were up to 39 times less where geomorphological control was greatest. These results have important implications for understanding and for accurately measuring and modelling boulder entrainment and transport. Coastal managers require these data for assessing erosion risk. © 2016 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献