Venus Express arrives     

Andrew Coates 《Astronomy& Geophysics》2006,47(3):3.13-3.15

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Ion escape at Mars: Comparison of a 3-D hybrid simulation with Mars Express IMA/ASPERA-3 measurements     

E. Kallio  A. Fedorov  T. Säles  W. Schmidt  P. Riihelä  R. Lundin  H. Gunell  Y. Futaana  M. Yamauchi  J.-A. Sauvaud  J.D. Winningham  J.R. Sharber  A.J. Coates  D.O. Kataria  J.G. Luhmann  D. Williams  C.C. Curtis  B.R. Sandel  M. Carter  S. Orsini  M. Maggi  P. Bochsler  J. Woch  K. Asamura 《Icarus》2006,182(2):350-359

We have analysed ion escape at Mars by comparing ASPERA-3/Mars Express ion measurements and a 3-D quasi-neutral hybrid model. As Mars Express does not have a magnetometer onboard, the analysed IMA data are from an orbit when the IMF clock angle was possible to determine from the magnetic field measurements of Mars Global Surveyor. We found that fast escaping planetary ions were observed at the place which, according to the 3-D model, is anticipated to contain accelerated heavy ions originating from the martian ionosphere. The direction of the interplanetary magnetic field was found to affect noticeably which regions can be magnetically connected to Mars Express and to the overall 3-D Mars-solar wind interaction.  相似文献   

First observation of energetic neutral atoms in the Venus environment     

A. Galli  P. Wurz  S. Barabash  Y. Futaana  H. Gunell  R. Lundin  K. Brinkfeldt  N. Krupp  W. Baumjohann  T.L. Zhang  A.J. Coates  D.O. Kataria  K.C. Hsieh  J.A. Sauvaud  C. Mazelle  M. Grande  T. Sales  P. Riihela  J. Kozyra  S. McKenna-Lawlor  R. Cerulli-Irelli  A. Milillo  E. Roelof  C.T. Russell  D. Winningham  J. Scherrer 《Planetary and Space Science》2008,56(6):807-811

The ASPERA-4 instrument on board the Venus Express spacecraft offers for the first time the possibility to directly measure the emission of energetic neutral atoms (ENAs) in the vicinity of Venus. When the spacecraft is inside the Venus shadow a distinct signal of hydrogen ENAs usually is detected. It is observed as a narrow tailward stream, coming from the dayside exosphere around the Sun direction. The intensity of the signal reaches several , which is consistent with present theories of the plasma and neutral particle distributions around Venus.  相似文献   

Ray perturbation theory and the Born approximation   总被引：1，自引：0，他引：1  

R. T. Coates  C. H. Chapman 《Geophysical Journal International》1990,100(3):379-392

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International solar terrestrial energy programme and the UK participation     

M. Lester  A. J. Coates  R. A. Harrison  D. Rees  J. G. Roederer  M. J. Rycroft  M. A. Saunders 《Surveys in Geophysics》1993,14(6):555-583

The Solar Terrestrial Energy Programme (STEP) aims to improve our general understanding of how mass, energy and momentum are transferred between the various regions that form the Solar Terrestrial environment. STEP began in 1990 and will continue until 1997, during which time a number of major new spacecraft and ground-based projects will become operational. Six Working Groups form the basis of STEP, covering topics such as the Sun as a source of energy and disturbance, energy and mass transfer through the interplanetary medium and the magnetosphere-ionosphere system, ionosphere-thermosphere coupling and response to energy and momentum inputs, middle atmosphere responses to forcing from above and below, solar variability effects in the human environment, and informatics. A Royal Astronomical Society Geophysics Discussion meeting took place in March 1992 to draw to the attention of UK scientists the diverse nature of STEP and the opportunities offered by STEP. This paper consists of individual sections prepared by the speakers at the meeting and which cover most of the STEP Working Group topics. The main aims of each section are to provide a benchmark for the present status of the research area and to look ahead to the possible contributions that UK scientists can make during STEP.  相似文献   

Energy deposition and primary chemical products in Titan’s upper atmosphere     

P. Lavvas  M. Galand  A.N. Heays  G.R. Lewis  A.J. Coates 《Icarus》2011,213(1):233-251

Cassini results indicate that solar photons dominate energy deposition in Titan’s upper atmosphere. These dissociate and ionize nitrogen and methane and drive the subsequent complex organic chemistry. The improved constraints on the atmospheric composition from Cassini measurements demand greater precision in the photochemical modeling. Therefore, in order to quantify the role of solar radiation in the primary chemical production, we have performed detailed calculations for the energy deposition of photons and photoelectrons in the atmosphere of Titan and we validate our results with the Cassini measurements for the electron fluxes and the EUV/FUV emissions. We use high-resolution cross sections for the neutral photodissociation of N₂, which we present here, and show that they provide a different picture of energy deposition compared to results based on low-resolution cross sections. Furthermore, we introduce a simple model for the energy degradation of photoelectrons based on the local deposition approximation and show that our results are in agreement with detailed calculations including transport, in the altitude region below 1200 km, where the effects of transport are negligible. Our calculated, daytime, electron fluxes are in good agreement with the measured fluxes by the Cassini Plasma Spectrometer (CAPS), and the same holds for the measured FUV emissions by the Ultraviolet Imaging Spectrometer (UVIS). Finally, we present the vertical production profiles of radicals and ions originating from the interaction of photons and electrons with the main components of Titan’s atmosphere, along with the column integrated production rates at different solar zenith angles. These can be used as basis for any further photochemical calculations.  相似文献   

Cassini observations of Saturn's inner plasmasphere: Saturn orbit insertion results     

E.C. Sittler Jr.  M. Thomsen  R.E. Hartle  D. Chornay  D. Simpson  A.J. Coates  D.J. McComas  D. Reisenfeld  N. Andre 《Planetary and Space Science》2006,54(12):1197-1210

We present new and definitive results of Cassini plasma spectrometer (CAPS) data acquired during passage through Saturn's inner plasmasphere by the Cassini spacecraft during the approach phase of the Saturn orbit insertion period. This analysis extends the original analysis of Sittler et al. [2005. Preliminary results on Saturn's inner plasmasphere as observed by Cassini: comparison with Voyager. Geophys. Res. Lett. 32, L14S07, doi:10.1029/2005GL022653] to L∼10 along with also providing a more comprehensive study of the interrelationship of the various fluid parameters. Coincidence data are sub-divided into protons and water group ions. Our revised analysis uses an improved convergence algorithm which provides a more definitive and independent estimate of the spacecraft potential Φ_SC for which we enforce the protons and water group ions to co-move with each other. This has allowed us to include spacecraft charging corrections to our fluid parameter estimations and allow accurate estimations of fluctuations in the fluid parameters for future correlative studies. In the appendix we describe the ion moments algorithm, and minor corrections introduced by not weighting the moments with sinθ term in Sittler et al. [2005] (Correction offset by revisions to instruments geometric factor). Estimates of the spacecraft potential and revised proton densities are presented. Our total ion densities are in close agreement with the electron densities reported by Moncuquet et al. [2005. Quasi-thermal noise spectroscopy in the inner magnetosphere of Saturn with Cassini/RPWS: electron temperatures and density. Geophys. Res. Lett. 32, L20S02, doi:10.1029/2005GL022508] who used upper hybrid resonance (UHR) emission lines observed by the radio and plasma wave science (RPWS) instrument. We show a positive correlation between proton temperature and water group ion temperature. The proton and thermal electron temperatures track each with both having a positive radial gradient. These results are consistent with pickup ion energization via Saturn's rotational electric field. We see evidence for an anti-correlation between radial flow velocity V_R and azimuthal velocity V_φ, which is consistent with the magnetosphere tending to conserve angular momentum. Evidence for MHD waves is also present. We show clear evidence for outward transport of the plasma via flux tube interchange motions with the radial velocity of the flow showing positive radial gradient with functional dependence for 4<L<10 (i.e., if we assume to be diffusive transport then D_LL∼D₀L¹¹ for fixed stochastic time step δt). Previous models with centrifugal transport have used D_LL∼D₀L³ dependence. The radial transport seems to begin at Enceladus’ L shell, L∼4, where we also see a minimum in the W⁺ ion temperature . For the first time, we are measuring the actual flux tube interchange motions in the magnetosphere and how it varies with radial distance. These observations can be used as a constraint with regard to future transport models for Saturn's magnetosphere. Finally, we evaluate the thermodynamic properties of the plasma, which are all consistent with the pickup process being the dominant energy source for the plasma.  相似文献   

Dissolved oxygen as a physico-chemical supporting element in the Water Framework Directive   总被引：1，自引：0，他引：1  

Best MA  Wither AW  Coates S 《Marine pollution bulletin》2007,55(1-6):53-64

For transitional and coastal waters the Water Framework Directive identifies 5 "General chemical and physiochemical elements supporting the biological elements". The five elements are transparency, thermal conditions, oxygenation conditions, salinity and nutrient conditions. "Supporting" in the context of the directive means that the values of the physicochemical quality elements are such as to support a biological community of a certain ecological status, recognising the fact that biological communities are products of their physical and chemical environment. Physicochemical and hydromophological aspects fundamentally determine the type of water body and habitat, and hence the type specific biological community. The directive does not intended that these supporting elements should be used as surrogates for the biological elements in monitoring. The monitoring and assessment of the physical and physicochemical quality elements will support the interpretation, assessment and classification of the results arising from the monitoring of the biological quality elements. This paper considers the challenges involved in the development of oxygen standards for the directive, their relationship to the biological elements and normative conditions of the directive and to regulatory requirements.  相似文献   

Archival light curves from the Bamberg Sky Patrol: CF Octantis, 1964–76     

J. L. Innis  A. P. Borisova  D. W. Coates  M. K. Tsvetkov 《Monthly notices of the Royal Astronomical Society》2004,355(2):591-600

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Potential performance of parametric communications     

Kopp  L. Cano  D. Dubois  E. Wang  L. Smith  B. Coates  R.F.W. 《Oceanic Engineering, IEEE Journal of》2000,25(3):282-295

From a designer viewpoint, a parametric array should not appear different from any other type of acoustic transducer and should be described by a limited set of design equations together with their range of validity. In this paper, these design equations are stated and discussed. They are used to optimize the acoustic parameters of an underwater communication system using parametric transduction and to evaluate its performance in terms of signal-to-noise ratio and data-rate limits as a function of transmission range. It turns out that, for a maximum data transmission rate at a given range, there is a set of optimum design parameters which is a function of the array size only. This means that, once given an operational range, the primary frequency, the electrical power, the maximum acoustic source level, and the directionality of the transducer can be deduced directly from the array diameter  相似文献