Cerenkov emission of quasiparallel whistlers by fast electron phase-space holes during magnetic reconnection.

Kinetic simulations of magnetotail reconnection have revealed electromagnetic whistlers originating near the exhaust boundary and propagating into the inflow region. The whistler production mechanism is not a linear instability, but rather is Cerenkov emission of almost parallel whistlers from localized moving clumps of charge (finite-size quasiparticles) associated with nonlinear coherent electron phase space holes. Whistlers are strongly excited by holes without ever growing exponentially. In the simulation the whistlers are emitted in the source region from holes that accelerate down the magnetic separatrix towards the x line. The phase velocity of the whistlers vφ in the source region is everywhere well matched to the hole velocity vH as required by the Cerenkov condition. The simulation shows emission is most efficient near the theoretical maximum vφ=half the electron Alfven speed, consistent with the new theoretical prediction that faster holes radiate more efficiently. While transferring energy to whistlers the holes lose coherence and dissipate over a few local ion inertial lengths. The whistlers, however, propagate to the x line and out over many 10's of ion inertial lengths into the inflow region of reconnection. As the whistlers pass near the x line they modulate the rate at which magnetic field lines reconnect.

A magnetic reconnection X-line extending more than 390 Earth radii in the solar wind.

Magnetic reconnection in a current sheet converts magnetic energy into particle energy, a process that is important in many laboratory, space and astrophysical contexts. It is not known at present whether reconnection is fundamentally a process that can occur over an extended region in space or whether it is patchy and unpredictable in nature. Frequent reports of small-scale flux ropes and flow channels associated with reconnection in the Earth's magnetosphere raise the possibility that reconnection is intrinsically patchy, with each reconnection X-line (the line along which oppositely directed magnetic field lines reconnect) extending at most a few Earth radii (R(E)), even though the associated current sheets span many tens or hundreds of R(E). Here we report three-spacecraft observations of accelerated flow associated with reconnection in a current sheet embedded in the solar wind flow, where the reconnection X-line extended at least 390R(E) (or 2.5 x 10(6) km). Observations of this and 27 similar events imply that reconnection is fundamentally a large-scale process. Patchy reconnection observed in the Earth's magnetosphere is therefore likely to be a geophysical effect associated with fluctuating boundary conditions, rather than a fundamental property of reconnection. Our observations also reveal, surprisingly, that reconnection can operate in a quasi-steady-state manner even when undriven by the external flow.

Composition and dynamics of plasma in Saturn's magnetosphere.

During Cassini's initial orbit, we observed a dynamic magnetosphere composed primarily of a complex mixture of water-derived atomic and molecular ions. We have identified four distinct regions characterized by differences in both bulk plasma properties and ion composition. Protons are the dominant species outside about 9 RS (where RS is the radial distance from the center of Saturn), whereas inside, the plasma consists primarily of a corotating comet-like mix of water-derived ions with approximately 3% N+. Over the A and B rings, we found an ionosphere in which O2+ and O+ are dominant, which suggests the possible existence of a layer of O2 gas similar to the atmospheres of Europa and Ganymede.

Ulysses solar wind plasma observations at high southerly latitudes.

Solar wind plasma observations made by the Ulysses spacecraft through -80.2 degrees solar latitude and continuing equatorward to -40.1 degrees are summarized. Recurrent high-speed streams and corotating interaction regions dominated at middle latitudes. The speed of the solar wind was typically 700 to 800 kilometers per second poleward of -35 degrees . Corotating reverse shocks persisted farther south than did forward shocks because of the tilt of the heliomagnetic streamer belt. Sporadic coronal mass ejections were seen as far south as -60.5 degrees . Proton temperature was higher and the electron strahl was broader at higher latitudes. The high-latitude wind contained compressional, pressure-balanced, and Alfvénic structures.

Jupiter's Magnetosphere: Plasma Description from the Ulysses Flyby.

Plasma observations at Jupiter show that the outer regions of the Jovian magnetosphere are remarkably similar to those of Earth. Bow-shock precursor electrons and ions were detected in the upstream solar wind, as at Earth. Plasma changes across the bow shock and properties of the magnetosheath electrons were much like those at Earth, indicating that similar processes are operating. A boundary layer populated by a varying mixture of solar wind and magnetospheric plasmas was found inside the magnetopause, again as at Earth. In the middle magnetosphere, large electron density excursions were detected with a 10-hour periodicity as planetary rotation carried the tilted plasma sheet past Ulysses. Deep in the magnetosphere, Ulysses crossed a region, tentatively described as magnetically connected to the Jovian polar cap on one end and to the interplanetary magnetic field on the other. In the inner magnetosphere and lo torus, where corotation plays a dominant role, measurements could not be made because of extreme background rates from penetrating radiation belt particles.

Linear electric field mass analysis: a technique for three-dimensional high mass resolution space plasma composition measurements.

A revolutionary type of three-dimensional space plasma composition analyzer has been developed that combines very high-resolution mass composition measurements on a fraction of the incident ions simultaneously with lower mass resolution but high sensitivity measurements of the remaining population in a single compact and robust sensor design. Whereas the lower mass resolution measurements are achieved using conventional energy/charge (E/q) and linear time-of-flight analysis, the high mass resolution measurements are made by timing reflected E/q analyzed ions in a linear electric field (LEF). In a LEF the restoring (reflecting) force that an ion experiences in the direction parallel to the field is proportional to the depth it travels into the LEF region, and its equation of motion in that direction is that of a simple harmonic oscillator. Consequently, an ion's travel time is independent of its initial angle and energy and is simply proportional to the square root of the ion's mass/charge (m/q). The measured m/q resolution, (m/q)/Delta(m/q), for a small LEF-based prototype that we have developed and tested is approximately 20. In addition, our laboratory measurements with the prototype instrument show that characteristic time-of-flight spectra allow the resolution of atomic and molecular species with nearly identical m/q values. The measured response of the prototype is in excellent agreement with computer simulations of the device. Advanced design work using this computer simulation indicates that three-dimensional plasma composition analyzers with m/q resolutions of at least 50 are readily achievable.

Comet giacobini-zinner: plasma description.

A strong interaction between the solar wind and comet Giacobini-Zinner was observed oh 11 September 1985 with the Los Alamos plasma electron experiment on the International Cometary Explorer (ICE) spacecraft. As ICE approached an intercept point 7800 kilometers behind the nucleus from the south and receded to the north, upstream phenomena due to the comet were observed. Periods of enhanced electron heat flux from the comet as well as almost continuous electron density fluctuations were measured. These effects are related to the strong electron heating observed in the cometary interaction region and to cometary ion pickup by the solar wind, respectively. No evidence for a conventional bow shock was found as ICE entered and exited the regions of strongest interaction of the solar wind with the cometary environment. The outer extent of this strong interaction zone was a transition region in which the solar wind plasma was heated, compressed, and slowed. Inside the inner boundary of the transition region was a sheath that enclosed a cold intermediate coma. In the transition region and sheath, small-scale enhancements in density were observed. These density spikes may be due to an instability associated with cometary ion pickup or to the passage of ICE through cometary ray structures. In the center of the cold intermediate coma a narrow, high-density core of plasma, presumably the developing plasma tail was found. In some ways this tail can be compared to the plasma sheet in Earth's magnetotail and to the current sheet in the tail at Venus. This type of configuration is expected in the double-lobe magnetic topology detected at the comet, possibly caused by the theoretically expected draping of the interplanetary magnetic field around its ionosphere.

Information systems for general practitioners for quality assessment: III. Suggested new prescribing profile.

The information that is supplied to general practitioners by the Prescription Pricing Authority and family practitioner committees has severe limitations if used for self audit of prescribing. We studied the demand for and the extent to which general practitioners would collaborate in developing a system for providing more pertinent information about patterns of personal and practice prescribing. One hundred and eighty two doctors (36% of respondents to a questionnaire) who wished to learn more about their repeat prescribing were invited to help to generate this information and to create profiles of their personal prescribing rates based on a denominator of doctor-patient contacts. Nearly all of them translated intention into participation and also recruited 28 more doctors, since all partners in a practice had to take part. Overall, 202 doctors (40%) took part, 83% of whom participated in the combined study of repeat prescribing and rate of prescribing and 17% in the repeat prescribing exercise only. The examples of the new profiles that are provided show a more accurate representation of personal and practice prescribing patterns, differentiate between face to face contacts and repeat prescriptions, and are likely to stimulate improvements in personal or practice prescribing. We believe that this system should be offered to all practices in the United Kingdom.

Information systems for general practitioners for quality assessment: I. Responses of the doctors.

A questionnaire was sent to all general practitioner principals in Leicestershire and Lincolnshire (n = 669) to determine (a) the extent to which they would participate in quality assessment activities based on objective evidence of performance and (b) the personal and professional characteristics of interested doctors. The overall response rate to the questionnaire was 76% (508 replies). The highest response rates were recorded by trainers (100%), principals in training practices (94%), and younger doctors (80-86%), the lowest by overseas graduates (59%) and older doctors (65%). Distinctive patterns of interest and participation in three types of audit activities were clearly evident. Overall, 61% (310) of respondents wished to be provided with profiles of practice activity from their family practitioner committees, 36% (183) volunteered to participate in a prescribing study, and 34% (172) expressed interest in carrying out an audit in depth. Proportionately, the most enthusiastic and active groups were trainers 88%, 70%, 62%), principals in training practices (74%, 49%, 47%), and members or fellows of the Royal College of General Practitioners (71%, 50%, 45%). Also active were younger doctors, vocationally trained doctors, and principals in large group practices. These figures suggest that roughly 15 000 general practitioners in the United Kingdom would be prepared to participate in performance review activities using information provided by external agencies, 10 000 would if they had to generate some of the information, and 7500 would if they had to produce all the information themselves.

Information systems for general practitioners for quality assessment: II. Information preferences of the doctors.

In this part of the study we intended to determine (a) the extent to which currently supplied information was used by general practitioners to assess their performance and (b) the preferences of the doctors for new information. Four aspects of professional activity were investigated: prescribing, practice activity as shown by family practitioner committee quarterly returns, hospital use, and audit in depth. The results are from 508(76%) questionnaires returned from the 669 general practitioners circulated in Leicestershire and Lincolnshire. The prescribing habits of most doctors are influenced both by factual information about drugs from many sources and by feedback on their personal prescribing or that of their practice, which is supplied by the Prescription Pricing Authority, particularly regarding prescribing costs. Little use is made of data from the family practitioner committee. A distinct pattern of preferences for particular items of information emerged. Most doctors wished to receive information that would enable them to compare their personal performance or that of their practice with their local colleagues from the Prescription Pricing Authority (66%), the family practitioner committee (58%), and hospital sources (57%). Because doctors chose particular items of information that they would like to have, systems that are developed to provide such information are likely to be used. The need to incorporate comparison with peers is particularly important.

Effects of a long entrance aperture upon the azimuthal response of spherical section electrostatic analyzers.

The transmission characteristics of spherical section electrostatic analyzers with long entrance apertures have been studied. The presence of a long entrance aperture appreciably broadens the normally narrow azimuthal response of such analyzers at large incident polar angles. A technique for calculating the transmission at any polar angle is presented. Calculated azimuthal response curves at polar angles of 0 degrees , 25 degrees , and 50 degrees agree well with laboratory measurements for a 90 degrees section analyzer. In the limit of zero polar angle, our calculations reveal that a previously derived and widely used analytical expression for the integrated energy-angle response underestimates that response by 12%-25% depending upon the analyzer bending angle. An analytical expression that better approximates the true response is presented.

Radiance calibration of the High Altitude Observatory white-light coronagraph on Skylab.

The High Altitude Observatory coronagraph produced over 35,000 photographs of the solar corona over 9 mo. Images were obtained on Kodak special film type 026-02, a 3400 (Pan-X) emulsion modified by Kodak for minimal reciprocity losses at the exposure times (3 sec, 9 sec, 27 sec) used on the coronagraph. The film was processed in a specially developed chemistry to obtain the best compromise between speed, low fog, and modulation transfer function. The calibration of a nineteen-step wedge within the coronagraph is based on previously calibrated glass opal filters. The step wedge, illuminated by attenuated sunlight, is imaged on each photograph made by the instrument. Data reduction procedures employ average characteristic curves for each data set (approximately 4000 frames). It is found that the effects of radiation fog and latent image loss are negligible within these sets. The relative coronal radiance error, determined by measuring the coronal plus stray light radiance over the solar pole, is found to be le s than 8%. Based on an estimated error of 15% in the absolute calibration of the step wedge, the net absolute accuracy of a given radiance measurement is estimated to be 20%.