Energetic particles at high latitudes

We review work on diffusion coefficients of energetic particles with an attempt to extract implications on their behaviour at high latitudes. In the ecliptic plane results from solar energetic particle propagation between the Sun and about 5 AU can be described by an effective radial mean free path _r which is approximately constant as a function of distancer. When particle propagation in three dimensions in the heliosphere is considered it is not sufficient to consider _r only. Jovian electrons can be used as probes to determine the parameters of three-dimensional diffusion. In the polar regions diffusion is dominated by its parallel component. Some predictions how should vary with latitude are discussed. For different choices of this variation we present expectations for intensity-time profiles of solar particle events during the Ulysses polar passages.     

Coronal mass ejections at high heliographic latitudes: Ulysses

Nine coronal mass ejections (CMEs) have been detected in the solar wind by the Ulysses plasma experiment between 31° and 61° South. One of these events, which was also a magnetic cloud, was directly associated with an event observed by the soft X-ray telescope on Yohkoh in which large magnetic loops formed in the solar corona directly beneath Ulysses. This association suggests that the flux rope topology of the magnetic cloud resulted from reconnection between the legs of neighboring magnetic loops within the rising CME. The average CME speed (740 km s^–1) at these latitudes was comparable to that of the normal solar wind there and is much greater than average CME speeds observed either in the solar wind in the ecliptic plane or in the corona close to the Sun. We suggest that the same basic acceleration process applies to both slow CMEs and the normal solar wind at any latitude.     

Interplanetary type III radio bursts observed from high southern heliographic latitudes

Type III radio bursts observed from high southern latitudes are analyzed for the first time. The continual observation of these radio bursts by Ulysses from after the Jupiter swing-by to 50°S latitude argues for a wide latitudinal directivity of type III radiation. From this high latitude perspective, type III radio sources that lie in the far hemisphere of the Sun with respect to Ulysses are unambiguously resolved for the first time. Using the Ulysses direction-finding capabilities, the radio source locations in the 3-D heliosphere are derived for a radio event on 31 January 1994 when Ulysses was 45°S latitude. The source locations describe a spiral-like trajectory originating from the far side of the Sun. The angular radii of these radio sources are compared to angular radii that were previously derived from in-ecliptic observations.     

Ulysses observations of a coronal origin particle event at 32° south heliographic latitutde

A remarkable streaming beam-like particle event of 60 keV-5 MeV ions and of 38–315 keV electrons has been reported previously. This event has been associated with the passage of a Coronal Mass Ejection (CME) over the Ulysses spacecraft on June 9–13, 1993. At this time, the spacecraft was located at 4.6 AU from the sun and at an heliolatitude of 32° south. It was proposed (Armstrong et al., 1994) that the particle injection source could have been of coronal origin. In this study, we analyse the solar activity during this period. We identify a region of solar radio noise storms in the corona and in particular, a flare on June 7 that presents all the required characteristics to produce the hot plasma beam observed in the interplanetary medium.     

A summary of solar wind observations at high latitudes: Ulysses

The Ulysses mission has provided the first in-situ observations of the solar wind covering all solar latitudes from the equator to the poles in both hemispheres. The measurements from the first polar passes, made at near-minimum solar activity conditions, have confirmed the basic picture established on the basis of remote sensing techniques: the high-latitude wind is fast, and originates in the polar coronal holes. The detailed in-situ observations have, however, revealed a number of features related to the global solar wind structure that were not expected: the transition between slow and fast wind was relatively abrupt, followed by a slight increase in speed toward the poles; the mass flux is almost independent of latitude, with only a modest increase at the equator; the momentum flux is significantly higher over the poles than near the equator, suggesting a non-circular cross-section for the flanks of the heliosphere.     

The elemental composition in energetic particle events at high heliospheric latitudes

The relative abundances of low energy ions (0.6–2.0 MeV/n) in solar energetic particle (SEP) and corotating interaction region (CIR) events have been measured by the EPAC experiment aboard Ulysses since launch in October 1990 until the present time. We give an overview of the abundances of heavy ions (He, C, Ne, Fe) relative to oxygen during energetic particle events lasting longer than 5 days during the in- and out-of-ecliptic phase of the mission. While the period Oct. 1990 to Aug. 1992 was dominated by high solar activity the Ulysses out of ecliptic passage at solar latitudes up to 45° went parallel to the declining phase of solar activity. Thus a very clear structure of corotating interaction regions was observed. While the in-ecliptic composition is in general agreement with measurements made near the Earth, the development of the CIR-composition shows two phases: From Aug. 1992 to May 1993 the C/O-ratio is 0.55–0.70, afterwards it increases to 0.8–0.9. This increase is correlated to the disappearance of the current sheet at 30° solar latitude reported by Smithet al. (1993).     

Motion of the heliospheric termination shock at high heliographic latitude

We expect the mean distance of the heliospheric termination shock to be greater (smaller) at polar latitudes than at equatorial latitudes, depending on whether the mean dynamic pressure of the solar wind is greater or smaller at high latitudes. The heliospheric termination shock is expected to move in response to variation in upstream solar wind conditions, so that at any particular instant the termination shock will resemble a distorted asymmetric balloon with some parts moving inward and others moving outward. If the shock is a gasdynamic or magnetohydrodynamic shock the results of the analysis depend only very weakly on the nature of the upstream disturbance; typical speeds of the disturbed shock are 100 to 200 km/s. In the absence of a significant latitude gradient of the typical magnitude of solar wind disturbances typical motions of the disturbed shock at polar latitudes would be about twice as fast, due to the higher speed of the high-latitude wind. If the dynamics of the termination shock are dominated by acceleration of the aromalous component of the cosmic rays, the motion of the shock in response to a given disturbance is substantially slower than in the gasdynamic case. Conceivably, particle acceleration might be a less important effect at higher latitudes, and we envision the possibility of a termination shock that is dominated by particle acceleration at lower latitudes and is an MHD shock at high latitudes. In this event high latitude solar wind disturbances would produce substantially larger inward and outward motions of the shock in the polar regions.     

Ground-based ELF/VLF observations at high latitudes during passes of GEOS-1 and ISEE-1 and -2

Recordings of ELF/VLF radio signals were made, as a contribution to the International Magnetospheric Study, in Iceland (17 August to 5 September 1977) and Norway (21 October to 15 December 1977; and 11 January to 27 February 1978) by the Space Radio Physics group. The equipment used at each of three sites was a goniometer (direction finding) receiver. As an example of the results obtained, recordings of risers, occurring at a rate up to 10 min^-1 and with frequencies (1.0 to 1.5 kHz) just greater than those of simultaneous hissy chorus signals, made between 10:20 and 11:00 UT on 31 August 1977, are discussed. These risers (downcoming whistler mode signals) are shown to have well defined exit points from the ionosphere which are located, to within an uncertainty of typically ±40 km, by triangulation. The observations are broadly consistent with there being a single exit point which, on this occasion, happens to be almost on the flux tube through the geomagnetic observatory at Leirvogur. Simultaneous ground-based magnetometer observations, and also wave and energetic charged particle observations made aboard GEOS-1, have been studied. The electron spectra and pitch angle distributions are as required for the operation of the electron cyclotron instability in which whistler mode signals are amplified.     

Elemental abundances in corotating interaction regions at high solar latitudes

Throughout 1993, as the Ulysses spacecraft traveled from 23° to 45° south heliolatitude, the HI-SCALE instrument on the spacecraft measured a recurrent series of enhanced particle fluxes with a recurrence period of 26.5 days. These particles are accelerated from a background seed population by the corotating interaction regions (CIRs) associated with a southern solar polar coronal hole. Using the Wart detector telescope of the HI-SCALE instrument, we have analyzed the elemental abundances of C, N, O, and Fe relative to He for 0.5–4.0 MeV/nucl ions and Ne, Mg, and Si for 1.0–4.0 MeV/nucl ions in the CIRs. We compare the relative abundances to some previous measurements reported from 1 A.U. as well as with solar photosphere abundances. We note that HI-SCALE measurements of the heliolatitude dependence of the oxygen abundance and spectrum as reported by Lanzerottiet al. (1994) suggest that a substantial fraction of the seed population for the CIR-accelerated oxygen is likely to be the anomalous oxygen component of the cosmic rays.     

Spatial distribution and orbital properties of interplanetary dust at high latitudes

Although the interplanetary dust cloud is assumed to be mainly concentrated in the ecliptic plane, there is a component of dust particles on highly inclined orbits that forms the out-of-ecliptic distribution. The ULYSSES mission for the first time makes this component accessible to in-situ, detection. Evidence for this dust component is also provided from the analysis of the Zodiacal light brightness and especially from the spherical shape of the solar F — corona. An obvious source for an out-of-ecliptic dust population is the activity of comets on high eccentric, highly inclined orbits. We discuss the dynamical conditions of particles under the influence of the radiation pressure when released from the comet and discuss their input to the dust cloud based on brightness analysis and in-situ results.     

Recent results from satellite measurements of low-energy particles precipitated at high latitudes

Space Science Reviews -     

Energetic particle transport coefficients in the heliosphere

It is the purpose of this review to summarize and discuss recent research done in the field of particle propagation in the heliosphere. Several lines of approach have been followed to treat this problem. As a starting point the different forms of the transport equation are discussed. Quasi-Linear Theory (QLT) relates the power contained in fluctuations of the Interplanetary Magnetic Field (IMF) to the transport coefficients of energetic particles, an outline of the basic results of this theory is presented followed by a discussion of subsequent corrections made to the original formulation with an emphasis in recent developments where the effects of wave polarization, its propagation respect to the solar wind and the dissipation of power at large frequencies have been taken into account. The numerical approach using test particle trajectory integrations to obtain transport coefficients based on in situ satellite measureents is also discussed. It is well known that the determination of the particles mean free path for solar particle events by alternative methods leads to conflicting results, corrections made to original QLT are attempts to bridge the gap. Determination of the transport parameters from different lines of approach in a comparative basis have been done recently by calculating power spectra of IMF measured at the time solar particles were detected on the same spaceprobe, and performing numerical simulations with equivalent IMF data. Some of the results of such studies point to the solution of the conflicting determinations of the mean free path which has existed for nearly 30 years. An assesment of the present situation in this respect is given. Numerical determinations of transport parameters in the outer heliosphere are also reviewed and its consequences for solar modulation of galactic cosmic rays discussed. Space Science Reviews 62: Printed in Belgium.     

Energetic particle transport coefficients in the heliosphere

It is the purpose of this review to summarize and discuss recent research done in the field of particle propagation in the heliosphere. Several lines of approach have been followed to treat this problem. As a starting point the different forms of the transport equation are discussed. Quasi-Linear Theory (QLT) relates the power contained in fluctuations of the Interplanetary Magnetic Field (IMF) to the transport coefficients of energetic particles, an outline of the basic results of this theory is presented followed by a discussion of subsequent corrections made to the original formulation with an emphasis in recent developments where the effects of wave polarization, its propagation respect to the solar wind and the dissipation of power at large frequencies have been taken into account. The numerical approach using test particle trajectory integrations to obtain transport coefficients based on in situ satellite measureents is also discussed. It is well known that the determination of the particles mean free path for solar particle events by alternative methods leads to conflicting results, corrections made to original QLT are attempts to bridge the gap. Determination of the transport parameters from different lines of approach in a comparative basis have been done recently by calculating power spectra of IMF measured at the time solar particles were detected on the same spaceprobe, and performing numerical simulations with equivalent IMF data. Some of the results of such studies point to the solution of the conflicting determinations of the mean free path which has existed for nearly 30 years. An assesment of the present situation in this respect is given. Numerical determinations of transport parameters in the outer heliosphere are also reviewed and its consequences for solar modulation of galactic cosmic rays discussed. Space Science Reviews 62: Printed in Belgium.     

ATS-6 Energetic Particle Radiation Measurement at Synchronous Altitude

The Aerospace Corporation energetic electron-proton spectrometer operating on Applications Technology Satellite-6 (ATS-6) detects energetic electrons in four channels between 140 keV and greater than 32 MeV, and measures energetic protons in five energy channels between 2.3 and 80 MeV and energetic alpha particles in three channels between 9.4 and 94 MeV. After more than a year of operation in orbit, the experiment continues to return excellent data on the behavior of energetic magnetospheric electrons as well as information regarding the fluxes of solar protons and alpha particles.     

基于激光诱导荧光的高速飞行粒子低温段测温方法

针对当前高速飞行固体粒子在低温段测温困难的问题,提出了一种基于激光诱导荧光的固体测温方法来显示高速粒子飞行过程中的温度变化过程。使用掺杂罗丹明B染料的醋酸纤维粒子的600 nm荧光信号和激光的532 nm信号之比,能进一步排除激光光强波动对测温结果的干扰。对固体荧光粉末在20~80 ℃温度下的光谱学特征进行分析,研究发现:系统的荧光信号强度、温度灵敏度(80 ℃下温度系数为-0.012 5 ℃-1,20 ℃下温度系数为-0.037 9 ℃-1)、测量精度均随温度的下降显著上升,验证了该方法在低温段温度测量的应用潜力。基于该方法对高速气流下粒子撞靶的温度变化规律进行定性分析。      

机头颗粒微扰动对战斗机大迎角航向气动特性的影响研究(英文)

本文重点介绍了在机头周向角±45°处的颗粒微扰动对战斗机大迎角航向气动特性的影响进行了数值模拟研究。结果表明:在机头周向角±45°处的颗粒对大迎角下飞机的航向气动特性影响明显,能够使大迎角偏航力矩具有确定的方向。对流场结构分析发现:颗粒所在一侧脱离出明显强于没有颗粒一侧的小涡,从而在机头该侧诱导出更强的分离涡,进而导致了飞机大迎角非对称气动力的出现。     

Present status of very high energy gamma ray observations

Recent results from observations of the southern sky objects are summarized. The unpulsed, persistent very high energy (VHE) emission from the gamma ray pulsars, the Crab and PSR1706-44, is discussed. A process of energetic electrons ejection may take place from a variety of other objects such as from X-ray binaries, similarly to the pulsars. Such an effect may be seen also in pair halos around extragalactic VHE gamma ray emitters, the observational study of which is still in a preliminary stage in the southern hemisphere.     

Ariel 6 observations of Cyg X-1 in the high state

Whereas nearly all previous observations of Cyg X-1 with good time resolution have been made when the source was in its low emission state, Ariel-6 has been fortunate to observe it during 1980 June–July mainly in its high state, i.e. with enhanced low energy emission. The fluctuations were studied on all time-scales down to 2 ms and appeared similar to those previously reported for the low state. The cross-correlation of rapid fluctuations between two bands above and below 3.5 keV however showed a small but significant asymmetry with the high energy emission delayed.