Recent space shuttle observations of the South Atlantic Anomaly and the radiation belt models.

Active instruments consisting of a tissue equivalent proportional counter (TEPC) and a proton and heavy ion detector (PHIDE) have been carried on a number of Space Shuttle flights. These instruments have allowed us to map out parts of the South Atlantic Particle Anomaly (SAA) and to compare some of its features with predictions of the AP-8 energetic proton flux models. We have observed that consistent with the generally observed westward drift of the surface features of the terrestrial magnetic field the SAA has moved west by about 6.9 degrees longitude between the epoch year 1970 of the AP-8 solar maximum model and the Space Shuttle observations made twenty years later. However, calculations indicate that except for relatively brief periods following very large magnetic storms the SAA seems to occupy the same position in L-space as in 1970. After the great storm of 24 March 1991 reconfiguration of the inner radiation belt and/or proton injection into the inner belt, a second energetic proton belt was observed to form at L approximately = 2. As confirmed by a subsequent flight observations, this belt was shown to persist at least for six months. Our measurements also indicate an upward shift in the L location of the primary belt from L = 1.4 to L = 1.5. In addition we confirm through direct real time observations the existence and the approximate magnitude of the East-West effect.     

Solar particle dynamics during magnetic storms of July 23–27, 2004

It is a case study of a chain of three magnetic storms with a special attention to the particle dynamics based on CORONAS-F and SERVIS-1 low altitude satellite measurements. Solar proton penetration inside the polar cap and inner magnetosphere and dynamics at different phases of the magnetic storms was studied. We found, that solar protons were captured to the inner radiation belt at the recovery phase of the first and the second magnetic storms and additionally accelerated during the last one. No evidence of sudden commencement (SC) particle injection was found. Enhanced solar proton belt intensity with small pitch angles decreased slowly during satellite orbits for 30 days until the next magnetic storm. Then in 20–30 h we registered strong precipitation of these protons followed by the trapped proton flux dropout. Intensity decrease was more pronounced at lower altitudes and higher particle energies.     

Near-Earth radiation model deficiencies as seen on CRRES.

The Space Radiation (SPACERAD) experiments on the Combined Release and Radiation Effects Satellite (CRRES) gathered 14 months of radiation particle data in an 18 degrees inclination orbit between 350 km and 36000 km from July 1990 to October 1991. When compared to the NASA radiation belt models AP8 and AE8, the data show the proton model (AP8) does not take into account a second belt formed after major solar flare/shock injection events, and the electron model (AE8) is misleading, at best, in calculating dose in near-Earth orbits. The second proton belt, although softer in energy than the main proton belt, can produce upsets in proton sensitive chips and would produce significant dose in satellites orbiting in it. The MeV electrons observed on CRRES show a significant particle population above 5 MeV (not in the AE8 model) which must be included in any meaningful dose predictions for satellites operating between L-shells of 1.7 and 3.0 RE.     

Direct comparison of transient radiation belt topology and dynamics in 1991 based on measurements onboard Mir space station and NOAA satellite.

In March 1991 the CRRES spacecraft measured a new transient radiation belt resulting from a solar proton event and subsequent geomagnetic disturbance. The presence of this belt was also noted by dosimeter-radiometers aboard the Mir space station (approx. 400 km, 51 degrees orbit) and by particle telescopes on the NOAA-10 spacecraft (850 km, 98 degrees). This event provides a unique opportunity to compare particle flux and dose measurements made by different instruments in different orbits under changing conditions. We present here a comparison of the measurements made by the different detectors. We discuss the topology and dynamics of the transient radiation belt over a period of more than one year.     

Description, analysis and impact of major solar activity during recent U.S. Shuttle missions.

Since STS-26, three large solar events have occurred during Shuttle missions; a geomagnetic storm during STS-29 and solar particle events (SPEs) during STS-28 and -34. The maximum dose to a crew attributed to an SPE was estimated to be 30 microGy (70 microSv). Time-resolved dosimetry measurements of the SPE dose during STS-28 were made using the Air Force Radiation Monitoring Equipment (RME)-III. Comparison of calculated and measured dose demonstrated a discrepancy, possibly a result of deficiencies in the geomagnetic cutoff model used. This experience demonstrates that dose from an SPE is strongly dependent on numerous factors such as orbit inclination, SPE start time, spectral parameters and geomagnetic field conditions; the exact combination of these factors is fortuitous. New sources of data and procedures are being investigated, including real-time tracking of auroral oval positions or determination of particle cutoff latitudes, for incorporation into operational Shuttle radiation support practices.     

Comment on estimating the solar proton environment that may affect Mars missions.

Estimates of the energetic proton environment for a Mars mission are generally extrapolated from the solar proton observations at 1 AU. We find that solar particle events may be divided into two general classes. Events dominated by a near-sun injection of particles onto interplanetary magnetic field lines leading to the spacecraft position represent the "classical" solar particle event associated with solar activity. This class of event will scale in radial distance by the classical power law extrapolation. The extended-interplanetary-shock source generates a maximum flux as the shock passes the detection location. This class of event typically generates maximum fluence, but in this case, the flux and fluence will not scale in the classical manner with radial distance.     

Anatomical models for space radiation applications: an overview.

Extremely detailed computerized anatomical male (CAM) and female (CAF) models that have been developed for use in space radiation analyses are discussed and reviewed. Recognizing that the level of detail may currently be inadequate for certain radiological applications, one of the purposes of this paper is to elicit specific model improvements or requirements from the scientific user-community. Methods and rationale are presented which describe the approach used in the Space Shuttle program to extrapolate dosimetry measurements (skin doses) to realistic astronaut body organ doses. Several mission scenarios are presented which demonstrate the utility of the anatomical models for obtaining specific body organ exposure estimates and can be used for establishing cancer morbidity and mortality risk assessments. These exposure estimates are based on the trapped Van Allen belt and galactic cosmic radiation environment models and data from the major historical solar particle events.     

The natural background at shuttle altitudes

Optical measurements made from the Space Shuttle include several sources of emission, each modified according to viewing configuration, Shuttle altitude, solar activity, local time, and latitude. These sources include the atmospheric emissions and emissions of non-terrestrial origin (such as stellar, interstellar, and interplanetary), together with any contamination emission induced by the Shuttle itself. In order to make astronomical observations from the Shuttle, the observer needs good information on the intensities and spectral characteristics of these various sources. In this paper we present a model spectrum for one of these components, the natural airglow background. The spectrum is modeled over a wavelength range extending from the extreme ultraviolet to the near infrared. This model is based on our present knowledge of the upper atmosphere. The effect of different viewing configurations is illustrated, together with day to night variations. The results synthesized here assume an ideal vehicle in the sense that no contaminant emissions are induced by the Shuttle and payload. These spectra therefore represent a baseline which can be used to locate unanticipated or non-ambient features.     

Trapped particle energy spectrum in shuttle middeck

We describe the differential energy spectrum of trapped particles measured by a solid-state charged particle telescope in the mid-deck of the Space Shuttle during the period of solar maximum. The telescope was flown in two high altitude flights at 28.5° and 57° inclination. Assuming, as is normally done, that the variations of Shuttle orientation during the missions lead to average isotropic incident spectra, the observed spectrum disagrees significantly from AP8 model calculations. This indicates the need to take into consideration the variations of solid-angle direction relative to the magnetic field. The measurements show that there is a very significant flux of secondary light ions. The energy spectra of these ions does not agree with the production spectrum from radiation transport calculations based on omni-directional AP8 Max model as an input energy spectrum.

We also describe measurements of linear energy transfer spectra using a tissue equivalent proportional counter (TEPC) flown both in the mid-deck and the payload bay of the Space Shuttle. Comparisons are made between linear energy transfer spectral measurements AP8 model-based radiation transport predictions, and thermoluminescent dosimeter (TLD) measurements. The absorbed dose-rate measurements using TLD's are roughly 25% lower than the TEPC-measured dose rate measurements.     

A study of the ground level enhancement of 23 February 1956

One of the greatest and most famous increase of solar cosmic rays over the neutron monitor epoch is the ground level enhancement in 1956. All future proton events are inevitable when compared with this one and therefore it is necessary to provide the efficiency of such a comparison derived from the existing data. In this paper, we return to the analysis of ground level observations on 23 February 1956 in order to model more precisely the solar cosmic ray behaviour. The extremely high magnitude of this effect allowed various spectral characteristics of solar cosmic rays, their anisotropy, differential and integral proton fluxes, and angular distribution of the source of solar particle anisotropy to be obtained with sufficient accuracy on the basis of available data from 13 neutron monitors. The most outstanding feature of this event was a narrow and extremely intensive beam of ultra relativistic particles arriving at Earth at the beginning of the event. This unique beam was not long and its width did not exceed 30–40°, thus, its contribution to solar particle density was not significant. Many features of this GLE are apparently explained by the peculiarity of particle interplanetary propagation from a remote (limb or behind of limb) source.     

Solar particle events as seen on CRRES.

High energy proton detectors on the Combined Release and Radiation Effects Satellite (CRRES) were used to measure near-Earth solar protons in an 18 degrees inclination orbit between 350 km and 36000 km from July 1990 to October 1991. CRRES data from the major solar particle event on 23-25 March 1991 show conclusively that MeV solar protons can penetrate deep inside the magnetosphere (to an L-shell of 2.5 RE) when a large shock-induced Sudden Storm Commencement (SSC) occurs and significant solar particle populations are present at geosynchronous altitudes. The penetration of solar particles well inside boundaries predicted by Stormer theory occurred during every large solar event of the CRRES mission, as well as many of the smaller ones. Often the deep penetrations occurred simultaneously with the formation of new trapped radiation populations which peak at L-values between 2.3 and 4 RE (depending on particle energy) and which last from days to months.     

Unexpected burst of solar activity recorded by neutron monitors during October–November 2003

During the extreme burst of solar activity in October–November 2003, a series of outstanding events distinguished by their magnitude and peculiarities were recorded by the ground based neutron monitor network. The biggest and most productive in 23rd solar cycle active region 486 generated the most significant series of solar flares among of which the flare X28/3B on November 4, 2003 was the mostly powerful over the history of X-ray solar observations. The fastest arrival of the interplanetary disturbance from the Sun after the flare event in August 1972 and the highest solar wind velocity and IMF intensity were observed during these events. In one-week period three ground level enhancements (GLEs) of solar cosmic rays were recorded by neutron monitor network (28, 29 October and 2 November 2003). Maximum proton energy in these events seems to be ranged from 5 to 10 GeV. Joint analysis of data from ground level stations (neutron monitors) and satellite measurements allows the estimation of the particle path length, the onset time of the injection on the Sun and some other proton flux characteristics.     

Evaluation of solar proton spectra using balloon cosmic ray observations and Monte Carlo simulation results

We have developed a method to evaluate the spectrum of solar energetic protons at the top of the Earth’s atmosphere from the measurements of our balloon cosmic ray experiment. By using the Monte Carlo PLANETOCOSMICS code based on Geant4 we compute the interaction of solar protons [10 MeV–10 GeV] with the Earth’s atmosphere. We obtain the angular and energy distributions of secondary particles (p, e⁻, e⁺, photons, muons) at different atmospheric levels as a function of primary proton spectra. By comparing the calculated depth dependence of the particle flux with the data obtained by our balloon experiment we can deduce the parameters of the solar proton spectrum that best fit the observations. In this paper we discuss our solar proton spectrum estimation method, and present results of its application to selected solar proton events from 2001 to 2005.     

Relativistic solar protons in the ground level event of 23 February 1956: New study

In this study we applied again to the outstanding solar particle event of 23 February 1956, the largest one in the entire history of observations of solar cosmic rays. Due to significant improvement of the analysis/modeling techniques and new understanding of physical processes in the solar atmosphere and interplanetary space, a possibility arises to interpret the old data in the light of modern concept of multiple particle acceleration at/near the Sun. In our new analysis the data of available then neutron monitors and muon telescopes are used. The technique of the analysis includes: (a) calculation of asymptotic cones of ground-based detectors; (b) modeling of cosmic ray detector responses at variable parameters of the flux of solar relativistic protons; (c) determination of primary solar proton parameters outside magnetosphere by comparison of computed responses with observations. Certain evidence was obtained that the flux of relativistic solar protons consisted of two distinct components: prompt and delayed ones. The prompt component with exponential energy spectrum caused a giant impulse-like increase at a number of European cosmic ray stations. The delayed component had a power-law spectrum and was a cause of gradual increase at cosmic ray stations in the North American region. A numerical simulation of the proton acceleration in the vicinity of the magnetic reconnection region brings to the proton spectrum with exponential dependence on energy. This agrees with observational data for the prompt component. It is also shown that the huge increase in ∼5000% on neutron monitors was due to the prompt component only with the exponential proton spectrum. The power-law spectrum of comparable intensity gave considerably smaller effect.     

The features of radiation dose variations onboard ISS and Mir space station: comparative study.

The dynamics of the ISS-measured radiation dose variations since August 2000 is studied. Use is made of the data obtained with the R-16 instrument, which consists of two ionization chambers behind different shielding thicknesses. The doses recorded during solar energetic particle (SEP) events are compared with the data obtained also by R-16 on Mir space station. The SEP events in the solar maximum of the current cycle make a much smaller contribution to the radiation dose compared with the October 1989 event recorded on Mir space station. In the latter event, the proton intensity was peaking during a strong magnetic storm. The storm-time effect of solar proton geomagnetic cutoff decreases on dose variations is estimated. The dose variations on Mir space stations due to formation of a new radiation belt of high-energy protons and electrons during a sudden commencement of March 24, 1991 storm are also studied. It was for the first time throughout the ISS and Mir dose measurement period that the counting rates recorded by both R-16 channels on ISS in 2001-2002 were nearly the same during some time intervals. This effect may arise from the decreases of relativistic electron fluxes in the outer radiation belt.     

Galactic cosmic radiation model and its applications.

A model for the differential energy spectra of galactic cosmic radiation as a function of solar activity is described. It is based on the standard diffusion-convection theory of solar modulation. Estimates of the modulation potential based on fitting this theory to observed spectral measurements from 1954 to 1989 are correlated to the Climax neutron counting rates and to the sunspot numbers at earlier times taking into account the polarity of the interplanetary magnetic field at the time of observations. These regression lines then provide a method for predicting the modulation at later times. The results of this model are quantitatively compared to a similar Moscow State University (MSU) model. These model cosmic ray spectra are used to predict the linear energy transfer spectra, differential energy spectra of light (charge < or = 2) ions, and single event upset rates in memory devices. These calculations are compared to observations made aboard the Space Shuttle.     

The particle environment on-orbit: Observations,calculations, and implications

The full potential for making remote observations from space free from atmospheric attenuations and distortions may not be realized due to the residual environment surrounding orbital experiments: particulates could overwhelm or severely complicate remote astronomical or atmospheric sounding observations. Small particles are lifted into space by the observatory and its carrier and take considerable time to evolve from surfaces. Single near-field particles have been observed which produce irradiance levels larger than the brightest stars and brighter than the emission from the entire earth limb airglow layer.The existing data bases are reviewed including: 1) the low light level camera videotape data of STS-3 in which large persistent particles were observed; 2) the data from the stereo cameras which were part of the Induced Environmental Contamination Monitor pallet assembled by NASA Marshall - which is being analyzed to obtain particle number densities, trajectories, and decay times; and 3) data from the Particle Analysis Camera for Shuttle which was part of the HITCHHIKER pallet on a January 1986 Mission is current being analyzed to obtain decay rates and correlations with orbital activities. The implications for several other data bases such as the Infrared Telescope is also described.The analysis of these spectrally broad band observations is further complicated by the nature of the particle's scattering of light. Depending on wavelength and particle size, the scattering of solar radiation or earth radiation, or particle self emission will dominate the optical signature. The scattering and emission from particulates will likely be highly structured as a function of wavelength. We present Mie scattering calculations for particle size distributions observed on-orbit. Finally, we assess the consequences of the observations and calculations on future space-based observations.     

太阳周期活动对低高度内辐射带高能质子的影响

利用NOAA-15卫星1998年到2011年近13年的高能质子全向通量观测资料, 分析了一个太阳活动周内, 低高度内辐射带高能质子通量的分布变化特性及其物理原因, 比较了观测结果与AP8模型的不同. 研究表明, 低高度内辐射带高能质子通量与太阳活动水平的反相关关系与磁壳参数L值及磁场B值有关; L值越低, B值越大的空间点, 其高能质子通量与太阳活动水平的反向相关性越明显. 高能质子通量随太阳活动水平的变化存在明显滞后现象, L值越高、 B值越小的空间点, 滞后现象就越明显, 滞后严重时可以达到一年左右的时间; 这种滞后现象反映出低高度内辐射带高能质子的源与损失达到平衡是一个中长期过程. 通过与AP8模型计算结果的比较分析可以看出, 利用AP8模型时, 仅考虑地磁场长期变化对质子通量的影响可能会夸大低高度内辐射带局部高能质子通量的增强.      

Plasma interactions in the space shuttle orbiter environment

Attempts to measure the ambient ionospheric plasma environment in the vicinity of the payload bay of the Space Shuttle Orbiter have shown that the plasma is quite different, in a variety of characteristics, from the ionospheric plasma at low earth orbit altitudes. It appears that the large size, complex geometry and various outgassing characteristics of a typical Orbiter payload can all contribute to modifications of the plasma environment of the Space Shuttle Orbiter. The measurements indicate that the plasma is often quite turbulent and contains populations more energetic than the ambient ionospheric plasma. Pronounced wake and ram effects have been observed, and at times the data can be interpreted as plasma number density enhancements of an order of magnitude or greater over the ambient, undisturbed plasma concentration. There is evidence that this enhanced plasma concentration contains molecular ions, not occurring naturally at low earth orbit altitudes. In addition to describing the observations, the electrodynamics of enhanced Orbiter-generated plasma and its possible impact on optical measurements from the Space Shuttle Orbiter will be discussed.     

一个基于观测的太阳风背景模型

建立由太阳光球磁场和日冕偏振亮度等观测约束的单流体太阳风模型,包括日冕和太阳风的等离子体密度、速度和磁场,温度还有待于以后处理.这里采用高山观测台(HAO)MKⅢ的日冕偏振亮度(pB)在1.36Rs上的观测概图,根据Guhathakurta在1996年发展的日冕电子密度反演模型确定日冕的电子密度分布.同时采用Wilcox太阳观测台(WSO)的光球磁场视向分量的观测概图作为底部边界,根据Zhao等在1994年发展的水平电流-电流片(HCCS)模型得到全球磁场.Phillips在1995年及McComas在2003年分别用Ulysses第一次和第二次跨极飞行的观测发现,归一化到1 AU的太阳风动量流密度除了在10°～30°的纬度范围内略低以外几乎不变.根据这一结论,结合已经得到的密度数据,就可以得到日冕和太阳风的速度.将上面的模型应用于1918卡林顿自转周稳态太阳风的研究,结果与太阳活动极小期的观测基本相符,但是与观测相比较低速高密度区偏大,因此密度模型还有待改进.