Fundamental Technologies

Interplanetary Monitoring Platform:
Charged Particle Measurement Experiment

Selected Recent Publications
Co-Authored by Fundamental Technologies Personnel

Solar Cycle Variations in Solar and Interplanetary Ions Observed with IMP8, K. D. C. Simunac and T. P. Armstrong, Journal of Geophysical Research, 109, A10101, doi: 10.1029/2003JA010194, 2004. Journal abstract with link to full article.

  Abstract (draft). Energetic protons (0.39 to 440 MeV), alpha particles (0.59 to 52 MeV/nucleon), and medium nuclei (Carbon, Nitrogen, and Oxygen, 0.7 to 8.8 MeV/nucleon) have been observed with the Charged Particle Measurement Experiment (CPME) aboard the IMP 8 spacecraft from 1973 to the present. We summarize the results obtained for the period October 1973 through November 2000, more than two complete solar cycles. We believe that these observations of solar and interplanetary particles are the longest set from a single instrument yet obtained. Artifacts have been carefully removed from this data set, including background changes due to the failure in 1989 of an electronic anti-coincidence shield. We have computed averages over individual solar cycles as well as “grand” averages of everything seen over the 27 year period. The “grand” average energy spectrum of protons, alphas, and medium nuclei is well described by a power law function in total energy with exponent -2 where E is in units of MeV total energy and flux is particles/(cm2 sec sr MeV). Compositional abundance ratios for energetic nuclei at the same speeds are calculated for times of minimum (H/He=30; He/Medium=95) and maximum (H/He=61; He/Medium=45) solar activity. We also considered possible relationships between sunspot number and interplanetary particle flux using a variety of averaging intervals and time lags and leads, but found no result that could be used to predict particle fluxes from sunspot numbers over short intervals (typically several solar rotations).

Correlation of Solar Energetic Protons and Polar Cap Absorption, J. D. Patterson, T. P. Armstrong, C. M. Laird, D. L. Detrick, and A. T. Weatherwax, Journal of Geophysical Research, 106, 149, 2001. Journal abstract with link to full article.

  Abstract (draft). This study shows the results of a model of polar cap absorption events (PCAs) using solar energetic proton flux as an input. The proton data are recorded by the Charged Particle Measurement Experiment (CPME) on board the IMP 8 satellite and are collected by the Applied Physics Laboratory at Johns Hopkins University. The IMP 8 satellite orbits the Earth at distances between 30 and 35 Earth radii, which places it in the solar energetic particle environment throughout most of its orbit. It has been shown in previous studies that these solar energetic particles have direct and immediate access to the polar atmosphere (Reid, 1970). Our model shows that the majority of the ionization resulting from the influx of solar energetic protons occurs in the altitude range from ~50-90 km. Excess ionization at these altitudes causes enhanced absorption of cosmic HF radio waves. The levels of absorption used for comparison in this study were measured directly by the riometer at South Pole Station, Antarctica. The results show a very strong correlation between the incident proton flux and measured path-integrated cosmic HF radio noise absorption for significant events, involving absorptions greater than 1.0 dB. For absorption levels lower than this, it is obvious that other phenomena dominate. For HF radio waves the primary contributors to PCA are protons with energies near 20 MeV. This study extends the correlated observations of interplanetary particles and PCA throughout a 9-year period. The close quantitative agreement between the measured and calculated values of absorption supports the validity of the assumptions and suppositions made by this model. The data also suggest a method by which the path-integrated cosmic noise absorption may be used to probe the E and D layers of the ionosphere to determine the effective ion-electron recombination coefficients within these regions.

(Reference: Reid, G. C., in Intercorrelated Satellite Observations Related to Solar Events, p. 319, D. Reidel, 1970.)

Major Solar Proton Events Observed by IMP-8 (from November 1973 to May 2001), D. Lario, R. B. Decker, and T. P. Armstrong, Proceedings ICRC 2001, pp. 1-4, 2001.

  Abstract (draft). The unprecedented long and still ongoing mission of the IMP 8 spacecraft has generated a uniform and nearly time-continuous data base of energetic particle events for the last two solar cycles and the rising phase of the solar cycle 23. In this paper we use energetic proton (0.3-440 MeV) intensities from the CPME instrument in order to select the major solar energetic proton (SEP) events observed during this long-term period (November 1973 - March 2001). We examine their time-intensity profiles and their temporal distribution within the sunspot solar cycles. We compare the two recent large SEP events observed so far in solar cycle 23 (i.e., the Bastille Day 2000 event and the November 9, 2000, event) with the other major SEP events observed over the last two solar cycles. These two events show by far the most intense SEP fluxes ever observed by IMP 8. The study of these observations will help us to determine how intense a SEP event can be.

Computed Contributions to Odd Nitrogen Concentrations in the Earth's Polar Middle Atmosphere by Energetic Charged Particles, F. M. Vitt, T. P. Armstrong, T. E. Cravens, G. A. M. Dreschhoff, C. H. Jackman, and C. M. Laird, J. Atmospheric and Solar Terrestrial Physics, 62, 669, 2000. Journal abstract with link to full article.

  Abstract (draft).  A two-dimensional photochemical transport model which has inputs that characterize the odd nitrogen production associated with galactic cosmic rays, solar particle events (SPEs), and lower thermospheric contributions (auroral electrons and solar EUV and soft X-rays) is used to compute odd nitrogen concentrations in the polar middle atmosphere from 1 January 1970 to 31 December 1994.  We are able to separate out of the total odd nitrogen budget the contributions of the energetic charged particles according to type. The SPE contributions to annual average odd nitrogen concentrations in the polar stratosphere (latitudes >50 deg) are computed to be significant (>10%) only for the larger events of  August 1972 and October 1989. The SPE contributions to odd nitrogen concentrations in the polar middle atmosphere are found to be asymmetric with respect to hemispheres. The computed SPE contributions to odd nitrogen concentrations at 30 km are significant more often over the South Pole than the North Pole. The thermospheric contributions to odd nitrogen concentrations in the polar middle atmosphere are asymmetric with respect to hemispheres. A stronger thermospheric influence in the stratosphere is computed over the South Pole than the North Pole. An attempt has been made to compare the modeled odd nitrogen of the polar middle atmosphere to an ultra-high resolution polar ice cap nitrate sequence to examine the hypothesis that the nitrate sequences exhibit a signal associated with energetic particles. Variations of odd nitrogen production and modeled concentrations associated with energetic particles themselves cannot explain all of the huge variations observed in the fine structure present in nitrate data from the polar ice cap nitrates, but may be able to explain parts of some of them.

Energetic Particle Observations from the CPME and EPE Instruments on IMP-8 during the Bastille Day 2000 Event, R. B. Decker, D. Lario, E. C. Roelof, D. G. Mitchell, and T. P. Armstrong, Fall AGU Meeting, December 2000.

  Abstract (draft). We report on energetic particles measured by the CPME (Charged Particle Measurement Experiment) and EPE (Energetic Particle Experiment) instruments onboard the IMP-8 spacecraft during a period of several days centered on the Bastille Day solar storm. The CPME instrument provides intensities of protons (>0.3 MeV), several ion species (>0.6 MeV/nuc), and electrons (>0.22 MeV) in multiple energy ranges at 20 second time resolution. The EPE instrument provides intensities of ions (>0.05 MeV) and electrons (>0.03 MeV) in a number of energy ranges and in 16 angular sectors (20 second time resolution). IMP-8 performs a near-circular orbit about Earth of radius ~35 RE, spending 60% or more of each 12 day orbit in the solar wind and the rest of its time in the magnetosheath/sphere. During 14-15 July (DOY 196-197) IMP-8 was in the solar wind upstream from the dusk bow shock. Particle intensity increases associated with the fast halo CME launched on day 196 were most striking for higher energy particles (intensities at lower energies were already significantly enhanced by injections from previous solar activity). For example, between 0900-1200 on day 196, intensities had increased by factors  of ~4000 and ~2000 for protons (50-100 MeV) and electrons (0.22 - 0.50 MeV), respectively. The shock arrival at ~1437 UT on day 197 (Bastille Day) was marked by a sharp, narrow (~2-hour wide) shock spike with peak intensity of 0.05-0.22 MeV ions  ~7 x 106/cm2 s sr MeV. Thereafter, in the post-shock plasma the intensity in this channel remained relatively flat at ~3 x 106/cm2 s sr MeV for about 5 hours, dropping abruptly with the arrival of the CME at ~2000 UT. Flat post-shock intensities followed by rapid intensity drops at the leading edge of the CME proper occurred over a wide range of energies and for several particles species.

Solar Proton Events During Solar Cycles 19, 20, and 21, J. Feynman, T. P. Armstrong, L. Dao-Gibner, and S. Silverman, Solar Physics, 126, 385, 1990. Journal abstract with link to full article.

  Abstract (draft). Solar proton events have been studied for over 30 years and a great deal of lore has grown around them. It is the purpose of this paper to test some of this lore against the actual data. Data on solar proton events now exist for the period from 1956 to 1985, during which time 140 events took place in which the event integrated fluxes for protons of energy  >30 MeV was larger than 105 particles cm-2. We have studied statistical properties of event integrated fluxes for particles with energy >10 MeV and for particles with energy >30 MeV. Earlier studies based on a single solar cycle had resulted in a sharp division of events into "ordinary" and "anomalously large" events. Two such entirely separate distributions imply two entirely separate acceleration mechanisms, one common and the other very rare. We find that the sharp division is neither required nor justified by this larger sample. Instead, the event intensity forms a smooth distribution for intensities up to the largest observed, implying that any second acceleration mechanism cannot be rare. We have also studied the relation of event sizes to the sunspot number and the solar cycle phase. We find a clear bimodal variation of annual integrated flux with solar cycle phase but no statistically significant tendency for the large events to avoid sunspot maximum. We show there is almost no relation between the maximum sunspot number in a solar cycle and the solar cycle integrated flux. We also find that for annual sunspot numbers greater than 35 (i.e., non-minimum solar cycle conditions) there is no relation whatsoever between the annual sunspot numbers and annual integrated flux.

New Interplanetary Proton Fluence Model, J. Feynman, T. P. Armstrong, L. Dao-Gibner, and S. Silverman, J. Spacecraft, 27, 403, 1990.

  Abstract (draft). A new predictive engineering model for the interplanetary fluence of protons with energies >10 MeV and >30 MeV is described. The data set used is a combination of observations made from the Earth's surface and from above the atmosphere between 1956 and 1963 and observations made from spacecraft in the vicinity of Earth between 1963 and 1985. The data cover a time period three times as long as the period used in earlier models. With the use of this data set the distinction between "ordinary proton events" and "anomalously large events" made in earlier work disappears. This permitted the use of statistical analysis methods developed for "ordinary events" on the entire data set. The >10 MeV fluences at 1 AU calculated with the new model are about twice those expected on the basis of models now in use. At energies >30 MeV, the old and new models agree. In contrast to earlier models, the results do not depend critically on the fluence from any one event and are independent of sunspot number. Mission probability curves derived from the fluence distribution are presented.

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T. P. Armstrong, armstrong@ftecs.com

Updated Dec. 29, 2006, T. Hunt-Ward