U21B-01 INVITED
A perspective on radiation belt science
Data from Explorer I (launched 31 January 1958) and Explorer 3 (launched 26 March 1958) provided the first space-age scientific discovery: The existence of a doughnut-shaped region of charged particle radiation trapped by Earth's magnetic field. We now see that radiation belt processes are universal phenomena. Results from recent space missions have shown clear evidence that radiation belts exist at all strongly magnetized planets throughout the solar system. Highly dynamical behavior of radiation belts still remains a mystery even 50 years after the original discoveries by J.A. Van Allen and coworkers. During increased solar and geomagnetic activity, radiation levels across the belts vary over orders of magnitude on the timescales of minutes to days. A large range of acceleration and loss mechanisms operating at different spatial and temporal scales compete over the global extent of the belts. While a number of local and global mechanisms have been identified as potentially important, their relative role is not understood. This presentation will provide a perspective on radiation belt processes as addressed in this special session.
U21B-02 INVITED
The Foundations of Radiation Belt Research
The United States undertook the launching of an artificial Earth satellite as part of its contribution to the International Geophysical Year. The Vanguard program was established to meet that commitment, and it developed a launch vehicle, ground station network, and suite of scientific payloads, including the cosmic ray experiment proposed by James A. Van Allen. Although Vanguard eventually exceeded all of its pre-stated goals, the preemptive launches of Sputniks I and II by the Soviets in October and November 1957 spurred the U.S. into a frenzy of activity, resulting in the launches of Explorers I and III in January and March of 1958. The data from those two satellites quickly revealed the lower boundary of an unexpected region of high intensity radiation trapped in the Earth's magnetic field. The original announcement in May 1958 stated that the radiation was probably composed of either protons or electrons, and that, if electrons, it was probably bremsstrahlung formed in the satellite shell. Immediately following that announcement, approval was received for what became Explorer IV, whose announced purpose was to follow up on the new discovery. Another reason for the satellite, unmentioned at the time, was its inclusion as a component of the highly classified Argos program, a covert military program to test whether the detonation of nuclear devices at high altitude would inject measurable numbers of charged particles into durable trajectories in the Earth's magnetic field. Our team at Iowa produced the satellites under the oversight of, and with assistance by, the Army Ballistic Missile Agency in Huntsville, and with the contributions of key hardware from several other government laboratories. The project was completed in the unbelievably short period of seventy-seven days from approval to launch. Launched into a higher-inclination orbit than the earlier Explorers, Explorer IV confirmed the discovery and greatly expanded our understanding of the natural phenomenon. It also provided the first hint that there were two distinct radiation belts, although that conclusion was not reached until later. Although that new information was quickly announced, the results of the high altitude nuclear detonations were kept secret until well into 1959. They clearly revealed the charged particle shells created by the Argos nuclear detonations. The next major step in mapping and understanding the high-intensity radiation involved the launch of deep space probes Pioneers III and IV in December 1958 and March 1959. Although both launches fell short in their primary objective, to reach the moon, they traveled far enough from the Earth to fully meet the needs of the scientific experiment. They very clearly showed the two-radiation belt structure, and mapped its extent. They also showed the probable effect of a magnetic storm on 25 February, thus indicating the direct influence of solar activity on the outer belt. By the end of 1959, the existence of the Van Allen Radiation Belts and their general structure were solidly established, early information about the composition of the radiation was appearing in print, and energetic work was under way to understand the physics of the processes involved.
U21B-03 INVITED
Current Understanding of Radiation Belt Acceleration, Transport and Loss
This invited talk will review the major acceleration, transport, and loss processes that govern the topology and dynamics of the Earth's radiation belts. The belts are typically divided into an inner belt and an outer belt, with a slot of comparatively low flux intensity in between. The hallmark of the inner belt is intense energetic proton flux, co-located with a still-largely-unknown electron population. The slot is a loosely defined region that fills with energetic electrons during storms, and sometimes contains an extension of the inner belt protons or even additional transient proton belts. The outer zone consists primarily of energetic electrons, and is very dynamic, experiencing dramatic emptying and refilling during even modest magnetic activity. Transport, often implying acceleration, is thought to be a combination of two sources: occasional coherent injections associated with solar wind pressure enhancements or shocks, and more routine stochastic radial diffusion associated with ULF fluctuations. Loss is thought to be a combination of drift into the magnetopause and scattering into the atmosphere. Chorus, hiss, magnetosonic, and electromagnetic ion cyclotron plasma waves all contribute to acceleration and loss, but their relative importance remains an area of active research.
U21B-04 INVITED
Radiation Belts Throughout the Solar System
The several preceding decades of deep space missions have demonstrated that the generation of planetary radiation belts is a universal phenomenon. All strongly magnetized planets show well developed radiation regions, specifically Earth, Jupiter, Saturn, Uranus, and Neptune. The similarities occur despite the tremendous differences between the planets in size, levels of magnetization, external environments, and most importantly, in the fundamental processes that power them. Some planets like Jupiter are powered overwhelmingly by planetary rotation, much like astrophysical pulsars, whereas others, like Earth and probably Uranus, are powered externally by the interplanetary environment. Uranus is a particularly interesting case in that despite the peculiarities engendered by its ecliptic equatorial spin axis orientation, its magnetosphere shows dynamical behavior similar to that of Earth as well as radiation belt populations and associated wave emissions that are perhaps more intense than expected based on Earth-derived theories. Here I review the similarities and differences between the radiation regions of radiation belts throughout the solar system. I discuss the value of the comparative approach to radiation belt physics as one that allows critical factors to be evaluated in environments that are divorced from the special complex conditions that prevail in any one environment, such as those at Earth.
U21B-05 INVITED
The Outer Radiation Belt Injection, Transport, Acceleration and Loss Satellite (ORBITALS): A Canadian Mission to the Van Allen Belts
The Outer Radiation Belt Injection, Transport, Acceleration and Loss Satellite (ORBITALS) mission is proposed as a Canadian Space Agency satellite mission contribution to ILWS. The ORBITALS will provide a unique view of the largely previously unexplored inner magnetosphere, and will embrace a new paradigm of cross-energy coupling needed to understand Van Allen belt dynamics. Its mission goal to "understand the acceleration, global distribution, and variability of energetic electrons and ions in the inner magnetosphere" is perfectly aligned with the top geospace priority for the LWS and ILWS programs. In a 12 hour low inclination orbit, the ORBITALS will come into once daily apogee conjunctions with the extensive ground- based Canadian Geospace Monitoring (CGSM) instrumentation as well as with GOES East and West. Baseline raised perigee will provide both long outer radiation belt dwell times as well as coverage of the outer-most inner radiation belt. In combination, the ORBITALS-CGSM-GOES conjuctions will provide a unique data set with which to address fundamental radiation belt science questions such as the competition between ULF and VLF acceleration processes, the role of EMIC and VLF waves in loss, and the relationship between these processes and plasmaspheric cold plasma dynamics. The ORBITALS will also address inter- related science questions about the structure of inner magnetosphere electric and magnetic field structure, plasmaspheric dynamics, including thermal ion injection and loss, and the dynamics of the ring current population in the inner magnetosphere during storms. In combination with the approved NASA LWS RBSP mission, and the proposed Japanese ERG satellite, the ORBITALS-RBSP-ERG three petal constellation will resolve the spatio-temporal ambiguities which have clouded previous studies. Together, these mssions will uncover the processes responsible for the existence, and global dynamics and morphology, of the Earth's Van Allen radiation belts.
U21B-06
Radiation Belt Storm Probes Mission
Radiation Belt Storm Probes (RBSP) is a NASA Living With a Star (LWS) mission dedicated to understanding how populations of relativistic electrons and ions in space form and change in response to variable energy inputs from the Sun. Fifty years after the discovery of trapped radiation, RBSP aims to understand the trapped radiation populations ideally to the point of predictability. Understanding and prediction are essential for designing and operating governmental and commercial space assets that are imbedded in, and transit, Earth's space environment. This talk will outline the objectives and capabilities of the RBSP program, and will place the program in some historical context of radiation belt studies over the last five decades.
U21B-07
Myths and Mysteries of Solar Wind Speed and MeV Electrons in the Magnetosphere
The remarkable correlation between high speed solar wind and the enhancement of energetic electrons in the magnetosphere has been identified for over four decades, yet the mystery of this correlation remains. Recently, several interpretations about this correlation have been proposed and most of them are incomplete and some of them may have generated the widespread verdict (or myth) that enhanced ULF waves alone lead to enhanced MeV electrons in the radiation belts. In this presentation, we present e brief review of the association of high speed solar wind and energetic electrons across the entire relevant energy range (10s of keV to multi-MeV). We discuss the incompleteness of existing interpretations and we describe a more complete picture in understanding this mystery.