Showing papers by "Mary K. Hudson published in 2007"
TL;DR: In this paper, the authors present results from a numerical study of shock-induced transport and energization of outer zone electrons in the 1-7 MeV range, resulting in a newly formed 10-20 MeV electron belt near L ∼ 3.
Abstract: [1] Prior to 2003, there are two known cases where ultrarelativistic (≳10 MeV) electrons appeared in the Earth's inner zone radiation belts in association with high speed interplanetary shocks: the 24 March 1991 and the less well studied 21 February 1994 storms. During the March 1991 event electrons were injected well into the inner zone on a timescale of minutes, producing a new stably trapped radiation belt population that persisted for ∼10 years. More recently, at the end of solar cycle 23, a number of violent geomagnetic disturbances resulted in large variations in ultrarelativistic electrons in the inner zone, indicating that these events are less rare than previously thought. Here we present results from a numerical study of shock-induced transport and energization of outer zone electrons in the 1–7 MeV range, resulting in a newly formed 10–20 MeV electron belt near L ∼ 3. Test particle trajectories are followed in time-dependent fields from an MHD magnetospheric model simulation of the 29 October 2003 storm sudden commencement (SSC) driven by solar wind parameters measured at ACE. The newly formed belt is predominantly equatorially mirroring. This result is in part due to an SSC electric field pulse that is strongly peaked in the equatorial plane, preferentially accelerating equatorially mirroring particles. The timescale for subsequent pitch angle diffusion of the new belt, calculated using quasi-linear bounce-averaged diffusion coefficients, is in agreement with the observed delay in the appearance of peak fluxes at SAMPEX in low Earth orbit. We also present techniques for modeling radiation belt dynamics using test particle trajectories in MHD fields. Simulations are performed using code developed by the Center for Integrated Space Weather Modeling.
88 citations
TL;DR: In this article, the authors analyzed a series of solar energetic particle events in late April and early May of 1998, during which lunar surface potentials reached values as large as ∼−4.5 kV (the largest recorded by Lunar Prospector).
Abstract: [1] We analyzed a series of solar energetic particle events in late April and early May of 1998, during which lunar surface potentials reached values as large as ∼−4.5 kV (the largest recorded by Lunar Prospector). The two largest surface charging events during this time period correspond to energetic particle injections, when the electron flux between 50 keV and 5 MeV exceeded the proton flux over the same energy range. We searched the entire Lunar Prospector data set for other large negative surface charging events, and found that they occur almost exclusively during magnetotail crossings (when the Moon encounters the plasmasheet) and solar energetic particle events. Lunar surface charging (and its effect on the lunar dust environment) during inherently unpredictable space weather events represents a significant hazard for exploration.
85 citations
01 Dec 2007
TL;DR: In this article, the authors present the first quantitative measurements of lunar surface charging during solar energetic particle (SEP) events, during which they find that the nightside surface reaches potentials of up to −4.5 kV, with negative potentials often observed.
Abstract: [1] We analyzed lunar surface charging during solar energetic particle (SEP) events, utilizing Lunar Prospector measurements of surface potentials and electron fluxes, and upstream energetic particle data. Outside of the magnetosphere, we find a nearly one-to-one correspondence between extreme negative lunar surface charging and large solar proton events. Using new techniques to correct for spacecraft potential, we present the first quantitative measurements of lunar charging during SEP events, during which we find that the nightside surface reaches potentials of up to −4.5 kV, with negative potentials of a kilovolt or larger often observed. These potentials are far higher than typical nightside potentials of a few hundred volts negative and may increase the risk of electrostatic discharge and/or dust effects, introducing an additional hazard to the already dangerous radiation environment. For eight of eleven event periods, surface potentials correlate with electron temperature and with the ratio of energetic electron flux to both energetic proton flux and total electron flux. For these eight events, charging models taking into account both thermal/suprathermal and energetic particle fluxes, as well as secondary emission, can successfully predict surface potentials. However, during the other three events, surface potentials do not correlate with the same measurable quantities, and charging models cannot reproduce measured potentials. In order to develop reliable and accurate models for lunar surface charging during SEP events, we will need better measurements of ion and energetic particle behavior in the lunar environment, secondary electron emission from lunar materials, and lunar surface potentials.
40 citations