B. T. Kress

Simulated magnetopause losses and Van Allen Probe flux dropouts

Three radiation belt flux dropout events seen by the Relativistic Electron Proton Telescope soon after launch of the Van Allen Probes in 2012 (Baker et al., 2013a) have been simulated using the Lyon-Fedder-Mobarry MHD code coupled to the Rice Convection Model, driven by measured upstream solar wind parameters. MHD results show inward motion of the magnetopause for each event, along with enhanced ULF wave power affecting radial transport. Test particle simulations of electron response on 8 October, prior to the strong flux enhancement on 9 October, provide evidence for loss due to magnetopause shadowing, both in energy and pitch angle dependence. Severe plasmapause erosion occurred during ~ 14 h of strongly southward interplanetary magnetic field Bz beginning 8 October coincident with the inner boundary of outer zone depletion.

Modeling CME-shock-driven storms in 2012–2013: MHD test particle simulations

The Van Allen Probes spacecraft have provided detailed observations of the energetic particles and fields environment for coronal mass ejection (CME)-shock-driven storms in 2012 to 2013 which have now been modeled with MHD test particle simulations. The Van Allen Probes orbital plane longitude moved from the dawn sector in 2012 to near midnight and prenoon for equinoctial storms of 2013, providing particularly good measurements of the inductive electric field response to magnetopause compression for the 8 October 2013 CME-shock-driven storm. An abrupt decrease in the outer boundary of outer zone electrons coincided with inward motion of the magnetopause for both 17 March and 8 October 2013 storms, as was the case for storms shortly after launch. Modeling magnetopause dropout events in 2013 with electric field diagnostics that were not available for storms immediately following launch have improved our understanding of the complex role that ULF waves play in radial transport during such events.

Global storm time depletion of the outer electron belt

Abstract The outer radiation belt consists of relativistic (>0.5 MeV) electrons trapped on closed trajectories around Earth where the magnetic field is nearly dipolar. During increased geomagnetic activity, electron intensities in the belt can vary by orders of magnitude at different spatial and temporal scales. The main phase of geomagnetic storms often produces deep depletions of electron intensities over broad regions of the outer belt. Previous studies identified three possible processes that can contribute to the main‐phase depletions: adiabatic inflation of electron drift orbits caused by the ring current growth, electron loss into the atmosphere, and electron escape through the magnetopause boundary. In this paper we investigate the relative importance of the adiabatic effect and magnetopause loss to the rapid depletion of the outer belt observed at the Van Allen Probes spacecraft during the main phase of 17 March 2013 storm. The intensities of >1 MeV electrons were depleted by more than an order of magnitude over the entire radial extent of the belt in less than 6 h after the sudden storm commencement. For the analysis we used three‐dimensional test particle simulations of global evolution of the outer belt in the Tsyganenko‐Sitnov (TS07D) magnetic field model with an inductive electric field. Comparison of the simulation results with electron measurements from the Magnetic Electron Ion Spectrometer experiment shows that magnetopause loss accounts for most of the observed depletion at L>5, while at lower L shells the depletion is adiabatic. Both magnetopause loss and the adiabatic effect are controlled by the change in global configuration of the magnetic field due to storm time development of the ring current; a simulation of electron evolution without a ring current produces a much weaker depletion.

Rebuilding of the Earth's outer electron belt during 8–10 October 2012

Geomagnetic storms often include strong magnetospheric convection caused by sustained periods of southward interplanetary magnetic field. During periods of strong convection, the Alfven layer, which separates the region of sunward convection from closed drift shells, is displaced earthward allowing plasma sheet particles with energies in the hundreds of keV direct access inside of geosynchronous. Subsequent outward motion of the Alfven boundary and adiabatic energization during storm recovery traps plasma sheet electrons on closed drift shells providing a seed population for the outer radiation belts. In situ observations of the 8–10 October 2012 geomagnetic storm and MHD test particle simulations illustrate the morphology of this process. Data and modeling results support the conclusion that recovery of ~ 1 MeV electrons at geosynchronous is mainly due to global convection and dipolarization associated injections from the plasma sheet.

Observations of the inner radiation belt: CRAND and trapped solar protons

Measurements of inner radiation belt protons have been made by the Van Allen Probes Relativistic Electron-Proton Telescopes as a function of kinetic energy (24 to 76 MeV), equatorial pitch angle, and magnetic L shell, during late 2013 and early 2014. A probabilistic data analysis method reduces background from contamination by higher-energy protons. Resulting proton intensities are compared to predictions of a theoretical radiation belt model. Then trapped protons originating both from cosmic ray albedo neutron decay (CRAND) and from trapping of solar protons are evident in the measured distributions. An observed double-peaked distribution in L is attributed, based on the model comparison, to a gap in the occurrence of solar proton events during the 2007 to 2011 solar minimum. Equatorial pitch angle distributions show that trapped solar protons are confined near the magnetic equator but that CRAND protons can reach low altitudes. Narrow pitch angle distributions near the outer edge of the inner belt are characteristic of proton trapping limits.

Atmospheric Ionizing Radiation from Galactic and Solar Cosmic Rays

Christopher J. Mertens1, Brian T. Kress2, Michael Wiltberger3, W. Kent Tobiska4, Barbara Grajewski5 and Xiaojing Xu6 1NASA Langley Research Center, Hampton, Virginia 2Dartmouth College, Hanover, New Hampshire 3 High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colorado 4 Space Environment Technologies, Pacific Palisades, California 5National Institute for Occupational Safety and Health, Cincinnati, Ohio 6Science Systems and Applications, Inc. USA

Development of Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS) model

In this paper an overview is given of the development of a new nowcast prediction of aircrew radiation exposure from both background galactic cosmic rays (GCR) and solar energetic particle events (SEP) that may accompany solar storms. The new air-crew radiation exposure model is called the Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS) model. NAIRAS will provide global, data-driven, real-time radiation exposure predictions of biologically harmful radiation at commercial airline altitudes. Observations are utilized from the ground (neutron monitors), from the atmosphere (the NCEP Reanalysis and NCEP Global Forecasting System), and from space (NASA/ACE and NOAA/GOES). Atmospheric observations provide the overhead shielding information and the ground- and space-based observations provide boundary conditions on the incident GCR and SEP particle flux distributions for transport and dosimetry simulations. Exposure rates are calculated using the physics-based HZETRN (High Charge and Energy Transport) code. Recent progress in the model implementation is reported and examples of the model results are shown for a representative high-energy SEP event during the Halloween 2003 superstorm, with emphasis on the high-latitude and polar region. The suppression of the geomagnetic cutoff rigidity during these storm periods and their subsequent influence on atmospheric radiation exposure is characterized. 1.0 System Architecture In its first year of performance, using rapid-prototyping methods, Space Environment Technologies (SET) has used team member (stake-holder) participation to identify the critical input data streams. As a result, the NAIRAS high-level design architecture

Influence of Space Weather on Aircraft Ionizing Radiation Exposure

There is a growing concern for the health and safety of commercial aircrew and passengers due to their exposure to ionizing radiation with high linear energy transfer (LET), particularly at high latitudes. The International Commission of Radiobiological Protection (ICRP), the EPA, and the FAA consider the crews of commercial aircraft as radiation workers. During solar energetic particle (SEP) events, radiation exposure can exceed annual limits, and the number of serious health effects, especially to the unborn child of a pregnant air traveler, is expected to be quite high if precautions are not taken. There is a need for a capability to monitor the real-time radiation levels at commercial airline altitudes in order to: (1) provide a continuous assessment of the ionizing radiation field for tracking individual aircrew exposures levels, for the airlines and the FAA to develop policy and procedure for recommending aircrew radiation exposure limits and exposure mitigation; (2) provide time-critical data during SEP events for airline management and pilots to make decisions that balance the cost to flight path alterations against radiation exposure and health risks to passenger and crew; and (3) provide the airline industry with an archived database of radiation exposure levels for assessing the impact of ionizing radiation on the global air transportation system, especially in view of the current and future exponential increase in the number of polar routes. Currently under development is the Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS) model, which provides a global, data-driven, real-time, radiation dose prediction for archiving and assessing the biologically harmful radiation exposure levels at commercial airline altitudes. The NAIRAS model brings to bear the best available suite of Sun-Earth observations and models for simulating the atmospheric ionizing radiation environment. Observations are utilized from ground (neutron

Space Weather Nowcasting of Atmospheric Ionizing Radiation for Aviation Safety

There is a growing concern for the health and safety of commercial aircrew and passengers due to their exposure to ionizing radiation with high linear energy transfer (LET), particularly at high latitudes. The International Commission of Radiobiological Protection (ICRP), the EPA, and the FAA consider the crews of commercial aircraft as radiation workers. During solar energetic particle (SEP) events, radiation exposure can exceed annual limits, and the number of serious health effects is expected to be quite high if precautions are not taken. There is a need for a capability to monitor the real-time, global background radiations levels, from galactic cosmic rays (GCR), at commercial airline altitudes and to provide analytical input for airline operations decisions for altering flight paths and altitudes for the mitigation and reduction of radiation exposure levels during a SEP event. The Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS) model is new initiative to provide a global, real-time radiation dosimetry package for archiving and assessing the biologically harmful radiation exposure levels at commercial airline altitudes. The NAIRAS model brings to bear the best available suite of Sun-Earth observations and models for simulating the atmospheric ionizing radiation environment. Observations are utilized from ground (neutron monitors), from the atmosphere (the METO analysis), and from space (NASA/ACE and NOAA/GOES). Atmospheric observations provide the overhead shielding information and the groundand space-based observations provide boundary conditions on the GCR and SEP energy flux distributions for transport and dosimetry simulations. Dose rates are calculated using the parametric AIR (Atmospheric Ionizing Radiation) model and the physics-based HZETRN (High Charge and Energy Transport) code. Empirical models of the near-Earth radiation environment (GCR/SEP energy flux distributions and geomagnetic cut-off rigidity) are benchmarked against the physics-based CMIT (Coupled MagnetosphereIonosphere-Thermosphere) and SEP-trajectory models.

Energetic Particles in the Magnetosphere and their Relationship to Solar Wind Drivers

Enhancements in fluxes of energetic protons, heavy ions and relativistic electrons in planetary environments are initiated by solar and heliospheric processes: (1) directly, as a result of a propagating electromagnetic disturbance which impacts the magnetosphere, modifying the planetary magnetic configuration on the impulse propagation time scale; (2) indirectly, by exciting electromagnetic oscillations in the magnetosphere which diffuse particles across field lines or energize them on given field lines over hours to days. In a magnetized plasma energization of long-term trapped particles is due to a set of different physical processes which violate one or more of the adiabatic invariants. We survey geomagnetic modifications due to solar/heliospheric drivers, geomagnetic eigenoscillations and the mechanisms which break down invariants of trapped particle dynamics, and investigate the resulting effects on observed fluxes. The mechanisms include (a) radial diffusion due to ultra low-frequency (ULF) electromagnetic oscillations and fluctuations in the convection electric field, (b) transittime damping due to fast mode waves, (c) diffusion due to electromagnetic ion-cyclotron or whistler waves and (d) sudden deformation of the magnetic field configuration. The latter can cause trapping of Solar Energetic Particles (SEPs) on a drift time scale to form transient proton and heavy ion belts deep in the magnetosphere (L = 2-3). Radial and energy diffusion time scales become comparable for MeV electrons around the plasmapause (L = 4-5).