Xinlin Li - US grants

The two most significant periods when magnetospheric energy is transported from one region to another and shifted from magnetic fields to particles are during magnetic storms and substorms. In particular, during storms and substorms a substantial portion of the energy to converted into the high-energy portion of the particle distributions. This research program will use theoretical techniques and numerical test particle tracing techniques to examine how the energization of particles takes place and how the energetic particles are transported within the magnetosphere. The ultimate goal is to produce a predictive model of energetic particle injection during storms and substorms. This model could then be used in the construction of the GGCM.

This project will utilize data from several different satellites along with transport models of energetic particles to determine the source region for the energetic electrons that create the radiation belts during magnetic storms. In addition, the modeling effort will examine the processes by which the electrons are energized. This proposal is linked to a companion proposal from the University of California, Berkeley, (ATM99-09358, M. Temerin, PI).

This project will extend the results of the PI's previous model for energetic electrons at geosynchronous orbit to cover the entire inner magnetosphere from 3-10 R. It will also determine the physical basis of the correlation between the solar wind speed and electron flux enhancements. The magnetic storm events chosen for detailed study by the Geospace Environment Modeling (GEM) program campaign on the Inner Magnetosphere and Storms will be used to compare the results of the modeling effort to the measured data. Particular emphasis will be placed on the question of whether the transport and energization of the electrons can be accounted for as a result of diffusion or whether other mechanisms are required.

The source of the highly energetic electrons in the out radiation belt has remained a mystery. A model explaining the origin of the electrons through inward radial diffusion has been utilized to successfully explain many features of the radiation belt but the model requires a source of electrons with a high phase space density which must lie outside the radiation belt region. The radial transport model assumes that the first and (usually) the second adiabatic invariants are conserved, but the third is not. This implies that electrons must be transported inward from a region of higher phase space density. This project will utilize data from the Polar, Wind, SAMPEX and Los Alamos satellites to determine where that source region is and how it varies with solar wind conditions. The radial transport model will then be utilized to quantify the electron energization and compare the process with other competing processes such as localized heating by waves and recirculation.

A major objective of National Space Weather Program (NSWP) is to transfer the techniques and knowledge from scientific research to the operational forecasting activities and to improve present capabilities in forecasting and specifying conditions in the space environment. This project will advance current prediction models to make quantitative real-time forecasts and specifications of the Earth's electron radiation belts from L=3 to L=8. A radial diffusion model has been developed and has achieved great success in predicting the electron enhancements at geosynchronous orbit. However, the current model has only limited application because the model only produces daily averaged electron fluxes at geosynchronous orbit. This project will enhance the model to make high time resolution (<1 hour) forecasts of energetic electron fluxes up to 48 hours in advance. It will also provide specifications of the radiation belt electrons from L=3 to L=8 for different local times. It will also examine the effectiveness of radial transport in accelerating electrons. The work will be mostly carried out by a graduate student under the supervision of the principal investigator.

The forecast and specification results will be posted and archived on the web to be accessible to the public and the website will be made interactive to allow interested researchers and industrial partners to acquire the results at specified times and locations.

An important objective of magnetospheric research is the understanding and eventual accurate prediction of the variability of energetic particles in the radiation belts. Electrons in the energy range of a few hundred thousands of electron volts (keV) to a few millions of electron volts (MeV) can have deleterious effects on spacecraft electronics through radiation damage and deep dielectric charging. Though significant progress has been made in predicting MeV electrons at and inside geosynchronous orbit using the radial diffusion model, the quantitative contribution of different physical mechanisms governing the variability of these electrons are still unclear. Previous radial diffusion models have assumed a source population at the outer boundary of the radiation belt, but it has been difficult to confirm the validity of this assumption due to limited observations. This uncertainty also raises the question of the validity of the radial diffusion coefficients and loss rates used.

This project will eliminate this uncertainty by using actual measurements of electrons as the source population. This will be accomplished by using data from Los Alamos National Laboratory (LANL) sensors at geosynchronous orbit. The goal is to quantify the contribution of radial diffusion to the acceleration of MeV electrons inside geosynchronous orbit. The project will incorporate realistic loss rates into the diffusion model by using data from the SAMPEX and Polar satellites. The model results inside geosynchronous orbit will be compared to Polar measurements. This comparison will make it possible to determine how much enhancement of MeV electrons can be attributed to radial diffusion. A significant portion of the research will be carried out by a graduate student under the direction of the Principal Investigator.

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

A major objective of the Geospace Environment Modeling (GEM) Focus Group on Space Radiation Climatology is to investigate the relationships between interplanetary conditions and trapped radiation belt particles and how these relationships change on long time scales (over a solar cycle) and apply this knowledge to the development of inner magnetospheric components of a Geospace General Circulation Model (GGCM). It is known that magnetic storms vary with solar wind conditions and that magnetospheric energetic particles have their largest variations during magnetic storms. However, the origin of radiation belt particles is still not fully understood and that has made it difficult to understand the physical mechanisms controlling the variability of these particles.

The radial profile of the phase space density (PSD) of the radiation belt electrons for the first and second adiabatic invariants can provide insight of the source and the acceleration mechanisms. However, such a PSD radial profile is often difficult to obtain, mainly because of the lack of multipoint measurements and reliable magnetic field models with temporal scales on the order of 10 minutes, the drift period of a 1 MeV electron near geosynchronous orbit.

This project is a two year research effort to determine the location of the energetic particle heating region by measuring the radial gradient of the PSD of energetic electrons and ions at and beyond geosynchronous orbit prior to and immediately after sharp solar wind pressure enhancements. From these measurements one can obtain the PSD at different radial distances prior to the solar wind pressure enhancements. Test-particle simulations will be performed to validate the PSD analysis and provide an estimate of the actual position of the particles before the arrival of the solar wind pressure enhancement. Sharp solar wind pressure enhancements, which can be due to interplanetary shocks and high speed solar wind streams, occur throughout the solar cycle. A statistical survey over a long term (approximately 1.5 solar cycles) will reveal any solar cycle and seasonal dependencies of the radial gradient.

Electrons in Earth's radiation belts can have serious effects on spacecraft electronics through radiation damage and deep dielectric charging. The physical mechanisms governing the variability of these energetic electrons are still hot topics of debate. The paradigm for explaining the creation of the electron radiation belts has recently been shifting from one using only the theory of radial diffusion to one including an important role for plasma waves. The interaction of plasma waves with the electrons can result in in situ heating. This project will investigate the relative contribution of radial diffusion and in situ heating to the enhancement of MeV electrons inside geosynchronous orbit. An internal source term will be added to a currently existing radial diffusion model. Measurements of electrons using Los Alamos National Laboratory (LANL) satellite data at geosynchronous orbit will be used to determine the source population. Realistic loss rates will be determined from data taken from the SAMPEX satellite. The model results will then be compared to GPS satellite measurements inside geosynchronous orbit. In this way, it will be possible to determine how much enhancement of the MeV electrons measured by GPS can be attributed to inward radial transport and how much to in situ heating.

This project will include research and training for graduate students. The results will enhance our ability to predict an important space weather phenomenon.

The objective of this three-year cross-disciplinary team effort is to build and operate a tiny, so-called CubeSat, spacecraft. The purpose of the 3U Cubesat carrying an energetic particle sensor is to address fundamental space weather science questions relating to the relationship between solar flares, energetic particles, and geomagnetic storms in the near Earth space environment. The particle instrument is the Relativistic Electron and Proton Telescope integrated little experiment (REPTile). REPTile is designed to measure directional differential flux of energetic protons, 10-40 MeV, and electrons, 0.5 to >3 MeV. The instrument is a miniaturization of the Relativistic Electron and Proton Telescope (REPT) currently being developed and built at the Laboratory for Atmospheric and Space Physics (LASP) for the NASA/Radiation Belt Storm Probe (RBSP) mission. Energetic protons and electrons coming from both the Sun during Solare Energetic Particle (SEP) events and the Earth's radiation belt will be measured. The energetic particle measurements will be used in conjunction with solar flare measurements from other spacecraft, e.g., NASA's Solar Dynamics Observatory Extreme Ultraviolet Variability Experiment and current NOAA's GOES-Solar X-ray Imager, to investigate the correlations between flare parameters and SEP characteristics. The specific science objectives for the project are to investigate the relationships between solar energetic particles, flares, and coronal mass ejections, and to characterize the variations of the Earth's radiation belt electrons.

Space weather refers to conditions in space that can influence the performance and reliability of space-borne and ground-based technological systems. Understanding the relationships between SEPs observed at the ground and solar flares and CMEs, eventually leading to the prediction of SEP events, is a high priority space weather research goal, as is the full characterization of the variations of the Earth's radiation belt electrons. In addition, the development of the miniature REPTile instrument will facilitate future space weather research and monitoring conducted by constellations of small (cubesat-sized) spacecraft and demonstrate the usefulness of nano-satellites as space weather monitors.

The project will pursue scientific discovery while providing unique and inspiring educational opportunities. It relies on extensive undergraduate and graduate student involvement through all aspects of the mission. This is a collaborative effort between the Department of Aerospace Engineering Sciences and the Laboratory for Atmospheric and Space Physics at the University of Colorado, which includes the integration of students, faculty, and professional engineers. The project is focused around a currently existing space hardware design course. The new, largely unproven technology involved in cubesat missions, inherently makes the project associated with significant risks. On the other hand, however, the project has tremendous potential to be transformational not only within its own research area but also for the larger field of space science and atmospheric research as well as within aerospace engineering and education.

This project is a collaborative effort with scientists at the Los Alamos National Laboratory to develop a real-time model for specifying and forecasting the state of Earth's radiation belt. The project will utilize data assimilation methods in conjunction with physical models and modern machine learning techniques to examine the acceleration, transport and loss processes for energetic electrons in the radiation belt. The resulting model will include confidence limits on the system-wide forecasts, making the results useful for operational space weather predicitions. The project will benefit society by making improved radiation-belt predictions at reduced operational costs and the forecasts will be made freely available online.

The project includes a strong educational and teaching component through the participation of graduate students at the University of Colorado. In addition the research will be integrated with the Los Alalmos Space Science Outreach (LASSO) program, which offers teacher training to underrepresented groups and individuals with disabilities.

The electron radiation environment around Earth is a major hazard to spaceflight assets. Understanding it, ideally to the point of predictive modeling of its response to changing solar wind driving conditions, is a central goal of magnetospheric physics. The condition in the radiation belts at any given time is the result of a delicate balance between energization and loss processes operating on the particles in the near-Earth environment. Neither of these is well understood at present. This project will use new measurements from a NSF-funded CubeSat mission that was recently carried out together with numerical modeling to determine the energetic electron loss rate. Only when the loss rate is accurately determined will it be possible to fully model the radiation belt dynamics.

The Colorado Student Space Weather Experiment (CSSWE) is a tiny, so-called CubeSat, satellite mission funded by NSF and launched into a high inclination, low-altitude orbit as a secondary payload under NASA?s Educational Launch of Nanosatellites (ELaNa) program in September 2012. The entire CSSWE system, including its ground station, was designed, built, calibrated, tested, delivered, and operated by students, with mentoring and help provided by faculty and professional engineers at the Laboratory for Atmospheric and Space Physics at University of Colorado. The satellite project far exceeded it?s expected life-time and has collected more than 12 months worth of high quality data on energetic electrons and protons in Low-Earth-Orbit. The advanced data analysis to be done under this award will continue the exploitation of this unique dataset and, in turn, will help to maximize the scientific return on investment of this already highly successful CubeSat project. For the most part, the scientific investigation is designed for and will be carried out by graduate students under the supervision of the PI and collaborators.

To date, the precipitation loss rate of the outer radiation belt electrons has not been quantified and resolved. The electron loss rates in current published papers are erratic and diverge by an order of magnitude. The goal of this study is to quantify the precipitation losses and their dependence on longitude, L, and MLT directly from the data with advanced modeling, thus providing a quantitative answer to the research community on this important issue. Specifically, this effort will analyze over a year's worth of CSSWE data in conjunction with the NASA Van Allen Probes to determine the loss rates into the ionosphere during periods of gradual decay, during episodes of fast loss and during episodes of large gain. Analyzing CSSWE data during periods of gradual loss will determine how much additional energization occurs during such periods to maintain the radiation belts; analyzing the data during periods of fast loss will determine how much of the loss occurs by scattering into the ionosphere versus loss due to outward radial diffusion; analyzing the loss during periods of large gains will determine how much additional energization is needed to produce the observed gains in electron flux. The impact of such precipitation loss to the overall dynamics of radiation belt electrons will then be assessed by comparing the measurements of CSSWE and the corresponding modeling results with measurements from the Van Allen Probes at the same times and locations.