The Dominant Role of the Electron Isotropy Boundary in Controlling Earth's Outer Radiation Belt Electron Lifetimes
Year: 2026
Type: article
Abstract: Field‐line curvature scattering (FLCS) is believed to be the primary mechanism forming electron isotropy boundaries (IB) and can rapidly scatter relativistic electrons from the outer radiation belt. However, its direct and quantitative impact on controlling outer belt electron lifetimes has never been directly assessed. Using simultaneous observations of IBs from low‐altitude satellites and in situ electron fluxes from equatorial satellites, we report IBs intruding into the outer belt (reaching L ∼ 4.5), closely synchronized with sharp flux radial gradients near IBs, caused by significant electron loss outside IBs during a 4‐day storm recovery period. By combining observations with simulations, we provide the first direct and quantitative evidence that FLCS‐induced electron loss outside the IB dominantly controls the outer belt electron lifetimes. Our findings reveal that this simple yet fundamental physical process, which has been historically neglected in global radiation belt models, can explain the outer electron belt configuration.
Source: Geophysical Research Letters
DOI: 10.1029/2025gl120881
Authors: Man Hua, Xiaofei Shi, Jacob Bortnik, Anton Artemyev, Vassilis Angelopoulos, Yoshizumi Miyoshi, Takefumi Mitani, James L. Burch, Takeshi Takashima, Tomoaki Hori, Ayako Matsuoka, Mariko Teramoto, Kazuhiro Yamamoto, Yoshiya Kasahara, Fuminori Tsuchiya, Atsushi Kumamoto, Atsuki Shinbori, Iku Shinohara
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,190
Awards: GEM: From the Micro to the Macro--Identifying the Mechanisms Responsible for Megaelectron-Volt (MeV) Electron Microbursts and Quantifying Their Role in Global Radiation Belt Losses, Collaborative Research: Causes and Consequences of Relativistic Electron Precipitation as Revealed by the CubeSat Mission ELFIN’s Pitch-Angle Resolved Loss Cone Measurements, G3949233605, CubeSat: Electron Losses and Fields INvestigation (ELFIN), THE ELFIN-STAR (ELFIN*) CUBESAT WILL RESOLVE THE ROLE OF ELECTROMAGNETIC ION CYCLOTRON (EMIC) WAVES FOR (AND DETERMINE THE RATE OF) RELATIVISTIC ELECTRON PRECIPITATION DURING STORMS. FROM A NEAR-POLAR (I>65O) LOW-EARTH (400KM ALTITUDE) ORBIT ELFIN* WILL PROVIDE UNIQUE PITCH-ANGLE- AND ENERGY-RESOLVED SPECTRA OF RELATIVISTIC ELECTRON FLUXES WITHIN THE LOSS CONE TO DETERMINE WHETHER THEY BEAR THE CHARACTERISTIC SIGNATURES OF EQUATORIAL SCATTERING BY EMIC WAVES. COMPARING ITS OBSERVATIONS WITH DIFFUSION MODELS FOR EMIC CHORUS MAGNETOPAUSE SHADOWING AND OTHER LOSS MECHANISMS ELFIN* WILL ESTABLISH WHETHER LOSSES ARE DOMINATED BY EMIC WAVES OR ARE DUE TO OTHER PROCESSES. ENERGETIC PARTICLE DETECTOR (EPD) ELECTRON MEASUREMENTS (0.1-5MEV) AT RESOLUTION 11.25O (0.4O 0.8O AT THE EQUATOR AT L=5-7) RESOLVING THE LOSS-CONE INCLUDING TRAPPED PARTICLES ACHIEVE CLOSURE. IF EMIC WAVES PROPAGATE TO THE IONOSPHERE ELFIN* S MAGNETOMETER (MAG) WILL ALSO DETECT THEM (DESIRED BUT NEITHER NECESSARY NOR SUFFICIENT FOR CLOSURE). ELFIN* S INTEGRATED DATA ANALYSIS APPROACH AND RAPID DISSEMINATION STRATEGIES VIA THE SPACE ENVIRONMENT DATA ANALYSIS SYSTEM (SPEDAS AN OFF-SPRING OF THEMIS) OPTIMIZE SCIENCE YIELD AND ENSURE WIDEST COMMUNITY BENEFITS. ELFIN* S POTENTIAL IS COMPOUNDED BY CONJUNCTIONS WITH CONCURRENT EQUATORIAL MISSIONS IN 2016 (THEMIS RBSP ERG MMS) THAT WILL COMPLEMENT ITS UNIQUE LOSS-CONERESOLVING SPECTRA.OUR SIMILAR PROPOSAL TO NSF IN 2012 (ELFIN) IS ONE OF TWO FRONT-RUNNERS BUT HAS NOT BEEN SELECTED (YET) DUE TO PROGRAMMATIC CONSIDERATIONS IN A TOUGH FISCAL ENVIRONMENT. IF ELFIN IS SELECTED BY NSF WE HEREBY PROPOSE UNDER H-TIDES TO EXECUTE ELFIN* S STAR OPTION. ELFIN* WILL BUILD AN IDENTICAL SATELLITE TO NSF S ELFIN AND RELEASE IT ON THE SAME LAUNCH VEHICLE INTO A FORMATION ORBIT WITH ITS TWIN. SPRING-SEPARATION PROVIDES A NATURAL VARIATION OF THE INTER-CUBESAT DISTANCE WITH A FULL-ORBIT LAP ONCE PER 30DAYS.ELFIN* S SMALL-SEPARATION RADIATION BELT CROSSINGS (0-15MIN 33% OF THE TIME) WILL RESOLVE THE TEMPORAL VARIABILITY (LOSS-CONE FILL RATE) AND SPATIAL EXTENT OF THE RELATIVISTIC ELECTRON PRECIPITATION AND DETERMINE ITS AGREEMENT WITH EQUATORIAL EMIC WAVE DIFFUSION RATES OVER TIME SCALES COMPARABLE TO SUCH DIFFUSION (MINUTES). THUS FOR AT LEAST 2 STORM-TIME PRECIPITATION EVENTS OVER ITS BASELINE (6- MONTH) MISSION ELFIN* WILL DETERMINE THE GLOBAL ROLE OF EMIC WAVES ON RADIATION BELT PRECIPITATION. A RADIATION MARGIN OF>2 AND EMPHASIS ON PARTS SELECTION FOR A>1YR DESIGN-LIFE IS EXPECTED TO DOUBLE THIS SCIENCE YIELD TO>4 STORMS.ELFIN* RESOLVES A FUNDAMENTAL SPACE- AND PLASMA-PHYSICS QUESTION RELATED TO RELATIVISTIC ELECTRON SCATTERING AND LOSS IN THE OUTER RADIATION BELT. ITS STAR OPTION IF EXERCISED WILL DETERMINE THE GLOBAL EFFECTS OF SUCH SCATTERING. FOR PURPOSES OF UNDERSTANDING SPACE WEATHER AND FUNDAMENTAL PLASMA PROCESSES DETERMINING STORM-TIME OUTER BELT ELECTRON LOSS RATES AND MECHANISMS IS JUST AS IMPORTANTAS DETERMINING ACCELERATION OR TRANSPORT. ELFIN* IS THEREFORE KEY IN THE HELIOPHYSICS DISCIPLINE S ASPIRATION BOTH FOR A COMPREHENSIVE NATIONAL SPACE WEATHER PROGRAM AND TO UNDERSTAND FUNDAMENTAL MICROSCOPIC PHYSICS AS WELL AS THE GLOBAL SYSTEM BEHAVIOR AS RECOMMENDED BY THE 2012 HELIOPHYSICS DECADAL SURVEY. ELFIN* DIRECTLY ADDRESSES ALL THREE STATED HELIOPHYSICS OBJECTIVES (IN THE 2010 SMD SCIENCE PLAN) TO UNDERSTAND: THE FUNDAMENTAL PHYSICAL PROCESSES OF THE SPACE ENVIRONMENT HOW TECHNOLOGICAL SYSTEMS ARE AFFECTED BY SOLAR VARIABILITY AND DEVELOPING THE CAPABILITY TO PREDICT EXTREME AND DYNAMIC CONDITIONS IN SPACE . THESE ALSO TIEDIRECTLY TO HELIOPHYSICS SCIENCE GOALS #2 AND #4 LISTED IN THE DECADAL SURVEY (P-S2). ELFIN* S APPROACH TO ADDRESS LOSSES SYSTEM-WIDE BY INTEGRATING ITS UNIQUE DATASET WITH THOSE OF OTHER NASA MISSIONS ADDRESSES THE PRIMARY RECOMMENDATION OF THE DECADAL SURVEY(FIG. 1.2) FOR SYSTEM-SCIENCE WITH THE INTEGRATED HELIOPHYSICS SYSTEM OBSERVATORY., Collaborative Research: GEM--The Upper Limit of the Earth's Outer Radiation Belt Electron Fluxes, G718453068
OpenAlex ID: W7127041680