Year: 2025
Type: article
Abstract: The magnetotail current sheet plays a crucial role in substorm dynamics, affecting the entire magnetosphere. Formation and reconnection of thin (ion‐gyroscale) current sheets initiate magnetospheric substorms. Theoretical models suggest that a transient, demagnetized ion population is key element of the thin current sheet configuration. At lunar distances, the magnetotail provides a unique opportunity for in situ investigation of this population due to the high fraction of hot demagnetized ions. Using observations of thin current sheets by the Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun mission, we show that the relative drift between demagnetized hot ions and magnetized cold ions, likely driven by a strong polarization electric field, reduces the ion current density to nearly zero in the spacecraft rest frame. Hot ions exhibit a crescent‐like velocity distribution, contributing to ion agyrotropy. We discuss this population in the context of advanced thin current sheet models, including transient ions performing Speiser‐like motion. These observations provide valuable insights for numerical and theoretical studies.
Source: Geophysical Research Letters
DOI: 10.1029/2024gl114522
Institution: University of California, Los Angeles
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,190
Awards: G251828814, G3313399750, MAGNETIC RECONNECTION TRIGGERED BY PLASMA INSTABILITIES IN THIN CURRENT SHEETS PLAYS A CRUCIAL ROLE IN THE MAGNETOTAIL KINETIC AND DYNAMIC PROCESSES. IT IS RESPONSIBLE FOR THE GENERATION OF FLUX ROPES (FRS) BURSTY BULK FLOWS (BBFS) AND DIPOLARIZING FLUX BUNDLES (DFBS) WHICH PROPAGATE TOWARD THE EARTH OR FURTHER DOWN TAIL. THEREFORE ALTHOUGH MAGNETOTAIL RECONNECTION IS LOCALIZED IN A SMALL SCALE REGION IT HAS GLOBAL CONSEQUENCES. IT IS KNOWN THAT PARTICLES ARE ACCELERATED (TO ENERGIES ~KEV) BY MAGNETOTAIL RECONNECTION AND FURTHER ACCELERATED (UP TO MEV) VIA INTERACTION WITH THE CONSEQUENT KINETIC STRUCTURES AND INJECTION INTO THE INNER MAGNETOSPHERE. HOWEVER (1) HOW PARTICLES ARE ACCELERATED BY MAGNETOTAIL RECONNECTION AND ITS CONSEQUENT KINETIC STRUCTURES AND (2) HOW THESE ACCELERATED PARTICLES ARE INJECTED INTO THE INNER MAGNETOSPHERE VIA THE INTERACTION OF THESE EARTHWARD PROPAGATING STRUCTURES WITH DIPOLE FIELD ARE STILL NOT WELL UNDERSTOOD. TO REVEAL THESE TWO IMPORTANT PROCESSES WE PROPOSE A SYNERGISTIC STUDY USING MULTISPACECRAFT OBSERVATIONS AND PARTICLE-IN-CELL (PIC) SIMULATIONS. WE WILL USE THEMIS AND ARTEMIS SPACECRAFT SIMULTANEOUS OBSERVATIONS IN THE MAGNETOTAIL AT DIFFERENT GEOCENTRIC DISTANCES TO INVESTIGATE PARTICLE ENERGIZATION AND INJECTION DURING RECONNECTION AND EARTHWARD/ TAILWARD TRANSPORT. WE WILL USE LARGE-SCALE TWO-DIMENSIONAL (2-D) AND THREE-DIMENSIONAL (3-D) PIC MODELS GUIDED BY OUR OBSERVATIONS AND PHYSICAL INTUITIONS TO SIMULATE THE ENERGETIC PARTICLE ACCELERATION AND INJECTION PROCESSES. SCIENCE GOAL AND OBJECTIVES: BY COMPREHENSIVE USE OF MULTISPACECRAFT DATASETS AND NUMERICAL SIMULATIONS WE WILL: (1) INVESTIGATE THE MULTISTAGE SUCCESSIVE PARTICLE ACCELERATION PROCESS BY MAGNETOTAIL COLLISIONLESS RECONNECTION AND ITS CONSEQUENT KINETIC STRUCTURES: FRS BBFS AND DFBS. (2) EXPLORE HOW THE ACCELERATED PARTICLES ARE INJECTED INTO THE INNER MAGNETOSPHERE VIA THE INTERACTION BETWEEN THESE EARTHWARD PROPAGATING STRUCTURES WITH THE GEOMAGNETIC DIPOLE FIELD. RELEVANCE TO ONE OR MORE OF THE FOUR DECADAL SURVEY GOALS: THIS PROPOSED RESEARCH CONTRIBUTES TO TWO OF THE FOUR HIGH LEVEL SCIENCE GOALS FROM THE HELIOPHYSICS DECADAL SURVEY NAMELY 2. DETERMINE THE DYNAMICS AND COUPLING OF EARTH S MAGNETOSPHERE IONOSPHERE AND ATMOSPHERE AND THEIR RESPONSE TO SOLAR AND TERRESTRIAL INPUTS AND 4. DISCOVER AND CHARACTERIZE FUNDAMENTAL PROCESSES THAT OCCUR BOTH WITHIN THE HELIOSPHERE AND THROUGHOUT THE UNIVERSE . METHODOLOGY: DATA ANALYSIS AND MODELING: (1) WE WILL USE STATISTICS OF FIVE THEMIS SPACECRAFT OBSERVATIONS IN 2008-2009 TO INVESTIGATE THE EFFICIENCY OF ACCELERATION ASSOCIATED WITH PLASMA FLOWS ORIGINATING FROM THE RECONNECTION AND PROPAGATING EARTHWARD. STATISTICS OF THREE THEMIS SPACECRAFT IN 2010-2017 WILL BE USED TO COLLECT INFORMATION ABOUT PARTICLE ENERGIZATIONS AND INJECTIONS. SIMULTANEOUS OBSERVATIONS OF THEMIS AND ARTEMIS SPACECRAFT WILL SERVE FOR INVESTIGATION OF EFFICIENCY OF PARTICLE ACCELERATION WITHIN EARTHWARD AND TAILWARD FLOWS. (2) WE WILL USE LARGE-SCALE 2-D AND 3-D PIC SIMULATIONS IN WHICH ELECTROMAGNETIC FIELDS ARE UPDATED BY SOLVING MAXWELL S EQUATIONS WITH AN EXPLICIT LEAPFROG SCHEME AND PARTICLES (ELECTRONS AND IONS) ARE ADVANCED RELATIVISTICALLY IN THE FIELDS. THE SIMULATIONS EMPLOY AN INITIAL CONFIGURATION OF A DIPOLE FIELD PLUS A THIN HARRIS CURRENT SHEET. NO INITIAL PERTURBATIONS OR EXTERNAL DRIVING FIELDS WILL BE IMPOSED MULTIPLE X-LINE RECONNECTION WILL BE TRIGGERED SPONTANEOUSLY AND NUMBERS OF FRS BBFS AND DFBS ARE EXPECTED TO BE GENERATED AND PROPAGATE TOWARD THE EARTH/TAIL., G54188565, G5561424898, G5953495884, G767677632, G8874547989
OpenAlex ID: W4409946926