Coordinated observations on the spatiotemporal development of global-scale dipolarizations and their coupling to meso-scale dipolarizations
Year: 2025
Type: article
Abstract: Global- and meso-scale dipolarizations are well-known features of Earth’s magnetosphere, but their coupling remains poorly understood. Here, using a new approach that combines 2D ionospheric field-aligned current (FAC) maps with coordinated observations from a network of magnetospheric satellites, we directly show that individual global-scale dipolarizations can expand from the nightside to, or even into, the dayside. These expansions are enduring (20–30 minutes), slow (2–4 deg/min), and global in extent (up to 12 hours in local time), consistent with previous statistical inferences but now explicitly observed. The expanding FACs form a two-sheet current system as described by the Boström II model. In contrast, meso-scale dipolarizations are bursty (a few minutes), fast (10s deg/min, 10s = several ten), and localized (several hours in local time), as evidenced by auroral expansions and satellite data. They are associated with the line-current system as described by the Boström I model, i.e., the substorm current wedge. Notably, meso-scale dipolarizations often emerge near the expanding edge of a global-scale dipolarization, suggesting a dynamic coupling between the two scales. These observations provide a complementary scenario to the simulation-based interpretation that global-scale dipolarizations result from the accumulation of meso-scale dipolarizations. Here, meso-scale dipolarizations appear far less frequently than in simulations and occur around the edge of global-scale dipolarizations. This implies that meso-scale dipolarizations may be sporadically triggered during the azimuthal expansion of global-scale dipolarizations.
Source: Earth and Planetary Physics
DOI: 10.26464/epp2026021
Authors: Tian Sheng, M. Weygand J., Liu J., R. Wygant J., Lyons L., Angelopoulos V., Bortnik J., D. Reeves G.
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,324
Awards: THE EARTH S MAGNETOSPHERE IS HIGHLY DYNAMIC. THROUGHOUT THE MAGNETOSPHERE THE PLASMA IS IN MOTION. ONE CONSEQUENCE OF THIS MOTION IS THE EARTHWARD TRANSPORT OF PLASMA ON CLOSED MAGNETIC FIELD LINES IN THE MAGNETOTAIL. AS THE PLASMA CONVECTS IT IS HEATED ADIABATICALLY AND THE PLASMA PRESSURE INCREASES. AS SUCH WHAT WAS PLASMA FLOW ENERGY IN THE OUTER MAGNETOSPHERE HAS BECOME THERMAL ENERGY IN THE INNER MAGNETOSPHERE. OR IN TERMS OF PRESSURE DYNAMIC PRESSURE FROM THE FLOW HAS BECOME THERMAL PRESSURE. THESE PRESSURES BOTH CONTRIBUTE TO THE FORCE BALANCE WITHIN THE PLASMA. THERE IS A THIRD CONTRIBUTOR TO THE FORCE BALANCE AND THAT IS THE FORCE ASSOCIATED WITH MAGNETIC FIELD PRESSURE AND CURVATURE THAT IS THE JXB FORCE. IN THE INNER MAGNETOSPHERE WHERE THE THERMAL PRESSURE FREQUENTLY DOMINATES THE DYNAMIC PRESSURE THE JXB FORCE MAINLY BALANCES THE THERMAL PRESSURE FORCE. BUT WHEN THE MAGNETOSPHERE IS DYNAMIC AS OCCURS DURING SUBSTORMS THE DYNAMIC PRESSURE BECOMES AN IMPORTANT CONTRIBUTOR. WHILE THE PLASMA MUST BE IN LOCAL FORCE BALANCE IN THE ABSENCE OF PARALLEL ELECTRIC FIELDS THE FIELD LINES ARE EQUIPOTENTIALS AND SINCE THE FIELD LINES THREAD THE IONOSPHERE ANY MAGNETOSPHERIC FLOW PATTERN MAPS TO THE IONOSPHERE. THE IONOSPHERE HOWEVER IS HIGHLY COLLISIONAL AND THE NEUTRAL ATMOSPHERE ACTS TO SLOW DOWN ANY IMPOSED FLOW. THERE MUST THEREFORE BE A JXB FORCE ACTING IN THE IONOSPHERE AS WELL TO OVERCOME THE FRICTIONAL DRAG FROM THE NEUTRALS. BECAUSE OF THE COLLISIONS THE IONOSPHERE IS GENERALLY DISSIPATIVE (J.E>0) AND THE MAGNETIC FIELD DOES WORK ON THE PLASMA. THE PERPENDICULAR CURRENTS THAT OVERCOME THE FRICTION MUST CLOSE VIA FIELD-ALIGNED CURRENTS TO REGIONS WERE THE CURRENTS ARE GENERATED I.E. J.E<0. THIS COUPLING IS INHERENTLY COMPLEX SINCE WITHIN THE MAGNETOSPHERE THERE ARE ALSO REGIONS WHERE J.E>0. BUT THE POINT HERE IS THAT FORCE BALANCE IN THE IONOSPHERE REQUIRES FIELD-ALIGNED CURRENTS THAT IN TURN CLOSE WITH PERPENDICULAR CURRENTS IN THE MAGNETOSPHERE. THE RESULTANT JXB FORCE BALANCES THE PLASMA THERMAL AND DYNAMIC PRESSURE FORCES. BASED ON THE DIFFERENT CONTRIBUTORS TO THE FORCE BALANCE IN THE MAGNETOSPHERE THE FIELD-ALIGNED CURRENT CLOSURE IN THE MAGNETOSPHERE MAY BE ASSOCIATED WITH THERMAL PRESSURE GRADIENTS FLOW BRAKING OR VORTICITY IN THE PLASMA FLOW. THE BASIC OBJECTIVE OF THE PROPOSED RESEARCH IS TO DETERMINE THE RELATIONSHIP BETWEEN THE VARIOUS FORCES AND ASSOCIATED CURRENTS IN THE COUPLED TIME-VARYING MAGNETOSPHERE-IONOSPHERE SYSTEM. THE PROPOSED RESEARCH USES A COMBINATION OF DATA AND SIMULATIONS. DATA FROM THE LOW EARTH ORBITING FAST AURORAL SNAPSHOT (FAST) SMALL EXPLORER PROVIDE INFORMATION ON THE FIELD-ALIGNED CURRENTS AND THE ASSOCIATED PARTICLE DISTRIBUTIONS ABOVE THE IONOSPHERE. THE LATTER CAN BE USED TO CONSTRAIN WHERE THE FIELD-LINES PASSING THROUGH THE FAST SPACECRAFT MAP TO IN THE MAGNETOSPHERE. FOR EXAMPLE THE PRESENCE OF A DOUBLE LOSS-CONE FEATURE IN THE IONS SUGGESTS THAT THE FIELD LINES MAP TO THE INNER MAGNETOSPHERE WHERE PITCH-ANGLE SCATTERING IS REDUCED. IN SITU OBSERVATIONS FROM THE THEMIS SPACECRAFT CAN FURTHER CONSTRAIN THE MAPPING. WE WILL ALSO MAKE USE OF GROUND-BASED RESOURCES SUCH AS ALL SKY IMAGERS (ASIS) AND MAGNETOMETERS. MAGNETOMETER MEASUREMENTS CAN BE USED TO CREATE EQUIVALENT CURRENT SYSTEM MAPS TO PLACE THE MORE LOCAL FAST MEASUREMENTS INTO A GLOBAL CONTEXT. FINALLY WE WILL MAKE USE OF NUMERICAL SIMULATIONS TO GUIDE US IN OUR INTERPRETATION OF THE IN SITU OBSERVATIONS AND ALLOW US TO DETERMINE THE RELATIVE IMPORTANCE OF FLOW SHEAR FLOW BRAKING OR PRESSURE GRADIENTS. THE PROPOSED RESEARCH ADDRESSES TWO SCIENCE GOALS AS GIVEN IN THE HELIOPHYSICS DECADAL SURVEY: (1) DETERMINE THE DYNAMICS AND COUPLING OF THE EARTH S MAGNETOSPHERE IONOSPHERE AND ATMOSPHERE AND THEIR RESPONSE TO SOLAR TERRESTRIAL INPUTS; AND (2) DISCOVER AND CHARACTERIZE FUNDAMENTAL PROCESSES THAT OCCUR BOTH WITHIN THE HELIOSPHERE AND THROUGHOUT THE UNIVERSE., G1359114879, G1542932375, G1799348198, SCIENCE GOALS AND OBJECTIVES THE OVERARCHING GOAL OF THIS PROPOSAL IS TO UNDERSTAND THE CHARACTERISTICS OF THE IONOSPHERIC CURRENTS OF RECONNECTION-GENERATED FAST FLOWS THAT CAUSE EITHER GLOBAL SUBSTORMS OR LOCALIZED PSEUDO BREAKUPS. SPECIFICALLY WE AIM TO QUANTITATIVELY ASSESS BOTH THE LOCALIZED AND GLOBAL RESPONSES OF EQUIVALENT IONOSPHERIC CURRENTS (EICS) AND FIELD ALIGNED CURRENTS (FACS) TO DIFFERENT TYPES OF FAST FLOWS: WITH OR WITHOUT GLOBAL SUBSTORMS; WITH DIPOLARIZATION FRONTS OR SLOWED FLOWS IN THE BREAKING REGION. THE SPECIFIC SCIENCE QUESTIONS THAT WILL BE ADDRESSED ARE: 1. WHAT ARE THE TYPICAL CHARACTERISTICS OF THE IONOSPHERIC RESPONSE OF EICS AND FACS TO DIFFERENT TYPES OF FAST FLOWS? A. HOW DO THE IONOSPHERIC CURRENTS VARY IN LATITUDE LOCAL TIME INTENSITY WITH DIFFERENT FLOWS? B. UNDER WHAT CONDITIONS DO CURRENT VORTICES APPEAR AND WHERE DO THESE VORTICES APPEAR WITH RESPECT TO THE HARANG DISCONTINUITY? 2. WHAT ARE THE TYPICAL CHARACTERISTICS OF DIFFERENT TYPES OF FAST FLOWS? A. DO THE FLUX TRANSPORT RATE AND ENTROPY OF FLOWS DETERMINE WHETHER A GLOBAL SUBSTORM CAN BE TRIGGERED? B. ARE THE CHANGES IN THE LOBE MAGNETIC FIELD STRENGTH AND OPEN LOBE MAGNETIC FLUX DIFFERENT FOR DIFFERENT TYPES OF FLOWS? 3. WHAT ARE THE POTENTIAL PHYSICAL QUANTITIES THAT DETERMINE WHETHER A FAST FLOW WILL TRIGGER A GLOBAL SUBSTORM OR A LOCALIZED PSEUDO BREAKUP? METHODOLOGY THE PROPOSED PROJECT WILL COMBINE THE FIELD AND PARTICLE DATA OF FAST FLOWS OBSERVED BY NASA S THEMIS VAN ALLEN PROBE (VAP) AND MMS; IONOSPHERIC EICS AND CURRENT AMPLITUDES (I.E. A PROXY FOR THE FACS) OBTAINED FROM THE SEC METHODS; AND A NEURAL NETWORK MODEL OF THE IONOSPHERIC CURRENTS TO ADDRESS THE ABOVE IMPORTANT SCIENCE QUESTIONS. MORE SPECIFICALLY 1. USING EXISTING LISTS OF FAST FLOWS AND SUBSTORM ONSETS GENERATED BY OUR TEAM [CHU ET AL. JGR 2015] WE WILL CATEGORIES FAST FLOWS WITH AND WITHOUT GLOBAL SUBSTORMS; FAST FLOWS WITH DIPOLARIZATION FRONT AND SLOWED FLOWS IN THE BREAKING REGION. 2. USING THE HIGH SPATIOTEMPORAL RESOLUTION DATA OF EICS OBTAINED FROM THE SPHERICAL ELEMENTARY CURRENT SYSTEM (SEC) METHOD BY OUR TEAM [WEYGAND ET AL. JGR 2011] WE WILL DEVELOP A NEURAL NETWORK (NN) MODEL OF THE IONOSPHERIC CURRENTS WHICH PROVIDES FULL LOCAL TIME COVERAGE. THIS MODEL RESOLVES THE PROBLEM THAT PERIODICALLY NO DATA ARE AVAILABLE ON THE NIGHTSIDE WHEN THE MAGNETOMETERS ARE LOCATED AT OTHER LOCAL TIMES AND GREATLY INCREASES THE NUMBER OF CONJUNCTIONS WITH SATELLITES. 3. USING THE MODELED IONOSPHERIC CURRENT DATA WE WILL CONSTRUCT THE CHARACTERISTICS OF THE IONOSPHERIC RESPONSE TO DIFFERENT CATEGORIES OF FAST FLOWS. 4. FOR DIFFERENT CATEGORIES OF FAST FLOWS WE WILL STUDY THE CHARACTERISTICS OF THESE FLOWS (ENTROPY AND FLUX TRANSPORT RATE) AND THE MAGNETOSPHERIC RESPONSE (CHANGE IN THE LOBE MAGNETIC FIELD AND AMOUNT OF FLUX RELEASED BY THE TAIL RECONNECTION). RELEVANCE TO THE DECADAL SURVEY GOALS AND THE H-SR PROGRAM OUR PROPOSED PROJECT DIRECTLY ADDRESSES THE MOST IMPORTANT QUESTIONS IN MAGNETOSPHERIC RECONNECTION WHICH IS CURRENTLY ONE OF NASA S HIGHEST PRIORITIES. THE PROPOSED RESEARCH IS HIGHLY RELEVANT TO GOAL 2 FROM THE HELIOPHYSICS DECADAL SURVEY WHICH IS TO DETERMINE THE DYNAMICS AND COUPLING OF EARTH S MAGNETOSPHERE IONOSPHERE AND ATMOSPHERE AND THEIR RESPONSE TO SOLAR AND TERRESTRIAL INPUTS . THE PROPOSED PROJECT PERFECTLY FITS THE SCOPE OF HELIOPHYSICS SR PROGRAM., G2311491520, G2693931063, G2848425133, G308878704, G3283688573, G3392305090, THE OBJECTIVE OF OUR PROPOSAL IS TO UNDERSTAND THE DYNAMICS OF THE EARTH S MAGNETOPAUSE IN THE PRESENCE OF FLOW SHEARS AND THE EFFECTS OF THESE DYNAMICS ON SOLAR WIND-MAGNETOSPHERE COUPLING AND THE GLOBAL FIELD-ALIGNED CURRENT SYSTEM. ALTHOUGH UBIQUITOUS IN THE GEOSPACE ENVIRONMENT THE VELOCITY SHEARS THAT TRIGGER THE ONSET OF THE KELVIN-HELMHOLTZ INSTABILITY (KHI) AND GENERATE FLOW VORTICITY ARE PARTICULARLY PROMINENT ON THE MAGNETOPAUSE AND ALONG THE INNER EDGE OF THE LOW-LATITUDE BOUNDARY LAYER. SIMULATIONS AND RECENT MULTI-SPACECRAFT OBSERVATIONS SUGGEST THAT THE KHI AND MAGNETIC RECONNECTION CAN OPERATE SIMULTANEOUSLY ON MAGNETOPAUSE AND ALSO THAT FLOW VORTICES CAN GENERATE FIELD-ALIGNED CURRENTS IN THE REGION-1 CURRENT SYSTEM SENSE. THESE STUDIES INDICATE THAT THE ROLES AND EFFECTS OF FLOW SHEARS AROUND THE MAGNETOPAUSE RANGE FROM THE MICROSCOPIC INTERACTIONS WITH RECONNECTION AND CONSEQUENT MODIFICATION OF RECONNECTION PROCESSES TO THE MACROSCOPIC ASPECTS SUCH AS MASS MOMENTUM ENERGY TRANSFER ACROSS THE MAGNETOPAUSE AND THE VORTEX-GENERATED FIELD-ALIGNED CURRENTS THAT CONTRIBUTE TO THE GLOBAL CURRENT SYSTEM. YET OUR KNOWLEDGE OF THE ACTUAL INFLUENCE AND IMPORTANCE OF FLOW VELOCITY SHEAR IN SUCH MICRO-TO-MACROPHYSICAL PROCESSES REMAINS PRIMITIVE. VIA OUR PROJECT WE AIM TO ANSWER INFLUENCES OF FLOW SHEAR AND KINETIC-SCALE VORTICES ON RECONNECTION PROCESSES AND HOW KHI AND RECONNECTION INTERACT ON THE MICROAND MESO-SCALES (Q1) ION/ELECTRON VORTEX DYNAMICS IN TERMS OF THE ORIENTATION/MAGNITUDE OF FLOW VORTICIES (Q2) AND THEIR EFFECT ON THE REGION-1 CURRENT SYSTEM (Q3). THESE TOPICS ARE WELL INTEGRATED TO MAXIMIZE THE SCIENTIFIC RETURN FROM MMS ABILITY TO CALCULATE THE ION AND ELECTRON FLOW VORTICITIES USING ITS TETRAHEDRON FORMATION WITH VARYING INTER-SPACECRAFT SEPARATION DOWN TO THE ELECTRON SCALE. OUR AIM IN ANSWERING Q1-3 IS TO BRING THE MICRO-TO-MACROSCOPIC PIECES OF FLOW SHEAR PROCESSES TOGETHER TO CONSTRUCT A COMPREHENSIVE PICTURE OF THE ROLES AND IMPACTS OF FLOW VORTICES ON THE SOLAR WIND-MAGNETOSPHERE-IONOSPHERE COUPLING. WE WILL ADDRESS THESE QUESTIONS USING A COMBINATION OF METHODOLOGIES THAT INCORPORATE THE AMPLE MMS (FPI FGM EDP EPD HPCA ETC.) OBSERVATIONS OF RECONNECTION WITH/WITHOUT FLOW SHEAR KH VORTICES AND CONJUGATE GROUND MAGNETOGRAMS AND NUMERICAL SIMULATIONS. TO DETERMINE SOLAR WIND AND BOUNDARY CONDITIONS AND PLACE THE MMS OBSERVATIONS IN CONTEXT WE USE SIMULTANEOUS OBSERVATIONS FROM WIND ACE ARTEMIS CLUSTER AND GEOTAIL. WE WILL MAKE FULL USE OF HIGH PERFORMANCE SIMULATION TOOLS 3-D PIC SIMULATIONS. OUR PLAN IS VIA COMPARATIVE STUDIES TO INTEGRATE OUR PHYSICAL UNDERSTANDING GAINED FROM THE SIMULATIONS WITH IN-SITU MMS OBSERVATIONS. UNDERSTANDING THE IMPORTANCE AND EFFECTS OF ION AND ELECTRON FLOW VORTICES GENERATED ALONG THE MAGNETOPAUSE WILL IMPROVE OUR UNDERSTANDING OF THE DYNAMICS AND COUPLING OF EARTH S MAGNETOSPHERE IONOSPHERE AND ATMOSPHERE AND THEIR RESPONSE TO SOLAR AND TERRESTRIAL INPUTS (DSG #2). IN PARTICULAR OUR STUDY WILL ADDRESS TWO OF THE MOST CRUCIAL PHYSICAL PROCESSES I.E. KHI AND MAGNETIC RECONNECTION THAT ARE FUNDAMENTAL PROCESSES THAT OCCUR BOTH WITHIN THE HELIOSPHERE AND THROUGHOUT THE UNIVERSE (DSG #4). ALL THESE ASPECTS MANIFEST THE RELEVANCE OF OUR PROJECT TO THE FOUR GOALS IN THE HELIOPHYSICS DECADAL SURVEY. THIS PROJECT IS ALSO KEY TO MMS MISSION. THE PROPOSED INVESTIGATION IS DIRECTLY RELEVANT TO THE GOALS OF MMS MISSION: INVESTIGATION OF THE VELOCITY SHEAR EFFECTS ON THE SMALL-SCALE THREE-DIMENSIONAL STRUCTURE AND DYNAMICS OF THE THIN CURRENT LAYERS AND FAST-MOVING ELECTRON DIFFUSION REGION., Collaborative Research: Flow Channel Control of Substorm Expansion Phase Spatial Coverage and Duration, G4201635079, G54188565, G5953495884, G5995242478, G6770359845, G6872388977
OpenAlex ID: W4417272441
FWCI:
Cites:
Cited by:
Related to: