Title: Exact Alpha‐Beta Mapping of IGRF Magnetic Field in the Ionosphere
Abstract Finding the magnetic flux mapping in the ionosphere is very important. It would not only divide the surface into the elements with the same flux, but also indicate locations of conjugated points. It is important for studies of field aligned currents and bouncing of energetic charged particles and their precipitation. The existing methods involve numerical magnetic field lines tracing in the entire volume of the magnetosphere or numerical integration along assumed contour lines of the Euler potentials on the surface of the ionosphere. It is possible to determine the mapping with these methods near the magnetic equator, but not on middle latitudes and near and inside the polar caps. Our approach is to search for the Euler potentials as a sum of basic functions with their coefficients. Each basic function is a product of a sine or cosine of longitude multiplied bymand the Legendre polynomial of the colatitude angle cosine and of the ordern. Maxima ofmandnin this calculation were set to 13. The difference between the radial component from the cross product of the Euler potentials gradients and from International Geomagnetic Reference Field is less than 0.01 percent. We discuss the possibility of using orthogonal coordinates defined on the sphere's surface, which remain finite functions ofθandφeverywhere except for the vicinities of the North and South poles. The issues with numerical errors accumulated on long tracing are avoided when using this approach. more »« less
An analytical solution for the long-standing problem of the exact Euler potentials mapping in the
ionosphere is foundThe mapping is applied to the International Geomagnetic Reference Field magnetic fieldIt is also applicable for other models, including T04
Vandas, Marek; Romashets, Evgeny
(, Solar Physics)
Leblaher, John
(Ed.)
Abstract Romashets and Vandas (2024) derived a method for the determination of Euler potentials at a spherical surface and applied it to the geomagnetic field. Here, we apply it to find Euler potentials at the source surface. A regular mesh defined by Euler potentials divides the source surface to surface elements with the same magnetic flux. By tracing magnetic-field lines away from the source surface, Euler potentials can be extended into the heliosphere.
Abstract Magnetic fields likely play an important role in the formation of young protostars. Multiscale and multiwavelength dust polarization observations can reveal the inferred magnetic field from scales of the cloud to core to protostar. We present continuum polarization observations of the young protostellar triple system IRAS 16293-2422 at 89μm using HAWC+ on SOFIA. The inferred magnetic field is very uniform with an average field angle of 89° ± 23° (E of N), which is different from the ∼170° field morphology seen at 850μm at larger scales (≳2000 au) with JCMT POL-2 and at 1.3 mm on smaller scales (≲300 au) with Atacama Large Millimeter/submillimeter Array. The HAWC+ magnetic field direction is aligned with the known E-W outflow. This alignment difference suggests that the shorter wavelength HAWC+ data is tracing the magnetic field associated with warmer dust likely from the outflow cavity, whereas the longer wavelength data are tracing the bulk magnetic field from cooler dust. Also, we show in this source the dust emission peak is strongly affected by the observing wavelength. The dust continuum peaks closer to source B (northern source) at shorter wavelengths and progressively moves toward the southern A source with increasing wavelength (from 22 to 850μm).
Artemyev, A. V.; Angelopoulos, V.; Zhang, X. ‐J.; Runov, A.; Petrukovich, A.; Nakamura, R.; Tsai, E.; Wilkins, C.
(, Journal of Geophysical Research: Space Physics)
Abstract The magnetospheric substorm is a key mode of flux and energy transport throughout the magnetosphere associated with distinct and repeatable magnetotail dynamical processes and plasma injections. The substorm growth phase is characterized by current sheet thinning and magnetic field reconfiguration around the equatorial plane. The global characteristics of current sheet thinning are important for understanding of magnetotail state right before the onset of magnetic reconnection and of the key substorm expansion phase. In this paper, we investigate this thinning at different radial distances using plasma sheet (PS) energetic (>50 keV) electrons that reach from the equator to low altitudes during their fast (∼1 s) travel along magnetic field lines. We perform a multi‐case study and a statistical analysis of 34 events with near‐equatorial observations of the current sheet thinning by equatorial missions and concurrent, latitudinal crossings of the ionospheric projection of the magnetotail by the low‐altitude Electron Losses and Fields Investigation (ELFIN) CubeSats at approximately the same local time sector. Energetic electron fluxes thus collected by ELFIN provide near‐instantaneous (<5 min duration) radial snapshots of magnetotail fluxes. Main findings of this study confirm the previously proposed concepts with low‐altitude energetic electron measurements: (a) Energy distributions of low‐altitude fluxes are quantitatively close to the near‐equatorial distributions, which justifies the investigation of the magnetotail current sheet reconfiguration using low‐altitude measurements. (b) The magnetic field reconfiguration during the current sheet thinning (which lasts ≥ an hour) results in a rapid shrinking of the low‐altitude projection of the entire PS (from near‐Earth, ∼10RE, to the lunar orbit ∼60RE) to 1–2° of magnetic latitude in the ionosphere. (c) The current sheet dipolarization, common during the substorm onset, is associated with a very quick (∼10 min) change of the tail magnetic field configuration to its dipolar state, as implied by a poleward expansion of the PSPS at low altitudes.
Barnes, Peter J.; Ryder, Stuart D.; Novak, Giles; Crutcher, Richard M.; Fissel, Laura M.; Pitts, Rebecca L.; Schap III, William J.
(, The Astrophysical Journal)
Abstract We present Stratospheric Observatory For Infrared Astronomy (SOFIA) + Atacama Large Millimeter/submillimeter Array (ALMA) continuum and spectral-line polarization data on the massive molecular cloud BYF 73, revealing important details about the magnetic field morphology, gas structures, and energetics in this unusual massive star formation laboratory. The 154μm HAWC+ polarization map finds a highly organized magnetic field in the densest, inner 0.55 × 0.40 pc portion of the cloud, compared to an unremarkable morphology in the cloud’s outer layers. The 3 mm continuum ALMA polarization data reveal several more structures in the inner domain, including a parsec-long, ∼500M⊙“Streamer” around the central massive protostellar object MIR 2, with magnetic fields mostly parallel to the east–west Streamer but oriented north–south across MIR 2. The magnetic field orientation changes from mostly parallel to the column density structures to mostly perpendicular, at thresholdsNcrit= 6.6 × 1026m−2,ncrit= 2.5 × 1011m−3, andBcrit= 42 ± 7 nT. ALMA also mapped Goldreich–Kylafis polarization in12CO across the cloud, which traces, in both total intensity and polarized flux, a powerful bipolar outflow from MIR 2 that interacts strongly with the Streamer. The magnetic field is also strongly aligned along the outflow direction; energetically, it may dominate the outflow near MIR 2, comprising rare evidence for a magnetocentrifugal origin to such outflows. A portion of the Streamer may be in Keplerian rotation around MIR 2, implying a gravitating mass 1350 ± 50M⊙for the protostar+disk+envelope; alternatively, these kinematics can be explained by gas in free-fall toward a 950 ± 35M⊙object. The high accretion rate onto MIR 2 apparently occurs through the Streamer/disk, and could account for ∼33% of MIR 2's total luminosity via gravitational energy release.
Wang, Shuo; Zou, Ying; Hu, Qiang; Shi, Xueling; Hasegawa, Hiroshi
(, Journal of Geophysical Research: Space Physics)
Abstract Flux transfer events (FTEs) are a type of magnetospheric phenomena that exhibit distinctive observational signatures from the in situ spacecraft measurements. They are generally believed to possess a magnetic field configuration of a magnetic flux rope and formed through magnetic reconnection at the dayside magnetopause, sometimes accompanied with enhanced plasma convection in the ionosphere. We examine two FTE intervals under the condition of southward interplanetary magnetic field (IMF) with a dawn‐dusk component. We apply the Grad‐Shafranov (GS) reconstruction method to the in situ measurements by the Magnetospheric Multiscale (MMS) spacecraft to derive the magnetic flux contents associated with the FTE flux ropes. In particular, given a cylindrical magnetic flux rope configuration derived from the GS reconstruction, the magnetic flux content can be characterized by both the toroidal (axial) and poloidal fluxes. We then estimate the amount of magnetic flux (i.e., the reconnection flux) encompassed by the area “opened” in the ionosphere, based on the ground‐based Super Dual Auroral Radar Network (SuperDARN) observations. We find that for event 1, the FTE flux rope is oriented in the approximate dawn‐dusk direction, and the amount of its total poloidal magnetic flux falls within the range of the corresponding reconnection flux. For event 2, the FTE flux rope is oriented in the north‐south direction. Both the FTE flux and the reconnection flux have greater uncertainty. We provide a detailed description about a formation scenario of sequential magnetic reconnection between adjacent field lines based on the FTE flux rope configurations from our results.
Romashets, E, and Vandas, M. Exact Alpha‐Beta Mapping of IGRF Magnetic Field in the Ionosphere. Retrieved from https://par.nsf.gov/biblio/10538999. Journal of Geophysical Research: Space Physics 129.1 Web. doi:10.1029/2023JA032131.
Romashets, E, & Vandas, M. Exact Alpha‐Beta Mapping of IGRF Magnetic Field in the Ionosphere. Journal of Geophysical Research: Space Physics, 129 (1). Retrieved from https://par.nsf.gov/biblio/10538999. https://doi.org/10.1029/2023JA032131
@article{osti_10538999,
place = {Country unknown/Code not available},
title = {Exact Alpha‐Beta Mapping of IGRF Magnetic Field in the Ionosphere},
url = {https://par.nsf.gov/biblio/10538999},
DOI = {10.1029/2023JA032131},
abstractNote = {Abstract Finding the magnetic flux mapping in the ionosphere is very important. It would not only divide the surface into the elements with the same flux, but also indicate locations of conjugated points. It is important for studies of field aligned currents and bouncing of energetic charged particles and their precipitation. The existing methods involve numerical magnetic field lines tracing in the entire volume of the magnetosphere or numerical integration along assumed contour lines of the Euler potentials on the surface of the ionosphere. It is possible to determine the mapping with these methods near the magnetic equator, but not on middle latitudes and near and inside the polar caps. Our approach is to search for the Euler potentials as a sum of basic functions with their coefficients. Each basic function is a product of a sine or cosine of longitude multiplied bymand the Legendre polynomial of the colatitude angle cosine and of the ordern. Maxima ofmandnin this calculation were set to 13. The difference between the radial component from the cross product of the Euler potentials gradients and from International Geomagnetic Reference Field is less than 0.01 percent. We discuss the possibility of using orthogonal coordinates defined on the sphere's surface, which remain finite functions ofθandφeverywhere except for the vicinities of the North and South poles. The issues with numerical errors accumulated on long tracing are avoided when using this approach.},
journal = {Journal of Geophysical Research: Space Physics},
volume = {129},
number = {1},
publisher = {Wiley},
author = {Romashets, E and Vandas, M},
editor = {Pierrard, Viviane}
}
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