Space Physics
See recent articles
Showing new listings for Tuesday, 3 December 2024
- [1] arXiv:2412.01081 [pdf, html, other]
-
Title: Effect of 2009 major SSW event on the mesospheric CO2 coolingComments: 10 pages, 8 figuresSubjects: Space Physics (physics.space-ph)
Carbon dioxide (CO2), an important trace species that is gradually increasing in the atmosphere due to anthropogenic activities, causes enhanced warming in the lower atmosphere. The increased concentration of CO2 in the upper atmosphere results in enhanced radiative cooling rates leading to the contraction of the upper atmosphere. Due to its long lifetime and large vertical gradient, CO2 concentration is also influenced by large dynamic events. We report a startling case of variability in CO2 density and its infrared radiative cooling rates in the mesosphere and lower thermospher during a major sudden stratospheric warming (SSW) event. A counter-intuitive connection between CO2 density and resulting CO2 radiative cooling has been observed during the 2009 major SSW event. The behaviour of CO2 cooling rates during such a dramatic events draw attention to our current understanding of CO2 infrared cooling variation and its connection to changes in CO2 concentration. The significance of temperature and atomic oxygen variability in the observed cooling patterns despite changes in CO2 concentration, is also highlighted.
- [2] arXiv:2412.01796 [pdf, html, other]
-
Title: Suppression of the collisionless tearing mode by flow shear: implications for reconnection onset in the Alfv\'enic solar windComments: 14 pages, 3 figures, submitted to Journal of Plasma PhysicsSubjects: Space Physics (physics.space-ph); Solar and Stellar Astrophysics (astro-ph.SR); Plasma Physics (physics.plasm-ph)
We analyse the collisionless tearing mode instability of a current sheet with a strong shear flow across the layer. The growth rate decreases with increasing shear flow, and is completely stabilized as the shear flow becomes Alfvénic. We also show that in the presence of strong flow shear, the tearing mode growth rate decreases with increasing background ion-to-electron temperature ratio, the opposite behaviour to the tearing mode without flow shear. We find that even a relatively small flow shear is enough to dramatically alter the scaling behaviour of the mode, because the growth rate is small compared to the shear flow across the ion scales (but large compared to shear flow across the electron scales). Our results may explain the relative absence of reconnection events in the near-Sun Alfvénic solar wind observed recently by NASA's Parker Solar Probe.
New submissions (showing 2 of 2 entries)
- [3] arXiv:2412.00072 (cross-list from cs.LG) [pdf, html, other]
-
Title: The Muon Space GNSS-R Surface Soil Moisture ProductComments: 23 pages, 10 figuresSubjects: Machine Learning (cs.LG); Computational Engineering, Finance, and Science (cs.CE); Computer Vision and Pattern Recognition (cs.CV); Space Physics (physics.space-ph)
Muon Space (Muon) is building a constellation of small satellites, many of which will carry global navigation satellite system-reflectometry (GNSS-R) receivers. In preparation for the launch of this constellation, we have developed a generalized deep learning retrieval pipeline, which now produces operational GNSS-R near-surface soil moisture retrievals using data from NASA's Cyclone GNSS (CYGNSS) mission. In this article, we describe the input datasets, preprocessing methods, model architecture, development methods, and detail the soil moisture products generated from these retrievals. The performance of this product is quantified against in situ measurements and compared to both the target dataset (retrievals from the Soil Moisture Active-Passive (SMAP) satellite) and the v1.0 soil moisture product from the CYGNSS mission. The Muon Space product achieves improvements in spatial resolution over SMAP with comparable performance in many regions. An ubRMSE of 0.032 cm$^3$ cm$^{-3}$ for in situ soil moisture observations from SMAP core validation sites is shown, though performance is lower than SMAP's when comparing in forests and/or mountainous terrain. The Muon Space product outperforms the v1.0 CYGNSS soil moisture product in almost all aspects. This initial release serves as the foundation of our operational soil moisture product, which soon will additionally include data from Muon Space satellites.
- [4] arXiv:2412.00365 (cross-list from astro-ph.SR) [pdf, html, other]
-
Title: Cross Helicity and the Helium Abundance as a Metric of Solar Wind Heating and Acceleration: Characterizing the Transition from Magnetically Closed to Magnetically Open Solar Wind Sources and Identifying the Origin of the Alf\'enic Slow WindSubjects: Solar and Stellar Astrophysics (astro-ph.SR); Space Physics (physics.space-ph)
The two-state solar wind paradigm is based on observations showing that slow and fast solar wind have distinct properties like helium abundances, kinetic signatures, elemental composition, and charge-state ratios. Nominally, the fast wind originates from solar sources that are continuously magnetically open to the heliosphere like coronal holes while the slow wind is from solar sources that are only intermittently open to the heliosphere like helmet streamers and pseudostreamers. The Alfvénic slow wind is an emerging 3rd class of solar wind that challenges the two-state fast/slow paradigm. It has slow wind speeds but is highly Alfvénic, i.e. has a high correlation between velocity and magnetic field fluctuations along with low compressibility typical of Alfvén waves, which is typically observed in fast wind. Its other properties are also more similar to the fast than slow wind. From 28 years of Wind observations at 1 AU, we derive the solar wind helium abundance ($A_\mathrm{He}$), Alfvénicity ($\left|\sigma_c\right|$), and solar wind speed ($v_\mathrm{sw}$). Characterizing vsw as a function of $\left|\sigma_c\right|$ and $A_\mathrm{He}$, we show that the maximum solar wind speed for plasma accelerated in source regions that are intermittently open is faster than the minimum solar wind speed for plasma accelerated in continuously open regions. We infer that the Alfvénic slow wind is likely solar wind originating from open-field regions with speeds below the maximum solar wind speed for plasma from intermittently open regions. We then discuss possible implications for solar wind heating and acceleration. Finally, we utilize the combination of helium abundance and normalized cross helicity to present a novel solar wind categorization scheme.
- [5] arXiv:2412.00519 (cross-list from astro-ph.EP) [pdf, html, other]
-
Title: Terrestrial atmospheric ion implantation occurred in the nearside lunar regolith during the history of Earth's dynamoComments: Original version submitted to Science Advances on April 19, 2024, but no longer under consideration there. Revised version presently under consideration in Communications Earth & Environment. 60 pages, 11 figures, 7 tables, including supplementary information, and extended dataSubjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR); Geophysics (physics.geo-ph); Space Physics (physics.space-ph)
Light volatile elements in lunar regolith are thought to be a mixture of the solar wind and Earth's atmosphere, the latter sourced in the absence of geomagnetic field. However, the extent to which both the current and primitive geodynamo influence the transport of terrestrial ions still remains unclear, and this uncertainty is further complicated by the enigmatic composition and poorly constrained location of the Eoarchean exosphere. Here we use 3-D MHD numerical simulations with present-day magnetized and Archean unmagnetized atmospheres to investigate how Earth's intrinsic magnetic field affects this transfer, aiming to constrain how and when the lunar isotopic signature provides a record of Earth's paleoatmosphere. We find that atmospheric transfer is efficient only when the Moon is within Earth's magnetotail. The non-solar contribution to the lunar soil is best explained by implantation during the long history of the geodynamo, rather than any short, putatively unmagnetized epoch of early Earth. This further suggests the history of the terrestrial atmosphere, spanning billions of years, could be preserved in buried lunar soils. Our results indicate that the elemental abundances of Apollo samples are very sensitive to Earth's exobase altitude, which, at the time of ion implantation, was never smaller than 190 km.
- [6] arXiv:2412.00564 (cross-list from astro-ph.HE) [pdf, html, other]
-
Title: Maximum Energy of Particles in PlasmasComments: 18 pages, 4 figures; accepted for publication in Astrophysical JournalSubjects: High Energy Astrophysical Phenomena (astro-ph.HE); Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR); Plasma Physics (physics.plasm-ph); Space Physics (physics.space-ph)
Particles are accelerated to very high, non-thermal energies in space, solar, and astrophysical plasma environments. In cosmic ray physics, the "Hillas limit" is often used as a rough estimate (or the necessary condition) of the maximum energy of particles. This limit is based on the concepts of one-shot direct acceleration by a system-wide motional electric field, as well as stochastic and diffusive acceleration in strongly turbulent environments. However, it remains unclear how well this limit explains the actual observed maximum energies of particles. Here we show, based on a systematic review, that the observed maximum energy of particles -- those in space, solar, astrophysical, and laboratory environments -- often reach the energy predicted by the Hillas limit. We also found several exceptions, such as electrons in solar flares and jet-terminal lobes of radio galaxies, as well as protons in planetary radiation belts, where deviations from this limit occur. We discuss possible causes of such deviations, and we argue in particular that there is a good chance of detecting ultra-high-energy ($\sim$100 GeV) solar flare electrons that have not yet been detected. We anticipate that this study will facilitate further interdisciplinary discussions on the maximum energy of particles and the underlying mechanisms of particle acceleration in diverse plasma environments.
Cross submissions (showing 4 of 4 entries)
- [7] arXiv:2312.11130 (replaced) [pdf, html, other]
-
Title: Empirical model of SSUSI-derived auroral ionization ratesComments: 15 pages, 6 figures, published in Earth and Space ScienceJournal-ref: Earth Space Sci., volume 11, issue 11, p. e2024EA003578, Nov 2024Subjects: Atmospheric and Oceanic Physics (physics.ao-ph); Earth and Planetary Astrophysics (astro-ph.EP); Space Physics (physics.space-ph)
We present an empirical model for auroral (90--150 km) electron--ion pair production rates, ionization rates for short, derived from SSUSI (Special Sensor Ultraviolet Spectrographic Imager) electron energy and flux data. Using the Fang et al., 2010 parametrization for mono-energetic electrons, and the NRLMSISE-00 neutral atmosphere model, the calculated ionization rate profiles are binned in 2-h magnetic local time (MLT) and 3.6$^{\circ}$ geomagnetic latitude to yield time series of ionization rates at 5-km altitude steps. We fit each of these time series to the geomagnetic indices Kp, PC, and Ap, the 81-day averaged solar F$_{\text{10.7}}$ radio flux index, and a constant term. The resulting empirical model can easily be incorporated into coupled chemistry--climate models to include particle precipitation effects.
- [8] arXiv:2403.04992 (replaced) [pdf, html, other]
-
Title: Probing the Solar System for Dark Matter Using the Sagnac EffectComments: 17 pages, 2 figures, 2 tablesSubjects: General Relativity and Quantum Cosmology (gr-qc); Space Physics (physics.space-ph)
This study investigates the potential of the Sagnac Effect for detecting dark matter in the Solar System, particularly within the Sun. Originating from the relative delay and interference of light beams traveling in opposite directions on rotating platforms, the effect can account for how varying gravitational conditions affect its manifestation. We analyze the Sagnac time in two static, spherically symmetric spacetimes: Schwarzschild and one incorporating dark matter, in the form of a perfect fluid. Comparing the relative deviations in Sagnac time calculated for these metrics in the reference frame of satellites orbiting our star, which serve as a rotating circular platform and emit laser beams in opposite directions, with the precision of onboard atomic clocks (about $10^{-11}$), allows us to evaluate the potential for detecting dark matter's gravitational influence through this effect.
- [9] arXiv:2409.12063 (replaced) [pdf, html, other]
-
Title: Post-Keplerian perturbations of the hyperbolic motion in the field of a rotating massive object. Analysis in terms of osculating and nonosculating (contact) elementsComments: LaTex2e, 22 pages, 5 tables, no figures. Accepted for publication in The Astrophysical Journal. Typo corrected in Equation (34)Journal-ref: ApJ 977 44 (2024)Subjects: General Relativity and Quantum Cosmology (gr-qc); Earth and Planetary Astrophysics (astro-ph.EP); Space Physics (physics.space-ph)
The perturbations of the hyperbolic motion of a test particle due to the general relativistic gravitoelectromagnetic Schwarzschild and Lense-Thirring components of the gravitational field of a rotating massive body are analytically worked out to the first post-Newtonian level in terms of the osculating Keplerian orbital elements. To the Newtonian order, the impact of the quadrupole mass moment of the source is calculated as well. The resulting analytical expressions are valid for a generic orientation in space of both the orbital plane of the probe and the spin axis of the primary, and for arbitrary values of the eccentricity. They are applied to 'Oumuamua, an interstellar asteroid which recently visited our solar system along an unbound heliocentric orbit, and to the Near Earth Asteroid Rendezvous (NEAR) spacecraft during its flyby of the Earth. The calculational approach developed can be straightforwardly extended to any alternative models of gravity as well.