The catastrophic eruption of Hunga Tonga-Hunga Ha'apai volcano (20.54° S, 175.38° W, hereafter the Tonga volcano) at 04:14:45 UT 15 January 2022 released an estimated energy between 10 and 28 EJ into the atmosphere, which is believed to be the largest since the 1883 Krakatoa eruption (Wright et al., 2022). The extreme eruption not only triggered earthquakes and tsunamis, but also caused significant disturbances in the upper atmosphere
Geomagnetic activity in Earth's outer magnetosphere stimulates intense electromagnetic power flows that propagate to the high-latitude ionosphere as low-loss shear Alfvén waves-a type of magnetically guided, incompressible magnetohydrodynamic (MHD) wave (Alfvén, 1942;Hasegawa & Uberoi, 1982). Injection of Alfvénic power into Earth's Polar Regions has several important consequences. Alfvén waves signal the coming arrival in the ionosphere of disturbances in flows and magnetic fields in the outer reaches of the magnetosphere (Ferdousi & Raeder, 2016). Alfvén wave-induced electron precipitation produces spectacular dynamic aurora (Kataoka et al., 2021;Keiling et al., 2003). The waves contribute to the energization and exodus of heavy ions (principally O + ) from the ionosphere into space (Chaston et al., 2004;Hatch et al., 2016;Hull et al., 2019). And their collisional absorption in the cusp-region ionosphere-thermosphere locally heats and upwells the upper atmosphere (Dessler, 1959;Hogan et al., 2021;Tu et al., 2011), contributing to enhanced satellite drag in low-earth orbit. The distribution, intensity, and causality of low-altitude Alfvénic energy deposition thus underlies many space weather phenomena.The pattern of Alfvénic Poynting flux flowing to low altitude at frequencies exceeding 5.5 mHz has been termed the "Alfvénic oval" (Keiling, 2021). Its statistical distribution inferred from satellite measurements depends on the level of geomagnetic activity and has the form of an irregular, ≈10° wide band in magnetic latitude (MLAT) with nonuniform intensity in magnetic local time (MLT). The average Poynting flux is most persistent on the
The thermospheric winds at high latitudes are impacted by both the pressure gradient changes via Joule heating and the ionospheric convection through ion drag, which are both associated with the energy deposition from the magnetosphere. Therefore, the high-latitude thermospheric winds are important indicators of the dynamic coupling process of the magnetosphere-ionosphere-thermosphere system. Over the past decades, thermospheric winds have been observed by satellite instruments (
It is commonly believed that the magnitude and orientation of interplanetary magnetic field (IMF) together with the solar wind (SW) velocity have the most important impact on the cross polar cap potential ( pc ), so that little attention has been given to the effect of SW density, especially under northward IMF conditions. Previous studies have shown that pc increases with SW density as a response to the changes in magnetosheath force balance, while our study shows that pc has more complicated responses to the SW density depending on the magnitude of IMF rather than a simple linear response as reported previously. The pc may be insensitive to SW density increasing at moderate IMF B z (cf. 8 nT) and at intense B z (20 nT) under large-density conditions. The different behavior of SW density in regulating pc is mainly due to the competing effects originated from viscous interaction and magnetic reconnection. Further, the physical mechanisms are explored, including the driving sources of the viscous potential and affecting factors of reconnection potential. These results pave the way for better understanding of the SW density effects on solar wind-magnetosphere-ionosphere (SW-M-I) interactions.Plain Language Summary Ionospheric electric potential in the polar region is primarily generated due to the interaction between solar wind (SW) and magnetosphere. The cross polar cap potential ( pc ), which represents difference between the maximum and minimum electric potentials in the polar cap, is closely related to the upstream interplanetary magnetic field and SW driving. SW density is one of the important dominant factors of pc , while its physical mechanism has not been fully understood. A systematic research is conducted by using the LFM magnetosphere model to clarify the mechanism of SW density affecting pc under purely northward interplanetary magnetic field (IMF). The simulation results demonstrate that pc responses differently to the increasing SW density under different IMF B z . Under small IMF B z , pc increases linearly with SW density, and as B z increases, pc becomes stable and changes little with SW density increasing. Under large IMF, pc first increases and then becomes insensitive. These results pave the way for better understanding of the SW density effects on SW-M-I interactions.
According to the expressions of orbital angular momentum modes in optical fibers, we reveal the physical meanings of the corresponding angular and radial mode orders of the even and odd vector modes. Then we demonstrate that just like orbital angular momentum modes can be represented with linear combinations of even and odd vector modes in optical fibers, even and odd vector modes can in turn be represented with linear combinations of orbital angular momentum modes. The final results suggest that the even and odd vector modes in optical fibers can be considered as single-photon spin-orbit entangled states, indicating the possibility of using optical fiber structures to generate single-photon spin-orbit entangled states.
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