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Abstract Nitric oxide (NO) emission via 5.3 µm wavelength plays dominant role in regulating the thermospheric temperature due to thermostat nature. The response of NO 5.3 mm emission to the negative pressure impulse during November 06–09, 2010 is studied by using Sounding of Atmosphere by Broadband Emission Radiometry (SABER) observations onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite and model simulations. The TIMED/SABER satellite observations demonstrate a significant enhancement in the high latitude region. The Open Geospace General Circulation Model (OpenGGCM), Weimer model simulations and Active Magnetosphere and Planetary Electrodynamics Response Experiment measurements exhibit intensification and equatorward expansion of the field-aligned-currents (FACs) post-negative pressure impulse period due to the expansion of the dayside magnetosphere. The enhanced FACs drive precipitation of low energy particle flux and Joule heating rate affecting whole magnetosphere–ionosphere–thermosphere system. Our study based on electric fields and conductivity derived from the EISCAT Troms$${\o }$$ $ø$radar and TIEGCM simulation suggests that the enhanced Joule heating rate and the particle precipitations prompt the increase in NO cooling emission. 

Abstract We present the observations of field‐aligned currents and the equatorial electrojet during the 23 March 2023 magnetic storm, focusing on the effect of the drastic decrease of the solar wind dynamic pressure occurred during the main phase. Our observations show that the negative pressure pulse had significant impact to the magnetosphere‐ionosphere system. It weakened large‐scale field‐aligned currents and paused the progression of the storm main phase for ∼3 hr. Due to the sudden decrease of the plasma convection after the negative pressure pulse, the low‐latitude ionosphere was over‐shielded and experienced a brief period of westward penetration electric field, which reversed the direction of the equatorial electrojet. The counter electrojet was observed both in space and on the ground. A transient, localized enhancement of downward field‐aligned current was observed near dawn, consistent with the mechanism for transmitting MHD disturbances from magnetosphere to the ionosphere after the negative pressure pulse. 

Abstract We examined rapid variations in the electron zebra stripe patterns, specifically atL = 1.5, over a three‐month duration, using twin Van Allen Probes within Earth's inner magnetosphere. During geomagnetically quiet intervals, these stripes exhibit a peak‐to‐valley ratio (Δj) ∼1.25 in detrended electron fluxes. However, during geomagnetic storms, they became highly prominent, with Δj > 2.5. The correlation between Δjand net field‐aligned currents (FACs) is observed to be high (0.70). Global magnetohydrodynamic (MHD) simulation results indicate that the westward electric field at midnight at low latitudes in the deep inner magnetosphere correlates well with net FACs. An increase in net FACs could amplify the dawn‐to‐dusk electric field in the deep inner magnetosphere, thereby causing the inward transport of electrons. Given that FACs are linked to the interaction between solar wind and the magnetosphere, our findings emphasize the importance of solar wind‐magnetosphere coupling in the deeper regions of the inner magnetosphere. 

Abstract One of the major processes that solar wind drives is the outflow and escape of ions from the planetary atmospheres. The major ion species in the upper ionospheres of both Earth and Mars is O⁺, and hence it is more likely to dominate the escape process. On Earth, due to a strong intrinsic magnetic field, the major ion outflow pathways are through the cusp, polar cap, and the auroral oval. In contrast, Mars has an induced magnetosphere, where the ionosphere is in direct contact with the shocked solar wind plasma. Therefore, physical processes underlying the ion energization and escape rates are expected to be different on Mars as compared to Earth. In the current work, we study the near-simultaneous ion outflow event from both Earth and Mars during the passage of a stream interaction region/high-speed stream (SIR/HSS) during 2016 May, when both the planets were approximately aligned on the same side of the Sun. The SIR/HSS propagation was recorded by spacecraft at the Sun–Earth L1 point and Mars Express at 1.5 au. During the passage of the SIR, the dayside and nightside ion outflows at Earth were observed by Van Allen Probes and Magnetospheric Multiscale Mission orbiters, respectively. At Mars, the ion energization at different altitudes was observed by the STATIC instrument on board the MAVEN orbiter. We observe evidence for the enhanced ion outflow from both Earth and Mars during the passage of the SIR, and identify the dominant drivers of the ion outflow. 

Abstract In this study, we present ionospheric observations of field‐aligned currents from AMPERE and the ESA Swarm A satellite, in conjunction with high‐resolution thermospheric density measurements from accelerometers on board Swarm C and GRACE‐FO, for the third and 4 February 2022 geomagnetic storms that led to the loss of 38 Starlink internet satellites. We study the global storm time response of the thermospheric density enhancements, including their decay and latitudinal distribution. We find that the thermospheric density enhances globally in response to high‐latitude energy input from the magnetosphere‐solar wind system and takes at least a full day to recover to pre‐storm density levels. We also find that the greatest density perturbations occur at polar latitudes consistent with the magnetosphere‐ionosphere dayside cusp, and that there appeared to be a saturation of the thermospheric density during the geomagnetic storm on the fourth. Our results highlight the critical importance of high‐latitude ionospheric observations when diagnosing potentially hazardous conditions for low‐Earth‐orbit satellites. 

Abstract This study investigates the comprehensive magnetospheric and ionospheric phenomena during a substorm event on 14 December 2013. The methodology involves analyzing data from satellites located within the plasmasphere at dusk‐side of the Earth, as well as data from ionospheric satellites mapped in the subauroral region. Magnetospheric data were analyzed to identify key features during the substorm event. Proton injection into the ring current, presence of proton and helium band electromagnetic ion cyclotron (EMIC) waves with different polarization characteristics, and harmonic structures in these EMIC waves were identified. These harmonic structures coincided with the appearance of magnetosonic waves characterized by rising tone structures and heating of low‐energy protons (<100 eV). Ionospheric satellites (DMSP F17 and POES 15) recorded enhanced proton precipitation contributing to the intensification of subauroral proton arcs. The analysis revealed that these enhanced proton fluxes were associated with variations in field‐aligned currents (FACs) and drove dynamics within the Sub‐Auroral Polarization Streams (SAPS). By combining and analyzing the magnetospheric and ionospheric data sets, this study provides a comprehensive understanding of magnetosphere‐ionosphere coupling during substorms, particularly on the duskside. The complex interdependence and causal relationships among EMIC waves, proton precipitation, subauroral proton arcs, FAC variations, and SAPS dynamics were highlighted. 

Abstract High latitude upper atmospheric inter‐hemispheric asymmetry (IHA) tends to be enhanced during geomagnetic storms, which may be due to the complex spatiotemporal changes and magnitude modifications in field aligned currents (FACs) and particle precipitation (PP). However, the relative contribution of FACs and PP to IHA in high‐latitude forcing and energy is not well understood. The IHA during the 2015 St. Patrick’s Day storm has been investigated using the global ionosphere thermosphere model (GITM), driven by FACs from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) and PP from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE). A comprehensive study of the (a) relative contributions of FACs and PP to electric potential and Joule heating and (b) sensitivity of electric potential and Joule heating to the changes in magnitude and distribution of FACs and PP is presented. The results indicate that FACs lead to larger potential and Joule heating changes compared with PP. The spatial variations of potential and Joule heating are also affected by variation in FACs. As for asymmetric magnitude and distribution, it is found that electric potential and Joule heating are more sensitive to changes in the distribution of FACs and PP than the magnitude of FACs and PP. A new spatial asymmetry index (SAI) is introduced, which reveals spatial asymmetric details that are often overlooked by previous studies. This sensitivity study reveals the relative contributions in high‐latitude forcing and emphasizes the importance of obtaining accurate FACs and PP in both hemispheres. 

Abstract In this study, we investigate the effects caused by interplanetary (IP) shock impact angles on the subsequent grounddB/dtvariations during substorms. IP shock impact angles have been revealed as a major factor controlling the subsequent geomagnetic activity, meaning that shocks with small inclinations with the Sun‐Earth line are more likely to trigger higher geomagnetic activity resulting from nearly symmetric magnetospheric compressions. Such field variations are linked to the generation of geomagnetically induced currents (GICs), which couple to artificial conductors on the ground leading to deleterious consequences. We use a sub‐set of a shock data base with 237 events observed in the solar wind at L1 upstream of the Earth, and large arrays of ground magnetometers at stations located in North America and Greenland. The spherical elementary current system methodology is applied to the geomagnetic field data, and field‐aligned‐like currents in the ionosphere are derived. Then, such currents are inverted back to the ground anddB/dtvariations are computed. Geographic maps are built with these field variations as a function of shock impact angles. The main findings of this investigation are: (a) typicaldB/dtvariations (5–10 nT/s) are caused by shocks with moderate inclinations; (b) the more frontal the shock impact, the more intense and the more spatially defined the ionospheric current amplitudes; and (c) nearly frontal shocks trigger more intensedB/dtvariations with larger equatorward latitudinal expansions. Therefore, the findings of this work provide new insights for GIC forecasting focusing on nearly frontal shock impacts on the magnetosphere. 

Abstract Since the discovery of the large‐scale field‐aligned currents it is widely acknowledged that gaps exist between the Region 1 (R1) and Region 2 (R2) currents in which the current values are relatively small as compared to neighboring regions. Assuming that the field‐aligned currents are generated by plasma pressure gradients, we analyzed data collected by the THEMIS satellites between 2007 and 2011 to identify regions with very low plasma pressure gradients (pressure plateaus), which could be responsible for the appearance of these gaps. It was found that the pressure profiles with low radial gradients are typically located between 8 and 10 Radii around the Earth. Projections of pressure plateau regions onto ionospheric altitudes, for both individual events and on a statistical basis, coincide with the locations of gaps between Iijima and Potemra field‐aligned currents. The role played by identified pressure plateaus in shaping the pattern of large‐scale field‐aligned currents is discussed. 

Abstract New, open access tools have been developed to validate ionospheric models in terms of technologically relevant metrics. These are ionospheric errors on GPS 3D position, HF ham radio communications, and peak F‐region density. To demonstrate these tools, we have used output from Sami is Another Model of the Ionosphere (SAMI3) driven by high‐latitude electric potentials derived from Active Magnetosphere and Planetary Electrodynamics Response Experiment, covering the first available month of operation using Iridium‐NEXT data (March 2019). Output of this model is now available for visualization and download viahttps://sami3.jhuapl.edu. The GPS test indicates SAMI3 reduces ionospheric errors on 3D position solutions from 1.9 m with no model to 1.6 m on average (maximum error: 14.2 m without correction, 13.9 m with correction). SAMI3 predicts 55.5% of reported amateur radio links between 2–30 MHz and 500–2,000 km. Autoscaled and then machine learning “cleaned” Digisonde NmF2 data indicate a 1.0 × 10¹¹ el. m³median positive bias in SAMI3 (equivalent to a 27% overestimation). The positive NmF2 bias is largest during the daytime, which may explain the relatively good performance in predicting HF links then. The underlying data sources and software used here are publicly available, so that interested groups may apply these tests to other models and time intervals.