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The High‐latitude Ionosphere Dynamics for Research Applications (HIDRA) model is part of the Multiscale Atmosphere‐Geospace Environment model under development by the Center for Geospace Storms NASA DRIVE Science Center. This study employs HIDRA to simulate upflows of H+, He+, O+, and N+ ions, with a particular focus on the relative N+ concentrations, production and loss mechanisms, and thermal upflow drivers as functions of season, solar activity, and magnetospheric convection. The simulation results demonstrate that N+ densities typically exceed He+ densities, N+ densities are typically ∼10% O+ densities, and N+ concentrations at quiet‐time are approximately 50%–100% of N+ concentrations during storm‐time. Furthermore, the N+ and O+ upflow fluxes show similar trends with variations in magnetospheric driving. The inclusion of ion‐neutral chemical reactions involving metastable atoms is shown to have significant effects on N+ production rates. With this metastable chemistry included, the simulated ion density profiles compare favorably with satellite measurements from Atmosphere Explorer C and Orbiting Geophysical Observatory 6. Key Points: Simulated N+ and O+ densities increase while N+ to O+ density ratios decrease with solar activityN+ concentrations typically exceed He+ densities and N+ fluence rates versus solar activity qualitatively resemble those for O+The inclusion of metastable chemical production of N+ is critical to numerically reproduce observations [ABSTRACT FROM AUTHOR]

The ion upflow has great significance for the transport and exchange of particles during magnetosphere‐ionosphere coupling process. Previous studies focus on the ion upflow in the polar region, and find that ion upflow has hemispheric asymmetries. In subauroral region, the ion upflow is closely related with subauroral ion drift (SAID). However, the characteristics of ion upflow associated with SAID in both northern and southern hemispheres are still unknown. Based on the observation of DMSP satellites F16‐F18 from 2010 to 2020, we investigate the north‐south hemisphere distributions of ion upflow associated with SAID during quiet and disturbed time. The ion upflow rate presents localized features in both hemispheres. The ion upflow rate in the southern hemisphere is slightly higher/lower than that in the northern hemisphere before/after 1900 MLT. The ion upflow velocity in the southern hemisphere shows a clear dependence on magnetic local time (MLT). Furthermore, We find that the hemispheric asymmetry of ion upflow is closely related to the asymmetric configuration of the ionospheric parameters such as plasma density, conductance and solar elevation angle during magnetosphere‐ionosphere coupling process. The result also indicates that SAID and sunlight condition play important roles in the ion upflow in subauroral region. Key Points: Ion upflow occurrence rate in the southern hemisphere is slightly higher/lower than that in the northern hemisphere before/after 1900 MLTThe ion upflow velocity exhibits a strong dependence on MLT, which was observed in the southern hemisphere in this studyBesides subauroral ion drift, the sunlight condition also affects the occurrence rate and velocity of ion upflow in both hemispheres [ABSTRACT FROM AUTHOR]

The connection between energy inputs and the generation of ion upflows and outflows is a topic of keen scientific interest and the subject of a number of empirical studies. Despite this interest, it remains uncertain how different ion species respond to energy input, what defines the upper and lower bounds of the ion flux, and what role solar illumination plays in regulating the relationship between energy input and ion upflows/outflows. This work simulates how ion flux scales with low and high altitude energization, and to a combination of both. Furthermore, we examine the influence of solar illumination on these relationships by considering how the scaling of ion flux with energy input changes over the solar cycle, comparing solar minimum and maximum, as well as how they change from day to night conditions. We find O+ flux tends to respond more strongly to energy inputs than H+ flux, with the O+ flux often exhibiting a lower activation energy and a greater dynamic range. The lower bound of the ion flux at 4,000 km is typically defined by the polar wind H+, although O+ upflows can dominate at low altitudes in the presence of significant frictional heating of the ion gas or soft electron precipitation. However, when significant soft electron precipitation and wave‐particle interactions are present simultaneously the lower bound of the ion flux at 4,000 km is defined by the O+. Finally, we find a difference between the steady state response of the outflow to energy input and the peak response. Key Points: O+ flux tends to respond more strongly to energy inputs than H+ fluxThe lower bound of the ion flux at 4,000 km is typically defined by the polar wind H+ except when large e− precipitation is presentThe peak response of the outflow to energy input can be different than the steady state response [ABSTRACT FROM AUTHOR]

Previous studies have shown that solar flares can significantly affect Earth's ionosphere and induce ion upflow with a magnitude of ∼110 m/s in the topside ionosphere (∼570 km) at Millstone Hill (42.61°N, 71.48°W). We use simulations from the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM) and observations from Incoherent Scatter Radar (ISR) at Millstone Hill to reveal the mechanism of ionospheric ion upflow near the X9.3 flare peak (07:16 LT) on 6 September 2017. The ISR observed ionospheric upflow was captured by the TIEGCM in both magnitude and morphology. The term analysis of the F‐region ion continuity equation during the solar flare shows that the ambipolar diffusion enhancement is the main driver for the upflow in the topside ionosphere, while ion drifts caused by electric fields and neutral winds play a secondary role. Further decomposition of the ambipolar diffusive velocity illustrates that flare‐induced changes in the vertical plasma density gradient is responsible for ion upflow. The changes in the vertical plasma density gradient are mainly due to solar extreme ultraviolet (EUV, 15.5–79.8 nm) induced electron density and temperature enhancements at the F2‐region ionosphere with a minor and indirectly contribution from X‐ray (0–15.5 nm) and ultraviolet (UV, 79.8–102.7 nm). Plain Language Summary: Solar flares with a sudden enhancement in solar X‐ray and extreme ultraviolet (EUV) radiation heat the upper atmosphere and increase electron density dramatically, leading to an expansion of Earth's upper atmosphere. Previous observations have shown an upward ion motion of ∼110 m/s at middle latitudes during solar flares; however, the cause of it remains largely speculative. In this paper, we provide a quantitative analysis of the ionospheric ion upflow during the 6 September 2017 X9.3 flare via model‐data comparison. During solar flares, X‐ray and EUV radiation are intensified at different degrees, thus producing different magnitudes of enhancement in ionospheric plasma density and temperature at different altitudes. Enhanced electron density and temperature at ionospheric F‐region due to solar EUV photoionization build up an additional upward pressure gradient force, pushing the plasmas upward. Key Points: Flare‐induced ionospheric ion upflow at midlatitudes was simulated by a 3‐D ionosphere‐thermosphere coupled modelThe midlatitude ion upflow was mainly due to changes in ambipolar diffusion during flaresThe solar extreme ultraviolet (EUV) enhanced electron density and temperature were the primary driver of ambipolar diffusion velocity changes [ABSTRACT FROM AUTHOR]

During the magnetic storm starting on September 7, 2017, the MEP‐i instrument onboard the Arase (ERG) satellite observed molecular ions (O2+/NO+/N2+) in the ring current. The molecular ions were observed by Arase in four orbits during this magnetic storm. This indicates that there was a continuous molecular ion supply from the ionosphere. During the storm main phase around the second Dst minimum (∼−100 nT) on September 8, 2017, the European Incoherent Scatter (EISCAT) radar observed the ion upflow (∼50–150 m s−1) in the low‐altitude (250–350 km) ionosphere together with strong ion heating up to >2,000 K. The convective electric field derived from the electron heating observed by EISCAT at an altitude of approximately 110 km was also enhanced by a factor of 2. The observations suggest that the additional ion heating at low altitudes helps to cause the fast upflow and transport molecular ions upward. The flux decreases from 280 to 350 km altitudes due to the dissociative recombination was estimated to be approximately two orders of magnitude. This resulted in significant molecular ion flux remaining at 350 km altitude. These results suggest that the low‐altitude ion upflow caused by the ion frictional heating enables molecular ions to escape to space against rapid loss by the dissociative recombination. Plain Language Summary: Molecular ions (O2+/NO+/N2+) in the ring current are sometimes observed during magnetic storms. These molecular ions come from the deep ionosphere and considered good tracers of escape mechanisms from the Earth's ionosphere to the magnetosphere. However, it has not been revealed how these molecular ions are transported upward, especially by ion upflows in the low‐altitude ionosphere (∼250–350 km). It is difficult to transport sufficient flux of molecular ions due to deceleration by the strong gravitational force and rapid decrease by dissociative recombination even during magnetic storms. In this paper, we report the analysis results of the fast ion upflow (∼100 m s−1) event in the low‐altitude ionosphere observed by the European Incoherent Scatter (EISCAT) radar, while the Arase (ERG) satellite observed molecular ions in the inner magnetosphere during the magnetic storm starting on September 7, 2017. The results suggest that ion frictional heating created the ion upflow and could be a source of outflows at higher altitudes in the ionosphere to supply the molecular ions into the magnetosphere. Key Points: Arase satellite observed molecular ions in the ring current during the magnetic storm starting on September 7, 2017An ion upflow from the deep ionosphere was observed with enhancements of electric field and ion temperature by EISCATThe fast upflow caused by the ion frictional heating enables molecular ions to escape to space against dissociative recombination [ABSTRACT FROM AUTHOR]

Ion upflow in the F region and topside ionosphere can greatly influence the ion density and fluxes at higher altitudes and thus has significant impact on ion outflow. We investigated the statistical characteristics of ion upflow and downflow using a 3‐year (2011–2013) data set from the Poker Flat Incoherent Scatter Radar (PFISR). Ion upflow is twice more likely to occur on the nightside than on the dayside in PFISR observations, while downflow events occur more often in the afternoon sector. Upflow and downflow on the dayside tend to occur at altitudes ~500 km, higher than those on the nightside. Both upflow and downflow occur more frequently as ion convection speed increases. Upflow observed from 16 to 6 magnetic local time through midnight is associated with temperature and density enhancements. Occurrence rates of upflow on the nightside and downflow on the dayside increase with geomagnetic activity level. On the nightside, occurrence rate of ion upflow increases with enhanced solar wind and interplanetary magnetic field (IMF) drivers as well as southwestward local magnetic perturbations. The lack of correlation of upflow on the dayside with the solar wind and IMF parameters is because PFISR is usually equatorward of the dayside auroral zone. Occurrence rate of downflow does not show strong dependence on the solar wind and IMF conditions. However, it occurs much more frequently on the dayside when the IMF By > 10 nT and the IMF Bz < −10 nT, which we suggest is associated with the decaying of the dayside storm‐enhanced density (SED) and the SED plume. Key Points: The occurrence frequency of ion upflow increases with enhanced geomagnetic activity level and stronger solar wind and IMF drivingIon upflow at PFISR latitude is twice more likely to occur on the nightside than on the daysidePeak ion downflow occurrence rate reaches 30% on the dayside during strongly positive IMF By and negative Bz, associated with SED and plume [ABSTRACT FROM AUTHOR]

We present a statistical study of the ion upflow associated with subauroral polarization streams (SAPS) in the ionospheric subauroral region at different substorm times using three Defense Meteorological Satellite Program satellite (F16–F18) data for five years (2010–2014) in the Northern Hemisphere. The results show similarities between SAPS and the ion upflow at different intensity of substorms both in occurrence rate distribution and velocity distribution. In comparison to SAPS, the distribution of the ion upflow shows the smaller occurrence region and lower velocity. We also find that frictional heating plays an important role in ion upflow from the SAPS region. The intense substorms can trigger strong SAPS channels, enhanced frictional heating, and large ion upflow. In addition, there is a moderate linear correlation between SAPS velocity and field‐aligned velocity that is consistent with some previous findings. Our results also show that frictional heating can gradually dominate the ion upflow process in intense substorms, while it may not be the only factor to affect the whole upflow process. Key Points: Ion upflow is frequently observed near the SAPS flow channel, with similar distributions in the occurrence and velocity as SAPSStatistical analysis shows that field‐aligned (ion upflow) velocity has moderate linear correlation with SAPS velocity indeedFrictional heating can gradually dominate the ion upflow process, while it may not be the only factor to affect such process [ABSTRACT FROM AUTHOR]

Auroral emission at 427.8‐nm from N2+ ions is caused by precipitation of energetic electrons, or by resonant scattering of sunlight by auroral N2+ ions. The latter often causes impressive purple aurora at high altitudes. However, statistical characteristics of auroral 427.8‐nm emission have not been well studied. In this paper we report occurrence characteristics of high 427.8‐nm emission intensities (more than 100 R) at subauroral latitudes, based on measurements by a filter‐tilting photometer over 14 years (2005–2018) at Athabasca, Canada (magnetic latitude: ~62°). We divided the data set into solar elevation angles (θs) more than and less than −24° (shadow height of sunlight: 600 km) to separate the 427.8‐nm emissions caused by resonant scattering of sunlight and those excited by auroral electrons, respectively. The occurrence rate of 427.8‐nm emissions of more than 100 R is 10.6% and 7.65% for θs more than and less than −24°, respectively, confirming that resonant scattering of sunlight by N2+ ions is a cause of the strong 427.8‐nm emissions of more than 100 R in the sunlit ionosphere. The occurrence rate is high in the postmidnight sector and increases with increasing geomagnetic activity, solar wind speed, and density. The occurrence rate is lowest in winter. A high occurrence rate was observed in 2015–2018, during the declining phase of the 11‐year solar activity. Superposed epoch analysis indicates that the 427.8‐nm emission exceeds 100 R when solar wind speed increases and solar wind density concurrently decreases, though the standard deviation of the data is rather large. Plain Language Summary: Purple auroras can be caused either by energetic electrons at low altitudes (about 100 km), or by scattering of sunlight at much higher altitudes where the auroral curtains are in the Sun although the ground is in darkness. We have studied both types by sorting measurements of the purple emission from ionized nitrogen molecules depending on how far the Sun is below the horizon. We used 14 years' worth of data in order to study the effects over more than a solar cycle (11 years typically). The emission is stronger when general auroral activity increases, which is in turn related to solar wind speed and density. Same result was obtained by binning solar wind and geomagnetic activity data, timing them relative to strong purple aurora. It is also highest in the declining phase of the solar cycle. The emission intensity becomes low in winter. Recently, a type of purple aurora outside of the normal auroral oval has been reported, called "STEVE." We note that we have studied the "traditional" type of purple aurora. Key Points: We made a statistical study of auroral/resonant‐scattering 427.8‐nm emission observed at subauroral latitudes over 14 yearsThe resonant‐scattering 427.8‐nm emission indicates upflow of ionospheric nitrogen ions to higher altitudesThe emission increases during magnetic active periods and is associated with increases of solar wind speed and density [ABSTRACT FROM AUTHOR]

We investigate the statistical characteristics of the ion upflow occurrence in association with ion and electron heatings in the polar ionosphere using the European Incoherent Scatter Svalbard Radar during the period of 2000–2015. The ion upflow events are classified as four types: with ion temperature increase (Type 1), with electron temperature increase (Type 2), with both ion and electron temperature increases (Type 3), and without any temperature increase (Type 4). These four types of upflow events are statistically analyzed with various geophysical conditions. We found that the overall occurrence of ion upflow is highest for Type 3 and then followed by Type 2, Type 1, and Type 4. This result indicates that the ion upflow is highly associated with soft particle precipitation induced electron heating, which becomes more effective with simultaneous friction induced ion heating. The statistical characteristics of ion upflow is summarized as follows: (1) It is most highly distributed in the daytime with a double peak structure but a deep minimum at dusk, (2) the highest occurrence appears at about 350‐ to 450‐km altitude for most of local time but extended to higher altitude near the magnetic local noon, (3) the ions mostly reach only up to about 200 km above their initiated altitudes, (4) it tends to increase with magnetic activity, particularly during the daytime, but (5) decreases and distributed at higher altitude with increasing solar activity, and (6) finally, the maximum occurrence appears in December solstice but the minimum in June solstice for most of local times. Key Points: Ambipolar electric field with electron heating may be more effective to produce ion upflow when the ions are also simultaneously heatedDiurnal variation of ion upflow occurrence shows a double peak structure during the day and a deep minimum at duskMaximum occurrence appears in December solstice but minimum in June solstice [ABSTRACT FROM AUTHOR]

The altitude and the local solar time dependence of the electron pressure and the resulting ambipolar electric field in the Martian ionosphere have been investigated by utilizing the electron density and temperature measurements obtained by the Langmuir Probe and Waves instrument aboard the Mars Atmosphere and Volatile Evolution mission (MAVEN) spacecraft. The magnitude of the ambipolar electric field is estimated to be 1–2 μV/m on the dayside—producing, on average, a total potential drop of up to 800 mV below 600 km. These calculations, when combined with the previous understandings on the significance of the Poynting flux in the Martian ionosphere, suggest that the ambipolar electric field and the Poynting flux are equally important in establishing a steady state in which the ions are transported from below the exobase to higher altitudes. Key Points: The critical altitude at which the ions transition from unmagnetized to magnetized varies between 150 and 210 km and shows an asymmetry with local solar timeThe total potential drop between the transition altitude and the topside ionosphere (600 km) can reach to values above 800 mVThe role of the draped magnetic field topology on the balance of the various terms in the ion momentum equation is explored [ABSTRACT FROM AUTHOR]

Abstract: By analyzing a five‐year period (2010–2014) of Defense Meteorological Satellite Program (DMSP) plasma data, we investigated ion upflow occurrence, speed, density, and flux above the polar cap in the northern hemisphere under different solar zenith angle (SZA), solar activity (F10.7), and convection speed. Higher upflow occurrence rates in the dawn sector are associated with regions of higher convection speed, while higher upflow flux in the dusk sector is associated with higher density. The upflow occurrence increases with convection speed and solar activity but decreases with SZA. Upflow occurrence is the lowest when the SZA > 100° and the convection speeds are low. While, the upflow velocity and flux show a clear seasonal dependence with higher speed in the winter and higher flux in the summer during low convection conditions. However, they are detected for the first time to be both higher in summer during high convection conditions. These results suggest that ion upflow in the polar cap is controlled by the combination of convection, solar activity, and solar illumination. [ABSTRACT FROM AUTHOR]