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Key developments have been made to the NCAR Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X). Among them, the most important are the self‐consistent solution of global electrodynamics, and transport of O+ in the F‐region. Other ionosphere developments include time‐dependent solution of electron/ion temperatures, metastable O+ chemistry, and high‐cadence solar EUV capability. Additional developments of the thermospheric components are improvements to the momentum and energy equation solvers to account for variable mean molecular mass and specific heat, a new divergence damping scheme, and cooling by O(3P) fine structure. Simulations using this new version of WACCM‐X (2.0) have been carried out for solar maximum and minimum conditions. Thermospheric composition, density, and temperatures are in general agreement with measurements and empirical models, including the equatorial mass density anomaly and the midnight density maximum. The amplitudes and seasonal variations of atmospheric tides in the mesosphere and lower thermosphere are in good agreement with observations. Although global mean thermospheric densities are comparable with observations of the annual variation, they lack a clear semiannual variation. In the ionosphere, the low‐latitude E × B drifts agree well with observations in their magnitudes, local time dependence, seasonal, and solar activity variations. The prereversal enhancement in the equatorial region, which is associated with ionospheric irregularities, displays patterns of longitudinal and seasonal variation that are similar to observations. Ionospheric density from the model simulations reproduces the equatorial ionosphere anomaly structures and is in general agreement with observations. The model simulations also capture important ionospheric features during storms. Plain Language Summary A comprehensive numerical model, the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X), has been improved, in order to simulate the entire atmosphere and ionosphere, from the Earth's surface to ∼700 km altitude. This new version (v. 2.0) adds the capability to calculate the motions and temperatures of ions and electrons in the ionosphere. The model results compare well with available ground‐based and satellite observations, under both quiet and disturbed space weather conditions. Even with constant solar forcing, the model displays large day‐to‐day weather changes in the upper atmosphere and ionosphere, with basic patterns that agree with observations. This demonstrates the model ability to describe the connections between weather near the surface and weather in space. Key Points The Whole Atmosphere Community Climate Model has been extended to include ionospheric electrodynamics WACCM‐X simulates the interaction of lower atmosphere and solar influences in the ionosphere Preliminary validation demonstrates agreement with observations

Quasi-periodic pulsations (QPPs) are intrinsically connected to the mechanism of solar flares. They are regularly observed in the impulsive phase of flares since the 1970s. In the past years, the studies of QPPs regained interest with the advent of a new generation of soft X-ray/extreme ultraviolet radiometers that pave the way for statistical surveys. Since the amplitude of QPPs in these wavelengths is rather small, detecting them implies that the overall trend of the time series needs to be removed before applying any Fourier or wavelet transform. This detrending process is known to produce artificial detection of periods that must then be distinguished from real ones. In this paper, we propose a set of criteria to help identify real periods and discard artifacts. We apply these criteria to data taken by the Extreme Ultraviolet Variability Experiment (EVE)/ESP onboard the Solar Dynamics Observatory (SDO) and the Large Yield Radiometer (LYRA) onboard the PRoject for On-Board Autonomy 2 (PROBA2) to search for QPPs in flares stronger than M5.0 that occurred during Solar Cycle 24.

Solar extreme ultraviolet (EUV, 10–100 nm) and X‐ray (<10 nm) photons are the primary ionization source for the dayside Mars ionosphere. Their fluxes, especially at short wavelengths, increase significantly during solar flares. Among the series of solar flares and solar storms encountered by Earth and Mars in May 2024, one of the strongest solar flares occurred on 20 May 2024 when the Mars Atmospheric and Volatile EvolutioN (MAVEN) spacecraft was entering the Mars ionosphere. This event provides a unique opportunity to study the Mars ionospheric response to the onset and early phase of an extremely intense flare. This study utilizes two particle measurements onboard MAVEN to infer the flare timeline and a flare class of X12.8. The observed main ionospheric response is the increased O+${\\mathrm{O}}^{+}$density at ∼400 km altitude at the flare onset and at ∼300 km altitude near the flare peak.

The highly variable solar extreme ultraviolet (EUV) radiation is the major energy input to the Earth’s upper atmosphere, strongly impacting the geospace environment, affecting satellite operations, communications, and navigation. The Extreme ultraviolet Variability Experiment (EVE) onboard the NASA Solar Dynamics Observatory (SDO) will measure the solar EUV irradiance from 0.1 to 105 nm with unprecedented spectral resolution (0.1 nm), temporal cadence (ten seconds), and accuracy (20%). EVE includes several irradiance instruments: The Multiple EUV Grating Spectrographs (MEGS)-A is a grazing-incidence spectrograph that measures the solar EUV irradiance in the 5 to 37 nm range with 0.1-nm resolution, and the MEGS-B is a normal-incidence, dual-pass spectrograph that measures the solar EUV irradiance in the 35 to 105 nm range with 0.1-nm resolution. To provide MEGS in-flight calibration, the EUV SpectroPhotometer (ESP) measures the solar EUV irradiance in broadbands between 0.1 and 39 nm, and a MEGS-Photometer measures the Sun’s bright hydrogen emission at 121.6 nm. The EVE data products include a near real-time space-weather product (Level 0C), which provides the solar EUV irradiance in specific bands and also spectra in 0.1-nm intervals with a cadence of one minute and with a time delay of less than 15 minutes. The EVE higher-level products are Level 2 with the solar EUV irradiance at higher time cadence (0.25 seconds for photometers and ten seconds for spectrographs) and Level 3 with averages of the solar irradiance over a day and over each one-hour period. The EVE team also plans to advance existing models of solar EUV irradiance and to operationally use the EVE measurements in models of Earth’s ionosphere and thermosphere. Improved understanding of the evolution of solar flares and extending the various models to incorporate solar flare events are high priorities for the EVE team.

This paper shows that the relationship between solar EUV flux and the F10.7 index during the extended solar minimum (Smin) of 2007–2009 is different from that in the previous Smin. This difference is also seen in the relationship between foF2 and F10.7. We collected SOHO/SEM EUV observations and the F10.7 index, through June 2010, to investigate solar irradiance in the recent Smin. We find that, owing to F10.7 and solar EUV flux decreased from the last Smin to the recent one with different amplitudes (larger in EUV flux), EUV flux is significantly lower in the recent Smin than in the last one for the same F10.7. Namely, F10.7 does not describe solar EUV irradiance in the recent Smin as it did in the last Smin. That caused remarkable responses in ionospheric foF2. For the same F10.7, foF2 in the recent Smin is lower than that in the last one; further, it is also lower than that in other previous Smins. Therefore, F10.7 is not an ideal indicator of foF2 during the recent Smin, which implies that F10.7 is not an ideal proxy for solar EUV irradiance during this period, although it has been adequate during previous Smins. Solar irradiance models and ionospheric models will need to take this into account for solar cycle investigations. Key Points The relationship between EUV flux and F10.7 is unusual in the recent minimum Lowest foF2 values of its historical records in the recent minimum are reached F10.7 does not indicate foF2 in the recent minimum as it did in previous minima

Using the 8.5‐year Venus Express measurements, we demonstrate the asymmetric plasma distributions in the Venusian magnetosheath. An escaping plume is formed by pickup oxygen ions in the hemisphere where the motional electric field points outward from Venus, while the velocity of solar wind protons is faster in the opposite hemisphere. The pickup O+ escape rate is estimated to be (3.6 ± 1.4) × 1024 s−1 at solar maximum, which is comparable to the ion loss rate through the magnetotail, and (1.3 ± 0.4) × 1024 s−1 at solar minimum. The increase of O+ fluxes with extreme ultraviolet (EUV) intensity is significant upstream of the bow shock, partially attributed to the increase of exospheric neutral oxygen density. However, the solar wind velocity just has a slight effect on the pickup O+ escape rate in the magnetosheath, while the effect of solar wind density is not observed. Our results suggest the pickup O+ escape rate is mainly controlled by EUV radiation. Plain Language Summary The atmospheric evolution and water escape of Venus might be influenced by the solar wind‐Venus interaction. The atoms outside the induced magnetosphere are ionized by the solar radiation and accelerated to the escape velocity by solar wind electric field. In this way, the oxygen ions are picked up by solar wind and lost from the atmosphere to space. We use the data from Venus Express spacecraft to analyze the distribution of pickup oxygen ions in the vicinity of the planet. The planetary oxygen ions form a strong escaping plume, indicating the pickup process is an efficient escape channel removing the atmospheric particles. With an enhanced solar extreme ultraviolet radiation, the escape rate through this channel would be higher because more ions are produced and then picked up. This indicates an enhanced ion loss billions of years ago since the young Sun is more active, which might be a reason for the disappearance of a presumably‐existed ocean. Key Points The pickup O+ escape rate at Venus increases with solar activity, and it is comparable to the ion loss rate through the magnetotail The solar wind velocity has a slight effect on the pickup O+ escape rate in the magnetosheath The neutral oxygen density upstream of the bow shock might increase by a factor of two from solar minimum to maximum

Synoptic maps of solar EUV intensities have been constructed for many decades in order to display the distribution of the different EUV emissions across the solar surface, with each map representing one Carrington rotation ( i.e. one rotation of the Sun). This article presents a new solar EUV synoptic map dataset based on full-disk images from the Solar and Heliospheric Observatory/Extreme Ultraviolet Imaging Telescope (SOHO/EIT) and Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA). In order to remove the significant and complicated drift of EIT and AIA EUV intensities due to sensor degradation, we construct the synoptic maps in standardized intensity scale. We describe a method of homogenizing the SOHO/EIT maps with SDO/AIA maps by transforming the EIT intensity histograms to AIA levels. The new maps cover the years from 1996 to 2018 with 307 SOHO/EIT and 116 SDO/AIA synoptic maps, respectively. These maps provide a systematic and homogeneous view of the entire solar surface in four EUV wavelengths, and are well suited, e.g. , for studying long-term coronal hole evolution.

Simulations based on physical models of the thermosphere‐ionosphere system suggest that the ionosphere will sink as the thermosphere cools and contracts in response to increasing greenhouse gas concentrations. As a consequence, long‐term trends can be expected in ionospheric parameters such as: total electron content (TEC), the critical frequency of the F2 layer, foF2, and its peak height, hmF2. Since early 1990s, foF2 and hmF2, though to a lesser extent, have been widely analyzed to find these trends. This study shows long‐term TEC trends for the period 1999–2023 from available global International GNSS service TEC maps. Using F30, F10.7 or MgII as proxies to filter out the effect of solar EUV, the trends are negative, not only for the mean global value but also for most regions with very few exceptions. This would align with the greenhouse effect hypothesis, even though our results show higher negative trend values than expected theoretically. Plain Language Summary The Earth's ionosphere presents long‐term trends besides regular changes such as daily and seasonal, and irregular variations of transient character. Many studies suggest that the long‐term increase in greenhouse gas concentrations will produce a global cooling in the upper atmosphere together with the global warming in the troposphere. Therefore, long‐term trends can be expected in the ionosphere total electron content (TEC), the critical frequency of the F2 layer, foF2, and its peak height, hmF2, which are the three most important ionospheric parameters used in several applications. TEC measurements have the advantage over other parameters that characterize the upper atmosphere having 24 × 365 worldwide coverage thanks to the continuous International GNSS service (IGS). Trends in the ionosphere are much weaker than those associated with the solar cycle, thus its effects were removed using different solar EUV radiation proxies. The trends are negative, as expected, not only for the mean global value case but also for most of the regional values with very few exceptions. Key Points Trend depends on the solar EUV proxy used for filtering being most negative with MgII and non‐significant with SN Based on recommended solar proxies, noon total electron content (TEC) global average reveal a negative significant trend along 1999–2023 The negative trend of the global TEC at noon is much more pronounced than the theoretical prediction

We investigate the coronal imaging capabilities of the Solar UltraViolet Imager (SUVI) on board the Geostationary Operational Environmental Satellite-R series spacecraft. Nominally Sun-pointed, SUVI provides solar images in six extreme ultraviolet (EUV) wavelengths. On-orbit data indicated that SUVI had sufficient dynamic range and sensitivity to image the corona to the largest heights above the Sun to date while simultaneously imaging the Sun. We undertook a campaign to investigate the existence of the EUV signal well beyond the nominal Sun-centered imaging area of the solar EUV imagers. We off-pointed the SUVI line of sight by almost one imaging area around the Sun. We present the details of the campaign we conducted when the solar cycle was at near the minimum and some results that confirm that EUV emission is present to beyond three solar radii.

The long‐standing “energy crisis” at the giant planets refers to the anomalous heating of planetary thermospheres compared to the available energy from solar irradiance. The coupling between planetary magnetospheres and their upper atmospheres is thought to address these crises, though the sources and pathways of energy transport have not been fully explored at each system. In particular, the total available energy from the upstream solar wind at each planet has not been comprehensively quantified. Here we apply recently developed models of energy conversion by magnetic reconnection and the Kelvin‐Helmholtz instability to each of the Giant Planets, providing estimates of the average external energy inputs for each system between 1985 and 2020. We find that external energy associated with solar‐wind‐magnetospheric coupling significantly exceeds that from solar extreme ultraviolet photons. While internal energy sources are known to dominate at Jupiter and Saturn, external sources may be significant at Uranus and Neptune. Plain Language Summary The upper atmospheres of Jupiter, Saturn, Uranus, and Neptune are all hotter than would be predicted by their exposure to sunlight alone. The space plasma environment around each planet provides an additional reservoir of energy that can be used to provide this heating. Here we quantify the average energy input to each planetary system due to variation of the photons and plasmas emitted from the Sun. We find that the interaction between a planetary magnetic field and the solar interplanetary magnetic field provides a strong source of external energy at each of the planets, on average significantly more than that of light from the Sun. Key Points Solar wind‐magnetospheric‐coupling provides higher energy input than solar extreme ultraviolet at the giant planets Solar activity drives solar‐wind‐magnetospheric coupling much more strongly than planetary season The solar wind may drive the energy input to the upper atmospheres at Uranus and Neptune