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The approximately 11-year solar cycle has been shown to impact the heavy ion composition of the solar wind, even when accounting for streams of differing speeds; however, the heavy ion composition observed between the same specific phases of a past solar cycle and the current cycle has rarely, if ever, been compared. Here, we compare the heavy ion composition of the solar wind, as measured in situ during the solar cycle 23 and 25 ascending phases. We examine the mean iron and oxygen charge state composition and the O7+/O6+ ratio in multiple ranges of associated bulk wind speeds. Then, we compare the iron and oxygen charge state composition and relative abundance of iron to oxygen in the traditionally defined fast and slow solar wind. Finally, to determine the impact of individual ion contributions on the solar wind iron abundance, we examine individual ratios of iron and oxygen ions. Although the charge state composition remained broadly similar between these two ascending phases, both the O7+/O6+ ratio and iron fractionation in fast-speed streams were higher in the solar cycle 25 ascending phase than they were during the solar cycle 23 ascending phase, suggesting that equatorial coronal hole fields more frequently reconnected with helmet streamers or active regions in the latter of the two ascending phases; however, more work will need to be done to connect these observations back to their coronal origins. The individual ion ratios used in this work provided a spectrum to analyze the aggregate elemental abundances, and this work, as a whole, is an important step in determining how conditions in the corona may vary between solar cycles between the same phases. [ABSTRACT FROM AUTHOR]

Mercury's nightside magnetosphere is investigated under the impact of a coronal mass ejection (CME) and a high‐speed stream (HSS) with MErcury Surface, Space ENviroment, GEochemistry, and Ranging (MESSENGER) observations. The CME was shown to produce a low plasma β (ratio of thermal pressure to magnetic pressure) magnetosheath, while the HSS creates a higher β magnetosheath. Reconnection at the dayside magnetopause was found to be stronger during the CME than the HSS, but both were stronger than the average condition (Slavin et al., 2014, https://doi.org/10.1002/2014JA020319). Here we show that the CME and HSS events produced large numbers of flux ropes and dipolarization fronts in the plasma sheet. The occurrence rates for the structures were approximately 2 orders of magnitude higher than under average conditions with the rates during CME's being twice that of HSS's. The flux ropes appeared as quasiperiodic flux rope groups. Each group lasted approximately 1 min and had a few large flux ropes followed by several smaller flux ropes. The lobe magnetic flux accounted for around half of the Mercury's available magnetic flux with the flux during CME's being larger than that of HSS's. The CME produced a more dynamic nightside magnetosphere than the HSS. Further, for the CME event, the tail magnetic reconnection produced a distorted Hall magnetic field pattern and the X‐line had a dawn‐dusk extent of 20% of the tail width. No magnetic flux loading and unloading events were observed suggesting that, during these intense driving conditions, Mercury's magnetosphere responded with a type of quasi‐steady convection as opposed to the tail flux loading‐unloading events seen at Earth. Key Points: Coronal mass ejections drive more intense nightside reconnection than high speed streamsUnder extreme conditions, magnetic reconnection produces a distorted Hall magnetic field pattern in the plasma sheetContinued intense solar wind forcing does not produce substorm magnetic flux loading and unloading of tail lobe instead steady convection [ABSTRACT FROM AUTHOR]

Abstract: Normal solar wind flows and intense solar transient events interact directly with the upper Martian atmosphere due to the absence of an intrinsic global planetary magnetic field. Since the launch of the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, there are now new means to directly observe solar wind parameters at the planet's orbital location for limited time spans. Due to MAVEN's highly elliptical orbit, in situ measurements cannot be taken while MAVEN is inside Mars' magnetosheath. To model solar wind conditions during these atmospheric and magnetospheric passages, this research project utilized the solar wind forecasting capabilities of the WSA‐ENLIL+Cone model. The model was used to simulate solar wind parameters that included magnetic field magnitude, plasma particle density, dynamic pressure, proton temperature, and velocity during a four Carrington rotation‐long segment. An additional simulation that lasted 18 Carrington rotations was then conducted. The precision of each simulation was examined for intervals when MAVEN was in the upstream solar wind, that is, with no exospheric or magnetospheric phenomena altering in situ measurements. It was determined that generalized, extensive simulations have comparable prediction capabilities as shorter, more comprehensive simulations. Generally, this study aimed to quantify the loss of detail in long‐term simulations and to determine if extended simulations can provide accurate, continuous upstream solar wind conditions when there is a lack of in situ measurements. [ABSTRACT FROM AUTHOR]