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This study introduces five linear regression models developed to accurately predict proton intensities in the critical energy range of 92.2–159.7 keV. To achieve this task we utilized 14 years of data sourced from the Cluster's RAPID experiment and NASA's OMNI database. This data was then aligned with the Solar wind‐Magnetosphere‐Ionosphere Link Explorer (SMILE) mission's trajectory, to increase model accuracy in the relevant regions. Our approach diverges from existing methodologies by offering a user‐friendly model that doesn't require specialized software, making it accessible for broader applications in satellite mission planning and risk assessment. The research segregates the data set into four distinct regions, each analyzed for proton intensity dynamics. In the outer regions (| $\vert $YGSE|≥6RE $\vert \ge 6\,{R}_{E}$) there is a pronounced dependence on radial distance and solar wind speed. In contrast, the inner regions (| $\vert $YGSE|≤6RE $\vert \le 6\,{R}_{E}$) demonstrate a significant dependence of proton intensities on the absolute value of the z‐coordinate and the magnetic field line topology. Our models achieved a Spearman correlation ranging from 0.57 to 0.72 on the test set, indicating good predictive capabilities. The findings emphasize the role of regional characteristics in space weather prediction and underscore the potential for tailored approaches in future research. Plain Language Summary: We developed a new model to predict space weather, specifically focusing on proton intensities, which can impact how well satellites work in space. We used 14 years of space observations to create five easy‐to‐use numerical models. These models are designed to help with planning and protecting future satellite missions, such as the upcoming SMILE mission, from space weather effects. In our study, we looked closely at different areas in space around Earth. We found that in the outer areas (| $\vert $YGSE|≥6RE $\vert \ge 6\,{R}_{E}$), the distance from Earth and the speed of the solar wind are important for understanding proton behavior. However, in areas (| $\vert $YGSE|≤6RE $\vert \le 6\,{R}_{E}$), the vertical distance from Earth's equatorial plane measured along the north‐south axis and the type of magnetic field lines play a more significant role. This shows us that different areas in space around Earth can be affected by space weather in different ways. Our models did a good job of predicting these effects, showing that choosing a tailored approach can be useful when forecasting proton intensities. Key Points: Developed models predict soft proton intensities impacting satellites, aiding space weather mission planningDifferent regions in space showcase distinct relations between proton intensities and predicting parametersThe study shows that solar wind speed and magnetic field topology are the most significant predictors for proton intensity besides location [ABSTRACT FROM AUTHOR]

In‐situ spacecraft missions are powerful assets to study processes that occur in space plasmas. One of their main limitations, however, is extrapolating such local measurements to the global scales of the system. To overcome this problem at least partially, multi‐point measurements can be used. There are several multi‐spacecraft missions currently operating in the Earth's magnetosphere, and the simultaneous use of the data collected by them provides new insights into the large‐scale properties and evolution of magnetospheric plasma processes. In this work, we focus on studying the Earth's magnetopause (MP) using a conjunction between the Magnetospheric Multiscale and Cluster fleets, when both missions skimmed the MP for several hours at distant locations during radial interplanetary magnetic field (IMF) conditions. The observed MP positions as a function of the evolving solar wind conditions are compared to model predictions of the MP. We observe an inflation of the magnetosphere (∼0.7 RE), consistent with magnetosheath pressure decrease during radial IMF conditions, which is less pronounced on the flank (<0.2 RE). There is observational evidence of magnetic reconnection in the subsolar region for the whole encounter, and in the dusk flank for the last portion of the encounter, suggesting that reconnection was extending more than 15 RE. However, reconnection jets were not always observed, suggesting that reconnection was patchy, intermittent or both. Shear flows reduce the reconnection rate up to ∼30% in the dusk flank according to predictions, and the plasma β enhancement in the magnetosheath during radial IMF favors reconnection suppression by the diamagnetic drift. Key Points: Simultaneous observations of the equatorial subsolar magnetopause and dusk flank during time‐extended radial interplanetary magnetic fieldThe magnetosphere enlarges ∼0.7 RE in the subsolar region but <0.2 RE in the flank due to the reduced pressure exerted by the solar windSimultaneous reconnection evidence in the subsolar and flank regions more than 15 RE apart is observed during part of the encounter [ABSTRACT FROM AUTHOR]

The LEXI and SMILE missions will provide soft X-ray images of the Earth's magnetosheath and cusps after their anticipated launch in 2023 and 2024, respectively. The IBEX mission showed the potential of an Energetic Neutral Atom (ENA) instrument to image dayside magnetosheath and cusps, albeit over the long hours required to raster an image with a single pixel imager. Thus, it is timely to discuss the two imaging techniques and relevant science topics. We simulate soft X-ray and low-ENA images that might be observed by a virtual spacecraft during two interesting solar wind scenarios: a southward turning of the interplanetary magnetic field and a sudden enhancement of the solar wind dynamic pressure. We employ the OpenGGCM global magnetohydrodynamics model and a simple exospheric neutral density model for these calculations. Both the magnetosheath and the cusps generate strong soft X-rays and ENA signals that can be used to extract the locations and motions of the bow shock and magnetopause. Magnetopause erosion corresponds closely to the enhancement of dayside reconnection rate obtained from the OpenGGCM model, indicating that images can be used to understand global-scale magnetopause reconnection. When dayside imagers are installed with high-ENA innermagnetosphere and FUV/UV aurora imagers, we can trace the solar wind energy flow from the bow shock to the magnetosphere and then to the ionosphere in a self-standing manner without relying upon other observatories. Soft X-ray and/or ENA imagers can also unveil the dayside exosphere density structure and its response to space weather. [ABSTRACT FROM AUTHOR]

Space plasma instruments provide 3D particle velocity distribution functions. Because of telemetry limitations, these cannot be transmitted in high time resolution and the plasma needs to be characterized by moments of the velocity distribution function. These moment uncertainties have vital effects on the reliability and accuracy of onboard plasma moments. We assess the measurement accuracy for magnetosheath and solar wind ions using an ion spectrometer with an asymmetric field of view designed for the all-sky measurement of low-energy ions in the magnetosheath and solar wind. We focus on moment uncertainties for the ideal spectrometer, not considering the background counts, which may have considerable effects on the uncertainties in real life. To obtain number density, bulk velocity, and temperature, different orders of moments are integrated assuming a Maxwellian velocity distribution. Based on the design specifications, we use simulations to estimate systematic and random errors for typical plasma conditions. We find that the spectrometer resolution is adequate for determining the density of solar wind (∼7% error) and magnetosheath ions (∼4% error). The resolution is also adequate for determining the temperature of solar wind (∼10% error) and magnetosheath ions (∼2% error). For high speed flows with a bulk velocity of 750 km/s and a temperature of 20 eV, the maximum density and temperature errors become 9% and 7%, respectively. The bulk velocity errors are less than 2% for all cases. The contributions of heavy ions to the systematic errors are less than 5% for magnetosheath ions and less than 8% for solar wind ions. [ABSTRACT FROM AUTHOR]

The foreshock, extending upstream of Earth's bow shock, is a region of intense electromagnetic wave activity and nonlinear phenomena, which can have global effects on geospace. It is also the first geophysical region encountered by solar wind disturbances journeying toward Earth. Here, we present the first observations of considerable modifications of the foreshock wave field during extreme events of solar origin called magnetic clouds. Cluster's multispacecraft data reveal that the typical quasi‐monochromatic foreshock waves can be completely replaced by a superposition of waves each with shorter correlation lengths. Global numerical simulations further confirm that the foreshock wave field is more intricate and organized at smaller scales. Ion measurements suggest that changes in shock‐reflected particle properties may cause these modifications of the wave field. This state of the foreshock is encountered only during extreme events at Earth, but intense magnetic fields are typical close to the Sun or other stars. Plain Language Summary: Solar storms are giant clouds of particles ejected from the Sun into space during solar eruptions. When solar storms are directed toward Earth, they can cause large disturbances in near‐Earth space, for example, disrupting communications or damaging spacecraft electronics. Understanding in detail what happens when solar storms reach Earth is crucial to mitigate their effects. Using measurements from the Cluster spacecraft, we investigate how solar storms modify the properties of the very first region of near‐Earth space they encounter when journeying toward Earth. This region, called the foreshock, extends ahead of the protective bubble formed by the Earth's magnetic field, the magnetosphere. The foreshock is home to intense electromagnetic waves, and disturbances in this region can perturb the Earth's magnetosphere. Our study reveals that solar storms modify profoundly the foreshock, resulting in a more complex wave activity. Global numerical simulations performed with the Vlasiator code confirm our findings. These changes could affect the regions of space closer to Earth, for example, in modifying the wave properties or the amount of solar particles entering the Earth's magnetosphere. This needs to be taken into account to better anticipate the effects of solar storms at Earth. Key Points: When reaching geospace, magnetic clouds modify significantly the properties of the first geophysical region they encounter, the foreshockTypical quasi‐monochromatic foreshock waves are replaced by a superposition of waves at different periods with a shorter transverse extentMultiple field‐aligned beams observed during one event suggest a link between the multiple wave periods and the suprathermal ion properties [ABSTRACT FROM AUTHOR]

The soft X‐ray emissions from the Earth's magnetosheath and cusp regions are simulated under different solar wind conditions, based on the PPMLR‐MHD code. The X‐ray images observed by a hypothetical telescope are presented, and the basic responses of the magnetopause and cusp regions are discernable in these images. From certain viewing geometries, the magnetopause position in the equatorial plane, as well as the latitudinal scales and azimuthal extent of cusp can be directly extracted from the X‐ray images. With these reconstructed positions, the issues we are able to analyze include but are not limited to the compression of magnetopause and widening of the cusp after an enhancement of solar wind flux, as well as the erosion of the magnetopause and equatorward motion of cusp after the southward turning of the interplanetary magnetic field. Hence, the X‐ray imaging is an appropriate technique to study the large‐scale motion of magnetopause and cusps in response to solar wind variations. Key Points: X‐ray images are estimated based on MHD simulations under different solar wind conditionsResponses of the magnetopause to solar wind changes are analyzed from X‐ray imagesResponses of the cusp to solar wind variations are presented via X‐ray images [ABSTRACT FROM AUTHOR]

Compressible turbulence in the solar wind is a topic of much recent debate. To understand the various compressive fluctuations at scales comparable to proton characteristic lengths, we use multipoint magnetic field and density data (derived from spacecraft potential which allows higher time resolution than is typically possible than with particle instruments) from the Cluster spacecraft when they were in undisturbed intervals of slow and fast solar wind. The application of the multipoint signal resonator technique is performed for the first time, to the analysis of scalar time series. Fluctuations in the measurements of electron density and in magnitude of the magnetic field (used as a proxy for compressible magnetic fluctuations) are used as inputs in addition to the traditional vector components of the magnetic field. This analysis is performed on two streams of solar wind, one which can be classed as a slow stream and one which can be classed as a fast stream to investigate the difference in the compressible components in the two types of wind. The recovered plasma frame frequencies for the incompressible component show low propagation speed in the plasma frame consistent with previous applications of the method, while the compressible components are more scattered, some with very high phase speeds. Based on these results, we propose a picture of compressive solar wind turbulence as a mixed state of (1) linear modes such as kinetic Alfvén, kinetic slow, and ion Bernstein modes; (2) coherent structures with very small intrinsic frequencies; and (3) nonlinear or sideband modes. [ABSTRACT FROM AUTHOR]

An analytical model of magnetosheath plasma flow is described and compared with a large dataset of magnetosheath ion flow velocity measurements from Cluster and THEMIS spacecraft. The model is based on previous works by Kobel and Flückiger (1994) and Génot et al. (2011) and has been modified to overcome the restrictions of these models on the shape of model magnetopause and bow shock. Our model is compatible with any parabolic bow shock model and arbitrary magnetopause model. The model is relatively simple to implement and computationally inexpensive, and its only inputs are upstream solar wind parameters. Comparison with observed data yields a good correspondence: median error in the direction of flow velocity is comparable with the instrumental error, and flow magnitude is predicted with a reasonable accuracy (relative error in flow speed was less than 25% for 86.5% of observations). [ABSTRACT FROM AUTHOR]