The Whole Heliosphere and Planetary Interactions (WHPI) is an international initiative to study the most recent solar minimum and its impact on the interconnected solar‐heliospheric‐planetary system by facilitating and encouraging interdisciplinary activities. Particular WHPI science foci include the global connected structure of the heliosphere and planetary space environments/atmospheres, the origins and impacts of high‐speed solar wind streams, coronal mass ejections from Sun‐to‐Heliopause, and comparative solar minima. This is achieved through a series of coordinated observing campaigns, including Parker Solar Probe perihelia, and scientific virtual interactions including a dedicated workshop where observers and modelers gathered to discuss, compare, and combine research results. This introduction sets the scene for the WHPI interval, placing it into the context of prior initiatives and describing the overall evolution of the system between 2018 and 2020. Along with the accompanying articles, it presents a selection of key scientific results on the interconnected solar‐heliospheric‐planetary system at solar minimum.
The Whole Heliosphere and Planetary Interactions initiative was established to leverage relatively quiet intervals during solar minimum to better understand the interconnectedness of the various domains in the heliosphere. This study provides an expansive mosaic of observations spanning from the Sun, through interplanetary space, to the magnetospheric response and subsequent effects on the ionosphere‐thermosphere‐mesosphere (ITM) system. To accomplish this, a diverse set of observational datasets are utilized from 2019 July 26 to October 16 (i.e., over three Carrington rotations, CR2220, CR2221, and CR2222) with connections of these observations to the more focused studies submitted to this special issue. Particularly, this study focuses on two long‐lived coronal holes and their varying impact in sculpting the heliosphere and driving of the magnetospheric system. As a result, the evolution of coronal holes, impacts on the inner heliosphere solar wind, glimpses at mesoscale solar wind variability, magnetospheric response to these evolving solar wind drivers, and resulting ITM phenomena are captured to reveal the interconnectedness of this system‐of‐systems.
more » « less- Award ID(s):
- 2002574
- NSF-PAR ID:
- 10423580
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 128
- Issue:
- 6
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The magnetic fields of interplanetary coronal mass ejections (ICMEs), which originate close to the Sun in the form of a flux rope, determine their geoeffectiveness. Therefore, robust flux rope‐based models of CMEs are required to perform magnetohydrodynamic (MHD) simulations aimed at space weather predictions. We propose a modified spheromak model and demonstrate its applicability to CME simulations. In this model, such properties of a simulated CME as the poloidal and toroidal magnetic fluxes, and the helicity sign can be controlled with a set of input parameters. We propose a robust technique for introducing CMEs with an appropriate speed into a background, MHD solution describing the solar wind in the inner heliosphere. Through a parametric study, we find that the speed of a CME is much more dependent on its poloidal flux than on the toroidal flux. We also show that the CME speed increases with its total energy, giving us control over its initial speed. We further demonstrate the applicability of this model to simulations of CME‐CME collisions. Finally, we use this model to simulate the 12 July 2012 CME and compare the plasma properties at 1 AU with observations. The predicted CME properties agree reasonably with observational data.
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Abstract The vast size of the Sun’s heliosphere, combined with sparse spacecraft measurements over that large domain, makes numerical modeling a critical tool to predict solar wind conditions where there are no measurements. This study models the solar wind propagation in 2D using the BATSRUS MHD solver to form the MSWIM2D data set of solar wind in the outer heliosphere. Representing the solar wind from 1 to 75 au in the ecliptic plane, a continuous model run from 1995–present has been performed. The results are available for free at
http://csem.engin.umich.edu/mswim2d/ . The web interface extracts output at desired locations and times. In addition to solar wind ions, the model includes neutrals coming from the interstellar medium to reproduce the slowing of the solar wind in the outer heliosphere and to extend the utility of the model to larger radial distances. The inclusion of neutral hydrogen is critical to recreating the solar wind accurately outside of ∼4 au. The inner boundary is filled by interpolating and time-shifting in situ observations from L1 and STEREO spacecraft when available. Using multiple spacecraft provides a more accurate boundary condition than a single spacecraft with time shifting alone. Validations of MSWIM2D are performed using MAVEN and New Horizons observations. The results demonstrate the efficacy of this model to propagate the solar wind to large distances and obtain practical, useful solar wind predictions. For example, the rms error of solar wind speed prediction at Mars is only 66 km s−1and at Pluto is a mere 25 km s−1. -
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Abstract The activity of the Sun alternates between a solar minimum and a solar maximum, the former corresponding to a period of “quieter” status of the heliosphere. During solar minimum, it is in principle more straightforward to follow eruptive events and solar wind structures from their birth at the Sun throughout their interplanetary journey. In this paper, we report analysis of the origin, evolution, and heliospheric impact of a series of solar transient events that took place during the second half of August 2018, that is, in the midst of the late declining phase of Solar Cycle 24. In particular, we focus on two successive coronal mass ejections (CMEs) and a following high‐speed stream (HSS) on their way toward Earth and Mars. We find that the first CME impacted both planets, whilst the second caused a strong magnetic storm at Earth and went on to miss Mars, which nevertheless experienced space weather effects from the stream interacting region preceding the HSS. Analysis of remote‐sensing and in‐situ data supported by heliospheric modeling suggests that CME–HSS interaction resulted in the second CME rotating and deflecting in interplanetary space, highlighting that accurately reproducing the ambient solar wind is crucial even during “simpler” solar minimum periods. Lastly, we discuss the upstream solar wind conditions and transient structures responsible for driving space weather effects at Earth and Mars.
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Abstract The fast solar wind that fills the heliosphere originates from deep within regions of open magnetic field on the Sun called ‘coronal holes’. The energy source responsible for accelerating the plasma is widely debated; however, there is evidence that it is ultimately magnetic in nature, with candidate mechanisms including wave heating 1,2 and interchange reconnection 3–5 . The coronal magnetic field near the solar surface is structured on scales associated with ‘supergranulation’ convection cells, whereby descending flows create intense fields. The energy density in these ‘network’ magnetic field bundles is a candidate energy source for the wind. Here we report measurements of fast solar wind streams from the Parker Solar Probe (PSP) spacecraft 6 that provide strong evidence for the interchange reconnection mechanism. We show that the supergranulation structure at the coronal base remains imprinted in the near-Sun solar wind, resulting in asymmetric patches of magnetic ‘switchbacks’ 7,8 and bursty wind streams with power-law-like energetic ion spectra to beyond 100 keV. Computer simulations of interchange reconnection support key features of the observations, including the ion spectra. Important characteristics of interchange reconnection in the low corona are inferred from the data, including that the reconnection is collisionless and that the energy release rate is sufficient to power the fast wind. In this scenario, magnetic reconnection is continuous and the wind is driven by both the resulting plasma pressure and the radial Alfvénic flow bursts.more » « less
