The physics of space weather/solar-terrestrial physics (STP): what we know now and what the current and future challenges are

<p class="rtejustify"><span style="font-size:12px"><span style="font-family:sans-serif">Major geomagnetic storms are caused by un-</span><span style="font-family:sans-serif">usually intense solar wind southward magnetic fields that</span><span style="font-family:sans-serif">impinge upon the Earth\textquoterights magnetosphere (Dungey, 1961).</span><span style="font-family:sans-serif">How can we predict the occurrence of future interplane</span><span style="font-family:sans-serif">tary events? Do we currently know enough of the underly</span><span style="font-family:sans-serif">ing physics and do we have sufficient observations of so</span><span style="font-family:sans-serif">lar wind phenomena that will impinge upon the Earth\textquoterights</span><span style="font-family:sans-serif"> magnetosphere? We view this as the most important chal</span><span style="font-family:sans-serif">lenge in space weather. We discuss the case for magnetic</span><span style="font-family:sans-serif"> clouds (MCs), interplanetary sheaths upstream of interplan</span><span style="font-family:sans-serif">etary coronal mass ejections (ICMEs), corotating interaction</span><span style="font-family:sans-serif">regions (CIRs) and solar wind high-speed streams (HSSs).</span><span style="font-family:sans-serif">The sheath- and CIR-related magnetic storms will be dif</span><span style="font-family:sans-serif">ficult to predict and will require better knowledge of the</span><span style="font-family:sans-serif"> slow solar wind and modeling to solve. For interplanetary</span><span style="font-family:sans-serif">space weather, there are challenges for understanding the flu</span><span style="font-family:sans-serif">ences and spectra of solar energetic particles (SEPs). This</span><span style="font-family:sans-serif"> will require better knowledge of interplanetary shock prop</span><span style="font-family:sans-serif">erties as they propagate and evolve going from the Sun to</span><span style="font-family:sans-serif">1 AU (and beyond), the upstream slow solar wind and ener</span><span style="font-family:sans-serif">getic \textquotedblleftseed\textquotedblright particles. Dayside aurora, triggering of night-</span><span style="font-family:sans-serif">side substorms, and formation of new radiation belts can </span><span style="font-family:sans-serif">all be caused by shock and interplanetary ram pressure im</span><span style="font-family:sans-serif">pingements onto the Earth\textquoterights magnetosphere. The accelera</span><span style="font-family:sans-serif">tion and loss of relativistic magnetospheric \textquotedblleftkiller\textquotedblright electrons</span><span style="font-family:sans-serif">and prompt penetrating electric fields in terms of causing</span><span style="font-family:sans-serif">positive and negative ionospheric storms are reasonably well</span><span style="font-family:sans-serif"> understood, but refinements are still needed. The forecasting </span><span style="font-family:sans-serif">of extreme events (extreme shocks, extreme solar energeticparticle events, and extreme geomagnetic storms (Carrington events or greater)) are also discussed. Energetic parti</span><span style="font-family:sans-serif">cle precipitation into the atmosphere and ozone destruction</span><span style="font-family:sans-serif">are briefly discussed. For many of the studies, the Parker So</span><span style="font-family:sans-serif">lar Probe, Solar Orbiter, Magnetospheric Multiscale Mission</span><span style="font-family:sans-serif">(MMS), Arase, and SWARM data will be useful.</span></span></p>