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1. STARFORGE: the effects of protostellar outflows on the IMF

   https://doi.org/10.1093/mnras/stab278  

   Guszejnov, Dávid; Grudić, Michael Y; Hopkins, Philip F; Offner, Stella S; Faucher-Giguère, Claude-André (February 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT The initial mass function (IMF) of stars is a key quantity affecting almost every field of astrophysics, yet it remains unclear what physical mechanisms determine it. We present the first runs of the STAR FORmation in Gaseous Environments project, using a new numerical framework to follow the formation of individual stars in giant molecular clouds (GMCs) using the gizmo code. Our suite includes runs with increasingly complex physics, starting with isothermal ideal magnetohydrodynamics (MHD) and then adding non-isothermal thermodynamics and protostellar outflows. We show that without protostellar outflows the resulting stellar masses are an order of magnitude too high, similar to the result in the base isothermal MHD run. Outflows disrupt the accretion flow around the protostar, allowing gas to fragment and additional stars to form, thereby lowering the mean stellar mass to a value similar to that observed. The effect of jets upon global cloud evolution is most pronounced for lower mass GMCs and dense clumps, so while jets can disrupt low-mass clouds, they are unable to regulate star formation in massive GMCs, as they would turn an order unity fraction of the mass into stars before unbinding the cloud. Jets are also unable to stop the runaway accretion of massive stars, which could ultimately lead to the formation of stars with masses $${\gt}500\, \mathrm{M}_{\rm \odot }$$. Although we find that the mass scale set by jets is insensitive to most cloud parameters (i.e. surface density, virial parameter), it is strongly dependent on the momentum loading of the jets (which is poorly constrained by observations) as well as the temperature of the parent cloud, which predicts slightly larger IMF variations than observed. We conclude that protostellar jets play a vital role in setting the mass scale of stars, but additional physics are necessary to reproduce the observed IMF. 

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2. Solar Wind Ion Entry Into the Magnetosphere During Northward IMF

   https://doi.org/10.1029/2019JA026728  

   Sorathia, K. A.; Merkin, V. G.; Ukhorskiy, A. Y.; Allen, R. C.; Nykyri, K.; Wing, S. (July 2019, Journal of Geophysical Research: Space Physics)
3. Ion Heating in the Polar Cap Under Northwards IMF Bz

   https://doi.org/10.1029/2021JA029155  

   Lamarche, Leslie J.; Varney, Roger H.; Reimer, Ashton S. (November 2021, Journal of Geophysical Research: Space Physics)

   Abstract Joule heating deposits a significant amount of energy into the high‐latitude ionosphere and is an important factor in many magnetosphere‐ionosphere‐thermosphere coupling processes. We consider the relationship between localized temperature enhancements in polar cap measured with the Resolute Bay Incoherent Scatter Radar‐North (RISR‐N) and the orientation of the interplanetary magnetic field (IMF). Based on analysis of 10 years of data, RISR‐N most commonly observes ion heating in the noon sector under northwards IMF. We interpret heating events in that sector as being primarily driven by sunwards plasma convection associated with lobe reconnection. We attempt to model two of the observed temperature enhancements with a data‐driven first principles model of ionospheric plasma transport and dynamics, but fail to fully reproduce the ion temperature enhancements. However, evaluating the ion energy equation using the locally measured ion velocities reproduces the observed ion temperature enhancements. This result indicates that current techniques for estimating global plasma convection pattern are not adequately capturing mesoscale flows in the polar cap, and this can result in underestimation of the energy deposition into the ionosphere and thermosphere. 

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4. Diffusive Plasma Transport by the Magnetopause Kelvin-Helmholtz Instability During Southward IMF

   https://doi.org/10.3389/fspas.2021.809045  

   Nakamura, T. K.; Blasl, K. A.; Liu, Y. -H.; Peery, S. A. (January 2022, Frontiers in Astronomy and Space Sciences)

   At the Earth’s low-latitude magnetopause, the Kelvin-Helmholtz (KH) waves, which are driven by the super-Alfvénic velocity shear across the magnetopause, have been frequently observed during periods of northward interplanetary-magnetic-field (IMF) and believed to contribute to efficiently transporting the solar wind plasmas into the magnetosphere. On the other hand, during southward IMF periods, the signatures of the KH waves are much less frequently observed and how the KH waves contribute to the solar wind transport has not been well explored. Recently, the Magnetospheric Multiscale (MMS) mission successfully detected signatures of the KH waves near the dusk-flank of the magnetopause during southward IMF. In this study, we analyzed a series of two- and three-dimensional fully kinetic simulations modeling this MMS event. The results show that a turbulent evolution of the lower-hybrid drift instability (LHDI) near the low-density (magnetospheric) side of the edge layer of the KH waves rapidly disturbs the structure of the layer and causes an effective transport of plasmas across the layer. The obtained transport rate is comparable to or even larger than that predicted for the northward IMF. These results indicate that the diffusive solar wind transport induced by the KH waves may be active at the flank-to-tail magnetopause during southward IMF. 

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5. Interhemispheric Asymmetry Due To IMF By Within the Cusp Spherical Elementary Currents

   https://doi.org/10.1029/2023JA031430  

   Weygand, J M; Hartinger, M D; Strangeway, R J; Welling, D T; Kim, Hyomin; Matzka, Jürgen; Clauer, C Robert (June 2023, Journal of Geophysical Research: Space Physics)