37 research outputs found
Magnetopause Reconnection as Influenced by the Dipole Tilt Under Southward IMF Conditions: Hybrid Simulation and MMS Observation
Using a threeâdimensional (3âD) globalâscale hybrid code, the Magnetospheric Multiscale (MMS) reconnection event around 02:13 UT on 18 November 2015, highlighted in the Geospace Environment Modeling (GEM) Dayside Kinetic Challenge, is simulated, in which the interplanetary magnetic field (IMF) points southward and the geomagnetic field has a â27° dipole tilt angle. Strong southward plasma jets are found near the magnetopause as a result of the dayside reconnection. Our results indicate that the subsolar magnetopause reconnection X line shifts from the subsolar point toward the Northern Hemisphere due to the effect of the tilted geomagnetic dipole angle, consistent with the MMS observation. Subsequently, the reconnection X lines or sites and reconnection flux ropes above the equator propagate northward along the magnetopause. The formation and global distribution of the X lines and the structure of the magnetopause reconnection are investigated in detail with the simulation. Mirror mode waves are also found in the middle of the magnetosheath downstream of the quasiâperpendicular shock where the plasma properties are consistent with the mirror instability condition. As a special outcome of the GEM challenge event, the spatial and temporal variations in reconnection, the electromagnetic power spectra, and the associated Dâshaped ion velocity distributions in the simulated reconnection event are compared with the MMS observation.Key PointsSubsolar magnetopause X lines shift toward the Northern Hemisphere due to the effect of the negative tilted geomagnetic dipole angleThe hybrid simulation magnetic fields and plasma date match MMS3 observations well during the magnetopause crossingMirror mode waves appear in the middle of the magnetosheath downstream of the quasiâperpendicular shockPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/162687/2/jgra55909_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162687/1/jgra55909.pd
Work-Life Balance Starts with Proper Deadlines and Exemplary Agencies
Diversity, equity and inclusion (DEI) programs can only be implemented
successfully if proper work-life balance is possible in Heliophysics (and in
STEM field in general). One of the core issues stems from the culture of
"work-above-life" associated with mission concepts, development, and
implementation but also the expectations that seem to originate from numerous
announcements from NASA (and other agencies). The benefits of work-life balance
are well documented; however, the entire system surrounding research in
Heliophysics hinders or discourages proper work-life balance. For example,
there does not seem to be attention paid by NASA Headquarters (HQ) on the
timing of their announcements regarding how it will be perceived by
researchers, and how the timing may promote a culture where work trumps
personal life. The same is true for remarks by NASA HQ program officers during
panels or informal discussions, where seemingly innocuous comments may give a
perception that work is expected after "normal" work hours. In addition, we are
calling for work-life balance plans and implementation to be one of the
criteria used for down-selection and confirmation of missions (Key Decision
Points: KDP-B, KDP-C).Comment: White paper submitted to the Decadal Survey for Solar and Space
Physics (Heliophysics) 2024-2033; 6 page
Classification of Cassiniâs Orbit Regions as Magnetosphere, Magnetosheath, and Solar Wind via Machine Learning
Several machine learning algorithms and feature subsets from a variety of particle and magnetic field instruments on-board the Cassini spacecraft were explored for their utility in classifying orbit segments as magnetosphere, magnetosheath or solar wind. Using a list of manually detected magnetopause and bow shock crossings from mission scientists, random forest (RF), support vector machine (SVM), logistic regression (LR) and recurrent neural network long short-term memory (RNN LSTM) classification algorithms were trained and tested. A detailed error analysis revealed a RNN LSTM model provided the best overall performance with a 93.1% accuracy on the unseen test set and MCC score of 0.88 when utilizing 60 min of magnetometer data (|B|, BΞ, BÏ and BR) to predict the region at the final time step. RF models using a combination of magnetometer and particle data, spanning H+, He+, He++ and electrons at a single time step, provided a nearly equivalent performance with a test set accuracy of 91.4% and MCC score of 0.84. Derived boundary crossings from each modelâs region predictions revealed that the RNN model was able to successfully detect 82.1% of labeled magnetopause crossings and 91.2% of labeled bow shock crossings, while the RF model using magnetometer and particle data detected 82.4 and 74.3%, respectively
Magnetohydrodynamic With Embedded Particle-In-Cell Simulation of the Geospace Environment Modeling Dayside Kinetic Processes Challenge Event
We use the magnetohydrodynamic (MHD) with embedded particle-in-cell model (MHD-EPIC) to study the Geospace Environment Modeling (GEM) dayside kinetic processes challenge event at 01:50-03:00 UT on 18 November 2015, when the magnetosphere was driven by a steady southward interplanetary magnetic field (IMF). In the MHD-EPIC simulation, the dayside magnetopause is covered by a PIC code so that the dayside reconnection is properly handled. We compare the magnetic fields and the plasma profiles of the magnetopause crossing with the MMS3 spacecraft observations. Most variables match the observations well in the magnetosphere, in the magnetosheath, and also during the current sheet crossing. The MHD-EPIC simulation produces flux ropes, and we demonstrate that some magnetic field and plasma features observed by the MMS3 spacecraft can be reproduced by a flux rope crossing event. We use an algorithm to automatically identify the reconnection sites from the simulation results. It turns out that there are usually multiple X-lines at the magnetopause. By tracing the locations of the X-lines, we find that the typical moving speed of the X-line endpoints is about 70 km/s, which is higher than but still comparable with the ground-based observations
Massâloading the Earth's dayside magnetopause boundary layer and its effect on magnetic reconnection
When the interplanetary magnetic field is northward for a period of time, O+ from the highâlatitude ionosphere escapes along reconnected magnetic field lines into the dayside magnetopause boundary layer. Dualâlobe reconnection closes these field lines, which traps O+ and mass loads the boundary layer. This O+ is an additional source of magnetospheric plasma that interacts with magnetosheath plasma through magnetic reconnection. This mass loading and interaction is illustrated through analysis of a magnetopause crossing by the Magnetospheric Multiscale spacecraft. While in the O+ârich boundary layer, the interplanetary magnetic field turns southward. As the Magnetospheric Multiscale spacecraft cross the highâshear magnetopause, reconnection signatures are observed. While the reconnection rate is likely reduced by the mass loading, reconnection is not suppressed at the magnetopause. The highâlatitude dayside ionosphere is therefore a source of magnetospheric ions that contributes often to transient reduction in the reconnection rate at the dayside magnetopause.publishedVersio
Interplanetary mesoscale observatory (InterMeso): A mission to untangle dynamic mesoscale structures throughout the heliosphere
Mesoscale dynamics are a fundamental process in space physics, but fall within an observational gap of current and planned missions. Particularly in the solar wind, measurements at the mesoscales (100s RE to a few degrees heliographic longitude at 1 au) are crucial for understanding the connection between the corona and an observer anywhere within the heliosphere. Mesoscale dynamics may also be key to revealing the currently unresolved physics regulating particle acceleration and transport, magnetic field topology, and the causes of variability in the composition and acceleration of solar wind plasma. Studies using single-point observations do not allow for investigations into mesoscale solar wind dynamics and plasma variability, nor do they allow for the exploration of the sub-structuring of large-scale solar wind structures like coronal mass ejections (CMEs), co-rotating/stream interaction regions (CIR/SIRs), and the heliospheric plasma sheet. To address this fundamental gap in our knowledge of the heliosphere at these scales, the Interplanetary Mesoscale Observatory (InterMeso) concept employs a multi-point approach using four identical spacecraft in Earth-trailing orbits near 1 au. Varying drift speeds of the InterMeso spacecraft enable the mission to span a range of mesoscale separations in the solar wind, achieving significant and innovative science return. Simultaneous, longitudinally-separated measurements of structures co-rotating over the spacecraft also allow for disambiguation of spatiotemporal variability, tracking of the evolution of solar wind structures, and determination of how the transport of energetic particles is impacted by these variabilities
The Future of Heliophysics Research through Targeted use of Constellations
This white paper seeks to outline the benefits and challenges of constellations, ranging from the Heliophysics System Observatory, to constellations consisting of a small number of spacecraft, to large-number constellations. In moving toward this constellation era, investments are required by our sponsors to best enable our continued scientific advancement in Solar and Space Physics
Kinetic Interaction of Cold and Hot Protons With an Oblique EMIC Wave Near the Dayside Reconnecting Magnetopause
We report observations of the ion dynamics inside an Alfvén branch wave that propagates near the reconnecting dayside magnetopause. The measured frequency, wave normal angle and polarization are consistent with the predictions of a dispersion solver. The magnetospheric plasma contains hot protons (keV), cold protons (eV), plus some heavy ions. While the cold protons follow the magnetic field fluctuations and remain frozen-in, the hot protons are at the limit of magnetization. The cold protons exchange energy back and forth, adiabatically, with the wave fields. The cold proton velocity fluctuations contribute to balance the Hall term fluctuations in Ohm's law, and the wave E field has small ellipticity and right-handed polarization. The dispersion solver indicates that increasing the cold proton density facilitates propagation and amplification of these waves at oblique angles, as for the observed wave
NGTS-21b: An Inflated Super-Jupiter Orbiting a Metal-poor K dwarf
We report the discovery of NGTS-21b, a massive hot Jupiter orbiting a
low-mass star as part of the Next Generation Transit Survey (NGTS). The planet
has a mass and radius of M, and
R, and an orbital period of 1.543 days. The host is a K3V (, K) metal-poor (, dex) dwarf
star with a mass and radius of , M,and , R. Its age and rotation period of , Gyr
and , d respectively, are in accordance with the observed
moderately low stellar activity level. When comparing NGTS-21b with currently
known transiting hot Jupiters with similar equilibrium temperatures, it is
found to have one of the largest measured radii despite its large mass.
Inflation-free planetary structure models suggest the planet's atmosphere is
inflated by , while inflationary models predict a radius consistent
with observations, thus pointing to stellar irradiation as the probable origin
of NGTS-21b's radius inflation. Additionally, NGTS-21b's bulk density (, g/cm) is also amongst the largest within the population of
metal-poor giant hosts ([Fe/H] < 0.0), helping to reveal a falling upper
boundary in metallicity-planet density parameter space that is in concordance
with core accretion formation models. The discovery of rare planetary systems
such as NGTS-21 greatly contributes towards better constraints being placed on
the formation and evolution mechanisms of massive planets orbiting low-mass
stars.Comment: 12 pages, 13 figures, accepted for publication in MNRA