Grooming at the cusp: all-orders predictions for the transition region of jet groomers

Jet grooming has emerged as a necessary and vital tool for mitigating contamination radiation in jets. The additional restrictions on emissions imposed by the groomer can result in non-smooth behavior of resulting fixed-order distributions of observables measured on groomed jets. As a concrete example, we study the cusp in the hemisphere mass distribution of e+e−→ hadrons events groomed with soft drop. We identify the leading emissions that contribute in the region about the cusp and formulate an all-orders factorization theorem that describes how the cusp is resolved through arbitrary strongly-ordered soft and collinear emissions. The factorization theorem exhibits numerous novel features such as contributions from collinear modes that can cross hemisphere boundaries as well as requiring explicit subtraction of the limit in which resolved emissions become collinear to the hard core. We present resummation of the cusp region through next-to-leading logarithmic accuracy and describe how it can be matched with established factorization theorems that describe other groomed phase space regions.

Ion properties of Mercury’s northern cusp under extreme solar wind observed by MESSENGER

<p>Mercury’s magnetic cusp allows solar wind plasma to precipitate into the magnetosphere, exosphere, and directly to the surface. This precipitation of solar wind leads to the production of neutrals in the exosphere and/or ions in the magnetosphere and thus it has an important role in shaping Mercury’s space environment. Characterizing the ion properties in the cusp region is important for obtaining a better understanding of the Sun-planet interactions and assessing the solar wind penetration in Mercury’s magnetosphere.</p><p>The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft has observed the northern cusp regularly during its orbital phase. We have analyzed plasma data obtained by the Fast Imaging Plasma Spectrometer (FIPS) onboard MESSENGER under extreme solar wind events and compared the resulting ion properties in the northern cusp with those under non-extreme solar wind events for the first time. <span>We found that (1) flux enhancement is confirmed under the extreme solar wind, and (2) the ion distribution in the cusp has a smaller kappa value than in the magnetosheath, suggesting ion acceleration occurs in the magnetosphere.</span></p>

Large scale thermospheric density enhancements in relation to downward Poynting fluxes: Statistics from CHAMP, AMPERE and SuperDARN

<p>Large thermospheric neutral density enhancements in the cusp region have been examined for many years. The CHAMP satellite for example has enabled many observations of the perturbation, showing that it is mesoscale in size and exists on statistical timescales. Further studies examining the relationship with magnetospheric energy input have shown that fine-scale Poynting fluxes are associated with the density perturbations on a case-by-case basis, whilst others have found that mesoscale downward fluxes also exist in the cusp region statistically.</p><p>In this study, we use nearly 8 years of the overlapping SuperDARN and AMPERE datasets to generate global-scale patterns of the high-latitude and height-integrated Poynting flux into the ionosphere, with a time resolution of two minutes. From these, average patterns are generated based on the IMF orientation. We show the cusp is indeed an important feature in the Poynting flux maps, but the magnitude does not correlate well with statistical neutral mass density perturbations observed by the CHAMP satellite on similar spatial scales. Mesoscale height-integrated Poynting fluxes thus cannot fully account for the cusp neutral mass density enhancement, meaning energy deposition in the F-region or on fine-scales, which is not captured by our analysis, could be the primary driver.</p>

Time-dependent responses of the neutral mass density to magnetospheric energy inputs into the cusp region in the thermosphere: A high-resolution two-dimensional local modeling

Remarkable enhancements of the thermospheric mass density around the 400-km altitude in the cusp region have been observed by the CHAllenging Minisatellite Payload (CHAMP) satellite. We employed a high-resolution two-dimensional local model to gain insights into the extent to which the neutral-ion drag process controls the mass density’s enhancements under the energy inputs typical of the cusp. We expressed those energy inputs by quasi-static electric fields and electron precipitation. We compared two cases and calculated the thermospheric dynamics with and without neutral-ion drags. We found that in the more realistic case containing the neutral-ion drag, the calculated mass density enhancement was 10% at most, which is dramatically smaller than the observations by the CHAMP satellite (33% on average). The results also showed that the neutral-ion drag process suppresses Joule heating and neutral mass density enhancements, as well as the chemical reaction process. The discrepancy between our modeling result and the satellite observation suggests the existence of additional energy sources, such as Alfvén waves propagating from the magnetosphere, which play an important role in the cusp’s density enhancement.

Impact of the low/high Alfven Mach number regime of the solar wind on the Aflven transition Layer of the cusp for IMF North: 3D global PIC simulation.

<p> CLUSTER experimental observations of  Lavraud et al. (2005) have evidenced the presence of a particular layer (so –called herein Alfven Transition Layer or ATL) almost adjacent to the upper edge of the stagnant exterior cusp (SEC), through which the plasma flow transits from super-(from magnetosheath) to sub- (to SEC) Alfvenic regime as the interplanetary magnetic field (IMF) is northward. Three dimensional globa PIC simulations have been recently used  (Cai et al., 2015) to analyze the main features of the cusp for an IMF configuration similar that in the observations. These simulations have allowed us to complete the global view of the cusp region  (in particular the features not accessible by MHD approach).  A  detailed analysis has allowed to retrieve the features of the ATL which reveals to be associated to the complicated 3D particles entry into the cusp region and exhibit an internal conic depletion region (CDR) where the ion fluxes concentrate and are very strong (which suggests very local ion precipitation). Moreover, simulation results show that the ATL expands towards areas out and even far from the cusp region and outside the meridian plane.</p><p>                     In the present work, the study is extended for different Ma regimes of the solar wind, as the IMF stays in northward  configuration. Results show the impact of this Ma variation on the 3D features of the overall magnetosphere and in particular on the cusp region, i.e. (i) on the 3D ATL structures/spatial scales, (ii) on the extension of the region surrounded by the ATL, and (iii) on the structures, the spatial scales and the dynamics of the CDR itself.</p><p> </p><p> </p>

The dependence of deep-nightside Martian ionosphere TEC on crustal magnetic field

<p>It has been clear that the main cause of Martian deep-nightside ionosphere is electron precipitation, which is dominated by Martian crustal magnetic field. In this research, the dependence of deep-nightside Martian ionosphere TEC (Total Electron Content) on crustal magnetic field was studied based on Martian ionospheric TEC data from MEX/MARSIS and 400km crustal magnetic field data from MGS. It is found that the strength and inclination of crustal magnetic field have great effects on Martian deep-nightside ionospheric TEC. This kind of effects are worth to be compared with the effects of crustal magnetic field on electron precipitation studied in previous researches (such as Lillis and Brain, 2013, Nightside electron precipitation at Mars: Geographic variability and dependence on solar wind conditions) to find out more about the formation of Martian deep-nightside ionosphere. It is also found that, in a Martian crustal magnetic field cusp region, the observed deep-nightside ionospheric TECs in the center of the cusp are lower than those in the edge of the cusp, a phenomenon not noticed before. It indicates that there may be more precipitated electrons moving along the closed crustal magnetic lines than moving along open crustal magnetic lines, and these precipitated electrons in closed magnetic lines can be related to the energy processes in the nightside of Mars, such as magnetic reconnections.</p>

Mid-altitude cusp dynamics and properties during the IMF By dominated intervals

<p>Observations inside the cusp can be used as distant monitoring of the large-scale geometry and properties of the magnetic reconnection at the magnetopause. The recent modelling and observations of the cusp and flux transfer events in the vicinity of the magnetopause show that the reconnection can occur along the X-line extended over many hours of magnetic local time (MLT), comprising sites of both component and anti-parallel reconnection scenarios. Such observations are in contradiction to the statistical DMSP studies showing that the cusp is rather limited in magnetic local time with an average size 2.5 hours of MLT. Moreover, some past observations indicate that the cusp is moving in response to the changes of the IMF By component, suggesting that the cusp is formed due to anti-parallel reconnection along the X-line limited in MLT.</p><p>In this presentation we analyse several events of the mid-altitude cusp observations during the Cluster campaign when the satellites cross the cusp mainly along the longitude in a string-of-pearls configuration during an Interplanetary Magnetic Field (IMF) configuration with a stable and dominant IMF By-component. During this particular Cluster orbit it was possible to define the dawn and dusk cusp boundaries and to study plasma parameters inside different parts of the cusp region. The observations will be discussed in terms of the cusp extension, cusp motion, and possible formation of the ‘double’ cusp structures. Finally, we will consider what these observations reveal about the large-scale reconnection geometry at the magnetopause.</p>

Characterization of turbulent magnetic reconnection in solar flares with microwave imaging spectroscopy

<p>Magnetic reconnection plays a central role in highly magnetized plasma, for example, in solar corona. Release of magnetic energy due to reconnection is believed to drive such transient phenomena as solar flares, eruptions, and jets. This energy release should be associated with a decrease of the coronal magnetic field. Quantitative measurements of the evolving magnetic field strength in the corona are required to find out where exactly and with what rate this decrease takes place. The only available methodology capable of providing such measurements employs microwave imaging spectroscopy of gyrosynchrotron emission from nonthermal electrons accelerated in flares. Here, we report microwave observations of a solar flare, showing spatial and temporal changes in the coronal magnetic field at the cusp region; well below the nominal reconnection X point. The field decays at a rate of ~5 Gauss per second for 2 minutes. This fast rate of decay implies a highly enhanced, turbulent magnetic diffusivity and sufficiently strong electric field to account for the particle acceleration that produces the microwave emission. Moreover, spatially resolved maps of the nonthermal and thermal electron densities derived from the same microwave spectroscopy data set allow us to detect the very acceleration site located within the cusp region. The nonthermal number density is extremely high, while the thermal one is undetectably low in this region indicative of a bulk acceleration process exactly where the magnetic field displays the fast decay. The decrease in stored magnetic energy is sufficient to power the solar flare, including the associated eruption, particle acceleration, and plasma heating. We discuss implications of these findings for understanding particle acceleration in solar flares and in a broader space plasma context.</p>