Cusp Region Research Articles

Particle‐In‐Cell Modeling of Martian Magnetic Cusps and Their Role in Enhancing Nightside Ionospheric Ion Escape

AbstractAmongst various escape channels, ion outflow is a major contributor to atmospheric loss at Mars over geologic time. On Mars' nightside, observations have indicated that cusp regions within crustal magnetic fields are associated with phenomena such as accelerated particle populations, discrete auroral emissions, and ionospheric outflow; however, the kinetic physics occurring within crustal magnetic cusps is poorly understood. Here, we present 1.5‐dimensional particle‐in‐cell simulations of magnetospheric‐ionospheric interactions within martian crustal magnetic cusp regions of varying strength. Simulation results demonstrate the formation of quasi‐static, field‐aligned potentials pointing away from Mars that accelerate electrons into the martian atmosphere while accelerating ions away, thereby enhancing ionospheric escape. Escaping ionospheric flux scales with crustal field strength, with 160 nT crustal fields yielding >2× the ion escape flux than in the case with no crustal fields. We discuss these results and conclude that magnetic cusp regions may be significant sources of ion loss at Mars.

Numerical study of penetration and distribution of charged particles in the magnetosphere during southward IMF case

AbstractThe energetic charged particles penetration in the plasmasphere are carried out using the updated version of 3D Stanford PIC code. We considered slow and fast wind streams to know the penetration of the energetic charged particles (electrons and ions) having different velocities into four regions i.e. cusp, plasmasphere, sunward, and tailward sides. It is observed that the ion penetrations are higher than electrons for solar slow wind streams in the plasmasphere, while it is reverse for the solar fast streams. Also, the results show that the percentage of penetration of the energetic charged particles (both electrons and ions) are the same into the cusp and subsolar point reconnection region. It is different for the higher speed of fast streams; so that the penetrated electrons reached about 10–20 times than penetrated ions. The results show that for the tailward reconnection region, the penetration of ions is 2–3 times higher than the penetration of electrons, but it is the same for the case of higher solar fast speed.

Overview of the Rocket Experiment for Neutral Upwelling Sounding Rocket 2 (RENU2)

AbstractThe Rocket Experiment for Neutral Upwelling 2 (RENU2) rocket was launched on 13 December 2015 at 07:34 UT. The payload transited the cusp region during a neutral upwelling event, supported by a comprehensive set of onboard and ground‐based instrumentation. RENU2 data highlight two important processes. One is that a proper understanding of neutral upwelling by Poleward Moving Auroral Forms (PMAFs) requires a treatment that mimics the quasiperiodic passage of a sequence of PMAFs. As a PMAF reaches a flux tube, its physical consequences must be determined including the residual history of effects from previous passages, implying that understanding such a process requires an accounting of the system hysteresis. Second, RENU2 observations suggest that neutral density enhancements driven by precipitation and/or Joule heating can be highly structured in altitude and latitude. In addition, timescales involving neutral dynamics suggest that the structuring must be slowly changing, for example, over the course of 10 to tens of minutes.

Novel strategy of remote magnetic navigation-guided ablation for ventricular arrhythmias from right ventricle outflow tract

The optimized strategy to further increase the success rate of ablation for ventricular arrhythmias (VAs) from the right ventricular outflow tract (RVOT) is challenging. Recent studies have shown that the pulmonary sinus cusp (PSC) region may be the origin of certain RVOT VAs. We evaluated the efficacy of preferential ablation below the pulmonary valve (PV) and alternated radiofrequency delivery in the PSC using remote magnetic navigation (RMN). Sixty-five (65) consecutive patients experiencing VAs with RVOT-like appearance were included in this study. Mapping and ablation were preferentially performed below the PV. Ablation in the PSC would only be attempted when intensified ablation below the PV could not eliminate VAs. Finally, if ablation in the RVOT region failed, the aortic sinus cusp (ASC) would be mapped. Sixty-one (61) of 65 (93.8%) patients achieved procedural success. Except 7 cases of which the VAs were ablated in the ASC, the rest 54 VAs were thought to be originate from the RVOT region. Fifty (50) of 54 VAs were successfully ablated below the PV, and in the presence of a local special signal in the bipolar electrogram a more aggressive ablation was required. Subsequent ablation in the PSC with assistance of the RMN system achieved success in the remaining 4 patients. No complications occurred in this study. Our strategy of using RMN-guided ablation below the PV for VAs of RVOT origin was proved to be effective. PSC mapping and ablation using a magnetic catheter may provide the optimal strategy for treating these types of arrhythmias.

The Polar Cap (PC) Index: Invalid Index Series and a Different Approach

AbstractThe Polar Cap (PC) indices are derived from the magnetic variations generated by the transpolar convection of magnetospheric plasma and embedded magnetic fields driven by the interaction with the solar wind. The PC indices are potentially very useful for space weather monitoring and forecasts and for related research. However, this study suggests that the PC index series in the near‐real‐time and final versions endorsed by the International Association for Geomagnetism and Aeronomy (IAGA) are invalid and unreliable. Both versions include solar wind sector (SWS) effects in the calculation of the reference levels from which magnetic disturbances are measured. The SWS effects are caused by current systems in the dayside Cusp region related to the Y‐component, BY, of the interplanetary magnetic field (IMF). However, the IAGA‐endorsed handling of SWS effects may generate unfounded PC index changes of up to 4 mV/m at the nightside away from the Cusp. For the real‐time PCN and PCS indices, the cubic spline‐based reference level construction may cause additional unjustified index excursions of more than 3 mV/m with respect to the corresponding final index values. Noting that PC index values above 2 mV/m indicate geomagnetic storm conditions, such unjustified contributions invalidate the PC index series and prove the IAGA‐endorsed derivation methods erroneous. Alternative derivation methods are shown to provide more consistent index reference levels for both final and real‐time PC indices, to reduce their unfounded excursions, and to significantly increase their reliability.

The Influence of Interplanetary Magnetic Field Direction on Martian Crustal Magnetic Field Topology

AbstractCrustal magnetic fields influence a range of plasma processes at Mars, guiding the flow of energy from the solar wind into the planet's atmosphere at some locations while shielding the atmosphere at others. In this study we investigate how the topology of crustal fields varies with changes in the direction of the incoming interplanetary magnetic field (IMF). Using plasma measurements from Mars Atmosphere and Volatile Evolution (MAVEN) and Mars Global Surveyor (MGS), we identify magnetic topology throughout the Martian ionosphere and perform a statistical analysis of crustal magnetic field topology during different IMF configurations. We find that the topology of crustal field cusp regions is dependent on IMF direction and that cusps transition between open and closed topology regularly as they rotate through the nightside of Mars. Finally, we determine that cusps often become topologically closed due to reconnection with open magnetic fields in the Martian magnetotail, creating large closed loops that connect the dayside and nightside of Mars.

Source Region and Propagation of Dayside Large‐Scale Traveling Ionospheric Disturbances

AbstractWe examined the source region of dayside large‐scale traveling ionospheric disturbances (LSTIDs) and their relation to cusp energy input. Aurora and total electron content (TEC) observations show that LSTIDs propagate equatorward away from the cusp and demonstrate the cusp region as the source region. Enhanced energy input to the cusp initiated by interplanetary magnetic field (IMF) southward turning triggers the LSTIDs, and each LSTID oscillation is correlated with a TEC enhancement in the dayside oval with tens of minutes periodicity. Equatorward‐propagating LSTIDs are likely gravity waves caused by repetitive heating in the cusp. The cusp source can explain the high LSTID occurrence on the dayside during geomagnetically active times. Poleward‐propagating ΔTEC patterns in the polar cap propagate nearly at the convection speed. While they have similar ΔTEC signatures to gravity wave‐driven LSTIDs, they are suggested to be weak polar cap patches quasiperiodically drifting from the cusp into the polar cap via dayside reconnection.

A New Technique for Estimating the Lifetime of Bursts of Electron Precipitation From Sounding Rocket Measurements

AbstractAt 0735 UT on 13 December 2015, the Rocket Experiment for Neutral Upwelling‐2 experiment launched north toward the auroral cusp region from Andoya, Norway. The instrumented rocket included an electron spectrometer, photometers that measured the auroral redline and greenline, and an instrument that measured ionospheric thermal electron temperature. On the down leg, just south of Svalbard, the rocket entered a region of poleward moving auroral forms that were characterized by narrow structures due to a combination of spatial and temporal variations. A noticeable feature was that the redline to greenline brightness ratio was much smaller than expected. A model is developed that shows that these emissions can be used to estimate the lifetimes of bursty electron precipitation. This model is shown to be consistent with some poleward moving auroral form lifetimes being on the order of 100 ms. The correlation between the precipitation and temperature bursts suggest that some transport occurred.

Statistical Study of the Relationship Between Ion Upflow and Field‐Aligned Current in the Topside Ionosphere for Both Hemispheres During Geomagnetic Disturbed and Quiet Time

AbstractA statistical study of ion upflow and field‐aligned currents (FACs) has been performed in the topside ionosphere of both hemispheres for magnetic quiet and disturbed times by using DMSP satellite observations from 2010–2013. Distributions in MLT/MLat reveal that ion upflow occurrence shows a dawn‐dusk asymmetry distribution that matches well with the Region 1 FACs. In addition, there are highest occurrence regions near noon and within the midnight auroral disturbance area, corresponding to dayside cusp and nightside auroral disturbance regions, respectively. Both the ion upflow occurrence and FAC regions expand equatorward to a wider area during disturbed times.

Factors Controlling O+ and H+ Outflow in the Cusp During a Geomagnetic Storm: FAST/TEAMS Observations

AbstractFactors related to two sources of energy input to the ionosphere, the Poynting flux associated with both quasistatic fields (Sdc) and Alfvénic fluctuations (Sac), and the soft electron precipitation, are investigated to evaluate their correlations with the O+ and the H+ outflows in the dayside cusp region by using recalibrated FAST/Time‐of‐Flight Energy, Angle, and Mass Spectrograph (TEAMS) data during the 24–25 September 1998 geomagnetic storm studied by Strangeway et al. (2005, https://doi.org/10.1029/2004JA010829). The Poynting flux and the soft electron precipitation are well correlated with ion outflow flux in the dayside cusp region. Sdc shows the highest correlation with the O+ outflows, while it is the electron number flux that correlates best with the H+ outflows. The Alfvénic waves play an essential role in accelerating outflows. The averaged O+/H+ flux ratio is 3.0 and is positively correlated to the Poynting flux, suggesting that the O+ flux increases more strongly with the energy input.

Predictors for low TAVI-prosthesis position assessed by fusion imaging of pre- and post-procedural CT angiography

BackgroundLow prosthesis position after transcatheter aortic valve implantation (TAVI) is associated with higher rates of new onset conduction disturbances and permanent pacemaker implantations. Purpose of this study was to investigate possible predictors of a low prosthesis position of the SAPIEN 3 (Edwards Lifesciences, Irvine, California, USA) valve type using fusion imaging of pre- and post-procedural computed tomography angiography (CTA).MethodsCTA fusion imaging was performed in 120 TAVI-patients with 3D-reconstruction of the transcatheter heart valve (THV) position within the device landing zone. A low implantation position was defined according to the manufacturer’s recommendations as > 30% of the prosthesis below the native annulus plane.ResultsA low THV position was found in 17 patients (14%). Patients with low THV position had less calcification of the annulus region and a smaller annulus size compared to patients with a normal or high THV position (P = 0.003 and 0.041, respectively). The only independent predictor of a low THV position in multivariate logistic regression analysis was the extent of calcification of the cusp region (odds ratio [CI] 0.842 [0.727–0.976], P = 0.022).ConclusionsFusion imaging of pre-and post-procedural CTA identified reduced calcification of the cusp region as an independent predictor of a low THV position of the SAPIEN 3. This should be considered when planning the TAVI procedure.Graphic abstractCorrelation of cusp region calcification and prosthesis position after TAVI

The Shape of Mercury's Magnetopause: The Picture From MESSENGER Magnetometer Observations and Future Prospects for BepiColombo

AbstractThe MErcury Surface, Space Environment, GEochemistry, and Ranging (MESSENGER) spacecraft orbited Mercury between March 2011 and April 2015, typically passing through the magnetosphere, magnetosheath, and interplanetary magnetic field, on each orbit. Using data from the Magnetometer, we identify magnetopause crossings for the complete orbital mission and model the average boundary shape. We find that Mercury's average magnetopause is well modeled by both an axisymmetric shape and a three‐dimensional shape containing indentations in the cusp regions and a magnetotail that is wider in the north‐south versus east‐west direction. Examination of MESSENGER data and the use of simulated crossings show that coverage is very limited in the cusp region. Parameters describing the indentation are poorly constrained, and model fits may be biased due to the combination of orbital geometry and magnetospheric dynamics. The distribution of MESSENGER data inside the magnetopause, together with minimum variance analysis of a representative subset of magnetopause crossings, hints at the presence of a cusp indentation, though likely shallower than that estimated from the observed crossing positions. The BepiColombo spacecraft will arrive at Mercury in 2025. We simulate expected data coverage and magnetopause crossings using both axisymmetric and three‐dimensional magnetopause models. BepiColombo will improve our understanding of the magnetopause shape by providing data over the southern hemisphere and regions of the northern cusp indentation not covered by MESSENGER. There is also the potential for simultaneous measurements of the interplanetary magnetic field and magnetopause position.

A modified bonded RPE appliance

In case of banded Rapid Palatal Expansion (RPE) appliance, it is very easy to assess the amount of expansion by viewing the cuspal relation of posterior teeth, as this type of design doesn’t cover the tooth surface completely. But the design of bonded RPE appliance is such that it covers the complete posterior teeth surfaces. Hence, it becomes very difficult to assess the amount of expansion achieved clinically. To overcome this, an identification marking line is prepared on the palatal cusp region of maxillary posteriors, which when coincides with the buccal cusps of mandibular posterior teeth, suggests the optimum amount of expansion achieved. Keywords: Rapid palatal expansion, Modified design, Identification marking line.

Estimating the fate of oxygen ion outflow from the high-altitude cusp

Abstract. We have investigated the oxygen escape-to-capture ratio from the high-altitude cusp regions for various geomagnetic activity levels by combining EDI and CODIF measurements from the Cluster spacecraft. Using a magnetic field model, we traced the observed oxygen ions to one of three regions: plasma sheet, solar wind beyond a distant X-line or dayside magnetosheath. Our results indicate that 69 % of high-altitude oxygen escapes the magnetosphere, from which most escapes beyond the distant X-line (50 % of total oxygen flux). Convection of oxygen to the plasma sheet shows a strong dependence on geomagnetic activity. We used the Dst index as a proxy for geomagnetic storms and separated data into quiet conditions (Dst>0 nT), moderate conditions (0>Dst>-20 nT), and active conditions (Dst<-20 nT). For quiet magnetospheric conditions we found increased escape due to low convection. For active magnetospheric conditions we found an increase in both parallel velocities and convection velocities, but the increase in convection velocities is higher, and thus most of the oxygen gets convected into the plasma sheet (73 %). The convected oxygen ions reach the plasma sheet in the distant tail, mostly beyond 50 RE.

Steady state densities in a plasma confined by a dipole magnet: Diffusion induced transport explored through direct measurements and modeling

Steady state densities in a plasma confined by a permanent dipole magnet are determined through detailed experiments and modeling. Two diffusion models are developed, and the resulting equations are solved numerically to yield the radial and angular plasma density profiles, which are compared with those obtained experimentally. The models consider the fluid and continuity equations along with Fick’s law and take into account the experimentally determined electron temperature (Te) and the static dipole magnetic fields (B) in space, as a common input. In model I, the equation of motion for both charges (ions and electrons) is used to self-consistently generate the ambipolar electric field (E), while model II considers the electron equation of motion and takes into account the experimentally determined plasma potential (Vs) as another input, whose gradient provides the ambipolar electric field. Results indicate that the plasma density peaks around r ∼ (2–12) cm depending on the polar angle and the discharge pressure and decreases for large r, while its angular variation shows a maximum in the equatorial plane (θ = 90°) and decreases toward the polar regions. Te and Vs are higher in the polar cusp regions and decrease toward the equatorial plane, with the profiles becoming more spherically symmetric away from the magnet. The numerically obtained density profiles from the models agree well with those obtained experimentally. The phenomenon of inward diffusion resulting in peaked density profiles as reported by earlier authors is found to be a natural outcome of the solution of the diffusion equation.

Energetic Ion Dynamics Near the Cusp Region of Mercury

Abstract Energetic ions in Mercury’s magnetosphere are very dynamic, similar to those in the magnetosphere of Earth. In this study, we present two energetic proton observations by MErcury Surface, Space ENvironment, GEochemistry and Ranging near the cusp region of Mercury. For one case, we have observed a large flux of energetic protons while the other case has almost no flux, indicating that the near-cusp region may trap energetic particles under particular conditions. In order to understand under what conditions the near-cusp region of Mercury could trap energetic particles, we have used test particle simulations to trace the trajectories of single particles of different energies and pitch angles with a magnetic field model, KT17, that could closely represent the observed in situ magnetic field. Under different magnetic field geometries, the motions of single particles with various energies and pitch angles are different. The test particles can be trapped around the cusp region when the solar disturbance activity that generates the magnetic field local minimum near the cusp region is strong, while the particles cannot be trapped and escape along the magnetic field through the dawnside cusp when there is little solar activity.

The Relationship Between Cusp Region Ion Outflows and East‐West Magnetic Field Fluctuations at 4,000‐km Altitude

AbstractA number of interdependent conditions and processes contribute to ionospheric‐origin energetic ( 10 eV to several keV) ion outflows. Due to these interdependences and the associated observational challenges, energetic ion outflows remain a poorly understood facet of atmosphere‐ionosphere‐magnetosphere coupling. Here we demonstrate the relationship between east‐west magnetic field fluctuations ( ) and energetic outflows in the magnetosphere‐ionosphere transition region. We use dayside cusp region FAST satellite observations made near apogee ( 4,180‐km altitude) near fall equinox and solstices in both hemispheres to derive statistical relationships between ion upflow and spectral power as a function of spacecraft frame frequency bands between 0 and 4 Hz. Identification of ionospheric‐origin energetic ion upflows is automated, and the spectral power in each frequency band is obtained via integration of power spectral density. Derived relationships are of the form for upward ion flux at 130‐km altitude, with the mapped upward ion flux for a nominal spectral power nT . The highest correlation coefficients are obtained for spacecraft frame frequencies 0.1–0.5 Hz. Summer solstice and fall equinox observations yield power law indices 0.9–1.3 and correlation coefficients , while winter solstice observations yield 0.4–0.8 with . Mass spectrometer observations reveal that the oxygen/hydrogen ion composition ratio near summer solstice is much greater than the corresponding ratio near winter. These results reinforce the importance of ion composition in outflow models. If observed perturbations result from Doppler‐shifted wave structures with near‐zero frequencies, we show that spacecraft frame frequencies 0.1–0.5 Hz correspond to perpendicular spatial scales of several to tens of kilometers.

The Rapid Imaging Planetary Spectrograph: Observations of Mercury’s Sodium Exosphere in Twilight

Abstract Ground-based observations of Mercury’s exosphere are intrinsically difficult due to its proximity to the Sun and must be made in daylight or during brief windows at twilight. While the dimmer twilight background is far preferred, high airmass seeing and haze through Earth’s atmosphere, windshake, and guiding all present formidable challenges toward spatially resolving the exosphere’s structure. This study explores how such effects can be mitigated using results from a new instrument for high cadence spectroscopy, the Rapid Imaging Planetary Spectrograph. While high cadence observations do not significantly improve upon the resolution floor imposed by atmospheric seeing, the method does mitigate obstacles such as telescope tracking inaccuracy, windshake, and flux calibration. Whereas daytime observing has been the predominant methodology in past exosphere studies, the twilight observations performed here easily resolve distinct brightness enhancements near 50°–60° latitude, just equatorward of magnetic cusp regions. The exosphere in these locations is diagnostic of space weather effects such as charged particle precipitation. The structure in the sodium exosphere generally appears both more extended and brighter over the southern cusp, which has a broader open magnetic field line region. However, a northern enhancement during one observation confirms that the exosphere responds dynamically to environmental drivers, presumably changes in the solar wind dynamic pressure and/or interplanetary magnetic field.

Multi‐Instrument Observations of Ion‐Neutral Coupling in the Dayside Cusp

AbstractUsing data from the Scanning Doppler Imager, the Super Dual Auroral Radar Network, the EISCAT Svalbard Radar, and an auroral all‐sky imager, we examine an instance of region neutral winds which have been influenced by the presence of poleward moving auroral forms near the dayside cusp region. We observe a reduction in the time taken for the ion drag force to reorientate the neutrals into the direction of the convective plasma (on the order of minutes), compared to before the auroral activity began. Additionally, because the ionosphere near the cusp is influenced much more readily by changes in the solar wind via dayside reconnection, we observe the neutrals responding to an interplanetary magnetic field change within minutes of it occurring. This has implications on the rate that energy is deposited into the ionosphere via Joule heating, which we show to become dampened by the neutral winds.

Determining primates bite force from histological tooth sections.

The ability to accurately estimate bite force (BF) in extant and fossil primates is valuable to biological anthropologists. BF is generally evaluated using complex jaw musculature and lever arm analyses employing numerous assumptions and requiring complete cranial morphology. Here, a simple method to determine BF from data measured on histological sections of fossil teeth is proposed. Published sections of molar teeth encompassing 27 different extinct and extant primates dating back to as early as 17 million years ago were examined. Focusing on the cusp region, the extracted data include characteristic enamel thickness dc and dentin horn angle φ. The occlusal force needed to fracture a cusp, PF , was determined from these variables with the aid of a finite element stress analysis similarly to a previous study on postcanine human teeth. The bite force was obtained by linking BF to PF using a universal constant. The measured variables dc and φ are conclusively linked. This link produces a virtually constant fracture force PF and in turn bite force BF for all cusps in the molar row. An explicit formula tying BF to dc and φ was derived. For nonhominin taxa the bite force, molar crown area, and body mass are found to be intimately related. The case of hominins is more involved. The so determined BF is gender-averaged, with the bite force of males estimated to be ≈12% greater than that of females. The use of "fracture mechanics" concepts from mechanics of materials facilitates determination of critical bite force in primates based on characteristic enamel thickness dc and dentin horn angle φ as extracted from histological sections of molar teeth. This novel approach enables quantitative insight into the role played by crown area, body mass and bite force on evolutionary trends. The conclusive link between cuspal enamel thickness and dentin horn angle facilitates optimal food processing without hindering cusp resilience. The proposed approach may be extended to mammals having asymmetric cusp structures.