The Extreme Ultraviolet (EUV) monitor is an instrument on the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, designed to measure the variability of the solar soft x-rays and EUV ...irradiance at Mars. The solar output in this wavelength range is a primary energy input to the Mars atmosphere and a driver for the processes leading to atmospheric escape. The MAVEN EUV monitor consists of three broadband radiometers. The radiometers consist of silicon photodiodes with different bandpass-limiting filters for each channel. The filters for the radiometers are: Channel A: thin foil C/Al/Nb/C for 0.1–3 nm and 17–22 nm, Channel B: thin foil C/Al/Ti/C for 0.1–7 nm, and Channel C: interference filter for 121–122 nm. A fourth, covered photodiode is used to monitor variations in dark signal due to temperature and radiation background changes. The three science channels will monitor emissions from the highly variable corona and transition region of the solar atmosphere. The EUV monitor is mounted on the top deck of the MAVEN spacecraft and is pointed at the Sun for most of its orbit around Mars. The measurement cadence is 1-second. The broadband irradiances can be used to monitor the most rapid changes in solar irradiance due to flares. In combination with time-interpolated observations at Earth of slower varying solar spectral emissions, the broadband MAVEN EUV monitor measurements will also be used in a spectral irradiance model to generate the full EUV spectrum at Mars from 0 to 190 nm in 1-nm bins on a time cadence of 1-minute and daily averages.
We study the response of Auger electrons, He-II photoelectrons, and thermal electrons in the dayside Martian ionosphere to the solar soft X-rays (SXR; 0.1–7 nm), 30.5 nm, and the extreme ultraviolet ...(EUV; 20–90 nm) irradiances, respectively. For this purpose, the suprathermal electron fluxes measured by the Solar Wind Electron Analyzer (SWEA) and densities of the thermal electrons measured by Langmuir Probe and Waves (LPW) instruments, both on the Mars Atmosphere and Volatile Evolution (MAVEN) mission, have been used. The data used in the present study span from January 2015 (Martian Year (MY) 32, solar longitude, Ls = 263°) to December 2019 (MY 35, Ls = 110°), which falls in the declining phase of solar cycle 24. The solar irradiances are taken from the extreme ultraviolet monitor instrument on MAVEN and also from the Flare Irradiance Spectral Model for Mars. The results of the present study show that the fluxes of the suprathermal electrons and the densities of the thermal electrons are drastically reduced during solar minimum. The Auger electrons show a significant correlation and have an almost linear relationship with the SXR irradiance; both of which are independent of altitude. The response of the He-II photoelectrons to 30.5 nm solar irradiance deviates slightly from the linear relationship, particularly in the altitude range of 225–350 km and the solar zenith angle (SZA) range of 45°-65°. At these altitude and SZA ranges, the thermal electrons show a power law dependence on the EUV irradiance. The responses of the He-II photoelectrons and thermal electrons to their respective solar irradiances decrease on either side of the altitude and SZA range of maximum response (225–350 km and 45°-65°, respectively). The energy dependent response of the electrons to the solar irradiances and their altitude and SZA variation are explained by considering their dependence on electron temperature, and ionization and the neutral heating efficiencies. The responses of the He-II photoelectrons and thermal electrons to their respective solar irradiances decrease near the terminator.
•Response of the Martian ionospheric Auger, He-II photo and thermal electrons to solar forcing is studied using MAVENdata.•Auger electrons show significant correlation with the solar soft x-ray irradiances (0.1–7 nm) and are linearly related•The response of the He-II photoelectrons to 30.5 nm solar irradiance increases at altitudes of 225–350 km and SZAs of 45°−65°•In the 225–350 km altitude and 45°−65° SZA range, the thermal electrons show power law dependence on the EUV irradiance
The Mars Atmosphere and Volatile Evolution mission has obtained comprehensive particle and magnetic field measurements. The Solar Wind Electron Analyzer provides electron energy‐pitch angle ...distributions along the spacecraft trajectory that can be used to infer magnetic topology. This study presents pitch angle‐resolved electron energy shape parameters that can distinguish photoelectrons from solar wind electrons, which we use to deduce the Martian magnetic topology and connectivity to the dayside ionosphere. Magnetic topology in the Mars environment is mapped in three dimensions for the first time. At low altitudes (<400 km) in sunlight, the northern hemisphere is found to be dominated by closed field lines (both ends intersecting the collisional atmosphere), with more day‐night connections through cross‐terminator closed field lines than in the south. Although draped field lines with ~100 km amplitude vertical fluctuations that intersect the electron exobase (~160–220 km) in two locations could appear to be closed at the spacecraft, a more likely explanation is provided by crustal magnetic fields, which naturally have the required geometry. Around 30% of the time, we observe open field lines from 200 to 400 km, which implies three distinct topological layers over the northern hemisphere: closed field lines below 200 km, open field lines with foot points at lower latitudes that pass over the northern hemisphere from 200 to 400 km, and draped interplanetary magnetic field above 400 km. This study also identifies open field lines with one end attached to the dayside ionosphere and the other end connected with the solar wind, providing a path for ion outflow.
Key Points
Pitch angle‐resolved electron energy shape parameters are used to deduce magnetic topology
Closed magnetic field lines dominate low altitudes (<400 km) of the northern hemisphere on the dayside
The 3‐D view of the Martian magnetic topology is presented for the first time
Background
Given the rapid increase of Internet use for effective health communication, it is important for health practitioners to be able to identify and mobilize active users of online health ...information across various web‐based health intervention programmes. We propose the concept ‘health e‐mavens’ to characterize individuals actively engaged in online health information seeking and sharing activities.
Objectives
This study aimed to address three goals: (i) to test the factor structure of health e‐mavenism, (ii) to assess the reliability and validity of this construct and (iii) to determine what predictors are associated with health e‐mavenism.
Methods
This study was a secondary analysis of nationally representative data from the 2010 Health Tracking Survey. We assessed the factor structure of health e‐mavenism using confirmatory factor analysis and examined socio‐demographic variables, health‐related factors and use of technology as potential predictors of health e‐mavenism through ordered regression analysis.
Results
Confirmatory factor analyses showed that a second‐order two‐factor structure best captured the health e‐maven construct. Health e‐mavenism comprised two second‐order factors, each encompassing two first‐order dimensions: information acquisition (consisting of information tracking and consulting) and information transmission (consisting of information posting and sharing). Both first‐order and second‐order factors exhibited good reliabilities. Several factors were found to be significant predictors of health e‐mavenism.
Discussion and conclusion
This study offers a starting point for further inquiries about health e‐mavens. It is a fruitful construct for health promotion research in the age of new media technologies. We conclude with specific recommendations to further develop the health e‐maven concept through continued empirical research.
The Magnetic Pileup Boundary or Induced Magnetosphere Boundary (IMB) has been an enigma in Mars aeronomy. Previously dubbed the planetopause, magnetopause, ion‐composition boundary, and protonopause, ...identification of this unique plasma region has been marked by difficulty. In this case study, we used data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission to identify IMB crossings and configurations during the month of September 2017, with a particular focus on the September 10, 2017 solar events. It was concluded that the Interplanetary Coronal Mass Ejection had no statistically significant impact on the IMB standoff locations. This study also investigated the effects of upstream dynamic pressure, thermal pressure from the magnetosheath, magnetic pressure from the magnetic pileup region (MPR), thermal pressure associated with the ionosphere, and Extreme Ultraviolet irradiance on the IMB during September 2017. We have found that during the 163 IMB crossings, magnetic pressure in the MPR and thermal pressure in the ionosphere had the largest influence on the IMB standoff distance.
Plain Language Summary
The plasma environment of Mars is a dynamic and complex place. There are multiple layers and confines of plasma formed from the interaction of plasma from planetary origin and the plasma of the solar wind. One such complicated plasma boundary is the Induced Magnetosphere Boundary (IMB) which is one of many located in the solar wind/ionosphere interface region. The IMB is widely known to be affected by solar wind dynamic pressure and solar irradiance flux. However, there are other pressures that sway the position and shape of the IMB as well. September 2017 brought about an intense pressure event due to the solar eruptive activity. All aspects of the Martian plasma environment were affected. We therefore took this opportunity to examine how the IMB reacted to different plasma pressures brought about by the solar events. We also tried to determine which pressure(s) were most influential in determining the IMB's standoff distance.
Key Points
The Interplanetary Coronal Mass Ejection during September 2017 had no statistically significant impact on the Induced Magnetosphere Boundary (IMB) standoff location
The magnetic pressure of the magnetic pileup region and the thermal pressure of the ionosphere had the greatest influence on the IMB standoff distance during September 2017
The presence of plasma waves upstream from the Martian bow shock, with frequencies near the local proton cyclotron frequency in the spacecraft frame, constitutes, in principle, an indirect signature ...for the existence of planetary protons from the ionization of Martian exospheric hydrogen. In this study, we determine the "proton cyclotron wave” (PCW) occurrence rate between October 2014 and February 2020, based on Magnetometer and Solar Wind Ion Analyzer measurements from the Mars Atmosphere and Volatile EvolutioN mission. We characterize its dependence on several wave and solar wind (SW) properties, and solar longitude ranges. We confirm a previously reported long‐term trend with more PCWs near perihelion, likely associated with changes in exospheric hydrogen density. Furthermore, we report for the first time a decrease in median PCW amplitude for each consecutive Martian perihelion. Such variability cannot be attributed to differences in the distribution of SW conditions. This trend could be associated with changes in solar inputs, foreshock effects, and asymmetries due to the SW convective electric field influencing newborn protons. In addition, we observe PCWs more frequently for low to intermediate interplanetary magnetic field (IMF) cone angles, slower SW speeds, and higher SW proton densities. The IMF cone angle preference likely results from the trade‐off between associated linear wave growth rates, wave saturation energies, and pick‐up proton densities. Moreover, the dependencies on SW speed and density indicate the importance of the characteristic SW transit timescale and the charge exchange process coupling SW protons with the hydrogen exosphere.
Key Points
We confirm an annual periodicity of proton cyclotron wave occurrence rate upstream from the Martian bow shock between October 2014 and February 2020
We report a decrease in median wave amplitude for each consecutive Martian perihelion based on available sampling of the Martian upstream region
PCWs occur more frequently near perihelion for low to intermediate interplanetary magnetic field cone angles, slower solar wind speeds and higher solar wind densities
The Imaging Ultraviolet Spectrograph (IUVS) is one of nine science instruments aboard the Mars Atmosphere and Volatile and EvolutioN (MAVEN) spacecraft. MAVEN, launched in November 18, 2013 and ...arriving at Mars in September 2014, is designed to explore the planet’s upper atmosphere and ionosphere and examine their interaction with the solar wind and solar ultraviolet radiation. IUVS is one of the most powerful spectrographs sent to another planet, with several key capabilities: (1) separate Far-UV & Mid-UV channels for stray light control, (2) a high resolution echelle mode to resolve deuterium and hydrogen emission, (3) internal instrument pointing and scanning capabilities to allow complete mapping and nearly-continuous operation, and (4) optimization for airglow studies.
The Mars Atmosphere and Volatile EvolutioN (MAVEN) Neutral Gas and Ion Mass Spectrometer (NGIMS) provides sensitive detections of neutral gas and ambient ion composition. NGIMS measurements of nine ...atomic and molecular neutral species, and their variation with altitude, latitude, and solar zenith angle are reported over several months of operation of the MAVEN mission. Sampling NGIMS signals from multiple neutral species every several seconds reveals persistent and unexpectedly large amplitude density structures. The scale height temperatures are mapped over the course of the first few months of the mission from high down to midlatitudes. NGIMS measurements near the homopause of 40Ar/N2 ratios agree with those reported by the Sample Analysis at Mars investigation and allow the altitude of the homopause for the most abundant gases to be established.
Key Points
Neutral density structure measured with high temporal resolution
Scale height temperature of the upper atmosphere reported
Homopause altitude identified
Large-scale code reuse significantly reduces both development costs and time. However, the massive share of third-party code in software projects poses new challenges, especially in terms of ...maintenance and security. In this paper, we propose a novel technique to specialize dependencies of Java projects, based on their actual usage. Given a project and its dependencies, we systematically identify the subset of each dependency that is necessary to build the project, and we remove the rest. As a result of this process, we package each specialized dependency in a jar file. Then, we generate specialized dependency trees where the original dependencies are replaced by the specialized versions. This allows building the project with significantly less third-party code than the original. As a result, the specialized dependencies become a first-class concept in the software supply chain, rather than a transient artifact in an optimizing compiler toolchain. We implement our technique in a tool called D ep T rim , which we evaluate with 30 notable open-source Java projects. D ep T rim specializes a total of 343 (86.6%) dependencies across these projects, and successfully rebuilds each project with a specialized dependency tree. Moreover, through this specialization, D ep T rim removes a total of 57,444 (42.2%) classes from the dependencies, reducing the ratio of dependency classes to project classes from 8.7× in the original projects to 5.0× after specialization. These novel results indicate that dependency specialization significantly reduces the share of third-party code in Java projects.
Mars' Ionopause: A Matter of Pressures Sánchez‐Cano, Beatriz; Narvaez, Clara; Lester, Mark ...
Journal of geophysical research. Space physics,
September 2020, 2020-09-00, 20200901, Letnik:
125, Številka:
9
Journal Article
Recenzirano
Odprti dostop
This study assesses under what circumstances the Martian ionopause is formed on the dayside, both in regions where there are strong crustal magnetic fields and areas where these fields are small ...(<30 nT). Multiple data sets from three MAVEN dayside deep dip campaigns are utilized between periapsis and 600–1,000 km, as well as solar wind observations from Mars Express. The ionopause is identified as a sudden decrease of the electron density with increasing altitude and a simultaneous increase of the electron temperature and variability below 400 km. This is a physically robust approach as the electron temperature is a key parameter in determining the structure of the ionospheric profile, and, therefore, also a strong indicator of the ionopause location. We find that 36% (54%) of the electron density profiles over strong (weak) crustal magnetic field regions had an ionopause event. We also evaluate the roles of ionospheric thermal and magnetic pressures on the ionopause formation as well as the presence of solar wind particles, H+, down to the location of the ionopause. We found that the topside ionosphere is typically magnetized at mostly all altitudes. The ionopause, if formed, occurs where the total ionospheric pressure (magnetic + thermal) equals the upstream solar wind dynamic pressure. Moreover, the lower edge of the ionopause coincides with the altitude where the solar wind flow stops: The thermal pressure suffers a significant reduction with increasing altitude and the solar wind proton density has a prominent increase.
Plain Language Summary
The ionosphere of Mars is the layer of its atmosphere where gases are separated into ions and electrons by solar radiation. The ionopause is the uppermost region where the ionosphere terminates. However, the Martian ionopause is not well‐understood because it does not always form, and when it does, it is located over a large range of altitudes, varies rapidly, and is highly structured. This paper does a statistical analysis of the different parameters that play a role in ionopause formation, both over and far from the strong Martian crustal magnetic field regions. The study focuses on observations from the dayside of Mars, and analyzes several data sets from the MAVEN and Mars Express missions. It is found that the ionosphere almost always contains magnetic fields within it and that there is a pressure balance at its upper boundary (the ionopause) between the solar wind and the ionosphere. Moreover, there are more ionopause events far from the surface magnetic field regions than over them.
Key Points
Mars' ionopause identification is based on simultaneous electron density and electron temperature changes
When the Martian ionopause is formed, the upstream solar wind dynamic pressure is enough to equal the total pressure of the ionosphere
Fewer ionopauses are identified over strong crustal magnetic fields because the total ionospheric pressure is larger and excludes the solar wind from penetrating into the ionosphere
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