# EPP

ISSN  2096-3955

CN  10-1502/P

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SPACE PHYSICS: MAGNETOSPHERIC PHYSICS
Recently Published, doi: 10.26464/epp2023002
[Abstract](59) [FullText HTML](35) [PDF 2114KB](8)
Abstract:
Tailward ion outflows in the Martian-induced magnetotail are known to be one of the major channels for Martian atmospheric escape. On the basis of nearly 6.5 years of observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we investigate the statistical distribution of tailward and Marsward fluxes of heavy ions (i.e., O+ and \begin{document}${\rm{O}}_2^+$\end{document}) in the near-Mars magnetotail and explore their characteristic responses to the corotating interaction region (CIR), solar wind dynamic pressure, and local magnetic field intensity. Our results show that the tailward fluxes of oxygen ions and molecular oxygen ions in the magnetotail are significantly greater than their Marsward fluxes and that the tailward flux of molecular oxygen ions is generally larger than that of oxygen ions. Furthermore, the tailward ion flux distribution exhibits dependence on the CIR, solar wind dynamic pressure, and local magnetic field strength in a manner stronger than the Marsward ion flux distribution. According to the distribution of tailward ion fluxes, we calculate the corresponding escape rates of heavy ions and show that when the CIR occurs, the total escape rates of oxygen ions and molecular oxygen ions increase by a factor of ~2 and ~1.2, respectively. We also find that the escape rates of heavy ions increase with the enhancement of solar wind dynamic pressure, whereas the overall effect of the local magnetic field is relatively weak. Our study has important implications for improved understanding of the underlying mechanisms responsible for the Martian atmospheric escape and the evolution of the Martian atmospheric climate.
SPACE PHYSICS: IONOSPHERIC PHYSICS
Recently Published, doi: 10.26464/epp2023001
[Abstract](122) [FullText HTML](34) [PDF 1600KB](8)
Abstract:
In this study, we investigate the generation of parametric decay instability, Langmuir turbulence formation, and electron acceleration in ionospheric heating via a two-fluid model using the Fokker–Planck equation and Vlasov–Poisson system simulations. The simulation results of both the magnetofluid model and the kinetic model demonstrate the dynamics of electron acceleration. Further, the results of the Vlasov–Poisson simulations suggest the formation of electron holes in phase space at the same spatial scale as the Langmuir wave, which are shown to be related to electron acceleration. In addition, electron acceleration is enhanced through the extension of the wavenumber spectrum caused by strong Langmuir turbulence, leading to more electron holes in phase space.

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PLANETARY SCIENCES
2022, 6(5): 431 -450. doi: 10.26464/epp2022042
Abstract:
For decades, the search for potential signs of Martian life has attracted strong international interest and has led to significant planning and scientific implementation. Clearly, in order to detect potential life signals beyond Earth, fundamental questions, such as how to define such terms as “life” and “biosignature”, have been given considerable attention. Due to the high costs of direct exploration of Mars, Mars-like regions on Earth have been invaluable targets for astrobiological research, places where scientists could practice the search for “biosignatures” and refine ways to detect them. This review summarizes scientific instrumental techniques that have resulted from this work. Instruments must necessarily be our “eyes” and “hands” as we attempt to identify and quantify biosignatures on Mars. Scientific devices that can be applied in astrobiology include mass spectrometers and electromagnetic-spectrum-based spectrometers, redox potential indicators, circular dichroism polarimeters, in situ nucleic acid sequencers, life isolation/cultivation systems, and imagers. These devices and how to interpret the data they collect have been tested in Mars-analog extreme environments on Earth to validate their practicality on Mars. To anticipate the challenges of instrumental detection of biosignatures through the full evolutionary history of Mars, Terrestrial Mars analogs are divided into four major categories according to their similarities to different Martian geological periods (the Early−Middle Noachian Period, the Late Noachian−Early Hesperian Period, the Late Hesperian−Early Amazonian Period, and the Middle−Late Amazonian Period). Future missions are suggested that would focus more intensively on Mars’ Southern Hemisphere, once landing issues there are solved by advances in spacecraft engineering, since exploration of these early terrains will permit investigations covering a wider continuum of the shifting habitability of Mars through its geological history. Finally, this paper reviews practical applications of the range of scientific instruments listed above, based on the four categories of Mars analogs here on Earth. We review the selection of instruments suitable for autonomous robotic rover tests in these Mars analogs. From considerations of engineering efficiency, a Mars rover ought to be equipped with as few instrument assemblies as possible. Therefore, once candidate landing regions on Mars are defined, portable suites of instruments should be smartly devised on the basis of the known geological, geochemical, geomorphological, and chronological characteristics of each Martian landing region. Of course, if Mars sample-return missions are successful, such samples will allow experiments in laboratories on Earth that can be far more comprehensive and affordable than is likely to be practicable on Mars. To exclude false positive and false negative conclusions in the search for extraterrestrial life, multiple diverse and complementary analytical techniques must be combined, replicated, and carefully interpreted. The question of whether signatures of life can be detected on Mars is of the greatest importance. Answering that question is extremely challenging but appears to have become manageable.
PLANETARY SCIENCES
2022, 6(5): 451 -464. doi: 10.26464/epp2022040
Abstract:
A meteor radar chain located along the 120°E meridian in the Northern Hemisphere from low to middle latitudes provides long-term horizontal wind observations of the mesosphere and lower thermosphere (MLT) region. In this study, we report a seasonal variation and its latitudinal feature in the horizontal mean wind in the MLT region observed by six meteor radar instruments located at Mohe (53.5°N, 122.3°E), Beijing (40.3°N, 116.2°E), Mengcheng (33.4°N, 116.5°E), Wuhan (30.6°N, 114.4°E), Kunming (25.6°N, 108.3°E), and Fuke (19.5°N, 109.1°E) stations. In addition, we compare the wind in the MLT region measured by the meteor radar stations with those simulated by the Whole Atmosphere Community Climate Model (WACCM). In general, the WACCM appears to capture well the seasonal and latitudinal variations in the zonal wind component. In particular, the temporal evolution of the eastward zonal wind maximum shifts from July to May as the latitude decreases. However, the simulated WACCM meridional wind exhibits differences from the meteor radar observations.
SPACE PHYSICS: MAGNETOSPHERIC PHYSICS
2022, 6(5): 465 -473. doi: 10.26464/epp2022041
Abstract:
Kinetic Alfvén waves (KAWs), with a strong parallel disturbed electric field, play an important role in energy transport and particle acceleration in the magnetotail. On the basis of high-resolution observations of the Magnetospheric Multiscale (MMS) Mission, we present a detailed description of the acceleration process of electrons by KAWs in the plasma sheet boundary layer (PSBL). The MMS observed strong electromagnetic disturbances carrying a parallel disturbed electric field with an amplitude of up to 8 mV/m. The measured ratio of the electric to magnetic field perturbations was larger than the local Alfvén speed and was enhanced as the frequency increased, consistent with the theoretical predictions for KAWs. This evidence indicates that the electromagnetic disturbances should be identified as KAWs. During the KAWs, the energy flux of electrons at energies above 1 keV in the parallel and anti-parallel directions are significantly enhanced, implying occurrences of electron beams at higher energies. Additionally, the KAWs became more electrostatic-like and filled with high-frequency ion acoustic waves. The energy enhancement of electron beams is in accordance with the derived work done with the observed parallel disturbed electric field of KAWs, indicating electron acceleration caused by KAWs. Therefore, these results provide direct evidence of electron acceleration by KAWs embodying electrostatic ion acoustic waves in the PSBL.
SPACE PHYSICS: IONOSPHERIC PHYSICS
2022, 6(5): 474 -486. doi: 10.26464/epp2022043
Abstract:
Parametric decay instability (PDI) is an important process in ionospheric heating. This paper focuses on the frequency and wavevector matching condition in the initial PDI process, the subsequent cascade stage, and the generation of strong Langmuir turbulence. A more general numerical model is established based on Maxwell equations and plasma dynamic equations by coupling high-frequency electromagnetic waves to low-frequency waves via ponderomotive force. The primary PDI, cascade process, and strong Langmuir turbulence are excited in the simulation. The matching condition in the initial PDI stage and cascade process is verified. The result indicates that the cascade ion acoustic wave may induce or accelerate the formation of cavitons and lead to the wavenumber spectrum being more enhanced at 2kL (where kL is the primary Langmuir wavenumber). The wavenumber spectra develop from discrete to continuous spectra, which is attributed to the caviton collapse and strong Langmuir turbulence.
SOLID EARTH: MARINE GEOPHYSICS
2022, 6(5): 487 -494. doi: 10.26464/epp2022044
Abstract:
First-arrival seismic traveltime tomography (FAST) is a well-established technique to estimate subsurface velocity structures. Although several existing open-source packages are available for first-arrival traveltime tomography, most were written in compiled languages and lack sufficient extendibility for new algorithms and functionalities. In this work, we develop an open-source, self-contained FAST package based on MATLAB, one of the most popular interpreted scientific programming languages, with a focus on ocean bottom seismometer refraction traveltime tomography. Our package contains a complete traveltime tomography workflow, including ray-tracing-based first-arrival traveltime computation, linearized inversion, quality control, and high-quality visualization. We design the package as a modular toolbox, making it convenient to integrate new algorithms and functionalities as needed. At the current stage, our package is most efficient for performing FAST for two-dimensional ocean bottom seismometer surveys. We demonstrate the efficacy and accuracy of our package by using a synthetic data example based on a modified Marmousi model.
2018, 2(4): 257-275doi: 10.26464/epp2018025
[Abstract](8920) [FullText HTML](4337) [PDF](333)
2017, 1(1): 2-12doi: 10.26464/epp2017002
[Abstract](8138) [FullText HTML](2744) [PDF](195)
2017, 1(1): 13-25doi: 10.26464/epp2017003
[Abstract](7642) [FullText HTML](3157) [PDF](170)
2018, 2(1): 52-66doi: 10.26464/epp2018005
[Abstract](7434) [FullText HTML](2435) [PDF](158)
2017, 1(1): 26-34doi: 10.26464/epp2017004
[Abstract](9937) [FullText HTML](2831) [PDF](153)
2018, 2(6): 527-537doi: 10.26464/epp2018051
[Abstract](13002) [FullText HTML](1681) [PDF](153)
2021, 5(2): 123-140doi: 10.26464/epp2021014
[Abstract](4003) [FullText HTML](716) [PDF](109)
2020, 4(5): 532-542doi: 10.26464/epp2020048
[Abstract](2751) [FullText HTML](622) [PDF](102)
2020, 4(3): 179-205doi: 10.26464/epp2020028
[Abstract](3985) [FullText HTML](883) [PDF](102)
2018, 2(4): 327-341doi: 10.26464/epp2018030
[Abstract](4702) [FullText HTML](1028) [PDF](99)

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