ALBERT

Description: [1]  Kinetic Alfvén waves (KAWs) can play an important role in the energization of plasma particles and the formation of filamentous structures, which commonly are encountered and frequently accompanied by field-aligned currents in various magneto-plasmas, such as laboratory, auroral, and coronal plasmas. Based on a low-frequency kinetic dispersion equation in frequency ω  〈  ω ci (the ion cyclotron frequency), KAW instability driven by a field-aligned current, which is carried by the field-aligned drift of electrons at velocity V D , is investigated in a low- β plasma of β  〈  Q  ≪ 1, where β is the kinetic-to-magnetic pressure ratio and Q (≡ m e / m i  ≪ 1) is the mass ratio of electrons to ions. An instability condition and the corresponding growth rate are obtained, which depends on the plasma β parameter as well as the drift velocity V D . The results show that the KAW instability occurs in the perpendicular wave-number range of , in which the growth rate reaches its maximum at for fixted V D and β . As V D increases, this growing wave-number range widens and the growth rate increases, but the maximal-growing wavenumber decreases. On the other hand, as the plasma β parameter decreases, the growing wave-number range also widens, and the maximal-growing wavenumber and growth rate both increase. These results have potential importance in understanding the physics of the electric current dissipation and plasma active phenomena since the field-aligned current is one of the most active factors in space and astrophysical plasmas.

Description: Sensitive long-wavelength radar observations of absolute velocity never previously published from Jicamarca are brought to bear on the long-standing problem of radar detection of slow-moving meteors. Attention is devoted to evaluating the ionization coefficient β(V) in the critically important velocity range of 11-20 km/s in recent laboratory measurements of Thomas et al. (2016). Theoretical predictions for β(V) based on the laboratory data, on Jones (1997), on Janches et al. (2014) and on Verniani and Hawkins (1964) are used to correct the incoming meteor velocities measured with the sensitive Jicamarca HPLA radar operating at 6 m wavelength. All corrected distributions are consistent with the predictions of the Nesvorný model in showing pronounced monotonic increases down to the escape velocity (11km/s). Such distributions may be essential to explaining the pronounced ledge in nighttime electron density and the rapid disappearance of electrons in meteor trails in the altitude range of 80-85 km.

Description: The ionosphere scale height is one of the most significant ionospheric parameters, which contains information about the ion and electron temperatures and dynamics in upper ionosphere. In this paper, an empirical orthogonal function (EOF) analysis method is applied to process all the ionospheric radio occultations of GPS/COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) from the year 2007 to 2011 to reconstruct a global ionospheric scale height model. This monthly medium model has spatial resolution of 5° in geomagnetic latitude (-87.5° ~ 87.5°), and temporal resolution of 2 hours in local time. EOF analysis preserves the characteristics of scale height quite well in the geomagnetic latitudinal, anural, seasonal and diurnal variations. In comparison with COSMIC measurements of the year of 2012, the reconstructed model indicates a reasonable accuracy. In order to improve the topside model of International Reference Ionosphere (IRI), we attempted to adopt the scale height model in the Bent topside model by applying a scale factor q as an additional constraint. With the factor q functioning in the exponent profile of topside ionosphere, the IRI scale height should be forced equal to the precise COSMIC measurements. In this way, the IRI topside profile can be improved to get closer to the realistic density profiles. Internal quality check of this approach is carried out by comparing COSMIC realistic measurements and IRI with or without correction respectively. In general, the initial IRI model overestimates the topside electron density to some extent, and with the correction introduced by COSMIC scale height model, the deviation of vertical total electron content (VTEC) between them is reduced. Furthermore, independent validation with Global Ionospheric Maps (GIM) VTEC implies a reasonable improvement in the IRI VTEC with the topside model correction.

Description: Abstract Although steady, isotropic Darcy flows are inherently laminar and non‐mixing in the absence of diffusion, it is well understood that transient forcing via engineered pumping schemes can induce rapid, chaotic mixing flows in groundwater. In this study we explore the propensity for such mixing to arise in natural groundwater systems subject to cyclical forcings, e.g. tidal or seasonal influences. Using a conventional linear groundwater flow model subject to tidal forcing, we show that under certain conditions these flows generate Lagrangian transport and mixing phenomena (chaotic advection) near the tidal boundary. We show that aquifer heterogeneity, storativity, and forcing magnitude cause reversals in flow direction over the forcing cycle which, in turn, generate coherent Lagrangian structures and chaos. These features significantly augment fluid mixing and transport, leading to anomalous residence time distributions, flow segregation, and the potential for profoundly altered reaction kinetics. We define the dimensionless parameter groups which govern this phenomenon and explore these groups in connection with a set of well‐characterised tidal systems. The potential for Lagrangian chaos to be present near discharge boundaries must be recognized and assessed in field studies.

Description: Increasing total electron content (TEC) measurements from the low earth orbiting (LEO) satellites to Global Positioning System (GPS) satellites flourish the exploration of the ionosphere and plasmasphere for decades. This paper indicates a method that 3-D Var is applied to assimilate precise orbit determination (POD) antenna TEC measurements of Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites into the background Global Core Plasma Model (GCPM). The slant TEC data archived in the COSMIC Data Analysis and Archive Center (CDAAC) from 500 km to 20,200 km are used to reconstruct a new electron density model. This model has temporal resolution of 2 hours and spatial resolution of 2.5° in geomagnetic latitude, 5° in longitude, 50 km in the upper ionosphere and several hundred kilometers in the plasmasphere. Preliminary results show that the data assimilation modifies the initial GCPM forecast to be better coincident with actual COSMIC measurements in internal quality check. Furthermore, independent validation with upper ionosphere retrieved electron density, and TEC of Global Ionosphere Maps (GIM) implies a reasonable improvement in the estimation of plasmaspheric electron density after the assimilation.

Description: Due to having strong anisotropy in their polarization state and spatial structure, it is believed that kinetic Alfvén waves (KAWs) can play an important role in various energization phenomena of plasma particles and the fine-structure formation in magneto-plasma environments. The filamentous fine-structures are a kind of the common density inhomogeneity phenomena in magneto-plasmas, and hence, the density gradient is one of the sources of free energy that can lead to KAWs instabilities. In this paper, based on the two-fluid model in which ions and electrons are treated as separate fluids, we investigate the effect of density gradient inhomogeneous on the dispersion and instability of KAWs in a magneto-plasma. The results show that KAW instability can be excited effectively by the density gradient. Especially, both the real frequency ω R and the growth rate ω I of KAWs are dramatically dependent on the spatial position x in the presence of an inhomogeneous density gradient. The results also show that the real frequency increases with the characteristic spatial scale of inhomogeneity , while the growth rate of KAWs has maximum in the growing ranges of . On the other hand, the excited KAWs are weakly dispersive with λ e k x  〈 1. The results have potential importance for better understanding the microphysics of the filamentous fine-structure formation since the phenomena of density gradient inhomogeneous are ubiquitous in various magneto-plasmas, such as in the laboratory plasma as well as in both the solar coronal and terrestrial auroral plasmas.

Description: A full kinetic elve model with a wide time range from microseconds to seconds and its spectral range from UV, visible to near-infrared wavelengths is developed. Not only the fast electron-impact emissions N2 1P (B3Πg - A3Σu+), N2 2P(C3Πu - B3Πg), N2 Lyman-Birge-Hopfield (a1Πg - X1Σg+), N2+ 1N (B2Σu+ - X2Σg+) and O2+ 1N (b4Σg− – a4Πu) but also the post-impulse chemiluminescenses, O2 atmospheric band (b1Σg+ – X3Σg−), O(1S – 1D) at 557.7 nm and O(1D – 3P) at 630 nm, are considered in the elve model. We calculate the dominant emissions and possible weak emissions in our elves model to analyze the relative importance of emission intensity, measured by the ISUAL imager with 5 selectable band pass filters (N21P, 762, 630, 557.7, 427.8 nm filter). The modeling emission intensities were well consistent with the measurements by Imager with different filters. This comparison could also be useful in designing the imager filters for future TLE survey missions in Earth orbit.

Description: A thermodynamic analysis is performed with a Gibbs free energy minimization method to compare the conventional steam reforming of ethanol (SRE) process and sorption-enhanced SRE (SE-SRE) with three different sorbents, namely, CaO, Li 2 ZrO 3 , and hydrotalcite-like compounds (HTlc). As a result, the use of a CO 2 adsorbent can enhance the hydrogen yield and provide a lower CO content in the product gas at the same time. The best performance of SE-SRE is found to be at 500 °C with an HTlc sorbent. Nearly 6 moles hydrogen per mole ethanol can be produced, when the CO content in the vent stream is less than 10 ppm, so that the hydrogen produced via SE-SRE with HTlc sorbents can be directly used for fuel cells. Higher pressures do not favor the overall SE-SRE process due to lower yielding of hydrogen, although CO 2 adsorption is enhanced. The current research status of thermodynamic analysis on ethanol steam reforming (SRE) and sorption-enhanced SRE (SE-SRE) is surveyed. Hydrotalcite-like compounds (HTlc), CaO, and Li 2 ZrO 3 as three typical CO 2 sorbents for SE-SRE are compared for the first time. The simulated results agree well with other publications.

Description: A thermodynamic analysis is performed with a Gibbs free energy minimization method to compare the conventional steam reforming of ethanol (SRE) process and sorption-enhanced SRE (SE-SRE) with three different sorbents, namely, CaO, Li 2 ZrO 3 , and hydrotalcite-like compounds (HTlc). As a result, the use of a CO 2 adsorbent can enhance the hydrogen yield and provide a lower CO content in the product gas at the same time. The best performance of SE-SRE is found to be at 500 °C with an HTlc sorbent. Nearly 6 moles hydrogen per mole ethanol can be produced, when the CO content in the vent stream is less than 10 ppm, so that the hydrogen produced via SE-SRE with HTlc sorbents can be directly used for fuel cells. Higher pressures do not favor the overall SE-SRE process due to lower yielding of hydrogen, although CO 2 adsorption is enhanced. The current research status of thermodynamic analysis on ethanol steam reforming (SRE) and sorption-enhanced SRE (SE-SRE) is surveyed. Hydrotalcite-like compounds (HTlc), CaO, and Li 2 ZrO 3 as three typical CO 2 sorbents for SE-SRE are compared for the first time. The simulated results agree well with other publications.

Description: Alfvénic turbulent cascade perpendicular and parallel to the background magnetic field is studied accounting for anisotropic dispersive effects and turbulent intermittency. The perpendicular dispersion and intermittency make the perpendicular-wavenumber magnetic spectra steeper and speed up production of high ion-cyclotron frequencies by the turbulent cascade. On the contrary, the parallel dispersion makes the spectra flatter and decelerate the frequency cascade above the ion-cyclotron frequency. Competition of these factors results in spectral indices distributed in the interval [-2,-3], where -2 is the index of high-frequency space-filling turbulence, and -3 is the index of low-frequency intermittent turbulence formed by tube-like fluctuations. Spectra of fully intermittent turbulence fill a narrower range of spectral indices [-7/3,-3], which almost coincides with the range of indexes measured in the solar wind. This suggests that the kinetic-scale turbulent spectra are mainly shaped by the dispersion and intermittency. A small mismatch with measured indexes of about 0.1 can be associated with damping effects not studied here.