ALBERT

Description: We show that ~1 Hz magnetic compressional waves observed in Mercury's inner magnetosphere could be interpreted as ion-Bernstein waves in a moderate proton beta ~0.1 plasma. An observation of a proton distribution with a large planetary loss-cone is presented, and we show that this type of distribution is highly unstable to the generation of ion-Bernstein waves with low magnetic compression. Ray tracing shows that as these waves propagate back and forth about the magnetic equator they cycle between a state of low and high magnetic compression. The group velocity decreases during the high compression state leading to a pile up of compressional wave energy, which could explain the observed dominance of the highly compressional waves. This bi-modal nature is due to the complexity of the index of refraction surface in a warm plasma whose upper branch has high growth rate with low compression, and its lower branch has low growth/damping rate with strong compression. Two different cycles are found, one where the compression maximum occurs at the magnetic equator and one where the compression maximum straddles the magnetic equator. The later cycle could explain observations where the maximum in compression straddles the equator. Ray tracing shows that this mode is confined within ±12° magnetic latitude which can account for the bulk of the observations. We show that the Doppler shift can account for the difference between the observed and model wave frequency, if the wave vector direction is in opposition to the plasma flow direction. We note that the WKB approximation breaks down during the pile up of compressional energy and that a study involving full wave solutions is required.

Description: Abstract A hybrid gyrofluid‐kinetic electron model is adapted and used to simulate poloidal standing modes for different electron temperatures and azimuthal mode numbers. As in previous studies of toroidal standing modes, mirror force effects lead to increased parallel potential drops, monoenergetic electron energization, and wave energy dissipation as the ambient electron temperature is increased. A similar trend is also observed when the electron temperature is held fixed and the azimuthal mode number increased—owing to the narrowing of the azimuthal flux tube width, which necessitates more electron energization to carry the increased parallel current density. In both cases, the increase in electron energization eventually leads to more rapid decreases in the parallel current with time because of the dissipation of wave energy.

Description: Abstract Organic matter (OM) and suspended sediment are abundant, and interact with each other, in rivers and lakes. OM is usually adsorbed by suspended sediment and causes either particle stabilization or flocculation. In this study, the OM composition and suspended sediment flocculation potential of river water were regularly measured throughout the year 2016. The OM composition of the river water samples was measured with a liquid chromatography‐organic carbon detection system and fluorescence excitation‐emission matrix spectroscopy, and the flocculation potential was measured in a standard jar test experiment. Results from the OM analyses and flocculation potential tests, in association with a multivariate data analysis, demonstrated that the OM composition and flocculation potential of the river water were dynamic under different meteorological, hydrological, ecological, and anthropogenic conditions and closely correlated with each other. Dry seasons with low rainfall and water discharge induced a lacustrine condition and led to the OM composition being more aquagenic and flocculation‐favorable. The most favorable condition for the enhancement of flocculation was during algae bloom and associated with the production of biopolymers from algae. In contrast, rainy seasons were advantageous for stabilization of suspended sediment because of excessive transport of terrigenous humic substances from catchment areas into the river. Such terrigenous humic substances enhanced stabilization by creating enhanced electrostatic repulsion via adsorption onto the sediment surface. Findings from this research provide a better insight into the highly complex behaviors of and interactions between OM and suspended sediment in natural water environments.

Description: The UCSD interplanetary scintillation (IPS) time-dependent kinematic 3D-reconstruction technique has been used and expanded upon for over a decade, to provide predictions of heliospheric solar wind parameters. These parameters include global reconstructions of velocity, density and also (through potential field modeling and extrapolation upward from the solar surface) radial and tangential interplanetary magnetic fields. Time-dependent results can be extracted at any solar distance within the reconstructed volume and are now being exploited as inner-boundary values to drive the ENLIL 3D-MHD model in near real-time. The advantage of this coupled system is that it uses the more complete physics of 3D-MHD modeling to provide an automatic prediction of coronal mass ejections (CMEs) and solar wind stream structures several days prior to their arrival at Earth without employing coronagraph observations. Here we explore, with several examples, the current differences between the IPS real-time kinematic analyses and those from the ENLIL 3D-MHD modeling using IPS-derived real-time boundaries. Future possibilities for this system include incorporating many different worldwide IPS stations as input to the remote sensing analysis using ENLIL as a kernel in the iterative 3D-reconstructions.

Description: Magnetospheric compression due to impact of enhanced solar wind dynamic pressure P dyn has long been considered as one of the generation mechanisms of electromagnetic ion cyclotron (EMIC) waves. With the Van Allen Probe-A observations, we identify three EMIC wave events that are triggered by P dyn enhancements under prolonged northward IMF quiet time preconditions. They are in contrast to one another in a few aspects. Event 1 occurs in the middle of continuously increasing P dyn while Van Allen Probe-A is located outside the plasmapause at post-midnight and near the equator (magnetic latitude (MLAT) ~ -3 o ). Event 2 occurs by a sharp P dyn pulse impact while Van Allen Probe-A is located inside the plasmapause in the dawn sector and rather away from the equator (MLAT ~ 12 o ). Event 3 is characterized by amplification of a pre-existing EMIC wave by a sharp P dyn pulse impact while Van Allen Probe-A is located outside the plasmapause at noon and rather away from the equator (MLAT ~ -15 o ). These three events represent various situations where EMIC waves can be triggered by P dyn increases. Several common features are also found among the three events. (i) The strongest wave is found just above the He + gyrofrequency. (ii) The waves are nearly linearly polarized with a rather oblique propagation direction (~28 o to ~39 o on average). (iii) The proton fluxes increase in immediate response to the P dyn impact, most significantly in tens of keV energy, corresponding to the proton resonant energy. (iv) The temperature anisotropy with T ⊥  〉 T || is seen in the resonant energy for all the events, although its increase by the P dyn impact is not necessarily always significant. The last two points (iii) and (iv) may imply that, in addition to the temperature anisotropy, the increase of the resonant protons must have played a critical role in triggering the EMIC waves by the enhanced P dyn impact.

Description: A strongly energy-dependent ring current ion loss was measured by the RBSPICE instrument on the Van Allen Probes A spacecraft in the local evening sector during the 17 March 2015 geomagnetic storm. The ion loss is found to be energy dependent where only ions with energies measured above  ∼  150 keV have a significant drop in intensity. At these energies the ion dynamics are principally controlled by variations of the geomagnetic field which, during magnetic storms, exhibits large scale variations on timescales from minutes to hours. Here we show that starting from  ∼  19:10 UTC on March 17 the geomagnetic field increased from 220 to 260 nT on a time scale of about an hour as captured by RBSPICE-A close to spacecraft apogee, L = 6.1 and MLT = 21.85 hr. [GSM coordinates X=-4.89, Y=3.00, Z=-0.73)]. We demonstrate the relationship between this large geomagnetic field increase and the drop-outs of the 150 keV ring current ions.

Description: Van Allen radiation belt is characterized by energetic electrons and ions trapped in the Earth's dipolar magnetic field lines, and persisting for long periods. It is also permeated by high-frequency electrostatic fluctuations whose peak intensity occurs near the upper-hybrid frequency. Such a phenomenon can be understood in terms of spontaneous emission of electrostatic multiple harmonic electron cyclotron waves by thermal plasmas. In the literature, the upper-hybrid fluctuations are used as a proxy for determining the electron number density, but they also contain important information concerning the energetic electrons in the radiation belt and possibly the ring current electrons. The companion paper [ Hwang et al. , 2016] analyzes sample quiet time events and demonstrates that the upper-hybrid fluctuations are predominantly emitted by tenuous population of energetic electrons. The present paper supplements detailed formalism of spontaneous thermal emission of multiple-harmonic cyclotron waves that include upper-hybrid fluctuations.

Description: We have statistically studied sudden commencement (SC) by using the data acquired from Van Allen Probes (VAP) in the inner magnetosphere ( L = 3.0–6.5) and GOES spacecraft at geosynchronous orbit ( L = ∼6.7) from October 2012 and September 2017. During the time period, we identified 85 SCs in the inner magnetosphere and 90 SCs at geosynchronous orbit. Statistical results of the SC events reveal the following characteristics. (1) There is strong seasonal dependence of the geosynchronous SC amplitude in the radial B V component at all local times. However, B V shows weak seasonal variation on the dayside in the inner magnetosphere. (2) The local time dependence of the SC amplitude in the compressional B H component at geosynchronous orbit is similar to that in the inner magnetosphere. (3) In a nighside region of L = 5.0–6.5, ∼19% of B H events are negative, while ∼58% of B H events are negative at geosynchronous orbit. (4) The amplitude of the SC-associated E y perturbations varies systematically with local time with a morning-afternoon asymmetry near noon. These observations can be explained by spatial and/or temporal changes in the magnetopause and cross-tail currents, which are caused by changes in the solar wind dynamic pressure, with respect to spacecraft positions.

Description: We quantify methane (CH 4 ) emissions in California's San Joaquin Valley (SJV) using four days of aircraft measurements from a field campaign during May-June 2010 together with a Bayesian inversion method and a mass-balance approach. For the inversion estimates, we use the FLEXible PARTicle dispersion model (FLEXPART) to establish the source-receptor relationship between sampled atmospheric concentrations and surface fluxes. Our prior CH 4 emissions estimates are from the California Greenhouse Gas Emissions Measurements (CALGEM) inventory. We use three meteorological configurations to drive FLEXPART and subsequently construct three inversions to analyze the final optimized estimates and their uncertainty (one standard deviation) . We conduct May and June inversions independently, and derive similar total CH 4 emissions estimates for the SJV: 135 ± 28 Mg/hr in May and 135 ± 19 Mg/hr in June. The inversion result is 1.7 times higher than the prior estimate from CALGEM. We also use an independent mass-balance approach to estimate CH 4 emissions in the northern SJV for one flight when meteorological conditions allowed. The mass-balance estimate provides a confirmation of our inversion results, and these two independent estimates of the total CH 4 emissions in the SJV are consistent with previous studies. In this study, we provide optimized CH 4 emissions estimates at 0.1° horizontal resolution. Using independent spatial information on major CH 4 sources, we estimate that livestock contribute 75–77% and oil/gas production contributes 15–18% of the total CH 4 emissions in the SJV. Livestock explain most of the discrepancies between the prior and the optimized emissions from our inversion.

Description: The solar wind electron temperature anisotropy is regulated by a number of physical processes, which include adiabatic expansion, electron Coulomb collisions, and micro-instabilities. In the collisionless limit, the measured electron temperature anisotropy is constrained by the marginal threshold conditions for whistler (electromagnetic electron cyclotron or EMEC) and firehose instabilities, which are excited by excessive perpendicular and parallel temperature anisotropies, respectively. In the literature, these thresholds are expressed as inverse relationships between the electron temperature ratio and parallel beta, which are constructed on the basis of linear stability analysis and empirical fitting. In the present paper, macroscopic quasilinear kinetic theory of whistler (or EMEC) instability is employed in order to investigate the time development of the instability. One-dimensional particle in-cell (PIC) simulation is also carried out and it is found that PIC simulation confirms the validity of the macroscopic quasilinear approach. It is also found that the saturation stage of the instability naturally corresponds to the threshold condition, thus confirming the inverse relationship. The present finding shows that the macroscopic quasilinear kinetic theory may be a valid theoretical tool for dynamical description of the solar wind.