ALBERT

Description: The ability to perform data assimilation in the Whole Atmosphere Community Climate Model eXtended version (WACCMX) is implemented using the Data Assimilation Research Testbed (DART) ensemble adjustment Kalman filter. Results are presented demonstrating that WACCMX+DART analysis fields reproduce the middle and upper atmosphere variability during the 2009 major sudden stratospheric warming (SSW) event. Compared to specified dynamics WACCMX, which constrains the meteorology by nudging towards an external reanalysis, the large-scale dynamical variability of the stratosphere, mesosphere, and lower thermosphere are improved in WACCMX+DART. This leads to WACCMX+DART better representing the downward transport of chemical species from the mesosphere into the stratosphere following the SSW. WACCMX+DART also reproduces most aspects of the observed variability in ionosphere total electron content (TEC) and equatorial vertical plasma drift during the SSW. Hindcast experiments initialized on January 5, 10, 15, 20, and 25 are used to assess the middle and upper atmosphere predictability in WACCMX+DART. A SSW, along with the associated middle and upper atmosphere variability, is initially predicted in the hindcast initialized on January 15, which is ∼10 days prior to the warming. However, it is not until the hindcast initialized on January 20 that a major SSW is forecast to occur. The hindcast experiments reveal that dominant features of the TEC can be forecast ∼10-20 days in advance. This demonstrates that whole atmosphere models that properly account for variability in lower atmosphere forcing can potentially extend the ionosphere-thermosphere forecast range.

Description: No abstract is available for this article.

Description: Among the several GLE (Ground Level Enhancements) that have presumptuously occurred in the period 2012-2015 the 17th May 2012 is that which is more widely accepted to be a GLE, in view of the high number of high latitude Neutron Monitor (NM) stations that have registered it. In spite of the small amplitude, it was the more prominent of the predicted GLE´s of the present decade (Pérez-Peraza & Juarez-Zuñiga, 2015). However, the lack of latitude effect makes it difficult to study the characteristics of this event in the high energy extreme of the spectrum. Nevertheless, several outstanding works have been able to derive observational spectra at the top of the earth atmosphere for this peculiar GLE. Some of these works find that the flow of protons is characterized by two components. Quite a great number of works have been published in relation with observational features obtained with different instrumentation, but the source phenomena, regarding the generation processes and source physical parameters have not been scrutinized. The main goal of this work is to look at such aspects by means of the confrontation of the different approaches of the observational spectra with our analytical theoretical spectra based on stochastic acceleration and Electric field acceleration from reconnection processes. In this way, we derive a set of parameters which characterize the sources of these two GLE components, leading us to propose possible scenarios for the generation of particles in this particular GLE event.

Description: It has long been a goal of the heliophysics community to understand solar wind variability at heliocentric distances other than 1 AU, especially at ∼1.5 AU not only due to the steepening of solar wind stream interactions outside 1 AU but also the number of missions available there to measure it. In this study, we use 35 months of solar wind and IMF data taken at Mars by the MAVEN spacecraft to conduct an autocorrelation analysis of the solar wind speed, density, and dynamic pressure, which is derived from the speed and density, as well as the IMF strength and orientation. We found that the solar wind speed is coherent, i.e. has an autocorrelation coefficient above 1/e, over roughly 56 hours, while the density and pressure are coherent over smaller intervals of roughly 25 and 20 hours, respectively, and that the IMF strength is coherent over time intervals of approximately 20 hours, while the cone and clock angles are considerably less steady but still somewhat coherent up to time lags of roughly 16 hours. We also found that when the speed, density, pressure, or IMF strength is higher than average, the solar wind or IMF becomes uncorrelated more quickly, while when they are below average, it tends to be steadier. This analysis allows us to make estimates of the values of solar wind plasma and IMF parameters when they are not directly measured, as well as provide an approximation of the error associated with that estimate.

Description: The influence of the interplanetary magnetic field (IMF) cone angle θ (the angle between the IMF direction and the Sun-Earth line) on the invariant latitudes (ILATs) of the footprints of the field-aligned currents (FACs) in the magnetotail has been investigated. We performed a statistical study of 542 FAC cases observed by the four Cluster spacecraft in the northern hemisphere. The results show that there are almost no FACs when the IMF cone angle is less than 10°, and there are indications of the FACs in the PSBLs being weak under the radial IMF conditions. The footprints of the large FAC (〉10 nA/m 2 ) cases are within ILATs 〈71° and mainly within IMF cone angles θ〉60°, which implies that the footprints of the large FACs mainly expand equatorward with large IMF cone angle. The equatorward boundary of the FAC footprints in the polar region decreases with increasing IMF cone angle (and has a better correlation for northward IMF), which shows that the IMF cone angle plays an important controlling role in FAC distributions in the magnetosphere-ionosphere coupling system. There is almost no correlation between the poleward boundary and the IMF cone angle for both northward and southward IMF. This is because the poleward boundary movement is limited by an enhanced lobe magnetic flux. This is the first time a correlation between FAC foot prints in the polar region and IMF cone angles has been determined.

Description: Both ray theory and full-wave models of Very Low Frequency transmission through the ionospheric D-layer predict that the transmission is greatly suppressed near the geomagnetic equator. We use data from the low-inclination Communication/Navigation Outage Forecast System satellite to test this semi-quantitatively, for broadband Very Low Frequency emissions from lightning. Approximate ground-truthing of the incident wavefields in the Earth Ionosphere Waveguide is provided by the World Wide Lightning Location Network. Observations of the wavefields at the satellite are provided by the Vector Electric Field Instrument aboard the satellite. The data set comprises whistler observations with the satellite at magnetic latitudes 〈 26 deg. Thus our conclusions, too, must be limited to the near-equatorial region, and are not necessarily predictive of mid-latitude whistler properties. We find that in most broadband recordings of radio waves at the satellite, very few of the lightning strokes result in a detectable radio pulse at the satellite. However, in a minority of the recordings, there is enhanced transmission of Very Low Frequency lightning emissions through the D-layer, at a level exceeding model predictions by at least an order-of-magnitude. We show that kilometric-scale D-layer irregularities may be implicated in the enhanced transmission. This observation of sporadic enhancements at low magnetic latitude, made with broadband lightning emissions, is consistent with an earlier review of D-layer transmission for transmission from powerful man-made radio beacons.

Description: We have developed a four dimensional variation data assimilation technique (4D-var), and utilized it to reconstruct 3-dimensional images of the ionospheric hole created during Kwangmyongsong-4 rocket launch. Kwangmyongsong-4 was launched southwards from North Korea Sohae space center (124.7 o E, 39.6 o N) at 00:30 UT on February 7, 2016. The data assimilated were GPS-TEC (Global Positioning System - Total Electron Content) from the South Korean GPS-receiver network. Due to lack of publicized information about Kwangmyongsong-4, the rocket was assumed to inherit its technology from previous launches (Taepodong -2). The created ionospheric hole was assumed to be made by neutral molecules, water (H 2 O) and hydrogen (H 2 ), deposited in exhaust plumes. The dispersion model was developed based on advection and diffusion equation, and a simple asymmetric diffusion model assumed. From the analysis, using the adjoint technique, we estimated an ionospheric hole with the largest depletion existing around 6-7 mins after launch and gradually recovering within ~30 minutes. These results are in agreement with temporal TEC analyses of the same event from previous studies. Furthermore, Kwangmyongsong-4 second stage exhaust emissions were estimated as 1.9  ×  10 26 s −1 of which 40 % was H 2 and the rest H 2 O.

Description: Juno's Jupiter Energetic particle Detector Instrument (JEDI) often detects energetic electron beams over Jupiter's polar regions. In this paper, we document a subset of intense magnetic field-aligned beams of energetic electrons moving away from Jupiter at high magnetic latitudes both north and south of the planet. The number fluxes of these beams are often dominated by electrons with energies above about 1 MeV. These very narrow beams can create broad angular responses in JEDI with unique signatures in the detector count rates, probably because of 〉10 MeV electrons. We use these signatures to identify the most intense beams. These beams occur primarily above the swirl region of the polar cap aurora. This polar region is described as being of low brightness and high absorption and the most magnetically "open" at Jupiter.

Description: The conductivity of the ionosphere is extremely important in geophysical processes and plays a critical role in magnetosphere-ionosphere-thermosphere coupling. Understanding its nature is essential to understand the physics of ionospheric electrodynamics. Earth's magnetic field, which varies greatly in geological timescales, is among the main variables involved in ionospheric conductivity. The present field can be approximated by a magnetic dipole that accounts for ~80% of the magnetic field at the Earth's surface, plus multipolar components making up the remaining ~20%. During a polarity transition the field magnitude diminishes to about 10% of its normal value at the expense, most likely, of decreasing the dipolar component and becoming mostly multipolar in nature. The effects of geomagnetic field variations on the spatial structure of Hall and Pedersen conductances are analyzed in the present work considering some possible reversal scenarios. The spatial structure of both conductances changes significantly with sharp spatial gradients. The conductivity peak heights also change, moving to upper heights as expected for weaker field configurations.

Description: Using a three-dimensional particle-in-cell simulation, we investigate the formation of dawn-dusk asymmetry in Earth's magnetotail. The magnetotail current sheet is compressed by an external driving electric field down to a thickness on the order of ion kinetic scales. In the resultant thin current sheet (TCS) where the magnetic field line curvature radius is much smaller than ion gyroradius, a significant portion of the ions becomes unmagnetized and decoupled from the magnetized electrons, giving rise to a Hall electric field E z and an additional cross-tail current j y caused by the unmagnetized ions being unable to comove with the electrons in the Hall electric field. The Hall electric field transports via E  ×  B drift magnetic flux and magnetized plasma dawnward, causing a reduction of the current sheet thickness and the normal magnetic field B z on the duskside. This leads to an even stronger Hall effect (stronger j y and E z ) in the duskside TCS. Thus, due to the internal kinetic effects in the TCS, namely the Hall effect and the associated dawnward E  ×  B drift, the magnetotail dawn-dusk asymmetry forms in a short time without any global, long-term effects. The duskside preference of reconnection and associated dynamic phenomena (such as substorm onsets, dipolarizing flux bundles, fast flows, energetic particle injections, and flux ropes) which has been pervasively observed by spacecraft in the past twenty years can thus be explained as a consequence of this TCS asymmetry.