M. Wilber

Energy deposition by Alfvén waves into the dayside auroral oval: Cluster and FAST observations

[1]xa0We report in situ observations from the Cluster and FAST spacecraft showing the deposition of energy into the auroral ionosphere from broadband ULF waves in the cusp and low-latitude boundary layer. A comparison of the wave Poynting flux with particle energy and flux at both satellites indicates that energy transfer from the broadband waves to the plasma occurs through field-aligned electron acceleration, transverse ion acceleration, and Joule heating. These processes are shown to result in precipitating electron fluxes sufficient to drive bright aurora and cause outflows of energized electrons and O+ ions from the ionosphere into the low-latitude boundary layer. By solving an eigenmode equation for Alfven waves in the observed plasma environment, it is shown that the broadband waves observed at Cluster and FAST are dispersive Alfven waves. It is demonstrated that these waves have wavelengths perpendicular to the geomagnetic field extending from significant fractions of an L shell down to ion gyroradii and electron inertial lengths and wave frequencies in the plasma frame from 1 mHz up to 50 mHz. These waves are shown to have wavelengths along the geomagnetic field of the order of the field line length between the ionosphere and the equatorial plane and become field line resonances (FLRs) when on closed field lines. It is shown that the inclusion of nonlinear and/or nonlocal kinetic effects is required in the description of these waves to account for accelerated particles observed. On the basis of the wave polarization and spectral properties observed from Cluster and FAST it is speculated that these waves are generated through the mode conversion of surface Alfven waves driven by tailward flows in the low-latitude boundary layer.

Context-dependent conservation responses to emerging wildlife diseases

Emerging infectious diseases pose an important threat to wildlife. While established protocols exist for combating outbreaks of human and agricultural pathogens, appropriate management actions before, during, and after the invasion of wildlife pathogens have not been developed. We describe stage-specific goals and management actions that minimize disease impacts on wildlife, and the research required to implement them. Before pathogen arrival, reducing the probability of introduction through quarantine and trade restrictions is key because prevention is more cost effective than subsequent responses. On the invasion front, the main goals are limiting pathogen spread and preventing establishment. In locations experiencing an epidemic, management should focus on reducing transmission and disease, and promoting the development of resistance or tolerance. Finally, if pathogen and host populations reach a stable stage, then recovery of host populations in the face of new threats is paramount. Successful management of wildlife disease requires risk-taking, rapid implementation, and an adaptive approach.

Large‐amplitude electrostatic waves observed at a supercritical interplanetary shock

[1]xa0We present the first observations at an interplanetary shock of large-amplitude (> 100 mV/m pk-pk) solitary waves and large-amplitude (∼30 mV/m pk-pk) waves exhibiting characteristics consistent with electron Bernstein waves. The Bernstein-like waves show enhanced power at integer and half-integer harmonics of the cyclotron frequency with a broadened power spectrum at higher frequencies, consistent with the electron cyclotron drift instability. The Bernstein-like waves are obliquely polarized with respect to the magnetic field but parallel to the shock normal direction. Strong particle heating is observed in both the electrons and ions. The observed heating and waveforms are likely due to instabilities driven by the free energy provided by reflected ions at this supercritical interplanetary shock. These results offer new insights into collisionless shock dissipation and wave-particle interactions in the solar wind.

Simultaneous observations of field‐aligned beams and gyrating ions in the terrestrial foreshock

[1] We examine an energetic (2–30 keV) upstream ion event presenting a clear doublepeak spectrum observed � 1 RE upstream from the bow shock. The lower-energy (E � 3.5 keV) peak is associated with an ion beam propagating along the magnetic field direction, while the higher-energy (E � 13 keV) peak is associated with gyrating ions having pitch angles � 30� . The latter population progressively extends to lower energies over the span of the event. During times when the field-aligned beams were observed, the interplanetary magnetic field was remarkably steady, while the appearance of the 30� pitch angle gyrating ions was accompanied by the onset of large-amplitude ultralow frequency fluctuations of the magnetic field. Our analysis indicates that the gyrating ions had guiding centers on field lines downstream of the field-aligned component but that both populations could be sampled simultaneously because of the orbits of the former. We find that the downstream limit of the field-aligned beams is populated with protons having a speed 1.68 times the solar wind velocity, which is inconsistent with any known shockrelated emission mechanisms. This boundary makes an angle of 77� with respect to the Sun-Earth line in agreement with theoretical predictions. Just downstream of this rapid transition, gyrating ions having a flow speed of 1.52 times the solar wind speed are observed in association with ULF waves. Like the field-aligned beams, the gyrating ions reported here have streaming speeds inconsistent with any known shock emission mechanisms. While the simultaneous observation of field-aligned and gyrating components is possible because of the large gyration orbits of the latter, the observational sequence is consistent with a very sharp (]1 gyroradius) boundary separating the guiding centers of each. Explicit observations of such a sharp demarcation between these populations have not been reported before, and they place a significant constraint on the production mechanisms of the two populations. Our interpretation of these observations provides a refinement of the usual framework for foreshock morphology. INDEX TERMS: 2116 Interplanetary Physics: Energetic particles, planetary; 2164 Interplanetary Physics: Solar wind plasma; 2134 Interplanetary Physics: Interplanetary magnetic fields; 2154 Interplanetary Physics: Planetary bow shocks; 7851 Space Plasma Physics: Shock waves; KEYWORDS: foreshock boundary, ultralow frequency waves, bow shock, field-aligned beam, magnetic moment, shock emission mechanism

Time development of field‐aligned currents, potential drops, and plasma associated with an auroral poleward boundary intensification

[1] We present a detailed case study of the plasma and fields measured by the Cluster spacecraft fleet at the high-altitude auroral zone (-3.5 R E ) across the plasma sheet boundary layer and into the polar cap. This event, which occurred during quiet geomagnetic conditions (Kp = 1 + , AE = 50 nT), is of particular interest in that Cluster provides measurements at key instances during the time development of a new large-scale auroral arc system. Central to the formation of the arc system is the depletion of ionospheric plasma through a region of small-scale, field-aligned currents having the properties of Alfven waves. This depletion occurred prior to the growth of and ultimately bounded a well-defined equatorward moving, upward and downward current sheet pair. In association with the transverse scales approaching the electron inertial scale, the Alfvenic currents have amplitudes that appear to be attenuated subsequent to the formation of the cavity. Potential structures essentially time invariant over particle transit times (quasi-static) associated with the current pair are identified and observed to drive a poleward boundary intensification (PBI) identified in coincident IMAGE satellite far ultraviolet measurements. The PBI formed in association with a local thickening of the plasma sheet via the injection of new magnetospheric plasma, which may be the result of a bursty, patchy reconnection process. Estimates of the ionospheric equatorward velocity and thickness of the PBI are consistent with their ionospheric mapped cavity counterparts, suggesting that the motion and thickness are controlled by the plasma and electrodynamic features at or above the altitude sampled by Cluster. The magnitude of the upward and downward current region parallel potentials is correlated with the temperature of the newly injected electrons suggesting that the electron temperature is an important controlling factor. These novel observations indicate that quasi-static systems of field-aligned currents do form out of the highly dynamic Alfvenic region at the plasma sheet boundary layer, and perhaps suggest that the Alfvenic region can be the initial stage in the development of quasi-static systems. The observed time sequence of the currents is qualitatively similar to the expectations of transient response models of magnetospheric-ionospheric coupling, however, such models may need to be modified to account for the attenuation of electron inertial scale currents/Alfven waves.

Shocklets, SLAMS, and field‐aligned ion beams in the terrestrial foreshock

We present Wind spacecraft observations of ion distributions showing field-aligned beams (FABs) and large-amplitude magnetic fluctuations composed of a series of shocklets and short large-amplitude magnetic structures (SLAMS). We show that the SLAMS are acting like a local quasi-perpendicular shock reflecting ions to produce the FABs. Previous FAB observations reported the source as the quasi-perpendicular bow shock. The SLAMS exhibit a foot-like magnetic enhancement with a leading magnetosonic whistler train, consistent with previous observations. The FABs are found to have T_b ~ 80-850 eV, V_b/V_sw ~ 1-2, T_{b,perp}/T{b,para} ~ 1-10, and n_b/n_i ~ 0.2-14%. Strong ion and electron heating are observed within the series of shocklets and SLAMS increasing by factors geq 5 and geq 3, respectively. Both the core and halo electron components show strong perpendicular heating inside the feature.

Larmor radius size density holes discovered in the solar wind upstream of Earth’s bow shock

The Cluster and Double Star satellites recently observed plasma density holes upstream of Earth’s collisionless bow shock to apogee distances of ∼19 and 13 earth radii, respectively. A survey of 147 isolated density holes using 4s time resolution data shows they have a mean duration of ∼17.9±10.4s, but holes as short as 4s are observed. The average fractional density depletion (δn∕n) inside the holes is ∼0.68±0.14. The upstream edge of density holes can have enhanced densities that are five or more times the solar wind density. Particle distributions show the steepened edge can behave like a shock. Multispacecraft analyses show the density holes move with the solar wind, can have an ion gyroradius scale, and could be expanding. A small normal electric field points outward. Similarly shaped magnetic holes accompany the density holes indicating strong coupling between fields and particles. The density holes are only observed with upstream particles, suggesting that backstreaming particles interacting with t...

Cluster observations of velocity space-restricted ion distributions near the plasma sheet

[1]xa0We present Cluster ion observations obtained at 18 RE in the magnetotail on 1 October 2001. According to a recent analysis, the quartet encountered a reconnection region and a tailward-moving neutral line. We examine in detail selected 3-D ion distributions, which through much of the hour following 0925 UT were non-gyrotropic. B-perpendicular slices of velocity space showed crescent-shaped regions. Occupied gyrophases were consistent over a wide range of parallel velocities, stable over time, and occurred unaccompanied by strong ion gyrofrequency waves. We interpret these observations as signatures of remote sensing near sharp particle gradients. In this view, distributions obtained simultaneously while Cluster straddled the current sheet are simply explained. Additionally, the computed first moments can have large transverse ( × B) components (, a unit boundary normal), without net plasma transport. We infer separate O+ layers above and below the current sheet.

Kinetic aspects of foreshock cavities

[1]xa0We have investigated the kinetic signatures within, and at the edges of, a foreshock cavity. Such cavities are believed to be formed when an isolated collection of interplanetary magnetic field lines connect to quasi-parallel regions of the Earths bow shock, allowing energetic ions to flow upstream and excavate a local cavity. Observations by the Cluster spacecraft show precisely this configuration. The suprathermal ions can be seen just outside the edges of the cavity within a restricted range of gyrophases, consistent with their gyromotion tangential to the layer containing the cavity. Foreshock cavities, if sufficiently common, may play significant roles in triggering magnetospheric events. Thus our confirmation of their relatively simple formation mechanism lends support to their inferred frequency.

Moving Beyond Too Little, Too Late: Managing Emerging Infectious Diseases in Wild Populations Requires International Policy and Partnerships

Emerging infectious diseases (EIDs) are on the rise due to multiple factors, including human facilitated movement of pathogens, broad-scale landscape changes, and perturbations to ecological systems (Jones et al. 2008; Fisher et al. 2012). Epidemics in wildlife are problematic because they can lead to pathogen spillover to new host organisms, erode biodiversity and threaten ecosystems that sustain human societies (Fisher et al. 2012; Kilpatrick 2011). There have been recent calls for large-scale research approaches to combat the threats EIDs pose to wildlife (Sleeman 2013). While it is true that developing new analytical models, diagnostic assays and molecular tools will significantly advance our abilities to respond to disease threats, we also propose that addressing difficult problems in EIDs will require considerable shifts in international health policy and infrastructure. While there are currently international organizations responsible for rapidly initiating and coordinating preventative measures to control infectious diseases in human, livestock, and arable systems, there are few comparable institutions that have the authority to implement transnational responses to EIDs in wildlife. This absence of well-developed infrastructure hampers the rapid responses necessary to mitigate international spread of EIDs.