Advanced infrared astronomy

This task supports the application of infrared heterodyne and Fourier transform spectroscopy to ultra-high resolution studies of molecular constituents of planetary astomspheres and cometary comae. High spectral and spatial resolutions are especially useful for detection and study of localized, non-thermal phenomena in low temperature and low density regions, for detection of trace constituents and for measurement of winds and dynamical phenomena such as thermal tides. Measurement and analysis of individual spectial lines permits retrieval of atmospheric molecular abundances and temperatures and thus, information on local photochemical processes. Determination of absolute line positions to better than 10 to the minus eighth power permits direct measurements of gas velocity to a few meters/sec. Observations are made from ground based heterodyne spectrometers at the Kitt Peak McMath solar telescope and from the NASA infrared Telescope Facility on Mauna Kea, Hawaii. Wind velocities at 110km altitude on Venus were extracted approximately 1 m/sec from measurements of non-thermal emission cores of 10.3 micron CO2 lines. Results indicate a subsolar to antisolar circulationwith a small zonal retrograde component

Parallel electric fields are inefficient drivers of energetic electrons in magnetic reconnection

We present two-dimensional kinetic simulations, with a broad range of initial guide fields, that isolate the role of parallel electric fields ($E_\parallel$) in energetic electron production during collisionless magnetic reconnection. In the strong guide field regime, $E_\parallel$ drives essentially all of the electron energy gain, yet fails to generate an energetic component. We suggest that this is due to the weak energy scaling of particle acceleration from $E_\parallel$ compared to that of a Fermi-type mechanism responsible for energetic electron production in the weak guide-field regime. This result has important implications for energetic electron production in astrophysical systems and reconnection-driven dissipation in turbulence

The role of three-dimensional transport in driving enhanced electron acceleration during magnetic reconnection

Magnetic reconnection is an important driver of energetic particles in many astrophysical phenomena. Using kinetic particle-in-cell (PIC) simulations, we explore the impact of three-dimensional reconnection dynamics on the efficiency of particle acceleration. In two-dimensional systems, Alfv\'enic outflows expel energetic electrons into flux ropes where they become trapped and disconnected from acceleration regions. However, in three-dimensional systems these flux ropes develop axial structure that enables particles to leak out and return to acceleration regions. This requires a finite guide field so that particles may move quickly along the flux rope axis. We show that greatest energetic electron production occurs when the guide field is of the same order as the reconnecting component: large enough to facilitate strong transport, but not so large as to throttle the dominant Fermi mechanism responsible for efficient electron acceleration. This suggests a natural explanation for the envelope of electron acceleration during the impulsive phase of eruptive flares

An Algorithm for constructing Hjelmslev planes

Projective Hjelmslev planes and Affine Hjelmselv planes are generalisations of projective planes and affine planes. We present an algorithm for constructing a projective Hjelmslev planes and affine Hjelsmelv planes using projective planes, affine planes and orthogonal arrays. We show that all 2-uniform projective Hjelmslev planes, and all 2-uniform affine Hjelsmelv planes can be constructed in this way. As a corollary it is shown that all 2-uniform Affine Hjelmselv planes are sub-geometries of 2-uniform projective Hjelmselv planes.Comment: 15 pages. Algebraic Design Theory and Hadamard matrices, 2014, Springer Proceedings in Mathematics & Statistics 13

On the 3-D structure and dissipation of reconnection-driven flow-bursts

The structure of magnetic reconnection-driven outflows and their dissipation are explored with large-scale, 3-D particle-in-cell (PIC) simulations. Outflow jets resulting from 3-D reconnection with a finite length x-line form fronts as they propagate into the downstream medium. A large pressure increase ahead of this ``reconnection jet front'' (RJF), due to reflected and transmitted ions, slows the front so that its velocity is well below the velocity of the ambient ions in the core of the jet. As a result, the RJF slows and diverts the high-speed flow into the direction perpendicular to the reconnection plane. The consequence is that the RJF acts as a thermalization site for the ion bulk flow and contributes significantly to the dissipation of magnetic energy during reconnection even though the outflow jet is subsonic. This behavior has no counterpart in 2-D reconnection. A simple analytic model predicts the front velocity and the fraction of the ion bulk flow energy that is dissipated

Coronal Electron Confinement by Double Layers

In observations of flare-heated electrons in the solar corona, a longstanding problem is the unexplained prolonged lifetime of the electrons compared to their transit time across the source. This suggests confinement. Recent particle-in-cell (PIC) simulations, which explored the transport of pre-accelerated hot electrons through ambient cold plasma, showed that the formation of a highly localized electrostatic potential drop, in the form of a double layer (DL), significantly inhibited the transport of hot electrons (T.C. Li, J.F. Drake, and M. Swisdak, 2012, ApJ, 757, 20). The effectiveness of confinement by a DL is linked to the strength of the DL as defined by its potential drop. In this work, we investigate the scaling of the DL strength with the hot electron temperature by PIC simulations, and find a linear scaling. We demonstrate that the strength is limited by the formation of parallel shocks. Based on this, we analytically determine the maximum DL strength, and find also a linear scaling with the hot electron temperature. The DL strength obtained from the analytic calculation is comparable to that from the simulations. At the maximum strength, the DL is capable of confining a significant fraction of hot electrons in the source