Generation of a North/South Magnetic Field Component from Variations in the Photospheric Magnetic Field

We address the problem of calculating the transverse magnetic field in the solar wind outside of the hypothetical sphere called the source surface where the solar wind originates. This calculation must overcome a widely used fundamental assumption about the source surface -- the field is normally required to purely radial at the source surface. Our model rests on the fact that a change in the radial field strength at the source surface is a change in the field line density. Surrounding field lines must move laterally in order to accommodate this field line density change. As the outward wind velocity drags field lines past the source surface this lateral component of motion produces a tilt implying there is a transverse component to the field. An analytic method of calculating the lateral translation speed of the field lines is developed. We apply the technique to an interval of approximately two Carrington rotations at the beginning of 2011 using 2-h averages of data from the Helioseismic Magnetic Imager instrument on the Solar Dynamics Observatory spacecraft. We find that the value of the transverse magnetic field is dominated on a global scale by the effects of high latitude concentrations of field lines being buffetted by supergranular motions.Comment: 23 pages with 8 figures. Accepted by Solar Physics (LaTeX processing with aastex6.cls instead of solarphysics.cls due to compatibility issues

Edge states and the bulk-boundary correspondence in Dirac Hamiltonians

We present an analytic prescription for computing the edge dispersion E(k) of a tight-binding Dirac Hamiltonian terminated at an abrupt crystalline edge. Specifically, we consider translationally invariant Dirac Hamiltonians with nearest-layer interaction. We present and prove a geometric formula that relates the existence of surface states as well as their energy dispersion to properties of the bulk Hamiltonian. We further prove the bulk-boundary correspondence between the Chern number and the chiral edge modes for quantum Hall systems within the class of Hamiltonians studied in the paper. Our results can be extended to the case of continuum theories which are quadratic in the momentum, as well as other symmetry classes.Comment: 8 pages + appendice

Electronic and Thermoelectric Properties of Few-Layer Transition Metal Dichalcogenides

The electronic and thermoelectric properties of one to four monolayers of MoS$_{2}$, MoSe$_{2}$, WS$_{2}$, and WSe$_{2}$ are calculated. For few layer thicknesses,the near degeneracies of the conduction band $K$ and $\Sigma$ valleys and the valence band $\Gamma$ and $K$ valleys enhance the n-type and p-type thermoelectric performance. The interlayer hybridization and energy level splitting determine how the number of modes within $k_BT$ of a valley minimum changes with layer thickness. In all cases, the maximum ZT coincides with the greatest near-degeneracy within $k_BT$ of the band edge that results in the sharpest turn-on of the density of modes. The thickness at which this maximum occurs is, in general, not a monolayer. The transition from few layers to bulk is discussed. Effective masses, energy gaps, power-factors, and ZT values are tabulated for all materials and layer thicknesses

Infrared variability of Jupiter and Saturn

Infrared spectroscopy provides unique insights into the chemistry and dynamics of the atmospheres of Jupiter and Saturn, and of the enigmatic satellite of Saturn, Titan. The 5 micron spectral region of these objects is transparent to deep levels, and is therefore particularly useful for the identification of molecules that are present at very low (parts per billion) concentrations. In Titan, 5 micron observations probe atmospheric layers at or near the surface. Ground-based spectroscopy complements Voyager, Galileo, and Cassini measurements. The spectroscopy is sensitive to lower mixing ratios for selected molecules, while the on-board mass and infrared spectrometers probe molecules and levels that are inaccessible form the ground. The observations also provide time-based data for preparation of the upcoming missions

Solar Sources of Interplanetary Magnetic Clouds Leading to Helicity Prediction

This study identifies the solar origins of magnetic clouds that are observed at 1 AU and predicts the helical handedness of these clouds from the solar surface magnetic fields. We started with the magnetic clouds listed by the Magnetic Field Investigation (MFI) team supporting NASA's WIND spacecraft in what is known as the MFI table and worked backwards in time to identify solar events that produced these clouds. Our methods utilize magnetograms from the Helioseismic and Magnetic Imager (HMI) instrument on the Solar Dynamics Observatory (SDO) spacecraft so that we could only analyze MFI entries after the beginning of 2011. This start date and the end date of the MFI table gave us 37 cases to study. Of these we were able to associate only eight surface events with clouds detected by WIND at 1 AU. We developed a simple algorithm for predicting the cloud helicity which gave the correct handedness in all eight cases. The algorithm is based on the conceptual model that an ejected flux tube has two magnetic origination points at the positions of the strongest radial magnetic field regions of opposite polarity near the places where the ejected arches end at the solar surface. We were unable to find events for the remaining 29 cases: lack of a halo or partial halo CME in an appropriate time window, lack of magnetic and/or filament activity in the proper part of the solar disk, or the event was too far from disk center. The occurrence of a flare was not a requirement for making the identification but in fact flares, often weak, did occur for seven of the eight cases.Comment: 18 pages, 8 figures, 2 table