Effects of solar wind density on auroral electrojets and brightness under influence of substorms

Using the auroral electrojet indices and Polar Ultraviolet Imager auroral images, we examined two fortuitous events during which the solar wind density had clear enhancements while the other solar wind parameters were relatively constant. Two electrojet enhancements were found in each event. The first electrojet enhancement was likely to be related to a substorm in which an auroral bulge appeared at premidnight. The second electrojet enhancement was driven by the density enhancement in the solar wind. The auroral oval became wider in latitude and the auroral distribution became dispersed after the density enhancement arrived at the Earth. The total auroral power integrated over the entire nightside region from 50 to 80° MLAT, however, did not increase significantly in response to the density enhancement. Our interpretation is that the substorm that occurred prior to the solar wind density enhancement had drained out a significant portion of the stored energy in the magnetotail; therefore, less precipitation energy was deposited into the auroral ionosphere by the density enhancement

Chaos in driven Alfvén systems: unstable periodic orbits and chaotic saddles

International audienceThe chaotic dynamics of Alfvén waves in space plasmas governed by the derivative nonlinear Schrödinger equation, in the low-dimensional limit described by stationary spatial solutions, is studied. A bifurcation diagram is constructed, by varying the driver amplitude, to identify a number of nonlinear dynamical processes including saddle-node bifurcation, boundary crisis, and interior crisis. The roles played by unstable periodic orbits and chaotic saddles in these transitions are analyzed, and the conversion from a chaotic saddle to a chaotic attractor in these dynamical processes is demonstrated. In particular, the phenomenon of gap-filling in the chaotic transition from weak chaos to strong chaos via an interior crisis is investigated. A coupling unstable periodic orbit created by an explosion, within the gaps of the chaotic saddles embedded in a chaotic attractor following an interior crisis, is found numerically. The gap-filling unstable periodic orbits are responsible for coupling the banded chaotic saddle (BCS) to the surrounding chaotic saddle (SCS), leading to crisis-induced intermittency. The physical relevance of chaos for Alfvén intermittent turbulence observed in the solar wind is discussed

The semiannual variation of geomagnetic activity: phases and profiles for 130 years of /aa data

Abstract We determined the phases of the maxima (spring, fall) and minima (summer, winter) in the curve of smoothed daily averages of the aa geomagnetic index, available from 1868 to 1998. The dates we obtained are consistent with the equinoctial hypothesis which has aberration-adjusted theoretical maxima, for a ∼440 km s −1 (modern epoch) average solar wind speed, on 25 March (experimentally determined to be 27 March, with an uncertainty of ±2 days) and 27 September (27 September) and minima on 25 June (26 June) and 26 December (27 December). We also show that the overall shape of the 30-day smoothed modulation curve throughout the year (broad minima, narrow peaks) bears greater ÿdelity (|r| = 0:96) to the aberration-shifted solar declination (the controlling angle, on average, for the seasonal variation under the equinoctial hypothesis) than to the solar B0 angle (r = 0:76; axial hypothesis) or the solar P angle (r = 0:86; Russell-McPherron e ect). Lastly, a three-parameter ÿt of the smoothed annual variation of the aa data with a function consisting of the sum of the smoothed yearly curves for the ; B0, and P angles yielded an amplitude of 0:58 ± 0:07 for the component vs. 0:16 ± 0:03 for B0 and 0:20 ± 0:04 for P. Thus, the phases and proÿles of the 6-month wave in the long-running mid-latitude aa range index are consistent with control by a dominant equinoctial mechanism

Theory of superconductivity of carbon nanotubes and graphene

We present a new mechanism of carbon nanotube superconductivity that originates from edge states which are specific to graphene. Using on-site and boundary deformation potentials which do not cause bulk superconductivity, we obtain an appreciable transition temperature for the edge state. As a consequence, a metallic zigzag carbon nanotube having open boundaries can be regarded as a natural superconductor/normal metal/superconductor junction system, in which superconducting states are developed locally at both ends of the nanotube and a normal metal exists in the middle. In this case, a signal of the edge state superconductivity appears as the Josephson current which is sensitive to the length of a nanotube and the position of the Fermi energy. Such a dependence distinguishs edge state superconductivity from bulk superconductivity.Comment: 5 pages, 2 figure