Does the spacecraft trajectory strongly affect the detection of magnetic clouds?

Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs) where a magnetic flux rope is detected. Is the difference between MCs and ICMEs without detected flux rope intrinsic or rather due to an observational bias? As the spacecraft has no relationship with the MC trajectory, the frequency distribution of MCs versus the spacecraft distance to the MCs axis is expected to be approximately flat. However, Lepping and Wu (2010) confirmed that it is a strongly decreasing function of the estimated impact parameter. Is a flux rope more frequently undetected for larger impact parameter? In order to answer the questions above, we explore the parameter space of flux rope models, especially the aspect ratio, boundary shape, and current distribution. The proposed models are analyzed as MCs by fitting a circular linear force-free field to the magnetic field computed along simulated crossings. We find that the distribution of the twist within the flux rope, the non-detection due to too low field rotation angle or magnitude are only weakly affecting the expected frequency distribution of MCs versus impact parameter. However, the estimated impact parameter is increasingly biased to lower values as the flux-rope cross section is more elongated orthogonally to the crossing trajectory. The observed distribution of MCs is a natural consequence of a flux-rope cross section flattened in average by a factor 2 to 3 depending on the magnetic twist profile. However, the faster MCs at 1 AU, with V>550 km/s, present an almost uniform distribution of MCs vs. impact parameter, which is consistent with round shaped flux ropes, in contrast with the slower ones. We conclude that either most of the non-MC ICMEs are encountered outside their flux rope or near the leg region, or they do not contain any

Tzitzeica solitons versus relativistic Calogero–Moser three-body clusters

We establish a connection between the hyperbolic relativistic Calogero–Moser systems and a class of soliton solutions to the Tzitzeica equation (also called the Dodd–Bullough–Zhiber–Shabat–Mikhailov equation). In the 6N-dimensional phase space Omega of the relativistic systems with 2N particles and N antiparticles, there exists a 2N-dimensional Poincaré-invariant submanifold OmegaP corresponding to N free particles and N bound particle-antiparticle pairs in their ground state. The Tzitzeica N-soliton tau functions under consideration are real valued and obtained via the dual Lax matrix evaluated in points of OmegaP. This correspondence leads to a picture of the soliton as a cluster of two particles and one antiparticle in their lowest internal energy state

Are constant loop widths an artifact of the background and the spatial resolution?

We study the effect of the coronal background in the determination of the diameter of EUV loops, and we analyze the suitability of the procedure followed in a previous paper (L\'opez Fuentes, Klimchuk & D\'emoulin 2006) for characterizing their expansion properties. For the analysis we create different synthetic loops and we place them on real backgrounds from data obtained with the Transition Region and Coronal Explorer (\textit{TRACE}). We apply to these loops the same procedure followed in our previous works, and we compare the results with real loop observations. We demonstrate that the procedure allows us to distinguish constant width loops from loops that expand appreciably with height, as predicted by simple force-free field models. This holds even for loops near the resolution limit. The procedure can easily determine when loops are below resolution limit and therefore not reliably measured. We find that small-scale variations in the measured loop width are likely due to imperfections in the background subtraction. The greatest errors occur in especially narrow loops and in places where the background is especially bright relative to the loop. We stress, however, that these effects do not impact the ability to measure large-scale variations. The result that observed loops do not expand systematically with height is robust.Comment: Accepted for publication in Ap

Constraints on filament models deduced from dynamical analysis

The conclusions deduced from simultaneous observations with the Ultra-Violet Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission satellite, and the Multichannel Subtractive Double Pass (MSPD) spectrographs at Meudon and Pic du Midi observatories are presented. The observations were obtained in 1980 and 1984. All instruments have almost the same field of view and provide intensity and velocity maps at two temperatures. The resolution is approx. 0.5 to 1.5" for H alpha line and 3" for C IV. The high resolution and simultaneity of the two types of observations allows a more accurate description of the flows in prominences as functions of temperature and position. The results put some contraints on the models and show that dynamical aspects must be taken into account

Plasma composition in a sigmoidal anemone active region

Using spectra obtained by the EIS instrument onboard Hinode, we present a detailed spatially resolved abundance map of an active region (AR)-coronal hole (CH) complex that covers an area of 359 arcsec x 485 arcsec. The abundance map provides first ionization potential (FIP) bias levels in various coronal structures within the large EIS field of view. Overall, FIP bias in the small, relatively young AR is 2-3. This modest FIP bias is a consequence of the AR age, its weak heating, and its partial reconnection with the surrounding CH. Plasma with a coronal composition is concentrated at AR loop footpoints, close to where fractionation is believed to take place in the chromosphere. In the AR, we found a moderate positive correlation of FIP bias with nonthermal velocity and magnetic flux density, both of which are also strongest at the AR loop footpoints. Pathways of slightly enhanced FIP bias are traced along some of the loops connecting opposite polarities within the AR. We interpret the traces of enhanced FIP bias along these loops to be the beginning of fractionated plasma mixing in the loops. Low FIP bias in a sigmoidal channel above the AR's main polarity inversion line where ongoing flux cancellation is taking place, provides new evidence of a bald patch magnetic topology of a sigmoid/flux rope configfiuration.Comment: For on-line animation, see http://www.mssl.ucl.ac.uk/~db2/fip_intensity.gif. Accepted by Ap

Shallow water tomography with a sparse array during the INTIMATE'98 sea trial

Invert acoustic data using sparse arrays - at the limit with a single hydrophone - is a challenging task. The final goal is to obtain a rapid environmental assessment with systems both easier to deploy and less expensive than full vertical arrays. In this paper, it is shown that using a known broadband source signal and an array with few hydrophones, ocean acoustic tomography can be performed, even in a complex internal waves induced highly variable ocean. The inversion approach presented herein is based on an arrival matching processor and a genetic algorithm search procedure. Due to the poor accuracy on the a priori knowledge of the source range, source depth and water depth, the inversion procedure was split in two stages: in the first stage the geometric parameters where estimated and in the second stage sound speed estimates where obtained. This procedure was applied to field data, acquired during the INTIMATE'98 sea trial, in a shallow water area off the coast of France in the Gulf of Biscay. That area is expected to have a relatively high internal wave activity, specially during the summer. A 4 sec long - 700 Hz bandwidth linear frequency modulated signal was transmitted from a ship suspended sound source and received on a 4 element vertical array at a range of approximately 10.5 km, over a relatively range-independent area. The results from the inversion of the acoustic data are in line with those obtained by concurrent non acoustic data like GPS source range, measured source depth, XBT casts and temperature sensors

INTIMATE'96. A shallow water tomography experiment devoted to the study of internal tides

The INTIMATE (INternal Tide Investigation by Means of Acoustic Tomography Experiment) project is devoted to the study of internal tides by use of acoustic tomography. The first exploratory experiment was carried out in June 1996 on the continental shelf off the west coast of Portugal. A towed broadband acoustic source and a 4-hydrophone vertical array were used. Acoustic data were collected for 5 days, including legs where the source ship was moving and legs with the ship on station. The purpose of this paper is to briefly discuss some effects of the environment on acoustic fluctuations.PRAXIS XX

PUPHS2D 2.0 User\u27s Manual

The Purdue University Program for Heterostructure Simulation in Two Dimensions (PUPHS2D) solves Poisson\u27s equation and the electron and hole continuity equations within a two-dimensional heterostructure device. The program will compute the electrostatic potential, electron and hole densities, recombination rate, and other quantities of interest as a function of applied bias. Like its predecessor, version 2.0 allows extensive analysis of solar cells, including computation of the current-voltage characteristics of two-terminal devices, solar cell parameters, quantum efficiency, and current versus solar intensity. Extensions to version 2.Q include transient analysis and bipolar transistor capability. The heterojunction bipolar transistor routines allow computation of dc currents as a function of applied bias, as well as quasi-static evaluation of the high-frequency behavior. A simplified energy balance equation has been added in the interest of more accurately computing high-field characteristics, and should be viewed as a preliminary step toward this goal. PUPHS2D stands as an accurate model for computing low-field device characteristics and recombinative losses. While PUPHS2D was written for the ternary AlxGai1-xAs, all material specific parameters are contained within a single subroutine (BANDX), except for absorption coefficient and carrier mobilities which are computed in subroutines ALGABS and SETMOB, respectively. Material-specific parameters used for the energy balance equation are found in subroutines INITMU and INITAU. The program may be readily modified to analyze other semiconductors. For a more thorough discussion of the theoretical basis and numerical implementation of PUPHS2D, the user is directed to the references. Materials parameters are described in reference [I]. Various phases of the development of PUPHS2D have been supported by the Semiconductor Research Corporation, Sandia National Laboratories/ the Eastman Kodak Company, and by Research Triangle Institute

Broadband source localization with a single hydrophone

Source localization with vertical arrays in shallow water has been a topic of intense research in the last 20 years. Although horizontal arrays can (and have) been used, vertical arrays are better suited for extracting signal modal structure and thus provide a source-location estimate in range and depth. It is well known that broadband signals have a localization capability superior to that of narrowband signals. One question that remains largely unresolved is whether frequency extent can compensate for the spatial diversity provided by sensor arrays, i.e., at the limit, can a broadband signal be localized with a single sensor ? This communication presents theoretical, simulated, and practical evidence that a multipath-delay maximum-likelihood estimator does provide enough signal to background discrimination for localizing a 500 Hz bandwidth signal at 5 km range in a 130 m depth shallow water channel with a single hydrophone. The real data used in this study was collected during the INTI-MATE'96 experiment which was conducted off the west of Portugal in June 1996 during an internal tide tomography experiment. Comparison with localization results provided by direct match between the received and the model-generated arrival patterns will be discussed

Intimate '96: shallow water tomography in the sea of the condemned

As is well-known, the tidal force of the moon and the sun can cause notable changes in the sea level. Besides this so-called barotropic effect, the tidal force also drives internal waves in a daily rhythm. Thus, the internal wave spectrum is often dominated by a single component with perhaps 10 km from crest to crest. This ‘‘internal tide’’ tends to propagate toward shore and has its greatest height near the shelfbreak