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Non-radial solar wind flows induced by the motion of interplanetary coronal mass ejections
A survey of the non-radial flows (NRFs) during
nearly five years of interplanetary observations revealed
the average non-radial speed of the solar wind flows to
be �30 km/s, with approximately one-half of the large
(>100 km/s) NRFs associated with ICMEs. Conversely, the
average non-radial flow speed upstream of all ICMEs is
�100 km/s, with just over one-third preceded by large NRFs.
These upstream flow deflections are analysed in the context
of the large-scale structure of the driving ICME. We chose
5 magnetic clouds with relatively uncomplicated upstream
flow deflections. Using variance analysis it was possible to
infer the local axis orientation, and to qualitatively estimate the point of interception of the spacecraft with the ICME. For all 5 events the observed upstream flows were in agreement with the point of interception predicted by variance analysis. Thus we conclude that the upstream flow deflections in these events are in accord with the current concept of the large scale structure of an ICME: a curved axial loop connected to the Sun, bounded by a curved (though not necessarily circular)cross section
Modelling interplanetary CMEs using magnetohydrodynamic simulations
International audienceThe dynamics of Interplanetary Coronal Mass Ejections (ICMEs) are discussed from the viewpoint of numerical modelling. Hydrodynamic models are shown to give a good zero-order picture of the plasma properties of ICMEs, but they cannot model the important magnetic field effects. Results from MHD simulations are shown for a number of cases of interest. It is demonstrated that the strong interaction of the ICME with the solar wind leads to the ICME and solar wind velocities being close to each other at 1 AU, despite their having very different speeds near the Sun. It is also pointed out that this interaction leads to a distortion of the ICME geometry, making cylindrical symmetry a dubious assumption for the CME field at 1 AU. In the presence of a significant solar wind magnetic field, the magnetic fields of the ICME and solar wind can reconnect with each other, leading to an ICME that has solar wind-like field lines. This effect is especially important when an ICME with the right sense of rotation propagates down the heliospheric current sheet. It is also noted that a lack of knowledge of the coronal magnetic field makes such simulations of little use in space weather forecasts that require knowledge of the ICME magnetic field strength
First Cluster results of the magnetic field structure of the mid- and high-altitude cusps
International audienceMagnetic field measurements from the four Cluster spacecraft from the mid- and high-altitude cusp are presented. Cluster underwent two encounters with the mid-altitude cusp during its commissioning phase (24 August 2000). Evidence for field-aligned currents (FACs) was seen in the data from all three operating spacecraft from northern and southern cusps. The extent of the FACs was of the order of 1 RE in the X-direction, and at least 300 km in the Y-direction. However, fine-scale field structures with scales of the order of the spacecraft separation (300 km) were observed within the FACs. In the northern crossing, two of the spacecraft appeared to lie along the same magnetic field line, and observed very well matched signals. However, the third spacecraft showed evidence for structuring transverse to the field on scales of a few hundred km. A crossing of the high-altitude cusp from 13 February 2001 is presented. It is revealed to be a highly dynamic structure with the boundaries moving with velocities ranging from a few km/s to tens of km/s, and having structure on timescales ranging from less than one minute up to several minutes. The cusp proper is associated with the presence of a very disordered magnetic field, which is entirely different from the magnetosheath turbulence
Development and calibration of a sand pluviation device for preparation of model sand bed for centrifuge tests
A bespoke 0.068m3 (18.5 gallon) sand hopper is employed at the newly established 50gTon centrifuge facility at the University of Sheffield. The sand hopper employs a series of mesh inserts of different diameters which control the flow rate and thus the relative density of the model. A series of calibration tests on equivalent Fraction E and Fraction C sands were performed to calibrate the mesh diameter and drop height for a desired relative density. Result showed that the sand hopper is capable of delivering repeatable relative densities in the range of 30% to above 90%, for both kinds of sand grades. This wide range relative density is considered sufficient to satisfy the needs of researchers preparing dry sand models for testing in the center
Heritability and complex segregation analysis of deafness in Jack Russell Terriers
This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens
Analysis and Modeling of Two Flare Loops Observed by AIA and EIS
We analyze and model an M1.0 flare observed by SDO/AIA and Hinode/EIS to
investigate how flare loops are heated and evolve subsequently. The flare is
composed of two distinctive loop systems observed in EUV images. The UV 1600
\AA emission at the feet of these loops exhibits a rapid rise, followed by
enhanced emission in different EUV channels observed by AIA and EIS. Such
behavior is indicative of impulsive energy deposit and the subsequent response
in overlying coronal loops that evolve through different temperatures. Using
the method we recently developed, we infer empirical heating functions from the
rapid rise of the UV light curves for the two loop systems, respectively,
treating them as two big loops of cross-sectional area 5\arcsec by 5\arcsec,
and compute the plasma evolution in the loops using the EBTEL model (Klimchuk
et al. 2008). We compute the synthetic EUV light curves, which, with the
limitation of the model, reasonably agree with observed light curves obtained
in multiple AIA channels and EIS lines: they show the same evolution trend and
their magnitudes are comparable by within a factor of two. Furthermore, we also
compare the computed mean enthalpy flow velocity with the Doppler shift
measurements by EIS during the decay phase of the two loops. Our results
suggest that the two different loops with different heating functions as
inferred from their footpoint UV emission, combined with their different
lengths as measured from imaging observations, give rise to different coronal
plasma evolution patterns captured both in the model and observations.Comment: Accepted for publication in Ap
Comparison of Hinode/XRT and RHESSI detection of hot plasma in the non-flaring solar corona
We compare observations of the non-flaring solar corona made simultaneously
with Hinode/XRT and with RHESSI. The analyzed corona is dominated by a single
active region on 12 November 2006. The comparison is made on emission measures.
We derive emission measure distributions vs temperature of the entire active
region from multifilter XRT data. We check the compatibility with the total
emission measure values estimated from the flux measured with RHESSI if the
emission come from isothermal plasma. We find that RHESSI and XRT data analyses
consistently point to the presence of a minor emission measure component
peaking at log T ~ 6.8-6.9. The discrepancy between XRT and RHESSI results is
within a factor of a few and indicates an acceptable level of
cross-consistency.Comment: 12 pages, 3 figures, Letter accepted for publicatio
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A comparison between ion characteristics observed by the POLAR and DMSP spacecraft in the high-latitude magnetosphere
We study here the injection and transport of ions in the convection-dominated region of the Earth’s magnetosphere. The total ion counts from the CAMMICE MICS instrument aboard the POLAR spacecraft are used to generate occurrence probability distributions of magnetospheric ion populations. MICS ion spectra are characterised by both the peak in the differential energy flux, and the average energy of ions striking the detector. The former permits a comparison with the Stubbs et al. (2001) survey of He2+ ions of solar wind origin within the magnetosphere. The latter can address the occurrences of various classifications of precipitating particle fluxes observed in the topside ionosphere by DMSP satellites (Newell and Meng, 1992). The peak energy occurrences are consistent with our earlier work, including the dawn-dusk asymmetry with enhanced occurrences on the dawn flank at low energies, switching to the dusk flank at higher energies. The differences in the ion energies observed in these two studies can be explained by drift orbit effects and acceleration processes at the magnetopause, and in the tail current sheet. Near noon at average ion energies of _1 keV, the cusp and open LLBL occur further poleward here than in the Newell and Meng survey, probably due to convectionrelated time-of-flight effects. An important new result is that the pre-noon bias previously observed in the LLBL is most likely due to the component of this population on closed field lines, formed largely by low energy ions drifting earthward from the tail. There is no evidence here of mass and momentum transfer from the solar wind to the LLBL by nonreconnection coupling. At higher energies (_2–20 keV), we observe ions mapping to the auroral oval and can distinguish between the boundary and central plasma sheets. We show that ions at these energies relate to a transition from dawnward to duskward dominated flow, this is evidence of how ion drift orbits in the tail influence the location and behaviour of the plasma populations in the magnetosphere
Engine Component Retirement-For-Cause: A Nondestructive Evaluation (NDE) and Fracture Mechanics Based Maintainance Concep
Historically, cyclic life limited gas turbine engine components have been retired when they reach an analytically determined life where the first fatigue crack per 1000 parts could be expected. By definition, 99.9% of these components are being retired prematurely as they have considerable useful life remaining. Retirement for Cause is a procedure which would allow safe utilization of the full life capacity of each individual component. Since gas turbine engine rotor components are prime candidates and are among the most costly of engine components, adoption of a RFC maintenance philosophy could result in substantial engine systems life cycle cost savings. Two major technical disciplines must be developed and integrated to realize those cost savings: Fracture Mechanics and Nondestructive Evaluation. This paper discusses the methodology, and development activity required, to integrate these disciplines to provide a viable RFC system for use on military gas turbine engines, and illustrates potential benefits of its application
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