15 research outputs found
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Modeling the observed proton aurora and ionospheric convection responses to changes in the IMF clock angle: 1. Persistence of cusp proton aurora
We employ a numerical model of cusp ion precipitation and proton aurora emission to fit variations of the peak Doppler-shifted Lyman-a intensity observed on 26 November 2000 by the SI-12 channel of the FUV instrument on the IMAGE satellite. The major features of this event appeared in response to two brief swings of the interplanetary magnetic field (IMF) toward a southward orientation. We reproduce the observed spatial distributions of this emission on newly opened field lines by combining the proton emission model with a model of the response of ionospheric convection. The simulations are based on the observed variations of the solar wind proton temperature and concentration and the interplanetary magnetic field clock angle. They also allow for the efficiency, sampling rate, integration time and spatial resolution of the FUV instrument. The good match (correlation coefficient 0.91, significant at the 98% level) between observed and modeled variations confirms the time constant (about 4 min) for the rise and decay of the proton emissions predicted by the model for southward IMF conditions. The implications for the detection of pulsed magnetopause reconnection using proton aurora are discussed for a range of interplanetary conditions
Observation of O+ (4P-4D0) lines in electron aurora over Svalbard
This work reports on observations of O+ lines in aurora over Svalbard, Norway. The Spectrographic Imaging Facility measures auroral spectra in three wavelength intervals (H, N+2 1N(0,2) and N+2 1N(1,3)). The oxygen ion 4P-4D0 multiplet (4639–4696 A° ) is blended with the N+2 1N(1,3) band. It is found that in electron aurora, the brightness of this multiplet, is on average, about 0.1 of the N+2 1N(0,2) total brightness. A joint optical and incoherent scatter radar study of an electron aurora event shows that the ratio is enhanced when the ionisation in the upper E-layer (140–190 km) is significant with respect to the E-layer peak below 130 km. Rayed arcs were observed on one such occasion, whereas on other occasions the auroral intensity was below the threshold of the imager. A one-dimensional electron transport model is used to estimate the cross section for production of the multiplet in electron collisions, yielding 0.18×10-18 cm2
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Modeling the observed proton aurora and ionospheric convection responses to changes in the IMF clock angle: 2. Persistence of ionospheric convection
[1] We apply a numerical model of time-dependent ionospheric convection to two directly driven reconnection pulses during a 15-min interval of southward IMF on 26 November 2000. The model requires an input magnetopause reconnection rate variation, which is here derived from the observed variation in the upstream IMF clockangle, θ. The reconnection rate is mapped to an ionospheric merging gap, the MLT extent of which is inferred from the Doppler-shifted Lyman-α emission on newly opened field lines, as observed by the FUV instrument on the IMAGE spacecraft. The model is used to reproduce a variety of features observed during this event: SuperDARN observations of the ionospheric convection pattern and transpolar voltage; FUV observations of the growth of patches of newly opened flux; FUV and in situ observations of the location of the Open-Closed field line Boundary (OCB) and a cusp ion step. We adopt a clock angle dependence of the magnetopause reconnection electric field, mapped to the ionosphere, of the form Enosin4(θ/2) and estimate the peak value, Eno, by matching observed and modeled variations of both the latitude, ΛOCB, of the dayside OCB (as inferred from the equatorward edge of cusp proton emissions seen by FUV) and the transpolar voltage ΦPC (as derived using the mapped potential technique from SuperDARN HF radar data). This analysis also yields the time constant tOCB with which the open-closed boundary relaxes back toward its equilibrium configuration. For thecase studied here, we find tOCB = 9.7 ± 1.3 min, consistent with previous inferences from the observed response of ionospheric flow to southward turnings of the IMF. The analysis confirms quantitatively the concepts of ionospheric flow excitation on which the model is based and explains some otherwise anomalous features of the cusp precipitation morphology
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IMF control of cusp proton emission intensity and dayside convection: implications for component and anti-parallel reconnection
We study a brightening of the Lyman-? emission
in the cusp which occurred in response to a short-lived southward
turning of the interplanetary magnetic field (IMF) during
a period of strongly enhanced solar wind plasma concentration.
The cusp proton emission is detected using the SI-12
channel of the FUV imager on the IMAGE spacecraft. Analysis
of the IMF observations recorded by the ACE and Wind
spacecraft reveals that the assumption of a constant propagation
lag from the upstream spacecraft to the Earth is not
adequate for these high time-resolution studies. The variations
of the southward IMF component observed by ACE
and Wind allow for the calculation of the ACE-to-Earth lag
as a function of time. Application of the derived propagation
delays reveals that the intensity of the cusp emission varied
systematically with the IMF clock angle, the relationship being
particularly striking when the intensity is normalised to
allow for the variation in the upstream solar wind proton concentration.
The latitude of the cusp migrated equatorward
while the lagged IMF pointed southward, confirming the lag
calculation and indicating ongoing magnetopause reconnection.
Dayside convection, as monitored by the SuperDARN
network of radars, responded rapidly to the IMF changes
but lagged behind the cusp proton emission response: this
is shown to be as predicted by the model of flow excitation
by Cowley and Lockwood (1992). We use the numerical
cusp ion precipitation model of Lockwood and Davis
(1996), along with modelled Lyman-? emission efficiency
and the SI-12 instrument response, to investigate the effect
of the sheath field clock angle on the acceleration of ions
on crossing the dayside magnetopause. This modelling reveals
that the emission commences on each reconnected field
line 2–2.5min after it is opened and peaks 3–5 min after it is
opened. We discuss how comparison of the Lyman-? intensities
with oxygen emissions observed simultaneously by the
SI-13 channel of the FUV instrument offers an opportunity
to test whether or not the clock angle dependence is consistent
with the “component” or the “anti-parallel” reconnection
hypothesis
Observation of O<sup>+</sup> (<sup>4</sup>P-<sup>4</sup>D<sup>0</sup>) lines in electron aurora over Svalbard
This work reports on observations of O+ lines in aurora over
Svalbard, Norway. The Spectrographic Imaging Facility measures auroral
spectra in three wavelength intervals
(Hβ, N+2 1N(0,2) and N+2 1N(1,3)).
The oxygen ion multiplet (4639-4696Å) is blended
with the band.
It is found that in electron aurora, the brightness
of this multiplet, is
on average, about 0.1 of the total brightness.
A joint optical and incoherent scatter radar study of an
electron aurora event shows that the ratio is enhanced
when the ionisation in the upper E-layer (140-190km)
is significant with respect to the E-layer peak
below 130km. Rayed arcs were observed on one such
occasion, whereas on other occasions the auroral
intensity was below the threshold of the imager.
A one-dimensional electron transport model is used to
estimate the cross section for production of the multiplet
in electron collisions, yielding 0.18x10-18cm2
Increased circulating normal and BCR-ABL+Ve progenitor numbers in Philadelphia chromosome-positive acute myeloid leukaemia
We recorded elevated numbers of circulating myeloid and erythroid colony-forming cells in 15 adult patients with acute myeloid leukaemia (AML) who presented with high blood white cell counts. Since leukaemic blasts from three of these patients were Philadelphia chromosome-positive (Ph+), we were able to determine if blood progenitors from these particular patients arose from the leukaemic clone or from residual normal progenitors. Blasts and colonies were intensively investigated using a combination of cell surface marker analysis by flow cytometry, RT-PCR and interphase fluorescence in situ hybridization (FISH). FISH detected rearrangements within the major breakpoint BCR (M-BCR) region in blasts and in some myeloid and erythroid colonies from patients 1 and 2. The minor breakpoint (m-BCR) region was detected in blasts and in some myeloid and erythroid colonies from patient 3. RT-PCR detected long b2a2 BCR-ABL transcripts in blasts from patients 1 and 2, although misspliced short e1a2 transcripts were also seen in patient 1. Only e1a2 transcripts were found in blasts from patient 3. Flow sorting demonstrated the B-cell marker CD19 on blasts and on a proportion of myeloid and erythroid progenitors from patients 1 and 3. RT-PCR also detected IgH rearrangements, further evidence of B-cell differentiation, in blasts from these two patients. We conclude that both normal and clonal circulating progenitor numbers can be raised in both M-BCR and m-BCR Ph+ AML. The underlying cause, perhaps efflux from a congested marrow, may be common to AML patients with a high blood white cell count. © 2002 Elsevier Science Ltd. All rights reserved