17 research outputs found
A shortening of the life-cycle of major tropical cyclones
In this study a comprehensive picture of the changing intensity life cycle of major (Category 3 and higher) tropical cyclones (TCs) is presented. Over the past decades, the lifetime maximum intensity has increased, but there has also been a significant decrease in duration of time spent at intensities greater than Category 1. These compensating effects have maintained a stable global meanâaccumulated cyclone energy of individual major TCs. The global mean duration of major TCs has shortened by about 1 day from 1982 to 2018. There has been both faster intensification (Categories 1 to 3) and weakening (Categories 3 to 1) by about 40%. The probabilities of rapid intensification and rapid weakening have both risen in the period 2000â2018 compared to 1982â1999. A statistically significant anticorrelation is found between the lifetime maximum intensity and the following duration of the final weakening. This suggests an element of selfâregulation of TC life cycles
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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
Cytokine enhancement of immunogenicity in chronic myeloid leukaemia
Various clinical and laboratory observations suggest that the leukaemia cells in chronic myeloid leukaemia (CML) are potentially immunogenic. Whilst the ability of the leukaemia cells to elicit an anti-leukaemic immune response in the allogeneic setting is established, it remains unclear why such anti-leukaemic response does not occur in vivo in the autologous setting. We previously demonstrated the presence of leukaemia-reactive T cells in a patient with CML. However, we found that the T cells were normally anergic unless pre-incubated in vitro in high-dose recombinant interleukin-2. We speculated that the T cell anergy was the result of a lack of the appropriate immune costimulatory molecules on the leukaemia cell surface. In this study, we confirm the absence of immune costimulatory molecules, CD80 (B7-1) and CD86 (B7-2), on leukaemia cells and demonstrated that these costimulatory molecules on the leukaemia cells can be upregulated by a combination of GM-CSF and IL-4. There was an associated restoration of leukaemia cell immunogenicity to autologous T cells in mixed lymphocyte leukaemia reactions, suggesting a possible enhancement of anti-leukaemic reaction. More importantly, T cells primed with 'activated' leukaemia cells were able to recognise fresh cytokine-naive leukaemia cells. Furthermore, leukaemia cells expressing the dendritic cell marker, CD1a, were also generated. Our findings therefore suggest the opportunity in future to use these combination cytokines in vivo or these leukaemia cells which have been activated in vitro for leukaemia immunotherapy
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
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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, Ξ. 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(Ξ/2) and estimate the peak value, Eno, by matching observed and modeled variations of both the latitude, ÎOCB, of the dayside OCB (as inferred from the equatorward edge of cusp proton emissions seen by FUV) and the transpolar voltage ΊPC (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 2â2.5min after it is opened and peaks 3â5 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 âcomponentâ or the âanti-parallelâ reconnection
hypothesis