777 research outputs found
Iron-rich solar particle events measured by SOHO/ERNE during two solar cycles
We study the differences in the heavy ion composition of solar energetic
particle (SEP) events between solar cycles 23 and 24. We have surveyed the
SOHO/ERNE heavy ion data from the beginning of solar cycle 23 until the end of
June 2015, that is, well into the declining phase of cycle 24. We used this
long observation period to study the properties of heavy ions (from C to Fe)
and to compare the two solar cycles in this respect. We surveyed the data for
SEP events with enhancements in the Fe/C and Fe/O intensity ratios in the
energy range 5-15 MeV per nucleon, and associated the events with solar flare
and coronal mass ejections (CME) when possible. We studied the properties of
heavy ions in these events and compared the average relative abundances of
heavy ions between the two solar cycles. We found that fewer days had C and O
intensities higher than ~10
cmsrs(MeVn) during solar cycle 24 than
during cycle 23. For Fe this difference was clear even at lower intensities. We
also found that fewer days had Fe/(C+O) > 0.183 during cycle 24. We identified
86 SEP events with at least one Fe-rich day, 65 of which occurred during cycle
23 and only 21 during cycle 24. We found that impulsive events have been almost
completely absent during cycle 24. Mean abundances of heavy ions in the events
were found to be significantly lower during cycle 24 than in cycle 23. Our
results reflect the reduced solar activity in cycle 24 and indicate lower
efficiency of particle acceleration processes for both gradual and impulsive
SEP events in cycle 24.Comment: 14 pages, 9 figures and 3 tables. To be published in A&
Fringe spacing and phase of interfering matter waves
We experimentally investigate the outcoupling of atoms from Bose-Einstein
condensates using two radio-frequency (rf) fields in the presence of gravity.
We show that the fringe separation in the resulting interference pattern
derives entirely from the energy difference between the two rf fields and not
the gravitational potential difference. We subsequently demonstrate how the
phase and polarisation of the rf radiation directly control the phase of the
matter wave interference and provide a semi-classical interpretation of the
results.Comment: 4 pages, 3 figure
Stimulated Raman scattering in an optical parametric oscillator based on periodically poled MgO-doped stoichiometric LiTaO3
The evolution versus pump power of the spectrum of a singly resonant optical
parametric oscillator based on an MgO-doped periodically poled stoichiometric
lithium tantalate crystal is observed. The onset of cascade Raman lasing due to
stimulated Raman scattering in the nonlinear crystal is analyzed. Spurious
frequency doubling and sum-frequency generation phenomena are observed and
understood. A strong reduction of the intracavity Raman scattering is obtained
by a careful adjustment of the cavity losses.Comment: 6 figure
Iron-rich solar particle events measured by SOHO/ERNE during two solar cycles
Aims. We study the differences in the heavy ion composition of solar energetic particle (SEP) events between solar cycles 23 and 24.
Methods. We have surveyed the SOHO/ERNE heavy ion data
from the beginning of solar cycle 23 until the end of June 2015, that
is, well into the declining phase of cycle 24. We used this long
observation period to study the properties of heavy ions (from C to Fe)
and to compare the two solar cycles in this respect. We surveyed the
data for SEP events with enhancements in the Fe/C and Fe/O intensity
ratios in the energy range 5–15 MeV per nucleon, and associated the
events with solar flare and coronal mass ejections (CME) when possible.
We studied the properties of heavy ions in these events and compared the
average relative abundances of heavy ions between the two solar cycles.
Results. We found that fewer days had C and O intensities higher than ~10 -3 cm-2 sr-1 s-1 (MeVn-1)-1
during solar cycle 24 than during cycle 23. For Fe this difference was
clear even at lower intensities. We also found that fewer days had
Fe/(C+O) > 0.183 during cycle 24. We
identified 86 SEP events with at least one Fe-rich day, 65 of which
occurred during cycle 23 and only 21 during cycle 24. We found that
impulsive events have been almost completely absent during cycle 24.
Mean abundances of heavy ions in the events were found to be
significantly lower during cycle 24 than in cycle 23. Our results
reflect the reduced solar activity in cycle 24 and indicate lower
efficiency of particle acceleration processes for both gradual and
impulsive SEP events in cycle 24.</p
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