94 research outputs found
P-mode leakage and Lyman-α intensity
We present an observational test of the hypothesis that leaking p modes heat the solar chromosphere. The amplitude of the leaking p modes in magneto-acoustic portals is determined using MOTH and MDI data. We simulate the propagation of these modes into the chromosphere to determine the height where the wave energy is dissipated by shock waves. A statistical approach is then used to check if this heating process could account for the observed variability of the intensity in the Lyman-α emissio
Acoustic power absorption and enhancement generated by slow and fast MHD waves
We used long duration, high quality, unresolved (Sun-as-a star) observations
collected by the ground based network BiSON and by the instruments GOLF and
VIRGO on board the ESA/NASA SOHO satellite to search for solar-cycle-related
changes in mode characteristics in velocity and continuum intensity for the
frequency range between 2.5mHz < nu < 6.8mHz. Over the ascending phase of solar
cycle 23 we found a suppression in the p-mode amplitudes both in the velocity
and intensity data between 2.5mHz <nu< 4.5mHz with a maximum suppression for
frequencies in the range between 2.5mHz <nu< 3.5mHz. The size of the amplitude
suppression is 13+-2 per cent for the velocity and 9+-2 per cent for the
intensity observations. Over the range 4.5mHz <nu< 5.5mHz the findings hint
within the errors to a null change both in the velocity and intensity
amplitudes. At still higher frequencies, in the so called High-frequency
Interference Peaks (HIPs) between 5.8mHz <nu < 6.8mHz, we found an enhancement
in the velocity amplitudes with the maximum 36+-7 per cent occurring for 6.3mHz
<nu< 6.8mHz. However, in intensity observations we found a rather smaller
enhancement of about 5+-2 per cent in the same interval. There is evidence that
the frequency dependence of solar-cycle velocity amplitude changes is
consistent with the theory behind the mode conversion of acoustic waves in a
non-vertical magnetic field, but there are some problems with the intensity
data, which may be due to the height in the solar atmosphere at which the VIRGO
data are taken.Comment: Accepted for publication in A&A. 10 pages, 9 figures
Evidence of increasing acoustic emissivity at high frequency with solar cycle 23 in Sun-as-a-star observations
We used long high-quality unresolved (Sun-as-a-star observations) data
collected by GOLF and VIRGO instruments on board the ESA/NASA SOHO satellite to
investigate the amplitude variation with solar cycle 23 in the high-frequency
band (5.7 < nu< 6.3 mHz). We found an enhancement of acoustic emissivity over
the ascending phase of about 18+-3 in velocity observations and a slight
enhancement of 3+-2 in intensity. Mode conversion from fast acoustic to fast
magneto-acoustic waves could explain the enhancement in velocity observations.
These findings open up the possibility to apply the same technique to stellar
intensity data, in order to investigate stellar-magnetic activity.Comment: Proceedings of the Stellar Pulsation. Santa Fe, USA. 3 pages, 5
figure
The Quasi-Biennial Periodicity (QBP) in velocity and intensity helioseismic observations
We looked for signatures of Quasi-Biennial Periodicity (QBP) over different
phases of solar cycle by means of acoustic modes of oscillation. Low-degree
p-mode frequencies are shown to be sensitive to changes in magnetic activity
due to the global dynamo. Recently have been reported evidences in favor of
two-year variations in p-mode frequencies. Long high-quality helioseismic data
are provided by BiSON (Birmingham Solar Oscillation Network), GONG (Global
Oscillation Network Group), GOLF (Global Oscillation at Low Frequency) and
VIRGO (Variability of Solar IRradiance and Gravity Oscillation) instruments. We
determined the solar cycle changes in p-mode frequencies for spherical degree
l=0, 1, 2 with their azimuthal components in the frequency range 2.5 mHz < nu <
3.5 mHz. We found signatures of QBP at all levels of solar activity in the
modes more sensitive to higher latitudes. The signal strength increases with
latitude and the equatorial component seems also to be modulated by the 11-year
envelope. The persistent nature of the seismic QBP is not observed in the
surface activity indices, where mid-term variations are found only time to time
and mainly over periods of high activity. This feature together with the
latitudinal dependence provides more evidences in favor of a mechanism almost
independent and different from the one that brings up to the surface the active
regions. Therefore, these findings can be used to provide more constraints on
dynamo models that consider a further cyclic component on top of the 11-year
cycle.Comment: 9 pages, 9 Figures, 2 Tables Accepted for publication in A&
Gossamer roadmap technology reference study for a solar polar mission
A technology reference study for a solar polar mission is presented. The study uses novel analytical methods to quantify the mission design space including the required sail performance to achieve a given solar polar observation angle within a given timeframe and thus to derive mass allocations for the remaining spacecraft sub-systems, that is excluding the solar sail sub-system. A parametric, bottom-up, system mass budget analysis is then used to establish the required sail technology to deliver a range of science payloads, and to establish where such payloads can be delivered to within a given timeframe. It is found that a solar polar mission requires a solar sail of side-length 100 â 125 m to deliver a âsufficient valueâ minimum science payload, and that a 2. 5ÎŒm sail film substrate is typically required, however the design is much less sensitive to the boom specific mass
Helioseismic Mapping of the Magnetic Canopy in the Solar Chromosphere
We determine the three-dimensional topography of the magnetic canopy in and around active regions by mapping the propagation behavior of high-frequency acoustic waves in the solar chromosphere
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