71 research outputs found
Comparison of 30 THz impulsive burst time development to microwaves, H-alpha, EUV, and GOES soft X-rays
The recent discovery of impulsive solar burst emission in the 30 THz band is
raising new interpretation challenges. One event associated with a GOES M2
class flare has been observed simultaneously in microwaves, H-alpha, EUV, and
soft X-ray bands. Although these new observations confirm some features found
in the two prior known events, they exhibit time profile structure
discrepancies between 30 THz, microwaves, and hard X-rays (as inferred from the
Neupert effect). These results suggest a more complex relationship between 30
THz emission and radiation produced at other wavelength ranges. The multiple
frequency emissions in the impulsive phase are likely to be produced at a
common flaring site lower in the chromosphere. The 30 THz burst emission may be
either part of a nonthermal radiation mechanism or due to the rapid thermal
response to a beam of high-energy particles bombarding the dense solar
atmosphere.Comment: accepted to Astronomy and Astrophysic
55. Reprise chirurgicale des carcinomes canalaires in situ pour exérÚse non in sano : existe-t-il des facteurs de risque ?
LOFAR tied-array imaging of Type III solar radio bursts
Context. The Sun is an active source of radio emission which is often associated with energetic phenomena such as solar flares and coronal mass ejections (CMEs). At low radio frequencies (< 100 MHz), the Sun has not been imaged extensively because of
Noise storm continua: power estimates for electron acceleration
We use a generic stochastic acceleration formalism to examine the power
() input to nonthermal electrons that cause
noise storm continuum emission. The analytical approach includes the derivation
of the Green's function for a general second-order Fermi process, and its
application to obtain the particular solution for the nonthermal electron
distribution resulting from the acceleration of a Maxwellian source in the
corona. We compare with the power observed in noise
storm radiation. Using typical values for the various parameters, we find that
, yielding an efficiency
estimate in the range 10^{-10} \lsim \eta
\lsim 10^{-6} for this nonthermal acceleration/radiation process. These
results reflect the efficiency of the overall process, starting from electron
acceleration and culminating in the observed noise storm emission.Comment: Accepted for publication in Solar Physic
Spectrum of Solar Type I Continuum Noise Storm in the 50 - 80 MHz band, and Plasma characteristics in the associated source region
Continuum observations of a solar noise storm in the frequency range of 50 -
80 MHz observed with the Gauribidanur radio spectrograph during 2000 September,
26 & 27, are presented here. The radio spectral index of the noise storm
continuum in the band 50 - 80 MHz is found to be ~3.65 during the above period.
The Noise Storm continuum radiation is explained as a consequence of the
non-thermal, plasma emission mechanism. The beam-density of suprathermal
electrons is estimated for the coronal plasma near the source region of storm
radiation. Supplementary evidence for the density-estimate is provided by way
of analysing the imaging data from the SXT on-board the Yohkoh spacecraft, and
the LASCO, MDI, and EIT on board the SoHO spacecraft.Comment: 43 pages; 5 tables; 15 figures (9 color). ApJ (Part I : accepted
The nowcasting SAF products and services: recent improvements in the new SW packages PPS v2018 and GEO v2018 and future plans
PresentaciĂłn realizada en la 3rd European Nowcasting Conference, celebrada en la sede central de AEMET en Madrid del 24 al 26 de abril de 2019
Tracking of an electron beam through the solar corona with LOFAR
The Sun's activity leads to bursts of radio emission, among other phenomena. An example is type-III radio bursts. They occur frequently and appear as short-lived structures rapidly drifting from high to low frequencies in dynamic radio spectra. They are usually interpreted as signatures of beams of energetic electrons propagating along coronal magnetic field lines. Here we present novel interferometric LOFAR (LOw Frequency ARray) observations of three solar type-III radio bursts and their reverse bursts with high spectral, spatial, and temporal resolution. They are consistent with a propagation of the radio sources along the coronal magnetic field lines with nonuniform speed. Hence, the type-III radio bursts cannot be generated by a monoenergetic electron beam, but by an ensemble of energetic electrons with a spread distribution in velocity and energy. Additionally, the density profile along the propagation path is derived in the corona. It agrees well with three-fold coronal density model by Newkirk (1961, ApJ, 133, 983).Financial support was provided by the German Federal Ministry of Education and Research (BMBF in the framework of the
Verbundforschung, D-LOFAR 05A11BAA)
The SURFEXv7.2 land and ocean surface platform for coupled or offline simulation of Earth surface variables and fluxes
CC Attribution 3.0 License.Final revised paper also available at http://www.geosci-model-dev.net/6/929/2013/gmd-6-929-2013.pdfInternational audienceSURFEX is a new externalized land and ocean surface platform that describes the surface fluxes and the evolution of four types of surface: nature, town, inland water and ocean. It can be run either coupled or in offline mode. It is mostly based on pre-existing, well validated scientific models. It can be used in offline mode (from point scale to global runs) or fully coupled with an atmospheric model. SURFEX is able to simulate fluxes of carbon dioxide, chemical species, continental aerosols, sea salt and snow particles. It also includes a data assimilation module. The main principles of the organization of the surface are described first. Then, a survey is made of the scientific module (including the coupling strategy). Finally the main applications of the code are summarized. The current applications are extremely diverse, ranging from surface monitoring and hydrology to numerical weather prediction and global climate simulations. The validation work undertaken shows that replacing the pre-existing surface models by SURFEX in these applications is usually associated with improved skill, as the numerous scientific developments contained in this community code are used to good advantage
Sources of SEP Acceleration during a Flare-CME Event
A high-speed halo-type coronal mass ejection (CME), associated with a GOES
M4.6 soft X-ray flare in NOAA AR 0180 at S12W29 and an EIT wave and dimming,
occurred on 9 November 2002. A complex radio event was observed during the same
period. It included narrow-band fluctuations and frequency-drifting features in
the metric wavelength range, type III burst groups at metric--hectometric
wavelengths, and an interplanetary type II radio burst, which was visible in
the dynamic radio spectrum below 14 MHz. To study the association of the
recorded solar energetic particle (SEP) populations with the propagating CME
and flaring, we perform a multi-wavelength analysis using radio spectral and
imaging observations combined with white-light, EUV, hard X-ray, and
magnetogram data. Velocity dispersion analysis of the particle distributions
(SOHO and Wind in situ observations) provides estimates for the release times
of electrons and protons. Our analysis indicates that proton acceleration was
delayed compared to the electrons. The dynamics of the interplanetary type II
burst identify the burst source as a bow shock created by the fast CME. The
type III burst groups, with start times close to the estimated electron release
times, trace electron beams travelling along open field lines into the
interplanetary space. The type III bursts seem to encounter a steep density
gradient as they overtake the type II shock front, resulting in an abrupt
change in the frequency drift rate of the type III burst emission. Our study
presents evidence in support of a scenario in which electrons are accelerated
low in the corona behind the CME shock front, while protons are accelerated
later, possibly at the CME bow shock high in the corona.Comment: Solar Physics, November 2007, in pres
Tracking of an electron beam through the solar corona with LOFAR
© ESO 2018. The Sun's activity leads to bursts of radio emission, among other phenomena. An example is type-III radio bursts. They occur frequently and appear as short-lived structures rapidly drifting from high to low frequencies in dynamic radio spectra. They are usually interpreted as signatures of beams of energetic electrons propagating along coronal magnetic field lines. Here we present novel interferometric LOFAR (LOw Frequency ARray) observations of three solar type-III radio bursts and their reverse bursts with high spectral, spatial, and temporal resolution. They are consistent with a propagation of the radio sources along the coronal magnetic field lines with nonuniform speed. Hence, the type-III radio bursts cannot be generated by a monoenergetic electron beam, but by an ensemble of energetic electrons with a spread distribution in velocity and energy. Additionally, the density profile along the propagation path is derived in the corona. It agrees well with three-fold coronal density model by (1961, ApJ, 133, 983)
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