Further constraints on electron acceleration in solar noise storms

We reexamine the energetics of nonthermal electron acceleration in solar noise storms. A new result is obtained for the minimum nonthermal electron number density required to produce a Langmuir wave population of sufficient intensity to power the noise storm emission. We combine this constraint with the stochastic electron acceleration formalism developed by Subramanian & Becker (2005) to derive a rigorous estimate for the efficiency of the overall noise storm emission process, beginning with nonthermal electron acceleration and culminating in the observed radiation. We also calculate separate efficiencies for the electron acceleration -- Langmuir wave generation stage and the Langmuir wave -- noise storm production stage. In addition, we obtain a new theoretical estimate for the energy density of the Langmuir waves in noise storm continuum sources.Comment: Accepted for publication in Solar Physic

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

Noise storm continua: power estimates for electron acceleration

We use a generic stochastic acceleration formalism to examine the power $L_{\rm in}$ (${\rm erg s^{-1}}$) 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 $L_{\rm in}$ with the power $L_{\rm out}$ observed in noise storm radiation. Using typical values for the various parameters, we find that $L_{\rm in} \sim 10^{23-26}$ ${\rm erg s^{-1}}$, yielding an efficiency estimate $\eta \equiv L_{\rm out}/L_{\rm in}$ 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

NWCSAF GEO v2016 : new products, changes and improvements

Ponencia presentada en: 2016 EUMETSAT Meteorological Satellite Conference, 26-30 September 2016, Darmstadt, GermanyThe objective of the Nowcasting Satellite Application Facility (NWC SAF) is the generation of satellite derived products for their direct application to Nowcasting for targeted users. To achieve this goal, the NWC SAF team develops, maintains and distributes software packages that allows the users to generate, at their premises and for the user defined area, satellite derived products with a direct application to Nowcasting. The NWC SAF distributes two different software packages for GEO and LEO satellites. Current operational software package for GEO satellites is MSG v2013, distributed in 2013 and applicable to MSG data. Products generated with MSG v2013 include Cloud Products (Cloud Mask, Cloud Top Temperature and Height, Cloud Type, Cloud phase), Precipitation Products (Probability of Precipitation and Convective Rainfall Rate and Probability of Precipitation and Convective Rainfall Rate from Cloud Microphysics), High Resolution Winds (HRW), Water content and Instability Indices, Automatic Satellite Image Interpretation and detection and tracking of Rapidly Developing Convective Cells. A new software package, GEO v2016, has been distributed in November 2016. Main changes and improvements of GEO v2016 respect to previous operational SW package MSG v2013 are highlighted in this paper

NWCSAF GEO v2016 : new products, changes and improvements

Póster presentado en: 2016 EUMETSAT Meteorological Satellite Conference, 26-30 September 2016, Darmstadt, GermanyThe objective of the Nowcasting Satellite Application Facility (NWC SAF) is the generation of satellite derived products for their direct application to Nowcasting for targeted users. To achieve this goal, the NWC SAF team develops, maintains and distributes software packages that allows the users to generate, at their premises and for the user defined area, satellite derived products with a direct application to Nowcasting. The NWC SAF distributes two different software packages for GEO and LEO satellites. Current operational software package for GEO satellites is MSG v2013, distributed in 2013 and applicable to MSG data. Products generated with MSG v2013 include Cloud Products (Cloud Mask, Cloud Top Temperature and Height, Cloud Type, Cloud phase), Precipitation Products (Probability of Precipitation and Convective Rainfall Rate and Probability of Precipitation and Convective Rainfall Rate from Cloud Microphysics), High Resolution Winds (HRW), Water content and Instability Indices, Automatic Satellite Image Interpretation and detection and tracking of Rapidly Developing Convective Cells. A new software package, GEO v2016, has been distributed in November 2016. Main changes and improvements of GEO v2016 respect to previous operational SW package MSG v2013 are highlighted in this paper

LOFAR tied-array imaging and spectroscopy of solar S bursts

Context. The Sun is an active source of radio emission that is often associated with energetic phenomena ranging from nanoflares to coronal mass ejections (CMEs). At low radio frequencies (<100 MHz), numerous millisecond duration radio bursts have been reported, such as radio spikes or solar S bursts (where S stands for short). To date, these have neither been studied extensively nor imaged because of the instrumental limitations of previous radio telescopes. Aims. Here, LOw Frequency ARray (LOFAR) observations were used to study the spectral and spatial characteristics of a multitude of S bursts, as well as their origin and possible emission mechanisms. Methods. We used 170 simultaneous tied-array beams for spectroscopy and imaging of S bursts. Since S bursts have short timescales and fine frequency structures, high cadence (~50 ms) tied-array images were used instead of standard interferometric imaging, that is currently limited to one image per second. Results. On 9 July 2013, over 3000 S bursts were observed over a time period of ~8 h. S bursts were found to appear as groups of short-lived (<1 s) and narrow-bandwidth (~2.5 MHz) features, the majority drifting at ~3.5 MHz s-1 and a wide range of circular polarisation degrees (2−8 times more polarised than the accompanying Type III bursts). Extrapolation of the photospheric magnetic field using the potential field source surface (PFSS) model suggests that S bursts are associated with a trans-equatorial loop system that connects an active region in the southern hemisphere to a bipolar region of plage in the northern hemisphere. Conclusions. We have identified polarised, short-lived solar radio bursts that have never been imaged before. They are observed at a height and frequency range where plasma emission is the dominant emission mechanism, however, they possess some of the characteristics of electron-cyclotron maser emission

The NWCSAF/GEO software package for the MSG/IODC satellite service

Póster presentado en: EUMETSAT Meteorological Satellite Conference celebrada del 2 al 6 de Octubre de 2017 en Roma

Use of NWCSAF NWC/GEO Software Package with MSG, HIMAWARI-8/9 and GOES-13/16 Satellites

Ponencias presentadas en: Joint EUMETSAT/AMS/NOAA Conference 2019 celebrada en Boston del 30 de septiembre al 4 de octubre de 2019

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

Presentación realizada en la 3rd European Nowcasting Conference, celebrada en la sede central de AEMET en Madrid del 24 al 26 de abril de 2019