scholarly journals Type III Radio Bursts Observations on 20th August 2017 and 9th September 2017 with LOFAR Bałdy Telescope

2021 ◽  
Vol 13 (1) ◽  
pp. 148
Author(s):  
Bartosz Dabrowski ◽  
Paweł Flisek ◽  
Katarzyna Mikuła ◽  
Adam Froń ◽  
Christian Vocks ◽  
...  
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
High Sensitivity ◽  
Single Mode ◽  
Solar Dynamics Observatory ◽  
Type Iii ◽  
Single Station ◽  
Solar Dynamics ◽  
Imaging Spectrograph ◽  
Radio Event

We present the observations of two type III solar radio events performed with LOFAR (LOw-Frequency ARray) station in Bałdy (PL612), Poland in single mode. The first event occurred on 20th August 2017 and the second one on 9th September 2017. Solar dynamic spectra were recorded in the 10 MHz up to 90 MHz frequency band. Together with the wide frequency bandwidth LOFAR telescope (with single station used) provides also high frequency and high sensitivity observations. Additionally to LOFAR observations, the data recorded by instruments on boards of the Interface Region Imaging Spectrograph (IRIS) and Solar Dynamics Observatory (SDO) in the UV spectral range complement observations in the radio field. Unfortunately, only the radio event from 9th September 2017 was observed by both satellites. Our study shows that the LOFAR single station observations, in combination with observations at other wavelengths can be very useful for better understanding of the environment in which the type III radio events occur.

scholarly journals Multi-Stranded Coronal Loops: Quantifying Strand Number and Heating Frequency from Simulated Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) Observations

Solar Physics ◽  
2021 ◽  
Vol 296 (6) ◽  
Author(s):  
Thomas Williams ◽  
Robert W. Walsh ◽  
Stephane Regnier ◽  
Craig D. Johnston
Keyword(s):  
Energy Content ◽  
Time Lag ◽  
Low Frequency ◽  
Building Blocks ◽  
Coronal Loops ◽  
Loop Model ◽  
Solar Dynamics Observatory ◽  
Heat Deposition ◽  
Total Energy Content ◽  
Solar Dynamics

AbstractCoronal loops form the basic building blocks of the magnetically closed solar corona yet much is still to be determined concerning their possible fine-scale structuring and the rate of heat deposition within them. Using an improved multi-stranded loop model to better approximate the numerically challenging transition region, this article examines synthetic NASA Solar Dynamics Observatory’s (SDO) Atmospheric Imaging Assembly (AIA) emission simulated in response to a series of prescribed spatially and temporally random, impulsive and localised heating events across numerous sub-loop elements with a strong weighting towards the base of the structure: the nanoflare heating scenario. The total number of strands and nanoflare repetition times is varied systematically in such a way that the total energy content remains approximately constant across all the cases analysed. Repeated time-lag detection during an emission time series provides a good approximation for the nanoflare repetition time for low-frequency heating. Furthermore, using a combination of AIA 171/193 and 193/211 channel ratios in combination with spectroscopic determination of the standard deviation of the loop-apex temperature over several hours alongside simulations from the outlined multi-stranded loop model, it is demonstrated that both the imposed heating rate and number of strands can be realised.

scholarly journals Signatures of red-shifted footpoints in the quiescent coronal loop system

2019 ◽  
Author(s):  
Yamini K. Rao ◽  
Abhishek K. Srivastava ◽  
Pradeep Kayshap ◽  
Bhola N. Dwivedi
Keyword(s):  
Spectral Data ◽  
Coronal Loop ◽  
Doppler Velocity ◽  
Coronal Loops ◽  
Solar Dynamics Observatory ◽  
Heating Mechanism ◽  
Multi Wavelength ◽  
Solar Dynamics ◽  
Impulsive Heating ◽  
Imaging Spectrograph

Abstract. We observed quiescent coronal loops using multi-wavelength observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) on 2016 April 13. The flows at the footpoints of such loop systems are studied using spectral data from Interface Region Imaging Spectrograph (IRIS). The Doppler velocity distributions at the footpoints lying in the moss region show the negligible or small flows at Ni I, Mg II k3 and C II line corresponding to upper photospheric and chromospheric emissions. Significant red-shifts (downflows) ranging from (1 to 7) km s−1 are observed at Si IV (1393.78 Å; log(T/K) = 4.8) which is found to be consistent with the existing results regarding dynamical loop systems and moss regions. Such downflows agree well with the impulsive heating mechanism reported earlier.

scholarly journals Evolution of downflows in the transition region above a sunspot over short time-scales

2020 ◽  
Vol 640 ◽  
pp. A120
Author(s):  
C. J. Nelson ◽  
S. Krishna Prasad ◽  
M. Mathioudakis
Keyword(s):  
Transition Region ◽  
Time Scales ◽  
Spectral Lines ◽  
Formation Mechanisms ◽  
Coronal Loops ◽  
Imaging Data ◽  
Solar Dynamics Observatory ◽  
Solar Dynamics ◽  
Short Time ◽  
Imaging Spectrograph

Context. Downflows with potentially super-sonic velocities have been reported to occur in the transition region above many sunspots; however, how these signatures evolve over short time-scales in both spatial and spectral terms is still unknown and requires further research. Aims. In this article, we investigate the evolution of downflows detected within spectral lines sampling the transition region on time-scales of the order of minutes and we search for clues as to the formation mechanisms of these features in co-temporal imaging data. Methods. For the purposes of this article, we used high-resolution spectral and imaging data sampled by the Interface Region Imaging Spectrograph on the 20 and 21 May 2015 to identify and analyse downflows. Additionally, photospheric and coronal imaging data from the Hinode and Solar Dynamics Observatory satellites were studied to provide context about the wider solar atmosphere. Results. Four downflows were identified and analysed through time. The potential super-sonic components of these downflows had widths of around 2″ and were observed to evolve over time-scales of the order of minutes. The measured apparent downflow velocities were structured both in time and space, with the highest apparent velocities occurring above a bright region detected in Si IV 1400 Å images. Downflows with apparent velocities below the super-sonic threshold that was assumed here were observed to extend a few arcseconds away from the foot-points, suggesting that the potential super-sonic components are linked to larger-scale flows. The electron density and mass flux for these events were found to be within the ranges of 109.6–1010.2 cm−3 and 10−6.81–10−7.48 g cm−2 s−1, respectively. Finally, each downflow formed at the foot-point of thin “fingers”, extending out around 3–5″ in Si IV 1400 Å data with smaller widths (< 1″) than the super-sonic downflow components. Conclusions. Downflows can appear, disappear, and recur within time-scales of less than one hour in sunspots. As the potential super-sonic downflow signatures were detected at the foot-points of both extended fingers in Si IV 1400 SJI data and sub-sonic downflows in Si IV 1394 Å spectra, it is likely that these events are linked to larger-scale flows within structures such as coronal loops.

scholarly journals Space Weather Study through Analysis of Solar Radio Bursts detected by a Single Station CALLSTO Spectrometer

2021 ◽  
Author(s):  
Theogene Ndacyayisenga ◽  
Ange Cynthia Umuhire ◽  
Jean Uwamahoro ◽  
Christian Monstein
Keyword(s):  
Space Weather ◽  
Solar Flares ◽  
Solar Radio ◽  
Low Cost ◽  
Radio Bursts ◽  
Solar Dynamics Observatory ◽  
Solar Radio Bursts ◽  
Type Iii ◽  
Type Iv ◽  
Single Station

Abstract. This article summarizes the results of an analysis of solar radio bursts detected by the e-Compound Astronomical Low cost Low-frequency Instrument for spectroscopy and Transportable Observatory (e-CALLISTO) spectrometer hosted by the University of Rwanda, College of Education. The data analysed were detected during the first year (2014–2015) of the instrument operation. The Atmospheric Imaging Assembly (AIA) images on board the Solar Dynamics Observatory (SDO) were used to check the location of propagating waves associated with type III radio bursts detected without solar flares. Using quick plots provided by the e-CALLISTO website, we found a total of 202 solar radio bursts detected by the CALLISTO station located in Rwanda. Among them, 5 are type IIs, 175 are type IIIs, and 22 type IVs radio bursts. It is found that all analysed type IIs and ∼37 % of type III bursts are associated with impulsive solar flares while Type IV radio bursts are poorly associated with flares. Furthermore, all of the analysed type II bursts are associated with CMEs which is consistent with the previous studies, and ∼44 % of type IIIs show association with CMEs. On the other hand it is observed that the majority of type IV radio bursts are believed to be originated from CME-driven shocks. Findings from this study confirms that solar radio bursts (SRBs) from ground observation and analysis constitute a clue to diagnose the space weather phenomena such as solar flare and CMEs and to some extent, they may serve as the advance warning of the related severe space weather hazards.

Strongly structured radio emission observed by LOFAR on August 25, 2014

2020 ◽  
Author(s):  
Jasmina Magdalenic ◽  
Christophe Marque ◽  
Richard Fallows ◽  
Gottfried Mann ◽  
Christian Vocks ◽  
...  
Keyword(s):  
Radio Emission ◽  
Electron Beams ◽  
Low Frequency ◽  
Impulsive Phase ◽  
Continuum Emission ◽  
Type Ii ◽  
Type Iii ◽  
Type Iv ◽  
Fine Structures ◽  
Radio Event

&lt;p&gt;On August 25, 2014, NOAA AR 2146 produced the M2.0 class flare (peaked at 15:11 UT). The flare was associated with a halo CME and a radio event observed by LOFAR (the LOw-Frequency Array). The radio event consisted of a type II, type III and type IV radio emissions. In this study, we present LOFAR observations of the type II (radio signatures of shock waves) and type III bursts (radio signatures of fast electron beams propagating along open or quasi open field lines). &amp;#160;Both, the type II burst and type III bursts show strong fragmentation of the radio emission. Although fine structures of type II bursts were already reported, the richness of the fine structures observed in the studied event is unprecedented. We found type II fine structures morphologically very similar to the ones sometimes seen superposed on type IV continuum emission, and similar to simple narrowband super short structures (Magdalenic et al., 2006). The group of type III bursts was as usually, observed during the impulsive phase of the flare. The high frequency/time resolution LOFAR observations reveal that only few of the observed type III bursts have a smooth emission profile, and the majority of bursts is strongly fragmented. Surprisingly, fine structures of some type III bursts show similarities to the fine structures observed in the type II burst, but on a smaller frequency scale. Some of the type III bursts show a non-organized patchy structure which gives an indication on the possibly related turbulence processes. We show that these LOFAR observations bring completely new insight and pose a new challenge for the physics of the acceleration of electron beams and associated emission processes.&lt;/p&gt;

scholarly journals Geomagnetically induced currents in the New Zealand power system

2021 ◽  
Author(s):  
Kamran Mukhtar
Keyword(s):  
New Zealand ◽  
High Frequency ◽  
Low Frequency ◽  
Power Network ◽  
Geomagnetically Induced Currents ◽  
Period Range ◽  
The North ◽  
Single Station ◽  
Frequency Components ◽  
Induced Currents

<p><b>This thesis focuses on the use of magnetotelluric (MT) data from both the North Island and South Island of New Zealand to model Geomagnetically Induced Currents (GIC) in the New Zealand power network. The model results have been compared with those from a previously used thin-sheet (TS) conductance model and with measured GIC. </b></p> <p>Initially, a single station modelling approach using a uniform conductivity Earth model is used to model the measured GIC in a transformer at Islington (ISL). This model is further improved by separately modelling low and high frequency components of GIC and then combining these to give full GIC. The model reproduces most of the GIC variations and the correlation coefficient is >70% for major magnetic storms from 2002-2015. As the model reproduces an average response of the network towards geoelectric fields it underestimates the most of extreme GIC. The analysis of GIC from other substations suggests that measured GIC depend on local geoelectric fields and the substation configuration within the network which cannot be captured using a single station approach. These limitations of single station model are addressed using more realistic geoelectric fields based on magnetotelluric data and consideration of the full network. </p> <p>To compute geoelectric fields in the whole network the gaps between MT sites are filled using a Nearest Neighbor interpolation technique. As the northern part of the North Island has no MT data an equivalent circuit approach is followed to model GIC for only the lower part of the network. The MT model GIC are in the period range of 2-30 minutes, based on the available MT data period range. Both the MT and TS techniques are used to compute geoelectric fields and to model GIC for the St. Patrick’s Day storm of 2015 and a 20 November 2003 magnetic storm. Both the MT and TS methods show the same transformers as experiencing large GIC during both storms. The primary difference between the models is that amplitudes of high frequency components of the TS model are significantly smaller than for the MT model. In particular they do not produce large GIC during the sudden storm commencement (SSC) of the St. Patrick’s Day magnetic storm. For the 20 November 2003 storm the TS model effectively reproduces the low frequency components and extreme GIC. The model results show that the North Island power network could be at risk during adverse space weather conditions.</p> <p>Although the South Island has sparser MT data the same technique is used to model SI GIC during both the St. Patrick’s Day and 2003 magnetic storms. Results are compared with measured data from ISL, South Dunedin (SDN) and Halfway Bush (HWB) transformers. The MT model effectively reproduces the measured GIC variations particularly during SSC during the St. Patrick’s Day storm. The TS model gives a very small GIC magnitude during the SSC. During the 20 November 2003 storm both the MT and TS models reproduce strong amplitudes of low frequency components seen in the ISL measured data. </p> <p>Both the MT and TS models show a substantial scale difference between measured and model GIC both for ISL and HWB transformers that needs to be further explored either in terms of better geoelectric interpolation or power network parameters. Overall, the MT model appears much more promising for future GIC modelling, particularly during a sudden storm commencement and for abrupt GIC variations.</p>

scholarly journals Geomagnetically induced currents in the New Zealand power system

2021 ◽  
Author(s):  
Kamran Mukhtar
Keyword(s):  
New Zealand ◽  
High Frequency ◽  
Low Frequency ◽  
Power Network ◽  
Geomagnetically Induced Currents ◽  
Period Range ◽  
The North ◽  
Single Station ◽  
Frequency Components ◽  
Induced Currents

<p><b>This thesis focuses on the use of magnetotelluric (MT) data from both the North Island and South Island of New Zealand to model Geomagnetically Induced Currents (GIC) in the New Zealand power network. The model results have been compared with those from a previously used thin-sheet (TS) conductance model and with measured GIC. </b></p> <p>Initially, a single station modelling approach using a uniform conductivity Earth model is used to model the measured GIC in a transformer at Islington (ISL). This model is further improved by separately modelling low and high frequency components of GIC and then combining these to give full GIC. The model reproduces most of the GIC variations and the correlation coefficient is >70% for major magnetic storms from 2002-2015. As the model reproduces an average response of the network towards geoelectric fields it underestimates the most of extreme GIC. The analysis of GIC from other substations suggests that measured GIC depend on local geoelectric fields and the substation configuration within the network which cannot be captured using a single station approach. These limitations of single station model are addressed using more realistic geoelectric fields based on magnetotelluric data and consideration of the full network. </p> <p>To compute geoelectric fields in the whole network the gaps between MT sites are filled using a Nearest Neighbor interpolation technique. As the northern part of the North Island has no MT data an equivalent circuit approach is followed to model GIC for only the lower part of the network. The MT model GIC are in the period range of 2-30 minutes, based on the available MT data period range. Both the MT and TS techniques are used to compute geoelectric fields and to model GIC for the St. Patrick’s Day storm of 2015 and a 20 November 2003 magnetic storm. Both the MT and TS methods show the same transformers as experiencing large GIC during both storms. The primary difference between the models is that amplitudes of high frequency components of the TS model are significantly smaller than for the MT model. In particular they do not produce large GIC during the sudden storm commencement (SSC) of the St. Patrick’s Day magnetic storm. For the 20 November 2003 storm the TS model effectively reproduces the low frequency components and extreme GIC. The model results show that the North Island power network could be at risk during adverse space weather conditions.</p> <p>Although the South Island has sparser MT data the same technique is used to model SI GIC during both the St. Patrick’s Day and 2003 magnetic storms. Results are compared with measured data from ISL, South Dunedin (SDN) and Halfway Bush (HWB) transformers. The MT model effectively reproduces the measured GIC variations particularly during SSC during the St. Patrick’s Day storm. The TS model gives a very small GIC magnitude during the SSC. During the 20 November 2003 storm both the MT and TS models reproduce strong amplitudes of low frequency components seen in the ISL measured data. </p> <p>Both the MT and TS models show a substantial scale difference between measured and model GIC both for ISL and HWB transformers that needs to be further explored either in terms of better geoelectric interpolation or power network parameters. Overall, the MT model appears much more promising for future GIC modelling, particularly during a sudden storm commencement and for abrupt GIC variations.</p>

scholarly journals Signatures of red-shifted foot points in the quiescent coronal loop system

2019 ◽  
Vol 37 (4) ◽  
pp. 765-773
Author(s):  
Yamini K. Rao ◽  
Abhishek K. Srivastava ◽  
Pradeep Kayshap ◽  
Bhola N. Dwivedi
Keyword(s):  
Spectral Data ◽  
Coronal Loop ◽  
Doppler Velocity ◽  
Coronal Loops ◽  
Solar Dynamics Observatory ◽  
Heating Mechanism ◽  
Multi Wavelength ◽  
Solar Dynamics ◽  
Impulsive Heating ◽  
Imaging Spectrograph

Abstract. We observed quiescent coronal loops using multi-wavelength observations from the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO) on 13 April 2016. The flows at the foot points of such loop systems are studied using spectral data from the Interface Region Imaging Spectrograph (IRIS). The Doppler velocity distributions at the foot points lying in the moss region show the negligible or small flows at the Ni I, Mg II k3, and C II line corresponding to upper photospheric and chromospheric emissions. Significant red shifts (downflows) ranging from 1 to 7 km s−1 are observed at Si IV (1393.78 Å; log⁡(T/K)=4.8), which is found to be consistent with the existing results regarding dynamical loop systems and moss regions. Such downflows agree well with the impulsive heating mechanism reported earlier.

Electrocorticographic Frequency Alteration Mapping: A Clinical Technique for Mapping the Motor Cortex

2007 ◽  
Vol 60 (suppl_4) ◽  
pp. ONS-260-ONS-271 ◽  
Author(s):  
Eric C. Leuthardt ◽  
Kai Miller ◽  
Nicholas R. Anderson ◽  
Gerwin Schalk ◽  
Joshua Dowling ◽  
...  
Keyword(s):  
Motor Cortex ◽  
High Frequency ◽  
Spectral Power ◽  
Low Frequency ◽  
Active Regions ◽  
High Sensitivity ◽  
Cortical Activation ◽  
Lower Sensitivity ◽  
Positive Electrodes ◽  
Frequency Bands

Abstract Objective: Electrocortical stimulation (ECS) has been well established for delineating the eloquent cortex. However, ECS is still coarse and inefficient in delineating regions of the functional cortex and can be hampered by after-discharges. Given these constraints, an adjunct approach to defining the motor cortex is the use of electrocor-ticographic signal changes associated with active regions of the cortex. The broad range of frequency oscillations are categorized into two main groups with respect to the sensorimotor cortex: low and high frequency bands. The low frequency bands tend to show a power reduction with cortical activation, whereas the high frequency bands show power increases. These power changes associated with the activated cortex could potentially provide a powerful tool in delineating areas of the motor cortex. We explore electrocorticographic signal alterations as they occur with activated regions of the motor cortex, as well as its potential in clinical brain mapping applications. Methods: We evaluated seven patients who underwent invasive monitoring for seizure localization. Each patient had extraoperative ECS mapping to identify the motor cortex. All patients also performed overt hand and tongue motor tasks to identify associated frequency power changes in regard to location and degree of concordance with ECS results that localized either hand or tongue motor function. Results: The low frequency bands had a high sensitivity (88.9–100%) and a lower specificity (79.0–82.6%) for identifying electrodes with either hand or tongue ECS motor responses. The high frequency bands had a lower sensitivity (72.7–88.9%) and a higher specificity (92.4–94.9%) in correlation with the same respective ECS positive electrodes. Conclusion: The concordance between stimulation and spectral power changes demonstrate the possible utility of electrocorticographic frequency alteration mapping as an adjunct method to improve the efficiency and resolution of identifying the motor cortex.

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