Browsing by Subject "Corona"

Sort by: Order: Results:

Now showing items 1-3 of 3
  • Majumdar, Satabdwa; Tadepalli, Srikar Paavan; Maity, Samriddhi Sankar; Deshpande, Ketaki; Kumari, Anshu; Patel, Ritesh; Gopalswamy, Nat (2021)
    We report on a multi-wavelength analysis of the 26 January 2014 solar eruption involving a coronal mass ejection (CME) and a Type-II radio burst, performed by combining data from various space and ground-based instruments. An increasing standoff distance with height shows the presence of a strong shock, which further manifests itself in the continuation of the metric Type-II burst into the decameter-hectometric (DH) domain. A plot of speed versus position angle (PA) shows different points on the CME leading edge traveled with different speeds. From the starting frequency of the Type-II burst and white-light data, we find that the shock signature producing the Type-II burst might be coming from the flanks of the CME. Measuring the speeds of the CME flanks, we find the southern flank to be at a higher speed than the northern flank; further the radio contours from Type-II imaging data showed that the burst source was coming from the southern flank of the CME. From the standoff distance at the CME nose, we find that the local Alfv en speed is close to the white-light shock speed, thus causing the Mach number to be small there. Also, the presence of a streamer near the southern flank appears to have provided additional favorable conditions for the generation of shock-associated radio emission. These results provide conclusive evidence that the Type-II emission could originate from the flanks of the CME, which in our study is from the southern flank of the CME.
  • Lumme, E.; Kazachenko, M. D.; Fisher, G. H.; Welsch, B. T.; Pomoell, J.; Kilpua, E.K.J. (2019)
    We study how the input-data cadence affects the photospheric energy and helicity injection estimates in eruptive NOAA Active Region 11158. We sample the novel 2.25-minute vector magnetogram and Dopplergram data from the Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory (SDO) spacecraft to create input datasets of variable cadences ranging from 2.25 minutes to 24 hours. We employ state-of-the-art data processing, velocity, and electric-field inversion methods for deriving estimates of the energy and helicity injections from these datasets. We find that the electric-field inversion methods that reproduce the observed magnetic-field evolution through the use of Faraday's law are more stable against variable cadence: the PDFI (PTD-Doppler-FLCT-Ideal, where PTD refers to Poloidal-Toroidal Decomposition, and FLCT to Fourier Local Correlation Tracking) electric-field inversion method produces consistent injection estimates for cadences from 2.25 minutes up to two hours, implying that the photospheric processes acting on time scales below two hours contribute little to the injections, or that they are below the sensitivity of the input data and the PDFI method. On other hand, the electric-field estimate derived from the output of DAVE4VM (Differential Affine Velocity Estimator for Vector Magnetograms), which does not fulfill Faraday's law exactly, produces significant variations in the energy and helicity injection estimates in the 2.25 minutes - two hours cadence range. We also present a third, novel DAVE4VM-based electric-field estimate, which corrects the poor inductivity of the raw DAVE4VM estimate. This method is less sensitive to the changes of cadence, but it still faces significant issues for the lowest of considered cadences (two hours). We find several potential problems in both PDFI- and DAVE4VM-based injection estimates and conclude that the quality of both should be surveyed further in controlled environments.
  • Kumari, Anshu (2022)
    We study the association of solar Type IV radio bursts with the location of active regions on the Sun during Solar Cycle 24. The active regions associated with moving and stationary Type IV bursts are categorized as close to disk center and far from disk center, based on their location on the solar surface (i.e. ≤ 45◦ or ≥ 45◦, respectively). The location of active regions associated with Type IV bursts accompanied with coronal mass ejections (CMEs) are also studied. We found that ≈ 30 – 40% of the active regions are located far from disk center for all the bursts. However, it is found that most of the active regions associated with stationary Type IV bursts are close to disk center (≈ 60 – 70%). The active regions associated with moving Type IV bursts are more evenly distributed across the surface, i.e. ≈ 56% and ≈ 44%, close to disk center and far from disk center, respectively. The fact that most of the bursts have active regions close to disk center indicates that these bursts can be used to obtain physical properties such as electron density and magnetic fields of the CMEs responsible for geomagnetic storms.