Presentation is loading. Please wait.

Presentation is loading. Please wait.

References [1] Handy, B.N., et al. Solar Phys., 187, 229, 1999. [2] Aschwanden, M.J., & Alexander, D., Solar Phys., 204, 91, 2001. [3] Khodachenko, M.L.,

Similar presentations


Presentation on theme: "References [1] Handy, B.N., et al. Solar Phys., 187, 229, 1999. [2] Aschwanden, M.J., & Alexander, D., Solar Phys., 204, 91, 2001. [3] Khodachenko, M.L.,"— Presentation transcript:

1 References [1] Handy, B.N., et al. Solar Phys., 187, 229, [2] Aschwanden, M.J., & Alexander, D., Solar Phys., 204, 91, [3] Khodachenko, M.L., et al., A&A, 433, 691, [4] Khodachenko, M.L., et al., Space Science Rev., 122, 137, [5] Dulk, G.A., 1985, Ann.Rev.Astron.Astrophys. 23, 169. [6] Aschwanden, M.J., et al., Solar Phys., 206, 99, ABSTRACT Low-frequency (LF) modulations of solar microwave radiation (37 GHz; 11.7 GHz), recorded at the Metsaehovi Radio Observatory, are considered. A fast Fourier transformation with a sliding window is used to obtain the dynamic spectra of the LF modulating signals. Special attention in the present study is paid to the analysis of modulations of microwave emission recorded at the same time when TRACE EUV telescope observed large scale oscillations of coronal loops. The applied data analysis technique, besides of the modulations probably connected with loop oscillations detected by TRACE, makes possible to detect additional modulations, which may be associated with oscillations of smaller (invisible for TRACE) loops. These modulations can be connected as well with specific wave modes (sausage mode) excited in solar coronal structures. Comparative analysis of phases of oscillations of TRACE loops and the microwave emission modulation allows deeper insight into the global dynamics and structure of solar active regions. 1. INTRODUCTION The solar corona has a highly dynamic and complex structure. It consists of a large number of constantly evolving, loops and filaments, which interact with each other and are closely associated with the local magnetic field. The non-stationary character of solar plasma-magnetic structures appears in various forms of the coronal magnetic loops dynamics (grow motions, oscillations, meandering, twisting) [1]. Energetic phenomena, related to these types of magnetic activity, range from tiny transient brightenings (micro-flares) and jets to large, active-region-sized flares and CMEs. They are naturally accompanied by different kinds of electromagnetic emission, covering a wide frequency band from radio waves to gamma-rays. Produced within a given plasma environment, the radiation carries signature of physical and dynamic conditions in a radiating source. Multi-frequency observations of solar active regions, including EUV, soft X-ray, and radio wavelengths indicate that quite often multiple loops are involved in flaring processes and post-flare dynamics [2]. Thus, it is natural to expect that structural complexity of active regions will manifest itself also in temporal peculiarities of the emitted radiation. Analysis of the Low-Frequency (LF) fluctuations of solar microwave radiation appears as a relatively new direction of investigations in the traditional branch of the microwave radio astronomy [3, 4]. A physical idea in the background of our approach consists in the following. Microwave radiation of solar flares is usually interpreted as a gyrosynchrotron radiation produced by fast electrons on harmonics of the gyrofrequency B in the magnetic field B of a flaring loop. In the case of a power-low distribution of electrons in energy n(E) ~ E -d, the intensity of gyrosynchrotron radiation from an optically thin loop is [5]: I ~ (sin Θ) – d B ( / B ) d ∎ 2. OBSERVATIONS We analyze the spectral and temporal evolution of the LF pulsations modulating solar microwave radiations recorded at the Metsähovi Radio Observatory (Finland) at 37 GHz and 11.7 GHz. Metsähovi radio telescope, having a 14-m dish, provides width of the antenna beam pattern at 37 GHz: 2.4' sensitivity of the receiver: ~ 0.1 sfu (10-23 W m-2 Hz-1) time resolution: s ‘Sliding window’ Fourier analysis with different kinds of windows, signal averaging and filtration techniques are applied to the experimental data for the study of LF modulation of the microwave radiation intensity. A sample of specially selected events, when TRACE observed oscillating coronal magnetic loops in EUV was considered. At 37 GHz the spatial resolution of the radio telescope allows to localize an active region containing the radiating source, which makes a possibility to perform direct comparison of the microwave radiation features and dynamics of coronal loops observed by TRACE. At 11.7 GHz the radiation is collected from the whole solar disc. But even in this case it is possible sometimes to distinguish the radiation features related to the energy release and dynamic phenomena in particular active regions. Detection of solar coronal magnetic loop oscillations in microwaves M.L. Khodachenko 1, A.G. Kislyakov 2,3, H.O. Rucker 1, V.V. Zaitsev 2, S. Urpo 4 1 Space Research Institute, Austrian Academy of Sciences, Schmiedlstr.6, A-8042 Graz, Austria 2 Institute of Applied Physics, Russian Academy of Sciences, Ulyanov str. 46, , Nizhny Novgorod, Russia 3 Lobachevsky’s State University, Gagarin av. 23, , Nizhny Novgorod, Russia 4 Metsaehovi Radio Observatory, Metsaehovintie 114, 02540, Kylmaelae, Finland Typical observed values: 2 < d < 7  I ~ (sin  ) 0.87… 4.12 B 1.58 … 6.08 Large-scale oscillations of a loop, containing the microwave source, can modulate I due to motion of the emission diagram beam. LF variations of the electric current in a radiating source, which in their turn produce the LF disturbances of B, can modulate I Therefore, the dynamical spectra of the LF pulsations can be used for diagnostics of magnetic field (electric currents) slow variations in a radiating source on the Sun (i.e. LF disturbances of B) study of the large-scale motion of radiating magnetic loops - Shape deformation  LF disturbances of B - Loop motion  motion of the emission diagram beam ∎ 3 events with oscillating loops, observed by TRACE and in microwaves are considered ∎ 2000-Mar-23, 11:30-12: AR8910; oscillating loops after M2.0 flare 37GHz (AR is well resolved) ∎ 2001-Sep-15, 11:23-12: AR9608; oscillating loops associated with M flare at 10: GHz (full disc) ∎ 2001-Sep-07, 15: AR9601; oscillating loops associated with M flare activity 11.7GHz (full disc) 2.1 OSCILLATING LOOPS on 2000-Mar-23 Oscillating loops were observed by TRACE in the active region AR 8910 (near western limb) at 11:30-12:00 after M2.0 flare [6]. Fig.1 Oscillating TRACE loops The period of loops oscillations observed by TRACE on Mar. 23, 2000 is 615 s (group of loops) ∎ Modulation of Microwave Radiation on 2000-Mar-23 The active region AR 8910 can be clearly seen on the radio map of the solar disk at 37 GHz on Mar. 23, 2000 (Fig.2a). a. b. Fig.2 a) 37GHz Radio map of the Sun b) Dynamic spectrum of LF modulation of the 37 GHz radiation a. b. Fig.3 a) Relative spectral density of modulating signals b) Comparison of the 10 min modulating signal and amplitude of the 10 min oscillation of TRACE loops AR 8910 Besides of the 10 min modulation which can be related to the observed by TRACE 10 min oscillations of coronal loops, 5 min; 159 s; 117 s; and 85 s modulations are detected in microwave radiation on Mar.23, 2000 after M2.0 flare at 11:30-12:00 (see Fig.3a). These may be may be caused by oscillations of smaller loops, or can be connected to specific wave modes (sausage) excited in coronal structures AR 8910 Filtered 10 min component of modulating signal Transverse motion of the loop Opposite phases of the 10 min modulation component and the amplitude of the TRACE loop oscillation (Fig.3b), together with the presence of the additional 5 min (=10 min / 2) modulation in microwave radiation could be an indication that 10 min modulation of radiation is due to the emission diagram motion, whereas 5 min component is caused by the accompanying magnetic stress which takes place twice per each kink period. 2.2 OSCILLATING LOOPS on 2001-Sep-15 Oscillating loops associated with M flare were observed by TRACE in the active region AR9608 at 10:58. Fig.4 Oscillating TRACE loops (12-15 min oscillations) 2.3 OSCILLATING LOOPS on 2001-Sep-07 Oscillating loops were observed by TRACE in the active region AR 9601 after M flare at 15:35. Fig.6 Oscillating TRACE loops (~10 min oscillations) AR CONCLUSION: Further development and testing of the pro- posed approaches is strongly dependent on a possibility of parallel ob servational campaigns (or availability of simultaneous data sets) cove- ring different frequency ranges (EUV, optics, Decameter radio). ∎ Modulation of Microwave Radiation on 2001-Sep-07 LF modulation of 11.7 GHz solar emission on Sep. 07, Similar to the event of Sep.15, 2001 all the flare related post-flare LF modulations can be identified (see Fig.7) as features started after the flare burst. Fig.7 Dynamic spectrum of LF modulation and microwave intensity profile after flare on Sep.07, 2001 The analysis of pre- and post- flare LF modulations of solar microwave radio emission during the event on Sep.07, 2001 allows to conclude that ● All modulations (except of 27 min) start after the flare and show damping ● Loop oscillations, corresponding to 10 min and 6.2 min lines may be ob- served by TRACE (fact of observations needs to be confirmed) ● 4.8 min, 3.9 min and 3 min modulations may be caused by oscillations of smaller loops, or can be connected to specific MHD loop modes. 4.3 mHz (~ 3.9 min) 3.5 mHz (~ 4.8 min) 5.5 mHz (~ 3 min) 2.7 mHz (~ 6.2 min) 1.7 mHz (~ 10 min) 0.6 mHz (~ 27 min) ∎ Modulation of Microwave Radiation on 2001-Sep-15 LF modulation of 11.7 GHz solar emission on Sep. 15, The active region can not be resolved by the radio telescope, but the flare related post- flare LF modulations can be clearly identified on Fig.5 as features started right after the flare burst. Fig.5 Dynamic spectrum of LF modulation and microwave intensity profile before and after flare on Sep. 15, 2001 The analysis of LF modulations of solar microwave radio emission during the event on Sep.15, 2001 allows to conclude that ● All modulations appeared after flare are damped during several periods ● 12 min modulation which is close to the period of coronal loop kink oscil- lation observed by TRACE may be connected to this oscillation. ● 7 min, 4.4 min and 3.3 min modulations may be caused by kink oscillati- ons of smaller loops, or can be connected to specific wave modes. Simul- taneous presence of 3.3 min and 7 min modulations may be a signature of the modulation mechanism connected with the emission diagram mo- tion (similar to the case on Mar, 23, 2000). ● 55 min modulation which exists also before the flare (see Fig.5), probably comes from another AR, or is connected to solar seismology processes. 5 mHz (~ 3.3 min) 3.8 mHz (~ 4.4 min) 2.4 mHz (~ 7 min) 1.4 mHz (~ 12 min) 0.3 mHz (~ 55 min) AR 9601 Ref.No. COSPAR2006-A This work was supported by grant of the Austrian FWF (Project P16919-N08)


Download ppt "References [1] Handy, B.N., et al. Solar Phys., 187, 229, 1999. [2] Aschwanden, M.J., & Alexander, D., Solar Phys., 204, 91, 2001. [3] Khodachenko, M.L.,"

Similar presentations


Ads by Google