The Astrophysical Journal, 752:70 (10pp), 2012 June 10 C 2012.
doi:10.1088/0004-637X/752/1/70
The American Astronomical Society. All rights reserved. Printed in the U.S.A.
OBSERVATIONS OF MULTIPLE SURGES ASSOCIATED WITH MAGNETIC ACTIVITIES IN AR 10484 ON 2003 OCTOBER 25 Wahab Uddin1 , B. Schmieder2 , R. Chandra3 , Abhishek K. Srivastava1 , Pankaj Kumar4 , and S. Bisht3 1
Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, India;
[email protected] 2 LESIA, Observatoire de Paris-Meudon, 92195, Meudon Cedex, France 3 Department of Physics, DSB Campus, Kumaun University, Nainital 263002, India 4 Korea Astronomy and Space Science Institute (KASI), Daejeon 305-348, Republic of Korea Received 2011 December 30; accepted 2012 April 9; published 2012 May 25
ABSTRACT We present a multi-wavelength study of recurrent surges observed in Hα, UV (Solar and Heliospheric Observatory (SOHO)/EIT), and Radio (Learmonth, Australia) from the super-active region NOAA 10484 on 2003 October 25. Several bright structures visible in Hα and UV corresponding to subflares are also observed at the base of each surge. Type III bursts are triggered and RHESSI X-ray sources are evident with surge activity. The major surge consists of bunches of ejective paths forming a fan-shaped region with an angular size of (≈65◦ ) during its maximum phase. The ejection speed reaches up to ∼200 km s−1 . The SOHO/Michelson Doppler Imager magnetograms reveal that a large dipole emerges from the east side of the active region on 2003 October 18–20, a few days before the surges. On 2003 October 25, the major sunspots were surrounded by “moat regions” with moving magnetic features (MMFs). Parasitic fragmented positive polarities were pushed by the ambient dispersion motion of the MMFs and annihilated with negative polarities at the borders of the moat region of the following spot to produce flares and surges. A topology analysis of the global Sun using Potential Field Source Surface shows that the fan structures visible in the EIT 171 Å images follow magnetic field lines connecting the present active region to a preceding active region in the southeast. Radio observations of Type III bursts indicate that they are coincident with the surges, suggesting that magnetic reconnection is the driver mechanism. The magnetic energy released by the reconnection is transformed into plasma heating and provides the kinetic energy for the ejections. A lack of a radio signature in the high corona suggests that the surges are confined to follow the closed field lines in the fans. We conclude that these cool surges may have some local heating effects in the closed loops, but probably play a minor role in global coronal heating and the surge material does not escape to the solar wind. Key words: magnetic reconnection – Sun: chromosphere – Sun: corona – Sun: flares – Sun: magnetic topology – sunspots Online-only material: color figures
with flares (Schmieder et al. 1988, 1995; Uddin et al. 2004; Chandra et al. 2006), and magnetic reconnection may be responsible for the acceleration as well as the heating of the plasma. Another kind of reconnection could occur due to the collision of opposite polarity magnetic fluxes in the “moat region” (Brooks et al. 2007). Small, moving magnetic features (MMFs; Harvey & Harvey 1973; Sainz Dalda & L´opez Ariste 2007; Kitiashvili et al. 2010) are observed as moat regions. The formation of MMFs is closely related to the fragmentation and disintegration of sunspot magnetic fluxes. Recent studies show that the amount of magnetic flux lost by the sunspots is similar to the flux transported in the moat region (Kubo et al. 2008). The flux is annihilated at the border of the moat region, and in consequence, the subflares, jets, and surges may occur during the reconnection processes along neutral lines (Beck et al. 2007; Brooks et al. 2007, 2008; Engell et al. 2011). Theoretical models have been developed concerning canceling flux producing surges or jets. The emerging-flux model of Yokoyama & Shibata (1996) supports this kind of surge dynamics, which may be triggered due to the interaction of an emerging photospheric field with the pre-existing overlying coronal magnetic fields. Although magnetic reconnection and photospheric magnetic activities may be the key in driving many solar surges and other jets, several other mechanisms may also be responsible for the surge/jet dynamics. Pariat et al. (2010) have developed a three-dimensional reconnection model without evidence of an emerging flux. This model is able to generate untwisting
1. INTRODUCTION Solar surge is a collimated ejection of plasma material from the lower solar atmosphere into the corona. These ejecta also exhibit episodic heating and cooling, therefore, they may be visible in the range of emissions from Hα to EUV/UV and X-rays, and can be abbreviated in general as solar jets (Schmieder et al. 1995). The surges may have an initiation velocity of ∼50 km s−1 , which may further increase up to a maximum value of 100–300 km s−1 , and these surges may reach up to heights of 10–200 Mm or even more (Sterling 2000). The lifetime of surges is about 30 minutes, and they can be recurrent with a period of an hour or more (Schmieder et al. 1984, 1995). Usually, the surge is confined to one or several narrow threads of magnetic fields embedded in the plasma that shoot out above the solar surface. However, such surges are mostly associated with the flaring regions and the sites of solar transients where recurrent magnetic reconnection is dominant. The evolution of solar surges has been studied comprehensively in association with magnetic field emergence and cancellation, as well as flaring activities of the solar atmosphere where such plasma jets also appeared twisted and spiraled (e.g., Schmieder et al. 1994; Chae et al. 1999; Yoshimura et al. 2003; Liu & Kurokawa 2004 and references therein). The solar surges may occur in regions of emerging magnetic fluxes in the vicinity of satellite spots (Rust 1968; Roy 1973; Kurokawa & Kawai 1993). Often these surges are associated 1
The Astrophysical Journal, 752:70 (10pp), 2012 June 10
Uddin et al.
above questions and on the possible trigger of the surges: wave or reconnection.
jets when a stress is constantly applied at the photosphere (Rachmeler et al. 2010). Shibata et al. (1982) and Sterling et al. (1993) have reported that the pressure pulse can trigger solar surges of moderate height in the hydrodynamic regime of the solar atmosphere. Solar surges may also be accelerated due to the whip motion of the reconnection-generated, newly formed magnetic field (Shibata et al. 1992; Canfield et al. 1996a), while the reconnection-generated explosive events may also trigger such kinds of plasma dynamics (Madjarska et al. 2009). In addition to the typical solar surges, Georgakilas et al. (1999) have observed the polar surges as cool jets at polar region without any association with transients. Recently, the cool jets and surges have also been modeled, respectively, in the polar region as well as near the boundary of a nonflaring active region due to the reconnection-generated velocity pulses in the ideal magnetohydrodynamic (MHD) regime of the solar atmosphere (Srivastava & Murawski 2011; Kayshap et al. 2012). In conclusion, the solar surges and other various types of solar jets may be excited via both, e.g., the direct magnetic reconnection processes in the emerging field regions, as well as due to the magnetohydrodynamic wave activities. During 2003 October–November, major solar activity originated from three super-active regions, namely, NOAA AR 10484, 10486, and 10488. The active region NOAA 10484 (N05W29) evolved on 2003 October 25 and was very complex, having a βγ δ configuration. This active region has produced many recurrent surges and flare activities during its passage on the solar disk. It produced major surge activities on 2003 October 22 and 25. On October 25, we observed recurrent surges between 01:50 UT and 04:15 UT. A preliminary report on these observations has been presented in Uddin et al. (2010). In this active region, there was no evidence of strong emerging magnetic fluxes during the recurrent surges. Many questions arise around the surge activity. What is the trigger mechanism of the surges? Are they due to reconnection with the pre-existing field lines? What are the dynamics of the magnetic boundary causing the collision of opposite polarities? Are the pre-existing field lines open or closed at the periphery of the active region? Commonly, outflows are observed at the periphery of active regions (Harra et al. 2008; Del Zanna 2008). McIntosh & De Pontieu (2009) claimed that dynamic chromospheric spicules in the outskirts of active regions are related to these outflows. Warren et al. (2011) and Ugarte-Urra & Warren (2011) claimed that there is no direct relationship between these two populations of structures, i.e., the hot and cool loops maintained, respectively, at mega/sub-mega-Kelvin temperatures. The question arises whether or not these observed surges in AR 10484 may participate in the commonly observed outflows in the outskirts of active regions. To understand this issue, statistical studies should be done to find if any relationship between these cool jets and the outflows of hot plasma commonly observed at the periphery of active regions exists. However, this topic is out of the scope of the present work. In this paper, we present a detailed multi-wavelength study of recurrent surges and their associated events (e.g., flares) as occurred in AR 10484. In Section 2, we present the details of the data sets used in this study. The multi-wavelength evolution of the surges and their association with subflares are described in Section 3. In Section 4, we describe the magnetic field evolution of an active region before and during the surges and associated flares. We discuss the possibility for a decaying active region and its magnetic activities to produce surges, and in the last section, we present our conclusions from our results in the frame of the
2. OBSERVATIONAL DATA SETS The data sets used for our present study have been taken from the following sources. Hα Data. The Hα observations of the flare and associated surges were carried out at ARIES, Nainital, India by using the 15 cm f/15 Coud´e solar tower telescope equipped with Hα filter. The image size was enlarged by a factor of two using a Barlow lens. The images were recorded by a 16 bit 576×384 pixel CCD camera system having a pixel size of 22 μ2 . The resolution of the images is 1 pixel−1 . The cadence for the images is ∼15–20 s. Solar and Heliospheric Observatory (SOHO)/Michelson Doppler Imager (MDI) Data. To understand the evolution of the magnetic complexity of the active region, we use SOHO/MDI data. The magnetic field data were taken from the SOHO/MDI instrument (Scherrer et al. 1995). The cadence of images is 96 minutes and the pixel resolution is 1. 98. SOHO/EIT Data. SOHO/EIT (Delaboudini`ere et al. 1995) observes the full-disk Sun with a cadence of 12 minutes and a pixel resolution of 2. 5. It observes in four spectral bands centered on Fe ix/x (171 Å), Fe xii (195 Å), Fe xv (284 Å), and He ii (304 Å). For our current study, we used the 171 Å data. X-Ray Data. To understand the evolution of flares and associated surges, we reconstructed X-ray images from the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI; Lin et al. 2002). We reconstructed the images in the 6–12 keV energy band from collimators (3F to 9F) using the CLEAN algorithm, which has a spatial resolution of ≈7 (Hurford et al. 2002). 3. MULTI-WAVELENGTH OBSERVATIONS OF RECURRENT SURGES AND ASSOCIATED FLARES The multi-wavelength evolution of the observed solar surges and their association with flares are described in the following subsections. 3.1. Temporal Variations of Hα Surges and Flares The ARIES Hα images during the surge activities on 2003 October 25 from NOAA AR 10484 are presented in Figure 1. They show the dynamic evolution of the recurrent surge activity from 01:50 UT to 04:15 UT. During the above-mentioned time period, we observed several surges in Hα. The surge activity occurred in the following satellite sunspots of the active region NOAA AR 10484. Seven surges (Surge 1 to Surge 7) were identified (Figure 1, see the arrows). Four of them were clearly associated with Hα brightenings. To investigate in more detail the surge evolution and the Hα brightenings at their footpoints, we computed the Hα relative intensity profile of the brightenings, the time of the Hα brightening maxima, the onsets of surges, and the time when the surge vanishes (Figure 2 and Table 1). In Figure 2, we also present the GOES soft X-ray light curve obtained by the full-disk integration (top panel) and the RHESSI satellite thermal emission (6–12 keV) of the AR 10484 (middle panel). Unfortunately the latter curve has large time gaps, however, we are able to identify two flares at ∼3:00 UT and at ∼4:00 UT. By comparing the three light curves of Figure 2, we conclude that all the C class X-ray flares of the GOES curve (Flares 1, 2, and 3 with three bumps) occur in AR 10484, except for one at 02:02 UT which is observed in the 2
The Astrophysical Journal, 752:70 (10pp), 2012 June 10
Uddin et al.
Flare 1 Surge 1
Flare 2
Surge 2
Flare 3 Surge 3
Surge 4 Surge 5
Flare 3
Reference foot-point
Surge 6
Leading edge
Surge 7
Figure 1. Hα image sequence showing the recurrent flare/surge activities on 2003 October 25 in AR 10484. The field of view of each image is 320 × 200 . (A color version of this figure is available in the online journal.) Table 1 Details of the Surges and Flares Name of Surge
Surge Onset
Hα Max Intensity
Max GOES
Flare Class
No. of Flare
Max RHESSI
Max Surge Length
Type III
1 2 3 4 5 6 7
1:50 3:05 3:36 3:50 3:42
