Reizaburo Kitai

Chromospheric Anemone Jets as Evidence of Ubiquitous Reconnection

The heating of the solar chromosphere and corona is a long-standing puzzle in solar physics. Hinode observations show the ubiquitous presence of chromospheric anemone jets outside sunspots in active regions. They are typically 3 to 7 arc seconds = 2000 to 5000 kilometers long and 0.2 to 0.4 arc second = 150 to 300 kilometers wide, and their velocity is 10 to 20 kilometers per second. These small jets have an inverted Y-shape, similar to the shape of x-ray anemone jets in the corona. These features imply that magnetic reconnection similar to that in the corona is occurring at a much smaller spatial scale throughout the chromosphere and suggest that the heating of the solar chromosphere and corona may be related to small-scale ubiquitous reconnection.

Filament Oscillations and Moreton Waves Associated with EIT Waves

In this paper we compare EUV Imaging Telescope (EIT) waves with simultaneous phenomena seen in Hin order to address the question of what an EIT wave is. We surveyed the events associated with solar flares larger than GOES M-class in 1999-2002. The Hdata are taken with the Flare-monitoring Telescope (FMT) at the Hida Observatory of Kyoto University. Among 14 simultaneous observations of EIT waves and H� ,1 1 were found to have filament eruptions, three were associated with Moreton waves, and one was found to have only filament oscillations. This shows that we cannot see clear wave fronts in Heven if EITwaves exist, but that it is possible to recognize invisible waves by means of filament oscillations. The nature of filament oscillations and Moreton waves associated with EIT waves is examined in detail, and it is found that the filament oscillations were caused by EIT waves.

Simultaneous Observation of a Moreton Wave on 1997 November 3 in Hα and Soft X-Rays

We report the observation of a Moreton wave in Hα (line center and ±0.8 A) with the Flare Monitoring Telescope at the Hida Observatory of Kyoto University at 4:36-4:41 UT on 1997 November 3. The same region (NOAA Active Region 8100) was simultaneously observed in soft X-rays with the soft X-ray telescope on board Yohkoh, and a wavelike disturbance (X-ray wave) was also found. The position of the wave front as well as the direction of propagation of the X-ray wave roughly agree with those of the Moreton wave. The propagation speeds of the Moreton wave and the X-ray wave are about 490 ± 40 and 630 ± 100 km s-1, respectively. Assuming that the X-ray wave is an MHD fast-mode shock, we can estimate the propagation speed of the shock, on the basis of MHD shock theory and the observed soft X-ray intensities ahead of and behind the X-ray wave front. The estimated fast shock speed is 400-760 km s-1, which is in rough agreement with the observed propagation speed of the X-ray wave. The fast-mode Mach number of the X-ray wave is also estimated to be about 1.15-1.25. These results suggest that the X-ray wave is a weak MHD fast-mode shock propagating through the corona and hence is the coronal counterpart of the Moreton wave.

Spectropolarimetric Observation of an Emerging Flux Region: Triggering Mechanisms of Ellerman Bombs

A high spatial resolution observation of an emerging flux region (EFR) was made using a vector magnetograph and a Hα Lyot filtergraph with the Domeless Solar Telescope at Hida Observatory on 2006 October 22. In Hα wing images, we could see many Ellerman bombs (EBs) in the EFR. Observations in two modes, slit scan and slit fixed, were performed with the vector magnetograph, along with the Hα filtergraph. Using the Hα wing images, we detected 12 EBs during the slit scan observation period and 9 EBs during the slit fixed observation period. With the slit scan observation, we found that all the EBs were distributed in the area where the spatial gradient of vertical field intensity was large, which indicates the possibility of rapid topological change in the magnetic field in the area of EBs. With the slit fixed observation, we found that EBs were distributed in the areas of undulatory magnetic fields, in both the vertical and horizontal components. This paper is the first to report the undulatory pattern in the horizontal components of the magnetic field, which is also evidence for emerging magnetic flux triggered by the Parker instability. These results allow us to confirm the association between EBs and emerging flux tubes. Three triggering mechanisms for EBs are discussed with respect to emerging flux tubes: 9 out of 21 EBs occurred at the footpoints of emerging flux tubes, 8 occurred at the top of emerging flux tubes, and 4 occurred in the unipolar region. Each case can be explained by magnetic reconnection in the low chromosphere.

Numerical hydrodynamics of the jet phenomena in the solar atmosphere

One-dimensional hydrodynamic simulations of surges are performed in order to make clear their origin and structure. Surges are regarded as the jets resulting from a sudden pressure increase at the base of the model atmosphere. The height of the explosion (h0), which is measured from the level of τ5000 = 1, is regarded as a free parameter. Another free parameter is the strength of the sudden pressure increase (p/p0) at h0. Simulations are performed for values in the ranges of 540 km ≤ h0 ≤ 1920 km and 3 ≤ p/p0 ≤ 30. It was found that for a fixed p/p0 there exists a critical height (hc) in h0, which separates the jet (surge) models into two types. For h0 > hc, jets are produced directly by the pressure gradient force near h0, and made of the matter ejected from the explosion itself. The essential hydrodynamic structure of this type is the same as that in a shock tube (this type is called ‘shock tube’ type). For h0 < hc, jets are not the direct results of the pressure enhancement, but are produced by the shock wave which are generated by the pressure enhancement and which has propagated through the chromosphere (this type is called the ‘crest shock’ type). It is shown that the critical height (hc) ranges from 1000 km to 1500 km for 3 ≤ p/p0 ≤ 30. General properties of both types are investigated in detail. The results are compared with observations and it is concluded that small surges associated with Ellerman bombsbelong to the ‘crest shock’ type, i.e. they are produced by the shock wave.

On the mass motions and the atmospheric states of moustaches

Analyses of broad moustache profiles of Balmer lines and Ca ii H and K lines are performed based upon our spectroscopic observation under good seeing conditions. Hα emission profiles are found to consist of three components, i.e., a central absorption, a Gaussian core and a power-law wing. Each of them has a different Doppler shift from others. From the data of Doppler shifts, mass motions with velocity of about 6 km s−1 are found to be present in chromospheric levels of moustache atmospheres. Computations of Hα emission profiles radiated from a variety of model atmospheres are made. Comparison of computed profiles with the observed ones leads us to the conclusion that a broad Hα profile is due to a formation of heated (ΔT = 1500 K) and condensed (ϱ/ϱ0 = 5) chromospheric layers relative to the normal.

A study of a tiny two-ribbon flare driven by emerging flux

We present observations of the eruption of a miniature filament that occurred near NOAA Active Region 9537 on 2001 July 14. The eruption was observed by the Hida Observatory Domeless Solar Telescope, in the Hα line center and ±0.4 A wings, the Solar and Heliospheric Observatory EUV Imaging Telescope (EIT) and Michelson Doppler Imager, and the Yohkoh Soft X-Ray Telescope (SXT). The miniature filament began to form and was clearly visible in Hα images by around 06:50 UT. It erupted about 25 minutes later, accompanied by a small two-ribbon subflare (with an area of 61 arcsec2). The two ribbons were also found to approach each other at a speed of 3.33 km s-1. We found that this event was caused by the emergence of new magnetic flux in a quiet region. The emerging flux appeared as a bright region in the EIT and SXT images taken on the previous day. It moved southward into an area of preexisting opposite-polarity flux, where a cancelling magnetic flux region was formed. The miniature filament then appeared, and we suggest that it played some role in inhibiting the release of energy by delaying reconnection between the emerging and preexisting flux, as evidenced by the disappearance of the bright region between opposite polarities in the EUV and soft X-ray images. Consequently, magnetic energy was stored as a result of the slow converging motion of the two opposite-polarity flux regions (0.17 km s-1). Reconnection below the filament provoked the filament eruption, and the two-ribbon flare occurred. Miniature filaments are thought to be small-scale analogs of large-scale filaments. Our observations also suggest some common properties between small-scale and large-scale flares. These results support the view that a unified magnetic reconnection model may be able to explain all scales of flares.

Small-Scale Magnetic-Flux Emergence Observed with Hinode Solar Optical Telescope

We observed small-scale magnetic-flux emergence in a sunspot moat region by the Solar Optical Telescope (SOT) aboard the Hinode satellite. We analyzed filtergram images observed at wavelengths of Fe 6302 A, G band, and Ca II H. In Stokes I images of Fe 6302 A, emerging magnetic flux was recognized as dark lanes. In the G band, they showed to be their shapes almost the same as in Stokes I images. These magnetic fluxes appeared as dark filaments in Ca II H images. StokesV images of Fe 6302 A showed pairs of opposite polarities at footpoints of each filament. These magnetic concentrations were identified to correspond to bright points in G band/Ca II H images. From an analysis of time-sliced diagrams, we derived the following properties of emerging flux, which are consistent with those of previous studies: (1) Two footpoints separate each other at a speed of 4.2 km s 1 during the initial phase of evolution, and decrease to about 1 km s 1 10 minutes later. (2) Ca II H filaments appear almost simultaneously with the formation of dark lanes in Stokes I in an observational cadence of 2 minutes. (3) The lifetime of the dark lanes in the Stokes I and G band is 8 minutes, while that of Ca filament is 12 minutes. An interesting phenomena was observed, that an emerging flux tube expanded laterally in the photosphere with a speed of 3.8 km s . A discussion on the horizontal expansion of the flux tube is given with refernce to previous simulation studies.

Observations of Chromospheric Anemone Jets with Hinode Ca II Broadband Filtergraph and Hida Ca II Spectroheliograph

We report on the first simultaneous observations of chromospheric “anemone” jets in solar active regions with the Hinode Solar Optical Telescope (SOT) Ca II H broadband filtergraph and the Ca II K spetroheliograph on the Domeless Solar Telescope (DST) at Hida Observatory. During the period of coordinated observations, nine chromospheric anemone jets were simultaneously observed with the two instruments. These observations revealed three important features: (1) the jets are generated in the lower chromosphere; i.e., these cannot be seen in Ca II K3 ;( 2) the length and lifetime of the jets are 0.4–5 Mm and 40–320 s, respectively; (3) the apparent velocity of the jets observed with the SOT is 3–24 km s � 1 , while the Ca II K3 component at the jets shows a blueshift (in 5 events) in the range of 2–6 km s � 1 . The chromospheric anemone jets are associated with mixed polarity regions, which are either small emerging flux regions or moving magnetic features. It is found that the Ca II K line often shows red or blue asymmetry in the K2/K1 component; the footpoint of the jets associated with emerging flux regions often shows a redshift (2–16 km s � 1 ), while the one with moving magnetic features shows a blueshift (� 5k m s � 1 ). A detailed analysis of the magnetic evolution of the jet-forming regions revealed that the reconnection rate (or canceling rate) of the total magnetic flux at the footpoint of the jets is on the order of 10 16 Mx s � 1 , and the resulting magnetic energy release rate is (1.1–10) � 10 24 erg s � 1 , with a total energy release of (1–13) � 10 26 erg for the duration of the magnetic cancellation, � 130 s. These are comparable to the estimated total energy, � 10 26 erg, in a single chromospheric anemone jet. In addition to the DST Ca II K spectroheliogram and the SOT Ca II H broadband filtergram, we also used for analysis an SOT magnetogram as well as a Hida H˛ filtergram. We present a physical model of the jet based on the observation, and discuss the relation between chromospheric anemone jets and Ellerman bombs.

THE VELOCITY FIELD ASSOCIATED WITH THE BIRTH OF SUNSPOTS

A velocity field is found to occur prior to the birth of sunspots or during the rapidly developing phase of new spots. Fraunhofer lines are always shifted redwards in the observed active regions which are situated at various distances from the disk center. The velocity amplitude derived from Na i D1-line, λ 5895.940, amounts to, at maximum, 1.5 km s−1 which is always a little larger than that derived from the weaker line, NI i λ 5892.883. The velocity field disappears when the spot ceases to grow. The lifetime of the velocity is, at least, 1 hr. The velocity field is interpreted in terms of the continuous downward flow in the process of formation of sunspots.Bray and Loughhead (1964) regard the disturbance in the granulation pattern accompanying the birth and growth of sunspot pores as an evidence of the existence of rising loops of magnetic flux. In view of the similarity of the phase of development of active regions and the lifetime in the observations by Bray and Loughhead and by us, we suggest that the velocity field may be a spectroscopic feature accompanying the rising magnetic loops in the photosphere and the chromosphere. We briefly discuss the observed mode of penetration of the magnetic flux to the solar surface before and after the appearance of AFSs.