scholarly journals Statistical Study of Solar Eruptive Events Observed with Nobeyama Radioheliograph at 17 GHz

2001 ◽  
Vol 203 ◽  
pp. 401-403
Author(s):  
K. Hori
Keyword(s):  
White Light ◽  
Statistical Study ◽  
Solar Surface ◽  
Solar Maximum ◽  
Small Mass ◽  
Heating Process ◽  
Statistical Features ◽  
Outer Corona

We report statistical features of 49 eruptive prominences observed near solar maximum (1999-2000) with Nobeyama Radiohelograph. Here we focus on the location and related phenomena of the prominence activity. By using white light synoptic maps from LASCO C2 coronagraph, we found that most of the events are associated with some heating process taking place around the prominence site, and occur along pre-existing streamers associated with CMEs as well as small mass ejections. These features suggest that streamers connect the activity on the solar surface toward the outer corona.

scholarly journals Decameter Radio and White Light Observations of the 21 August 1973 Coronal Transient.

1980 ◽  
Vol 91 ◽  
pp. 245-249
Author(s):  
T. E. Gergely ◽  
M. R. Kundu
Keyword(s):  
White Light ◽  
Interplanetary Medium ◽  
Solar Maximum ◽  
Mechanical Energy ◽  
Physical Parameters ◽  
Total Mechanical Energy ◽  
Decameter Radio ◽  
Coronal Transient ◽  
Outer Corona ◽  
Different Parts

Observations from SKYLAB have shown that coronal transients, which involve mass ejections occur quite frequently, possibly up to three times a day at solar maximum (Hildner et al., 1976). An estimated mass of ≃1015 − 1016 g (Stewart et al., 1974) and a total mechanical energy in excess of 2×1031 ergs (Webb et al., 1978) is expelled from the Sun during each event. The transients therefore play a major role in the dynamics of the outer corona and of the interplanetary medium. Joint radio and white light observations provide the best opportunity to derive the physical parameters, such as the electron density and magnetic field in different parts of the transients, and consequently to estimate the forces driving the ejecta.

scholarly journals A statistical study of diurnal, seasonal and solar cycle variations of F-region and topside auroral upflows observed by EISCAT between 1984 and 1996

1998 ◽  
Vol 16 (10) ◽  
pp. 1144-1158 ◽  
Author(s):  
C. Foster ◽  
M. Lester ◽  
J. A. Davies
Keyword(s):  
Solar Cycle ◽  
Statistical Study ◽  
Solar Maximum ◽  
Selection Criterion ◽  
Plasma Temperature ◽  
Threshold Values ◽  
Ion Temperature ◽  
F Region ◽  
Diurnal Distribution ◽  
Velocity Selection

Abstract. A statistical analysis of F-region and topside auroral ion upflow events is presented. The study is based on observations from EISCAT Common Programmes (CP) 1 and 2 made between 1984 and 1996, and Common Programme 7 observations taken between 1990 and 1995. The occurrence frequency of ion upflow events (IUEs) is examined over the altitude range 200 to 500 km, using field-aligned observations from CP-1 and CP-2. The study is extended in altitude with vertical measurements from CP-7. Ion upflow events were identified by consideration of both velocity and flux, with threshold values of 100 m s–1 and 1013 m–2 s–1, respectively. The frequency of occurrence of IUEs is seen to increase with increasing altitude. Further analysis of the field-aligned observations reveals that the number and nature of ion upflow events vary diurnally and with season and solar activity. In particular, the diurnal distribution of upflows is strongly dependent on solar cycle. Furthermore, events identified by the velocity selection criterion dominate at solar minimum, whilst events identified by the upward field-aligned flux criterion dominated at solar maximum. The study also provides a quantitative estimate of the proportion of upflows that are associated with enhanced plasma temperature. Between 50 and 60% of upflows are simultaneous with enhanced ion temperature, and approximately 80% of events are associated with either increased F-region ion or electron temperatures.Key words. Ionosphere (auroral ionosphere; particle acceleration)

scholarly journals The Relevance of Foreshocks in Earthquake Triggering: A Statistical Study

2018 ◽  
Author(s):  
Eugenio Lippiello ◽  
Cataldo Godano ◽  
Lucilla De Arcangelis
Keyword(s):  
Statistical Study ◽  
Aftershock Sequence ◽  
Statistical Features ◽  
Earthquake Triggering ◽  
Etas Model ◽  
Epidemic Type Aftershock Sequence ◽  
The One ◽  
Triggering Process ◽  
Large Earthquakes ◽  
Good Agreement

An increase of seismic activity is often observed before large earthquakes. Events responsible for this increase are usually named foreshock and their occurrence probably represents the most reliable precursory pattern. Many foreshocks statistical features can be interpreted in terms of the standard mainshock-to-aftershock triggering process and are recovered in the Epidemic Type Aftershock Sequence ETAS model. Here we present a statistical study of instrumental seismic catalogs from four different geographic regions. We focus on some common features of foreshocks in the four catalogs which cannot be reproduced by the ETAS model. In particular we find in instrumental catalogs a significantly larger number of foreshocks than the one predicted by the ETAS model. We show that this foreshock excess cannot be attributed to catalog incompleteness. We therefore propose a generalized formulation of the ETAS model, the ETAFS model, which explicitly includes foreshock occurrence. Statistical features of aftershocks and foreshocks in the ETAFS model are in very good agreement with instrumental results.

Century long study of sunspot activity using the Kodaikanal white-light data

2018 ◽  
Vol 13 (S340) ◽  
pp. 173-174
Author(s):  
K. Amareswari ◽  
K. Sankarasubramanian ◽  
B. Ravindra
Keyword(s):  
White Light ◽  
Solar Surface ◽  
Calibration Procedure ◽  
Magnetic Activity ◽  
Sunspot Activity ◽  
Data Set ◽  
Emergence Patterns ◽  
Long Time ◽  
Solar Magnetic Activity ◽  
Digitized Images

AbstractSunspots are the most obvious and high contrast observable feature of solar magnetic activity in the photosphere. The morphological and kinematic behavior of sunspots on the solar surface need to be studied over a long time period to understand solar magnetic activity. For this, it is important to understand the long term emergence patterns, and developments, decay of the sunspots on the solar surface over many cycles. The long time sequence of the Kodaikanal white-light images provide a consistent data set for this study. The digitized images were calibrated for relative plate density and aligned in such a way that the solar north is in upward direction. A sunspot detection technique was used to identify the sunspots on the digitized images. In addition to describing the calibration procedure and availability of the data, we here present results on the sunspot, umbral and penumbral area measurements and their variation with time.

scholarly journals The Relevance of Foreshocks in Earthquake Triggering: A Statistical Study

Entropy ◽  
2019 ◽  
Vol 21 (2) ◽  
pp. 173 ◽  
Author(s):  
Eugenio Lippiello ◽  
Cataldo Godano ◽  
Lucilla de Arcangelis
Keyword(s):  
Statistical Study ◽  
Aftershock Sequence ◽  
Statistical Features ◽  
Earthquake Triggering ◽  
Etas Model ◽  
Epidemic Type Aftershock Sequence ◽  
The One ◽  
Triggering Process ◽  
Large Earthquakes ◽  
Good Agreement

An increase of seismic activity is often observed before large earthquakes. Events responsible for this increase are usually named foreshock and their occurrence probably represents the most reliable precursory pattern. Many foreshocks statistical features can be interpreted in terms of the standard mainshock-to-aftershock triggering process and are recovered in the Epidemic Type Aftershock Sequence ETAS model. Here we present a statistical study of instrumental seismic catalogs from four different geographic regions. We focus on some common features of foreshocks in the four catalogs which cannot be reproduced by the ETAS model. In particular we find in instrumental catalogs a significantly larger number of foreshocks than the one predicted by the ETAS model. We show that this foreshock excess cannot be attributed to catalog incompleteness. We therefore propose a generalized formulation of the ETAS model, the ETAFS model, which explicitly includes foreshock occurrence. Statistical features of aftershocks and foreshocks in the ETAFS model are in very good agreement with instrumental results.

scholarly journals Lost and found sunquake in the 6 September 2011 flare caused by beam electrons

2018 ◽  
Vol 619 ◽  
pp. A65 ◽  
Author(s):  
Connor Macrae ◽  
Sergei Zharkov ◽  
Valentina Zharkova ◽  
Malcolm Druett ◽  
Sarah Matthews ◽  
...  
Keyword(s):  
Acoustic Wave ◽  
White Light ◽  
Hydrodynamic Model ◽  
Acoustic Waves ◽  
Solar Surface ◽  
Statistical Significance ◽  
Onset Time ◽  
Solar Interior ◽  
Shock Propagation ◽  
X Rays

The active region NOAA 11283 produced two X-class flares on 6 and 7 September 2011 that have been well studied by many authors. The X2.1 class flare occurred on September 6, 2011 and was associated with the first of two homologous white light flares produced by this region, but no sunquake was found with it despite the one being detected in the second flare of 7 September 2011. In this paper we present the first observation of a sunquake for the 6 September 2011 flare detected via statistical significance analysis of egression power and verified via directional holography and time–distance diagram. The surface wavefront exhibits directional preference in the north-west direction We interpret this sunquake and the associated flare emission with a combination of a radiative hydrodynamic model of a flaring atmosphere heated by electron beam and a hydrodynamic model of acoustic wave generation in the solar interior generated by a supersonic shock. The hydrodynamic model of the flaring atmosphere produces a hydrodynamic shock travelling with supersonic velocities toward the photosphere and beneath. For the first time we derive velocities (up to 140 km s−1) and onset time (about 50 s after flare onset) of the shock deposition at given depths of the interior. The shock parameters are confirmed by the radiative signatures in hard X-rays and white light emission observed from this flare. The shock propagation in the interior beneath the flare is found to generate acoustic waves elongated in the direction of shock propagation, that results in an anisotropic wavefront seen on the solar surface. Matching the detected seismic signatures on the solar surface with the acoustic wave front model derived for the simulated shock velocities, we infer that the shock has to be deposited under an angle of about 30° to the local solar vertical. Hence, the improved seismic detection technique combined with the double hydrodynamic model reported in this study opens new perspectives for observation and interpretation of seismic signatures in solar flares.

scholarly journals Solar Observations with a New Earth-Orbiting Coronagraph

1980 ◽  
Vol 91 ◽  
pp. 55-59
Author(s):  
N. R. Sheeley ◽  
R. A. Howard ◽  
D. J. Michels ◽  
M. J. Koomen
Keyword(s):  
Spatial Resolution ◽  
White Light ◽  
Orbital Period ◽  
High Latitude ◽  
Sunspot Cycle ◽  
Satellite Observations ◽  
Solar Observations ◽  
The One ◽  
Outer Corona ◽  
White Light Corona

Since March 28, 1979, the Solwind coronagraph has been observing the Sun's white light corona (2.6 − 10.0 R⊙) routinely with a spatial resolution of approximately 1.25 arc min and a repetition rate of 10 minutes during the one-hour sunlit portion of each 97-minute satellite orbital period. These are the first satellite observations of the outer corona near the peak of a sunspot cycle when coronal transients and high-latitude streamers are common.

scholarly journals Statistical Study of Solar White-light Flares and Comparison with Superflares on Solar-type Stars

2018 ◽  
Vol 13 (S340) ◽  
pp. 221-224
Author(s):  
Kosuke Namekata ◽  
Takahito Sakaue ◽  
Kyoko Watanabe ◽  
Ayumi Asai ◽  
Hiroyuki Maehara ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
White Light ◽  
Decay Time ◽  
Solar Flares ◽  
Statistical Study ◽  
Scaling Law ◽  
Statistical Research ◽  
Solar Type

AbstractRecently, many superflares on solar-type stars were discovered as white-light flares (WLFs). A correlation between the energies (E) and durations (t) of superflares is derived as t∝E0.39, and this can be theoretically explained by magnetic reconnection (t∝E1/3). In this study, we carried out a statistical research on 50 solar WLFs with SDO/HMI to examine the t-E relation. As a result, the t-E relation on solar WLFs (t∝E0.38) is quite similar stellar superflares, but the durations of stellar superflares are much shorter than those extrapolated from solar WLFs. We present the following two interpretations; (1) in solar flares, the cooling timescale of WL emission may be longer than the reconnection one, and the decay time can be determined by the cooling timescale; (2) the distribution can be understood by applying a scaling law t∝E1/3B−5/3 derived from the magnetic reconnection theory.

scholarly journals The Structure of the White-Light Corona at the 1991 Eclipse

1994 ◽  
Vol 154 ◽  
pp. 217-221
Author(s):  
A. Sanchez-Ibarra ◽  
M. Cisneros-Molina ◽  
G. Hinojosa-Palafox ◽  
F. Cisneros-Peña ◽  
J. Guerrero de La Torre ◽  
...  
Keyword(s):  
Solar Eclipse ◽  
White Light ◽  
Coronal Holes ◽  
Total Solar Eclipse ◽  
Baja California Sur ◽  
Center Line ◽  
Fine Scale ◽  
Scale Structures ◽  
Outer Corona ◽  
White Light Corona

The total solar eclipse of July 11, 1991 was observed from “La Matanza”, Baja California Sur, México, only 5 km south of the center line of totality, with several small instruments intended to obtain images of the corona during totality, and using a range of exposure times which allowed us to detect both the inner and outer corona. Relations between large and fine scale structures of the corona, the photospheric and chromospheric activity, and the presence of coronal holes are presented.

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