BBSO/NJIT Contributions to the SPD Meeting June 2000, Lake Tahoe

BBSO/NJIT Contributions to the SPD Meeting
June 2000, Lake Tahoe

Contents

J. Chae, P. R. Goode, T. J. Spirock, H. Wang, S. F. Martin, H. S. Yun, J.-H. Kim, S. Lee:
Orientation of Emerging Bipoles in a Filament Channel
C. Denker, T. J. Spirock, H. Wang, and P.R. Goode:
Center-to-Limb Variation of Small-Scale Magnetic Features
P. R. Goode, J. Hickey, J. Qiu, V. B. Yurchyshyn, S. E. Koonin, T. Brown, E. Kolbe, M.-C. Chu:
Earthshine and the Earth's Reflectivity
J. Qiu, H. Wang, V. B. Yurchyshyn, P. R. Goode:
Energy Release in an Impulsive Flare
T. J. Spirock, C. Denker, H. Chen, J. Qiu, P. R. Goode, H. Wang:
First Results from the Big Bear Solar Observatory's Digital Vectormagnetograph
J. Varsik, M. Steinegger, C. Denker, P. R. Goode, H. Wang, G. Luo, D. Chen, Q. Zhang, W. Otruba, A. Hanslmeier, H. Freislich:
First Observations with the Global High-Resolution H-alpha Network
H. Wang, J. Qiu, C. Denker, T. J. Spirock, H. Chen, P. R. Goode:
High Cadence Flare Observations
M. F. Woodard, K. G. Libbrecht:
Photometric Measurements of the Solar Disk at BBSO
G. Yang
A Statistical Study of Filament and Prominence Disppearances
V. B. Yurchyshyn, H. Wang, J. Qiu, P. R. Goode, V. I. Abramenko:
Magnetic Topology in November 5, 1998 Two-Ribbon Flare as Inferred from Ground-Based Observations and Linear Force-Free Field Modeling

 
Orientation of Emerging Bipoles in a Filament Channel

Orientation of Emerging Bipoles in a Filament Channel

J. Chae1, P. R. Goode1, T. J. Spirock1, H. Wang1, S. F. Martin2, H. S. Yun3, J.-H. Kim3, S. Lee3
(1) Big Bear Solar Observatory/NewJersey Institute of Technology
(2) Helio Research
(3) Seoul National University

Observations have shown that quiescent prominences or filaments have a hemispheric magnetic pattern of chirality or handedness. Motivated by the question of whether the filament chirality is of sub-surface origin or not, we have studied magnetic bipoles emerging in a quiescent filament channel at latitude N45 deg. During our 5 day observing run performed in 1999 October, a huge filament erupted and another began to form in the same filament channel. Using high cadence deep line-of-sight magnetograms, we identified a total of 102 small emerging bipoles, which display the following statistical properties:

  1. an average flux of 1.2 x 1019 Mx and an average separation of 7200 km,
  2. an inferred global emergence frequency of 600 hr-1 all over the solar surface, and
  3. a preferred orientation that a negative (trailing) pole is located at the south-east of the companion positive (leading) pole.
The majority of the bipoles appear to be ephemeral regions which are systematically smaller than those previously studied with Kitt Peak full disk daily magnetograms. The preferred orientation of these bipoles differs greatly from both the filament axial field direction and the active region polarity law. We conclude that factors other than the Hale polarity law are the cause of asymmetry in the orientation of small bipoles having total magnetic fluxes below 2 x 1019 Mx.

 
Center-to-Limb Variation of Small-Scale Magnetic Features

Center-to-Limb Variation of Small-Scale Magnetic Features

C. Denker, T. J. Spirock, H. Wang, and P.R. Goode
Big Bear Solar Observatory/NewJersey Institute of Technology

During August/September 1999, we observed continuum images in the visible (520 nm) and infrared (1600 nm) of various active regions during their limb-to-limb passage. The images were obtained with the 65 cm vacuum reflector of the Big Bear Solar Observatory and speckle masking has been applied to obtain almost diffraction limited images of small-scale magnetic features such as pores, magnetic knots, and faculae. The infrared images were taken with a new 320 x 240 pixel, 12-bit, 30 fps InGaAs CCD camera. The continuum images are complemented by videomagnetograms obtained at CaI (610.3 nm) with the 25 cm vacuum refractor. We present the first results of a comprehensive study on the relationship of magnetic field strength and continuum contrast of small-scale magnetic features as a function of disk position. The underlying mechanism of small-scale flux tubes is of particular importance for solar irradiance variations over the 11 year solar activity cycle.


 
Earthshine and the Earth's Reflectivity

Earthshine and the Earth's Reflectivity

P. R. Goode1, J. Hickey1, J. Qiu1, V. B. Yurchyshyn1, S. E. Koonin2, T. Brown2, E. Kolbe3, M.-C. Chu4
(1) Big Bear Solar Observatory/NewJersey Institute of Technology
(2) California Institute of Technology
(3) Universität Basel, Switzerland
(4) Chinese University, Hong Kong

The earth's climate is driven by the net sunlight reaching the earth, which depends on the solar irradiance and the earth's reflectivity. Changes in the the solar irradiance have been well-studied for twenty years, but the degree of variation in the earth's albedo is not so clear. We have been measuring the earthshine from Big Bear Solar Observatory (BBSO) since December 1998. Earthshine, or "ashen light", is sunlight reaching the eye of a nighttime observer after being successively reflected from the day side of the earth, and the dark face of the moon. The ratio of reflected light from the dark part of the moon to that from the bright part provides an absolutely calibrated, large scale measure of the earth's albedo. We have solved the long-standing problem of determining the scattering of sunlight from the moon as a function of lunar phase. Earthshine measurements of the earth's albedo are complementary to those from satellites. We find the earth's albedo varies by 20% with season, and by as much at 5% from night to night. We put contemporaneous cloud cover data into a scene model and calculate a good agreement with our observations, but we also find some interesting differences. Using the scene model and monthly averaged cloud cover data from ISCCP, we find between 1986 and 1990 (solar minimum to near solar maximum) that the change in the net irradiance into the climate system is several times larger from the varying albedo than from the varying solar irradiance. The two changes are in phase.


 
Energy Release in an Impulsive Flare

Energy Release in an Impulsive Flare

J. Qiu, H. Wang, V. B. Yurchyshyn, P. R. Goode
Big Bear Solar Observatory/NewJersey Institute of Technology

We analyze the multi-spectral observations on an impulsive short-lived flare event, and demonstrate that the flare consisted of several flaring components with different evolution profiles, morphologies, energy spectra, and magnetic configurations. These observations suggest that the magnetic energy was released in this event in several ways.

  1. Two hard X-ray components were observed by Yohkoh HXT. One component was brightened and reached its emission maximum more slowly than the other component by >15 seconds, and the spectrum of the slow component was much softer than the fast component. The coordinated high resolution ground-based observations from Big Bear Solar Observatory (BBSO) further demonstrate that these two hard X-ray components were each co-aligned with complicated H-alpha and magnetic field structures. Therefore, the two hard X-ray components should come from different magnetic reconnection processes at different locations.
  2. Accompanying the flare, we find both hot and cool mass ejections. The cool mass ejection was related to the fast-varying non-thermal flare component, while the hot mass ejection was related to the flare component which exhibited a strong heating process. The hot mass ejection, or bright surge, also led to a long-lasting (for at least a few hours) bright EUV loop. Such observation offers a strong evidence that both pre-flare and post-flare heating of the chromospheric material occurred at the root of the bright surge.
  3. We study the magnetic field configurations of the flare components, and propose that both the non-thermal and thermal components of the flare, together with the cool and hot surges, were produced by the magnetic reconnection of the large scale over-lying open field lines with the low-lying magnetic loops, while the gradual and thermal flare components and bright surge were located in the area of magnetic quadrupolar structures where moving magnetic features and flux cancellation were observed. The observations suggest that the proper motions in the region of the quadrupolar structure may enhance electric current along the separatrix and neutral point, and produce heating via current dissipation in the quadrupolar areas in the lower atmosphere both before and after the fast reconnection occurred.
 

 
First Results from the Big Bear Solar Observatory's Digital Vectormagnetograph

First Results from the Big Bear Solar Observatory's Digital Vectormagnetograph

T. J. Spirock, C. Denker, H. Chen, J. Qiu, P. R. Goode, H. Wang
Big Bear Solar Observatory/NewJersey Institute of Technology

During the past three years the Big Bear Solar Observatory has begun an aggressive program to upgrade the observatory's instrumentation. In the forefront of this effort is the development of a highly sensitive, high cadence filter based digital vector magnetograph for the observatory's 10 inch vacuum-refractor to replace the old video magnetograph to improve our measurements of the FeI line at 6301Å. The hardware is being replaced by a 512 x 512, 12-bit, 30 frames per second CCD camera and high quality polarization optics. In addition, software tools are being written to aid instrument development by quickly evaluating images (bias, cross talk, etc.) and to generate near real-time vector magnetograms which will aid space weather forecasting and the support of space weather missions. Data acquisition, data calibration and flat fielding methods will be discussed and quiet sun and active region magnetograms will be presented.


 
First Observations with the Global High-Resolution H-alpha Network

First Observations with the Global High-Resolution H-alpha Network

J. Varsik1, M. Steinegger1, C. Denker1, P. R. Goode1, H. Wang1, G. Luo2, D. Chen2, Q. Zhang2, W. Otruba3, A. Hanslmeier3, H. Freislich3
(1) Big Bear Solar Observatory/NewJersey Institute of Technology
(2) Yunnan Astronomical Observatory
(3) Kanzelhöhe Solar Observatory

We are in the final stages of establishing a three-site global network for continuous full disk H-alpha observations based on our experience with making high-resolution full disk H-alpha observations at Big Bear Solar Observatory. Utilizing existing telescopes at Big Bear Solar Observatory (USA), Kanzelhoehe Solar Observatory (Austria), and Yunnan Astronomical Observatory (China), the three stations are each equipped with 2k X 2k CCD detectors and will monitor the Sun at a 1 minute cadence. We expect to monitor the emergence of each new flux region to obtain an unbiased data set in order to understand why some regions grow to super-activity while most decay quickly, as well as a more complete and uniform set of flare observations. We also expect to implement automatic detection of filament eruptions. Having high cadence data from three observing stations will also increase the accuracy of solar rotation rates as determined by feature tracking techniques. We will show the first data sets from the new network.


 
High Cadence Flare Observations

High Cadence Flare Observations

H. Wang, J. Qiu, C. Denker, T. J. Spirock, H. Chen, P. R. Goode
Big Bear Solar Observatory/NewJersey Institute of Technology

We analyzed high cadence observations of a C5.7 flare on 1999 August 23 at Big Bear Solar Observatory (BBSO). The observing wavelength was 1.3 Å in the blue line wing of H-alpha. In addition, the time profile of hard X-rays obtained by the Burst And Transient Source Experiment (BATSE) and BBSO high resolution magnetograms are compared with the H-alpha- observations to understand in detail the particle precipitation of this event. The important results are:

  1. In H-alpha - 1.3 Å, three flare kernels were observed in the early phase of the flare. The flare started in a non-magnetic area at the magnetic neutral line. We suggest that the top of a low-lying loop is the initial energy release site. While the other two kernels are the footpoints of another overlying flare loop formed after the magnetic reconnection.
  2. We analyzed the temporal behavior of the three flare kernels in the impulsive phase when hard X-ray (HXR) emission was significant. We found that during a 7 s period, the H-alpha - 1.3 Å brightenings at one of the footpoints showed a very good temporal correlation with the HXR flux variation. Therefore, from the spatially resolved H-alpha off-band observations, we identified this flare kernel as the source of HXR emission.
  3. From the footpoint which exhibits the best correlation with HXR emission, the H-alpha - 1.3 Å emission shows high frequency fluctuations at a time scale of a few tenths of a second. The amplitude of the fluctuations is more than three times above the noise. Such fluctuation is not evident in other flare kernels which also do not show good correlation with HXR emission. For this reason, we suggest that the observed high frequency fluctuations are signatures of temporal fine structure related to the HXR elementary bursts.
 

 
Photometric Measurements of the Solar Disk at BBSO

Photometric Measurements of the Solar Disk at BBSO

M. F. Woodard1, K. G. Libbrecht2
(1) Big Bear Solar Observatory/NewJersey Institute of Technology
(2) California Institute of Technology

Precise photometric measurements of the Sun have been obtained with the BBSO Solar Disk Photometer (SDP) since 1993. We describe our program to characterize sunspot, facular, and non-facular contributions to the spatial and temporal variations in solar irradiance using these data.


 
A Statistical Study of Filament and Prominence Disppearances

A Statistical Study of Filament and Prominence Disppearances

G. Yang
Big Bear Solar Observatory, New Jersey Institute of Technology

A statistical study of filament and prominence disappearances is described in this article. A nearly complete set of all Big Bear Solar Observatory H-alpha full disk images between January 1997 and June 1999 were searched for filament and prominence disappearances and a list of events was compiled. Comparison of these data with those from EIT, LASCO, and Yohkoh, and also data from ACE and WIND is being made to obtain (1) the relationship between CME events and filament disappearances and (2) the relationship between filament and prominence disappearances and other coronal phenomena such as the global rearrangement of magnetic field, as well as chromospheric H-alpha brightening. Early result shows that most of filament disappearance events seem to have no corresponding CME events. The reasons are discussed in the article.


 
Magnetic Topology in November 5, 1998 Two-Ribbon Flare as Inferred from Ground-Based Observations and Linear Force-Free Field

Magnetic Topology in November 5, 1998 Two-Ribbon Flare as Inferred from Ground-Based Observations and Linear Force-Free Field

V. B. Yurchyshyn1, 2, H. Wang1, J. Qiu1, P. R. Goode1, V. I. Abramenko2
(1) Big Bear Solar Observatory, New Jersey Institute of Technology
(2) Crimean Astrophysical Observatory, Ukraine

We analyzed the 3D structure of the linear force-free magnetic field in an active region. A longitudinal magnetogram of AR NOAA 8375 has been used as the photospheric boundary condition. The November 5, 1998 2B/M8.4 two-ribbon flare can be explained in the framework of quadrupolar reconnection theory: the interaction of two closed magnetic loops which have a small spatial angle. The energy derived from SXT/YOHKOH data (3-6 x 1030 ergs) is one order of magnitude higher than the lower limit of flare energy predicted by Melrose's model. The latter estimation was made using the linear force-free extrapolation. It is suggested that by taking into account the non-linear character of the observed magnetic field we can increase the lower limit of the magnetic energy stored in the studied magnetic configuration. The revealed magnetic configuration allows us to understand the observed location and evolution of the flare ribbons and the additional energy released during the gradual phase of the flare, as well. Also, the reconnection of closed magnetic loops can logically explain the connection between a two-ribbon flare and the giant X-ray post-flare arch which usually is observed after flare onset. We emphasize that unlike the Kopp and Pneuman configuration, the model discussed here does not necessarily need destabilization and opening of the magnetic field.


 
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