SOHO/TRACE JOP 106

Sigmoidal active region study

Sarah Gibson, Doug Biesecker, Volker Bothmer, Andy Breen, Joan Burkepile, Richard Canfield, Angela Colman, Lyndsay Fletcher, Andrzej Fludra, Madhulika Guhathakurta, Richard Harrison, Todd Hoeksema, Hugh Hudson, Charles Kankelborg, Masayoshi Kojima, Reni Kupke, Barry LaBonte, Alice Lecinski, K. D. Leka, Yan Li, Janet Luhmann, Alan McAllister, Piet Martens, Sara Martin, Helen Mason, Tom Metcalf, Zoran Mikic, Karin Muglach, Nariaki Nitta, Leon Ofman, Janardhan Padmanabhan, Dave Pike, Vic Pizzo, John Raymond, Pete Riley, Michael Sersen, Alphonse Sterling, Leonard Strachan, Ananthkrishnan Subramanian, Munetoshi Tokumaru, Barbara Thompson, Balasubramanian Veeraraghavan, S. T. Wu, Peter Young, Dominic Zarro, Xue Pu Zhao

Abstract

Observational Details of Proposed Study

Planned Analysis

Times for coordinating observations

Runs to date:

Abstract. Sigmoidal structures observed in X-rays have been shown to be precursors to some CMEs, existing in some cases for several days before an eruption (Sterling and Hudson, ApJ, 492, L55 1998, Canfield et al, GRL, 26, 6, 627, 1999). While these S-shaped structures are most apparent in X-ray active region observations, they may be manifestations of a more general helical magnetic structure having observational signatures at other wavelengths. Indeed, preliminary surveys of SOHO/CDS and EIT data have shown clear sigmoidal signatures in EUV associated with those seen in X-rays (Poster by Gibson et al, to be shown at SOHO 8 workshop, Paris, June 1999)

We will study sigmoidal structures and other CME tracers on the solar disk over a range of wavelengths, and also determine the underlying magnetic field from vector and line-of-sight magnetogram data. This will be a Target of Opportunity study during Whole Sun Month 3. We will choose a clear sigmoid appearing in the Eastern hemisphere, and follow it with coordinated observations of its structure in multiple wavelengths. If it is still sigmoidal when it reaches the West limb, we will add coronagraph data in order to better study its manifestation at the solar limb. If it erupts, we will gather pre-eruption and post-eruption on-disk and coronagraph data to be compared.We will also look for signatures in interplanetary scintillation observations (IPS), and study the geo-effectiveness of any eruption, using space and earth-based in-situ instrumentation.

Observational Details of Proposed Study

SOHO/MDI, Wilcox Solar Observatory (WSO): Daily line of sight magnetograms, high resolution magnetograms of sigmoid region (if possible) - contact Todd Hoeksema, Sarah Gregory

Mees Solar Observatory: Sigmoid Region Watch

Vector magnetograms with Haleakala Stokes Polarimeter for accurate measurement of magnetic flux and currents.

Vector magnetogram movies with Imaging Vector Magnetograph for measurement of field emergence and/or evolution.

H-alpha imaging spectra withe the Mees CCD Imaging Spectrograph, for mearurement of chromosperic restructuring before and during eruptive events.

Contact: Barry LaBonte

Yohkoh SXT: Primarily standard observations. Special observational details TBD during campaign. Contact: sxt_co

SOHO/UVCS: Off-limb UV spectroscopic observations in the corona above 1.5 solar radii. Contact: Leonard Strachan, Kuen Ko

SOHO/LASCO: Synoptic observations: White light CME data if there is a sigmoid eruption. Contact: Doug Biesecker

SOHO/CDS: Density and temperature diagnostics to map the sigmoid with height. Details. Contact: Dave Pike

SOHO/EIT: Synoptic observations. Contact: Barbara Thompson

TRACE:

full resolution 284 with AEC target class 3 (top4) to obtain stable, short exposure times. Try for ~ 1 min. cadence.

context images in 171, and possibly 195.

NOTE: revised observations during eclipse season will concentrate mainly on 171 in order to see moss

Charles Kankelborg,

Lyndsay Fletcher

Big Bear Solar Observatory: H-alpha observations. Contact Jiong Qiu

Huairou: Vector magnetograph observations. Contact Yuanyong Deng

Mauna Loa Solar Observatory: White light coronagraph data, H-alpha and Helium velocity images. Contact: Alice Lecinski , Joan Burkepile

Helio Research : H-alpha observations (details). Contact: Sara Martin

Modra Astronomical Observatory: H-alpha observations. Contact: Michael Sersen

Ooty Radio Telescope: IPS observations (details). Contact: Balasubramanian Veeraraghavan

Nagoya Radio Telescope: IPS observations (details). Contact: Masayoshi Kojima and Munetoshi Tokumaru

EISCAT Radio Telescope: IPS observations. Contact: Andy Breen

MAX Millenium study of eruptive flares associated with sigmoids: Campaign to be coordinated with this JOP. Contact: Richard Canfield

Planned Analysis

We will see to what extent the data answers questions such as:

What is the magnetic field topology associated with the sigmoid?

How does the appearance of the sigmoids vary over the lifetime of the structure?

Do the sigmoids observed at different wavelengths line up, or is there a spatial variation of angle of S that corresponds with height/temperature variation?

To what extent are filaments associated with the sigmoids?

After an eruption, how much if any of the S shape remains, and at what spatial and spectral locations?

Where, relative to the sigmoidal structures, do the CME tracers known as twin dimmings appear if they do appear during the eruption?

How close to the central meridian does the structure have to erupt to be geo-effective?

We will use the results of these observations to model the underlying magnetic field structure (Leka, Metcalf, Mikic, Muglach, Zhao), and to consider the energetics, force balance, and helicity of the internal field structure (what makes it look sigmoidal?) (Bothmer, Canfield, Colman, Gibson, Mikic, Nitta). We are also interested in how the field structure relates to the location and variation of heating throughout it (Gibson, Mason, Pike, Young). Moreover, if an eruption is observed we will study the CME onset conditions (Bothmer, Canfield, Colman, Nitta, Wu, Zarro ), look for the generation of waves in coronal loops due to the CME-produced shock wave (Ofman), and model the 3-d structure of the CME (Gibson, Guhathakurta , Ofman), and how the large scale magnetic field changes with the eruption (Li, Luhmann). We will also investigate the interplanetary signatures and geo-effectiveness of sigmoidal structures (Bothmer, Breen, Li, Luhmann, Martin, McAllister, Padmanabhan, Pizzo, Riley, Submramanium, Tokumaru, Veeraraghavan).