Transients on the Sun

 Megan Cartwright

UCLA

SHINE Student DayJune 22, 2008

Image of an erupting prominence from online SOHO gallery

Active Regions (AR)

Windows to the Universe original artwork by Randy Russell using an image from NASA's TRACE (Transition Region and Coronal Explorer) spacecraft.

• An active region on the sun is an area of very strong magnetic field, often observed as sunspots.

• Solar flares and CME’s are often associated with active regions.

Solar flares are impulsive, transient releases of magnetic energy that rapidly heat the surrounding plasma

EUV image of one of the largest solar flares observed, erupted in November 2003. Image courtesy of SOHO (NASA & ESA).

Coronal Mass Ejections are large scale magnetic structures which are released into the heliosphere

Figure 1 from Riley et al., (2008)

Prominences

• Suspensions of cool (T~104K), dense (n~1010-1011 cm-3) chromospheric material surrounded by the hot (T~106K) and tenuous (n~107-109 cm-3) corona

Image of a prominence from online SOHO gallery

Prominence Magnetic Fields: Origin of flux ropes?

Image of a prominence from HAO in H-alpha

Sigmoids: Shearing Observed in Soft X-Ray Regime

Persistent sigmoid (Left, Top) ;Transient sigmoid (Left, Bottom);Sigmoid associated with CME (Left, Bottom) -- Image from, DOI: 10.1007/s11214-006-9101-2

How are CMEs Initiated?

Flux Injection Model (Chen, 1989, 1996)

Flux Cancellation Models

The Breakout Model

MacNeice et al., 2004. Lynch et al.

• The interaction can be written in words– Expansion

• (Ambient mass density) X (Rate of expansion)2= Delta Pressure (inside – outside)

– Acceleration• (Mass of CME + Virtual mass) X Acceleration = Force

of gravity + Delta (outside magnetic and particle pressure on lower surface area – outside magnetic and particle pressure on upper surface area) – Drag

• Virtual mass allows us to correct for the force necessary to move all the ambient medium away = volume of cylinder time the mass density of the ambient medium.

– Problem is in turning this into equations.• Standard drag term CDAρ abs (VCME –Vsw) (VCME –Vsw)

where CD is a drag coefficient, and (VCME –Vsw) is relative velocities of CME and solar wind.

• How to do it is controversial.

CME Acceleration and Propagation

CME Propagation Model into Heliosphere: ENLIL (Sumerian God of the Wind)

ENLIL Simulation Run Results

Earth

Where to find ‘Solar Transients’ at SHINE/GEM

• Relevant sessions: 5, 9, 11, 14, 16, 18

Coronal Models: CME must be launched into an ambient solar wind.

SOLAR MODELS:

• PFSS: corona field model from 1.5-3.25Rs.

•MAS: 3D corona field model from 1-30 Rs.

• WSA: (A) Potential field + current sheet (B) WSA inner heliosphere

SWMF (UMich): 3D MHD coronal code & inner heliosphere code.

Images from CCMC website (Above Left is MAS model, Above Right is PFSS, & Bottom is magnetogram inputs