# Presentation: 174930

## Initiation and Acceleration of a Flare-associated Coronal Mass Ejection

**Peter T. Gallagher****1,3****, Gareth R. Lawrence****2,3****, and Brian R. Dennis****3**** **
***1******L-3 Communications EER Systems, Inc, ******2******Catholic University of America, ******3******NASA Goddard Space Flight Center***

***Further Information***
- Alexander, D., Metcalf, T. R., Nitta, N., GRL, 29(10), 1403, 2002.
- Gallagher, P. T., Lawrence, G. R., Dennis, B. R., ApJ, L53, 588, 2003.
- Gallagher, P. T., Dennis, B. R., Krucker, S., Schwartz, R. A., & Tolbert, A. K., Sol. Phys., 210, 341, 2002.
- Forbes, T. G.,  Priest, E. R., ApJ, 446, 377, 1995.
- Images, Movies, and  Reprints can be found at:
- 	_[http://hesperia.gsfc.nasa.gov/~ptg/hessi/20020421/](http://hesperia.gsfc.nasa.gov/~ptg/hessi/20020421/)_

**RHESSI 50-100 keV**

**RHESSI 12-25 keV**

**TRACE 19.5 nm **

- 	A high-velocity (~2500 km s-1) coronal mass ejection (CME) associated with the 2002 April 21 X1.5 flare is studied using a unique set of observations from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), the Transition Region and Coronal Explorer (TRACE), and the Ultraviolet Coronagraph Spectrometer (UVCS) and Large Angle and Spectroscopic Coronagraph (LASCO) instruments on board SOHO (see ***Figure 1***). The images in ***Figure 2*** show that the event was first observed as a rapid rise in RHESSI X-rays, followed by two simultaneous brightenings that appear to be connected by an ascending loop-like feature in TRACE (***Figure 3***). While expanding, the appearance of the feature remains remarkably constant as it passes through the TRACE 19.5 nm passband and LASCO fields of view, allowing its height-time behavior to be accurately determined (***Figures 4*** and ***5***). The acceleration is consistent with an exponential rise with an e-folding time of ~138 s and peaks at ~1500 m s-2 when the leading edge is at  1.7 R  from Sun center. The acceleration subsequently falls off with an e-folding time of over 1000 s. At distances beyond  3.4 R , the height-time profile is approximately linear with a constant velocity of  2500 km s-1. **Figure 6** shows multiple hard X-ray (>25 keV) bursts detected by RHESSI during the peak acceleration phase of the CME, while ***Figure 7*** shows the gradual rise of the soft X-ray source, presumed to be below the energy release site. These results are briefly discussed in light of recent kinematic models of flare-associated CMEs (see ***Figure 8***).

***Coronal Mass Ejection Dynamics***

**	*****Figure 5: (a)*** The height-time profile for ~00:47 - 03:20 UT.
- 	 ***(b)*** and ***(c)*** give the velocity and acceleration profiles obtained by taking the first and second numerical derivatives, respectively. The first-difference values are given as filled circles, while the three-point difference values are given using the same symbol scheme as in ***(a). ***The solid lines give the best fit to the data using ***Equation 4*** for an exponentially rising acceleration followed by an exponentially falling acceleration.
***	******(d)*** The *GOES-10* soft X-ray flux for the corresponding time period.

***	******Figure 3:****** ****Top panels: TRACE* 19.5 nm difference images created by subtracting each image from a frame taken at 00:42:30 UT. *Bottom panels:* LASCO C2 and C3 images showing the similar morphology of the eruption as it propagates away from the solar surface.

- To quantify the height-time profile, we consider three acceleration models. The first assumes constant acceleration, the second a simple exponential rise, while the third includes an exponential rise followed by an exponential decay. Each acceleration model can be numerically integrated to obtain the height-time profile as follows:
- where *t* is the time after initiation (taken to be ~00:47 UT), *h*0 and *v*0 are the initial height and velocity, respectively, and *a*(*t*) is the acceleration.

- Following Alexander et al. (2002), the simple case of constant acceleration (*a) *that might apply early in the time history is considered. The best-fit to the data points up to 01:06 UT gives *h*0 = 24 ± 3 Mm, *v*0 = 13 ± 13 km s-1, and *a* = 117 ± 24 m s-2. As can be seen from ***Figure 4***, the fit does not well represent the UVCS and LASCO C2 data points but is acceptable for heights within the *TRACE* field of view.
- A best-fit of an exponentially varying acceleration of the form *a*0 exp(*t*/) is also given in ***Figure 4***. As can be seen, this function, with *h*0 = 12 ± 3 Mm, *v*0 = 0 ± 13 km s-1, *a*0 = 48 ± 2 m s-2, and = 486 ± 8 s, provides an acceptable fit to the *TRACE*, UVCS, and LASCO C2 points.

***Figure 4:***** **Height-time evolution of the 2002 April 21 CME from *TRACE*, UVCS, and LASCO C2. The data are shown with ±5 pixel error bars. Also given are best fits for a constant and an exponentially increasing acceleration.

- The acceleration time data in ***Figure 5(c)****** ***suggests an exponential rise, followed by an exponential decay. A function that shows this behavior is
- where *a**r* and *a**d* are the initial accelerations and  *r* and *d* give the *e*-folding times for the rise and decay phases. A best fit to the height, velocity, and acceleration data was obtained with *h*0 = 25 ± 2 Mm, *v*0 = 40 ± 4 km s-1, *a**r* = 1 ± 1 m s-2,  *r* = 138 ± 26 s, *a**d* = 4950 ± 926 m s-2, and  *d* = 1249 ± 122 s and is shown in ***Figure 5***.

***Coronal Mass Ejection Models***

**RHESSI 12-25 keV**

**RHESSI 12-25 keV**
**RHESSI 50-100 keV**

**	*****Figure 1: ***The 2002 April 21 X-class flare and CME in RESSI, TRACE, EIT, and LASCO.

**	*****Figure 2:***** **TRACE 19.5 nm and RHESSI 12-25 and 50-100 keV images at four times during the flare. The RHESSI contour levels are at 25, 50 and 75% of the peak flux for each energy band.

***Figure 8:****** ***The Flux-Rope Model of Forbes & Priest (1995). ***(a)*** The height (*h*) above the solar surface of a two-dimensional flux rope as a function of footpoint separation, . ***(b) and (c)*** The flux-rope initially moves closer to the solar surface as the footpoints converge. A critical point is then reached which results in flux-rope ejection. ***(d)*** Subsequent current-sheet formation below the erupting flux-rope.

***Figure 6: ***RHESSI lightcurves for ~00:40 – 01:40 UT. The flare is first seen in the 3 - 6 and 6 – 12 keV energy ranges, starting at ~00:40 UT. After a gradual rise at soft X-ray energies, a rising loop-like feature is observed in the TRACE field-of-view, which moves away from the surface with an exponential acceleration profile. Hard X-ray impulses with energies >25 keV are only observed close to the peak of the CME acceleration profile.

***Introduction***

- v

***	******Figure 7:****** ***The height-time evolution of the soft X-ray source observed with RHESSI and the post-flare loop tops seen in the TRACE 19.5 nm images. The presumed rising energy release site results in the formation of hot loops that cool and appear sequentially in the different passbands of the two instruments. After ~03:00 UT, the cooling time from the ~15 MK temperatures seen by RHESSI to the 1.5 MK seen in the TRACE 19.5 nm bandpass is ~4-hours.