Current Sheet Evolution in the Aftermath of a CME Event

Abstract

We report on SOHO UVCS observations of the coronal restructuring following a coronal mass ejection (CME) on 2002 November 26, at the time of a SOHO-Ulysses quadrature campaign. Starting about 1.5 hr after a CME in the northwest quadrant, UVCS began taking spectra at 1.7 R , covering emission from both cool and hot plasma. Observations continued, with occasional gaps, for more than 2 days. Emission in the 974.8 8 line of [Fe xviii], indicating temperatures above 6 ; 10 6 K, was observed throughout the campaign in a spatially limited location. Comparison with EIT images shows the [Fe xviii] emission to overlie a growing post-flare loop system formed in the aftermath of the CME. The emission most likely originates in a current sheet overlying the arcade. Analysis of the [Fe xviii] emission allows us to infer the evolution of physical parameters in the current sheet over the entire span of our observations: in particular, we give the temperature versus time in the current sheet and estimate its density. At the time of the quadrature, Ulysses was directly above the location of the CME and intercepted the ejecta. High ionization state Fe was detected by the Ulysses SWICS throughout the magnetic cloud associated with the CME, although its rapid temporal variation suggests bursty, rather than smooth, reconnection in the coronal current sheet. The SOHOUlysses data set provided us with the unique opportunity of analyzing a current sheet structure from its lowest coronal levels out to its in situ properties. Both the remote and in situ observations are compared with predictions of theoretical CME models.

Review on Current Sheets in CME Development: Theories and Observations

“…Comparing it with those similar ones observed previously (Ciaravella et al 2002;Ko et al 2003;Webb et al 2003;Lin et al 2005;Bemporad et al 2006), we are able to identify this structure with the CME/flare current sheet. What is especially interesting was that a set of plasma blobs flowing in the sheet were seen between 12:18 and 12:35 UT.…”

“…Poletto et al (2004) extrapolated Ulysses measurements back to the Sun using the in situ measurement of the flow speed of the solar wind plasma, which gave a rough estimate of the origin time for the plasma, and yielded a positive identification of the plasma resulting from the 2002 November 26 CME by comparing features in the solar wind with phenomena directed toward Ulysses in the corona. Therefore, Bemporad et al (2006) concluded that a relation of the ICME detected by Ulyssees to the CME observed near the Sun by several other instruments could be set up, and the model shown in Fig. 2 fits the scenario manifested by this event very well.…”

“…The post-flare loop system continued to be observed in EIT Fe XII and He II for more than 24 hours, and its heights gradually rose from 0.06 to 0.34 R above the solar surface (see also Fig. 2 of Bemporad et al 2006, which displayed the images of the flare loop system at different times after the associated CME, as well as the change in the loop heights versus time). However, the typical cusp feature at the end of the CS did not appear in the EIT images, and it did not appear in the LASCO images, either.…”

“…Numerical experiments performed by Riley et al (2007) displayed bi-directional reconnection outflows along the CS in the solar eruptive events. , , Lin and Soon (2004), and Bemporad et al (2006) investigated the consequences of the reconnection process manifested by the thermal structures and kinetic behaviors of CMEs. They found that the CME bubble is surrounded by the hot reconnected plasma, and that the rapidly expanding CME bubbles are mainly due to the addition of magnetic flux brought by the reconnection outflow from the CS into the CME.…”

“…pointed out that the features seen in [Fe XVIII] line were quite likely the post-CME CS. Bemporad et al (2006) studied an event on 2002 November 26, at the time of a SOHOUlysses quadrature campaign, which made their work unique because the SOHO-Ulysses data set allowed them to analyze a current sheet structure from its lowest coronal levels out to its in situ properties. The event occurred over the northwest limb and produced a CME with speed at the front increasing from 90 to 420 km s −1 and a flare that the Geostationary Operational Environmental Satellite (GOES) system did not class because the main part of the flare was behind the limb, but the growth of the post-CME loop system could be clearly seen.…”