Abstract
Abstract. Using Advanced Composition Explorer (ACE) in situ data we identify and describe an interplanetary magnetic cloud (MC) observed near Earth on 13 April 2006. We also use multi-instrument and multi-wavelength observations from the Solar and Heliospheric Observatory (SOHO), the Transition Region and Coronal Explorer (TRACE) and ground-based solar observatories to determine the solar source of this magnetic cloud. A launch window for the MC between 9 and 11 April 2006 was estimated from the propagation time of the ejecta observed near Earth. A number of large active regions (ARs) were present on the Sun during this period, which were initially considered to be the most likely candidate source regions of the MC. However, it was determined that the solar source of the MC was a small, spotless active region observed in the Northern Hemisphere. Following an eruption from this region on 11 April 2006, the ACE spacecraft detected, 59 h later, the passage of the MC, preceded by the arrival of a weak, forward fast shock. The link between the eruption in this active region and the interplanetary MC is supported by several pieces of evidence, including the location of the solar source near to the disk centre and to the east of the central meridian (in agreement with the spacecraft trajectory through the western leg of the magnetic cloud), the propagation time of the ejecta, the agreement between the amount of flux in the magnetic cloud and in the active region, and the agreement between the signs of helicity of the magnetic cloud and the active region (which differs from the sign of helicity of each of the other active regions on the Sun at this time). In addition, the active region is located on the boundary of a coronal hole, and a high speed solar wind stream originating from this region is observed near Earth shortly after the passage of the magnetic cloud.
Highlights
Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs), and are defined by three main characteristics: the magnetic field rotates smoothly through a large angle during an interval of the order of one day, the magnetic field strength is higher than that in the average solar wind, while the temperature is lower than that in the average solar wind (Burlaga et al, 1981; Burlaga, 1995). Richardson and Cane (1995) found that ICMEs typically have Tp≤Tex, where Tp is the proton temperature and Tex is the “expected Tp” determined from the empirical correlation between the velocity of the solar wind and Tp
It was determined that the solar source of the MC was a small, spotless active region observed in the Northern Hemisphere
The time of eruption of the coronal mass ejection (CME) at the Sun is estimated and we describe the process used to determine the solar source in Sect. 4, and discuss the elimination of several larger active regions as the solar source
Summary
Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs), and are defined by three main characteristics: the magnetic field rotates smoothly through a large angle during an interval of the order of one day, the magnetic field strength is higher than that in the average solar wind, while the temperature is lower than that in the average solar wind (Burlaga et al, 1981; Burlaga, 1995). Richardson and Cane (1995) found that ICMEs typically have Tp≤Tex, where Tp is the proton temperature and Tex is the “expected Tp” determined from the empirical correlation between the velocity of the solar wind and Tp. ICME identification remains a fairly ambiguous process since many of the signatures associated with ICMEs are not present for every ICME, and they often do not define precisely the same boundaries. This is expected since the various signatures arise from different physical phenomenon The time of eruption of the coronal mass ejection (CME) at the Sun is estimated and we describe the process used to determine the solar source, and discuss the elimination of several larger active regions as the solar source.
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