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Linking two consecutive non-merging magnetic clouds with their solar sources  

Sergio Dasso   Submitted: 2008-11-19 10:18

On May 15, 2005, a huge interplanetary coronal mass ejection (ICME) was observed near Earth. It triggered one of the most intense geomagnetic storms of solar cycle 23 (Dstpeak = -263 nT). This structure has been associated with the two-ribbon flare, filament eruption and CME originating in active region (AR) 10759 (NOAA number). We analyze here the sequence of events, from solar wind measurements (at 1 AU) and back to the Sun, to understand the origin and evolution of this geoeffective ICME. From a detailed observational study of in situ magnetic field observations and plasma parameters in the interplanetary (IP) medium, and the use of appropriate models, we propose an alternative interpretation of the IP observations, different to those discussed in previous studies. In our view, the IP structure is formed by two extremely close consecutive magnetic clouds (MCs) that preserve their identity during their propagation through the interplanetary medium. Consequently, we identify two solar events in Hα and EUV which occurred in the source region of the MCs. The timing between solar and IP events, as well as the orientation of the MC axes and their associated solar arcades are in good agreement. Additionally, interplanetary radio type II observations allow the tracking of the multiple structure through inner heliosphere and to pin down the interaction region to be located midway between the Sun and the Earth. The chain of observations from the photosphere to interplanetary space is in agreement with this scenario. Our analysis allows the detection of the solar sources of the transients and explains the extremely fast changes of the solar wind due to the transport of two attached though non-merging MCs which affect the magnetosphere.

Authors: Dasso S., C.H. Mandrini, B. Schmieder, H. Cremades, C. Cid, Y. Cerrato, E. Saiz, P. Demoulin, A.N. Zhukov, L. Rodriguez, A. Aran, M. Menvielle, and S. Poedts
Projects: None

Publication Status: in press
Last Modified: 2008-11-19 13:00
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Subject will be restored when possible  

Sergio Dasso   Submitted: 2007-10-12 12:57

Magnetic clouds (MCs) are highly magnetized plasma structures that have a low proton temperature and a magnetic field vector that rotates when seen by a heliospheric observer. More than 25 years of observations of magnetic and plasma properties of MCs at 1 AU have provided significant knowledge of their magnetic structure. However, because in situ observations only give information along the trajectory of the spacecraft, their real 3D magnetic configuration remains still partially unknown. We generate a set of synthetic clouds, exploring the space of parameters that represents the possible orientations and minimum distances of the satellite trajectory to the cloud axis, p. The synthetic clouds have a local cylindrical symmetry and a linear force free magnetic configuration. From the analysis of synthetic clouds, we quantify the errors introduced in the determination of the orientation/size (and, consequently, of the global magneto-hydrodynamic quantities) by the Minimum Variance method when p is not zero.

Authors: A.M. Gulisano, S. Dasso, C.H. Mandrini, and P. Demoulin
Projects: None

Publication Status: in press
Last Modified: 2007-10-12 13:02
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Transformation of a flux rope to an ICME  

Sergio Dasso   Submitted: 2007-06-19 16:12

The solar wind conditions at one astronomical unit (AU) can be strongly disturbed by the interplanetary coronal mass ejections (ICMEs). A subset, called magnetic clouds (MCs), is formed by twisted flux ropes that transport an important amount of magnetic flux and helicity which is released in CMEs. At 1 AU from the Sun, the magnetic structure of MCs is generally modeled neglecting their expansion during the spacecraft crossing. However, in some cases, MCs present a significant expansion. We present here an analysis of the huge and significantly expanding MC observed by the Wind spacecraft during 9 and 10 November, 2004. This MC was embedded in an ICME. After determining an approximated orientation for the flux rope using the minimum variance method, we precise the orientation of the cloud axis relating its front and rear magnetic discontinuities using a direct method. This method takes into account the conservation of the azimuthal magnetic flux between the in- and out-bound branches, and is valid for a finite impact parameter (i.e., not necessarily a small distance between the spacecraft trajectory and the cloud axis). The MC is also studied using dynamic models with isotropic expansion. We have found (6.2 pm 1.5) imes 1020 Mx for the axial flux, and (78 pm 18) imes 1020 Mx for the azimuthal flux. Moreover, using the direct method, we find that the ICME is formed by a flux rope (MC) followed by an extended coherent magnetic region. These observations are interpreted considering the existence of a previous larger flux rope, which partially reconnected with its environment in the front. We estimate that the reconnection process started close to the Sun. These findings imply that the ejected flux rope is progressively peeled by reconnection and transformed to the observed ICME (with a remnant flux rope in the front part).

Authors: Dasso S., Nakwacki M.S., D'emoulin P., and Mandrini C.H.
Projects: None

Publication Status: Solar Physics (in press)
Last Modified: 2007-06-20 08:27
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A new model-independent method to compute magnetic helicity in magnetic clouds  

Sergio Dasso   Submitted: 2006-07-03 14:46

Magnetic clouds are transient magnetic structures expulsed from the Sun that travel toward the external heliosphere carrying a significant amount of magnetic flux and helicity. To improve our understanding of magnetic clouds in relation to their solar source regions, we need a reliable method to compute magnetic flux and helicity in both regions. Here we evaluate the sensitivity of the results using different models, methods and magnetic-cloud boundaries applied to the same magnetic cloud data. The magnetic cloud was observed by the spacecraft Wind on October 18-20, 1995. We analyze this cloud considering four different theoretical configurations (two force free and two non-force free) that have been previously proposed to model cloud fields. These four models are applied using two methods to determine the orientation of the cloud axis: minimum variance and simultaneous fitting. Finally, we present a new method to obtain the axial and azimuthal magnetic fluxes and helicity directly from the observed magnetic field when rotated to the cloud frame. The results from the fitted models have biases that we analyze. The new method determines the centre and the rear boundary of the flux rope when the front boundary is known. It also gives two independent measurements in the front and back parts for the fluxes and helicity; they are free of model and boundary biases. We deduce that the leading flux of the magnetic cloud had reconnected with the overtaken solar-wind magnetic field and estimate the fluxes and helicity present in the full cloud before this reconnection.

Authors: S. Dasso, C.H. Mandrini, P. D?emoulin, and M.L. Luoni
Projects: None

Publication Status: in press
Last Modified: 2006-07-03 14:49
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Linking two consecutive non-merging magnetic clouds with their solar sources
Subject will be restored when possible
Transformation of a flux rope to an ICME
A new model-independent method to compute magnetic helicity in magnetic clouds

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