On the Structure of a Long Interval of Extremely Low Speed Solar Wind Observed by STEREO, and Comparison to Similar Events in the Same Solar Cycle

Abstract:

The passage of a solar wind stream extending from October 24 to 30, 2010, with its magnetized plasma was well monitored, ahead of Earth’s location arrival of a possible corotating stream, with the help of the STEREO-A instruments IMPACT and PLASTIC. This was an extremely slow flow which exhibited the following features
a. An interval of over 2 days showing a solar wind speed below 250 km/s
b. At the start, an expanding magnetic cloud interval lasting about 14 hrs.
c. The presence of distinct ratios in charge states suggesting presence of transient at material in and outside the magnetic cloud.
d. The presence in the plasma of a sizeable amount of He⁺⁺ which we compare with the predictions made at the observed SW speed.

We check with Lopez (1987) the observed and predicted estimates of the thermal velocity of the protons observed for the interval. In addition we present the implication on the parker model for the possible temperature of the corona assuming the dominant aspects of the outflow correspond to the case of an steady solar wind. The lack of passage of the event near Earth location is discussed, and its implications regarding its extension in space of the solar outflow and the nature of its overall origin is assessed. Although not on the same year 2010, at the Lagrangian point L1, we observe with Wind the occurrence in 2007 to 2009 of several intervals of low speed solar wind, of which for a comparison we select the two low solar wind intervals starting Nov 29, and Dec 8, 2009 which extended over more than 5 days each. These intervals at Wind have a similar extension as the one at STEREO-A. However, the presence of a MC or not are less clear for these cases. Also charge states are compared as well as the presence of the alpha--to--proton number density ratio.