January 15, 2010, 12:30 pm - 1:30 pm
January 15, 2010, 12:30 pm - 1:30 pm
Eclipse Observations of the Fe XI 789.2 nm Line
Adrian Daw (Solar Physics Laboratory)
The first image of the corona in Fe XI 789.2 nm was taken during the total solar eclipse of 29 March 2006, revealing an emission extending out to at least 3 solar radii and localized regions of enhanced Fe10+ ion density relative to electrons. Subsequent observations of this spectral line were successfully made during the eclipses of 2008 and 2009. The Fe XI observations will be presented, together with simultaneous eclipse observations of the more widely observed Fe X 637.4, Fe XIII 1074.7 and Fe XIV 530.3 nm lines. The transition from collisionally to radiatively dominated excitation for these coronal lines will be discussed, and the data are combined to provide maps of the 2-D distribution of coronal electron temperature and iron charge state, which establishes the first direct link between the distribution of charge states in the inner corona and in interplanetary space.
Recent Results on the Solar Sources of Interplanetary Shocks
Natchimuthuk Gopalswamy (Solar Physics Laboratory)
Traveling interplanetary (IP) shocks were discovered in the early 1960s, but their solar origin has been controversial. Early research focused on solar flares as the source of the shocks, but when CMEs were discovered, it became clear that fast CMEs clearly can drive the shocks. Type II bursts are excellent signatures of shocks near the Sun (Type II radio bursts were known long before the detection of shocks and CMEs). The excellence correspondence between type II bursts and solar energetic particles (SEPs) made it clear that the same shock accelerates ions and electrons. A recent investigation involving a large number of IP shocks revealed that about 35% of IP shocks do not produce type II bursts (radio quiet) or SEPs. Comparing the RQ shocks with the radio loud (RL) ones revealed some interesting results, which will be summarized in this talk. (1) There is no evidence for blast waves. (2) Even a small fraction (20%) of RQ shocks is associated with ion enhancements at the shock when the shock passes the spacecraft. (3) The primary difference between the RQ and RL shocks can be traced to the different kinematic properties of the associated CMEs. On the other hand the shock properties measured at 1 AU are not too different for the RQ and RL cases. This can be attributed to the interaction with the IP medium, which seems to erase the difference. More details can be found in the preprint of a paper to appear in the Astrophysical Journal (http://adsabs.harvard.edu/abs/2009arXiv0912.4719G).
Examining Periodic Solar Wind Density Structures in SECCHI HI
Nicholeen M. Viall (NASA Postdoctoral Fellow, Solar Physics Laboratory)
We present an analysis of small-scale periodic solar wind density enhancements observed in SECCHI HI 1. We discuss their possible relationship to periodic fluctuations of the proton density observed in-situ with the Wind SWE data. Viall et al. [2008] used 11 years of solar wind density measurements at 1 AU and demonstrated that in addition to turbulent fluctuations, non-turbulent periodic density structures with length scales of tens to hundreds of megameters exist in the solar wind. Event studies of the periodic density structures reveal instances in which the density structures have alpha/proton abundance ratio changes associated with the density structures. Specifically, the alpha density varies with the same periodicity as the protons, but in antiphase. For those events, this strongly suggests either time varying or spatially varying coronal source plasma that created the density structures. If such periodic density structures observed at 1 AU are generated in the corona, then they may be observable in SECCHI HI1 data. We identify periodic density structures as they convect with the solar wind into the field of view of SECCHI HI and follow the train of structures as a function of time. The periodic density structures we analyze are comparable in size to the larger structures identified in-situ at 1 AU.