November 18, 2011, 12:00 pm - 1:00 pm
Director's Seminar
Sarah Jones (NASA/GSFC), Aurora: Remote Sensing of the
Earth's Magnetosphere
Abstract: The charged particles which cause the aurora generally come from trapped particle populations within the Earth’s magnetosphere which are then accelerated or scattered into the Earth’s atmosphere by various mechanisms. Thus the creation of the aurora is typically a direct result of magnetospheric processes with the shape and motion of the aurora providing valuable information as to the nature of these acceleration and scattering mechanisms. Because the aurora provides a visual manifestation of the coupling between the magnetosphere and ionosphere, the study of aurora provides an important means of remote sensing the magnetosphere. In the case of pulsating aurora, properly characterizing the widespread region of pulsating aurora is critical for identifying related magnetospheric structures and processes.
Larry Kepko (NASA/GSFC), Do Impulsive Solar Eruptions
Leave Tracers in Polar Ice?
Abstract: Solar cosmic rays, sometimes referred to as solar proton events, are the result of particle acceleration associated with sudden energy releases in the solar atmosphere. The visible manifestations of these energy releases are large solar flares and fast coronal mass ejections. The most energetic solar proton events, particularly those with high fluxes of solar protons, often have significant impacts on the terrestrial and geospace environments. Direct space measurements of solar cosmic ray events are limited to the last four solar cycles; however, ground-based instrumentation to monitor the cosmic ray flux has been in operation continuously since 1935. Several studies have suggested an association between impulsive nitrate enhancements observed in polar ice and solar proton events. If validated, this association would allow for the use of polar ice nitrate records as proxies for impulsive solar activity, and extend the solar record of large, impulsive events back several centuries. In this talk I first introduce the physical model accounting for nitrates in polar ice. I then present results from a high-resolution nitrate analysis of shallow Greenland ice cores. The analysis reveals sub-annual variations to a degree not available in previous studies, and I compare this nitrate record to the solar proton record. I show that the associate between impulsive nitrate enhancements in polar ice and large solar proton events is real, and that the timescale for deposition is on the order of a few weeks.