SPACE AND COSMIC RAY PHYSICS SEMINAR

University of Maryland
Atlantic Building, Room 2400
4:30 PM Monday, November 22, 2010
Coffee, Tea & Snacks 4:15-4:30 PM

Merav Opher
George Mason University
Is the magnetic field in the outer heliosphere laminar II:
the global structure of the sector region and observations from Voyager

Much of our current understanding of the edge of the solar system is being challenged with recent observations of missions such as Voyager and IBEX. The current global models of the heliosphere are based on the assumption that the magnetic field in the outer heliosheath close to the heliopause is laminar. In this talk we continue the exploration of the previous talk, arguing that in the outer heliosheath the heliospheric magnetic field is not laminar but instead consists of nested magnetic islands. We discuss the implications of these ideas to the global structure of the heliosphere and to observations. Recently, we proposed (Drake et al. 2009) that the annihilation of the “sectored” magnetic field within the heliosheath as it is compressed on its approach to the heliopause produces the anomalous cosmic rays and also energetic electrons. As a product of the annihilation of the sectored magnetic field, densely-packed magnetic islands are produced. These magnetic islands will be convected with the ambient flows as the sector boundary is carried to higher latitudes filling the outer heliosheath. We further argue that the magnetic islands will develop upstream within the heliosheath. As a result, the magnetic field in the heliosheath sector region will be disordered well upstream of the heliopause. We present a 3D MHD simulation with very high numerical resolution that captures the north-south boundaries of the sector region. We show that due to the high pressure of the interstellar magnetic field a north-south asymmetry develops such that the disordered sectored region fills a large portion of the northern part of the heliosphere with only a smaller extension in the southern hemisphere. We suggest that this scenario is supported by the following changes that occur around 2009.16 onward (and previously around 2008): a) the sudden decrease in the intensity of low energy electrons (0.02-1.5MeV) detected by Voyager 2 ; b) a sharp reduction in the intensity of fluctuations of the radial flow; and c) the dramatic differences in intensity trends between galactic cosmic ray electrons (3.8-59 MeV) at Voyager 1 and 2 (McDonald 2010). We argue that these observations are a consequence of Voyager 2 leaving the sector region of disordered field during these periods and crossing into a region of unipolar laminar field.


Sponsored by: Department of Physics and the Institute for Physical Science and Technology, University of Maryland. For information call Catha Stewart at (301) 405-4811 or go to the UMD Space Physics group seminar web site.

There is free parking after 4:00 PM in lot B (the big parking garage across the street from the ATL building). There are a limited number of spaces in lot Q next to the new ATL wing with free parking after 4PM even when there is a basketball game on campus.