SH53C-03
Probing the Boundaries of the Heliosphere by Analyzing the Temporal Variation of the Polar ENA Flux
Friday, 18 December 2015: 14:04
2011 (Moscone West)
Daniel Brett Reisenfeld1, Paul H Janzen2, Maciej Bzowski3, Kostas Dialynas4, Herbert O Funsten5, Stephen A Fuselier6, Nishu Karna7, Marzena A. Kubiak8, David J McComas6, Nathan Schwadron9 and Justyna M Sokol3, (1)University of Montana, Department of Physics & Astronomy, Missoula, MT, United States, (2)University of Montana, Missoula, MT, United States, (3)Space Research Center Polish Academy of Sciences, Warszawa, Poland, (4)Academy of Athens, Office for Space Research and Technology,, Athens, Greece, (5)Los Alamos Natl Laboratory, Los Alamos, NM, United States, (6)Southwest Research Institute, San Antonio, TX, United States, (7)George Mason University Fairfax, Fairfax, VA, United States, (8)Space Research Center Polish Academy of Sciences, Warsaw, Poland, (9)Solar System Exploration Research Virtual Institute, NASA Ames Research Center, Moffett Field, CA, United States
Abstract:
With nearly seven years of IBEX observations, we can now trace the time evolution of heliospheric ENAs through over half a solar cycle. At the north and south ecliptic poles, the spacecraft attitude allows for continuous coverage of the ENA flux; thus, signal from these vantages have much higher statistical accuracy and time resolution than anywhere else in the sky. By assuming pressure balance across the termination shock, and comparing the solar wind dynamic pressure measured at 1 AU with the heliosheath plasma pressure derived from the observed ENA fluxes, we show that the heliosheath pressure measured at the poles correlates well with the solar cycle. The analysis requires time-shifting the ENA measurements to account for the travel time out and back from the heliosheath. The time shifts at the north pole range from 5.1 years at 700 eV, the low end of the IBEX-Hi energy range, to 3.2 years at 4.3 keV, the top IBEX-Hi energy. These time shifts assume a common mean distance to the ENA source region for all energies. For the south pole, the best-fit time shifts range from 4.1 to 2.6 years across the IBEX-Hi energy range. Hence, the ENA source at the south is somewhat closer than at the north, consistent with an asymmetric heliosphere model. We will present the details of this analysis, as well as estimates of the scale size of the heliosheath in the polar directions.
