Cummings, A. C. and Tranquille, C. and Marsden, R. G. and Mewaldt, R. A. and Stone, E. C. (2009) Radial and latitudinal gradients of anomalous cosmic ray oxygen in the inner heliosphere. Geophysical Research Letters, 36 (18). L18103. ISSN 0094-8276 http://resolver.caltech.edu/CaltechAUTHORS:20091013-093452473
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We use data from the Ulysses, Advanced Composition Explorer, and Solar Terrestrial Relations Observatory spacecraft to determine the radial and latitudinal gradients of anomalous cosmic ray oxygen in two energy ranges from 4.5–15.6 MeV/nuc in the inner heliosphere for the first time during an A<0 part of the solar cycle. Using measurements from early 2007 to mid-2008, we find that the radial gradient is ∼48 ± 13%/AU, consistent with previous inferences for A<0 and larger than that determined in the inner heliosphere for A>0. The latitudinal gradient is consistent with zero and in the range −0.3 to 0.4%/degree, suggesting that during A<0 these particles are not able to propagate into the inner heliosphere by rapid drift along the heliospheric current sheet if the tilt of the sheet is as large as 30 degrees.
|Additional Information:||©2009 American Geophysical Union. Received 8 July 2009; accepted 18 August 2009; published 19 September 2009. We thank the Wilcox Solar Observatory for making the heliospheric current sheet data available. This work was supported by NASA at Caltech under grant NNX8AI11G and contract NAS5-03131. We acknowledge the use of the Ulysses Data System in the preparation of this paper.|
|Group:||Space Radiation Laboratory|
|Subject Keywords:||anomalous cosmic rays, gradients|
|Classification Code:||2104 Interplanetary Physics: Cosmic rays; 2114 Interplanetary Physics: Energetic particles (7514); 2162 Interplanetary Physics: Solar cycle variations (7536); 7807 Space Plasma Physics: Charged particle motion and acceleration; 7859 Space Plasma Physics:|
|Official Citation:||Cummings, A. C., C. Tranquille, R. G. Marsden, R. A. Mewaldt, and E. C. Stone (2009), Radial and latitudinal gradients of anomalous cosmic ray oxygen in the inner heliosphere, Geophys. Res. Lett., 36, L18103, doi:10.1029/2009GL039851.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||George Porter|
|Deposited On:||18 Oct 2009 23:46|
|Last Modified:||26 Dec 2012 11:28|
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