Multibeam energy moments of multibeam particle velocity distributions
File(s)Goldman_JGR_2020_submission2-accepted.pdf (1.74 MB)
Accepted version
Author(s)
Goldman, MV
Newman, DL
Eastwood, JP
Lapenta, G
Type
Journal Article
Abstract
High‐resolution electron and ion velocity distributions, f(v), which consist of N effectively disjoint beams, have been measured by NASA's Magnetospheric Multiscale Mission and in reconnection simulations. Commonly used standard velocity moments assume a single mean‐flow velocity for the entire distribution. This can lead to counterintuitive results for a multibeam f(v). An example is the standard thermal energy density moment (at a given space‐time point) of a pair of equal and opposite cold particle beams. This standard moment is nonzero even though each beam has zero thermal energy density. By contrast, a multibeam moment of two or more cold beams at a given position and time has no thermal energy. A multibeam moment is obtained by taking a standard moment of each beam and then summing over beams. In this paper we will generalize these notions, explore their consequences, and apply them to an f(v) which is a sum of tri‐Maxwellians. Both standard and multibeam energy moments have coherent and incoherent pieces. Examples of incoherent moments are the thermal energy density, the pressure, and the thermal energy flux (enthalpy flux plus heat flux). Corresponding coherent moments are the bulk kinetic energy density, the ram pressure, and the bulk kinetic energy flux. The difference between a standard incoherent moment and its multibeam counterpart will be defined as the “pseudothermal part” of the standard moment. The sum of a pair of corresponding coherent and incoherent moments is the undecomposed moment. Undecomposed standard moments are always equal to the corresponding undecomposed multibeam moments.
Date Issued
2020-12-01
Date Acceptance
2020-10-21
Citation
Journal of Geophysical Research: Space Physics, 2020, 125 (12), pp.1-19
ISSN
2169-9380
Publisher
American Geophysical Union
Start Page
1
End Page
19
Journal / Book Title
Journal of Geophysical Research: Space Physics
Volume
125
Issue
12
Copyright Statement
©2020. American Geophysical Union. All Rights Reserved. This is the accepted version of the following article: Goldman, M. V., Newman, D. L., Eastwood, J. P., & Lapenta, G. (2020). Multibeam energy moments of multibeam particle velocity distributions. Journal of Geophysical Research: Space Physics, 125, which has been published in final form at https://doi.org/10.1029/2020JA028340
Sponsor
Science and Technology Facilities Council (STFC)
Science and Technology Facilities Council (STFC)
Identifier
http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000603639900019&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=1ba7043ffcc86c417c072aa74d649202
Grant Number
ST/N000692/1
ST/S000364/1
Subjects
Science & Technology
Physical Sciences
Astronomy & Astrophysics
Publication Status
Published
Article Number
ARTN e2020JA028340
Date Publish Online
2020-10-26