NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
Magnetospheric State of Sawtooth EventsMagnetospheric sawtooth events, first identified in the early 1990s, are named for their characteristic appearance of multiple quasiperiodic intervals of slow decrease followed by sharp increase of proton differential energy fluxes in the geosynchronous region. The successive proton flux oscillations have been interpreted as recurrences of stretching and dipolarization of the nightside geomagnetic field. Due to their often extended intervals with 210 cycles, sawteeth occurrences are sometimes referred to as a magnetospheric mode. While studies of sawtooth events over the past two decades have yielded a wealth of information about such events, the magnetospheric state conditions for the occurrence of sawtooth events and how sawtooth oscillations may depend on the magnetospheric state conditions remain unclear. In this study, we investigate the characteristic magnetospheric state conditions (specified by Psw interplanetary magnetic field (IMF) Btot, IMF Bz Vsw, AE, Kp and Dst, all time shifted with respect to one another) associated with the intervals before, during, and after sawteeth occurrences. Applying a previously developed statistical technique, we have determined the most probable magnetospheric states propitious for the development and occurrence of sawtooth events, respectively. The statistically determined sawtooth magnetospheric state has also been validated by using out-of-sample events, confirming the notion that sawtooth intervals might represent a particular global state of the magnetosphere. We propose that the sawtooth state of the magnetosphere may be a state of marginal stability in which a slight enhancement in the loading rate of an otherwise continuous loading process can send the magnetosphere into the marginally unstable regime, causing it to shed limited amount of energy quickly and return to the marginally stable regime with the loading process continuing. Sawtooth oscillations result as the magnetosphere switches between the marginally stable (loading) and unstable (unloading) phases.
Document ID
20170002766
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Fung, Shing F.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Tepper, Julia A.
(Maryland Univ. College Park, MD, United States)
Cai, Xia
(Science Systems and Applications, Inc. Hampton, VA, United States)
Date Acquired
March 31, 2017
Publication Date
August 30, 2016
Publication Information
Publication: Journal of Geophysical Research: Space Physics
Publisher: American Geophysical Union
Volume: o 121
Issue: 8
ISSN: 2169-9380
e-ISSN: 2169-9402
Subject Category
Space Sciences (General)
Report/Patent Number
GSFC-E-DAA-TN40783
Distribution Limits
Public
Copyright
Other

Available Downloads

There are no available downloads for this record.
No Preview Available