[IGPP Everyone] EPSS Space Physics seminar announcement - Friday October 15, 2021 - 03:30 PM Pacific Time (US and Canada)

[Sowmendran, Margie (IGPP)]

SPACE PHYSICS SEMINAR

DEPARTMENT OF EARTH, PLANETARY, AND SPACE SCIENCES
DEPARTMENT OF ATMOSPHERIC AND OCEANIC SCIENCES
UNIVERSITY OF CALIFORNIA, LOS ANGELES

ZOOM LINK PROVIDED BELOW

 https://ucla.zoom.us/j/92101918782?pwd=Z2o5RmI4OEpBWW4zcG1DZStIUWgrZz09


Solar Wind Triggering of Substorms

Robert L McPherron
Distinguished Research Professor
Department of Earth, Planetary, and Space Sciences
University of California Los Angeles



We investigate whether substorms can be triggered by the solar wind. We conclude many are. A new program to identifies negative bay onsets in the AL index and finds omh106,527 onsets from 1981 to 2019. This list controls a superposed epoch analysis of the solar wind AL coupling function obtaining its average behavior relative to onset. Only 68,700 events have enough data to calculate coupling. Its average is a peak of about 4 hour’s duration with maximum at substorm onset. This is the origin of the concept of triggering by northward turnings. Close examination shows that the peak is preceded by a plateau followed by a sharp rise starting 13 minutes before onset. The average of the coupling derivative has two features. The first is a sinusoidal variation corresponding to the gradual increase and decrease in coupling. This the expected from regression to the mean. Superimposed on this is a positive pulse starting at -13 minutes, peaking at 7 minutes, and passing through zero at onset. The pulse is present in all subsets of the list except weak substorms. It is present at all levels of correlation of the average with every event.  Solar wind averages reveal that this trigger is caused by a transient event where the speed increases by 10% over an interval of 30 minutes. The transverse field increases by a similar amount and the clock angle factor increases by 25%. We speculate that the onset is triggered by a rapid increase in convection due the increase in coupling. We use statistical procedures to estimate the number of substorms that are triggered in this manner.

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Friday, October 15, 2021
3:30 - 5:00 PM

In-Charge:  Marco Velli

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