Event Title

The Possible Role of Magnetosphere-Ionosphere Coupling in Substorms

Location

Yosemite National Park

Start Date

2-10-2014 5:25 PM

End Date

2-10-2014 5:55 PM

Description

The magnetospheric substorm is the primary process by which magnetic field added to the tail lobes by dayside reconnection is returned to the dayside. An isolated substorm has three distinct phases: the growth phase, the expansion phase, and the recovery phase. In the growth phase magnetospheric convection is driven by the flow of plasma to the dayside reconnection site and by increased pressure of open magnetic flux added to the tail lobes. The convecting magnetospheric plasma facilitates particle precipitation to the ionosphere and drives field-aligned currents whose closure through the ionosphere causes heating and the outflow of ions. A delay in the onset of nightside reconnection results in a sequence of changes in the configuration of the tail that within an hour lead to the onset of nightside reconnection. Nightside reconnection produces bursts of high-speed flow that transport newly closed magnetic flux and bubbles of depleted plasma to the midnight magnetosphere. The aurora begins to expand azimuthally and poleward forming a large bulge of active aurora. The pressure gradients and changes in flux tube volume created by these localized changes produce a new field-aligned current system - the substorm current wedge. Up to a million Amps of current is diverted from the tail through the auroral bulge further altering the ionosphere through heating and ion outflow. Within 10-30 minutes the bulge ceases to expand and the current in the wedge reaches its maximum value. In the following one and a half hours the auroral activity disappears and the current wedge dies away. If the interplanetary magnetic field remains southward activity continues. If solar wind driving is moderate the magnetosphere enters a new mode of balanced reconnection where no configuration changes occur and no auroral expansion is observed. This is called steady magnetospheric convection. However, if the driving is strong the magnetosphere enters the sawtooth oscillation mode consisting of a quasi-periodic sequence of large substorms. It has been suggested that this mode is a result of feedback between ion outflow and the magnetotail reconnection process. In this paper we will review recent work on ion outflow during different phases of the substorm and speculate on possible effects of these ions. We will also investigate the temporal response of the substorm electrojet to the solar wind using linear prediction filters. Filters will be calculated for different substorms in a sequence of substorms to determine if there are progressive changes in temporal response that might be explained by the increasing presence of ions in the plasma sheet or by changes in ionospheric conductivity.

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Feb 10th, 5:25 PM Feb 10th, 5:55 PM

The Possible Role of Magnetosphere-Ionosphere Coupling in Substorms

Yosemite National Park

The magnetospheric substorm is the primary process by which magnetic field added to the tail lobes by dayside reconnection is returned to the dayside. An isolated substorm has three distinct phases: the growth phase, the expansion phase, and the recovery phase. In the growth phase magnetospheric convection is driven by the flow of plasma to the dayside reconnection site and by increased pressure of open magnetic flux added to the tail lobes. The convecting magnetospheric plasma facilitates particle precipitation to the ionosphere and drives field-aligned currents whose closure through the ionosphere causes heating and the outflow of ions. A delay in the onset of nightside reconnection results in a sequence of changes in the configuration of the tail that within an hour lead to the onset of nightside reconnection. Nightside reconnection produces bursts of high-speed flow that transport newly closed magnetic flux and bubbles of depleted plasma to the midnight magnetosphere. The aurora begins to expand azimuthally and poleward forming a large bulge of active aurora. The pressure gradients and changes in flux tube volume created by these localized changes produce a new field-aligned current system - the substorm current wedge. Up to a million Amps of current is diverted from the tail through the auroral bulge further altering the ionosphere through heating and ion outflow. Within 10-30 minutes the bulge ceases to expand and the current in the wedge reaches its maximum value. In the following one and a half hours the auroral activity disappears and the current wedge dies away. If the interplanetary magnetic field remains southward activity continues. If solar wind driving is moderate the magnetosphere enters a new mode of balanced reconnection where no configuration changes occur and no auroral expansion is observed. This is called steady magnetospheric convection. However, if the driving is strong the magnetosphere enters the sawtooth oscillation mode consisting of a quasi-periodic sequence of large substorms. It has been suggested that this mode is a result of feedback between ion outflow and the magnetotail reconnection process. In this paper we will review recent work on ion outflow during different phases of the substorm and speculate on possible effects of these ions. We will also investigate the temporal response of the substorm electrojet to the solar wind using linear prediction filters. Filters will be calculated for different substorms in a sequence of substorms to determine if there are progressive changes in temporal response that might be explained by the increasing presence of ions in the plasma sheet or by changes in ionospheric conductivity.