Magnetospheric sawtooth events during the solar cycle 23

Abstract

[1] The Earth's magnetosphere and ionosphere have a variety of responses to different solar activities. As a result, there are several types of magnetosphere response modes; one of which is termed sawtooth injection events. Currently, it is still unclear whether sawtooth events occurrence has a solar cycle dependence. Partially, this is due to a lack of an event list which covers a full solar cycle. In this research, we have extended our original event list to cover the solar cycle 23, which now includes 126 events from 1996 to 2007. Sawtooth events have been grouped into three categories based on their solar wind drivers: interplanetary coronal mass ejections, stream interaction regions, and others. Then we examine in detail whether sawtooth events occurrence has dependencies on solar cycle and season. We also test a hypothesis that sawtooth events occurrence is related to a threshold of total eroded magnetic flux at the magnetopause regardless of solar wind structures. This paper suggests understanding sawtooth events and other convection modes from solar wind magnetic flux or energy aspect rather than from structure aspect, which is an important idea to understand the complicated magnetosphere dynamics.

Observations of the relationship between ionospheric central polar cap and dayside throat convection velocities, and solar wind/IMF driving

“…Figure shows the time series of spatially averaged velocity magnitude for the two regions, with the blue line indicating a calculation of the solar wind driving, , where B t is the magnitude of the component of the IMF transverse to the magnetopause and θ is the IMF clock angle ( ). The units of this function are discussed in Cai and Clauer [], where the authors empirically determined that a normalization factor of 100 makes the unit Wb/s. As discussed in section 1, this product characterizes the dayside merging rate and has been shown to correlate well with measures of magnetospheric activity [ Newell et al , ].…”

GPS TEC variations in the polar cap ionosphere: Solar wind and IMF dependence

“…[], dΦ/d t “represents the rate magnetic flux is opened at the magnetopause.” If one wishes to express this as a real physical quantity in units of Wb/s, d Φ /d t in equation must be multiplied by a normalizing factor α . By comparing d Φ /d t with open magnetic flux in the polar cap, Cai and Clauer [] estimated this factor to be α = 10 4 km 2/3 s 1/3 nT 1/3 during periods of disturbed magnetospheric conditions associated with so‐called “magnetospheric sawtooth events.” Note that d Φ /d t × α would give magnetic flux transfer rate in units of mWb/s, which is easily converted to Wb/s. The reliability of this estimated normalization factor is not clear, especially when considering the entire range of possible solar wind and magnetospheric conditions, and thus, it is not applied in this paper.…”

Magnetospheric state of sawtooth events

“…The numbers in parentheses after each of the listed parameter ranges are the MS indices shown in . Bolded‐black entries are the ones that match the corresponding MS indices in associated with the out‐of‐sample STEs found in the extended STE list by Cai and Clauer []. The bolded entries thus validate the MS specifications given in .…”

“…If the loading process happens too quickly, the system can rapidly become fully unstable and subsequently release too much energy to remain marginally stable. Thus, the association of STEs with only a small range of eroded dayside magnetopause magnetic flux (10 6 –10 6.5 Wb) as found by Cai and Clauer [] may actually be related to the notion that both the loading and unloading processes for STEs are limited.…”