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Asymmetric Filling in the Northern and Southern Magnetospheric Lobes
Dependent Source of Asymmetry
Relative Importance – Secondary
Description:
The amount and composition of plasma going into each magnetospheric is asymmetric with more ionospheric plasma filling the lobe connected to the summer hemisphere than the winter hemisphere. The source of lobe plasma (i.e., ionosphere or solar wind) may also be asymmetric across the lobes due to dipole tilt changing the access paths into the lobes. Figure caption: An illustration of the asymmetric filling of the lobes (Glocer et al., 2020)
Causes: Dipole Tilt, Earth’s Rotation (Diurnal), Solar EUV
There is significant hemispheric asymmetry in the outflow of plasma from each hemisphere leading to asymmetric filling and composition in the lobes. In particular, there is significant seasonal effect where the summer hemisphere exhibits more outflow than the winter hemisphere (Lennartsson et al., 2004). In addition to more total outflow in the summer hemisphere, the outflow in this hemisphere contains more O+ than the outflow in the winter hemisphere. The result is that Earth’s magnetic lobes are being filled asymmetrically in terms of the total amount of plasma going into the lobes, and the composition of that plasma (Glocer et al., 2020).
Effects: Magnetotail Structure
The result of the asymmetry is potentially multiple: Plasma sheet and ring current: Under southward IMF conditions, lobe plasma is advected into the plasma sheet. It is well established that the ring current development is highly dependent on the amount and composition of plasma sheet supply. The degree to which asymmetric lobe composition plays a role in setting the plasma sheet and ring current populations compared to symmetric conditions is yet to be investigated thoroughly. Magnetotail tilt: Asymmetric filling of the lobes has been suggested to result in flapping of the magnetotail (Barakat et al., 2015). This suggestion was largely due to diurnal variation in the filling associated with the offset between the magnetic and rotation axis. The effect of asymmetric filling due to longer term season effects may also result in a systematic tilt in the magnetotail. Such an effect has yet to be investigated. Tail reconnection: Asymmetric composition in the lobes can also lead to asymmetric density and composition near the nightside x-line. PIC simulations indicate that the resulting asymmetry in the diffusion region can lead to motion of the reconnection location (Kolstø et al., 2020))
Modeling Capability:
Capturing this effect requires a global magnetosphere model with an outflow representation at the inner boundary that includes seasonal asymmetry. Single fluid MHD, for example, could track the asymmetric filling of the lobes without also tracking composition. Multifluid MHD would track both asymmetric lobe filling and composition.
BATS-R-US MHD
Can track asymmetric filling and composition when configured with multifluid MHD and coupled with PWOM. PWOM must be configured to provide separate solutions for northern and southern hemispheres (see Glocer et al., 2020)
LFM MHD
Unknown
OpenGGCM
Unknown
GUMICS
Unknown
Can track asymmetric filling and composition when configured with multifluid MHD and coupled with PWOM. PWOM must be configured to provide separate solutions for northern and southern hemispheres (see Glocer et al., 2020)
References:
https://doi.org/10.1029/2020JA028205 https://doi.org/10.1029/2004JA010690 https://doi.org/10.1029/2019GL085359
