Local time extent of magnetopause reconnection using space–ground coordination

Abstract

Abstract. Magnetic reconnection can vary considerably in spatial extent. At the Earth's magnetopause, the extent generally corresponds to the extent in local time. The extent has been probed by multiple spacecraft crossing the magnetopause, but the estimates have large uncertainties because of the assumption of spatially continuous reconnection activity between spacecraft and the lack of information beyond areas of spacecraft coverage. The limitations can be overcome by using radars examining ionospheric flows moving anti-sunward across the open–closed field line boundary. We therefore infer the extents of reconnection using coordinated observations of multiple spacecraft and radars for three conjunction events. We find that when reconnection jets occur at only one spacecraft, only the ionosphere conjugate to this spacecraft shows a channel of fast anti-sunward flow. When reconnection jets occur at two spacecraft and the spacecraft are separated by < 1 Re, the ionosphere conjugate to both spacecraft shows a channel of fast anti-sunward flow. The consistency allows us to determine the reconnection jet extent by measuring the ionospheric flows. The full-width-at-half-maximum flow extent is 200, 432, and 1320 km, corresponding to a reconnection jet extent of 2, 4, and 11 Re. Considering that reconnection jets emanate from reconnections with a high reconnection rate, the result indicates that both spatially patchy (a few Re) and spatially continuous and extended reconnections (> 10 Re) are possible forms of active reconnection at the magnetopause. Interestingly, the extended reconnection develops from a localized patch via spreading across local time. Potential effects of IMF Bx and By on the reconnection extent are discussed.

Geospace Plume and Its Impact on Dayside Magnetopause Reconnection Rate

“…The OCB appears as a distinct boundary in the SuperDARN spectral width data, where low spectral width values are observed equatorward of the boundary, and high, but variable spectral width values poleward of the boundary (Chisham & Freeman, 2003 , 2004 ; Chisham, Freeman, & Sotirelis, 2004 ; Chisham, Freeman, Lam, et al., 2005 ; Chisham, Freeman, Sotirelis, & Greenwald, 2005 ; Chisham, Freeman, Sotirelis, Greenwald, Lester, & Villain, 2005 ). The reconnection rate can then be estimated by measuring the magnetic flux transfer across the OCB in the frame of the OCB (Baker et al., 1997 ; Chisham et al., 2008 ; Chisham, Freeman, Coleman, et al., 2004 ; de la Beaujardiere et al., 1991 ; Freeman et al., 2007 ; Hubert et al., 2006 ; Pinnock et al., 1999 , 2003 ; Zou et al., 2019 ). Its value in the ionosphere is typically a few tens of mV/m, which often corresponds to ∼1 mV/m at the equatorial region of the magnetosphere.…”

Three‐Dimensional X‐line Spreading in Asymmetric Magnetic Reconnection

“…On the Sun, solar flare ribbons are observed to spread along the magnetic polarity inversion line unidirectionally or bidirectionally (Cheng et al, ; Fletcher et al, ; Isobe et al, ; Lee & Gary, ; Liu et al, ; Qiu, ; Qiu et al, ). In the Earth's magnetotail and magnetopause, a wide range of X‐line extents, from a few Earth radii to longer than 10 , along the current (out‐of‐plane) direction exists (Fuselier et al, ; Li et al, ; Nakamura et al, ; Phan et al, ; Zou et al, ). In the solar wind, a long extended X‐line of over hundreds of has also been reported (Phan et al, ).…”

The Spatial Extent of Magnetopause Magnetic Reconnection From In Situ THEMIS Measurements

“…(2013), Zou et al. (2019) and Zou et al. (2020), consider Δ V * > 0.5 as a reconnection event, as values of Δ V * closer to 1 mean better agreement with theory.…”

“…Ground‐based observations rely on energy transported along reconnected magnetic field lines into the ionosphere where enhanced plasma flows indicate the location and size of the X‐line. This observation method has shown broad X‐line length at the magnetopause (Fuselier et al., 2002; Milan et al., 2000; Pinnock et al., 2003), but also variability in X‐line length (Zou et al., 2019). Ground observations can also be used to determine X‐line spreading speeds (Zou et al., 2018).…”