Multispacecraft Observations of the Simultaneous Occurrence of Magnetic Reconnection at High and Low Latitudes During the Passage of a Solar Wind Rotational Discontinuity Embedded in the April 9‐11, 2015 ICME.

Numerous questions remain about how solar wind directional discontinuities, for example, rotational discontinuities (RDs), affect energy and transport processes at the magnetopause. The impact on the dayside magnetosphere of a solar wind RD is studied. The study shows that the RD leads to complex structures at the magnetopause, boundary layer, mantle, and cusp even though the geomagnetic activity level remains low. At low altitudes, the Defense Meteorological Satellite Program spacecraft observe a double cusp that is a signature of magnetic reconnection occurring at both high and low latitudes due to the dominant IMF By, while Cluster C2, located at high‐latitude and high‐altitude in the southern hemisphere, observes velocity fluctuations and reversals with peak‐to‐peak amplitudes >800 km s−1 as it crosses the magnetopause. A global MHD simulation of the event shows that the C2 observations are consistent with the spacecraft crossing reconnection outflows while moving from one side of the X‐line to the other. Plain Language Summary: Many studies of the geoffectiveness of the solar wind structures tend to focus on large structures such as coronal mass ejections or corotating high‐speed streams, which can drive large geomagnetic activities such as storms or substorms. Fewer studies focus on the smaller scale structures such as solar wind directional discontinuity (DD). Numerous questions remain about how DDs affect energy conversion and transport processes at the magnetopause. We present an example that shows that a solar wind rotational discontinuity (RD), which is a class of DD, and its accompanying flow rotation can lead to complex structures at the magnetopause, boundary layer, mantle, and cusp even though the geomagnetic activity level remains low. At low altitudes, the Defense Meteorological Satellite Program spacecraft observe a double cusp that is a signature of magnetic reconnection occurring at both high and low latitudes due to the dominant IMF By, which is corroborated in a global MHD simulation. Cluster C2, located at high‐latitude and high‐altitude, observes velocity fluctuations and reversals with peak‐to‐peak amplitudes >800 km s−1 as it crosses the magnetopause. The MHD simulation of the event shows that the C2 observations are consistent with the spacecraft crossing reconnection outflows while moving from one side of the X‐line to the other. Key Points: A solar wind rotational discontinuity can lead to complex structures at the magnetopause, boundary layer, and cusp even during quiet timesDefense Meteorological Satellite Program observes double cusp signatures indicating that reconnection is occurring at both high and low latitudes due to dominant IMF ByThe observed large velocity reversals at the magnetopause are consistent with Cluster moving from one side of the X‐line to the other [ABSTRACT FROM AUTHOR]