Lower thermospheric wind variations in auroral patches during the substorm recovery phase

Abstract

Measurements of the lower thermospheric wind with a Fabry‐Perot interferometer (FPI) at Tromsø, Norway, found the largest wind variations in a night during the appearance of auroral patches at the substorm recovery phase. Taking into account magnetospheric substorm evolution of plasma energy accumulation and release, the largest wind amplitude at the recovery phase is a fascinating result. The results are the first detailed investigation of the magnetosphere‐ionosphere‐thermosphere coupled system at the substorm recovery phase using comprehensive data sets of solar wind, geomagnetic field, auroral pattern, and FPI‐derived wind. This study used three events in November 2010 and January 2012, particularly focusing on the wind signatures associated with the auroral morphology, and found three specific features: (1) wind fluctuations that were isolated at the edge and/or in the darker area of an auroral patch with the largest vertical amplitude up to about 20 m/s and with the longest oscillation period about 10 min, (2) when the convection electric field was smaller than 15 mV/m, and (3) wind fluctuations that were accompanied by pulsating aurora. This approach suggests that the energy dissipation to produce the wind fluctuations is localized in the auroral pattern. Effects of the altitudinal variation in the volume emission rate were investigated to evaluate the instrumental artifact due to vertical wind shear. The small electric field values suggest weak contributions of the Joule heating and Lorentz force processes in wind fluctuations. Other unknown mechanisms may play a principal role at the recovery phase.

Simultaneous FPI and TMA Measurements of the Lower Thermospheric Wind in the Vicinity of the Poleward Expanding Aurora After Substorm Onset

“…In this study, we focus on the event at 00:30 UT because it is concurrent with the TMA measurement made with the DELTA-2 rocket. The latter two events had pulsating auroral patches (Oyama et al, 2010(Oyama et al, , 2016. Figure 1, a sudden increase in the emission intensity took place at 00:22 UT in association with the poleward expansion of brighter parts of the aurora.…”

“…In this study, we focus on the event at 00:30 UT because it is concurrent with the TMA measurement made with the DELTA‐2 rocket. The latter two events had pulsating auroral patches (Oyama et al, , ).…”

Observation of pulsating aurora signatures in cosmic noise absorption data

“…The KAIRA beams were mapped to their corresponding area in the ASC images at the altitude of 100 km, which is a common value for the peak emission during pulsating aurora [ Kataoka et al , ; Oyama et al , ]. The beam width corresponds to the beam full width at half maximum (−3 dB) at 30 MHz given by McKay‐Bukowski et al [].…”

Fabry‐Perot Interferometer Observations of Thermospheric Horizontal Winds During Magnetospheric Substorms

“…Observations by the Fabry-Perot interferometer (FPI) and its all-sky type, scanning Doppler imager, reveal that thermospheric winds are more dynamic and responsive to the magnetospheric forcing in both vertical and horizontal components than modeling or statistical studies typically show (Anderson et al, 2012a(Anderson et al, , 2012b(Anderson et al, , 2012cAruliah et al, 2005;Griffin et al, 2008). Mesoscale and small-scale winds have been found in association with auroral structures, such as auroral arcs (Conde et al, 2001;Kosch et al, 2010), poleward expanding aurora after substorm onset , and auroral patches inside pulsating aurora (Oyama et al, 2010(Oyama et al, , 2016. Those findings also suggest that the thermospheric wind has more rapid responses than theories have predicted.…”