Auroral particle precipitation characterized by the substorm cycle

Abstract

Substorms release a large amount of energy, some of which is used to energize the precipitating particles in the polar region. Superposed epoch analysis was performed with 11 years of DMSP SSJ/4/5 data to characterize the substorm cycle of the diffuse, monoenergetic, and broadband/wave precipitating electrons and precipitating ions. Although substorms only increase the ion pressure by 30%, they increase the power of the diffuse, monoenergetic, and wave electron aurora by 310%, 71%, and 170%, respectively. Substorms energize the ion aurora mainly in the 21:00–05:00 magnetic local time (MLT) sector. The dynamics of the diffuse electron aurora are different from those of the other two electron aurorae. The expansion phase duration is approximately 15 min for the monoenergetic and wave electron aurorae, whereas it is 1 h for the diffuse electron aurora. The monoenergetic and wave electron aurorae appear to complete the substorm cycle within a 5 h interval, whereas the diffuse electron aurora takes more than 5 h. The diffuse electron aurora power and energy flux start increasing at 15 min before the substorm onset, whereas those for the monoenergetic and wave electron aurorae start increasing at 1 h and 15 min before the onset. The increase in the monoenergetic electron aurora power and energy flux may result from the increase in the magnetotail stretching and region‐1 field‐aligned current during the growth phase. The monoenergetic electrons may also be associated with fast flows, which have been previously observed more frequently in the dusk‐midnight sector.

Pulsating aurora and cosmic noise absorption associated with growth-phase arcs

“…During the recovery phase, patches of pulsating auroral emission of ≈ 100 km horizontal extent switch on and off with a recurrence period ranging from a few seconds to a minute (Lessard et al, 2007). Satellite-based observations suggest that they are caused by time-varying flux of high-energy (> 10 keV) electrons (Wing et al, 2013). Weak pulsations in the CNA with close correlation to the optical phenomena have been reported (Brekke, 1971;Grandin et al, 2017).…”

“…The energetic particles released into the atmosphere during a substorm originate from the plasma sheet (Wing et al, 2013). They travel along the field lines and precipitate into the ionosphere.…”

Non-triggered auroral substorms and long-period (1–4 mHz) geomagnetic and auroral luminosity pulsations in the polar cap

“…Golovchanskaya et al (2015) reported a visible precursor approximately 40 min before a substorm onset (the so-called east-west type precursor activity of the auroral onset). Wing et al (2013) studied the power of wave/broadwave, monoenergetic, and diffuse auroral electrons 2 h before and 3 h after onset of an isolated substorm (i.e., a substorm which is separated by at least 5 h from other substorms) using data from DMSP satellites. It was reported that the wave power observed in the monoenergetic electron aurora peaked in the dusk-midnight sector and slowly started increasing about 1 h and 15 min before an onset.…”

Dawn‐Dusk Asymmetries in the Auroral Particle Precipitation and Their Modulations by Substorms

“…The increases are 71%, 170%, and 310% for the monoenergetic, broadband, and 456 diffuse electron auroral powers, respectively. In contrast, the ion pressure increases only by 30% 457 [Wing et al, 2013]. At the end of the expansion phase (maximum power), different types of 458 electron auroral power decays at different rates.…”

“…These dawn-dusk asymmetries can also manifest in the auroral 48 ion and electron precipitation in the ionosphere [e.g., Newell et al, 2010;Wing et al, 2013]. 49…”