On the 630 nm red‐line pulsating aurora: Red‐line Emission Geospace Observatory observations and model simulations

Abstract In this study, we present observations of red‐line (630 nm) pulsating auroras using the camera system of Red‐line Emission Geospace Observatory (REGO), during a geomagnetic storm interval. We also develop a time‐dependent model to simulate the 630 nm auroral pulsations in response to modulated precipitation inputs and compare the model outputs with REGO observations. Key results are as follows. (1) Notwithstanding the long radiative timescale of the 630 nm emission, red‐line auroras can still be modulated by pulsating electron precipitations and feature noticeable oscillations, which constitute the red‐line pulsating auroral phenomena. (2) In a majority of cases, the oscillation magnitude of red‐line pulsating auroras is substantially smaller than that of the concurrent pulsating auroras seen on Thermal Emission Imaging System whitelight images (generally dominated by 557.7 nm green‐line emissions). Under certain circumstances, e.g., when the characteristic energy of the precipitation is very high, some of the pulsating auroras may not show discernible imprints on red line. (3) The altitude range contributing most to the red‐line pulsating aurora is systematically lower than that of the steady‐state red‐line aurora, since the slower O( 1 D ) loss rate at higher altitudes tends to suppress the oscillation range of the 630 nm emission rate. (4) We find that some pulsating auroral patches are characterized by enhanced red‐to‐green color ratio during their on time, hinting that the percentage increase of the red‐line auroral component exceeds that of the green‐line auroral component for those patches. We suggest that those special patches might possibly be associated with lower energy (<1 keV) electron precipitations. Key Points We present an unprecedentedly detailed and systematic investigation on red‐line (630 nm) pulsating auroras We develop a time‐dependent model to simulate the 630 nm aurora in response to pulsating precipitation input and compare with observations Some pulsating auroral patches are characterized by enhanced red‐to‐green ratio, potentially hinting at a soft‐electron precipitation origin