Observation of 27 day solar cycles in the production and mesospheric descent of EPP‐produced NO

Abstract

Nitric oxide (NO) is produced by energetic particle precipitation (EPP) in the mesosphere‐lower thermosphere (MLT) region, and during the polar winter, NO can descend to stratospheric altitudes where it destroys ozone. In this paper, we study the general scenario, as opposed to a case study, of NO production in the thermosphere due to energetic particles in the auroral region. We first investigate the relationship between NO production and two geomagnetic indices. The analysis indicates that the auroral electrojet index is a more suitable proxy for EPP‐produced NO than the typically used midlatitude Ap index. In order to study the production and downward transport of NO from the lower thermosphere to the mesosphere, we perform superposed epoch analyses on NO observations made by the Solar Occultation For Ice Experiment instrument on board the Aeronomy of Ice in the Mesosphere satellite. The epoch analysis clearly shows the impact of the 27 day solar cycle on NO production. The effect is observed down to an altitude range of about 50 km to 65 km, depending on the hemisphere and the occurrence of stratospheric warmings. Initially, a rapid downward transport is noted during the first 10 days after EPP onset to an altitude of about 80–85 km, which is then followed by a slower downward transport of approximately 1–1.2 km/d to lower mesospheric altitudes in the order of 30 days.

Solar forcing for CMIP6 (v3.2)

“…The impact of magnetospheric particles on the atmosphere is strongly linked to the strength of geomagnetic activity; this has been shown both for the direct production of NO in the thermosphere (Marsh et al, 2004;Hendrickx et al, 2015) and mesosphere (Sinnhuber et al, 2016), for mesospheric OH production (Fytterer et al, 2015b), and for the EPP indirect effect Funke et al, 2014a). Geomagnetic activity can be constrained over centennial timescales by means of proxy data provided by geomagnetic indices.…”

NO<sub><i>y</i></sub> production, ozone loss and changes in net radiative heating due to energetic particle precipitation in 2002–2010

“…Aurorae and geomagnetic storms are much more frequent than solar proton events, and though particles do not precipitate as far down into the middle atmosphere, the amount of NO x formed due to these events likely is much larger, being the main source of the strong increase in NO in the high-latitude lower thermosphere. Variations in the density of NO x in the mesosphere and lower thermosphere related to geomagnetic activity as a proxy for auroral electron precipitation are reported based on observations, (e.g., by Kirkwood et al, 2015;Hendrickx et al, 2015;Sinnhuber et al, 2016). Mesospheric ozone loss and an increase in mesospheric OH have been observed to be related directly to increases in both electron fluxes Andersson et al, 2014a, b) and geomagnetic activity (Fytterer et al, 2015b).…”

Climate impact of idealized winter polar mesospheric and stratospheric ozone losses as caused by energetic particle precipitation

“…However, due to the simplification we cannot consider all features associated with EPP. In particular, three main effects are not taken into account: (a) energetic particles entering the atmosphere only over the auroral oval regions (Hendrickx et al, 2015;Fytterer et al, 2015); (b) the negative ozone signal due to EPP propagating from the stratopause in mid-winter to the lower stratosphere in spring within the polar vortex Damiani et al, 2016); and (c) that the polar vortex can shift off the pole to regions with more solar radiation. We, instead, apply constant ozone reduction between the stratopause and mid-stratosphere (1-10 hPa) over the entire polar cap.…”

“…In contrast, NO x persists for up to several months in the polar winter middle atmosphere. Inside the polar vortex, NO x can be transported downward from the lower thermosphere to the stratosphere, where it depletes ozone (e.g., Funke et al, 2017;Sinnhuber et al, 2014;Hendrickx et al, 2015). Observational evidence of polar winter stratospheric ozone loss due to EPP is still limited.…”