The response of mesospheric NO to geomagnetic forcing in 2002–2012 as seen by SCIAMACHY

Abstract

Daily NO number density, retrieved from measurements of the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) from 2002 to 2012 for polar summer in the mesosphere, is used to investigate the response of NO to geomagnetic activity, as expressed by the auroral electrojet (AE) index. Applying the superposed epoch analysis, we observe a clear response of NO to strong geomagnetic forcing at geomagnetic latitudes 55–75°N/S and altitudes above 66 km. The 27 day solar rotation cycle is observed, indicating that some of the observed geomagnetic events are related to solar coronal holes. We find a linear relationship between anomalies of AE and NO at geomagnetic latitudes 55–70°N/S and 70–74 km altitude. A clear auroral oval‐like structure is observed on days of strong geomagnetic forcing in both hemispheres, with small longitudinal inhomogeneities, which might be related to the South Atlantic Anomaly or the magnetic local time. The NO lifetime and production rate per AE anomaly has been derived from a least squares fit to the observations. Comparisons of results from a simple model using this empirical NO production and a lifetime varying from 1.2 days in summer to 10 days in winter to SCIAMACHY observations show good agreement. In particular, the strength and interannual variability of the wintertime maximum is well captured. This suggests that direct production of NO in the upper mesosphere above 72 km contributes substantially to the so‐called energetic particle precipitation indirect effect.

Thermospheric nitric oxide response to shock‐led storms

“…Sinnhuber et al . [] also concluded that some mesospheric NO x enhancements are the result of downward transport from auroral thermospheric altitudes during long polar night conditions. The important implication is that shock‐led ICMEs arriving at Earth during solstice months (even without an appreciable population of high‐energy solar energetic particles) can provide a source of NO that influences mesospheric‐stratospheric ozone chemistry and modulates thermospheric temperature.…”

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.…”

“…70-80 km in altitude). This altitude region was selected because of the clear and direct MEE impact seen in satellite observations (e.g., Andersson et al, 2014a, b;Fytterer et al, 2015b;Sinnhuber et al, 2016). WACCM version 4 (see above) was used with 1.9 • × 2.5 • horizontal resolution extending from the surface to 5.9 × 10 −6 hPa (≈ 140 km geometric height) in the specified dynamics mode, nudged to MERRA reanalysis at every dynamics time step below about 50 km.…”

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).…”