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

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
... mehr
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.