Local impact of solar variation on NO<SUB>2</SUB> in the lower mesosphere and upper stratosphere from 2007-2011

MIPAS/ENVISAT data of nighttime NO<SUB>2</SUB> volume mixing ratios (VMR) from 2007 until 2011 between 40 km and 62 km altitude are compared with the geomagnetic Ap index and solar Lyman α radiation. The local impact of variations in geomagnetic activity and solar radiation on the VMR of NO<SUB>2</SUB> in the lower mesosphere and upper stratosphere in the Northern Hemisphere is investigated by means of superposed epoch analysis. Observations show a clear 27 day period of the NO<SUB>2</SUB> VMR. This is positively correlated to the geomagnetic Ap index at 60-70° N geomagnetic latitude but also partially correlated to the solar Lyman α radiation. However, the dependency of NO<SUB>2</SUB> VMR on geomagnetic activity can be distinguished from the impact of solar radiation. This indicates a direct response of NO<SUB>x</SUB> (NO + NO<SUB>2</SUB>) to geomagnetic activity, probably due to precipitating particles. The response is detected in the range between 46 km and 52 km altitude. The NO<SUB>2</SUB> VMR epoch maxima due to geomagnetic activity is altitude-dependent and can reach up to 0.4 ppb, leading to mean production rates of 0.029 ppb (Ap d)<SUP>-1</SUP>. This is the first study showing the local impact of electron precipitation on trace gases at that altitudes in the spring/summer/autumn hemisphere.