Seeking sprite-induced signatures in remotely sensed middle atmosphere NO₂: Latitude and time variations

Recent research on sprites shows these and other transient luminous events can exert a local impact on atmospheric chemistry, although with minor effects at global scales. In particular, both modelling and remote sensing work suggest perturbations to the background NO_x up to a few tens of per cent can occur above active sprite-producing thunderstorms. In this study we present a detailed investigation of MIPAS/ENVISAT satellite measurements of middle atmospheric NO₂ in regions of high likelihood of sprite occurrence during the period August to December 2003. As a proxy of sprite activity we used ground based WWLLN detections of large tropospheric thunderstorms. By investigating the sensitivity of the analysis to the characteristics of the adopted strategy, we confirm the indication of sprite-induced NO₂ enhancements of about 10% at 52 km height and tens of per cent at 60 km height immediately after thunderstorm activity, as previously reported by Arnone et al (2008b Geophys. Res. Lett. 35 5807). A further analysis showed the enhancement to be dominated by the contribution from regions north of the Equator (5°N to 20°N) during the first 30 to 40 days of the sample (i.e. the tail of Northern Hemisphere summer) and in coincidence with low background winds.