Diurnal, Seasonal, and 11-yr Solar Cycle Variation Effects on the Virtual Ionosphere Reflection Height and Implications for the Met Office's Lightning Detection System, ATDnet.

The virtual ionosphere reflection height variation is investigated temporally and spatially, with specific reference to the Met Office's lightning detection network, the Arrival Time Difference Network (ATDnet). Data from this network, operating at 13.7 kHz, and a propagation model built by the Met Office based upon published theory were used to investigate this variation, specifically with regard to diurnal, seasonal, and 11-yr solar cycle variation. Variation over these temporal scales is chosen, since they correspond with variation in solar irradiance upon the earth's atmosphere, something known to drive ionosphere height variation. The virtual ionosphere reflection height is found to vary diurnally from ~65 km for the period 1000-1600 UTC to ~80 km for the period 2200-0400 UTC, from 1 June to 31 August 2013 inclusive. A similar magnitude of variation is also observed seasonally, with the ionosphere height for daytime in August 2013 being ~64 km and for December 2013 being ~76 km. No significant variation is observed between the minimum and maximum of the last solar cycle, with a difference in ionosphere height of ~1 km at most. The potential impacts of these results upon a very low-frequency (VLF) lightning detection network such as ATDnet are discussed, with solutions such as subnetting and wave-mode dominance analysis examined. [ABSTRACT FROM AUTHOR]