Nowadays, there is a great need for the preservation of historical data in earth sciences
as time series covering a long time period are of extreme importance in studying long-term
variations of the Earth’s environment. This is the case in the field of atmospheric
electricity research, too. In this work, we focus on one of the most frequently recorded
parameters of the discipline, the atmospheric electric potential gradient (PG).The
PG is the reverse of the vertical atmospheric electric field, a quasi-DC quantity
measured in Vm-1 units usually near the ground most often at 1–3 m heights [1]. The
PG has been measured quasi-continuously at the Széchenyi István Geophysical Observatory
near Nagycenk, Hungary (NCK, 47°38’ N, 16°43’ E) since 1962 [2]. Between 1962 and
2011, the PG was recorded on photo papers which were evaluated manually and the hourly
averaged PG values were archived. Nevertheless, the original photopapers, too, were
kept.In this contribution, we present a recently developed image processing algorithm
to digitize the analogue PG records on the old photo papers semi-automatically. By
means of this algorithm, PG averages can be obtained with a temporal resolution as
high as 30 s. In order to validate the digitized data, they have been compared to
the archived hourly PG averages between 1999 and 2009. The long-term, seasonal, and
diurnal variations of the PG at NCK between 1999 and 2009 based on the digitized and
the archived data are also presented.[1] Rycroft, M. J., Israelsson, S., and Price,
C.: The global atmospheric electric circuit, solar activity and climate change, J.
Atmos. Sol.-Terr. Phy., 62, 1563–1576, 2000.[2] Bór, J., Sátori, G., Barta, V., Szabóné-André,
K., Szendrői, J., Wesztergom, V., Bozóki, T., Buzás, A., and Koronczay, D.: Measurements
of atmospheric electricity in the Széchenyi István Geophysical Observatory, Hungary,
Hist. Geo Space. Sci., 11, 53–70, https://doi.org/10.5194/hgss-11-53-2020, 2020.
