A new multi-year data set of Potential Gradient variations at a suburban site in Northeastern Germany

We report the characteristics of a new multi-year atmospheric electricity data set obtained in a suburban area in Northeastern Germany, a region where comparable measurements have been missing so far. Specifically, a CS110 electric field mill (Campbell Scientific) operates since March 2021 as part of a small weather station located at the Herrenkrug campus of Magdeburg-Stendal University of Applied Sciences in Magdeburg, Germany (52.13939°N, 11.67628°E) at an altitude of approximately 50 m a.s.l. Continuous measurements have since been undertaken at 1-minute temporal resolution, providing valuable data on local atmospheric Potential Gradient (PG) variability and their linkages with Global Electric Circuit (GEC) characteristics.

PG values recorded at the site range from -1 to 1 kV/m. Typically, during undisturbed weather conditions, diurnal variation of the PG  shows a single maximum and ranges between 5 and 20 V/m. On most days, there is a noticeable drop around 6-7 UTC, followed by a maximum around 14-15 UTC. Measurements from Magdeburg demonstrate an unusually small range of daily variations compared to other sites. While theoretically expected PG values under fair weather conditions should be around 100 V/m, the local instrument has never reached such values. Recent PG measurements performed at three different stations of the GLOCAEM network with an identical instrument showed median PG values in a range between 60 and 240 V/m during unperturbed conditions (Nicoll et al. 2019), while our measurements exhibited a median value of only 13.5 V/m, demonstrating that both PG median amplitude and variability obtained at the site are smaller than would be expected. 

To further investigate this issue, a short campaign with parallel measurements using an identical reference instrument has been undertaken during summer and fall of 2024. Since the original field mill is located inside a fenced area, it might be expected that the surrounding metallic fence negatively affects the measurements. By conducting parallel measurements with the reference field mill also being placed inside the fenced area, we however did not find significant systematic effects of the fence on the measured PG values. 

A second series of measurements was conducted at about 200 m distance from the original field mill, where the surrounding area was relatively clear from any trees and built infrastructure. Measurements at this site have been obtained under different weather conditions. While there exists considerable co-variability between both sites during most of the day, we found much larger, even qualitative differences between both instruments arising during sunrise and sunset. 

The results of our parallel measurements contribute to identifying discrepancies between co-located electric field measurements, which have also been reported in other previous studies, and clarifying the underlying root causes. To this end, the reference measurements during daytime have been used to determine a statistical correction for the values obtained with our primary instrument, which will be further employed for calibrating our ongoing measurements. The thus obtained long-term time series of local PG variations provides a new dataset allowing further detailed studies of atmospheric electricity variations in suburban areas of Central Europe.