The effect of the atmospheric electric field on trees

Abstract. Between the ionosphere and the Earth's surface, a continuous electric field exists that is influenced by solar activity and, particularly in the lower atmosphere, by meteorological processes. The positively charged ionosphere induces a negative charge on the Earth's surface, resulting in a continuous current flow from the surface into the atmosphere. Irregularities in the electrical properties of the surface, such as trees, cause local variations in the atmospheric electric field, which can be measured as electrical potential gradients along the tree stem. Owing to its higher electrical conductivity compared with the surrounding air, a tree acts as a conductive pathway in the lower atmosphere, allowing variations in the atmospheric electric field to be directly reflected in stem potential measurements. The temporal variability of the measured signals is dominated by periodic components associated with solar radiation, consistent with thermally driven atmospheric tides that influence both the atmospheric electric field and sap flow in the tree. As a result, the individual contributions of these two effects cannot be separated. Superimposed on these patterns are meteorologically induced variations, including pronounced perturbations associated with electrically charged thunderclouds. Furthermore, directional dependencies in the measurements suggest sensitivity to wind-driven changes in the local atmospheric environment. At larger scales, enhanced potential gradients coincide with periods of increased solar activity, such as X-ray fluxes, particle events, and coronal mass ejections, indicating a coupling between space weather and near-surface electrical conditions. In contrast, no evidence for an influence of tidal gravitational forcing was found in this study.