Abstract. In 2003, a decreasing trend has been reported in the long-term (1962–2001) fair weather atmospheric electric potential gradient (PG) measured in the Széchenyi István Geophysical Observatory (NCK, 47°38' N, 16°43' E), Hungary, Central Europe. The origin of this reduction has been the subject of a long-standing debate, due to a group of trees near the measurement site which reached significant height since the measurements of PG have started. Those trees have contributed to the lowering of the ambient vertical electric field due to their electrostatic shielding effect. In the present study, we attempt to reconstruct the true long-term variation of the vertical atmospheric field at NCK. The time-dependent shielding effect of trees at the measurement site was calculated to remove the corresponding bias from the recorded time series. A numerical model based on electrostatic theory was set up to take into account the electrostatic shielding of the local environment. The validity of the model was verified by on-site measurement campaigns. The changing height of the trees between 1962 and 2017 was derived from national average age-height diagrams for each year. Modelling the time-dependent electrical shielding effect of the trees at NCK revealed that local effects played a pivotal role in the long-term decrease. The results suggest that earlier attempts could not quantify the shielding effect of the trees at NCK accurately. It was found that the reconstructed PG time series at NCK exhibits a significant increase between 1962 and 1997 followed by a decaying trend since 1997. It is pointed out that long-term variation in summertime and wintertime PG averages should be analyzed separately as these may contribute to trends in the annual mean values rather differently.

中文翻译：

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回顾在纳吉琴克，匈牙利，中欧测得的大气电势梯度的长期下降趋势

摘要。据报道，2003年长期（1962-2001年）在塞切尼伊斯特万地球物理观测站（NCK，北纬47°38'，北纬16°43'）中测得的大气大气电势梯度（PG）呈下降趋势。 ，匈牙利，中欧。这种减少的根源一直是一个长期争论的话题，因为自从开始测量PG以来，在测量地点附近的一群树木已经达到了很高的高度。这些树由于其静电屏蔽效应而有助于降低环境垂直电场。在本研究中，我们试图重建NCK垂直大气场的真实长期变化。计算树木在测量地点的时间依赖性屏蔽效应，以从记录的时间序列中消除相应的偏差。建立了基于静电理论的数值模型，以考虑局部环境的静电屏蔽。通过现场测量活动验证了该模型的有效性。1962年至2017年之间树木的高度变化是根据每年的全国平均年龄-高度图得出的。对NCK树木随时间变化的电屏蔽效应进行建模后发现，局部效应在长期下降中起着关键作用。结果表明，较早的尝试无法准确量化NCK树的屏蔽效果。研究发现，在１９６２年至１９９７年间，ＮＣＫ的重建PG时间序列表现出明显的增加，并自1997年以来呈下降趋势。