Supporting data for: Determining the time constant of the global atmospheric electric circuit through modelling and observations

The Icelandic Grimsvötn volcano erupted in May 2011, generating volcanic lightning which formed a significant contribution to the global lightning on 21st and 22nd May 2011. During the eruption, measurements of the atmospheric electric Potential Gradient (PG), and the current flowing to a horizontal flat plate (FP) were made at Reading University Atmospheric Observatory (RUAO), in the UK (51.44136°N, 0.93807°W). The RUAO sensors were originally sampled at 1s. The original 1s data for the PG on 21st and 22nd May have been retrieved and made available in this archive, together with derived 1 min and 5 min averages. The FP values for 21st and 22nd May are provided at 5min resolution. The archive atmospheric electricity data presented here was generated as part of routine measurements made at the Reading University Atmospheric Observatory (RUAO) (https://research.reading.ac.uk/meteorology/atmospheric-observatory/), extracted for this submission.Two of the routinely measured quantities are provided here, the Potential Gradient (PG), and the vertical current flowing to a flat plate which was flush with, but insulated from, the horizontal surface. The PG was measured using a JCI131 field mill, mounted facing upwards on a 3m mast, calibrated to the undisturbed potential at 1m using a passive wire method. The FP was of area 0.276 m2, with the current measured using an opamp electrometer circuit. Images of the flat plate arrangement and field mill are provided at https://research.reading.ac.uk/meteorology/atmospheric-observatory/atmospheric-electricity. Associated meteorological data at RUAO for this period are available within another archive: https://doi.org/10.17864/1947.000490.In addition to the observational data this archive contains the results of simulations of the global atmospheric electric circuit (GEC) due to the excitation by the Grimsvötn volcano lightning on 21st and 22nd May 2011 during 5 hours starting from 23:00 UTC, and its effects in the potential gradient in the fair weather and semi-fair weather regions of the circuit. The files contain the time series at 1min resolution of calculated amplitudes of the electric current source due to the volcano lightning (I_0L), simulated current generated due to the volcano lightning (I_L), the ionospheric potential (V_I), and the ground-level potential gradient in the fair weather (PG_FW), and semi fair weather area of the circuit (PG_SFW), representing the time variation of the GEC during the lightning activity. The source current was calculated from the flash rates detected by the ATDnet network and provided by the UK Met Office. The simulations were performed using OrCAD PSpice A/D simulation software. Other details are described in Rycroft et al., https://doi.org/10.1016/j.jastp.2024.106267.