Cosmic ray and air conductivity profiles retrieved from early twentieth century balloon soundings of the lower troposphere

Manned balloons were used in Europe to make atmospheric electricity research flights from the late nineteenth century. Subsequent ascents provide unique early twentieth century atmospheric electrical data above the continental boundary layer. Air conductivity data from three balloon ascents between 1905 and 1913 have been used to constrain a model of the atmospheric conductivity profile. At 1 m resolution, the model has been used to calculate the columnar resistance up to 5 km. The average columnar resistance to 5 km was found to be (163±16) PΩm2. The ionisation rate profile from cosmic rays was found to have reduced by approximately 8% per kilometre increase in altitude (between the surface and 5 km altitude) during the 50 yr between the mean date of the three ascents (∼1909) and measurements made near the middle of the century (∼1959). These results indicate a decrease in cosmic ray ion production in the lower troposphere during the first half of the twentieth century, due to decreased penetration into the troposphere. The associated increase in the cosmic ray component of the local columnar resistance was 0.3 PΩm2 yr−1 (0.2% yr−1).