Seasonality of ⁷Be concentrations in Europe and influence of tropopause height

Abstract

This study aims at analysing the latitudinal variability of both the yearly and seasonal pattern of 7Be surface activity concentrations, at addressing the impact of tropopause height (TPH) on 7Be distribution and at evaluating the time lag between TPH and 7Be at European level. With this aim, weekly 7Be and daily TPH data at 17 sampling stations during 10 yr (2001-2010) are analysed. 7Be shows a clear increasing tendency in the period and generally tends to increase with decreasing latitude. The seasonal pattern generally shows maxima during the warm period and minima during the cold one. The seasonal variogram analysis points out a good spatial correlation for TPH data while a weaker one is observed for 7Be, having TPH a larger influence on 7Be during summer. The influence of TPH on 7Be exhibits a large spatial variability, with a clear gap between south and north in the area of the polar front jet. The results identify the presence of two main groups, in particular separating between stations located in northern Europe (50 °N and higher) and stations in southern Europe (south of 50 °N). A similar behaviour for stations located in the same geographical area is also observed when looking at the day of maximum impact of TPH on 7Be concentrations. The results suggest that 7Be concentrations respond in different time ranges to changes in the TPH, observing seasonal differences in each group. These results represent the first European approach to the understanding of the TPH impact on 7Be concentrations at surface levels.