Seasonality of 7 Be 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 Be-7 surface activity concentrations, at addressing the impact of tropopause height (TPH) on Be-7 distribution and at evaluating the time lag between TPH and Be-7 at European level. With this aim, weekly Be-7 and daily TPH data at 17 sampling stations during 10 yr (2001-2010) are analysed. Be-7 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 Be-7, having TPH a larger influence on Be-7 during summer. The influence of TPH on Be-7 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 degrees N and higher) and stations in southern Europe (south of 50 degrees 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 Be-7 concentrations. The results suggest that Be-7 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 Be-7 concentrations at surface levels.