Influence of meteorological systems on the ionosphere over Europe

Ionosphere represents weakly ionized plasma that reflects both solar, geomagnetic activity and processes in the neutral atmosphere. Correlation coefficients of long time series of the critical frequencies from European stations measured by means of vertical sounding are analyzed with respect to latitudinal and longitudinal difference and surface distance of stations. Time series of critical frequencies are highly correlated reflecting the dominant solar influence. Correlation coefficients are high not only for raw data and subtracted mean courses but for fluctuations around mean as well. At the surface distance exceeding 1000 km and/or about 10° of latitudinal difference between stations, the correlation coefficient of fluctuations decrease rapidly. Such effect is less visible on the latitudinal dependence, where the correlation coefficients decrease with increasing distance with less pronounced threshold. We explain the existence of the 'break pointʼ at 10° in longitude and/or 1000 km by the 'localʼ influence of the neutral atmosphere and the wave activity. As a possible source of the common influence on scale 1000 km/10° we propose tropospheric systems that are known to be an important source of atmospheric waves in a broad period range. Large tropospheric mesoscale systems have typically up to 2000 km in diameter.