Anomalous behavior of Schumann resonances during the transition between 1995 and 1996

Abstract

Anomalous behavior of Schumann resonance (SR) parameters is presented in interannual relations for the first time. The mean daily intensity of the first three SR modes measured in the vertical electric component at the Nagycenk Observatory (47.6°N, 16.7°E), Central Europe, was significantly higher in December 1995 and January 1996 than in the same months 1 year before. The largest relative SR intensity deviations occurred in the third part of December 1995 and in the evening hours (2000–2200 UT), when the lightning activity of the South American thunderstorm region is the most intense. In January 1996 the largest relative SR intensity deviations appeared in the early morning hours (0000–0030 UT), when the worldwide thunderstorm activity is at a minimum. This result suggests that a lightning activity in the Pacific region was not as sparse in January 1996 as it was in January 1995. The time variation of the maxima of the SR intensity ratios indicates a westward propagation with trade wind speeds of about 2 to 8 m s−1 from the end of December 1995 about to the end of January 1996. The anomalous SR intensity in December 1995 is attributed to a small increase in the surface air temperature (about 0.2°C) and to the extension of the thunderstorm region indicated by the SR frequency range variation. It is also suggested that this warmer air mass was advected by easterlies from the end of December 1995 over the cooler Pacific in January 1996 causing more intense lightning activity there.