Observation of time correlation in cosmic air shower network

In order to measure time correlation of primary cosmic rays, a network observation of extensive air showers started in Japan. The network as Large Area Air Shower (LAAS) group consists of nine air-shower-stations (seven institutes and 26.000 km 2 ) using the Global Positioning System (GPS). We propose an analytical procedure to extract time-limited fractal structure from time series of arrival time intervals of successive air showers and present the results of the analysis by using the network data.