Yakutsk EAS array data on the variations in intensities of the highest energy cosmic rays

The results of analysis of arrival frequency of cosmic rays with energies $E_0\geq4\times10^{17}\,$ eV are presented based on the data collected on the Yakutsk array during its 24 years of continuous operation (1977–2000). It is shown that the intensity of cosmic rays is variable. At $E_0\leq(3-5)\cdot10^{18}\,$eV, the (2–3)-month data show many deviations by $(3-4)\sigma$ from the mean level. At $E_0\geq4\times10^{19}\,$eV, the intensities steadily decrease, on the average, by 1.5 times during the time period considered.