The long term stability of EAL and TAI (revisited)

International atomic time TAI gets its stability from some 300 atomic clocks worldwide that generate the free atomic scale EAL and its accuracy from a small number of primary frequency standards (PFS) which frequency measurements are used to steer the EAL frequency. While the long-term (above one year) stability of TAI is mostly driven by the PFS and therefore directly related to its accuracy, its stability for averaging times from one to a few months is mostly driven by EAL. Based on the analysis of 8 years (1999-2006) of TAI data, the paper presents several results. We estimate the long-term stability of EAL and TAI with respect to the latest realization of TT(BIPM), and the one-month stability of EAL from the statistics of the weighted clocks. We study the two principal classes of clocks which form EAL and evidence systematic rate variations in clock ensembles. Their effect on the long-term stability of EAL is discussed.