On the synoptic-scale lagrangian autocorrelation function

A large set of 10-day, quasi-two-dimensional atmospheric trajectory model data is used to compute Lagrangian autocorrelation functions for horizontal velocity components and to determine their integral timescale TL. The objectives of the study are to investigate the seasonal, interannual, and altitudinal behavior of TL and to present the Lagrangian autocorrelation functions corresponding to synoptic-scale flow. Results indicate that the integral timescale TL ranges from 15 to 24 h, with values for the meridional velocity component that are 10%-25% less than values for the zonal velocity component. The Lagrangian autocorrelation functions are modeled using Gaussian and second-order autoregressive autocorrelation models. The model fits to the observed autocorrelation functions were found to be of similar form to those determined for a 1-yr set of three-dimensional trajectory data, suggesting that these functions are robust with respect to synoptic-scale, tropospheric flow.