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 timescaleTL . The objectives of the study are to investigate the seasonal, interannual, and altitudinal behavior ofTL and to present the Lagrangian autocorrelation functions corresponding to synoptic-scale flow. Results indicate that the integral timescaleTL 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.