- Appendix B of McClean et al. (2002; JPO) [PDF] reviews some concepts of Lagrangian statistics, in particular the
*Lagrangian autocorrelation function*. In this case, the Lagrangian average is defined as the average over an ensemble of particles released randomly at a fixed point**x**. The resulting Lagrangian averages then depend on**x**and time. - A volume that might help is
*Statistical Fluid Mechanics*by Monin and Yaglom.