EULERIAN AND LAGRANGIAN CORRELATION STRUCTURES OF CONVECTIVE RAINSTORMS

The Eulerian and Lagrangian correlation structures of 13 convective ra instorms were investigated using rainfall data from the 1987 Convectiv e Initiation Downburst Experiment in Denver, Colorado. One minute rain fall data were available for two superposed raingage networks: 46 rain gages on the portable automated mesonet (PAM) network at a mean spacin g of 10.6 km and 31 additional raingages on the Federal Aviation Admin istration Lincoln Laboratory Operational Weather Studies (FLOWS) netwo rk at a mean spacing of 2.4 km. Eulerian correlation coefficients are low and often negative for high-resolution 1 min rainfall data. Correl ation increases with time-averaging, beyond 10-15 min for single rain cells on the FLOWS network and small-mesoscale rainstorms on the PAM n etwork. The average speed of rain cells and small-mesoscale rainstorms was found to be 76.5 and 56.4 km hr(-1), respectively. Storm kinemati c is identified as the cause of data scatter and low Eulerian correlat ions, Convective rainstorms are essentially uncorrelated in the Euleri an reference frame at a typical raingage spacing of 2-3 km for rain ce lls and 10-15 km for small mesoscale rainstorms. A spatial cross-corre lation analysis in a Lagrangian reference frame moving with the center of mass of the storm separates the kinematic component from the struc tural component of a rainfall field. The spatial cross correlations in the Lagrangian rainfall field show considerable improvement over the Eulerian spatial correlation plots, and data scatter is greatly reduce d. The increase in correlation coefficients from Eulerian to Lagrangia n reference frames typically ranged from 0.5 to 1.1.