Space‐time structure of rain rate fields

Abstract

Information on the spatial and temporal statistics of rain rate is needed for the design of remote sensing systems for the measurement of areal rainfall accumulation and for the design of millimeter wave communication systems. In this study, rain gage and radar data were used to determine empirically the spatial and temporal structure of the rain process as observed using rain rate as a tracer of the atmospheric motions and to test the validity of Taylor's hypothesis for relating their spatial and temporal statistics. Weather radar derived rain rate maps were employed to obtain one‐ and two‐dimensional spatial power spectra. Azimuthally averaged two‐dimensional spectra displayed the shape predicted for a passive scalar advected by a steady state field of two‐dimensional turbulence driven by the input of energy over a narrow band of wave numbers. One‐dimensional spatial spectra for a short line of rain gages had the same spectral shape as the azimuthally averaged spectra obtained from the radar data. Temporal spectra from the gage time series were nearly identical in shape to the one‐dimensional spatial spectra if less than a half hour of data were processed to generate a spectrum and a constant translation velocity was assumed to relate the temporal and spatial scales. For spectra corresponding to longer durations, a match could not be made.