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The Second-Moment Climatology of the GATE Rain Rate Data

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  • 1 Climate System Research Program, College of Geosciences and Maritime Studies, Texas A&M University, College Station, Texas
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The first part of this paper presents the description of the GARP (Global Atmospheric Research Program) Atlantic Tropical Experiment 1 rain-rate data and its two-dimensional spectral and correlation characteristics, which have made it possible to accomplish the following: to show the concentration of a significant power along the frequency axis in the spatiotemporal spectra; to detect a diurnal cycle (which has a range of variation of about 3.4–5.4 mm h−1) as one of the sources of bias in the rain statistics of satellite data; to study the distinction between the north–south and east–west transport of spatial rain-rate field and character of its anisotropy; to evaluate the scales of the distinction between second-moment estimates associated with ground and satellite samples; and to determine the appropriate spatial and temporal scales of simple linear stochastic models fitted to averaged rain-rate fields. The second part of this paper is devoted to an analysis of the diffusion of the rain rate by establishing a relationship between the parameters of the multivariate autoregressive model and the coefficients of a diffusion equation. This analysis led to the use of rain data to estimate the rain advection velocity as well as other coefficients of the diffusion equation of the corresponding field.

The results obtained can be used for comparison with corresponding estimates of other sources of data (satellite, Tropical Oceans Global Atmosphere Coupled Ocean–Atmosphere Response Experiment, or simulated by physical models), for generating multiple samples of any size, for solving the inverse problems of some of the hydrodynamic equations, and in some other areas of rain data analysis and modeling.

Corresponding author address: Ilya Polyak, Climate System Research Program, College of Geosciences and Maritime Studies, Texas A&M University, College Station, TX77843-3150.

The first part of this paper presents the description of the GARP (Global Atmospheric Research Program) Atlantic Tropical Experiment 1 rain-rate data and its two-dimensional spectral and correlation characteristics, which have made it possible to accomplish the following: to show the concentration of a significant power along the frequency axis in the spatiotemporal spectra; to detect a diurnal cycle (which has a range of variation of about 3.4–5.4 mm h−1) as one of the sources of bias in the rain statistics of satellite data; to study the distinction between the north–south and east–west transport of spatial rain-rate field and character of its anisotropy; to evaluate the scales of the distinction between second-moment estimates associated with ground and satellite samples; and to determine the appropriate spatial and temporal scales of simple linear stochastic models fitted to averaged rain-rate fields. The second part of this paper is devoted to an analysis of the diffusion of the rain rate by establishing a relationship between the parameters of the multivariate autoregressive model and the coefficients of a diffusion equation. This analysis led to the use of rain data to estimate the rain advection velocity as well as other coefficients of the diffusion equation of the corresponding field.

The results obtained can be used for comparison with corresponding estimates of other sources of data (satellite, Tropical Oceans Global Atmosphere Coupled Ocean–Atmosphere Response Experiment, or simulated by physical models), for generating multiple samples of any size, for solving the inverse problems of some of the hydrodynamic equations, and in some other areas of rain data analysis and modeling.

Corresponding author address: Ilya Polyak, Climate System Research Program, College of Geosciences and Maritime Studies, Texas A&M University, College Station, TX77843-3150.
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