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Elizabeth E. Ebert and Michael J. Manton

Abstract

Over 50 satellite rainfall algorithms were evaluated for a 5° square region in the equatorial western Pacific Ocean during TOGA COARE, November 1992–February 1993. These satellite algorithms used GMS VIS/IR, AVHRR, and SSM/I data to estimate rainfall on both instantaneous and monthly timescales. Validation data came from two calibrated shipboard Doppler radars measuring rainfall every 10 min.

There was large variation among algorithms in the magnitude of the satellite-estimated rainfall, but the patterns of rainfall were similar among algorithm types. Compared to the radar observations, most of the satellite algorithms overestimated the amount of rain falling in the region, typically by about 30%. Patterns of monthly observed rainfall were well represented by the satellite algorithms, with correlation coefficients with the observations ranging from 0.86 to 0.90 for algorithms using geostationary data and 0.69 to 0.86 for AVHRR and SSM/I algorithms when validated on a 0.5° grid. Patterns of instantaneous rain rates were also well analyzed, with correlation coefficients with the radar observations of 0.43–0.58 for the geostationary algorithms and 0.60–0.78 for SSM/I algorithms.

Two case studies are presented to demonstrate the capability of one IR algorithm and three microwave algorithms to estimate instantaneous rainfall rates in the Tropics. The three microwave algorithms differed in their estimates of rain area but all showed greater ability than the IR algorithm to reproduce the spatial pattern of rainfall.

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Elizabeth E. Ebert, Ulrich Schumann, and Roland B. Stull

Abstract

Large-eddy simulation is used to simulate quasi-steady state convection in a windless mixed layer over a uniform surface with constant heat flux. Different tracers are injected at each discrete height in the model to track vertical transport of tracers as a function of time. The resulting tracer source and destination information is presented in the form of transilient matrices.

These matrices are asymmetric for time increments on the order of the convective time scale, t *. They show nonlocal mixing occurring over a range of wavelengths up to the mixed layer depth, some convective overturning, and the loss of nearly all of the surface layer air into thermals. Measurements of transport across finite distances exhibit skewed distributions of vertical transport velocity. The relative importance of upward versus downward transport strongly depends on both height and time, as measured by the fractional transport and mixing lengths in each direction. Process, mass, and heat transport spectra show the relatively minor contribution made by small-size eddies as compared to the medium and large scales. Favorable comparisons of these results with a variety of traditional turbulence statistics exemplify the wealth of turbulence information that is captured within a transilient matrix.

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