Showing papers by "David A. Short published in 1990"
TL;DR: In this article, the authors developed a unified theory for the estimation of both total rainfall from an individual convective storm over its lifetime and the areawide instantaneous rainfall from a multiplicity of such storms by use of measurements of the areal coverage of the storms within a threshold rain intensity isopleth or the equivalent threshold radar reflectivity.
Abstract: This work develops a unified theory for the estimation of both total rainfall from an individual convective storm over its lifetime and the areawide instantaneous rainfall from a multiplicity of such storms by use of measurements of the areal coverage of the storms within a threshold rain intensity isopleth or the equivalent threshold radar reflectivity. The method is based upon the existence of a well-behaved probability density function (pdf) of rain rate either from the many storms at one instant or from a single storm during its life. In the first method, the lifetime storm rainfall volume is V = [〈A(τ)〉T]S(τ), where 〈A(τ)〉 is the average storm area over the life of the storm of duration, T, in which R > τ and the bracketed term is the area time integral. In the second method, the instantaneous areawide rain rate, 〈R〉 = F(τ)S(τ), where F(τ) is the fractional observed area with R > τ. In both methods, S(τ) is the climatological rain rate for the regime divided by the relative frequency with which R > τ. For thresholds exceeding some minimum value, S(τ) is essentially linear with τ for the kind of lognormal pdf which characterizes convective rain, and is a constant for specified τ. Thus both the lifetime V of the individual storm and the instantaneous 〈R〉 for a multiplicity of storms are linear functions of A(τ) and F(τ), respectively. This is in accord with the observations of Doneaud et al. (1984) and Chiu (1988a, b). Because the autocorrelation time of the areawide rain rate of convective storms in areas in excess of 104 km2 is about 5–6 hours, the snapshot 〈R〉 is representative of the rain for a few hours. This enhances the accuracy of snapshot measurements for climate purposes and also extends their utility to smaller time/space problems such as hydrology and numerical weather prediction. We also discuss ways of obtaining climatologically valid and unbiased values of S(τ) and means of establishing its values from aircraft and space.
128 citations
TL;DR: In this article, the bias in the rain estimation from satellites, associated with nonuniformly filled FOVs of spaceborne microwave sensors, were estimated using radar data collected during the GARP Atlantic Tropical Experiment.
Abstract: The bias in the rain estimation from satellites, associated with nonuniformly filled FOVs of spaceborne microwave sensors, were estimated using radar data collected during the GARP Atlantic Tropical Experiment. An approximate formula is derived which shows that this bias is closely related to the variance of rain rate within the FOV of the sensor. By applying simple models of rain field to the formula, it is shown that the formula is consistent with the variation of bias.
96 citations
TL;DR: In this article, a height-area rain threshold (HART) method was proposed to estimate the instantaneous area average rain rate (R) in millimeters per hour (R ) over a large domain by measuring the fraction of the area, F(τ), covered by rain intensity greater than a selected threshold τ and average precipitating cloud top heights.
Abstract: Estimates of instantaneous area average rain rate (〈R〉 in millimeters per hour) are obtained with 5–10% accuracy over a large domain simply by measuring (1) the fraction of the area, F(τ), covered by rain intensity greater than a selected threshold τ and (2) the average precipitating cloud top heights. In order to achieve this high accuracy the domain has to be large enough (about 104 km2) to include a representative sample of rain cells in different stages of their life cycle, and the measurement of the threshold rain intensity (τ) has to be unbiased. This Height-Area Rainfall Threshold (HART) method was tested with radar data of convective rains from Global Atmospheric Research Program (GARP) Tropical Atlantic Experiment (GATE) phase 3, South Africa, west Texas, and a small sample from Darwin, Australia. The results from all locations were found to be consistent and physically plausible. The cloud base temperature seems to play a major role in the determination of the constants of the HART method. The 〈R〉-F(τ) relations were found to be rather insensitive to variations in the Z-R relationships. However, any bias in the measurement of τ causes a similar bias in the derived 〈R〉. HART makes possible the accurate estimation of instantaneous rainfall from space when measuring the area and height of the convective rain systems with radar. Passive microwave observations may also be used over the ocean at wavelengths which allow setting a specified rain rate threshold, and when accompanied by IR measurements of storm top temperatures. Over tropical ocean domains of the order of 104 km2 or greater, the autocorrelation time of about 6 hours permits the area average instantaneous rate to represent the rate for a few hours.
75 citations
TL;DR: In this paper, a comparison of rain rates retrieved from the Nimbus 5 electronically scanning microwave radiometer brightness temperatures and observed from shipboard radars during the Global Atlantic Tropical Experiment (GATE) phase I showed that the beam filling error is the major source of discrepancy between the two.
Abstract: A comparison of rain rates retrieved from the Nimbus 5 electronically scanning microwave radiometer brightness temperatures and observed from shipboard radars during the Global Atlantic Tropical Experiment (GATE) phase I shows that the beam filling error is the major source of discrepancy between the two. When averaged over a large scene (the GATE radar array, 400 km in diameter), the beam filling error is quite stable, being 50 percent of the observed rain rate. This suggests the simple procedure of multiplying retrieved rain rates by 2 (correction factor). A statistical model of the beam filling error is developed by envisioning an idealized instrument field-of-view that encompasses an entire gamma distribution of rain rates. A modeled correction factor near 2 is found for rain rate and temperature characteristics consistent with GATE conditions. The statistical model also suggests that the correction factor varies from 1.5 to 2.5 for suppressed to enhanced tropical convective regimes, and decreases to 1.5 as the freezing level and average depth of the rain column decreases to 2.5 km.
73 citations
Journal Article•
TL;DR: In this article, a theory is developed which establishes the basis for the use of rainfall areas within present thresholds as a measure of either the instantaneous areawide rain rate of convective storms or the total volume of rain from an individual storm over its lifetime.
Abstract: A theory is developed which establishes the basis for the use of rainfall areas within present thresholds as a measure of either the instantaneous areawide rain rate of convective storms or the total volume of rain from an individual storm over its lifetime. The method is based upon the existence of a well-behaved pdf of rain rate either from the many storms at one instant or from a single storm during its life. The generality of the instantaneous areawide method was examined by applying it to quantitative radar data sets from the GARP Tropical Atlantic Experiment for South Africa, Texas, and Darwin (Australia). It is shown that the pdf's developed for each of these areas are consistent with the theory.
3 citations