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  • Author or Editor: A. Jones x
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D. M. A. Jones

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Douglas M. A. Jones

Abstract

Volume samples of raindrop spectra (26 865 m3) recorded at ten widely dispersed sites from the tropics to the Aleutian Islands yielded spectra with dominant modes in the range 0.8–1.6 mm. Peaks at the 0.9-mm diameter were found but were not significantly more frequent than other nearby sizes. Secondary peaks in the averaged spectra were detected for some rain-rate and site combinations but not uniformly in all samples.

This study provides an indication of the limits of the extent to which local peaks, resulting from size preferences during drop breakup, could be expected to be seen in data obtained with instruments of limited sample volumes.

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P. A. Jones

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Observations of cloud cover (in oktas or tenths) by ground-based observers have been studied to investigate the distribution of cloud-cover amounts and the correlation of cloud cover in time and space. The correlation between observations at the same station, at different times, was found to vary as an exponential of the time separation. Similarly, the correlation between observations at different stations at the same time was found to vary as an exponential of the distance between the stations. Characteristic scales of cloud variation in space and time were derived from these exponentials and the shape of the distribution (in oktas or tenths) of cloud cover was described by a shape parameter. It was found that the data show only weak correlations between these three derived parameters, although it may be expected from physical arguments that the parameters are related.

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R. Meneghini and J. A. Jones

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Estimates of rain rate derived from a spaceborne weather radar will be most reliable over an intermediate range of values. At light or heavy rain rates, where the signal-to-noise ratios are degraded either by small values of the backscattered power or by large attenuation, the accuracy will be poor. In forming an area average of the rain rate, an alternative to the averaging of the high-resolution estimates, irrespective of their individual accuracies, is a multiple threshold approach. The method is based on the fact that the Fractional area above a particular rain-rate threshold Rj is related to the cumulative distribution of rain rates evaluated at Rj. Varying the threshold over the effective dynamic range of the radar yields the cumulative distribution function over this range. To obtain the distribution at all rain rates, a lognormal or gamma test function is selected such that the mean-square error between the test function and the measured values is minimized. Once the unknown parameters are determined, the first-order statistics of the areawide rain-rate distribution can be found. Tests of the method with data from the SPANDAR radar provide comparisons between it and the single threshold and the direct averaging approaches.

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Thomas A. Jones and Sundar A. Christopher

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Many large grass fires occurred in north Texas and southern Oklahoma on 9 April 2009, destroying hundreds of homes and businesses and burning thousands of acres of grasslands, producing large smoke and debris plumes that were visible from various remote sensing platforms. At the same time, strong westerly winds were transporting large amounts of dust into the region, mixing with the smoke and debris already being generated. This research uses surface- and satellite-based remote sensing observations of this event to assess the locations of fires and the spatial distribution of smoke and dust aerosols. The authors present a unique perspective by analyzing radar observations of fire debris in conjunction with the satellite analysis of submicrometer smoke aerosol particles. Satellite data clearly show the location of the individual fires and the downwind smoke plumes as well as the large dust storm present over the region. In particular, Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical thickness at 0.55 μm within the dust plume was around 0.5, and it increased to greater than 1.0 when combined with smoke. Using the difference in 11- versus 12-μm brightness temperature data combined with surface observations, the large extent of the dust plume was evident through much of north-central Texas, where visibilities were low and the 11–12-μm brightness temperature difference was negative. Conversely, smoke plumes were characterized by higher reflectance at 0.6 μm (visible wavelength). Cross sections of radar data through the several smoke and debris plumes indicated the burnt debris reached up to 5 km into the atmosphere. Plume height output from modified severe storm algorithms produced similar values. Since smoke aerosols are smaller and lighter when compared with the debris, they were likely being transported even higher into the atmosphere. These results show that the combination of satellite and radar data offers a unique perspective on observing the characteristics and evolution of smoke and debris plume emanating from grass fire events.

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Patricia A. Jones and James E. Jiusto

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From historical weather records, a preliminary assessment was made of local climate changes in four major urban areas of New York State. Particular emphasis was placed on cold season precipitation and possible relationships to man's activities. Total snowfall was found to have increased significantly from about 1940, the start of a period of sharp increases in urbanization and industrialization. The relationship was merely coincidental, with the underlying cause of snowfall increases due to natural causes, apparently in part to a corresponding decline in ambient temperature. A few climate trends appeared linked to anthropogenic causes, particularly in New York City.

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A. H. Woodcock and Richard H. Jones

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A recent study in Queensland, Australia, associates long-term downward trends in rain amount with the productivity of the sugarcane industry. The relationship is attributed to an increasing colloidal stability in the clouds caused by additional cloud condensation nuclei shown to be present in the smoke coming from local cane-harvesting fires.

As an additional test of the hypothesis, the rainfall records of several sugar-producing areas in Hawaii are examined where burning prior to harvesting is also practiced. Two physically similar leeward coastal areas were selected for comparison, one because it is downwind from a major cane-growing region and the other because it is not. The data suggest a downward trend in rainfall over periods of 30–60 years at both areas, but the trends are not statistically significant. However, the records for areas along the windward coastal regions of the two northwesternmost islands indicate an upward trend. It is concluded that factors other than cane-fire smoke are probably involved in any rainfall trends which may exist.

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Arthur L. Sims and Douglas M. A. Jones

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Two-minute rainfall rates have been measured along lines of recording rain gages in Florida and Illinois. Knowledge of the frequencies of occurrence of short-duration rainfall rates is needed for estimating attenuation of radio communications and radars. Rainfall rate frequencies are also useful in estimating the erosion of high-speed devices by rain. Results are presented for one summer of data taken at each location. The Florida lines were 9.6 and 21.5 km in length and the Illinois lines 23.9 and 62.2 km. These line frequencies are compared with single gage frequencies at each location. The frequencies by which various rates are exceeded are shown for those that occur more than 0.001% of the time. Rain at rates greater than 0.1 mm h−1 occurred less than 6% of the time at either location and for the longest line lengths. For similar line lengths, most rainfall rates have higher frequencies of occurrence in Florida than in Illinois. The rainfall rate frequencies were not significantly different for differing line orientations.

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Douglas M. A. Jones and Wayne M. Wendland

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Known sources of data from arrays of instantaneous precipitation intensity recorders in southern Germany, east-central Illinois, northeastern Illinois, central Florida, and Hilo, Hawaii are obtained. These data are analyzed for line averages of the percent frequency of occurrence of the exceedance of selected threshold precipitation intensities. The correlation coefficients of the precipitation intensity at sites at varying distances from a reference site are determined. The decay in correlation is found to be a function of climatic region and the type of precipitation: showery or continuous. Showery rains are found to be essentially uncorrelated about 12 km from the reference site while continuous rain exhibits no correlation beyond about 50 km.

Single-station intensity data collected at Urbana, Illinois; Paris, France; Inyanga, Zimbabwe; Bogor, Indonesia; Reading, United Kingdom; Island Beach, New Jersey; Miami, Florida; Franklin, North Carolina; and Majuro, Marshall Islands, are compared.

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Douglas M. A. Jones and Arthur L. Sims

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Raingage records from four climatic zones (maritime subtropical, continental temperate, maritime temperate and midlatitude interior) were analyzed to study instantaneous rainfall rates as defined by 1 and 4 min accumulations. The frequency distribution of rainfall rates was determined for stations in each of these climatic zones and a zonal average frequency distribution calculated. A progression in the frequency of more intense precipitation was found from the North Pole to the Equator since all of the data were taken from the Northern Hemisphere. The most intense rainfalls were recorded at stations in the maritime subtropical zones and the least intense rainfalls in the maritime temperate zones.

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