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John E. Stout

Abstract

Rainfall samples collected on the high plains of West Texas exhibit a high degree of variability with respect to the concentration of dissolved solids. That such variations should occur is to be expected, but there remains some uncertainty regarding factors that influence the ionic composition of individual samples. Measurements often show a distinct decrease in concentration with increasing precipitation amount. The reason for this inverse relationship is not intuitively obvious; however, it can be explained from a theoretical perspective. A theory was proposed that describes the concentration of dissolved solids in a collected rainfall sample. The theoretical basis of the derived equation rests upon fundamental principles of conservation of fluid volume and conservation of mass. This equation, which provides valuable insight into the process, suggests that if the rain sampling tube is absolutely clean at the start of a rain event, then the rainfall sample will not be altered by its collection and, therefore, will provide a true measure of rainfall chemistry. However, if windblown dust or other impurities are allowed to deposit in the rain gauge prior to or during the early stages of a rain event, then the concentration of dissolved solids can be very large for small sample volumes and not at all representative of the true concentration within the rain cloud. Results suggest that impurities in the rain sample can be appreciably diluted by the addition of relatively pure rainwater such that the concentration will asymptotically approach the true concentration as the rainfall sample volume increases.

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John Stout and Edward B. Rodgers

Abstract

The Nimbus-7 Total Ozone Mapping Spectrometer (TOMS) was used to map the distribution of total ozone around western North Pacific tropical cyclones from 1979 to 1982. The strong correlation between total ozone distribution and tropopause height found in the subtropical and midlatitudes made it possible for TOMS to monitor the propagation of upper-tropospheric waves and the mutual adjustment between these waves and tropical cyclones during their interaction. Changes in these total ozone patterns reflect the three-dimensional upper-tropospheric transport processes that are involved in tropical cyclone intensity and intensity and motion changes. The total ozone distributions indicate that 1) the mean upper-tropospheric circulations associated with western North Pacific and Atlantic tropical cyclones are similar; 2) more intense tropical cyclones have higher tropopauses around their centers; 3) more intense tropical cyclones have higher tropopauses on the anticyclonic-shear side of their outflow jets, which indicate that the more intense tropical cyclones have stronger outflow channels than less intense systems; 4) tropical cyclones that intensify (do not intensify) are within 10° (15°) latitude of weak (strong) upper-tropospheric troughs that are moderately rich (very rich) in total ozone; and 5) tropical cyclones turn to the left (right) when they move within approximately 15° latitude downstream of an ozone-poor (ozone-rich) upper-tropospheric ridge (trough).

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John E. Stout and John A. Young

Abstract

The dynamics of low-level summer monsoon flow near 900 mb is studied using daily MONEX (1979) satellite wind data to estimate mechanisms influencing the horizontal momentum. We present an improved estimate of the large-scale monsoon geopotential field near the level of maximum wind, and a more approximate field of friction as well. Average fields for the premonsoon and established monsoon periods of 1.5 months are shown. The evolution of forces and accelerations along different trajectories crossing the western Indian Ocean are compared.

The net horizontal force, equal to the pressure gradient plus friction force, is obtained for the two periods by directly estimating the mean Coriolis and relative acceleration vectors. The contribution to mean acceleration by synoptic-scale transient eddies is significant only south of 30°S. Inertial acceleration by the mean flow produces a Rossby number in excess of 0.25 in an equatorial belt which expands to 10°N in the Somali Jet entrance.

A method is devised to split the observed net force field into its pressure gradient and friction force components; the method corresponds to solving the vorticity and divergence equations, respectively, and uses the property that pressure gradient is exactly irrotational and the assumption that friction force is mostly non-divergent. It is found that the diagnosed friction force tends to oppose the wind and is distinctly weaker than the pressure gradient force. The calculated geopotential field shows the development of a distinctive “reversed S” contour connecting the hemispheres and supporting strong cross-equatorial flow. The corresponding trajectories show that the degree of imbalance is greater in the Northern Hemisphere as the air adjusts to the changing Coriolis influence and monsoonal pressure gradient forces which increase and rotate. Northward moving air slows by friction as it approaches the equator, but increases speed in the Northern Hemisphere by flowing toward lower pressure. The assumptions involving frictional estimates for boundary conditions are evaluated using theory and wind data.

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John Schuetz and Glenn E. Stout

Preceding the development of a tornado at the ground a fingerline projection developed on the PPI in the SW corner of an echo. This was also visible on the three-dimensional models constructed from RHI data. The parent echo extended to 37,500 feet and was the highest echo in the vicinity. Tornado occurrence was simultaneous with a new cell merging with the finger. Photographs of the tornado, the lower level echo tilt, and winds aloft data all indicate the same direction of shear.

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Owen A. Kelley, John Stout, Michael Summers, and Edward J. Zipser

Abstract

Far from continents, a few storms lift precipitation-size ice particles into the stratosphere, 17 to 18 km above the tropical ocean. This study is the first to examine the observed properties of a large sample of these extremely tall convective storm cells. The central questions in this study are whether the unusually tall ocean cells have the slow updrafts known to be typical of oceanic convection, and if so, how can these tall cells reach such extreme heights. The precipitation radar on the Tropical Rainfall Measuring Mission (TRMM) satellite observed 174 extremely tall oceanic cells from 1998 to 2007. Relative updraft intensity is inferred from 17-km-tall oceanic cells having, on average, a 7-km lower 40-dBZ radar reflectivity height and an order of magnitude less lightning than do equally tall cells over the Sahel region of Africa, a region known for vigorous convective updrafts. Despite some ambiguity, the potential temperature and lapse rate of the NCEP reanalysis suggest that the environment in which these oceanic cells form is conducive to modest updrafts reaching extreme heights. Extrapolating based on the limited coverage of the TRMM satellite radar, it is likely that such extremely tall cells occur more often than once each day somewhere over the tropical ocean.

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Edward B. Rodgers, John Stout, Joseph Steranka, and Simon Chang

Abstract

The Nimbus-7 Total Ozone Mapping spectrometer (TOMS) was used to map the distribution of total Ozone in and around western Atlantic tropical cyclones from 1979 to 1982. It was found that the TOMS-observed total Ozone distribution within the subtropics during the tropical cyclone seasonal correlated well with the tropopause topoghraphy, similar to earlier middle-latitudinal observations. This relationship made it possible to use TOMS to monitor the propagation of upper-tropospheric subtropical transient waves and the mutual adjustment between the tropical cyclone and the upper-tropospheric waves during their interaction. These total ozone patterns reflected the three-dimensional upper-tropospheric transport processes that were conducive for storm intensification and weakening. It was also found from satellite observations and numerical model simulations that modification of the environmental distribution of total ozone by the tropical cyclones was primarily caused by the secondary circulation associated with the tropical cyclone's outflow jet and the intrusion of stratospheric air in the eyes of tropical cyclones.

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Edward Rodgers, John Stout, Joseph Steranka, and Simon Chang

Abstract

No abstract available.

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John S. Stout, David W. Martin, and Dhirendra N. Sikdar

Abstract

A method of estimating GATE rainfall from either visible or infrared images of geosynchronous satellites is described. Rain is estimated from cumulonimbus cloud area by the equation R = a 0 A + a 1 dA/dt, where R is volumetric rainfall (m3 s−1), A cloud area (m2), t time (s), and a 0 and a 1, are constants. Rainfall, calculated from 5.3 cm ship radar, and cloud area are measured from clouds in the tropical North Atlantic. The constants a 0 and a 1 are fit to these measurements by the least-squares method. Hourly estimates by the infrared version of this technique correlate well (correlation coefficient of 0.84) with rain totals derived from composited radar for an area of 105 km2. The accuracy of this method is described and compared to that of another technique using geosynchronous satellite images. We conclude that this technique provides useful estimates of tropical oceanic rainfall on a convective scale.

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Edward B. Rodgers, Simon W. Chang, John Stout, Joseph Steranka, and Jainn-Jong Shi

Abstract

The mutual adjustment between upper-tropospheric troughs and the structure of western Atlantic Tropical Cyclones Florence (1988) and Irene (1981) are analyzed using satellite and in situ data. Satellite-observed tracers (e.g., cirrus clouds, water vapor, and ozone) art used to monitor the circulation within the tropical cyclones' environment. The tropical cyclones' convection is inferred from satellite flown passive microwave and infrared sensors. In addition, numerical model simulations are used to analyze and interpret these satellite observations. The study suggests that the initiation and maintenance of intense convective outbreaks in these tropical cyclones during their mature stage are related to the channeling and strengthening of their outflow by upper-tropospheric troughs. The convection can be enhanced in response to the outflow jet-induced import of eddy relative angular momentum and ascending motion associated with the thermally direct circulation. The channeling and strengthening of the outflow occurs when the upper-tropospheric troughs are located in a favorable position relative to the tropical cyclones. Both Florence and Irene intensify after the onset of these intense convective episodes. Satellite observations also suggest that the cessation in the convection of the two tropical cyclones occurs when the upper-tropospheric troughs move near or over the tropical cyclones, resulting in the weakening of their outflow and the entrainment of dry upper-tropospheric air into their inner core.

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Cecilia Girz Griffith, William Lee Woodley, Pamela G. Grube, David W. Martin, John Stout, and Dhirendra N. Sikdar

Abstract

A diagnostic method to estimate rainfall over large space and time scales by the use of geosynchronous visible or infrared satellite imagery has been derived and tested. Based on the finding that arms of active convection and rainfall in the tropics are brighter or colder on the satellite visible or infrared photographs than inactive regions, ATS-3 and SMS/GOES images were calibrated with gage-adjusted 10 cm radar data over south Florida. The resulting empirical relationships require a time sequence of cloud area, measured from the satellite images at a specified threshold brightness or temperature to calculate rain volume over a given period.

Satellite rain estimates were made for two areas in south Florida that differ in size by an order of magnitude (1.3×104km2 vs 1.1×105km2) and verified by a combined system of gages and radar. Contrary to our expectations, the rain estimates for the smaller area agreed better with the raingage-radar groundtruth than the satellite rain estimates for the larger area. As expected, the accuracy of the rain estimates is a function of the period of rain estimation. The error and scatter of the hourly estimates are relatively large but both decrease as the estimates are accumulated with time. For periods of 6–9 h the mean absolute errors are factors of 1.50 and 1.90 using the visible and infrared imagery, respectively.

Additional tests for which groundtruth was available were also made to determine the applicability of this scheme to tropical areas other than the region of derivation. These include nine days over portions of Venezuela, five days over Honduras during the passage of Hurricane Fifi, and one day each of Hurricane Belle (1976) over the East Coast of the United States and Hurricane Agnes over Florida.

The potential of this method as a forecasting tool for hurricane-caused flooding is investigated in a study of selected Atlantic hurricanes between 1969 and 1977. Storms were ranked by satellite-calculated total daily rain volume and daily area-averaged rain depth. Relatively wet storms could be distinguished from the relatively dry storms. No correlation was found between volumetric storm rain output or area-averaged rainfall and storm intensity, which suggests that the location of latent heat releases and not its magnitude determines storm intensity.

Computer automation of the technique for real time and diagnostic estimates is discussed briefly. Satellite-inferred rains for the Big Thompson (Colorado) flood of 1976 and the Atlantic Ocean during GATE (summer 1974) are presented as examples of the real time and diagnostic computerized schemes, respectively.

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