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Joanne Simpson and Robert H. Simpson

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JOANNE SIMPSON and VICTOR WIGGERT

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A one-dimensional numerical cumulus model was tested against data from a randomized seeding experiment made in South Florida in 1968. Fourteen GO clouds were studied. Nine were seeded by pyrotechnics with 1 kg of silver iodide each, while five were studied identically as controls.

Various seeding subroutines and assumptions regarding the ice phase are compared. The experimental aircraft data are used to guide the modeling assumptions and to select the most realistic ones. Seedability and seeding effect correlate to 0.96 for seeded clouds in the three best models. A high correlation is found between seedability and radar-measured rainfall increase from seeding. Also, a high correlation is found between model predictions of the difference in precipitation fallout between seeded and control clouds and the measured rainfall differences, although the model predictions are much smaller in magnitude. A calculation is undertaken showing that coalescence within the cloud body on descent of the raindrops easily accounts for the discrepancy.

The model predictions for each GO cloud are discussed in comparison with actual measurements on the cloud.

The 1968 experiment was found to subdivide into two periods, one fair and one disturbed, with quite different effects of seeding. The two periods and corresponding cloud behavior are compared. It is concluded that the disturbed period was less favorable for seeding because of higher unseeded cloud growth and strong wind shear. Implications of this result for future modeling efforts are discussed.

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concerning weather modification

Testimony to the House Subcommittee on International Organizations and Movements

Joanne Simpson
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Joanne Simpson and Keith Seitter
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JOANNE SIMPSON and VICTOR WIGGERT

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This paper presents a model of the growth of cumulus clouds. The water content and maximum height of rising towers are calculated using a buoyancy equation with consideration of effects of entrainment and water load. The latter is subject to effects of modeled microphysical effects. Precipitation growth is parameterized in terms of an autoconversion equation and a collection equation. A precipitation fallout scheme is devised that depends on water content, drop spectrum, and the vertical rise rate of the tower.

Then “freezing subroutines” are devised to model the effects of silver-iodide seeding. A hierarchy of seeding routines, using different ice collection efficiencies and terminal velocities, is partially tested against the data of the Stormfury 1965 tropical cumulus-seeding experiment.

Some preliminary numerical experiments on warm clouds are performed, assuming changes in drop spectra from hygroscopic seeding.

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Joanne Malkus Simpson and R. H. Simpson

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Joanne Simpson and Margaret LeMone

A survey of women atmospheric scientists has been completed in late 1973 and is briefly summarized in this article. Complete results are on file at the Headquarters of The American Meteorological Society. For the United States, the survey comprised as many as possible of those females either with baccalaureate degrees or higher in atmospheric sciences and those working several years professionally in the field. The names of 247 women who met this definition came to our attention, excluding about 80 more listed as undergraduate majors. The 247 women were subdivided into the following categories: 1) 32 Ph.D.'s; 2) 76 non-student masters' degrees; 3) 84 non-student bachelors' degrees or equivalent; 4) 25 Ph.D. candidates and; 5) 30 masters' candidates. We were able to reach the majority of these women by questionnaire, letter and/or telephone.

The main findings were: 1) the high degree of productive employment in the Atmospheric Sciences or a closely related field (101 of 190 non-students) and 2) the sex-related difficulties noted by the majority (73% of the 150 non-students reporting). All the Ph.D.'s were employed full or part-time in atmospheric science or a related field, and most had received some significant honors. Many of the masters and bachelors had also had outstanding careers, although, in general, traceability and commitment decreased somewhat with the less advanced degrees. The prospects for young women are brighter now than a generation ago. Four young female atmospheric scientists are currently assistant professors in major atmospheric science departments and several are in rising professional situations in the operational weather services. The sex-related difficulties were of two distinct types, namely: 1) discrimination, now decreasing and 2) for married women, problems of co-location of careers with those of husbands and to an important but lesser degree, child care.

The survey exploded the myth that “it does not pay” to provide women with training and opportunity in atmospheric science. Nearly all areas of atmospheric science today have already been infiltrated by females, except that of top management. Related to this, the distributions of males versus females in the field are quite different. With females, 60% are in teaching and/or research, 32% in operations, and 8% in management, while the corresponding figures for males are 28%, 43% and 29% respectively. A surprising result of our survey was the high fraction of foreign born women in the advanced degree categories, decreasing to negligible with the baccalaureates.

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Joanne Simpson and Harry J. Cooper

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Wei-Kuo Tao and Joanne Simpson

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A multidimensional and time-dependent cloud scale model is used to investigate the dynamic and micro-physical processes associated with convective and stratiform regions within a tropical squall-type convective line. The evolution of the total convective and stratiform portions of rainfall is also estimated by using model output. A three-dimensional version of the model covers a horizontal domain about 96 × 96 km2. Frequently, the horizontal extent of an observed stratiform region is over a few hundred kilometers. Therefore, a two-dimensional version of the model with a 512 km horizontal length is also used to incorporate a complete stratiform region.

Two-dimensional model result recapture many interesting features as observed. In particular, the fractional portion of stratiform rain as well as its fractional area coverage are in good agreement with observations. A significant amount of ice particles melted to rain near the freezing level in the trailing part of the modeled squall system during its mature and dissipating stages. The mesoscale circulations above and beneath the freezing level in the stratiform region are also well simulated. Three-dimensional model results could not recapture these features associated with the stratiform region. But explosive growth and a convex-leading edge associated with the convective region are well simulated. The orientation of the three-dimensional simulated convective line is perpendicular to the environmental wind shear as observed. Both of the modeled propagation speeds for the squall systems are in fair agreement with observational case studies.

Sensitivity tests on ice-phase microphysical processes and mesoscale middle and upper level ascent are made to investigate their roles on the formation and structure of tropical squall-type convective lines. Parcel trajectory analyses are also performed to understand the dynamics of simulated squall-type convective lines. Specifically, the origins of air circulation in the convective and stratiform region are investigated using the model generated wind fields. The heat budgets and their associated microphysical processes within the convective and stratiform region are also examined using the model results.

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Alan K. Betts and Joanne Simpson

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We reexamine the idealized hurricane boundary layer budget from Malkus and Riehl using vector diagrams for the thermodynamic budgets in the light of recent observations studies. We conclude that a large air-sea temperature difference can only be maintained with both large fluxes through cloud-base level and a large evaporative cooling of the subcloud layer. The high θE values observed in hurricane eyewalls can be reached if these cloud-base and evaporative fluxes are reduced and the subcloud layer moves toward the sea surface virtual potential temperature.

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