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Richard G. Semonin

Abstract

Millipore filter samples obtained at the Mauna Loa Observatory and at Hillo, Hawaii, were analyzed for chloride particle concentrations. These data are used in a transport model to determine the removal efficiency of particles.

The most interesting result from the analysis is that the percentage of particles removed is uniform from the shore to the mountain observatory regardless of size. These results lead to calculations of the impaction-sedimentation ratio which range from 212 for 20μm diameter particles to 6413 for 4μm particles. The total impaction factors (removal by trees and other vegetation) ringed from 0.267 to 0.323 along the 60-km path.

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Robert Cataneo and Richard G. Semonin

Abstract

No abstract available.

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Kevin G. Doty and Richard G. Semonin

Abstract

To investigate the hypothesis that dust storms enhanced the calcium concentrations in precipitation in the mid-1950s, two case studies were performed for major dust events in the southern Plains of the United States during March and April of 1981. Forward trajectories were calculated from source areas of blowing dust and then compared with hourly radar summaries to see if the advected dust cloud intercepted precipitation over sites of the National Atmospheric Deposition Program. Four sites met these criteria between the two case studies and exhibited extremely high calcium concentration and deposition values for the study period.

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Harry T. Ochs III and Richard G. Semonin

Abstract

Observations showed increased concentrations of cloud condensation nuclei (CCN) in air samples collected over and downwind of St. Louis when compared to upwind samples. Aircraft observations of urban clouds showed corresponding increased concentrations of cloud base droplets. In addition, observations indicated higher cloud bases and decreased elevations of average first echo base heights in the St. Louis/East St. Louis area as compared with similar clouds over rural areas.

The purpose of this paper is to examine the possible role of CCN chemical composition and number concentration in producing the observed phenomena. A closed parcel model of condensation and collection was employed for this purpose. The results suggest that the observed differences of depth from cloud base to first echo height between urban and rural clouds do not result from concentration differences in any CCN size range. Results of model calculations also suggest that variations in chemical composition of the largest CCN (≥1.0 μm radius) were not responsible for the observed urban/rural differences. A hypothesis based on observations and model results is presented for explaining the observed differences in cloud base to first echo depth in terms of differences between the evolution and strength of updrafts in urban and rural clouds.

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Stanley A. Changnon Jr. and Richard G. Semonin

Illinois is completing a comprehensive statewide water plan. The plan selects three atmospheric issues, among the 11 identified as key issues facing the state's water resources. The issues selected include climate change and prediction, inadvertent weather and climate modification, and planned weather modification. Each atmospheric issue presents major resource or policy problems, with capabilities needed to enhance the quality and/or quantity of the state's waters. The identification of these atmospheric issues reveals awareness at the policy level of their importance. Policy and programmatic needs found to be common to each issue include 1) collection of more data and continued research (with an increasing state role); 2) coordinated policy development around atmospheric expertise from several agencies and universities; and 3) an expanded public information program. A Climate Detection and Assistance Board is to be established in Illinois to provide the planning, coordination, and assistance needed to address atmospheric issues.

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Wayne E. Bradley and Richard G. Semonin

Abstract

No abstract available.

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Stanley A. Changnon Jr. and Richard G. Semonin

A series of mesoscale meteorological research projects have developed since 1975 in the area over and around the south end of Lake Michigan. These regionally focused projects, under the label of the Chicago Area Program (CAP), are being performed by scientists from 12 research groups or universities using funds from a variety of state and federal agencies. Efforts to date have led to the installation and operation of a major rain gage network, other weather networks and sondes, several weather radars, meteorological aircraft, and a ship. This sizeable program is addressing five major study areas including lake meteorology, water resources and hydrometeorology, inadvertent weather modification, air pollution and its impacts, and severe weather. Multigroup field experiments and the exchange of data are coordinated at the scientist level.

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Stanley A. Changnon Jr., Floyd A. Huff, and Richard G. Semonin

METROMEX, a field project designed and now in progress at St. Louis, involves 4 research groups planning and working cooperatively to study inadvertent weather modification by urban-industrial effects, and, in particular, man-made changes of precipitation. Urban areas affect most forms of weather and some, such as winds, temperature, and visibility, are obvious and their changes are easily measured. Inadvertent precipitation changes are harder to measure, and except for the well-documented La Porte anomaly, urban-related rain changes have had only limited study. Examination of historical data at St. Louis has revealed summer increases in the immediate downwind area of: 1) rainfall (10–17%); 2) moderate rain days (11–23%); 3) heavy rainstorms (80%); 4) thunderstorms (21%); and 5) hailstorms (30%). METROMEX field measurements in the summer of 1971 involved 220 raingages and hailpads, 3 radar sets, 70 rainwater collectors, 14 pibal stations, 4 meteorological aircraft, unique atmospheric tracers, and a wide variety of standard and unusual meteorological equipment. These measurement tools were used to provide information on 1) the processes of cloud and precipitation formation, 2) the chemistry of aerosols and rainwater, 3) the urban heat budget, 4) the 3-D patterns of precipitation elements, and 5) the airflow and cloud development for numerical models.

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Robert Cataneo, John R. Adam, and Richard G. Semonin

Abstract

In the development of raindrops from cloud droplets in warm rain, the collision-coalescence process is considered to be the main growth mechanism for droplets of unequal size greater than 20 μm in diameter. However, due to the wake effect, the possibility of equal-sized droplets colliding does exist for some maximum vertical separation of the droplets. An empirical study has been performed which led to the determination of the maximum vertical separation required, as a function of droplet size, for equal-sized droplets to be influenced by the wake effect.

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