Search Results

You are looking at 1 - 10 of 26 items for

  • Author or Editor: Lawrence F. Radke x
  • Refine by Access: All Content x
Clear All Modify Search
Peter V. Hobbs and Lawrence F. Radke

Abstract

No abstract available.

Full access
Peter V. Hobbs and Lawrence F. Radke

Abstract

Airborne, ground and radar techniques used for evaluating the effects of artificial seeding on winter clouds and precipitation over the Cascade Mountains are described. The clouds were seeded for 1 or 2 h with silver iodide and/or Dry Ice, dispersed from an aircraft, at locations which particle trajectory analysis, based on field data, indicated would affect precipitation in a small (90 km2) predetermined target area straddling the Cascade crest. The effects of seeding on the clouds were determined from the aircraft through visual observations, ice nuclei measurements, and measurements of the type and concentrations of cloud particles. A Doppler radar located near the Cascade crest was used to measure the spectra of fallspeeds of the precipitation particles. At manned stations within the target area on the ground, measurements and observations were made before, during and after seeding of precipitation rates, the types, concentrations and degrees of riming of snow crystals, and the concentrations of freezing nuclei and silver in the snowfall.The effects of heavy seeding on the clouds were generally pronounced and measurable. Good physical evidence for artificial modifications of snowfall on the ground within the target area was not as common, but was obtained in a number of detailed case studies.

Full access
Lawrence F. Radke and Peter V. Hobbs

Abstract

Aircraft-borne measurements showed that five small cumulus clouds were surrounded by regions of high humidity out to distances of several cloud radii from their centers. Total particle concentrations in the regions of high humidity were about twice those in the air at the same level but well removed from the cloud boundaries. The regions of high humidity and particle concentrations also coincided with regions of high turbulence surrounding the clouds. In addition to affecting particle production, regions of high humidity surrounding clouds can be expected to affect chemical process and atmospheric radiation transfer.

Full access
David R. Dowling and Lawrence F. Radke

Abstract

A review of existing literature is made to determine typical values for the physical properties cirrus clouds. The properties examined (with typical values and measured ranges) are cloud-center altitude (9 km, 4 to 20 km), cloud thickness (1.5 km, 0.1 to 8 km), crystal number density (30 L−1, 10−4 to 10−4 L−1), condensed water content (0.025 g m −3, 10−4 to 1.2 g m −3), and crystal size (250 μm, 1 to 8000 μm). A typical crystal size distribution is also reported.

Full access
Lawrence F. Radke and Anthony C. Delany

Abstract

During the Cooperative Atmospheric–Surface Exchange Study in 1999 (CASES99), an intensive investigation of the stable nocturnal boundary layer, a versatile and sensitive cryogenically cooled thermal imaging radiometer, the Inframetrics PM 380 Thermal Camera, was deployed. The 60-m-high instrumented tower at the central CASES99 site provided the perch from which to survey the instrumented research field. The field of view of 16° (0.28 sr) and an angular resolution of 1/16° (0.0011 sr) enabled a segment of landscape 500 m distant, of approximately 150-m width, to be viewed with a resolution of approximately 0.5 m. Or, looking down from the 50-m level of the tower, a section of the ground surface 15 m on a side could be viewed with a resolution of 5 cm. The surface brightness temperature of any area could be surveyed with a temperature resolution of 0.1°C and a time resolution of 30 Hz. The information obtained from analysis of these thermal images uniquely complemented the data acquired by the more conventional radiometric and meteorological instrumentation. The thermal imager provided valuable information on the landscape-scale changes of surface temperature after sunset and yielded insights into the development of surface drainage flow and its initiation. Also during periods of nocturnal stability the movement of thermal features across the standing vegetation could be traced, allowing the propagation of eddies to be investigated. The examination of apparently uniform land surfaces enabled a quantified analysis of the inhomogeneities of longwave emission. This information is critically important for the understanding of errors in the surface energy balance. The nocturnal thermal images of mature deciduous trees illustrated the extent to which trees modulate local airflow patterns. Finally, the tantalizing prospect of utilizing the thermal image of the 60-m tower itself to achieve a surrogate air temperature profile was examined.

Full access
Dean A. Hegg, Lawrence F. Radke, and Peter V. Hobbs

Abstract

Preliminary measurements of several physical and chemical parameters associated with clouds in two cases of onshore flow over western Washington suggest that the physical and chemical properties of maritime, cloudy air passing over this region change over relatively small spatial and temporal scales (∼100–200 km, and 5- 15 h, respectively). These scales are similar to those for changes in precipitation chemistry in this region. This tentative conclusion concerning the scales for air mass changes differs from the assumption usually made concerning air mass characteristics and transport distances in the eastern United States.

Full access
Lawrence F. Radke, Peter V. Hobbs, and Dean A. Hegg

Abstract

Airborne measurements over periods of several hours were made in the effluents that collected in the boundary layer in the form of “ground clouds” when an Atlas/Centaur and Titan III rocket were launched at night-time from Cape Canaveral, Florida. The ground cloud produced by the ATLAS was dry, whereas that produced by the TITAN was initially wet, then dry, and finally wet again. Both clouds dispersed primarily in the horizontal plane. Their volumes at time t (min) were given by V = V 0 t n where V 0 = 1.3 × 106 m3 and n = 0.98 for the ATLAS and V 0 &equals 1.76 × 107 m3 and n = 0.94 for the TITAN.

The ATLAS ground cloud initially contained elevated concentrations of NO, N02, hydrocarbons and particulate mass. However, dispersion of the cloud quickly reduced these concentrations and the light-scattering coefficient of the cloud. Gas-to-particle conversion (postulated to be the result of the oxidation of NO to NO2 followed by the Formation of NH4NO3) produced smoke particles at a rate of - ∼1016 s−1 in the ATLAS ground cloud but these did not contribute significantly to the total mass of particles in the cloud.

Gas-to-particle conversion in the TITAN ground cloud during its dry phase (probably produced by the reaction of HCI, from the rocket exhausts, with NH3, from the ambient air, to produce NH4Cl) created mass at a sufficient rate (∼0.1 μg m−3 min−1) to provide the potential for a significant source of pollution for several days.

Full access
Edward E. Hindman, Lawrence F. Radke, and Mark W. Eltgroth

Abstract

Full access
Peter V. Hobbs, Jeffrey L. Stith, and Lawrence F. Radke

Abstract

The concentrations of cloud condensation nuclei (CCN) in the plumes from coal-fired electric power plants are generally about 2 to 5 times greater than in the ambient air unaffected by the plumes. However, if the ambient air is very clean, the concentrations of CCN in a coal power plant plume can be up to ∼80 times greater than in the ambient air. The rates of production of CCN due to gas-to-particle (g-to-p) conversion in the plume from one of the plants studied were measured on different occasions to be ∼2 × 1015 and ∼5 × 1013 CCN h−1 per mole of SO2. The maximum current of CCN to be expected in the plume from a coal power plant is ∼1017 CCN s−1. After a travel time of ∼1 h, most of the CCN in power plant plumes have been produced by g-to-p conversion rather than emitted directly from the stack.

The concentrations of ice nuclei in the plumes did not differ significantly from those in the ambient air.

The materials in a plume may be transported rapidly in the vertical if the plume is entrained into a convective cloud. The plume may cause a lowering in the altitude of the cloud base, but any effects that the plume may have on the drop size distribution in a convective cloud are often less than the natural variations. By contrast, in stratiform clouds a plume can produce marked increases in the concentration of small drops (∼10–20 μm diameter) and in the total concentrations of drops

Full access
Peter V. Hobbs, Lawrence F. Radke, and Marcia K. Politovich

Abstract

Full access