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Roscoe R. Braham Jr. and Milton Draginis

Abstract

In an effort to disentangle the “orographic barrier” and “high-level heat source” effects, as they may combine to lead to the development of summer convective clouds over mountains, a series of measurements was undertaken in Arizona. With use of an instrumented airplane, measurements of temperature and dew point were obtained for a series of passes up- and downwind across a 9000-ft mountain range. Passes ranged in altitude from 10,000 to 14,000 ft. Data obtained at sunrise show very clearly the barrier effect which forced air to ascend about 1000 ft in crossing the ridge. After the mountain slopes became heated by insolation, a convection core formed over and slightly downwind from the ridge. This core served as the root of several small cumulus clouds which developed during the time of measurement.

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Sam S. Chang and Roscoe R. Braham Jr.

Abstract

Using aircraft data collected during the University of Chicago Lake-Effect Snow Storm project, the results of a case study of the convective thermal internal boundary layer (TIBL) over Lake Michigan are presented. An intense cold air outbreak on 20 January 1984 featured a rapid growth of the convective TIBL thickness and the concurrent development of cloud and snow. The average slope of the TIBL top over a fetch of 123.7 km was 1.0%. Microphysical characteristics of cloud and snow along with the TIBL development are also presented. Results of the TIBL integrated budgets of heat and total water (including cloud and snow water) are given in detail. Over the surface of Lake Michigan the average downward snow flux (snow precipitation rate) was 0.79 mm (water) per day. The average sensible and latent heat fluxes at the water surface were 323 and 248 W m−2, respectively. About 13 percent of the total warming of this cloud-topped TIBL was due to radiation.

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Richard E. Passarelli Jr. and Roscoe R. Braham Jr.

Radar and aircraft data are presented, in the form of case studies, for three shoreline-parallel snow bands that occurred over Lake Michigan. In all three cases a winter land breeze from one or both shores is shown to have an important role in organizing the low-level convergence and convective motions. These cases are compared with earlier studies of lake-effect snow bands on Lakes Erie and Ontario.

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Roscoe R. Braham Jr. and David A. R. Kristovich

Abstract

Aircraft measurements of vertical air motions are used in a process of conditional sampling to select updraft and downdraft cores during a period of strong lake-effect convection. Corresponding measurements of temperature and moisture are used to calculate the buoyancies of the cores and to evaluate the dependence of the calculated buoyancy on the horizontal extent of core environment used in the calculations. Results suggest that calculated buoyancies are relatively insensitive to the definition of core environment.

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Paul A. Spyers-Duran and Roscoe R. Braham Jr.

Abstract

An instrument for collecting cloud particles from an airplane has been developed. Cloud particles are captured and permanently replicated using the well known Formvar technique. From the continuous record of hydrometeor replicas, the forms, sizes and frequency distributions can be established. Description of the instrument and examples of data collected from natural clouds are presented. Problems of calibration are discussed.

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EXECUTIVE COMMITTEE, Joanne Simpson, James R. Mahoney, Roscoe R. Braham Jr., Albert J. Kaehn Jr., Ian D. Rutherford, William D. Bonner, Richard E. Hallgren, and Kenneth C. Spengler
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EXECUTIVE COMMITTEE, Albert J. Kaehn Jr., Roscoe R. Braham Jr., J. Smagorinsky, C. J. Murino, Julia N. Paegle, Douglas H. Sargeant, and K. C. Spengler
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EXECUTIVE COMMITTEE, James R. Mahoney, William D. Bonner, Joanne Simpson, Roscoe R. Braham Jr., Robert J. Serafin, Paul D. Try, Richard E. Hallgren, and Kenneth C. Spengler
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