Search Results

You are looking at 1 - 10 of 73 items for

  • Author or Editor: Roland Stull x
  • All content x
Clear All Modify Search
Roland Stull

Abstract

Three of the atmospheric datasets that were originally used to verity statistical dispersion theory are reevaluated. These datasets are described as well by transilient turbulence theory as by statistical theory over the range of time periods of interest for practical dispersion problems. The limitations of transilient turbulence theory, particularly its inability to duplicate the linear growth of plume-width standard deviation at infinitesimally short times, are also investigated.

Full access
Roland Stull

Abstract

An equation is presented for wet-bulb temperature as a function of air temperature and relative humidity at standard sea level pressure. It was found as an empirical fit using gene-expression programming. This equation is valid for relative humidities between 5% and 99% and for air temperatures between −20° and 50°C, except for situations having both low humidity and cold temperature. Over the valid range, errors in wet-bulb temperature range from −1° to +0.65°C, with mean absolute error of less than 0.3°C.

Full access
Roland Stull
Full access
Roland Stull and Steven Businger

To document the inner workings of graduate degree programs, the authors surveyed the 67 American and Canadian universities that grant Doctor of Philosophy (Ph.D.) and/or Master of Science (M.S.) degrees in the atmospheric sciences and related fields. Topics included (a) admission standards such as graduate record exam scores and grade point averages; (b) start-up issues such as course requirements and computer programming skills; (c) M.S. attributes such as thesis length, years until graduation, and thesis versus nonthesis options; (d) Ph.D. procedures such as exam sequences and timing, thesis page length, workplace ethics and teamwork, and development of teaching skills; and (e) employment after graduation. This information could aid university departments in their future program planning.

Full access
Edi Santoso and Roland Stull

Abstract

No abstract available.

Full access
Qing Zhang and Roland Stull

Abstract

Two alternative parameterizations for nonlocal turbulence mixing are tested in a 1D boundary-layer model against a dataset from the 1983 Boundary-Layer Experiment (BLX83) in Oklahoma. One method, proposed previously by Stull and Driedonks, is based on a nonlocal approximation to the turbulence kinetic energy (TKE) equation. An alternate method, based on a nonlocal approximation to the Richardson number, is simplified here from earlier parameterizations for transilient turbulence theory. Convective mixed-layer simulations of the vertical profiles of mean variables and fluxes using both methods are compared to the BLX83 observations and to simulations using a traditional slab model.

The TKE method develops a surface layer that is too thick compared to BLX83 data, particularly in the early morning. It also lacks the subadiabatic lapse rate that is observed in the top of the mixed layer. The Richardson number approach produces more accurate mixed-layer profiles, but lacks the general physical interpretation of the TKE method. Nonlocal spectral decompositions of the flux and intensity of mixing confirm that large-size eddies dominate within the middle of the mixed layer. Based on this limited validation, the Richardson number method is recommended for convective boundary layers, but the TKE approach should be used for modeling more general boundary layers that can include clouds and stable and/or windy conditions.

Full access
Roland B. Stull

Abstract

A first-order turbulence theory is developed that describes eddy-like mixing. Named transilient theory after a Latin word meaning “leap across” this approach models the turbulent mixing between arrays of points separated in space. It differs from eddy-diffusivity theory in that it is not restricted to turbulent transfer between adjacent points. By explicitly including “large eddy” effects it can handle mixing across zero-gradient and counter-gradient situations such as found in convective mixed layers. Applications might include pollutant dispersion, boundary layer modeling and cloud entrainment studies.

Full access
Roland B. Stull

Abstract

Abstract not available.

Full access
Roland B. Stull

Abstract

No abstract available.

Full access
Doug McCollor and Roland Stull
Full access