Search Results

You are looking at 1 - 10 of 17 items for

  • Author or Editor: Joost A. Businger x
  • Refine by Access: All Content x
Clear All Modify Search
Joost A. Businger

Abstract

An outline is given of the procedure for obtaining the gas transfer across the air–sea interface when the heat flux from the water to the surface is known. An essential assumption is similarity between the fluxes of heat and other scalar quantities, such as trace gases.

Full access
Steven Businger
and
Joost A. Businger

Abstract

In this note the magnitude of the viscous dissipation of turbulence kinetic energy in the surface layer of storms is investigated. It is shown that the layer-integrated dissipative heating is a cubic function of the wind speed. The magnitude of the estimated heating at higher wind speeds confirms the importance to storm evolution of this term in the turbulence kinetic energy equation and suggests that dissipative energy should be included in numerical weather prediction models, particularly in models that resolve mesoscale structures in storms. A general discussion of the implications of the results for the energetics of a range of storm systems is provided.

Full access
Steven A. Stage
and
Joost A. Businger

Abstract

A model is presented for the growth and evolution of a cloud-topped marine boundary layer. In this model the entrainment rate is determined from the turbulence kinetic energy (TKE) budget. It is assumed that the TKE budget can be partitioned according to whether each process produces TKE or converts it into potential energy, and that dissipation is proportional to production. This leads to an entrainment relationship which is considerably different than used in previous cloud-topped models.

This model is used to study an episode of cold-air outbreak over Lake Ontario during the International Field Year for the Great Lakes (IFYGL). The model reproduces changes in potential temperature and dew point as the air crossed the lake and the associated time variation of these parameters at the down-wind shore with an accuracy of better than 1°C. Model and measured soundings closely match, especially with respect to the presence and location of such features as cloud layers. Depth of the mixed layer also was generally well modeled. Use of divergences measured by the lakewide IFYGL buoy network did not give good agreement with the data. It is believed that this indicates that mixed-layer depth is sensitive to divergences at a smaller scale than the size of the lake.

Full access
Steven A. Stage
and
Joost A. Businger

Abstract

The model for the cloud-topped marine boundary layer presented by Stage and Businger (1981) is discussed and compared with previous models. Our model gives a considerably different interpretation of the energetics of the layer and indicates that a much higher fraction (20%) of the layer turbulence kinetic energy production is available to drive entrainment than previously supposed. In a test case, the Lilly (1968) minimum entrainment model gives entrainment rates similar to ours; however, this model is based on physically unrealistic assumptions about layer energetics. It is noted that two soundings from the International Field Year for the Great Lakes (IFYGL) exhibit behavior not allowed by Deardorff’s (1976) model. In these cases our model gives a good fit to the data and Deardorff’s model predicted a boundary layer much deeper than observed. The depth of the layer of radiative cooling at cloud top is shown to be important only if it is a significant fraction of the mixed-layer depth zB . Layer energetics are shown to prevent the cloud-top entrainment instability condition from causing much difference in theentrainment rate

Full access
J. M. Wilczak
and
Joost A. Businger

Abstract

A method is developed for retrieving turbulent pressure fluctuations from tower measurements of velocity and temperature, through use of the equations of motion. This method is applied to a series of large-scale eddies which are defined by their characteristic temperature ramp structure. The variance of pressure is found to follow local free-convection.

Large-scale eddy (LSE) pressure fields are used to estimate the pressure transport and pressure-gradient interaction terms in the convective surface-layer budgets of heat flux, stress and turbulent kinetic energy. The LSE pressure terms are found to balance the budgets to within 20–30% of the size of the largest budget terms.

Ensemble fields are formed by averaging individual LSE pressure transport and pressure-gradient interaction fields. The basic characteristics of these ensemble pressure covariance fields are easily related to the cross-products of the ensemble fields of p′, ∂p′/∂x, w′, and so on. This offers a simple way of visualizing the source of the budget pressure covariances in terms of the average LSE structure.

Full access
J. M. Wilczak
and
Joost A. Businger

Abstract

The energetics of the dry convective boundary layer is studied by partitioning the turbulent heat flux into thermally indirect (w′θ′<0) and thermally direct (w′θ′>0) components as a function of z/Zi . It is found that except for the inversion transition region, the thermally direct and indirect fluxes each have linear profiles. The integrated profiles indicate that a fraction A of the buoyant production of thermal kinetic energy is available to do the work of entrainment, where A is the boundary layer entrainment coefficient. A simple mixing analysis shows that this would require the integrated production of energy due to surface heating to be independent of the entrainment process. Sub-partitioning the thermally indirect flux into two components (w′<, θ′>0 and w′>0, θ′<0) reveals that an upward flux of cold air is the dominant thermally indirect term throughout the bulk of the mixed layer. Further, in the inversion transition layer the measured negative mean entrainment beat flux (w′θ′) i is principally due to a net upward flux of locally colder air, and not to a net downward flux of locally warmer air. These results are interpreted in terms of a highly idealized dome-wisp model of the entrainment mechanism.

Full access
William J. Shaw
and
Joost A. Businger

Abstract

Aircraft data from the JASIN Experiment have been used to examine the role that intermittency plays in turbulent transfer in the near-neutral marine atmospheric boundary layer. Conditional sampling, using the time-varying dissipation rate as an indicator, was the technique chosen for studying the dimensions of observed bursts of dissipation and their relation to the turbulent transfer. Burst fractional area coverage, γ, showed significant height variability in the surface layer, from a value of 0.45 near the surface decreasing to a constant value of about 0.30 above Z=0.2Zi . It was shown that γ is quite sensitive in the surface layer to the height of measurement and to the surface roughness (scaling with u 2 */gZ ), while being independent of heat flux.

The plume model of Frisch provided an estimate of the physical dimensions of the bursts. Their area varied little with height and corresponded to an average diameter of 140 m, but the number density decreased with height. The regions of high turbulence activity showed an elongation of 10% in the mean wind direction throughout the ABL.

Bursts of dissipation rate were generally coincident with regions of enhanced flux. Conditional statistics showed that 50–60% of the vertical velocity variance, stress, and water vapor fluxes were concentrated in 30% of the area over most of the ABL. The mean vertical velocity difference, Δw, between the bursts and the ambient state was found to reflect buoyant input of energy into the ABL through a dependence on the convective scaling velocity w *. This observation, the roughness height dependence of γ, and various laboratory findings suggest that plumes may be generated by the shear properties of the flow, rather than by thermal instabilities.

The turbulence kinetic energy balance showed that bursts of dissipation are also regions of enhanced turbulent transfer. In the convective case, buoyant production is concentrated in these regions. The transport of turbulence kinetic energy out of the lower ABL by the bursts actually exceeds the net transport, so that the ambient state transports turbulence kinetic energy to the surface.

Full access
Joost A. Businger
and
Steven P. Oncley

Abstract

A method is proposed to measure scalar fluxes using conditional sampling. Only the mean concentrations of updraft and downdraft samples, the standard deviation of the vertical velocity, and a coefficient of proportionality, b, need to be known. The method has been simulated from existing time series of the vertical wind component, temperature, and humidity in the surface layer. It is found that b has an almost constant value of 0.6 for both scalars and over a wide stability range. This result encourages application to other scalars and suggests that the method may be used beyond the atmospheric surface layer in the lower part of the planetary boundary layer.

Full access
Noel R. Cheney
and
Joost A. Businger

Abstract

An accurate and fuss response thermocouple-based temperature system has been developed for use in the atmospheric surface layer. The absolute accuracy is better than ±0.01°C and the relative accuracy between thermocouples is ±0.01°C. A number of special features were incorporated into the system to achieve the required performance. These include front-end multiplexing to allow one amplifier to process all channels; microprocessor-based control; handling of large, fast-changing temperature variations with no degradation in performance; and sophisticated noise removal and error reduction techniques. The system can accommodate up to 22 thermocouples with a total data rate of 180 s−1. Humidity is measured by converting standard thermocouples to wet bulbs through the use of wetted wicks.

Full access
James W. Telford
and
Joost A. Businger

Abstract

No abstract available.

Full access