Mass-Flux Characteristics of Reactive Scalars in the Convective Boundary Layer

The transport of nonreactive and reactive bottom-up and top-down diffusing scalars in a solid-lid convective boundary layer is studied using large-eddy simulation (LES). The chemistry considered consists of an irreversible, binary reaction involving the bottom-up and top-down diffusing scalars. The mass-flux or top-hat characteristics of the reactive flow are determined. Also, several mass-flux schemes are run in an off-line mode, that is, with prescribed profiles of the mass flux and the updraft area fraction, and are compared to the LES. Top-hat approximations are found to capture about 25% of the covariance between two arbitrary (nonreacting or reacting) scalars and about 65% of the flux. Subplume fluxes are located either in the updraft for bottom-up diffusing scalars or in the downdraft for top-down diffusing scalars. The mass-flux scheme that is nearly identical to the exact plume-budget equations gives the best performance. For the parameterization of lateral exchange this mass-flux scheme includes gross exchange across the interface between updrafts and downdrafts, that is, includes also subinterface-scale exchange processes (like the other dynamical quantities also prescribed in an off-line mode using LES data). A simpler mass-flux scheme, which does not include the more sophisticated parameterizations of subplume fluxes and subinterface-scale lateral exchange, is found to perform only slightly worse. The results of this paper are also valid for the surface layer and lower mixed layer of the entraining convective boundary layer but not for the entrainment zone

Turbulent Transport in the Gray Zone: A Large Eddy Model Intercomparison Study of the CONSTRAIN Cold Air Outbreak Case

To quantify the turbulent transport at gray zone length scales between 1 and 10 km, the Lagrangian evolution of the CONSTRAIN cold air outbreak case was simulated with seven large eddy models. The case is characterized by rather large latent and sensible heat fluxes mention the meaning of SHF in the text below and remove from abstract and a rapid deepening rate of the boundary layer. In some models the entrainment velocity exceeds 4 cm/s. A significant fraction of this growth is attributed to a strong longwave radiative cooling of the inversion layer. The evolution and the timing of the breakup of the stratocumulus cloud deck differ significantly among the models. Sensitivity experiments demonstrate that a decrease in the prescribed cloud droplet number concentration and the inclusion of ice microphysics both act to speed up the thinning of the stratocumulus by enhancing the production of precipitation. In all models the formation of mesoscale fluctuations is clearly evident in the cloud fields and also in the horizontal wind velocity. Resolved vertical fluxes remain important for scales up to 10 km. The simulation results show that the resolved vertical velocity variance gradually diminishes with a coarsening of the horizontal mesh, but the total vertical fluxes of heat, moisture, and momentum are only weakly affected. This is a promising result as it demonstrates the potential use of a mesh size-dependent turbulent length scale for convective boundary layers at gray zone model resolutions

The variability of refractivity in the atmospheric boundary layer of a tropical island volcano measured by ground-based interferometric radar

For 24 h we measured continuously the variability of atmospheric refractivity over a volcano on the tropical island of Montserrat using a ground-based radar interferometer. We observed variations in phase that we interpret as due to changing water vapour on the propagation path between the radar and the volcano and we present them here in the context of the behaviour of the atmospheric boundary layer over the island. The water vapour behaviour was forced by diurnal processes, the passage of a synoptic-scale system and the presence of a plume of volcanic gas. The interferometer collected images of amplitude and phase every minute. From pairs of phase images, interferograms were calculated and analyzed every minute and averaged hourly, together with contemporaneous measurements of zenith delays estimated from a network of 14 GPS receivers. The standard deviation of phase at two sites on the volcano surface spanned a range of about 1–5 radians, the lowest values occurring at night on the lower slopes and the highest values during the day on the upper slopes. This was also reflected in spatial patterns of variability. Two-dimensional profiles of radar-measured delays were modelled using an atmosphere with water vapour content decreasing upwards and water vapour variability increasing upwards. Estimates of the effect of changing water vapour flux from the volcanic plume indicate that it should contribute only a few percent to this atmospheric variability. A diurnal cycle within the lower boundary layer producing a turbulence-dominated mixed layer during the day and stable layers at night is consistent with the observed refractivity

Industrial and Commercial Heat Pump Applications in the United States

The energy crisis of 1973 accelerated the development of large-scale heat pumps in the United States. Since that time, the commercial, institutional, and industrial applications of heat pumps for waste heat recovery have expanded. This paper reviews the trends in heat pump cycle developments and discusses both the closed vapor compression cycle and refrigerants most commonly used and the open-cycle mechanical vapor compression heat pumps. Waste heat sources, heat loads served by heat pumps--and typical applications using heat pumps for large-scale space heating, domestic water heating, and industrial process water heating-- are discussed. Typical installations include commercial applications in hotels, high-rise apartments and condominiums, and office buildings. Institutional installations discussed include hospitals, universities, wastewater treatment plants, and airport terminals. Industrial applications largely center on food processing industries, feedwater heating, metal fabricating, and other industries. Reference is also made to other applications and alternative energy sources now gaining acceptance, including groundwater/geothermal water