J. M. Reisner

Simulations of flow around a cubical building: comparison with towing-tank data and assessment of radiatively induced thermal effects

Abstract A three-dimensional (3-D) computational fluid dynamics (CFD) model, coupled with a meteorological radiation and surface physics package, is used to model the mean flow field and tracer dispersion in the vicinity of an idealized cubical building. We first compare the simulations with earlier numerical studies as well as towing-tank laboratory experiments, where radiation effects were not included. Our simulations capture most of the features revealed by the towing-tank data, including the variation of the flow reattachment point as a function of Froude number and the induction of a prominent lee wave in the low Froude number regime. The simulated tracer concentration also compares very favorably with the data. We then assess the thermal effects due to radiative heating on the ground and building including shading by the building, on the mean flow and tracer dispersion. Our simulations show that convergence within and beyond the cavity zone causes a substantial lofting of the air mass downstream from the building. This lofting results from the combination of thermal heating of the ground and building roof, and vortex circulation associated with the horseshoe eddy along the lateral sides of the building. The specific effect of shading on the flow field is isolated by comparing simulations for which the radiative heating and shading patterns are kept constant, but the environmental wind direction is altered. It is found that the shading exerts local cooling, which can be combined into the overall thermodynamic interaction, described above, to effectively alter the circulation downstream from the building.

Initial investigations of microscale cellular convection in an equatorial marine atmospheric boundary layer revealed by lidar

During the Combined Sensor Program (CSP) in March of 1996, the Los Alamos National Laboratory (LANL) fielded an advanced scanning Raman lidar. The lidar was part of a larger suite of micrometeorological sensors to quantify processes associated with the ocean-atmosphere interface, including intermittency and coherent atmospheric features in the {open_quotes}warm pool{close_quotes} of the Tropical Western Pacific (TWP) near Manus Island (2{degree}S. lat., 147{degree}E. long). Initial inspection of the data has revealed excellent information on the microscale vertical and horizontal spatial and temporal structure of the equatorial Marine Atmospheric Boundary Layer (MABL). The data from this experiment have added to the increasing body of measurements on surface layer convection and intermittency including, for the first time, the observation of microscale cellular convective structures such as hexagonal patterns associated with Rayleigh-B{acute e}nard cells.{copyright} 1997 American Geophysical Union

High-resolution modeling of LIDAR data mechanisms governing surface water vapor variability during SALSA.

An integrated tool that consists of a volume scanning high-resolution Raman water vapor LIDAR and a turbulence-resolving hydrodynamic model, called HIGRAD, is used to support the semi-arid land-surface‐atmosphere (SALSA) program. The water vapor measurements collected during SALSA have been simulated by the HIGRAD code with a resolution comparable with that of the LIDAR data. The LIDAR provides the required “ground truth” of coherent water vapor eddies and the model allows for interpretation of the underlying physics of such measurements and characterizes the relationships between surface conditions, boundary layer dynamics, and measured quantities. The model results compare well with the measurements, including the overall structure and evolution of water vapor plumes, the contrast of plume variabilities over the cottonwoods and the grass land, and the mid-day suppression of turbulent activities over the canopy. The current study demonstrates an example that such an integration between modeling and LIDAR measurements can advance our understanding of the structure of fine-scale turbulent motions that govern evaporative exchange above a heterogeneous surface.

Test of the Volume-of-Fluid Method on Simulations of Marine Boundary Layer Clouds

Abstract The impact of using grid-averaged thermodynamic properties (i.e., neglecting their subgrid variability due to partial cloudiness) to represent forcings for condensation or evaporation has long been recognized. In particular, numerical difficulties in terms of spurious oscillations and/or diffusion in vicinity of a cloud–environment interface have been encountered in most of the conventional finite-difference Eulerian advection schemes. This problem is equivalent to the inability of models to accurately track the cloud boundary within a grid cell, which eventually leads to spurious production or destruction of cloud water at leading or trailing edges of clouds. This paper employs a specialized technique called the “volume-of-fluid” (VOF) method to better parameterize the subgrid-scale advection process that accounts for the transport of material interfaces. VOF also determines the actual location of the partial cloudiness within a grid box. Consequently, relevant microphysical parameterizations in...

Probing boundary layer turbulence with data assimilation on lidar measurements

This study represents an integrated research capability based on (1) data from a scanning water vapor lidar, (2) a hydrodynamic model (HIGRAD) with a observing routine (VIEWER) that simulates the lidar scanning, and (3) an extended Kalman filter (EKF) algorithm for data assimilation which merges data into a model for the best estimate of the system under study. The purpose is to understand the degree to which the lidar measurements represent faithfully the atmospheric boundary layers spatial and temporal features and to extend this utility in studying other remote sensing capabilities employed in both field and laboratory experiments. Raman lidar water vapor data collected over the Pacific warm pool and the HIGRAD simulations were first compared with each other. Potential aliasing effects of the measurements are identified due to the relatively long duration of the lidar scanning. The problem is being handled by the EKF data assimilation technique which incorporates measurements, that are unevenly distributed in space and time, into a model that simulates the flow being observed. The results of this study in terms of assimilated data will help to resolve and describe the scales and mechanisms that govern the surface evaporation.

PROBING NEAR-SURFACE ATMOSPHERIC TURBULENCE WITH LIDAR MEASUREMENTS AND HIGH-RESOLUTION HYDRODYNAMIC MODELS

As lidar technology is able to provide fast data collection at a resolution of meters in an atmospheric volume, it is imperative to promote a modeling counterpart of the lidar capability. This paper describes an integrated capability based on data from a scanning water vapor lidar and a high-resoiution hydrodynamic model (HIGRAD) equipped with a visualization routine (VIEWER) that simulates the lidar scanning. The purpose is to better understand the spatial and temporal representativeness of the lidar measurements and, in turn, to extend their utility in studying turbulence fields in the atmospheric boundary layer. Raman lidar water vapor data collected over the Pacific warm pool and the simulations with the HIGRAD code are used for identifying the underlying physics and potential aliasing effects of spatially resolved lidar measurements. This capability also helps improve the trade-offbetween spatial-temporal resolution and coverage ofthe lidar measurements.