Publications

The Federal Aviation Administration (FAA) Integrated Terminal Weather System (ITWS) is supporting the development of products aimed at providing automated guidance to the air traffic managers for the anticipation of changes in ceiling and visibility (C&V) conditions and wake vortex behavior in the terminal area. Fine-resolution, one-dimensional (column) numerical models are being considered to provide information on the evolution of the local fine-scale structure of the lower atmosphere over the terminal area. The Code Brouillard Eau Liquids (COBEL) column model is being investigated for potential use within the ITWS. This one-dimensional numerical model has been developed for the short-term prediction of fog events in the north of France. This report describes initial progress in adapting the COBEL model to a wider range of meteorological conditions. A parameterization of surface frost deposition was implemented and a slight error in the computation of stability in a saturated atmosphere was corrected. Tests suggest that these modifications represent important features of the newest version of the COBEL model. Other significant modifications to the COBEL model were performed. Pressure tendencies and vertical motion (vertical advection) were implemented as additional external forcings to the column model. Sensitivity tests show that these forcings play important roles in determining the onset, evolution and dissipation of low stratiform clouds. Some further applications of the model are briefly discussed and future development efforts are suggested.

A Dynamic Atmospheric Vertical Structure Nowcast System (DAVS-NS) is being developed that will add value to the Integrated Terminal Weather System (ITWS) by providing current and short-term forecasts of the vertical atmospheric structure focused at specific sites within the terminal domain. Operational applications of these estimates of the atmospheric vertical structure include predicting changes in airport operation rates due to ceiling and visibility (C&V) changes and in predicting wake vortex behavior. The core of this system would be a one-dimensional boundary layer column model. This report summarizes the evaluation of a modified Oregon State University (OSU) column model using data collected during the fall 1994 combined National Aeronautics and Space Administration (NASA) wake vortex project and the ITWS site operations at Memphis International Airport (MEM). Further efforts are necessary to develop and test an operational DAVS-NS prototype. The accuracy typically seen in column model predictions of the vertical temperature structure will limit errors in wake vortex dissipation rates to within a factor of two. Given the current working hypothesis for the San Francisco stratus burn-off phenomenon that rests largely on warming of the marine boundary layer by surface heat flux, the OSU model will also appear to be well suited for addressing this particular problem.

The Federal Aviation Administration (FAA) Integrated Terminal Weather System (ITWS) is supporting the development of products important for air traffic control in the terminal area. Some ITWS is supporting the development of products important for air traffic control in the terminal area. Some ITWS products will allow air traffic managers to anticipate operationally significant short-term (0-30 min) changes in ceiling and visibility (C&V) and aircraft separations necessary to avoid encounters with wake vortices. Development of such products exploits data that will be available from new FAA terminal area sensor systems. These sensor systems include Terminal Doppler Weather Radar (TDWR), Next Generation Weather Radar (NEXRAD), the Meteorological Data Collection and Reporting System (MDCRS), and the Automated Surface Observing System (ASOS). A Dynamic Atmospheric Vertical Structure Nowcast System (DAVS-NS) is being developed that will add value to ITWS by providing current analyses and short-term forecasts of the vertical atmospheric structure focused at specific sites within the terminal domain. This report summarizes the initial evaluation of the Oregon State University one-dimensional boundary layer model for its potential role within a DAVS-NS.

The Planetary Boundary Layer (PBL) is that part of the atmosphere, which is directly influenced by the presence of the earth's surface, and which responds to surface forcing with a time-scale of an hour or less. The Residual Layer (RL) is the portion of the lower atmosphere, which was part of the PBL within the past several hours, and which has become separated from the influence of short-term surface forcing, usually by the formation of a cooler layer at the surface. In the mid-latitudes, the height of the combined PBL and RL is usually 1-2 kilometers. A column model is a one-dimensional prognostic model for the state of a single column of the atmosphere, with special attention to the processes in the lowest few kilometers. It is designed to diagnose and nowcast the vertical structure of the PBL. Important information for ITWS1 nowcast products are the vertical profiles of horizontal wind velocity, temperature, humidity, and turbulent kinetic energy (TKE) in the lowest few kilometers (Sankey, 1994). Traditionally, operational meteorologists have obtained estimates of these quantities by balloon soundings, a measurement process that is not well-suited for continuous updates. We are investigating the possibility of developing an operational column model to obtain this vertical structure information for use in the ITWS. Our approach involves using a combination of sensing technology and analysis techniques that have proven successful in several research programs. Column models are designed to mimic the processes by which the surface forces the processes in the low atmosphere at times when local radiation is a dominant factor. Fluxes are measures of the net rates of these transport processes. The widely used Oregon State University column model (OSUlDPBL) parameterizes the fluxes by gradient transfer techniques (Troen and Mahr!, 1986). This model has provided dependable service in several field experiments, providing information with a vertical resolution of tens of meters. It is not designed to provide a fine-scale description of the stable nocturnal PBL. The French model COB EL has been developed to forecast the occurrence of radiation fog, and therefore concentrates on modeling the stable nocturnal PBL (Bergot and Guedalia, 1994). It uses a prognostic equation to estimate TKE in the stable boundary layer and parameterizes the fluxes in tern1s of the TKE (Duynkerke, 1991). A discussion of the potential uses of the column model in the ITWS is followed by the considerations that motivate the design of an operational column model. The prototype design is described. We conclude with the results of a preliminary evaluation using STORMFEST data (STORM Project Office, 1992) and a discussion of plans for a more comprehensive evaluation.

The Federal Aviation Administration (FAA) Integrated Terminal Weather System (ITWS) is supporting the development of weather products important for air traffic control in the terminal area. These products will take advantage of new terminal area sensors, including Terminal Doppler Weather Radar (TDWR, Next Generation Weather Radar (NEXRAD), and the Meteorological Data Collection and Reporting System (MDCRS). Some of these ITWS products will allow air traffic managers to anticipate significant short-term changes in ceiling and visibility. This report focuses on the scientific data requirements for supporting prototype model-system development and diagnostics. Model diagnostics can include case studies to determine the most important physical processes that were responsible for a particular ceiling and visibility "event," providing the insight necessary for the development of effective ceiling and visibility product algorithms. In time such case study diagnostics could also include careful off-line "failure analyses" that may affect the disign of the operational system. General ceiling and visibility test beds are discussed. Updated reports will be released periodically as the ITWS ceiling and visibility project proceeds.

We present an overview of the product development strategy and discuss some of the technical considerations. It will be necessary to overcome significant scientific challenges in order to be successful. Our optimism comes from the improved operational meteorological data in the terminal area, from the ability to access and to process these data rapidly, and from ongoing advances in data assimilation for mesoscale models. Our role is to coordinate the fusion of these technical and scientific advances into operational aviation weather products and to evaluate the effectiveness of these products. Major scientific contributions are anticipated from the Forecast Systems Laboratory (FSL), the National Center for Atmospheric Research (NCAR), Pennsylvania State University, and Colorado State University.