Fog Simulation Research Articles

Simulation of fog with the ECMWF prognostic cloud scheme

AbstractA prognostic cloud scheme has been operational at the European Centre for Medium‐Range Weather Forecasts (ECMWF) since 1995. In this paper the performance of the cloud scheme in simulating fog is assessed. A case‐study is performed with the one‐column version of the ECMWF model in order to analyse how the model reproduces the main mechanisms of fog generation and dissipation. A climatology of the model's fog is produced using data from the ECMWF Re‐Analysis and compared with climatological data. High resolution (T213L31) operational forecasts with the prognostic cloud scheme are compared with synoptic reports of visibility for Europe. In this context the relation between fog and temperature, on the one hand, and fog and wind speed, on the other, is explored in some detail.The comparison between the simulated and the observed visibility, in the one‐column model case‐study, shows that the evolution of fog is properly simulated. the analysis of the behaviour of the different parametrized physical processes suggests that the subtle balance between the various processes, fundamental for a realistic fog simulation, is achieved. This study also shows that in radiation fog a cooling process like radiation, that only changes the temperature without changing the moisture, is rather essential in order to reach saturation. the comparison between the model's fog climatology and the climatological data shows that the model is able to reproduce most of the major fog areas, particularly over the ocean.The analysis of the results from high‐resolution fog forecasts for Europe and the comparison with synoptic observations of visibility shows that the model simulates realistically some of the fog over Europe, particularly at 00 and 06 UTC. At 12 UTC the fog in the model is usually underestimated. In general, the number of situations where the visibility is between 2 km and 11 km is underestimated by the model. It is shown that the model is always slightly closer to saturation than the observations and this might be helping the model in producing fog. the model reproduces the observed behaviour of fog as a function of temperature and wind speed rather realistically.

Visualization and view simulation based on transputers

N the Institute for Flight Mechanics at the German Research Establishment, several different types of simulations of flight vehicles are in use. There are realtime simulations based on transputers (FALKE Space Shuttle model, helicopter rotor model) or based on special simulation computers (ground-based simulators for the flying simulator ATT AS and ATTHeS on AD 100). Other simulations are calculated off-line on a mainframe computer (flight vehicles under development, e.g., X-31A). All these simulations need a realtime visualization tool to show a three-dimensional view of the flight vehicles and their movement in space. This tool was developed based on transputers, i.e., parallel processing. The resulting system is built-up modular and can be implemented on a scalable transputer architecture (i.e., different numbers of transputers). In this way the cost and complexity of the system can be adjusted to the application. The hardware (without the monitor) is contained in a small 19-in. rack and can be transported to applications in the field if necessary. The visualization system can be used to view the realtime movement of the simulated flight vehicles, to show, e.g., the simulated helicopter rotor or to replay and inspect image-byimage a recorded or off-line simulation. The system can be connected to a telemetry station such that a real flight vehicle can be observed as with a camera. By using enough transputers we can also show the flight vehicle moving in a landscape with texturing, fog simulation etc.; viewing from the cockpit of the flight vehicle results in a view simulation.

Low-Visibility Visual Simulation with Real Fog

An environmental fog simulation (EFS) attachment was developed to aid in the study of natural low-visibility visual cues and subsequently used to examine the realism effect upon the aircraft simulator visual scene. A review of the basic fog equations indicated that the two major factors must be accounted for in the simulation of low visibility-one due to atmospheric attenuation and one due to veiling luminance. These factors are compared systematically by: comparing actual measurements lo those computed from the Fog equations, and comparing runway-visual-range-related visual-scene contrast values with the calculated values. These values are also compared with the simulated equivalent equations and with contrast measurements obtained from a current electronic fog synthesizer to help identify areas in which improvements are needed. These differences in technique, the measured values, the Features of both systems, a pilot opinion survey of the EFS fog, and improvements (by combining features of both systems) that are expected to significantly increase the potential as well as flexibility for producing a very high-fidelity, low-visibility visual simulation are discussed.