Skill of an aircraft wake-vortex transport and decay model using short-term weather prediction and observation

Kurzfassung

In order to safely reduce aircraft separation during approach and landing, the wake vortex behavior along the glide path has to be known and predicted. This requires in principle the knowledge of wake vortex relevant meteorological parameters along the entire glide path where typically continuous meteorological measurements of all relevant variables are not feasible. For multiple purposes a one-year meteorological data base for the Frankfurt Terminal area has been generated using NOWVIV. The skill of the nowcasting system NOWVIV (Nowcasting Wake Vortex Impact Variables) to predict these environmental parameters is assessed. This one-year data set comprises typical weather conditions and includes already typical features of a long-term surface wind climatology. It enables to test new operational concepts with realistic meteorological input and to estimate the potential for aircraft separation reduction. It may also be used within risk assessments for prototype wake-vortex advisory systems. A subset of the one-year data base is analysed in detail for a period of 40 days where a dedicated wake measurement campaign was carried out at Frankfurt airport in fall 2004. In total 231 wake vortex pairs generated by heavy aircraft in ground proximity were tracked and characterized by LIDAR. During this measurement campaign a SODAR/RASS and a LIDAR provided profile measurements of meteorological variables. These data are used to analyse the quality of the predicted profiles of wind, temperature and turbulence. Furthermore we carry out a skill analysis to investigate the potential of NOWVIV as a real-time prediction system where we focus on the ability to predict pre-defined cross wind thresholds. The skill of NOWVIV is compared to the skill of a simple cross wind persistence model based on SODAR measurements. For this purpose we assume that a given measured cross wind profile is valid over the whole forecast lead time and evaluate the skill of the forecast with increasing lead time every 10 minutes. In a wake-vortex advisory system, the weather prediction and observation system is coupled to a wake vortex predictor. Therefore, we have to know how the predictive skill of the weather forcast system influences the predictive skill of the whole forecast system chain including the wake predictor. Consequently, we extend this analysis by coupling the Probabilistic Two-Phase wake vortex transport and decay model P2P to the NOWVIV system and investigate the predictive skill of P2P for pre-selected confidence levels of vortex position and strength. The skill is assessed by comparing the predictions against LIDAR measured wake vortex position and strength. Initially, the overall skill of the wake vortex forecast is analysed. We then analyse the skill of the models with respect to observed and predicted clearance of a safety corridor from wake vortices (WV). In particular, we focus on the frequency of non-conservative predictions, which refer to a situation where a wake vortex is predicted to be outside a predefined safety corridor while observations still indicate the presence of a wake vortex in the safety corridor. A non-conservative predictions refers to a potential risk for a following aircraft which has to be avoided.