Effects of weather condition on aircraft emissions in climb phase

Aircraft trajectory optimization is highly sensitive to atmospheric conditions; pressure, relative humidity, temperature, wind intensity and direction have various influences on thrust needed and the resulting air pollutant emissions. The airline flight plans are generally pre-calculated before take off in order to optimize fuel consumption, using information from weather predictions that may not be accurate enough. In this paper an evaluation of weather prediction accuracy and, in the case of inaccurate predictions, a comparison of estimated emissions of some flights in climb phase for different weather conditions are presented. Weather data used are from National Oceanic and Atmospheric Administration (NOAA) public domain data, specifically the GRIB (Gridded Binary) files of the 20 Km RAP (Rapid Refresh) model, containing the analysis of real weather of a certain day/hour and the forecasts of the following 18 hours. In order to better understand the relation between weather conditions and aircraft emissions we report a comparison between estimated emissions (fuel, CO2 and NOX) of a real trajectory calculated with real weather data and with predicted weather data (forecasts for 1h, 3h and 6h). In order to evaluate accuracy of forecasts we consider radar reflectivity and wind. Regarding evaluation of the presence of potentially dangerous clouds (level 2 or more), a threshold filter has been used to select regions above 36 dBZ in the weather analysis and in a previous forecast related to the same hour. In the first step, the radar reflectivity and wind of real USA weather data from four days of June 2012 were compared with the forecasts, using the Tanimoto Similarity Index for measuring accuracy. Given the exact shape on a grid of the region (in this case, the current weather analysis) and its approximation (in this case the forecast), the Tanimoto Index (TI) is defined as the number of “pixels” of intersection on the number of pixels of the union of the two images. Then each one of the weather analyses for the 4 days considered (96 hours total) was compared with the forecasts for that time from 1 to 6 hours before, computing the Tanimoto index and the total cloud coverage with a threshold at 36 dBz. Furthermore, the wind intensity and direction forecasts were analyzed, and the mean value and variance of the difference between real weather condition and forecasts are presented. In a second step, from the analysis of the results of the first step, we selected some regions where cloud and wind analysis were substantially different from forecasts. In this scenario, the climb phases from real aircraft trajectories were collected from the FlightAware database. In the region of bad weather, we selected the trajectories that were significantly different from those made from the same aircraft in days of good weather. The related emissions were estimated and compared with the emissions of the same trajectory using forecasted weather. The emission estimation model is based on BADA (Base of Performance Data) from EUROCONTROL, ICAO and weather data.