A diagnostic method for aircraft turbulence based on high-resolution numerical weather prediction products

Abstract

Forecasting aircraft turbulence accurately is of vital importance for route optimization and flight safety. The common methods including TI index and L-P are usually used to predict aircraft turbulence by diagnosing the strength of atmospheric turbulence, not taking into account the impact of aircraft itself and other elements, and can only be applied to the products with low horizontal resolutions. By considering factors that affect the aircraft lift, a new diagnostic index method, S Index (SI) method, is designed in this paper for aircraft turbulence, which can be applicable to high-resolution NWP products or analysis products. SI method mainly focuses on the factors that impact aircraft turbulence such as flight speed, wing loading, vertical velocity of air flow, horizontal wind speed, air density. The paper also provides a method of determining parameters based on the existing experience and mathematical techniques which are combined with aircraft reports and high-resolution NWP results. In addition, pointing to the level flight and takeoff/landing stages, SI analysis and calculation are carried out, respectively. To validate the application scope of the accuracy of SI method objectively, the physical quantity of turbulence area ratio (TAR), which is a statistical parameter to describe the ratio of turbulence area and the overall diagnostic region, is defined. In the case that the horizontal and vertical resolutions of weather research and forecasting (WRF) forecasts are 9 km and 300 m, respectively, the diagnostic results of SI show that for the stage of level flight, when the TAR ratio is 41 %, the overall forecast accuracy of aircraft turbulence can reach 74 %, of which the accuracy of moderate turbulence forecast is 60 % and the severe 27 %. For the stage with 20° elevation during the process of takeoff and landing, when the TAR ratio is 40 %, the overall forecast accuracy can get to 63 %, of which the accuracies of moderate and severe turbulence are 41 and 14 %, respectively.