When the atmospheric profile shows a strongly stratified stable layer capped by a weakly stratified, neutrally stable layer, thunderstorm development can induce a phenomenon known as gravity waves (i.e., buoyancy or density waves). These waves are characterized by alternating regions of convergence and divergence over a relatively short distance. Such aerodynamic shear can become hazardous to air traffic if the shear contained within the waves surpasses the threshold for air traffic safety. Gravity waves are particularly hazardous because they develop in seemingly benign weather surrounding the parent thunderstorm and in many cases are not associated with any visual storm feature. Several cases have been studied in which commercial aircraft have encountered gravity waves and have been adversely affected by their encounters. The purpose of this study is to show how gravity waves can have a detrimental effect on aircraft in flight, how gravity waves can be detected, and to show the need for a detection algorithm.
With the development of the National Weather Service's Next Generation Radar (WSR-88D NEXRAD) and the Federal Aviation Administration's Terminal Doppler Weather Radar (TDWR), the ability to detect gravity waves exists near many of America's major airports. Since gravity waves are a low-level phenomenon (generally below 2km), their presence should be of interest to aircraft in the takeoff and landing stages of flight. During operations at Lincoln Laboratory's Integrated Terminal Weather System (ITWS) prototype field site in Dallas there have been at least two incidents in which commercial aircraft experienced windshear of at least 40 knots on take-off, possibly caused by single or multiple gravity wave bands.
This study will look at 43 cases of gravity wave formation within the terminal areas of Dallas/Fort Worth International, Memphis International, and Orlando International airports. Statistics will be compiled to determine the frequency and severity of the gravity waves as well as their duration. The study will include Pilot Reports (PIREPS) from a few of these cases in which aircraft experienced windshear due to suspected encounters with gravity waves. It is the hope of the author that this study will lead to the development of a detection algorithm that will increase the safety of America's commercial air traffic.
* This work was sponsored by the Federal Aviation Administration. The views expressed are those of the authors and do not reflect the official policy or position of the U.S. Government.
+ Opinions, interpretations, conclusions and recommendations
are those of the authors and are not necessarily endorsed by the United
States Air Force.
The 8th Conference on Aviation, Range, and Aerospace Meteorology