Life Cycles of Periods of Very Low Eddy Dissipation Rate in the Boundary Layer at Memphis

The Federal Aviation Administration is interested in safely increasing throughput by decreasing the required spacing between aircraft. A key to accomplishing this goal is to accurately characterize the impact of Eddy Dissipation Rates (EDR) on wake decay. This is especially important in the lower end of the EDR spectrum at low levels where near-ground effects may also impact the wakes. Aircraft wakes existing in environments characterized by low EDR can have longer lifespans and may pose an increased safety risk to following aircraft. This study considers the question – if the current conditions exhibit low EDR, how long will this persist? Utilizing a two-year dataset collected in the vicinity of Memphis International Airport and geared towards wake studies [1], daily plots of key meteorological observations were generated for each day and examined for the presence of low EDR and correlations between EDR and other meteorological conditions such as stability, wind, and sky cover. As expected, extended periods of very low boundary-layer EDR were seen to usually take place overnight in an environment characterized by light winds, clear skies, and thermal stability. However, while this scenario predominates, low EDR were also observed when the nearby ASOS reported cloudy and/or foggy conditions, so these environmental characteristics were found to not be predictive without further context. A probability analysis of very low EDR periods will be presented, along with several case studies representing typical and atypical scenarios within their larger meteorological contexts. An ultimate goal is to isolate key characteristics and their synoptic and mesoscale drivers that could facilitate identification of similar likely low-EDR periods at other sites lacking explicit EDR observations.

[1] Pruis, Matthew J., et al. "Summary of NASA Wake and Weather Data Collection at Memphis International Airport: 2013-2015." 8th AIAA Atmospheric and Space Environments Conference. 2016.