Increased light, moderate, and severe clear-air turbulence in response to climate change

Abstract

Anthropogenic climate change is expected to strengthen the vertical wind shears at aircraft cruising altitudes within the atmospheric jet streams. Such a strengthening would increase the prevalence of the shear instabilities that generate clear-air turbulence. Climate modelling studies have indicated that the amount of moderate-or-greater clear-air turbulence on transatlantic flight routes in winter will increase significantly in future as the climate changes. However, the individual responses of light, moderate, and severe clear-air turbulence have not previously been studied, despite their importance for aircraft operations. Here, we use climate model simulations to analyse the transatlantic wintertime clear-air turbulence response to climate change in five aviation-relevant turbulence strength categories. We find that the probability distributions for an ensemble of 21 clear-air turbulence diagnostics generally gain probability in their right-hand tails when the atmospheric carbon dioxide concentration is doubled. By converting the diagnostics into eddy dissipation rates, we find that the ensembleaverage airspace volume containing light clear-air turbulence increases by 59% (with an intra-ensemble range of 43%-68%), light-to-moderate by 75% (39%-96%), moderate by 94% (37%-118%), moderate-to-severe by 127% (30%-170%), and severe by 149% (36%-188%). These results suggest that the prevalence of transatlantic wintertime clear-air turbulence will increase significantly in all aviation-relevant strength categories as the climate changes.

Multi‐model ensemble predictions of aviation turbulence

“…However, additional thresholds that range from light or greater to severe or greater turbulence were also calculated. Using multiple thresholds to predict different turbulence strength categories is similar to the approach used by Williams () and Storer et al (). Ellrod and Knapp () also discuss the use of higher thresholds for moderate and severe turbulence with the actual values used being model specific.…”

Aviation Turbulence: Dynamics, Forecasting, and Response to Climate Change

“…Several studies have reported that climate change will act to increase clear-air turbulence in the future, according to climate model simulations (Williams and Joshi 2013;Williams 2017;Storer et al 2017). The first study to look at this (Williams and Joshi 2013) focused on north Atlantic moderate-or-greater turbulence and showed that it would increase in frequency with climate change by around 40-170%.…”

“…The first study to look at this (Williams and Joshi 2013) focused on north Atlantic moderate-or-greater turbulence and showed that it would increase in frequency with climate change by around 40-170%. Williams (2017) then furthered the study to see how climate change might influence turbulence in five strength categories from light to severe, finding that all would increase in frequency with climate change. Storer et al (2017) then extended the work further to see how climate change will impact CAT globally, through all four seasons, and also at two flight levels in eight geographic regions.…”

“…In computational calculations using gridded data, numerical models rarely reach Ri = 0.25 due to the coarse resolutions, and therefore, thresholds of turbulence are model specific. To overcome this, Williams (2017) and Storer et al (2017) chose thresholds based on the distribution of turbulence in the atmosphere. For example, they assume that severe turbulence is found in 0.01% of the atmosphere, and therefore, they take the top 0.01% (99.9-100%) of the probability distribution to be severe turbulence.…”

“…These figures are similar to those of Sharman et al (2006) and, again, may underestimate the real statistics of turbulence injuries. These values could also be higher in the future, as climate change is likely to increase the frequency of turbulence around the world, particularly in the mid-latitudes (Williams and Joshi 2013;Williams 2017;Storer et al 2017). The cost of turbulence to the aviation industry is significant and comes from many sources, one of which is preventing aircraft from flying on the optimum route.…”