Clear-air turbulence trends over the North Atlantic in high-resolution climate models

Abstract

Clear-air turbulence (CAT) has a large impact on the aviation sector. Our current understanding of how CAT may increase with climate change in future is largely based on simulations from CMIP3 and CMIP5 global climate models (GCMs). However, these models have now been superseded by high-resolution CMIP6 GCMs, which for the first time have grid lengths at which individual turbulence patches may start to be resolved. Here we use a multi-model approach to quantify projected moderate CAT changes over the North Atlantic using CMIP6 models. The influence of the model resolution on CAT projections is analysed. Twenty-one CAT diagnostics are used, in order to represent uncertainties in CAT production mechanisms. Each diagnostic responds differently in time, but the majority display an increase in moderate CAT between 1950 and 2050. Although winter is historically the most turbulent season, there is strong multi-model agreement that autumn and summer will have the greatest overall relative increase in CAT frequency. By 2050, summers are projected to become as turbulent as 1950 winters and autumns. The global-mean seasonal near-surface temperature is used as a comparative metric. For every 1 °C of global near-surface warming, autumn, winter, spring, and summer are projected to have an average of 14%, 9%, 9%, and 14% more moderate CAT, respectively. Our results confirm that the aviation sector should prepare for a more turbulent future.

Past and Future Trends in Clear‐Air Turbulence Over the Northern Hemisphere

“…Component analysis of the TI1 CAT index leads to the conclusion that increases in MOG‐CAT frequency are mainly related to increases in VWS within the subtropical jet. Contrary to previous studies (P. D. Williams, 2017; Storer et al., 2017; Smith et al., 2023), our results show a slight decrease in MOG‐CAT frequency over the North Atlantic. The disagreement over this region can be explained by the fact that there are large uncertainties associated with the CAT indices used.…”

“…This is consistent with the study by Smith et al. (2023): they used three different models with high and coarse resolutions for each one, and they found no dependence on model resolution for moderate CAT projections over the North Atlantic.…”

“…Further, by comparing ERA5 in the native grid (∼25 km) and interpolated grid (∼100 km), we found very similar results in MOG-CAT climatology and trends. This is consistent with the study by Smith et al (2023): they used three different models with high and coarse resolutions for each one, and they found no dependence on model resolution for moderate CAT projections over the North Atlantic.…”

“…Using this subset therefore ensures that the results are as robust as possible. Note that our approach differs from previous studies, which use a large number of turbulence diagnostics (P. D. Williams, 2017;Storer et al, 2017;Smith et al, 2023); most of these diagnostics are important ingredients in CAT production but cannot be considered as CAT indices when used alone.…”

“…In contrast, DEF increases considerably (up to 500%), which is consistent with our results (Figure 10). More recently, Smith et al (2023) found that over the North Atlantic, 12 diagnostics projected a moderate CAT increase, while six projected a decrease. Furthermore, P. D. Williams and Storer (2022) showed a strong inter-diagnostic spread in CAT climatology and trends with ERA-interim reanalysis and HadGEM2-ES model.…”