A robust increase in the eddy length scale in the simulation of future climates

“The vertical velocity still depends on RHS, but changes in this would be expected to be relatively small given modest changes in eddy kinetic energy [57] and eddy length [40].”

“Considering the homogeneity and completeness of the dataset, reanalyses have acquired great importance in the weather and climate studies in recent times (Kidston et al. 2010; Kravtsov et al. 2014; Nkiaka et al. 2017).”

“• influences on eddy phase speed (Chen and Held, 2007); • influences on eddy length scales (Kidston et al., 2010; Rivière, 2011); • changes to the index of refraction for baroclinic systems (Simpson et al.”

“For example, if higher-order terms involving higher derivatives of the mean potential temperature need to be considered in the expansion (1), non-Gaussian statistics can arise through the terms that are nonlinear in h (Kimura and Kraichnan 1993).”

“One possibility is that the poleward shift of the jet streams in the future climate may come from the increased eddy length scale as suggested by Kidston et al. (2010). Very recently, Kidston et al.”

“…(2012) also conclude that changes in EHF are not consistent with the magnitude of the jet shift in their transient experiments. c. Eddy length scale Kidston et al. (2010) find that eddy length scales have increased in the SH over the past three decades, and Rivière (2011) argues that such a…”

“The extratropical eddy length has increased in the Southern Hemisphere in recent decades according to reanalysis data, and also increases in simulations of global warming scenarios (Kidston et al. 2010).”

“CCSM: Community Climate System Model project, supported by the, Directorate for Geosciences of the National Science Foundation, and the Office of Biological and Environmental Research of the U.S. Department of Energy.”

“We follow Vallis et al. (2004) and Barnes et al.”

“…increases in the phase speed of baroclinic eddies [Chen and Held, 2007; Chen et al., 2008], increases in the length scale of baroclinic eddies [Kidston et al., 2010; Kidston et al., 2011], increased wave reflection on the poleward flank of the jet [Lorenz, 2014], and biases in the…”

“A moderate increase of the eddy length with warming has also been found in other idealized models (Caballero and Hanley 2012) and in full GCM simulations of future climate (Kidston et al. 2010).”

“For example, one can compare Figure S3a multiplied by 2𝜋 with Figure 1 of Kidston et al. (2010).”

“Yet others suggest that increasing eddy length scales under global warming may play a role in storm track shifts (Kidston et al. 2010; Rivi (cid:1) ere 2011).”

“(6) Note that while 𝜆 is an imposed variable in the QG model, it can be readily measured in the data by computing the buoyancy frequency and tropopause height (see supporting information and Kidston et al., 2010).”

“Changes to the eddy length scale may also be a factor, perhaps in response to an increase in upper-tropospheric baroclinicity in the midlatitudes [19,157].”

“This poleward shift is especially interesting because the direct radiativeconvective effects of rising GHG seem to project much more strongly on the strength of the midlatitude jet.”

“Kidston et al. (2010, 2011) found a robust increase in eddy length scale in the CMIP3–IPCC AR4 models, which is possibly caused by increased static stability in the midlatitudes.”

“It is shown that in simulations of dry atmospheres, changes in the latitude of maximum MAPE are dominated by changes in near-surface meridional temperature gradients.”

“The first is associated with the fact that the basic state affects the preferred dynamical modes of variability and modes of response to radiative forcing (Ring and Plumb 2008; Sigmond and Scinocca 2010; Kidston et al. 2010; Barnes and Hartmann 2011; Simpson and Polvani 2016).”

“In addition to the direct effects of climate change, a poleward shift of the jet streams has been simulated by climate models (Yin 2005; Johanson and Fu 2009; Lu et al. 2007; Wu et al. 2010; Lorenz and DeWeaver 2007; Kushner et al. 2001) and predicted statistically and dynamically.”

“In addition, changes in advective forcing could be better understood by relating them to changes in eddy kinetic energy (O’Gorman 2010) and changes in the horizontal length scales of the geostrophic winds (Kidston et al. 2010).”

“Similarly for the comprehensive climate model projections, we find changes in zonal length of both signs depending on latitude in the CMIP5 models, but previous work has found robust increases in eddy length with warming [Kidston et al., 2010].”

“…have been proposed to understand the tropospheric circulation shift in response to global warming such as the increase in eddy phase speed (Lu et al. 2008; Chen et al. 2008), the rise in tropopause height (Lorenz andDeWeaver 2007), and the increase in eddy length scale (Kidston et al. 2010, 2011).”

“The eddy length scale is about 2500 km in the colder runs and increases slightly with temperature, as also found in many other models (Kidston et al. 2010).”

“The above scale-dependent wave response might be linked to the projected increase in the eddy length scale (i.e., the scale that holds most of the energy, Kidston et al., 2010).”

“…adjustment in response to stratospheric potential vorticity anomalies (Ambaum & Hoskins, 2002; Black, 2002; Hartley et al., 1998; Hoskins et al., 1985), and (3) stratospheric influences on tropospheric baroclinic systems (e.g. Chen & Held, 2007; Kidston et al., 2010; Wittman et al., 2007).”

“Kidston et al. (2010) demonstrated that the Coupled Model Intercomparison Project phase 3 (CMIP3) general circulation models (Meehl et al. 2007) exhibit a robust increase in zonal eddy length scale in future climates, and they suggest that this increase contributes to the predicted poleward…”

“…calculated using a single characteristic turbulent velocity, usually defined as the root-mean-square velocity (e.g., Sukoriansky et al. 2006; Kidston et al. 2010), or even a single characteristic velocity scale for a TC (an outer circulation velocity scale Uβ in CR19; a collective velocity…”

“As shown in T2018, this technique produces eddy length values that are quantitatively comparable to those obtained using Fourier transform techniques (Barnes & Hartmann, 2012; Frierson et al., 2006; Kidston et al., 2010).”

“O’Gorman, 2011) in warm climates, which may be due to an increase in static stability (Kidston et al., 2010), tropopause height (O’Gorman, 2011) or upper-level baroclinicity (Rivière, 2011), may affect the strength of the inverse and forward energy cascades.”

“CAM4 is the version of the community atmospheric model used for the CMIP5 project (Taylor et al. 2012) by NCAR and represents a significant improvement from the earlier version, while CM2.”

“To some extent, these mechanisms are related because eddy length depends on vertical stability, and eddy length is expected to change as a result of long-term changes in vertical stability (Kidston et al. 2010; Tandon et al. 2018b).”

“Possible contributors include changes in the characteristic wavelength of eddies, which can modulate the eddy‐jet feedback strength (Dai and Nie, 2020; Kidston et al., 2010), and biases in the models' climatological states that affect baroclinic instability and eddy dynamics (Chemke et al., 2022).”

“…because eddy length depends on vertical stability, and eddy length is expected108 to change as a result of long-term changes in vertical stability (Kidston et al, 2010;109 Tandon et al, 2018b).110 Despite the valuable insights gained from GCMs, understanding regional pro-111 cesses in GCMs is…”

“…possibility of the rising tropospheric static stability that shifts the Hadley Cell, the baroclinic instability zone and thus the midlatitude eddies poleward; Kidston et al. (2010) and Kidston et al. (2011) argued that the increase in eddy length scale can move the surface westerlies poleward.”