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![The future minus past difference in each of the vertically integrated zonal-mean momentum budget terms in (13) for (top to bottom) each season. Future minus past difference (black), climatology/10 (solid red), location of the climatological maximum wind stress or momentum flux convergence (vertical red dashed), and difference for each individual model (gray). (a) t u along with the sum of budget terms (black dashed), (b) 2(u H * y H * ) f , (c) 2(u S *y S *) f , (d) 2(u L *y L *) f , (e) 2([u][y]) f , and (f) mountain torque. Poleward shifts of t u are listed in (a) and the shift in t u due to the 2(u H *y H * ) f term alone is shown in (b). This is obtained by taking the future t u to consist of the past t u plus the implied future wind stress due to the 2(u 0 H y 0 H ) f change. Significance is defined as where the anomalies are statistically different from 0 at the 95% level by a two-tailed t test.](profile/Tiffany-Shaw/publication/274495689/figure/fig4/AS:614144948592642@1523434974141/The-future-minus-past-difference-in-each-of-the-vertically-integrated-zonal-mean-momentum.png)
The future minus past difference in each of the vertically integrated zonal-mean momentum budget terms in (13) for (top to bottom) each season. Future minus past difference (black), climatology/10 (solid red), location of the climatological maximum wind stress or momentum flux convergence (vertical red dashed), and difference for each individual model (gray). (a) t u along with the sum of budget terms (black dashed), (b) 2(u H * y H * ) f , (c) 2(u S *y S *) f , (d) 2(u L *y L *) f , (e) 2([u][y]) f , and (f) mountain torque. Poleward shifts of t u are listed in (a) and the shift in t u due to the 2(u H *y H * ) f term alone is shown in (b). This is obtained by taking the future t u to consist of the past t u plus the implied future wind stress due to the 2(u 0 H y 0 H ) f change. Significance is defined as where the anomalies are statistically different from 0 at the 95% level by a two-tailed t test.
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Zonal-mean or basin-mean analyses often conclude that the midlatitude circulation will undergo a poleward shift with global warming. In this study, the models from phase 5 of the Coupled Model Intercomparison Project are used to provide a detailed examination of midlatitude circulation change as a function of longitude and season. The two-dimension...
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... zonal-mean vertically integrated momentum budget for the 13 models highlighted in boldface in Table 1 is shown in Fig. 5. Figure 5a demonstrates that t u changes in a similar same way to the 700-hPa zonal wind of the 35 models in Fig. 4, indicating that the mean response of the 35 models is largely captured by this 13-model subset and that t u responds in a similar way to the lower- tropospheric zonal-mean zonal wind, as expected. Fur- thermore, the ...
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... zonal-mean vertically integrated momentum budget for the 13 models highlighted in boldface in Table 1 is shown in Fig. 5. Figure 5a demonstrates that t u changes in a similar same way to the 700-hPa zonal wind of the 35 models in Fig. 4, indicating that the mean response of the 35 models is largely captured by this 13-model subset and that t u responds in a similar way to the lower- tropospheric zonal-mean zonal wind, as expected. Fur- thermore, the future minus past difference in t u is captured well by the sum of terms in (13). ...
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... various components that contribute to the zonal- mean vertically integrated momentum budget are shown in the remaining panels of Fig. 5. The change in CROSS is not shown here as it is small. Comparing the t u response in Fig. 5a with the 2(u 0 H y 0 H ) f contribution in Fig. 5b it is clear that, in the extratropics for the multi- model mean, the dominant term in maintaining the anomalous surface wind stress is the high-frequency meridional eddy momentum flux ...
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... various components that contribute to the zonal- mean vertically integrated momentum budget are shown in the remaining panels of Fig. 5. The change in CROSS is not shown here as it is small. Comparing the t u response in Fig. 5a with the 2(u 0 H y 0 H ) f contribution in Fig. 5b it is clear that, in the extratropics for the multi- model mean, the dominant term in maintaining the anomalous surface wind stress is the high-frequency meridional eddy momentum flux convergence. In terms of the latitudinal shift of the jet, the high-frequency eddy momentum flux ...
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... various components that contribute to the zonal- mean vertically integrated momentum budget are shown in the remaining panels of Fig. 5. The change in CROSS is not shown here as it is small. Comparing the t u response in Fig. 5a with the 2(u 0 H y 0 H ) f contribution in Fig. 5b it is clear that, in the extratropics for the multi- model mean, the dominant term in maintaining the anomalous surface wind stress is the high-frequency meridional eddy momentum flux convergence. In terms of the latitudinal shift of the jet, the high-frequency eddy momentum flux convergence, if acting alone, would actually cause a ...
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... anomalous surface wind stress is the high-frequency meridional eddy momentum flux convergence. In terms of the latitudinal shift of the jet, the high-frequency eddy momentum flux convergence, if acting alone, would actually cause a larger poleward shift than observed. The shift due to 2(u H *y H * ) f acting alone is quoted for each hemisphere in Fig. 5b by taking the future wind to be the historical wind stress t u plus the future wind stress change due to the change in 2(u H *y H * ) f ; that ...
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... changes in the other terms are, however, non- negligible. In the NH tropics, climatologically the quasi- stationary component (Fig. 5c) contributes to the easterly t u of the trade winds and this seems to weaken in the future (i.e., the quasi-stationary component provides an anomalous westerly tendency). Other than that, it has the effect of broadening and strengthening the dipole in zonal wind anomalies that occur around the jet center. But, in the NH extratropics ...
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Citations
... Because of differences in the stationary wave and jet structure between the Northern and Southern Hemispheres (NH and SH), the magnitude and direction of projected jet shifts differ regionally. In some regions, the subtropical jet is projected to strengthen and shift equatorward [31][32][33][34]. These changes in the jet could conceivably allow more mid-latitude eddies to reach the tropics, and perhaps also allow for faster phase speeds. ...
... While our conclusions regarding the role of the jet for KW amplitude is not affected by this bias, it raises questions about the reliability of future projections in this region. If the future changes in the jets will be significantly different from the projections, the impact on the equatorial spectrum will also be different than previously projected [17,[31][32][33][34]. ...
Models from phase 6 of the Coupled Model Intercomparison Project (CMIP6), simulate an intensification in equatorial Kelvin Waves (KW) and the Madden-Julian Oscillation (MJO) with global warming. In contrast, the power spectrum is projected to weaken for most other wavenumber-frequency combinations, including higher wavenumber Equatorial Rossby waves (ER). The qualitatively different projected response of KW and ER suggest that dynamical forcings have an important role in the physical mechanism of the changes. This hypothesis is tested using targeted simulations of the Model of an Idealised Moist Atmosphere (MiMA) in which we impose perturbations in upper-tropospheric zonal winds that mimic projected end-of-century changes. These simulations demonstrate that future changes in KW and the MJO strongly depend on changes in the South Pacific subtropical jet. A similar dependence is also evident in CMIP6 models. These results have implications for future projections of KW and MJO activity in models with biased subtropical jets.
... But before the target of net-zero emission is accomplished, human activities will continue driving the rise of greenhouse gases in the Earth's atmosphere. The accompanying warming will increase the cooling demand and drive profound changes in the climate system, including the weakening (3,4), latitudinal shifts (5,6), and seasonality changes (7,8) of regional atmospheric circulation. Such changes affect the spatial-temporal distribution of wind resources and may bring unexpected challenges to electricity grids that increasingly rely on wind energy. ...
... Resolving these gaps has not been prioritized partly because the projected wind changes appear small (<5%) on an annual average basis (11-13, 18, 19, 23). But as implied by the research of large-scale atmospheric circulation (4,6,19), warming-induced changes in wind resources can be seasonally amplified (19). Few studies on wind energy have recognized this seasonal amplification and the potential risk compounding for electricity grids. ...
... Recent climate simulations suggest that future changes in temperature and wind speed have strong regional (6,19,22,28) and seasonal (6,19) variations. Here we analyze large-ensemble simulations from the Community Earth System Model 2 (CESM2) to show potential changes in an emission scenario that doubles CO2 emission by 2100 (SSP-370; Methods). ...
Wind energy is key for reducing greenhouse gas emissions and meeting increasing energy demand. Long-term changes in wind resources were extensively studied but notable gaps remain. Meanwhile, the temporal changes and compounding risks received little attention. Here we analyze large-ensemble climate simulations and show that anthropogenic warming can contribute to significant wind stilling, particularly in the warm season of the northern hemisphere midlatitudes. The stilling is related to the amplified warming of the midlatitude land and mid-to-upper troposphere. At representative US sites, the stilling will unlikely threaten the cost-competitiveness of onshore wind relative to fossil energy. However, its impact can exceed a large interest increase and make wind energy less cost-competitive than other clean energy. Moreover, the summertime stilling coincides with surging cooling demand in the midlatitudes and may bring challenges to energy security. The findings about wind stilling and its implications may help inform future energy investments.
... Over northeastern North America, the westerly is therefore stronger in the south and relatively weaker in the north, which is conducive to forming atmospheric anomalies with a northwest-southeast tilt. From PD to the future, however, the westerly wind speed accelerates at about 55°N but decelerates at about 40°N as a result of the poleward shift of the North Atlantic jet due to the greenhouse warming [57][58][59] . This climatological change weakens the meridional shear of the Atlantic jet at its northern edge, which forces the atmospheric anomaly to tilt in a northeast-southwest direction (Fig. 4) and eventually leads to the phase reversal of the NAO response. ...
El Niño-Southern Oscillation (ENSO) teleconnection to the Euro-Atlantic exhibits strong subseasonal variations, as the North Atlantic Oscillation (NAO) response systematically reverses its phase from early to late winter. Based on two sets of atmospheric model simulations in CMIP6 forced by historical and projected SST, we report a future disappearance of this teleconnection reversal, with the positive early winter ENSO-NAO correlation turning negative and the negative late winter correlation becoming stronger. We suggest that this negative NAO tendency is associated with the strengthening and eastward shift of the ENSO atmospheric teleconnection towards the Euro-Atlantic due to parallel changes in the ENSO tropical convection. While the early winter NAO phase transition is further facilitated by the mean state change in the North Atlantic jet meridional shear, which shifts the ENSO-driven Rossby wave-propagating direction, an intensified stratospheric pathway is demonstrated to play an additional role in strengthening the late winter NAO response.
... The expected poleward shift in the jet is also shown to differ considerably between regions and models. For example, in projections for the Northern Hemisphere winter, a poleward shift is shown for the eddy-driven jet in the West Pacific region accompanied by an equatorward shift in the East Pacific jet, impacted by changes in stationary waves across models (Simpson et al., 2014). Furthermore, in the Southern Hemisphere winter, near New Zealand, considerable zonal asymmetry is shown in the future eddy-driven jet shift due to the asymmetry in the climatological jet (i.e., split jet structure), leading to an apparent equatorward shift in the regional winter jet (Simpson et al., 2014). ...
... For example, in projections for the Northern Hemisphere winter, a poleward shift is shown for the eddy-driven jet in the West Pacific region accompanied by an equatorward shift in the East Pacific jet, impacted by changes in stationary waves across models (Simpson et al., 2014). Furthermore, in the Southern Hemisphere winter, near New Zealand, considerable zonal asymmetry is shown in the future eddy-driven jet shift due to the asymmetry in the climatological jet (i.e., split jet structure), leading to an apparent equatorward shift in the regional winter jet (Simpson et al., 2014). Some models may overestimate the future response to jet changes due to an equatorward biased climatological jet, which tends to enhance the sensitivity to future external forcings (Curtis et al., 2020;Kidston & Gerber, 2010;Vallis et al., 2015), although the underlying mechanism behind this is still subject to debate (e.g., Simpson & Polvani, 2016). ...
... In the context of regional precipitation changes, the need to study these different mechanisms on a seasonally varying basis is clear. Many examples can be given highlighting the importance of seasonality: future projections of the jets position/intensity and the associated mechanisms are known to differ considerably between seasons (Simpson & Polvani, 2016;Simpson et al., 2014), the waveguideing properties of the jet differ between seasons (McIntosh & Hendon, 2018); the impact of stratospheric ozone depletion and recovery in influencing Southern Hemisphere circulation trends is most pronounced in summer (e.g., Morgenstern et al., 2014;Son et al., 2010), and teleconnections have significant seasonal variability (Karoly, 1989;Trenberth et al., 1998). As such, these changes can be obscured, or the relevant mechanisms mixed, when not considered separately on a seasonal basis. ...
Large uncertainty exists in the sign of long‐term changes in regional scale mean precipitation across the current generation of global climate models. To explore the physical drivers of this uncertainty for New Zealand, here we adopt a storyline approach applying cluster analysis to spatial patterns of future projected seasonal mean precipitation change across CMIP6 models (n = 43). For the winter precipitation change signal, the models split roughly into two main groups: both groups have a very robust wet signal across the west coast of the South Island but differ notably in terms of the sign of precipitation change across the north of the North Island. These far north winter precipitation differences appear related to how far the Hadley cell edge and regional eddy‐driven jet shift across the models relative to their historical positions. In contrast, for summer, most models have a markedly weaker and spatially non‐uniform response, where internal variability often plays a large role. However, a small group of models predict a robust wet signal across most of the country in summer. This “wet model” group is characterized by a regional La Niña‐like increase in high pressure shifted further to the south‐east of New Zealand, associated with more frequent north‐easterly flow over the country and accompanied by significant warming of local sea surface temperatures. This regional circulation response appears related to changes in stationary Rossby wave paths as opposed to changes in La Niña occurrence frequency itself.
... As it is difficult to meaningfully interpret the zonal mean wind response in the NH, where there are large zonal variations in the midlatitude jet (Barnes and Polvani 2013;Simpson et al. 2014), we next compare the 850-hPa zonal wind changes between the NINT and OMA 4xCO 2 simulations, further distinguishing between fast and total responses (Fig. 3). We begin with the NINT equilibrated or total response (i.e., years 100-150), which consists of a poleward jet shift over the Pacific basin and an acceleration and eastward extension of the jet over the Atlantic and Eurasia (Fig. 3b). ...
Stratospheric ozone, and its response to anthropogenic forcings, provide an important pathway for the coupling between atmospheric composition and climate. In addition to stratospheric ozone’s radiative impacts, recent studies have shown that changes in the ozone layer due to 4xCO 2 have a considerable impact on the Northern Hemisphere (NH) tropospheric circulation, inducing an equatorward shift of the North Atlantic jet during boreal winter. Using simulations produced with the NASA Goddard Institute for Space Studies (GISS) high-top climate model (E2.2) we show that this equatorward shift of the Atlantic jet can induce a more rapid weakening of the Atlantic Meridional Overturning Circulation (AMOC). The weaker AMOC, in turn, results in an eastward acceleration and poleward shift of the Atlantic and Pacific jets, respectively, on longer timescales. As such, coupled feedbacks from both stratospheric ozone and the AMOC result in a two-timescale response of the NH midlatitude jet to abrupt 4xCO 2 forcing: a “fast” response (5–20 years) during which it shifts equatorward and a “total” response (~100–150 years) during which the jet accelerates and shifts poleward. The latter is driven by a weakening of the AMOC that develops in response to weaker surface zonal winds, that result in reduced heat fluxes out of the subpolar gyre and reduced North Atlantic Deep Water formation. Our results suggest that stratospheric ozone changes in the lower stratosphere can have a surprisingly powerful effect on the AMOC, independent of other aspects of climate change.
... In addition to these storm track changes, the zonal mean near-surface mid-latitude westerlies and eddy momentum flux convergence maximum also shift poleward (Kushner et al. 2001;Swart and Fyfe 2012; Barnes and Polvani 2013;Simpson et al. 2014;Shaw et al. 2016). ...
While a poleward shift of the near-surface jet and stormtrack in response to increased greenhouse gases appears to be robust, the magnitude of this change is uncertain and differs across models, and the mechanisms for this change are poorly constrained. An intermediate complexity GCM is used in this study to explore the factors governing the magnitude of the poleward shift and the mechanisms involved. The degree to which parameterized subgrid-scale convection is inhibited has a leading-order effect on the poleward shift, with a simulation with more convection (and less large-scale precipitation) simulating a significantly weaker shift, and eventually no shift at all if convection is strongly preferred over large-scale precipitation. Many of the physical processes proposed to drive the poleward shift are equally active in all simulations (even those with no poleward shift). Hence, we can conclude that these mechanisms are not of leading-order significance for the poleward shift in any of the simulations. The thermodynamic budget, however, provides useful insight into differences in the jet and stormtrack response among the simulations. It helps identify midlatitude moisture and latent heat release as a crucial differentiator. These results have implications for intermodel spread in the jet, hydrological cycle, and storm track response to increased greenhouse gases in intermodel comparison projects.
... Historical period data indicates a poleward displacement 54,56,57 , a finding supported by the most recent IPCC report 58 . Climate simulations examining the future Northern Hemisphere jet stream behavior echo the historical findings [59][60][61] . ...
The trigger, pace, and nature of the intensification of Northern Hemisphere Glaciation (iNHG) are uncertain, but can be probed by study of ODP Site 1208 North Pacific marine sediments. Herein, we present magnetic proxy data that indicate a 4-fold increase of dust between ~ 2.73 and ~ 2.72 Ma, with subsequent increases at the start of glacials thereafter, indicating a strengthening of the mid-latitude westerlies. Moreover, a permanent shift in dust composition after 2.72 Ma is observed, consistent with drier conditions in the source region and/or the incorporation of material which could not have been transported via the weaker Pliocene winds. The sudden increase in our dust proxy data, a coeval rapid rise in dust recorded by proxy dust data in the North Atlantic (Site U1313), and the Site 1208 shift in dust composition, suggest that the iNHG represents a permanent crossing of a climate threshold toward global cooling and ice sheet growth, ultimately driven by lower atmospheric CO2.
... When the full suite of CMIP5 models is considered, the range of inter-model differences is even larger ( Figure S3 in Supporting Information S1). This is likely caused in part by known differences in simulated mean North Pacific circulation (Huang & Stevenson, 2021), different magnitudes of internal variability, as well as differences in model representations of physical processes (Rupp et al., 2013) and models variability in midlatitude circulation patterns that exist within CMIP5 (Simpson et al., 2014). Models also generally capture the spatial structure of precipitation of California, with higher values of both mean and extreme precipitation overall in northern California compared to the southern part of the state (Figures 1b, 1d, 1g, and 1h). ...
The El Niño/Southern Oscillation (ENSO) affects the occurrence frequency and intensity of extreme precipitation through modulations of regional heat and moisture fluxes. California experiences particularly strong ENSO influences and models project different to its extreme precipitation. It remains unclear how diverse projections of future precipitation extremes relate to inter‐model differences for those changing signals. Here, we use “large ensemble” simulations with multiple climate models along with the Coupled Model Intercomparison Project Phase 5 to investigate the range of precipitation extreme changes over California and the influences from ENSO‐related teleconnections. We found that precipitation amount increases are much larger during El Niño relative to La Niña years, mainly caused by the differences in frequency of extreme events during different phases. The ENSO‐driven effect is even larger than the overall climate change signal for the most extreme events, implying uncertainties from inter‐model differences in ENSO‐related SST variability for extreme precipitation changes.
... In the upper troposphere, however, predicted warming is strongest in the tropics and hence a competing effect acts to push the jets poleward instead 7,8 . The opposition of these two effects leads to a relatively small projected poleward shift of the jet in response to tropical warming, which is partially offset by the effects of Arctic amplification [9][10][11][12][13] . ...
Climate models predict a weak poleward shift of the jets in response to continuing climate change. Here we revisit observed jet trends using 40 years of satellite-era reanalysis products and find evidence that general poleward shifts are emerging. The significance of these trends is often low and varies between datasets, but the similarity across different seasons and hemispheres is notable. While much recent work has focused on the jet response to amplified Arctic warming, the observed trends are more consistent with the known sensitivity of the circulation to tropical warming. The circulation trends are within the range of historical model simulations but are relatively large compared to the models when the accompanying trends in upper tropospheric temperature gradients are considered. The balance between tropical warming and jet shifts should therefore be closely monitored in the near future. We hypothesise that the sensitivity of the circulation to tropical heating may be one factor affecting this balance.
... In addition, transport pathways may change in the future as the spatiotemporal variability of midlatitude cyclones changes. While disagreement exists in projections of the NH storm tracks, one consistent projection is a seasonally non-uniform poleward shift (Simpson et al., 2014) coupled with an overall reduction in frequency (Chang et al., 2012). Recent projections also suggest an increase in midlatitude cyclone precipitation under future climate scenarios (Catto et al., 2019) that could act to increase aerosol removal during transport. ...
We examine the distribution of aerosol optical depth (AOD) across 27,707 northern hemisphere (NH) midlatitude cyclones for 2005–2018 using retrievals from the Moderate Resolution Spectroradiometer (MODIS) sensor on the Aqua satellite. Cyclone‐centered composites show AOD enhancements of 20%–45% relative to background conditions in the warm conveyor belt (WCB) airstream. Fine mode AOD accounts for 68% of this enhancement annually. Relative to background conditions, coarse mode AOD is enhanced by more than a factor of two near the center of the composite cyclone, co‐located with high surface wind speeds. Within the WCB, MODIS AOD maximizes in spring, with a secondary maximum in summer. Cyclone‐centered composites of AOD from the Modern Era Retrospective analysis for Research and Applications, version 2 Global Modeling Initiative (M2GMI) simulation reproduce the magnitude and seasonality of the MODIS AOD composites and enhancements. M2GMI simulations show that the AOD enhancement in the WCB is dominated by sulfate (37%) and organic aerosol (25%), with dust and sea salt each accounting for 15%. MODIS and M2GMI AOD are 60% larger in North Pacific WCBs compared to North Atlantic WCBs and show a strong relationship with anthropogenic pollution. We infer that NH midlatitude cyclones account for 355 Tg yr⁻¹ of sea salt aerosol emissions annually, or 60% of the 30–80°N total. We find that deposition within WCBs is responsible for up to 35% of the total aerosol deposition over the NH ocean basins. Furthermore, the cloudy environment of WCBs leads to efficient secondary sulfate production.
