Figure 5 - uploaded by Richard Seager
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Same as but for the twenty-first century trend in zonal mean Eady growth rate σ D in (a) DJF and (b) JJA, in colors, with the twentieth century climatology in contours. Contour intervals are 0.5 day−1. Units are day−1
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Storm tracks play a major role in regulating the precipitation and hydrological cycle in midlatitudes. The changes in the
location and amplitude of the storm tracks in response to global warming will have significant impacts on the poleward transport
of heat, momentum and moisture and on the hydrological cycle. Recent studies have indicated a polew...
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... the dry Eady growth rate is determined by both the meridional temperature gradient and static stability, future changes in both terms will impact the change in the baroclinic instability of the time-mean flow. The zonal mean of the dry Eady growth rate is shown in Fig. 5a and b for both DJF and JJA. The climatology maximizes in the midlatitudes and is stronger in the winter hemisphere due to stronger meridional temperature gradients. The change in the dry Eady growth rate follows that in the meridional temperature gradient, i.e. a poleward shift and an intensi- fication on the poleward flank in the ...
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... but the rising tropospheric static stability south of 40 o N helps to stabilize the subtropical jet streams on the equatorward flank whereas the reduced static stability north of 40 o N acts to enhance the instability of the jet streams on the poleward flank, which would assist a poleward shift of the storm tracks. Therefore, as can be seen in Fig. 5a and b, the poleward shift and enhancement of the dry Eady growth rate in the midlatitudes of both hemispheres in both seasons (except for the lower troposphere in northern winter) fully supports the storm track changes. The results in Fig. 5a and b confirm the relevance of the changing characteristics of baroclinic instability in ...
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... the poleward flank, which would assist a poleward shift of the storm tracks. Therefore, as can be seen in Fig. 5a and b, the poleward shift and enhancement of the dry Eady growth rate in the midlatitudes of both hemispheres in both seasons (except for the lower troposphere in northern winter) fully supports the storm track changes. The results in Fig. 5a and b confirm the relevance of the changing characteristics of baroclinic instability in driving the storm track changes. The results further indicate that eddies are influenced by the baroclinicity in the upper troposphere rather than the surface instability, as the enhancement of the instability growth rate in the upper troposphere ...
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Citations
... In addition, the tropical upper troposphere becomes anomalously warm due to a decreasing saturated lapse rate (Vallis et al., 2015). This causes the baroclinicity to weaken in the lower troposphere but strengthen in the upper troposphere (Wu et al., 2011;Yuval & Kaspi, 2016). The upper-level baroclinicity is tied to the near tropopause reverse temperature gradient that is ubiquitous in all our simulations. ...
The tropical overturning circulation is examined in a moist aquaplanet general circulation model forced using a non‐interactive sea‐surface temperature (SST) distribution that varies between a present‐day Earth‐like profile and one that is globally uniform. A Hadley cell (HC)‐like flow is observed in all experiments along with the poleward transport of heat and angular momentum. In simulations with non‐zero SST gradients, deep convection near the Equator sets up a deep tropical cell; midlatitude baroclinic Rossby waves flux heat and angular momentum poleward, reinforcing the thermally direct circulation. As the imposed SST gradient is weakened, the HC transitions from a thermally and eddy‐driven regime to one that is completely eddy‐driven. When the SST is globally uniform, equatorial waves concentrate precipitation in the Tropics and facilitate the lower‐level convergence necessary for the ascending branch of the HC. Midlatitude Rossby waves generated near the surface become very weak, but upper‐level baroclinicity generates waves that cause equatorward transport of heat and poleward transport of momentum. Moreover, these upper‐level waves induce a circulation that opposes the time‐mean HC, thus highlighting the role of tropical waves in driving an overturning circulation that looks similar to the present‐day Earth‐like case, even for the case with globally uniform SSTs. In all cases, anomalies associated with the tropical waves closely resemble those that sum to give the upper‐level zonal mean divergent outflow. Through their ability to modulate tropical rainfall and the related latent heating, equatorial waves cause considerable hemispheric asymmetry in the HC and impart synoptic and intraseasonal variability to the tropical overturning circulation.
... Arising from baroclinic instability, the Northern Hemisphere (NH) storm tracks are centred over the North Pacific and North Atlantic, while the Southern Hemisphere (SH) storm track is hemispheric. Storm tracks effectively transport heat, moisture and momentum poleward, contributing to the global energy balance [1][2][3] . They also have a profound impact on the day-to-day variability of local weather. ...
In a warming climate, storm tracks are projected to intensify on their poleward side. Here we use large-ensemble CO2 ramp-up and ramp-down simulations to show that these changes are not reversed when CO2 concentrations are reduced. If CO2 is removed from the atmosphere following CO2 increase, the North Atlantic storm track keeps strengthening until the middle of the CO2 removal, while the recovery of the North Pacific storm track during ramp-down is stronger than its shift during ramp-up. By contrast, the Southern Hemisphere storm track weakens during ramp-down at a rate much faster than its strengthening in the warming period. Compared with the present climate, the Northern Hemisphere storm track becomes stronger and the Southern Hemisphere storm track becomes weaker at the end of CO2 removal. These hemispherically asymmetric storm-track responses are attributable to the weakened Atlantic meridional overturning circulation and the delayed cooling of the Southern Ocean.
... Some recent studies have shown that with global warming the translational speed of TCs has slowed down (Kossin, 2018). Several other studies predicted a poleward movement of TCs due to global warming (Fyfe et al., 1999;Kossin and Camargo, 2009;Kushner et al., 2001;Miller et al., 2006;Wu et al., 2011). This phenomenon can lead to a decrease in TC counts making landfall in the US, particularly over the southern Gulf of Mexico and the Caribbean (Colbert et al., 2013). ...
... A key assumption of this work is that variability in LE and KE explained by ETCs is represented by changes in 2-8-day periods. In previous studies 2-8-day and 2-10-day periods for filtering midlatitude cyclones and baroclinic eddies was frequently used, with the choice of 8 or 10 days as an upper limit exhibiting little influence on the results (e.g., Blackmon & White, 1982;Wu et al., 2011). Increasing the range from 2-8 days to 2-10 days, for example, would increase the magnitude of the LE and KE slopes from ETCs since the Lanczos filter would include a wider range of data in the final computation. ...
... Furthermore, this work supports the idea that latent heat release from future moistening represents a key driver for cyclone strengthening (Marciano et al., 2015). Increased ocean heat content in both hemispheres, especially in the subtropical oceans, could also warrant examination and provide additional context for the increase in ETC moisture (Wu et al., 2011). Future climate modeling studies could also focus on the moistening of baroclinic eddies, where internal variability obfuscates cloud-radiation effects from decreased sea-ice coverage despite strong satellite-based evidence (Sledd & L'Ecuyer, 2021). ...
... ,Wu et al. (2011),Pan et al. (2017) andTan et al. (2019) showing a poleward shift in midlatitude storm tracks. This result also supports the findings of Chemke(2022), who showed a similar dipole feature for poleward eddy kinetic energy shifts in Coupled Model Intercomparison Project (CMIP) model projections. ...
Baroclinic or extratropical cyclones (ETCs) transport heat and moisture to higher latitudes, making it fundamentally important to understand how their influence changes as Earth's climate evolves. A 2–8‐day Lanzcos bandpass filter is applied to European Center for Medium Range Weather Forecasting 5th Generation Reanalysis latent energy (LE) and kinetic energy (KE) data to assess how ETCs have changed from 1940 to 2020 relative to full‐scale changes in LE and KE. Full‐scale KE trends are more positive at high latitudes relative to mid‐latitudes, confirming several previous studies that ETCs have shifted poleward. LE increases have occurred globally, and trends in both full‐scale LE and KE are statistically significant in the southern high latitudes. The high relative fractional contribution of 2–8‐day LE wave power and trend clearly suggest that ETCs have an increasingly important role in poleward moisture transport but are not solely responsible for the observed statistically significant increases.
... Klimaänderungssignale aus derartigen extremereignisfokussierten Studien zu Frequenz und Intensität der Stürme sind noch mit großen Unsicherheiten behaftet. Dennoch deutet sich an, dass ein wärmeres Klima die Zugbahnen der Sturmtiefs und damit auch die Niederschlagszonen in Richtung Pol verschieben (Barnes and Polvani 2013;Bengtsson et al. 2006;Harvey et al. 2020;Mbengue and Schneider 2013;Priestley and Catto 2022;Wu et al. 2011). Europa liegt am 4 "Ausgang" des nordatlantischen "Storm Tracks", also jenem Bereich, welcher klimatologisch ein lokales Maximum von durchziehenden intensiven Tiefdruckgebieten aufweist. ...
... Lu et al. (2022) also found a general reduction in midlatitude diffusivities in GCM simulations of the response to increased CO 2 concentration that allow for meridional temperature gradients to weaken (their Fig. 3). Finally, the coupled model simulations analyzed by Wu et al. (2011) show increases in diffusivity in both hemispheres in a DJF average of a transient warming scenario . We also note that diffusive theories developed for GCM simulations of climate change do require climate-state-dependent formulations to capture the behavior over a wide range of climates (e.g., Frierson et al. 2007;Bischoff and Schneider 2014;Liu et al. 2017;Merlis et al. 2022;Lu et al. 2022). ...
Atmospheric macroturbulence transports energy down the equator-to-pole gradient. This is represented by diffusion in energy balance models (EBMs), and EBMs have proven valuable to understanding and quantifying the pattern of surface temperature change. They typically assume climate-state independent diffusivity, chosen to well represent the current climate, and find that this is sufficient to emulate warming response in general circulation models (GCMs). Meanwhile, model diagnoses of GCM simulations have shown that the diffusivity changes with climate. There is also ongoing development for diffusivity theories based on atmospheric dynamics. Here, we examine the role that changes in diffusivity play in the large-scale equator-to-pole contrast in surface warming in EBMs, building on previous analytic EBM theories for polar amplified warming. New analytic theories for two formulations of climate-state dependent diffusivity capture the results of numerical EBM solutions. For reasonable choices of parameter values, the success of the new analytic theories reveals why the change of diffusivity is limited in response to radiative forcing and does not eliminate polar amplified warming.
... Next to thermodynamic causes, Sousa et al. (2020) and P. Zhang et al. (2021) attribute the increase in Arctic ARs to a poleward shift of the polar jet stream related to both thermodynamic and dynamic changes. While the cause of this poleward shift is still debated, most studies attribute it to a tropical ocean warming-related shift of the sinks or sources of Rossby waves (Chen & Held, 2007;Kidston & Gerber, 2010;Rivière, 2011;Tandon et al., 2013;Wu et al., 2011). The signal of this poleward shift (linked to ocean warming) is not very strong and inconsistent across climate models, partly because Arctic sea ice loss counteracts the response by favoring an equatorward shift of the jet stream Peings & Magnusdottir, 2014;Screen et al., 2022Screen et al., , 2013Smith et al., 2022). ...
Alongside mean increases in poleward moisture transport (PMT) to the Arctic, most climate models also project a linear increase in the interannual variability (IAV) with future warming. It is still uncertain to what extent atmospheric rivers (ARs) contribute to the projected IAV increase of PMT. We analyzed large‐ensemble climate simulations to (a) explore the link between PMT and ARs in the present‐day (PD) and in two warmer climates (+2 and +3°C compared to pre‐industrial global mean temperature), (b) assess the dynamic contribution to changes in future ARs, and (c) analyze the effect of ARs on Arctic climate on interannual timescales. We find that the share of AR‐related PMT (ARPMT) to PMT increases from 42% in the PD to 53% in the +3°C climate. Our results show that the mean increases in AR‐frequency and intensity are mainly caused by higher atmospheric moisture levels, while dynamic variability regulates regional ARs on an interannual basis. Notably, the amount of ARs reaching the Arctic in any given region and season strongly depends on the regional jet stream position and speed southwest of this region. This suggests that future changes in dynamics may significantly amplify or dampen the regionally consistent moisture‐induced increase in ARs in a warmer climate. Our results further support previous findings that positive ARPMT anomalies are profoundly linked to increased surface air temperature and precipitation, especially in the colder seasons, and have a predominantly negative effect on sea ice.
... In addition, the residual term that mainly includes sub-monthly transient eddy has a negative contribution in Cluster 2 and Cluster 4 (figure 6(u)), which partly explains precipitation decreases over SC. The change of transient eddies is projected to decrease in the subtropics during winter half year that is mainly associated with the transient eddy moisture transport in response to global warming (Seager et al 2010, Wu et al 2011 due to the westerly jet weakening in the region (Liang and Zhang 2021). As demonstrated by He (2023), the weakened southern branch westerly jet on the southern side of the Tibetan Plateau plays a key role in suppressing winter precipitation in the subtropical East Asian. ...
An ensemble of 28 models from the 6th Coupled Model Intercomparison Project was used to project future changes in annual mean precipitation over East China during 2046–2065 relative to 1995–2014 under the SSP2-4.5 scenario. A precipitation increase of 0.16 mm/day is projected over North China by the multi-model ensemble (MME) mean. However, large model uncertainty exists over South China (SC), reducing the fidelity of the MME mean projection. Thus, a clustering-based MME probabilistic projection is presented that projects four possible SC precipitation changes in the future. Precipitation increases are projected in Cluster 1, Cluster 3 and Cluster 4 for 0.51 mm/day, 0.2 mm/day and 0.23 mm/day, respectively, with occurrence probabilities of 14.3%, 35.7% and 25%, respectively. Conversely, the projected Cluster 2 precipitation decrease is 0.01 mm/day with an occurrence probability of 25%. The differences in precipitation change are mainly contributed by dynamic effect due to different circulation changes across clusters. During extended summer, different circulation anomalies over western North Pacific (WNP) among clusters arise from the sea surface temperature anomaly (SSTA) warming patterns over the equatorial central-eastern Pacific, which explain the different precipitation increases over SC. During extended winter, a strong zonal SSTA gradient between the South China Sea and adjacent WNP is projected in Cluster 2, stimulating a zonally vertical cell with anomalous descent over SC and resulting in markedly decreased precipitation. A similar but much weaker zonal SSTA gradient and circulation anomaly are projected in Cluster 3. Distinct meridional SSTA gradients over the WNP are projected in the rest clusters, stimulating shifted descents with a weak effect on SC precipitation.
... Future risk at sites of marginally influenced by cyclones. Tropical cyclones are likely to shift poleward in a warming climate [5][6][7] and some suggest that this trend is particularly obvious in the Southern Hemisphere 8 . Evidence of the poleward shifts in storm tracks have been found in both the reanalyses of the instrumental records 9,10 and projections from numerical models including models with enhanced greenhouse gas concentrations 1,5,8,[11][12][13][14] . ...
Shark Bay Marine Park is a UNESCO World Heritage Property located in a region of marginal tropical cyclone influence. Sustainable management of this unique environment as the climate changes requires a quantified understanding of its vulnerability to natural hazards. Here, we outline a structured analysis of novel historical archive information that has uncovered reports of an extreme storm surge associated with a Tropical Cyclone in 1921 that generated remarkable overland flow which left fish and sharks stranded up to 9.66 km (6 miles) inland. Weighted information from historical archives is placed in a new framework and provide inputs to modelling of this event which improves the understanding of its magnitude and furnishes records of the impacts of what occurred on that day and notably also in the years following. The suite of plausible tracks that reproduce the historical data contextualise the storm as a marginal Category 4 or 5 storm and its return interval as equivalent or slightly greater than the current local planning level for coastal flooding in the region. The outcome underscores the global importance of examining the probable maximum event for risk management in areas of marginal cyclone influence where vulnerable ecosystems or vital regional infrastructure of key economic importance are located, and the need to factor in TC risk in marine conservation and planning in the Shark Bay World Heritage Property.
... The North Pacific storm track (NPST) features intense activities of synoptic-scale eddies (Blackmon, 1976;Blackmon et al., 1977). It is accompanied by a large amount of poleward heat and moisture fluxes (Wu et al., 2011;Shaw et al., 2016), whose variations have been suggested to be of importance for regional and global climates (Zhang et al., 2002;Ashley and Black, 2008;Pfahl and Wernli, 2012;. ...
The North Pacific storm track (NPST) represents intense activity of synoptic-scale eddies that are important for Northern Hemisphere mid-latitude weather systems. According to the linear baroclinic instability theory, the strength of the NPST should peak in January and February but is substantially weaker than that in late fall and early spring, a phenomenon termed mid-winter suppression (MWS). This study investigates the characteristics of the MWS associated with central-Pacific (CP) and eastern-Pacific (EP) El Niños mainly based on composite analyses in the HadISSTv1.1 and ERA-5 datasets. It is found that over the southern North Pacific (NP; south of 40°N), the peak of the NPST delays until January and thus the MWS does not appear during CP El Niño as that in climatology. In contrast, a prominent MWS-like feature is identified in January over this region during EP El Niño. Over the northern NP (north of 40°N), the MWS is largely enhanced in January and February during CP El Niño. Quantitative diagnosis of eddy kinetic energy conversion further reveals that different features of the MWS are mainly caused by baroclinic conversion anomalies. The two types of El Niño may affect the NPST and MWS by modifying the atmospheric thermal structure and exciting cross-Pacific wave trains, which are associated with different convective anomalies.
