Influence of Reduced Winter Land–Sea Contrast on the Midlatitude Atmospheric Circulation

Portal, Alice; Pasquero, Claudia; D’Andrea, Fabio; Davini, Paolo; Hamouda, Mostafa E.; Rivière, Gwendal

doi:10.1175/jcli-d-21-0941.1

Cited by 8 publications

(8 citation statements)

References 73 publications

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“…The physical processes behind pan‐Atlantic cold and windy extremes likely involves the low‐frequency and the transient dynamics of the North Atlantic storm track. Indeed, the continuous generation of cold air over North America during boreal winter modulates the land‐sea contrast over the eastern coast of the continent and is a fundamental process for the dynamics of the North Atlantic storm track (Brayshaw et al., 2009; Held, 1983; Portal et al., 2022). However, drivers and possible modulators of this particular type of compound events remain up to now not fully clarified.…”

Section: Introductionmentioning

confidence: 99%

Multiple Large‐Scale Dynamical Pathways for Pan–Atlantic Compound Cold and Windy Extremes

Riboldi

Segalini

Messori

2023

Geophysical Research Letters

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Cold spells and windstorms are typical examples of cold-season extreme weather events with significant societal and economical impacts (e.g., Karremann et al., 2014;Ryti et al., 2016). The notable winter of 2013/14 featured the co-occurrence of frigid temperatures over North America and of extremely windy and wet conditions over the British Isles (Kendon & McCarthy, 2015), bringing to hypothesize a connection between cold spells over North America and cyclonic activity over western Europe (e.g., Huntingford et al., 2014;Knight et al., 2017). The observed co-occurrence of cold spells over the United States and of anomalously windy and wet conditions over Europe can be described as a spatially compounding extreme event, namely the co-occurrence of extremes in geographically remote regions in a short period of time (

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Section: Introductionmentioning

confidence: 99%

Multiple Large‐Scale Dynamical Pathways for Pan–Atlantic Compound Cold and Windy Extremes

Riboldi

Segalini

Messori

2023

Geophysical Research Letters

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“…Since the atmospheric response to deep mid-latitude heat sources or sinks is specially strong (Trenberth, 1983), and, on top of this, the winter midlatitude circulation is known to be highly sensitive to East Asia surface conditions (e.g. Portal et al, 2022;Cohen et al, 2001), Some relevant surface variables from the "cold TP composite" are presented in Figure 2. The near-surface temperature map features an intense cold anomaly on the orography of Central Asia, peaking over the TP and extending north-eastwards to the MP.…”

Section: Resultsmentioning

confidence: 99%

“…The LST corresponds to the climatology obtained from a SPEEDY ensemble run with a freely evolving LST scheme and with prescribed climatological SIC and evolving SSTs 1979-2008 from HadISST. Details on SPEEDY's LST scheme are available in the Appendix B of Portal et al (2022); two cold integrations with SST and SIC as in the control, and with LST forcing corresponding to the significant anomaly of surface temperature from the "cold TP composite" within 60-140 E and 20-60 N ("TP+MP experiment") or within 60-140 E and 38-60 N ("MP experiment"), interpolated onto SPEEDY's grid (Figure 3(a,e,i)).…”

Section: Idealised Experimentsmentioning

confidence: 99%

“…Cohen et al, 2014;Garfinkel et al, 2010;Henderson et al, 2018), the dynamical role of anomalous surface conditions over the Tibetan and Mongolian plateaux has been poorly investigated, notwithstanding its potentially high impact on East Asia. In a more idealised context, winter positive thermal forcing over mid-latitude land -as in a climate with a reduced winter land-sea thermal contrast caused by the faster warming of continents with respect to oceans -was analysed by Portal et al (2022). It was there shown that the atmospheric response to idealised warming over East Asia (including the orography) dominated over a pattern of similar intensity imposed in North America.…”

Section: Introductionmentioning

confidence: 99%

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Atmospheric response to wintertime Tibetan Plateau cold bias in climate models

Portal

D’Andrea²,

Davini³

et al. 2023

Preprint

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Abstract. Central Asia orography sets important features of the winter climate over East Asia and the Pacific. By deflecting the mid-latitude jet polewards it contributes to the formation of the Siberian High and, on the lee side, to the advection of dry cold continental air over the East Asian coast and the Pacific Ocean, where atmospheric instability and cyclogenesis thrive. While the mechanical forcing by the orography is assessed by a number of modelling studies, it is still not clear how near-surface temperature over the two most prominent orographic barriers of the Central Asian continent, namely the Tibetan and Mongolian plateaux, influences the winter climate downstream. Moreover, a well known issue of state-of-the art climate models is a cold land temperature bias over the Tibetan Plateau related with the difficulty in modelling land processes and land–atmosphere interaction over complex orography. Here we take advantage of the large spread in representing near surface temperature over the Central Asia plateaux among climate models taking part in the Coupled Model Inter-comparison Project, Phase 6 (CMIP6) to study how temperatures over these regions impact the atmospheric circulation. Based on composites of the CMIP6 models' climatologies showing a cold bias over the Tibetan Plateau, we find that negative temperature anomalies over Asian orography intensify the East Asia winter monsoon and, by enhancing the low-level baroclinicity in the region of the East China Sea, reinforce the southern flank of the Pacific jet. The results of the CMIP6 composite analysis are supported by the response of an intermediate-complexity atmospheric model to a similar pattern of cold surface temperatures over the Central Asia plateaux; we also distinguish the relative influence of the Tibetan and the Mongolian Plateau surface conditions. Thereby, based on the intensification of the East Asia winter monsoon in models characterised by a cold land temperature (bias) over Central Asia plateaux, we prospect that advances in the modelling of the land energy budget over this region may improve the simulation of the mean climate over the Asia/Pacific sector, together with the reliability of climate projections and the performance of shorter term forecasts.

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“…If the aerosols are driving some of the SPNA variability, then this would be expected to lead to predictable shifts in the jet speed, as discussed in the present paper. It should also be noted 620 that an aerosol-induced cooling of North America would strengthen the land-sea contrast, which would also be expected to drive a stronger jet (Portal et al, 2022). It is unclear if such a change in land-sea contrast alone can generate decadal timescale forecast skill.…”

Section: The Role Of Sulphate Aerosolsmentioning

confidence: 99%

Predictable Decadal Forcing of the North Atlantic Jet Stream by Sub-Polar North Atlantic Sea Surface Temperatures

Strommen¹,

Woollings²,

Davini³

et al. 2023

Preprint

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Abstract. It has been demonstrated that decadal variations in the North Atlantic Oscillation (NAO) can be predicted by current forecast models. While Atlantic Multidecadal Variability (AMV) in sea surface temperatures (SSTs) has been hypothesised as the source of this skill, the validity of this hypothesis and the pathways involved remain unclear. We show, using reanalysis and data from two forecast models, that the decadal predictability of the NAO can be entirely accounted for by the predictability of decadal variations in the speed of the North Atlantic eddy-driven jet, with no predictability of decadal variations in the jet latitude. The sub-polar North Atlantic (SPNA) is identified as the only potential source of an SST-based signal across the models and reanalysis, and the predictability of the jet speed is shown to be consistent with a forcing from the SPNA visible already within a single season. The pathway is argued to be tropospheric in nature, with the SPNA-induced heating extending up to the mid-troposphere, which alters the meridional temperature gradient around the climatological jet position. The link between SSTs and heatfluxes, which mediates the predictability, is shown to be underestimated in the forecast models by approximately a factor of two, with potential implications for the `signal-to-noise paradox'. The relative roles of anthropogenic aerosol emissions and the AMOC at generating predictable SPNA variability are also discussed. The analysis is extensively supported by the novel use of a set of seasonal hindcasts spanning the 20th century and forced with prescribed SSTs.

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Influence of Reduced Winter Land–Sea Contrast on the Midlatitude Atmospheric Circulation

Cited by 8 publications

References 73 publications

Multiple Large‐Scale Dynamical Pathways for Pan–Atlantic Compound Cold and Windy Extremes

Multiple Large‐Scale Dynamical Pathways for Pan–Atlantic Compound Cold and Windy Extremes

Atmospheric response to wintertime Tibetan Plateau cold bias in climate models

Predictable Decadal Forcing of the North Atlantic Jet Stream by Sub-Polar North Atlantic Sea Surface Temperatures

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