Southern westerlies in LGM and future (RCP4.5) climates

Chavaillaz, Y.; Codron, Francis; Kageyama, Masa

doi:10.5194/cp-9-517-2013

Cited by 72 publications

(94 citation statements)

References 35 publications

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“…The maximum of the corresponding parabola yields a better approximation of the exact latitude of the maximum jet wind. This method allows for a more accurate finding of the latitude of the jet maximum (Chavaillaz et al, 2013;Beghin et al, 2015). We find a good linear correlation between the shift of the North Atlantic jet and the Scandinavian precipitation anomaly during the winter season (Fig.…”

Section: Precipitation Changes Over Scandinavia: Implication Of the Jmentioning

confidence: 64%

“…Following the same approach, we examine whether a similar mechanism to the one found in (Beghin et al, 2015) may explain the precipitation changes over Scandinavia when the LIS characteristics (albedo and topography) are modified. Similarly to Chavaillaz et al (2013), we use the 850 hPa zonal wind to define the jet stream. The position of the jet displayed in Fig.…”

Section: Precipitation Changes Over Scandinavia: Implication Of the Jmentioning

confidence: 99%

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How might the North American ice sheet influence the northwestern Eurasian climate?

et al. 2015

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Abstract.It is now widely acknowledged that past Northern Hemisphere ice sheets covering Canada and northern Europe at the Last Glacial Maximum (LGM) exerted a strong influence on climate by causing changes in atmospheric and oceanic circulations. In turn, these changes may have impacted the development of the ice sheets themselves through a combination of different feedback mechanisms. The present study is designed to investigate the potential impact of the North American ice sheet on the surface mass balance (SMB) of the Eurasian ice sheet driven by simulated changes in the past glacial atmospheric circulation. Using the LMDZ5 atmospheric circulation model, we carried out 12 experiments under constant LGM conditions for insolation, greenhouse gases and ocean. In these experiments, the Eurasian ice sheet is removed. The 12 experiments differ in the North American ice-sheet topography, ranging from a white and flat (present-day topography) ice sheet to a fullsize LGM ice sheet. This experimental design allows the albedo and the topographic impacts of the North American ice sheet onto the climate to be disentangled. The results are compared to our baseline experiment where both the North American and the Eurasian ice sheets have been removed. In summer, the sole albedo effect of the American ice sheet modifies the pattern of planetary waves with respect to the no-ice-sheet case, resulting in a cooling of the northwestern Eurasian region. By contrast, the atmospheric circulation changes induced by the topography of the North American ice sheet lead to a strong decrease of this cooling. In winter, the Scandinavian and the Barents-Kara regions respond differently to the American ice-sheet albedo effect: in response to atmospheric circulation changes, Scandinavia becomes warmer and total precipitation is more abundant, whereas the Barents-Kara area becomes cooler with a decrease of convective processes, causing a decrease of total precipitation. The gradual increase of the altitude of the American ice sheet leads to less total precipitation and snowfall and to colder temperatures over both the Scandinavian and the Barents and Kara sea sectors. We then compute the resulting annual surface mass balance over the Fennoscandian region from the simulated temperature and precipitation fields used to force an ice-sheet model. It clearly appears that the SMB is dominated by the ablation signal. In response to the summer cooling induced by the American ice-sheet albedo, high positive SMB values are obtained over the Eurasian region, leading thus to the growth of an ice sheet. On the contrary, the gradual increase of the American ice-sheet altitude induces more ablation over the Eurasian sector, hence limiting the growth of Fennoscandia. To test the robustness of our results with respect to the Eurasian ice sheet state, we carried out two additional LMDZ experiments with new boundary conditions involving both the American (flat or full LGM) and high Eurasian ice sheets. The most striking result is that the Eurasian ice sheet is...

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Section: Precipitation Changes Over Scandinavia: Implication Of the Jmentioning

confidence: 64%

Section: Precipitation Changes Over Scandinavia: Implication Of the Jmentioning

confidence: 99%

How might the North American ice sheet influence the northwestern Eurasian climate?

et al. 2015

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“…This is despite the fact that nearly all CMIP5 models exhibit a poleward shift, and all models a strengthening, of the surface jet from 1900 to 2100 (Bracegirdle et al, 2013). Indeed Chavaillaz et al (2013) find that future-warming scenario RCP4.5 (Representative Concentration Pathway 4.5) shifts in the 850 hPa jet can be largely explained by tropospheric temperature differences between the southern high latitudes and the tropics. Bracegirdle et al (2013) and Kidston and Gerber (2010) examine another aspect: state dependency for Southern Ocean jet shifts and intensity changes, where state dependency is defined as the dependence of jet shifts on the start jet position.…”

Section: Existing Analyses Of Pmip2 and Pmip3mentioning

confidence: 76%

“…LGM simulation ensembles show considerable inter-model disagreement in PI to LGM southern hemispheric jet changes (Rojas, 2013;Chavaillaz et al, 2013). This is despite the fact that nearly all CMIP5 models exhibit a poleward shift, and all models a strengthening, of the surface jet from 1900 to 2100 (Bracegirdle et al, 2013).…”

Section: Existing Analyses Of Pmip2 and Pmip3mentioning

confidence: 80%

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Sea ice led to poleward-shifted winds at the Last Glacial Maximum: the influence of state dependency on CMIP5 and PMIP3 models

et al. 2016

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Abstract. Latitudinal shifts in the Southern Ocean westerly wind jet could drive changes in the glacial to interglacial ocean CO 2 inventory. However, whilst CMIP5 model results feature consistent future-warming jet shifts, there is considerable disagreement in deglacial-warming jet shifts. We find here that the dependence of pre-industrial (PI) to Last Glacial Maximum (LGM) jet shifts on PI jet position, or state dependency, explains less of the shifts in jet simulated by the models for the LGM compared with future-warming scenarios. State dependence is also weaker for intensity changes, compared to latitudinal shifts in the jet. Winter sea ice was considerably more extensive during the LGM. Changes in surface heat fluxes, due to this sea ice change, probably had a large impact on the jet. Models that both simulate realistically large expansions in sea ice and feature PI jets which are south of 50 • S show an increase in wind speed around 55 • S and can show a poleward shift in the jet between the PI and the LGM. However, models with the PI jet positioned equatorwards of around 47 • S do not show this response: the sea ice edge is too far from the jet for it to respond. In models with accurately positioned PI jets, a +1 • difference in the latitude of the sea ice edge tends to be associated with a −0.85 • shift in the 850 hPa jet. However, it seems that around 5 • of expansion of LGM sea ice is necessary to hold the jet in its PI position. Since the Gersonde et al. (2005) data support an expansion of more than 5 • , this result suggests that a slight poleward shift and intensification was the most likely jet change between the PI and the LGM. Without the effect of sea ice, models simulate poleward-shifted westerlies in warming climates and equatorward-shifted westerlies in colder climates. However, the feedback of sea ice counters and reverses the equatorward trend in cooler climates so that the LGM winds were more likely to have also been shifted slightly poleward.

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Changes in the position of the Subtropical Front south of New Zealand since the last glacial period

et al. 2015

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This study fills an important gap in our understanding of past changes in the Southern Subtropical Front (S-STF) in the southwest Pacific Ocean. Paleo-sea surface temperatures (SST) were estimated from planktic foraminiferal census counts from cores straddling the modern S-STF in the Solander Trough, south of New Zealand. The estimated SST were compared for 6 time slices; glacial period (25-21 ka), Last Glacial Maximum (LGM; 21-18 ka), early deglaciation (18-16 ka), late deglacial/early Holocene period (14-8 ka), mid-Holocene period (8-4 ka), and late Holocene period (4-0 ka). The position of the S-STF was determined by two methods:(1) the location of the 10°C isotherm and (2) the location of the highest SST gradients. These new results suggest that the S-STF was not continuous between east and west of New Zealand during the glacial period. Steep SST gradients indicate that a strong S-STF rapidly shifted south during the LGM and early deglaciation. During the late deglacial and Holocene periods the position of the S-STF differs between the two methods with reduced SST gradients, suggesting a more diffuse S-STF in the Solander Trough at this time. The glacial SST data suggest that the S-STF shifted north to the west of New Zealand, while to the east there was a stronger SST gradient across the front. This was possibly the result of an increased wind stress curl, which could have been caused by stronger, or more northerly Southern Hemisphere westerly winds (SHWW), or a merging of the SHWW split jet in this region.

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Southern westerlies in LGM and future (RCP4.5) climates

Cited by 72 publications

References 35 publications

How might the North American ice sheet influence the northwestern Eurasian climate?

How might the North American ice sheet influence the northwestern Eurasian climate?

Sea ice led to poleward-shifted winds at the Last Glacial Maximum: the influence of state dependency on CMIP5 and PMIP3 models

Changes in the position of the Subtropical Front south of New Zealand since the last glacial period

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