Sea ice led to poleward-shifted winds at the Last Glacial Maximum: the influence of state dependency on CMIP5 and PMIP3 models
Sea ice led to poleward-shifted winds at the Last Glacial Maximum: the influence of state dependency on CMIP5 and PMIP3 models
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DOI：
10.5194/cp-12-2241-2016
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发表时间：
2016-12
影响因子：
4.3
通讯作者：
L. Sime;D. Hodgson;T. Bracegirdle;C. Allen;Bianca B. Perren;S. Roberts;A. M. Boer
中科院分区：
文献类型：
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作者：
L. Sime;D. Hodgson;T. Bracegirdle;C. Allen;Bianca B. Perren;S. Roberts;A. M. Boer
抽象的。南大洋西风急流的垂直变化可能会导致冰期至间冰期海洋CO2存量的变化。然而，虽然CMIP 5模型的结果具有一致的未来变暖的喷流的变化，有相当大的分歧，冰川消退变暖喷流的变化。在这里，我们发现，工业化前（PI）末次冰期最大（LGM）喷流的位置，或状态依赖性的依赖性，解释较少的喷流的变化模拟模型的LGM相比，未来变暖的情况。国家的依赖性也较弱的强度变化，相比，在喷气机的纬度变化。冬季海冰在LGM期间相当广泛。由于海冰的变化，表面热通量的变化可能对急流产生了很大的影响。模拟海冰实际大面积扩张和50° S以南PI喷流的模型显示，55° S附近的风速增加，并且可以显示PI和LGM之间喷流的极向移动。然而，PI喷流位于赤道方向约47° S的模型没有显示出这种响应：海冰边缘距离喷流太远，无法做出响应。在精确定位PI喷流的模式中，海冰边缘纬度的+1°差异往往与850 hPa喷流的-0.85 °偏移有关。然而，似乎LGM海冰扩张5°左右是将喷流保持在其PI位置所必需的。由于Gersonde等人（2005年）的数据支持超过5°的扩张，这一结果表明，轻微的向极移动和加强是PI和LGM之间最有可能的喷流变化。在没有海冰影响的情况下，模式模拟了气候变暖时的极移西风带和气候寒冷时的赤道移西风带。然而，海冰的反馈在较冷的气候中抵消并逆转了向赤道的趋势，因此LGM风更有可能也轻微地向极地移动。
Abstract. Latitudinal shifts in the Southern Ocean westerly wind jet could drive changes in the glacial to interglacial ocean CO2 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.