Arctic Amplification Weakens the Variability of Daily Temperatures over Northern Middle-High Latitudes
Arctic Amplification Weakens the Variability of Daily Temperatures over Northern Middle-High Latitudes
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DOI：
10.1175/jcli-d-20-0514.1
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发表时间：
2021-04-01
影响因子：
4.9
通讯作者：
Deng, Jiechun
中科院分区：
文献类型：
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作者：
Dai, Aiguo;Deng, Jiechun
北极放大(AA)减少了北部中高纬度经向温度梯度(dt/dy)，这可能会减弱西风。有人建议，这可能会导致中纬度地区出现更不稳定和更极端的天气。然而，由于dt/dy的减少，在温室气体增加的情况下，北部中高纬度地区的温度变率减小。通过耦合模式模拟和ERA5再分析的分析表明，与前人的研究结果一致，即使在CO2增加的情况下抑制了AA和海冰损失，北部中高纬度地区的冷季地面和对流层中下层温度(T)变率也减少了；然而，AA和海冰损失进一步降低了T变率，导致概率分布变窄，相对于未来平均气候，冷或暖极端事件减弱。CO_2的增加增强了大部分北中高纬度经向风的波数为4的经向风，但减弱了经向热平流(dt/dy)，而AA则减弱了气候学的上、下风(dt/dy)。热力平流的减弱及其方差的减小是T变率减小的主要原因，T变率与变率(dT/dy)之间的正反馈增大了T变率的减小。AA不仅降低了dT/dy，还降低了其方差，从而进一步降低了T变异性(dt/dy)。虽然平均冰雪覆盖率减少，但在许多北部纬度地区，其可变性增加，这些变化并不会削弱T可变性。因此，AA对中纬度温度变率的影响主要来自于它对热平流的影响，而不是之前认为的对风的影响。
Arctic amplification (AA) reduces meridional temperature gradients (dT/dy) over the northern mid-high latitudes, which may weaken westerly winds. It is suggested that this may lead to wavier and more extreme weather in the midlatitudes. However, temperature variability is shown to decrease over the northern mid-high latitudes under increasing greenhouse gases due to reduced dT/dy. Here, through analyses of coupled model simulations and ERA5 reanalysis, it is shown that consistent with previous studies, cold-season surface and lower-mid troposphere temperature (T) variability decreases over northern mid-high latitudes even in simulations with suppressed AA and sea ice loss under increasing CO2; however, AA and sea ice loss further reduce the T variability greatly, leading to a narrower probability distribution and weaker cold or warm extreme events relative to future mean climate. Increased CO2 strengthens meridional wind (upsilon) with a wavenumber-4 pattern but weakens meridional thermal advection [-upsilon(dT/dy)] over most northern mid-high latitudes, and AA weakens the climatological upsilon and -upsilon(dT/dy). The weakened thermal advection and its decreased variance are the primary causes of the T variability decrease, which is enlarged by a positive feedback between the variability of T and -upsilon(dT/dy). AA not only reduces dT/dy, but also its variance, which further decreases T variability through -upsilon(dT/dy). While the mean snow and ice cover decreases, its variability increases over many northern latitudes, and these changes do not weaken the T variability. Thus, AA's influence on midlatitude temperature variability comes mainly from its impact on thermal advection, rather than on winds as previously thought.