Garfinkel Chaim I, Gordon Amit, Oman Luke D, Li Feng, Davis Sean, Pawson Steven
The Fredy and Nadine Herrmann Institute of Earth Sciences, Hebrew University of Jerusalem, Jerusalem, Israel.
NASA Goddard Space Flight Center, Greenbelt, MD, USA.
Atmos Chem Phys. 2018;18(7):4597-4615. doi: 10.5194/acp-18-4597-2018. Epub 2018 Apr 5.
A series of simulations using the NASA Goddard Earth Observing System Chemistry-Climate Model are analyzed in order to assess interannual and sub-decadal variability in the tropical lower stratosphere over the past 35 years. The impact of El Niño-Southern Oscillation on temperature and water vapor in this region is nonlinear in boreal spring. While moderate El Niño events lead to cooling in this region, strong El Niño events lead to warming, even as the response of the large scale Brewer Dobson Circulation appears to scale nearly linearly with El Niño. This nonlinearity is shown to arise from the response in the Indo-West Pacific to El Niño: strong El Niño events lead to tropospheric warming extending into the tropical tropopause layer and up to the cold point in this region, where it allows for more water vapor to enter the stratosphere. The net effect is that both strong La Niña and strong El Niño events lead to enhanced entry water vapor and stratospheric moistening in boreal spring and early summer. These results lead to the following interpretation of the contribution of sea surface temperatures to the decline in water vapor from the late 1990s to the early 2000s: the very strong El Niño event in 1997/1998, followed by more than two consecutive years of La Niña, led to enhanced lower stratospheric water vapor. As this period ended in early 2001, entry water vapor concentrations declined. This effect accounts for approximately one-quarter of the observed drop.
为评估过去35年热带低平流层的年际和年代际变率，对美国国家航空航天局戈达德地球观测系统化学气候模型进行了一系列模拟分析。在北半球春季，厄尔尼诺-南方涛动对该区域温度和水汽的影响是非线性的。虽然中等强度的厄尔尼诺事件会导致该区域降温，但强厄尔尼诺事件会导致升温，即便大尺度的布鲁尔-多布森环流的响应似乎与厄尔尼诺近乎呈线性关系。这种非线性源于印度洋-西太平洋对厄尔尼诺的响应：强厄尔尼诺事件会导致对流层变暖延伸至热带对流层顶区域并直至该区域的冷点，在那里会有更多水汽进入平流层。总体影响是，强拉尼娜事件和强厄尔尼诺事件都会导致北半球春季和初夏进入平流层的水汽增加以及平流层湿度增大。这些结果导致了对20世纪90年代末至21世纪初水汽下降的海表面温度贡献的如下解释：1997/1998年的极强厄尔尼诺事件之后，连续两年多出现拉尼娜现象，导致平流层下部水汽增加。随着这一时期在2001年初结束，进入平流层的水汽浓度下降。这种效应约占观测到的下降幅度的四分之一。
