Jaeglé Lyatt, Wood Robert, Wargan Krzysztof
Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA.
Science Systems and Applications Inc., Lanham, Maryland, USA.
J Geophys Res Atmos. 2017 Dec 27;122(24):13436-13457. doi: 10.1002/2017JD027656. Epub 2017 Dec 18.
We examine the role of extratropical cyclones in stratosphere-to-troposphere (STT) exchange with cyclone-centric composites of O retrievals from the Microwave Limb Sounder (MLS) and the Tropospheric Emission Spectrometer (TES), contrasting them to composites obtained with the Modern-Era Retrospective-analysis for Research and Applications (MERRA and MERRA-2) reanalyses and the GEOS-Chem chemical transport model. We identify 15,978 extratropical cyclones in the northern hemisphere (NH) for 2005-2012. The lowermost stratosphere (261 hPa) and middle troposphere (424 hPa) composites feature a 1,000 km-wide O enhancement in the dry intrusion (DI) airstream to the southwest of the cyclone center, coinciding with a lowered tropopause, enhanced potential vorticity, and decreased HO. MLS composites at 261 hPa show that the DI O enhancements reach a 210 ppbv maximum in April. At 424 hPa, TES composites display maximum O enhancements of 27 ppbv in May. The magnitude and seasonality of these enhancements are captured by MERRA and MERRA-2, but GEOS-Chem is a factor of two too low. The MERRA-2 composites show that the O-rich DI forms a vertically aligned structure between 300 and 800 hPa, wrapping cyclonically with the warm conveyor belt. In winter and spring DIs, O is enhanced by 100 ppbv or 100-130% at 300 hPa, with significant enhancements below 500 hPa (6-20 ppbv or 15-30%). We estimate that extratropical cyclones result in a STT flux of 119±56 Tg O yr, accounting for 42±20 % of the NH extratropical O STT flux. The STT flux in cyclones displays a strong dependence on westerly 300 hPa wind speeds.
我们利用微波临边探测仪（MLS）和对流层发射光谱仪（TES）反演得到的以气旋为中心的臭氧（O）合成数据，研究温带气旋在平流层到对流层（STT）交换中的作用，并将其与通过现代时代回顾性分析研究与应用（MERRA和MERRA - 2）再分析以及GEOS - Chem化学传输模型得到的合成数据进行对比。我们识别出2005 - 2012年北半球（NH）的15978个温带气旋。最低平流层（261百帕）和对流层中层（424百帕）的合成数据显示，在气旋中心西南方向的干侵入（DI）气流中，有一个宽度为1000公里的臭氧增强区域，同时伴有对流层顶降低、位势涡度增强和水汽含量降低。261百帕的MLS合成数据表明，4月DI臭氧增强最大值达到210 ppbv。在424百帕，TES合成数据显示5月臭氧增强最大值为27 ppbv。MERRA和MERRA - 2能够捕捉到这些增强的幅度和季节性，但GEOS - Chem的数据低了两倍。MERRA - 2合成数据表明，富含臭氧的DI在300至800百帕之间形成垂直对齐的结构，并随暖输送带呈气旋式环绕。在冬季和春季的DI中，300百帕处臭氧增强100 ppbv或100 - 130%，在500百帕以下有显著增强（6 - 20 ppbv或15 - 30%）。我们估计温带气旋导致的STT通量为119±56 Tg O yr，占北半球温带臭氧STT通量的42±20%。气旋中的STT通量强烈依赖于300百帕的西风风速。
