Descent and mixing in the 1999–2000 northern polar vortex inferred from in situ tracer measurements
Descent and mixing in the 1999–2000 northern polar vortex inferred from in situ tracer measurements
复制标题
根据原位示踪剂测量推断 1999-2000 年北极涡旋的下降和混合
DOI：
10.1029/2001jd000961
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发表时间：
2002
影响因子：
--
通讯作者：
D. Fahey
中科院分区：
文献类型：
--
作者：
E. Ray;F. Moore;J. Elkins;D. Hurst;P. Romashkin;G. Dutton;D. Fahey
[1]利用SAGE III臭氧损失和验证实验(SOLUE)期间进行的轻型航空色谱仪实验(LACE)和大气痕量物种航空色谱仪(ACATS-IV)的现场测量，研究了1999-2000年平流层北部极涡的下降和混合。LACES在气球平台上进行了两次飞行，一次是在1999年11月，就在涡旋形成之后，另一次是在2000年3月，旋涡寿命接近尾声。本文的目的是使用简单的涡旋输送模型来解释在两个涡旋飞行之间用LACE测量的长寿命示踪剂的变化。正是观测的高精确度和长期精确度，使得在不同飞行中获得的一些物种的数据中的微小差异可以用于推断运输过程。示踪剂剖面随高度或潜在温度的变化可归因于旋涡的下降。一项使用6个示踪剂的计算表明，在飞行间隔近4个月的时间里，总降幅是潜在温度的强烈函数，从平流层中部的200K下降到平流层下部的50K。观察到的长期示踪剂-示踪剂相关性的变化需要一个混合过程发生，因为仅靠下降不能改变相关性。两个简单的混合模型被用来检验示踪剂相关性的变化。其中一个模型模拟了中纬度空气通过涡旋边缘的卷吸作用，并在涡旋内进行了相对有效的混合。第二个模型模拟了差速下降和随后在完全与中纬度隔绝的涡旋内有效混合的效果。结果表明，在所有示踪关联中，微分下降和混合计算的结果比中纬度夹带的结果更加一致。SF6作为中间层空气示踪剂的独特敏感性使其在下降和混合计算中都是一个异常值。为了使SF6的混合和下降计算与其他示踪剂相一致，必须包括来自中间层的一小部分空气。关于涡旋下降和下降速率的结论与其他模拟研究一致。结果表明，中纬度空气与冬季涡旋的混合对1999/2000季节观测到的臭氧变化没有显著贡献。
[1] In situ measurements from the Lightweight Airborne Chromatograph Experiment (LACE) and the Airborne Chromatograph for Atmospheric Trace Species (ACATS-IV) taken during the SAGE III Ozone Loss and Validation Experiment (SOLVE) are used to examine the descent and mixing in the 1999–2000 northern stratospheric polar vortex. LACE was flown twice on an in situ balloon platform, in November 1999 just after the vortex formed and in March 2000 near the end of the vortex lifetime. The aim of this paper is to use simple models of vortex transport to try to explain the changes seen in the long-lived tracers measured by LACE between the two vortex flights. It is the high precision and long-term accuracy of the observations that allow small differences in the data from a number of species obtained on different flights to be used to infer transport processes. Changes in tracer profiles as a function of height or potential temperature can be attributed, to first order, to descent in the vortex. A calculation which used six tracers shows that the total descent was a strong function of potential temperature, from 200 K in the middle stratosphere to 50 K in the lower stratosphere over the nearly 4-month period between flights. Observed changes in long-lived tracer-tracer correlations require a mixing process to have occurred since descent alone cannot change the correlations. Two simple models of mixing are used to examine the tracer correlation changes. One model simulates entrainment of midlatitude air across the vortex edge with relatively efficient mixing within the vortex. A second model simulates the effect of differential descent and subsequent efficient mixing within a vortex that is entirely isolated from the midlatitudes. It is shown that the differential descent and mixing calculation produces results which are much more consistent among all the tracer correlations compared to the results from midlatitude entrainment. The unique sensitivity of SF6 as a tracer of mesospheric air makes it an outlier in both the descent and mixing calculations. The inclusion of a small fraction of air from the mesosphere is necessary to bring the SF6 mixing and descent calculations into agreement with the other tracers. The conclusions regarding descent and descent rates in the vortex are consistent with other modeling studies. The results indicate that mixing of midlatitude air into the winter vortex is not a significant contributor to the observed ozone changes in the 1999/2000 season.