Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138;
Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138.
Proc Natl Acad Sci U S A. 2017 Jun 20;114(25):E4905-E4913. doi: 10.1073/pnas.1619318114. Epub 2017 Jun 5.
We present observations defining () the frequency and depth of convective penetration of water into the stratosphere over the United States in summer using the Next-Generation Radar system; () the altitude-dependent distribution of inorganic chlorine established in the same coordinate system as the radar observations; () the high resolution temperature structure in the stratosphere over the United States in summer that resolves spatial and structural variability, including the impact of gravity waves; and () the resulting amplification in the catalytic loss rates of ozone for the dominant halogen, hydrogen, and nitrogen catalytic cycles. The weather radar observations of ∼2,000 storms, on average, each summer that reach the altitude of rapidly increasing available inorganic chlorine, coupled with observed temperatures, portend a risk of initiating rapid heterogeneous catalytic conversion of inorganic chlorine to free radical form on ubiquitous sulfate-water aerosols; this, in turn, engages the element of risk associated with ozone loss in the stratosphere over the central United States in summer based upon the same reaction network that reduces stratospheric ozone over the Arctic. The summertime development of the upper-level anticyclonic flow over the United States, driven by the North American Monsoon, provides a means of retaining convectively injected water, thereby extending the time for catalytic ozone loss over the Great Plains. Trusted decadal forecasts of UV dosage over the United States in summer require understanding the response of this dynamical and photochemical system to increased forcing of the climate by increasing levels of CO and CH.
我们提出了观测结果，定义了（）在美国夏季利用下一代雷达系统探测水进入平流层的频率和深度；（）在与雷达观测相同的坐标系中建立的无机氯的高度相关分布；（）美国夏季平流层的高分辨率温度结构，可解决空间和结构变化问题，包括重力波的影响；以及（）由此导致的主要卤代、氢和氮催化循环中臭氧的催化损耗率的放大。每个夏季，天气雷达平均观测到约 2000 次风暴，这些风暴平均达到快速增加可用无机氯的高度，再加上观测到的温度，预示着在普遍存在的硫酸盐-水气溶胶上迅速引发无机氯向自由基形式的非均相催化转化的风险；这反过来又引发了与美国中部夏季平流层臭氧损耗相关的风险因素，其反应机制与北极地区的平流层臭氧损耗相同。由北美季风驱动的美国上空高层反气旋环流的发展，为保留对流注入的水提供了一种手段，从而延长了大平原地区催化臭氧损耗的时间。要预测美国夏季的紫外线剂量，需要了解这个动力和光化学系统对 CO 和 CH 水平增加对气候的强迫的响应。
