Evaluating the Ozone Valley over the Tibetan Plateau in CMIP6 Models

Abstract

Total column ozone (TCO) over the Tibetan Plateau (TP) is lower than that over other regions at the same latitude, particularly in summer. This feature is known as the “TP ozone valley”. This study evaluates long-term changes in TCO and the ozone valley over the TP from 1984 to 2100 using Coupled Model Intercomparison Project Phase 6 (CMIP6). The TP ozone valley consists of two low centers, one is located in the upper troposphere and lower stratosphere (UTLS), and the other is in the middle and upper stratosphere. Overall, the CMIP6 models simulate the low ozone center in the UTLS well and capture the spatial characteristics and seasonal cycle of the TP ozone valley, with spatial correlation coefficients between the modeled TCO and the Multi Sensor Reanalysis version 2 (MSR2) TCO observations greater than 0.8 for all CMIP6 models. Further analysis reveals that models which use fully coupled and online stratospheric chemistry schemes simulate the anticorrelation between the 150 hPa geopotential height and zonal anomaly of TCO over the TP better than models without interactive chemistry schemes. This suggests that coupled chemical-radiative-dynamical processes play a key role in the simulation of the TP ozone valley. Most CMIP6 models underestimate the low center in the middle and upper stratosphere when compared with the Microwave Limb Sounder (MLS) observations. However, the bias in the middle and upper stratospheric ozone simulations has a marginal effect on the simulation of the TP ozone valley. Most CMIP6 models predict the TP ozone valley in summer will deepen in the future.

摘要

青藏高原“臭氧低谷”是指青藏高原上空的臭氧柱总量低于同纬度其它地区的现象, 在夏季更为明显. 本研究采用第六次国际耦合模式比较计划(CMIP6)中的模式, 评估了1984年至2100年期间高原地区臭氧柱总量和“臭氧低谷”的长期变化. 结果表明, 青藏高原“臭氧低谷”由两个低值中心组成, 一个位于对流层上部和平流层下部(UTLS), 另一个位于平流层中上部. 总体而言, CMIP6模式可以很好地模拟UTLS中的低臭氧中心, 重现高原“臭氧低谷”的空间特征和季节变化. 所有CMIP6模式模拟的臭氧柱总量和多传感器再分析资料(MSR2)的臭氧柱总量观测值之间的空间相关系数均大于0.8. 进一步分析表明, 采用全耦合和在线平流层化学方案的模式比没有采用交互化学方案的模式更好地模拟出了150 hPa位势高度与青藏高原“臭氧低谷”的反相关关系, 这说明化学-辐射-动力耦合过程在青藏高原“臭氧低谷”的模拟中起着关键作用. 与微波临边探测器(MLS)的观测结果相比, CMIP6模式大多低估了平流层中上部的臭氧低值中心, 然而平流层中上层臭氧模拟的偏差对青藏高原“臭氧低谷”的模拟影响并不大. 同时, 大部分CMIP6模式都预测青藏高原“臭氧低谷”将在未来加深.