Cooling of the mesosphere and lower thermosphere due to doubling of CO2
Cooling of the mesosphere and lower thermosphere due to doubling of CO2
复制标题
由于二氧化碳加倍，中层和下层热层变冷
DOI：
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
V. Fomichev
中科院分区：
文献类型：
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作者：
R. Akmaev;V. Fomichev
在光谱中间层/低热层模式(SMLTM)中加入了一个新的15μm CO_2波段红外辐射传输参数。该参数化适用于地面混合比在150-720ppm范围内的任意垂直CO2浓度廓线在约15公里以上的加热率的计算。研究了中间层和低热层(MLT)对CO_2倍增的敏感性。MLT中的热响应大多是负的(冷却)，并且比低层大气中的热响应要强得多。平流层顶的平均降温约为14K，在中上层逐渐降低到约8K，在热层又增加到约40-50K。冷却和相关的热收缩导致MLT的密度显著降低，在热层中达到40%-45%。讨论了各种辐射反馈、化学反馈和动态反馈对MLT热响应的潜在重要性。值得注意的是，模拟的结果与MLT的长期趋势观测结果惊人地相似。这表明，在过去的3-40年里，真实高层大气中的热结构在强迫的驱动下发生了实质性的变化，与二氧化碳倍增所造成的变化相当。
A new parameterization of infrared radiative transfer in the 15-μm CO2 band has been incorporated into the Spectral mesosphere/lower thermosphere model (SMLTM). The parameterization is applicable to calculations of heating rates above approximately 15 km for arbitrary vertical profiles of the CO2 concentration corresponding to the surface mixing ratio in the range 150–720 ppm. The sensitivity of the mesosphere and lower thermosphere (MLT) to doubling of CO2 has been studied. The thermal response in the MLT is mostly negative (cooling) and much stronger than in the lower atmosphere. An average cooling at the stratopause is about 14 K. It gradually decreases to approximately 8 K in the upper mesosphere and again increases to about 40–50 K in the thermosphere. The cooling and associated thermal shrinking result in a substantial density reduction in the MLT that reaches 40–45% in the thermosphere. Various radiative, chemical, and dynamical feedbacks potentially important for the thermal response in the MLT are discussed. It is noted that the results of simulations are strikingly similar to observations of long-term trends in the MLT. This suggests that during the last 3–4 decades the thermal structure in the real upper atmosphere has undergone substantial changes driven by forcing comparable with that due to doubling of CO2.