Radiative effects of CH4, N2O, halocarbons and the foreign‐broadened H2O continuum: A GCM experiment
Radiative effects of CH4, N2O, halocarbons and the foreign‐broadened H2O continuum: A GCM experiment
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CH4、N2O、卤化碳和国外拓宽的 H2O 连续体的辐射效应：GCM 实验
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
V. Ramaswamy
中科院分区：
文献类型：
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作者：
M. Schwarzkopf;V. Ramaswamy
地球物理流体动力学实验室和其他机构用于大气环流模式气候模拟的计算红外辐射传输的简化交换近似法已经更新，以便纳入甲烷（CH 4）、一氧化二氮（N2 O）、卤化碳和水-蒸汽-空气分子加宽（外来加宽）的影响。CH 4和N2 O的影响被纳入由插值线的线（LBL）transmittance计算评价在标准物种浓度;计算使用最近测得的频率依赖的吸收系数计算的透射率的卤代烃的影响。通过采用水蒸气连续统的“CKD”形式，包括外来加宽的影响[Clough等人，1989年]。对于一个标准的中纬度夏季廓线，由于包含CH 4和N2 O的现今浓度，模型对流层顶的净红外通量的变化被评估为在相应LBL结果的± 5%以内;包含1 ppbv的CFC-11、CFC-12、CFC-113和HCFC-22后，对流层顶的净通量的变化在LBL结果的± 10%以内。对流层加热率的变化所导致的微量物种（CH 4，N2 O，和卤烃）的引入计算到LBL的结果在0.03 K/d。CKD水汽连续体的引入导致LBL计算的加热率在对流层上部减少到10.4 K/d，在对流层中部增加到10.25 K/d; SEA方法给出的LBL值变化在10.05 K/d以内。经修订的战略环境评估公式已被纳入GFDL“SKYHI”GCM。已经进行了两次模拟（使用固定的海面温度和规定的云），以确定在包括（1）痕量物质和（2）外国扩大的水汽连续体后，模式气候与控制计算的变化。当添加痕量物种时，在年平均热带对流层上部出现统计上显著的变暖（10.1 K），而在平流层上部和平流层顶区域注意到冷却（10.1.5 K）。这些变化一般类似于使用辐射-对流模型（假设动力加热固定）进行的年平均平衡计算。CKD水汽连续体的影响包括在106公里以上的年平均对流层冷却（101 K），对流层低层显著变暖。当包括微量气体和CKD连续体的影响时，年平均温度在105公里以下增加，在5至10公里之间冷却，表明连续体效应在确定对流层中低层温度变化方面占主导地位。在上面，痕量气体的影响占主导地位，导致热带对流层上层变暖，中层大气大部分变冷。欧洲中期天气预报中心使用三种版本的SEA公式计算了观测大气廓线的晴空出射长波辐照度，包括（1）水蒸气、二氧化碳和臭氧的影响;（2）上述物种加上新痕量物种的现今浓度;（3）所有上述物种加上CKD H2O连续统。所有三种情况的结果都在相应的地球辐射收支实验晴空辐照度测量值的1000 W/m2范围内。微量气体和CKD连续体的综合效应导致计算的辐照度降低了1.8W/m2。
The simplified exchange approximation (SEA) method for calculation of infrared radiative transfer, used for general circulation model (GCM) climate simulations at the Geophysical Fluid Dynamics Laboratory (GFDL) and other institutions, has been updated to permit inclusion of the effects of methane (CH4), nitrous oxide (N2O), halocarbons, and water-vapor-air molecular broadening (foreign broadening). The effects of CH4 and N2O are incorporated by interpolation of line-by-line (LBL) transmissivity calculations evaluated at standard species concentrations; halocarbon effects are calculated from transmissivities computed using recently measured frequency-dependent absorption coefficients. The effects of foreign broadening are included by adoption of the “CKD” formalism for the water vapor continuum [Clough et al., 1989]. For a standard midlatitude summer profile, the change in the net infrared flux at the model tropopause due to the inclusion of present-day concentrations of CH4 and N2O is evaluated to within ∼5% of corresponding LBL results; the change in net flux at the tropopause upon inclusion of 1 ppbv of CFC-11, CFC-12, CFC-113, and HCFC-22 is within ∼10% of the LBL results. Tropospheric heating rate changes resulting from the introduction of trace species (CH4, N2O, and halocarbons) are calculated to within ∼0.03 K/d of the LBL results. Introduction of the CKD water vapor continuum causes LBL-computed heating rates to decrease by up to ∼0.4 K/d in the upper troposphere and to increase by up to ∼0.25 K/d in the midtroposphere; the SEA method gives changes within ∼0.05 K/d of the LBL values. The revised SEA formulation has been incorporated into the GFDL “SKYHI” GCM. Two simulations (using fixed sea surface temperatures and prescribed clouds) have been performed to determine the changes to the model climate from that of a control calculation upon inclusion of (1) the trace species and (2) the foreign-broadened water vapor continuum. When the trace species are added, statistically significant warming (∼1 K) occurs in the annual-mean tropical upper troposphere, while cooling (∼1.5 K) is noted in the upper stratosphere and stratopause region. The changes are generally similar to annual-mean equilibrium calculations made using a radiative-convective model assuming fixed dynamical heating. The effects of the CKD water vapor continuum include cooling (∼1 K) in the annual-mean troposphere above ∼6 km, with significant warming in the lower troposphere. When effects of both trace gases and the CKD continuum are included, the annual-mean temperature increases below ∼5 km and cools between 5 and 10 km, indicating that continuum effects dominate in determining temperature changes in the lower and middle troposphere. Above, trace gas effects dominate, resulting in warming in the tropical upper troposphere and cooling in most of the middle atmosphere. Clear-sky outgoing longwave irradiances have been computed for observed European Centre for Medium-Range Weather Forecasting atmospheric profiles using three versions of the SEA formulation, including the effects of (1) water vapor, carbon dioxide, and ozone; (2) the above species plus present-day concentrations of the new trace species; (3) all of the above species plus the CKD H2O continuum. Results for all three cases are within ∼10 W/m2 of corresponding Earth Radiation Budget Experiment clear-sky irradiance measurements. The combined effect of trace gases and the CKD continuum result in a decrease of ∼8 W/m2 in the computed irradiances.