A GCM study of the impact of greenhouse gas increase on the frequency of occurrence of tropical cyclones
A GCM study of the impact of greenhouse gas increase on the frequency of occurrence of tropical cyclones
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DOI：
10.1023/a:1005386312622
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发表时间：
1998-03-01
期刊：
影响因子：
4.8
通讯作者：
Grimal, D
中科院分区：
文献类型：
--
作者：
Royer, JF;Chauvin, F;Grimal, D
为了推断热带气旋生成频率未来可能的变化，我们将Gray（1975）提出的年生成参数（YGP）诊断计算应用于GCM模拟的大尺度场。YGP是一个基于六个物理参数的热带气旋（TC）频率的经验诊断，这些参数是从大气和海洋变量的季节平均值计算出来的。在本文中，我们应用YGP诊断与大气环流模式（GCM）的法国气象：ARPEGE-Climat进行的三个气候模拟的结果。在当前气候的控制模拟，它表明，该模式具有现实的热带气候学和计算的YGP再现热带气旋生成频率的地理分布。然后，YGP被应用到两个模拟对应的两种情况下的二氧化碳浓度加倍。这两个实验的不同之处在于海表温度（SST）作为下边界条件。在这两个模拟中，YGP给出了一个大的增加总的气旋生成频率，但没有扩大可能的气旋生成的区域。YGP的增加主要是由于海洋热能因子在热力学势中的贡献。相反，动力学参数限制了气旋生成的增加，是两个实验之间差异的主要解释。这与Ryan等人（1992）先前关于大尺度大气环流变化对热带气旋气候学的重要性的类似研究结果一致。在讨论了观测到的海洋表面温度和大尺度对流之间的关系，并质疑使用一个固定的温度阈值在诊断热带气旋的频率，我们提出了一个修改的YGP组成的替代由GCM计算的对流降水成比例的一项的位势。对于当前气候的模拟，这种修改仅略微影响热带气旋生成的地理分布，但对于CO2加倍的情况，修改后的YGP诊断出北方半球TC生成的增加更为有限，南半球略有减少，这似乎与最近使用高分辨率气候模式进行的其他模拟研究更一致（Bengtsson等人，1996年）。我们的结论是，修改后的YGP对流降水的基础上，可以作为一个有用的诊断热带气旋的成因，并应在模拟与其他GCM测试。
In order to make inferences on the possible future changes of tropical cyclogenesis frequency, we apply the diagnostic computation of the Yearly Genesis Parameter (YGP) proposed by Gray (1975) to the large-scale fields simulated by a GCM. The YGP is an empirical diagnostic of the frequency of Tropical Cyclones (TCs) based on six physical parameters computed from seasonal means of atmospheric and oceanic variables. In this paper, we apply the YGP diagnostic to the results of three climate simulations performed with the atmospheric General Circulation Model (GCM) of Meteo-France: ARPEGE-Climat. In a control simulation of the current climate, it is shown that the model has a realistic tropical climatology and that the computed YGP reproduces the geographical distribution of the tropical cyclogenesis frequency. The YGP is then applied to two simulations corresponding to two scenarios of doubled carbon dioxide concentration. The two experiments differ by the sea surface temperatures (SSTs) used as a lower boundary condition. In both simulations the YGP gives a large increase of total cyclogenesis frequency, but without extension of the area of possible cyclone genesis. The increase in YGP is due essentially to the contribution of the ocean thermal energy factor in the thermodynamical potential. The dynamical parameters, on the contrary, limit the cyclogenesis increase and are a major explanation of the difference between the two experiments. This is in agreement with the results of the previous similar study of Ryan et al. (1992) concerning the importance of large-scale atmospheric circulation modifications on tropical cyclone climatology. After discussing the observed relationships between ocean surface temperature and large-scale convection, and questioning the use of a fixed temperature threshold in the diagnosis of tropical cyclone frequency, we propose a modification to the YGP consisting in replacing the thermodynamical potential by a term proportional to the convective precipitation computed by the GCM. For the simulation of the present climate this modification affects only marginally the geographical distribution of tropical cyclone genesis, but for the doubled CO2 case, the modified YGP diagnoses a more limited increase in TC genesis in the Northern Hemisphere and a small reduction in the Southern Hemisphere, which seems in better agreement with other recent modelling studies with high resolution climate models (Bengtsson et al., 1996). We conclude that the modified YGP based on convective precipitation could serve as a useful diagnostic of tropical cyclone genesis, and should be tested in simulations with other GCMs.