What controls the size of a tropical cyclone? Investigations with an axisymmetric model
What controls the size of a tropical cyclone? Investigations with an axisymmetric model
复制标题
是什么控制着热带气旋的大小？
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
T. Frisius
中科院分区：
文献类型：
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作者：
T. Frisius
利用轴对称云模式HURMOD研究了热带气旋尺度的控制机制。与先前的HURMOD研究一致，模式结果显示存在与热带气旋相关的不动点吸引子。从无量纲化的模式方程中，导出了一个相似律，该相似律将六个模式参数与稳定状态下热带气旋的水平范围联系起来。每个参数都与以下过程之一相关联：行星旋转，凝结时间尺度，辐射弛豫时间尺度，水平扩散，垂直扩散和表面传输。参数的个体变化表明，最大水平风速半径对科里奥利参数、混合长度和辐射弛豫时间尺度非常敏感，而最小切向风半径仅取决于科里奥利参数、表面传输系数和辐射弛豫时间尺度。最大水平风速半径随垂直涡动扩散率的增大而沿着增大，并伴随着二次环流中翻转质量通量的增大。这与Held和Hou的Hadley细胞理论一致，他们也强调了垂直扩散的相关性。翻转质量通量的加强遵循类似于海洋模型研究中发现的幂律。此外，发现TC大小对环境条件敏感，包括规定的海面温度，对流层顶高度和静态稳定度，而相对湿度的敏感性相对较小。当上海绵层的转矩被关闭时，该模型在长期内完全满足稳态角动量收支方程。
Control mechanisms of tropical cyclone size are investigated with the axisymmetric cloud model HURMOD. In agreement with preceding HURMOD studies, the model results exhibit the existence of a fixed‐point attractor associated with a tropical cyclone. From the non‐dimensionalized model equations, a similarity law is derived, which relates six model parameters to the horizontal extent of the tropical cyclone in a steady state. Each parameter is associated with one of the following processes: planetary rotation, condensation time‐scale, radiative relaxation time‐scale, horizontal diffusion, vertical diffusion, and surface transfer. Individual variation of the parameters reveals that the radius of maximum horizontal wind speed is very sensitive to the Coriolis parameter, the mixing lengths and the radiative relaxation time‐scale, whereas the radius of minimum tangential wind merely depends on the Coriolis parameter, the surface transfer coefficients, and the radiative relaxation time‐scale. The increase of the radius of maximum horizontal wind speed with vertical eddy diffusivity goes along with an enhancement of the overturning mass flux within the secondary circulation. This agrees with the Hadley cell theory by Held and Hou who also emphasized the relevance of vertical diffusion. The strengthening of the overturning mass flux follows a power law similar to that found in an ocean modelling study. Moreover, TC size is found to be sensitive to environmental conditions comprising the prescribed sea‐surface temperature, tropopause height and static stability, while the sensitivity with respect to relative humidity is relatively small in the model. When the torque due to the upper sponge layer is switched off, the model exactly fulfills in the long run the steady state angular momentum budget equation.