Spatial Patterns of Precipitation Change in CMIP5: Why the Rich Do Not Get Richer in the Tropics
Spatial Patterns of Precipitation Change in CMIP5: Why the Rich Do Not Get Richer in the Tropics
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DOI：
10.1175/jcli-d-12-00543.1
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发表时间：
2013-06-01
影响因子：
4.9
通讯作者：
Martin, Gill
中科院分区：
文献类型：
--
作者：
Chadwick, Robin;Boutle, Ian;Martin, Gill
在典型浓度路径8.5（RCP 8.5）情景下，在耦合模式相互比较项目第5阶段（CMIP 5）GCM中分析了热带降水（P）和环流的变化。热带环流在各模式中都有明显的减弱，这与散度反馈有关，这种反馈在气候上升最大的地区起到了减少对流的作用。这与热带降水模式年际变化中的收敛反馈形成对比。对流质量通量变化的剩余型与SST梯度变化等机制引起的辐合区的移动有关，并且这种移动往往比辐散反馈引起的减弱更大。虽然热带平均降水量的增加是由于比湿增加导致的正热力学变化和环流减弱导致的对流质量通量减少之间的残差，但这两个分量的空间分布在很大程度上相互抵消。这种抵消几乎否定了上升区最大降水增加的富-富机制，解释了为什么CMIP 5多模式平均值在热带地区气候P和气候变化异常Δ P之间的空间相关性仅为0.2。这使得降水变化的空间格局主要由与辐合区的变化相关的分量主导，无论是在多模式平均值和模式间的不确定性，由于相对湿度变化的分量在陆地上也变得重要。
Changes in the patterns of tropical precipitation (P) and circulation are analyzed in Coupled Model Intercomparison Project phase 5 (CMIP5) GCMs under the representative concentration pathway 8.5 (RCP8.5) scenario. A robust weakening of the tropical circulation is seen across models, associated with a divergence feedback that acts to reduce convection most in areas of largest climatological ascent. This is in contrast to the convergence feedback seen in interannual variability of tropical precipitation patterns. The residual pattern of convective mass-flux change is associated with shifts in convergence zones due to mechanisms such as SST gradient change, and this is often locally larger than the weakening due to the divergence feedback.A simple framework is constructed to separate precipitation change into components based on different mechanisms and to relate it directly to circulation change. While the tropical mean increase in precipitation is due to the residual between the positive thermodynamic change due to increased specific humidity and the decreased convective mass flux due to the weakening of the circulation, the spatial patterns of these two components largely cancel each other out. The rich-get-richer mechanism of greatest precipitation increases in ascent regions is almost negated by this cancellation, explaining why the spatial correlation between climatological P and the climate change anomaly Delta P is only 0.2 over the tropics for the CMIP5 multimodel mean. This leaves the spatial pattern of precipitation change to be dominated by the component associated with shifts in convergence zones, both in the multimodel mean and intermodel uncertainty, with the component due to relative humidity change also becoming important over land.