The Response of Hadley Circulation Extent to an Idealized Representation of Poleward Ocean Heat Transport in an Aquaplanet GCM
The Response of Hadley Circulation Extent to an Idealized Representation of Poleward Ocean Heat Transport in an Aquaplanet GCM
复制标题
哈德利环流范围对水行星 GCM 中极地海洋热传输理想化表示的响应
DOI：
10.1175/jcli-d-18-0324.1
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发表时间：
2018
影响因子：
4.9
通讯作者：
D. Hartmann
中科院分区：
文献类型：
--
作者：
C. Hilgenbrink;D. Hartmann
通过探索纬向对称平板海洋水行星环流模式（GCM）对极地海洋热输运（OHT）的响应，对Hadley环流宽度和Hadley环流扩张机制有了更深入的理论认识。与没有OHT的模拟相比，向极地的OHT使HC的副热带边缘向极地移动了3°。这种HC变宽被解释为是由HC极向边缘附近斜压性的减少所驱动的，并分为三个部分：斜压性的减少是由于1)热带辐合带（ITCZ）在季节周期中系统的向极移动导致HC角动量的减少，从而导致纬向风垂直切变的减弱；(2)副热带静态稳定性的增加和HC的垂直范围的增加都是由OHT对全球平均温度的影响引起的；3) OHT使外热带和亚热带经向海表温度（SST）梯度松弛。虽然第三种机制对HC宽度对OHT的响应贡献最大，但前两种机制的贡献各占HC响应的20%-30%。这项工作强调了ITCZ位置在产生高压扩张和确定高压气候宽度方面的作用，这一作用一直被低估。这一研究表明斜压性在限制HC向极地扩展方面起着重要作用。
Deeper theoretical understanding of Hadley circulation (HC) width and the mechanisms leading to HC expansion is gained by exploring the response of a zonally symmetric slab ocean aquaplanet general circulation model (GCM) to imposed poleward ocean heat transport (OHT). Poleward OHT causes the subtropical edge of the HC to shift poleward by up to 3° compared to its position in simulations without OHT. This HC widening is interpreted as being driven by a decrease in baroclinicity near the poleward edge of the HC and is divided into three components: a decrease in baroclinicity due to 1) a systematic poleward shift of the intertropical convergence zone (ITCZ) during the seasonal cycle that drives a decrease in the angular momentum of the HC and, consequently, a weakening of the vertical shear of the zonal wind; 2) an increase in subtropical static stability and the vertical extent of the HC, both of which result from OHT’s effect on global-mean temperature; and 3) a relaxation of the meridional sea surface temperature (SST) gradient in the outer tropics and subtropics by OHT. Although the third mechanism contributes the most to the response of HC width to OHT, the contributions from the first two mechanisms each account for up to 20%–30% of the HC response. This work highlights the role of ITCZ position in producing HC expansion and in setting the climatological width of the HC, a role which has been underappreciated. This study indicates a fundamental role for baroclinicity in limiting the poleward extent of the HC.