ATMOSPHERIC HEAT REDISTRIBUTION ON HOT JUPITERS
ATMOSPHERIC HEAT REDISTRIBUTION ON HOT JUPITERS
复制标题
热木星上的大气热量重新分布
DOI：
10.1088/0004-637x/776/2/134
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
A. Showman
中科院分区：
文献类型：
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作者：
D. Perez;A. Showman
凌日热木星的红外光曲线显示出一种趋势，即最热行星的大气层在重新分配白天吸收的恒星能量方面效率较低，因此与较冷的行星相比，它们的昼夜温度差异更大。到目前为止，还没有发表过预测大气的模型来确定哪些动力机制决定了潮汐锁定的系外行星上大气热再分配的效率。在这里，我们提出了同步旋转行星的大气动力学的浅水模型，解释了为什么热再分配效率随着恒星日照增加而下降。我们的模型显示，具有弱摩擦和弱辐射的行星表现为带状带状流动，昼夜温差最小，而具有强辐射和/或强摩擦的模型表现为昼夜流动模式，昼夜温差为有序-单位分数。为了解释该模型，我们发展了一个尺度理论，该理论表明重力波在行星尺度上水平传播的时间尺度τ波在控制温度从小到大的转变中起着主导作用。这意味着热量再分配是由一种波状过程控制的，类似于造成地球热带地区微弱温度梯度的过程。当可以忽略大气阻力时，昼夜温差从小到大的转变发生在，其中τrad为辐射松弛时间，Ω为行星旋转频率。或者，这个过渡准则可以表示为τrad ~ τvert，其中τvert是流体包在昼夜厚度差异上垂直移动的时间尺度。这些结果包含了更广泛使用的时间尺度比较，用于估计τrad和水平昼夜平流时间尺度τadv之间的热量再分配效率。只有由于热木星的τadv ~ τvert，通常假设的τrad和τadv之间的时间尺度比较才能对热再分配效率产生近似正确的预测。
Infrared light curves of transiting hot Jupiters present a trend in which the atmospheres of the hottest planets are less efficient at redistributing the stellar energy absorbed on their daysides—and thus have a larger day–night temperature contrast—than colder planets. To this day, no predictive atmospheric model has been published that identifies which dynamical mechanisms determine the atmospheric heat redistribution efficiency on tidally locked exoplanets. Here we present a shallow-water model of the atmospheric dynamics on synchronously rotating planets that explains why heat redistribution efficiency drops as stellar insolation rises. Our model shows that planets with weak friction and weak irradiation exhibit a banded zonal flow with minimal day–night temperature differences, while models with strong irradiation and/or strong friction exhibit a day–night flow pattern with order-unity fractional day–night temperature differences. To interpret the model, we develop a scaling theory which shows that the timescale for gravity waves to propagate horizontally over planetary scales, τwave, plays a dominant role in controlling the transition from small to large temperature contrasts. This implies that heat redistribution is governed by a wave-like process, similar to the one responsible for the weak temperature gradients in the Earth's tropics. When atmospheric drag can be neglected, the transition from small to large day–night temperature contrasts occurs when , where τrad is the radiative relaxation time and Ω is the planetary rotation frequency. Alternatively, this transition criterion can be expressed as τrad ∼ τvert, where τvert is the timescale for a fluid parcel to move vertically over the difference in day–night thickness. These results subsume the more widely used timescale comparison for estimating heat redistribution efficiency between τrad and the horizontal day–night advection timescale, τadv. Only because τadv ∼ τvert for hot Jupiters does the commonly assumed timescale comparison between τrad and τadv yield approximately correct predictions for the heat redistribution efficiency.