Richardson Mark I, Wilson R John
Division of Geological and Planetary Sciences, California Institute of Technology, MC 150-21, Pasadena, California 91125, USA.
Nature. 2002 Mar 21;416(6878):298-301. doi: 10.1038/416298a.
Large seasonal and hemispheric asymmetries in the martian climate system are generally ascribed to variations in solar heating associated with orbital eccentricity. As the orbital elements slowly change (over a period of >104 years), characteristics of the climate such as dustiness and the vigour of atmospheric circulation are thought to vary, as should asymmetries in the climate (for example, the deposition of water ice at the northern versus the southern pole). Such orbitally driven climate change might be responsible for the observed layering in Mars' polar deposits by modulating deposition of dust and water ice. Most current theories assume that climate asymmetries completely reverse as the angular distance between equinox and perihelion changes by 180 degrees. Here we describe a major climate mechanism that will not precess in this way. We show that Mars' global north-south elevation difference forces a dominant southern summer Hadley circulation that is independent of perihelion timing. The Hadley circulation, a tropical overturning cell responsible for trade winds, largely controls interhemispheric transport of water and the bulk dustiness of the atmosphere. The topography therefore imprints a strong handedness on climate, with water ice and the active formation of polar layered deposits more likely in the north.
火星气候系统中巨大的季节性和半球不对称性通常归因于与轨道偏心率相关的太阳加热变化。随着轨道要素缓慢变化（超过104年的时间），气候特征如沙尘程度和大气环流的强度被认为会发生变化，气候的不对称性也应如此（例如，水冰在北极和南极的沉积情况）。这种由轨道驱动的气候变化可能通过调节沙尘和水冰的沉积，导致火星极地沉积物中观察到的分层现象。目前大多数理论认为，随着春分点和近日点之间的角距离变化180度，气候不对称性会完全反转。在此，我们描述了一种不会以这种方式进动的主要气候机制。我们表明，火星全球南北海拔差异迫使形成一个占主导地位的南半球夏季哈德利环流，该环流与近日点时间无关。哈德利环流是一个负责信风的热带翻转环流，在很大程度上控制着半球间的水汽输送和大气中的沙尘总量。因此，地形对气候产生了强烈的偏向性，使得水冰以及极地层状沉积物的活跃形成在北半球更为可能。
