Zonally Symmetric Adjustment in the Presence of Artificial Relaxation
Zonally Symmetric Adjustment in the Presence of Artificial Relaxation
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DOI：
10.1175/jas-d-14-0013.1
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发表时间：
2014-11-01
影响因子：
3.1
通讯作者：
Haynes, Peter H.
中科院分区：
文献类型：
--
作者：
Hitchcock, Peter;Haynes, Peter H.
在一个综合的、平流层分辨的大气环流模式中，为了研究它对下面自由演化的对流层的影响，进行了数值实验，其中平流层的纬向平均状态被强烈地松弛(或“轻推”)到参考的突然变暖事件的演化。类似的方法也被用于其他一些研究。这就提出了这样一个问题：即使在没有引起参考事件的平流层波驱动的情况下，这种人工弛豫是否会在推动区以下引起预期的绝热和非绝热调整。在这个问题的推动下，研究了被推到含时参考态的系统中纬向对称准地转非绝热响应对纬向力(代表波驱动)的响应。在与参考态不同的微动区中存在波驱动的情况下，参考态的经向质量环流仅在微微区下方被重现，直到与微微区的强度成反比的修正。由于在轻推层交界处有一个有效的边界条件，异常环流被限制了。轻推还会在轻推区域的正下方产生一个人造的“海绵层反馈”，以响应对流层波驱动的不同。这种人工反馈的强度与有效边界条件的强度密切相关；然而，建立海绵层反馈所需的时间尺度通常比约束所需的时间要长得多。
Numerical experiments, presented in a companion paper, have been performed in which the zonal-mean state of the stratosphere in a comprehensive, stratosphere-resolving, general circulation model is strongly relaxed (or "nudged") toward the evolution of a reference sudden warming event in order to investigate its influence on the freely evolving troposphere below. Similar approaches have been used in a number of other studies. This raises the question of whether such an artificial relaxation induces the adiabatic and diabatic adjustments expected below the region of nudging, even in the absence of the stratospheric wave driving responsible for the reference event.Motivated by this question, the zonally symmetric quasigeostrophic diabatic response to zonal forces (representing wave driving) in a system nudged to a time-dependent reference state is studied. In the presence of wave driving in the nudging region that differs from the reference state, the meridional mass circulation of the reference state is reproduced only in the region below the nudging up to a correction that is inversely proportional to the strength of the nudging. The anomalous circulation is confined because of an effective boundary condition at the interface of the nudging layer. The nudging also produces an artificial "sponge-layer feedback" immediately below the region of the nudging in response to differences in the tropospheric wave driving. The strength of this artificial feedback is closely related to the strength of the effective boundary condition; however, the time scale required for the sponge-layer feedback to be established is typically much longer than that required for the confinement.