The time-dependent response of the Hadley circulation to a periodic forcing is explored via a simplified nonlinear axisymmetric model. Thermal forcing towards a given equilibrium potential temperature drives the model atmosphere. The vertical stratification of this temperature is forced to become periodically neutral with a period it/isub0/sub. Simulations performed with values of it/isub0/sub ranging from 10 to 90?days exhibit stronger circulation compared to the results of a constant thermal forcing experiment. As the period increases, a transition occurs first from a stationary regime, obtained when forcing is constant, to a periodic (and possibly quasi-periodic) regime, and then to an intermittent regime, albeit one with a strong periodic component. The stream-function response to periodic forcing is generally a periodic oscillation, with two main frequencies dominating: one with a period equal or close to the forcing period and another with a period that is half of the forcing period. The former is dominant for values of it/isub0/sub larger than 30?days, whereas the latter is prevalent for it/isub0/sub smaller than 30?days. The periodic oscillations obtained in this model may be associated with the periodic oscillations observed in the tropical regions. In this case the periodic charge and discharge of moisture in the tropical atmosphere, with consequent change of stratification, may be linked to those oscillations. In the model, at forcing periods of over 63 days the response of the stream function periodically enters into a quasi-intermittent regime, exhibiting high-frequency chaotic oscillations that are modulated by the slow timescale of forcing. Sensitivity experiments for model parameters and configuration were performed to check whether results obtained are still valid under different conditions. Although for small changes of parameters the results are still valid, when parameters depart from the prescribed ones, we can observe change in the Hadley circulation dynamics.
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机译：通过简化的非线性轴对称模型，探索了哈德利环流对周期强迫的时变响应。朝向给定平衡势温度的热强迫驱动了模型大气。该温度的垂直分层被迫周期性地变为中性，周期为 t 0 。与恒定热强迫实验的结果相比，使用 t 0 的值在10到90天的范围内进行的模拟显示出更强的循环。随着周期的增加，首先会发生从固定状态的过渡，该过渡状态在强制作用不变的情况下过渡到周期性（可能是准周期性）状态，然后过渡到间歇状态，尽管该过渡状态具有很强的周期性成分。对周期性强迫的流函数响应通常是周期性振荡，其中两个主要频率占主导：一个周期等于或接近强迫周期，另一个周期为强迫周期的一半。前者在大于30天的 t 0 值中占主导地位，而后者在 t 0 时占主导地位。 >少于30天。在该模型中获得的周期性振荡可能与热带地区观测到的周期性振荡有关。在这种情况下，热带大气中水分的定期充放电和随之而来的分层变化可能与那些振荡有关。在该模型中，在超过63天的强迫周期中，流函数的响应周期性地进入准间歇状态，表现出高频混沌振荡，该振荡由缓慢的强迫时间尺度调制。进行了模型参数和配置的敏感性实验，以检查获得的结果在不同条件下是否仍然有效。尽管对于参数的微小变化，结果仍然有效，但是当参数偏离规定的参数时，我们可以观察到Hadley循环动力学的变化。
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