Abstract: A series of numerical simulations are conducted (using GFDL CM2.1) to investigate the global mean precipitation and temperature change in response to climate variation. Experiments under different carbon dioxide (CO2) forcing indicate an obvious precipitation hysteresis. There is a significant linear relationship between global mean precipitation and surface temperature, but precipitation is also influenced directly by CO2 concentration. During the experiments in which CO2 concentration rises up and then falls back, precipitation change lags behind surface temperature, which leads to the precipitation hysteresis. While CO2 increasing, the enhanced greenhouse effect will lead to immediate intension of atmospheric long-wave absorption, which will bring net radiative energy income to atmosphere. To balance the energy budget, upward latent heat has to be restrained, so the additional CO2 has inhibiting effect on precipitation. The subsequent warming mainly induces increasing in outgoing long wave radiation at TOA and backward long wave radiation at surface, which is equivalent to a radiative cooling for atmosphere, and then causes precipitation rising. While CO2 decreasing, on the contrary, the subdued greenhouse effect tends to intensify precipitation and the temperature reduction will reduce the precipitation. Different effects on precipitation from temperature and CO2 determine the precipitation hysteresis.

Key words: coupled model, greenhouse gas effect, varying climate, precipitation, hysteresis effect

摘要： 利用耦合气候模式(GFDL-CM2.1)研究变动气候背景下全球平均降水和温度的变化。不同情景CO2 强迫试验表明, 降水变化存在明显的迟滞效应。全球平均降水与地表温度的变化存在显著的线性关系, 但是降水同时也受到CO2 浓度的直接影响。在CO2 增加又恢复的试验中, 降水变化滞后于地表温度变化, 出现降水 “迟滞效应”。在CO2 增加过程中, 温室效应增强会立即导致大气长波吸收增强, 大气获得的净辐射能量增加, 为维持大气能量收支平衡, 地面向上潜热通量受到抑制, 形成CO2 增加对降水的抑制效应。随之而来的温度上升则主要引起大气层顶出射长波辐射以及大气对地表的长波回辐射增加, 大气净辐射能量减少, 地面潜热通量增加, 从而引起降水的增加。在CO2 减少过程中, 情况正好相反, 温室效应减弱会增加降水, 而温度降低会减少降水。温度和CO2 对降水的不同影响决定了降水的迟滞效应。

关键词: 耦合模式, 温室效应, 变动气候, 降水, 迟滞效应