大气酸沉降的自组织临界性

Self-organized Criticality of Atmospheric Acid Deposition

运用概率分布函数、矩分析、功率谱分析和无趋势波动分析（DFA）方法,分析了美国1978-2001年期间酸沉降数据,发现大气酸沉降事件类似于沙堆模型中的崩塌事件,具有自组织临界性（SOC）。降水中氢离子沉降量（WHD）的频率分布符合双幂律分布,即在由临界WHD所区分的两个区间内,WHD的频率分布分别呈幂律分布;双幂律分布及临界WHD刻画了酸沉降事件的宏观特征。WHD时间序列具有1/f^β噪声特征,在时域上具有长程相关性（LRC）。降水中硝酸根离子和硫酸根离子沉降量与WHD表现为类似行为。此外,将正常降水的酸度值或环境容量作为大气酸沉降的临界状态,并以此类比为沙堆模型的临界稳态角度。因此,酸沉降的演化符合具有自组织临界性的复杂系统的三个基本特征。据此,作者认为酸沉降在频域上的幂律分布及在时域上的长程相关性是污染胁迫下大气自组织临界行为的标志,自组织临界行为是控制酸沉降演化趋势的内在机制之一。

With empirical probability distribution function, moment, power spectrum and detrended fluctuation analysis （DFA）, the data of National Atmospheric Deposition Program, USA, are analyzed to investigate the characteristics of self-organized criticality （SOC） of atmospheric acid deposition. It is shown that acid deposition events are analogous to many other relaxational processes in nature such as earthquakes and avalanches of granular piles, suggesting the existence of SOC in acid deposition. Under a wide variety of circumstances, frequency distributions of weekly hydrogen deposition （WILD） of precipitation are consistent with double power-law in two different regimes separated by a characteristic crossover WILD. The double power-law scaling of acid deposition together with its characteristic size scales characterizes the macroscopic properties of the size of avalanches of acid deposition in various atmospheric conditions. WIlD series can be depicted as 1/f^β noise with long-range correlations （LRC）, implying that persistence of acid deposition may be one of the important factors inducing ecological changes of nature, and should be considered in the trend prediction of acid deposition evolutions. DFA shows that the scaling exponent for small time scale ranges from 0. 64 to 0. 76 （〉0. 5）, indicating LRC in temporal evolutions of acid deposition. However, the scaling exponent 〈0. 5 for low temporal resolution, indicating that LRC does not hold for large time scale. The switch in the WIlD series reflects the different characteristics of correlation structure of WIlD fluctuations for different temporal scales. Nitrate and sulphate depositions fluctuations in precipitation behave similarly to WHD. It is argued that the critical state of atmospheric acid deposition refers to the normal acidity of water in atmosphere, or the environmental capacity, which is analogous to the critical angle of repose in a sandpile model. It is believed, therefore, that acid deposition evolution is consistent with the three criteria of complex SOC systems, and that acid deposition events, with pollutants being continuously stored in the atmosphere and then suddenly released by bursts when the vapor condenses to water drops, do not look very different from avalanches from the point of view of SOC. It is thus suggested that SOC may be a possible mechanism for acid deposition evolution. The frequency-size power-law scaling and the temporal long-range correlations in acid deposition dynamics are considered to be indicators of SOC behavior of atmosphere under environmental pollution stress. The changes of crossover and the variations of power-law slopes of WHD may prove the influence of organization principles which refers to the differences of regional environmental characteristics of the system on the phenomenon of SOC.