北非沙尘排放通量的年际变化及其物理机制

Interannual variability of dust emission flux over North Africa: influencing factors and underlying mechanisms

摘要:

基于MERRA-2的气溶胶数据集,重点分析了北非的两个主要沙尘源区,即西北非(West North Africa,WNA)和中北非(Central North Africa,CNA),两个区域均具有显著的年际变化。其中WNA春季沙尘排放通量与前冬温度和春季风速相关,而CNA地区的沙尘排放通量的年际变化主要由风速主导。通过回归分析发现,负相位的北大西洋涛动(North Atlantic Oscillation,NAO)和厄尔尼诺会诱发WNA冬季的暖气温;而北太平洋海温暖异常(常伴随拉尼娜)则在春季对WNA风速的增加起到重要作用。CNA冬季的风速异常则与NAO(正相位)和北太平洋海温暖异常有关。研究结果表明,厄尔尼诺-南方涛动(El Niño-Southern Oscillation,ENSO)与北非沙尘排放通量的年际变率关系较弱,但北太平洋海温异常信号稳定且显著,可视为影响北非沙尘排放通量年际变化的海温指标。

Abstract:

Dust aerosols exert significant and multifaceted influences on the Earth system,affecting both climate and environmental conditions.They directly modify the planetary energy budget by scattering and absorbing solar radiation (direct effect) and indirectly influence cloud microphysics and lifetimes,thereby altering regional precipitation patterns.In addition,dust aerosols degrade air quality,pose risks to human health by exacerbating respiratory and cardiovascular diseases,and affect marine and terrestrial ecosystems through long-range nutrient transport and deposition.As the initial step in the dust cycle,the emission process plays a critical role in determining interannual variability in dust activity;however,the primary drivers of this variability remain insufficiently understood.
Using the MERRA-2 dataset,this study focuses on two major dust source regions in North Africa:West North Africa (WNA) and Central North Africa (CNA),both of which exhibit pronounced interannual variability.Dust activity in WNA peaks during boreal spring (March-April-May),while in CNA it peaks during winter (December-January-February-March).In WNA,spring dust emission flux is significantly correlated with preceding winter temperature and concurrent spring wind speed,while in CNA,interannual variability is primarily controlled by wind speed.
Spectral analysis reveals that dust activity in WNA exhibits quasi-3-year and quasi-6-year periodicities.The quasi-3-year cycle is influenced by both preceding winter temperature and spring wind speed,while the quasi-6-year cycle is mainly controlled by preceding winter temperature.Regression analyses indicate that the negative phase of the North Atlantic Oscillation (NAO) and El Niño events are associated with warmer winter temperatures in WNA.In addition,warm North Pacific sea surface temperature (SST) anomalies or La Niña conditions enhance spring wind speeds over WNA.In CNA,dust activity exhibits a quasi-4-year cycle consistent with wind speed variability,with winter wind anomalies linked to the positive phase of the NAO and warm North Pacific SST anomalies.
Overall,the relationship between the El Niño-Southern Oscillation (ENSO) and North African dust emission variability is relatively weak.However,the consistent influence of North Pacific SST anomalies suggest that they may play an important role alongside NAO.Specifically,a positive NAO phase in winter induces northeasterly wind anomalies over North Africa,promoting dust emission in CNA during winter while simultaneously causing cooling in WNA,which suppresses dust emission in the subsequent spring.ENSO influences are phase-dependent:La Niña events tends to enhance dust emission by strengthening near-surface winds,whereas El Niño events can favor increased dust emission in WNA by inducing winter warming.
By examining dust emission—the primary process in the dust cycle—this study provides a comprehensive assessment of the meteorological controls on interannual dust variability across North Africa.The results demonstrate that dominant controlling factors vary regionally and highlight the combined roles of atmospheric circulation and oceanic forcing.These findings improve understanding of the mechanisms driving dust variability and provide a scientific basis for predicting future dust activity and its impact on climate,ecosystems,and human health,as well as for developing targeted strategies for environmental management and sustainable development in North Africa.