基于IGS台网观测的2001—2008年赤道电离异常的强度和半球不对称特征

赤道电离异常（Equatorial Ionization Anomaly,EIA）是低纬电离层中的一个重要现象.本文基于IGS台网提供的2001—2008年期间的电离层总电子含量（Total Electron Content,TEC）数据,分析了120°E区的EIA强度和磁南北半球不对称性在磁平静时期的变化特征,包括对地方时、季节和太阳活动的依赖.本文结果表明,（1）EIA强度表现出显著的随地方时和季节的变化特征.EIA强度在0200LT和2000LT附近分别出现一个极值,且2000LT附近的EIA强度更大;EIA强度通常在春/秋季较大,在夏/冬季较小,且冬季要大于夏季.（2）EIA南北半球不对称也表现出随地方时和季节变化特征.EIA半球不对称在0200LT和2000-2200LT附近分别出现一个极值;EIA半球不对称的季节变化特征还依赖于太阳活动,太阳活动高年期间,EIA半球不对称通常在春/秋季更显著;太阳活动低年期间,EIA半球不对称通常在冬季更显著.（3）EIA强度和半球不对称性的逐日变化和月变化表现出对太阳活动存在一定的依赖,但依赖性并不显著.2000LT（0200LT）附近的EIA强度的月变化与太阳活动整体呈正（负）相关,而2200LT（0200LT）附近的EIA半球不对称的月变化与太阳活动整体呈负（负）相关.（4）影响EIA强度变化的主要因素可归于纬圈电场和中性风场;影响EIA半球不对称变化的主要因素可归因为子午中性风场.

     

The coupling instability of Rossby and topographic Rossby waves in the equatorial area

Before the 1980s, El Ni?o was believed as the sea surface warming along the coast of Peru in South America. As the positive anomaly strengths, the warm water expands westward along the equator to form large area of anomalous high sea surface temperature. Rasmusson and Carpenter (1982) summarized the de-velopment process of the sea surface warm water and the corresponding wind field[1] during ENSO cylce. However, this canonical El Ni?o was questioned by 1982-1983 warm episode and later dat…     

中国东部西南低空急流日变化特征及其机制

本文利用Final Global Data Assimilation System (FNL) 6小时再分析数据集分析了西南低空急流的日变化特征及其影响因子,结果表明:西南低空急流具有明显的日变化特征,在夜间和早晨(02LST,08LST)中国东南大部分地区急流发生频率较高,而在白天和傍晚(14LST,20LST)低空急流发生频率较低.经向地转风分量在一天内基本保持稳定,经向非地转分量在02LST最强,占实际风场强度50%以上,而在14LST和20LST,经向风场近似满足地转平衡.对风场非定常性、风速在流动方向上的非均匀性、流线弯曲和大气斜压性产生的地转偏差的分析结果表明,经向非地转风的日变化主要是由局地变压、水平风场涡度、垂直运动和温度梯度的日变化产生,副热带高压强度和位置的变化、青藏高原大地形加热效应和昼夜间海陆热力性质差异是造成经向非地转风夜间加强的重要原因.在中国东部地区,风速在流动方向的非均匀性虽然有利于非地转风的产生,但其没有明显的日变化,不是经向非地转风在夜间加强的主要原因.     

中国东部西南低空急流日变化特征及其机制

本文利用Final Global Data Assimilation System (FNL) 6小时再分析数据集分析了西南低空急流的日变化特征及其影响因子,结果表明:西南低空急流具有明显的日变化特征,在夜间和早晨(02LST,08LST)中国东南大部分地区急流发生频率较高,而在白天和傍晚(14LST,20LST)低空急流发生频率较低.经向地转风分量在一天内基本保持稳定,经向非地转分量在02LST最强,占实际风场强度50%以上,而在14LST和20LST,经向风场近似满足地转平衡.对风场非定常性、风速在流动方向上的非均匀性、流线弯曲和大气斜压性产生的地转偏差的分析结果表明,经向非地转风的日变化主要是由局地变压、水平风场涡度、垂直运动和温度梯度的日变化产生,副热带高压强度和位置的变化、青藏高原大地形加热效应和昼夜间海陆热力性质差异是造成经向非地转风夜间加强的重要原因.在中国东部地区,风速在流动方向的非均匀性虽然有利于非地转风的产生,但其没有明显的日变化,不是经向非地转风在夜间加强的主要原因.     

Lateral migration,thermoluminescence chronology and colour variation of longitudinal dunes near Birdsville in the Simpson Desert,central Australia

The longitudinal dunes of the Simpson Desert, in the vicinity of Birdsville, have been reworked largely during the Holocene from dunes deposited up to 80000 years ago or earlier. The widespread asymmetry of these roughly northward-trending dunes, with steeper eastern faces and more gentle western faces, supports wind-rose data showing sand-transporting winds from the southwest obliquely intersecting the dunes. While this suggests a change in the wind pattern since the dune field was oriented, it does not indicate that the dunes are necessarily shifting leeward (eastward) as a consequence. It is hypothesized that the direction of migration is controlled by the extent to which the dunes are vegetated. Relatively well-vegetated dunes can accrete sand on their gentle stoss slopes and erode on their lee slopes causing them to shift westward and hence obliquely into the wind, a condition that probably prevails in wetter regions and during episodes of relatively humid climate. In contrast, in very dry areas or during arid phases, sand can move unimpeded up a sparsely vegetated stoss face and over the crest to form an avalanche or slip face on the lee side, thereby causing the dunes to shift eastward. Despite evidence that longitudinal dune crests can shift laterally to some extent, the dunes in the western part of the Simpson Desert have not migrated, either westward or eastward, more than 100m or so from their Pleistocene cores. Aeolian transport and partial or complete removal of iron cutans from around quartz grains results in dunes of widely varying colour yet of similar age.