Millstone地区垂直等效风场的气候学变化

Climatology of the Effective Winds at Millstone

基于1976—2006年美国Millstone非相干散射雷达的电离层观测数据,分析了美国Millstone地区不同太阳活动条件下,包括中性风场和电场漂移共同贡献的垂直等效风场的变化特征.结果表明,Millstone地区的垂直等效风场表现出比较明显的周日、太阳活动和季节变化特征.晚间垂直向上的等效风较强,白天等效风较弱,甚至接近于零.在不同太阳活动和季节变化条件下,Millstone地区的等效风场都表现出类似的周日变化特征,低太阳活动条件下,晚间表现出较大的向上漂移.这种周日变化和太阳活动变化特征与Millstone地区受到极区热源驱动大气循环的调制以及离子曳力的增减有关.春季和秋季有相似的幅度和相位变化趋势,表现出分点对称性;冬季晚间向上漂移比夏季弱,且随着太阳活动增强,差异更加明显,这再次体现了极区热源驱动大气循环的影响.

The ionospheric data observed with the Millstone Hill incoherent scatter radar from 1976 to 2006 were analyzed to deduce the Vertical Equivalent Winds （VEW）, which are attributed to both the contributions of neutral wind and electric drifts under different conditions. The results suggest that the Millstone VEW show obvious diurnal, solar activity and seasonal variations. During the nighttime, Millstone VEW are mostly upward and strong, while the daytime VEW are relatively weak, even close to zero. This diurnal variation of Millstone VEW behaves similarly under different solar activities and seasons. Under solar low condition, the nighttime upward VEW are stronger than higher solar activity conditions. These characteristics of the diurnal and solar activity variations of Millstone VEW are closely related to the aurorally driven high-latitude circulation cell and ion drag. The equinoctial symmetry appears for the magnitudes and phase tendencies in spring and autunm are similar. The nighttime drift in winter is relatively weaker than that in summer, and this difference tends to be greater with the increasing solar activity, which shows the important effect of aurorally driven circulation on Millstone Hill ionosphere again. The VEW derived by three methods, i.e., by ion line-of-sight velocities of the F region ionization, servo theory and Ref.[1]＇s method are compared. The magnitudes and phase tendencies of the VEW derived by different methods are accorded well with each other at nighttime, while there are larger differences during daytime; this is possibly caused by that the servo constant adopted by the latter two methods plays an important role in modulating the daytime VEW, which has been discussed previously.