Four Martian years of nightside upper thermospheric mass densities derived from electron reflectometry: Method extension and comparison with GCM simulations
Four Martian years of nightside upper thermospheric mass densities derived from electron reflectometry: Method extension and comparison with GCM simulations
复制标题
DOI：
10.1029/2009je003529
复制
发表时间：
2009-09
影响因子：
--
通讯作者：
R. Lillis;S. Bougher;F. González-Galindo;F. Forget;Michael D. Smith;P. Chamberlin
中科院分区：
文献类型：
--
作者：
R. Lillis;S. Bougher;F. González-Galindo;F. Forget;Michael D. Smith;P. Chamberlin
外底（~160-200公里）附近的火星上层热层的长期动态仍然不太受数据的约束。电子反射仪（ER）提供了一种方法，从电子损失锥，中性质量密度在这些高度在夜半球。由于火星全球勘测者电子反射计不是为此目的设计的，因此个别测量的不确定性很大，因此只能在数周或更长的时间尺度上确定上层热层可变性的特征。从1999年4月到2006年11月，在当地时间凌晨2点和185公里的高度进行了密度测量，时间跨度约为4个火星年。我们观察到一个较弱的相关性较低的大气尘埃活动比在低热层和太阳EUV通量的相关性较弱，比在昼侧外逸层观察到的。季节性重复的特征是：（1）夜间热层随日心距离的整体扩张/收缩，（2）远日点冬季极的密度远低于近日点冬季极，（3）南半球远日点的局部密度最大值很短。还观察到年际差异，特别是，在南部冬季的低密度的间隔逐渐晚于太阳EUV通量从太阳最大值到太阳最小值的减少。结果与火星热层大气环流模型和LMD火星全球环流大气模型框架的预测进行了比较，LS = 90°-180°，它们通常分别低估和高估中性密度。这种分歧反映了模拟夜侧动力和冷却过程的困难。版权所有2010年由美国地球物理联盟。
The long-term dynamics of the Martian upper thermosphere near the exobase (~160-200 km) are still relatively poorly constrained by data. Electron reflectometry (ER) provides a way to derive, from electron loss cones, neutral mass densities at these altitudes in the night hemisphere. Because the Mars Global Surveyor Electron Reflectometer was not designed for this purpose, uncertainties in individual measurements are large and thus upper thermospheric variability can be characterized only on time scales of weeks or longer. Density measurements are presented at 2 A.M. local time and 185 km altitude, from April 1999 until November 2006, spanning ~4 Martian years. We observe a weaker correlation with lower atmospheric dust activity than is seen in the lower thermosphere and a weaker correlation with solar EUV flux than is observed in the dayside exosphere. Seasonally repeating features are (1) overall expansion/contraction of the nighttime thermosphere with heliocentric distance, (2) much lower densities at the aphelion winter pole compared to the perihelion winter pole, and (3) a short-lived local density maximum at aphelion in the southern hemisphere. Interannual differences are also observed; in particular, the interval of low densities in the southern winter occurs progressively later as solar EUV flux decreases from solar maximum to solar minimum. Results are compared with predictions from the Mars Thermosphere General Circulation Model and LMD Mars Global Circulation atmospheric model frameworks for Ls = 90°-180°, which generally underestimate and overestimate neutral densities, respectively. This disagreement reflects the difficulty in simulating nightside dynamical and cooling processes. Copyright 2010 by the American Geophysical Union.