New method in computer simulations of electron and ion densities and temperatures in the plasmasphere and low-latitude ionosphere
New method in computer simulations of electron and ion densities and temperatures in the plasmasphere and low-latitude ionosphere
复制标题
DOI：
10.5194/angeo-21-1601-2003
复制
发表时间：
2003-07
影响因子：
1.9
通讯作者：
A. Pavlov
中科院分区：
文献类型：
--
作者：
A. Pavlov
本文发展了一个新的地球中低纬电离层和等离子体层的理论模型。新模型在电离层和等离子体层模拟中使用了一种新的方法，该方法是模型模拟中的欧拉方法和拉格朗日方法的组合。电子和离子的连续性和能量方程在拉格朗日参考系中求解，该参考系与等离子体的单个包裹一起移动，其中局部等离子体漂移速度垂直于磁场和电场。结果表明，在这种拉格朗日坐标系下，只求解了一维含时电子和离子的连续性方程和能量方程。该方法利用空间坐标固定的欧拉计算网格，在每个时间步选择等离子体包的集合，使所有等离子体包在下一个时间步到达规则间隔的欧拉计算网格的网格线之间的点。通过插值得到了欧拉计算网格上的电子、离子密度Ne、Ni和温度Te、Ti的解。在新模型中，导出了确定电离层等离子体垂直于磁力线的轨迹的方程，并考虑了磁力线在电离层等离子体中的“冻结”。我们提出了一个模拟的NmF 2和hmF 2和NmF 2和hmF 2之间的比较，在异常峰和接近地磁赤道的同时，由万卡约，奇克拉约，塔拉拉，波哥大，巴拿马和波多黎各电离层探测器在1957年10月7日地磁平静期在太阳极大。模式计算表明，有必要修正Scherliess和Fe-jer（1999）给出的赤道向上E dad B漂移速度在平静日间春分条件下太阳活动极大期的模式当地时间依赖性。在计算的Ni，Ne，Te，和Ti的NRLMSISE- 00和MSIS-86中性温度和密度之间的差异，从EUV 97和EUVAC太阳通量之间的差异进行评估。从10月7日16：12 UT到23：12 UT，NRLMSISE-00模型（O）/（N2）比值降低了1.7-2.1倍，使模拟和测量的NmF 2和hmF 2达到令人满意的一致。结果表明，电离层测站上空Te、Ti的日间峰值是中性温度日间峰值的结果。我们的计算表明，在F2区高度的Te值变得几乎独立于沿着磁场线以上的Huancayo，奇克拉约，和Talara电离层站的电子热流，因为近水平的磁场抑制了电子的热流。地磁纬度的增加导致了电子热流沿着磁力线对Te的影响增强。结果表明，在日出时，光电子对周围电子的加热迅速，由于夜间电子密度小于白天，而早晨电子冷却又小于白天，因此电子温度与中性温度的差异会增大。这扩大了赤道附近离子温度低于电子温度的高度区域，并导致电离层测站上方hmF 2高度处的日出电子温度峰值。在日出时的突然增加之后，Te的值减小，这是由于热电子冷却速率的增加和电子热流沿着磁力线的相对作用相对于热电子冷却的减小而引起的电子密度的增加。这些物理过程导致创建的日出电子温度峰值以上的电离层测站在hmF 2高度计算。我们发现热电子的主要冷却速率是电子-离子库仑碰撞、N2和O2的振动激发以及N2的转动激发。结果表明，由于振动激发的N_2和O_2引起O ~+（4S）离子损失率的增加，导致计算的NmF_2减小1.06-1.44倍，计算的hmF_2增大，在地磁纬度-30 ~+30之间的低纬电离层中达到最大值32 km。
A new theoretical model of the Earth's low- and mid-latitude ionosphere and plasmasphere has been devel- oped. The new model uses a new method in ionospheric and plasmaspheric simulations which is a combination of the Eu- lerian and Lagrangian approaches in model simulations. The electron and ion continuity and energy equations are solved in a Lagrangian frame of reference which moves with an in- dividual parcel of plasma with the local plasma drift velocity perpendicular to the magnetic and electric fields. As a re- sult, only the time-dependent, one-dimension electron and ion continuity and energy equations are solved in this La- grangian frame of reference. The new method makes use of an Eulerian computational grid which is fixed in space co- ordinates and chooses the set of the plasma parcels at every time step, so that all the plasma parcels arrive at points which are located between grid lines of the regularly spaced Eule- rian computational grid at the next time step. The solution values of electron and ion densities Ne and Ni and temper- atures Te and Ti at the Eulerian computational grid are ob- tained by interpolation. Equations which determine the tra- jectory of the ionospheric plasma perpendicular to magnetic field lines and take into account that magnetic field lines are "frozen" in the ionospheric plasma are derived and included in the new model. We have presented a comparison between the modeled NmF2 and hmF2 and NmF2 and hmF2 which were observed at the anomaly crest and close to the geomagnetic equator simultaneously by the Huancayo, Chiclayo, Talara, Bogota, Panama, and Puerto Rico ionospheric sounders during the 7 October 1957 geomagnetically quiet time period at solar maximum. The model calculations show that there is a need to revise the model local time dependence of the equatorial upward E ◊ B drift velocity given by Scherliess and Fe- jer (1999) at solar maximum during quiet daytime equinox conditions. Uncertainties in the calculated Ni , Ne, Te, and Ti resulting from the difference between the NRLMSISE- 00 and MSIS-86 neutral temperatures and densities and from the difference between the EUV97 and EUVAC solar fluxes are evaluated. The decrease in the NRLMSISE-00 model (O)/(N2) ratio by a factor of 1.7-2.1 from 16:12 UT to 23:12 UT on 7 October brings the modeled and measured NmF2 and hmF2 into satisfactory agreement. It is shown that the daytime peak values in Te, and Ti above the ionosonde stations result from the daytime peak in the neutral tem- perature. Our calculations show that the value of Te at F2- region altitudes becomes almost independent of the electron heat flow along the magnetic field line above the Huancayo, Chiclayo, and Talara ionosonde stations, because the near- horizontal magnetic field inhibits the heat flow of electrons. The increase in geomagnetic latitude leads to the increase in the effects of the electron heat flow along the magnetic field line on Te. It is found that at sunrise, there is a rapid heat- ing of the ambient electrons by photoelectrons and the differ- ence between the electron and neutral temperatures could be increased because nighttime electron densities are less than those by day, and the electron cooling during morning con- ditions is less than that by day. This expands the altitude region at which the ion temperature is less than the electron temperature near the equator and leads to the sunrise electron temperature peaks at hmF2 altitudes above the ionosonde sta- tions. After the abrupt increase at sunrise, the value of Te de- creases, owing to the increasing electron density due to the increase in the cooling rate of thermal electrons and due to the decrease in the relative role of the electron heat flow along the magnetic field line in comparison with cooling of ther- mal electrons. These physical processes lead to the creation of sunrise electron temperature peaks which are calculated above the ionosonde stations at hmF2 altitudes. We found that the main cooling rates of thermal electrons are electron- ion Coulomb collisions, vibrational excitation of N2 and O2, and rotational excitation of N2. It is shown that the increase in the loss rate of O + ( 4 S) ions due to the vibrational excited N2 and O2 leads to the decrease in the calculated NmF2 by a factor of 1.06-1.44 and to the increase in the calculated hmF2, up to the maximum value of 32 km in the low-latitude ionosphere between -30 and +30 of the geomagnetic lati-