利用 CHAMP(CHAllenging Minisatellite Payload)、GRACE-A(Gravity Recovery and Climate Experiment-A)、SWARM-C(The Earth's Magnetic Field and Environment Explorers-C)等3颗极轨卫星的资料,研究360-480 km高层大气密度在低纬度区域的午夜极大值(Midnight Density Maximum,MDM)现象.MDM一般出现在23:00-02:00 LT(Local Time)之间,峰值位置在低纬度15°以内,谷值位置在中纬度35°-45°附近,整体略偏向南半球,振幅约为平均密度的26％.随着高度增大以及太阳辐射水平的增强,MDM振幅呈减小趋势;冬至和夏至日附近的季节效应会减弱MDM振幅,在春秋分日的振幅最大.用3个主流大气模型DTM2000(Drag Temperature Model 2000),NRLMSISE00(US Naval Research Laboratory,Mass Spectrom-eter and Incoherent Scatter radar)和JB2008(Jacchia-Bowman 2008 model)对MDM进行模拟,JB2008没有刻画出MDM现象;另两个模型低估了MDM效应,在360 km和480 km两个高度DTM2000模型的振幅仅为观测的46％和53％,NRLMSISE00模型仅为观测的33％和26％;模型没有准确刻画出MDM与高度、辐射水平和季节的关系.联合3颗卫星的资料,研究了一种基于地理纬度的6阶勒让德多项式,同时融合地方时和高度因素的经验函数,在振幅和相位上可以较好地刻画MDM特征,相关系数达到0.923,可为大气密度模型的修正提供借鉴,服务于低轨道航天器高精度轨道预报.
The Feature Analysis and Modeling of Upper Atmospheric Midnight Density Maximum
The features of upper atmospheric midnight density maximum(MDM)around low geo-graphic latitudes are studied based on neutral mass densities data at altitudes 360-480 km,derived from the accelerometer measurements aboard on the three polar orbiting satellites CHAMP(CHAllenging Minisatellite Payload),GRACE-A(Gravity Recovery and Climate Experiment-A)and SWARM-C(The Earth's Magnetic Field and Environment Explorers-C).The MDM appears during the local times from 23:00 to 02:00 LT,whose peak locates at the low latitudes within 15° and two valleys locate at the mid-dle latitudes between 35° and 45° on both hemispheres separately.The structure of MDM drifts toward the southern hemisphere overall.The MDM's amplitude decreases with increases in altitude and solar radiation level.The seasonal effect weakens the MDM's amplitudes around the summer and winter sol-stices,while the amplitudes around the spring and autumn equinoxes are extremely significant due to the slight seasonal difference between both hemispheres.Three atmospheric density models DTM2000(Drag Temperature Model 2000),NRLMSISE00(Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar Extended atmosphere model)and JB2008(Jacchia-Bowman 2008 model)are used to sim-ulate the MDM along these three satellites'orbits,and compared with the observations.It is found that the JB2008 model is failed to describe the MDM,and the other two models underestimate the MDM's amplitudes at altitudes 360 km and 480 km:the simulated amplitudes by the DTM2000 model are 46％and 53％of the observed amplitudes respectively,and only 33％and 26％for the NRLMSISE00 model.These three models are also failed to depict the MDM's variation with altitude,solar radiation level and seasonal effects.In order to correct the model prediction,a 6th-order Legendre polynomial of geographic latitude,coupled with arguments of local time and altitude,is designed to fit the MDM signals from the three satellites'observations.In terms of amplitude and phase of the MDM,the fitting results agree with the observations very well,and the correlation coefficient is 0.923.It indicates that this empirical polynomial could be helpful to the density model correction and high accuracy prediction of spacecrafts in low Earth orbits.
atmospheric effects:atmosphere density modelmethods:data analysis
NETL
NSTL
万方数据
维普
