Solar flux influence on the accuracy of plasma density measured by the spaceborne Langmuir probe
In this study,we performed a detailed comprehensive comparison of plasma density measured by Langmuir Probes(LP)on board satellites including CHAMP and Swarm C and plasma density measurements by Incoherent Scattering Radar(ISR)in Arecibo and Jicamarca.Besides,we also make a further reference using density data from GRACE K Band Ranging system.Generally,the plasma density datasets of CHAMP,GRACE and Swarm C show a good linear regression with electron density measurement of ISRs.The correlation coefficient of these 3 satellites are 0.96,0.97,0.96.However,in contrast to Grace and CHAMP dataset,the plasma density derived by Swarm LP shows an additional dependence on the solar flux comparing to ISR measurement.Combined with the changes in altitude and solar flux at which the three satellites were located,we suggest that the solar flux dependence of LP-derived plasma density is related to the ion composition change at altitude of satellite orbit,which is unconsidered in Swarm LP processing algorithm.An overestimation appears while more light ions(eg.H+)diffusing down from plasmasphere to Swarm altitude in low solar activity years.This effect mainly occurs during years of low solar activity and is significantly greater on the nightside than that on the dayside.Different from Swarm orbit,height of CHAMP orbit gets down(from 450 km to 320 km)and matches the tendency of solar flux decrease,keeping the ion composition stable on CHAMP orbit and the plasma density measurements haven't shown dependence on solar activity.In addition,although the GRACE satellite maintained its orbital altitude around 480 km during the 2008-2009 very low solar activity year,its measurements did not depend on the ion composition around the satellite.Therefore the bias between GRACE measurements and ISR observations didn't show a significant solar activity dependence.These results demonstrate that the top ionospheric plasma density based on the GRACE KBR provides a good reference for other LEO satellites based on Langmuir probe measurements,and contributes to the on-orbit calibration of plasma density measurements for other satellites.
Langmuir ProbePlasma density measurementIonospheric electron density
万方数据
维普
