Validation of electron density and temperature observed by DEMETER

Abstract

Measuring electron density (Ne) and temperature (Te) using a DC Langmuir probe in the ionosphere is very often degraded by the electrode contamination. In order to examine the accuracy of DEMETER observations, we compared DEMETER Ne and Te with several other satellites observations and IRI2012 as reference data. DEMETER Ne and Te show well-known dependencies on the solar irradiance except for the range of F10.7 > 100. However, DEMETER Ne are about 70% lower than those of IRI in day time data and its solar irradiance dependency is consistent with the reference data in night time data. It was confirmed that the negative slope appears in deep solar minimum solar cycle 23/24. DEMETER Te are higher than IRI data by 500-1500 K in day time and by 800 K in night time. The relation between Ne and Te is well defined by a negative slope both in DEMETER and IRI during day time, while such a similarity is not recognized in night time data. DEMETER Te is 700 K higher than IRI Te for the same value of Ne. When Ne is less than 10(4) cm(-3) in night time, significant reductions in DEMETER Te are observed, which is close to expected values. Such discrepancies from the reference data and some peculiar behaviors of DEMETER Te and Ne data necessitate a careful attention in using them in consideration of their data alterations. However, their relative variations and averaged behavior in time contain useful information for scientific studies such as dependencies on solar irradiance and wave-4 longitudinal structure under certain conditions (Ne > 10(4) cm(-3) and F10.7 < 100). (C) 2013 COSPAR. Published by Elsevier Ltd. All rights reserved

The asymmetrical features in electron density during extreme solar minimum

“…Another problem is about the ISL data quality, which was often argued on the photoelectron contamination and data processing techniques (Lebreton et al, 2006;Zhang et al, 2013). According to the study of Kakinami et al (2013), DEMETER Ne was about 70% lower than those of IRI in daytime and its solar irradiance dependency is consistent with the reference data in nighttime. And they thought the relative variations and averaged behavior in time of Ne and Te contained useful information for scientific studies.…”

DC Langmuir Probe for Measurement of Space Plasma: A Brief Review

“…If we fit the theoretical curve to the small number of observed data points, where some of the data points are near space potential and are not on the fitting curve, the result is that T e is higher than the true value. The T e values measured by the DEMETER satellite are 2-3 times higher than what we think is the true T e (Kakinami et al 2013). The high temperature is due to contamination of the electrode.…”

“…However, despite this simplicity, it does not always provide reliable results, especially for T e measurement. Even now we encounter problems in using T e data that are erroneously measured by satellites (Kakinami et al 2013). N e is automatically calculated incorrectly because N e is a function of T e as is related to by the equation I e = S e ·N e ·e (kT e /2πm e ) 1/2 in Langmuir probe theory, in addition to the reduction of probe current caused by electrode contamination.…”

Analysis of the enhanced negative correlation between electron density and electron temperature related to earthquakes

“…Generally, all four seasons' pictures show that at low latitudes N e changes a lot but T e varies little, while at midlatitudes N e and T e are dispersed, especially in June and December. In a previous study, the absolute values of N e and T e from DEMETER were not very accurate, with T e being much higher than it is supposed to be (Kakinami et al, 2013); therefore, in this paper only the relative variations in N e and T e are taken into account. To reveal the relationship of N e and T e at different latitudes, Fig.…”