Comparison of Thermospheric Density Between GUVI Dayside Limb Data and CHAMP Satellite Observations: Based on Empirical Model

et al. 2020

Space Weather

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We define a new thermospheric concept, the reference heights of O/N 2 , referring to a series of thermospheric heights corresponding to the fixed ratios of O to N 2 number density. Here, based on Global Ultraviolet Imager (GUVI) limb measurement, we compare O/N 2 column density ratio (∑O/N 2 ) and the reference heights of O/N 2 . We choose the transition height of O and N 2 (transition height hereafter), a special reference height at which O number density is equal to N 2 number density, to verify the connection with ∑O/N 2 during geomagnetically quiet periods. It is found that transition height and ∑O/N 2 have noticeable negative correlation with correlation coefficient of -0.887. An empirical model of transition height (O/N 2 model hereafter) is established based on nonlinear least-squares-fitting method. The considerable correlation (greater than 0.96), insignificant errors (less than 4%) and the great influencing weight of ∑O/N 2 to reference heights indicate the validity of O/N 2 model and the existence of quantitative relation between ∑O/N 2 and transition height. Besides, it is verified that the similar quantitative relation also exists between ∑O/N 2 and reference heights of other O/N 2 values. Namely, using the O/N 2 model coefficients, we can roughly get the whole altitude profiles of O/N 2 within 6% precision for any given ∑O/N 2 .

Section: Introductionmentioning

confidence: 71%

Section: Appendix B: Guvi Data Volume In Fixed Binsmentioning

confidence: 99%

mentioning

confidence: 99%

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Comparison of Reference Heights of O/N₂ and ∑O/N₂ Based on GUVI Dayside Limb Measurement

et al. 2020

Space Weather

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“…Third, the above decomposed EOFs are further fitted to the dayside total mass density from the GUVI EM model (ρ E ),

ρ^{E} ()(,,,,, doy, φ, λ, {LT}_{normald}, h) = \sum_{normalk = 1}^{N} A_{k}^{E} ()(,,, doy, φ, λ) \cdot E_{k}^{M} ()(,, {LT}_{normald}, h),

where N is the truncation order of the EOFs and is set to 5, which is explained above. LT d represent the dayside time, 7–11 LT and 14–18 LT, namelythe time period that has adequate GUVI data volume described in the previous work (Yu et al, ). ρ E is the corresponding dayside results of GUVI EM density.…”

Section: Methodsmentioning

confidence: 99%

“…However, the uneven coverage of GUVI data volume and observation gaps especially in nightside limit the application of GUVI limb observations for the thermospheric structures and their variability studies (Yu et al, ). Therefore, making better use of the sparse GUVI limb altitude profiles are the developmental imperative of thermosphere study.…”

Section: Introductionmentioning

confidence: 99%

A New Method for Deriving the Nightside Thermospheric Density Based on GUVI Dayside Limb Observations

et al. 2020

Space Weather

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We propose a new method to derive the nightside thermospheric density by extending Global Ultraviolet Imager (GUVI) dayside limb observations using empirical orthogonal function (EOF) analysis. First, we acquire the GUVI dayside total mass density during 2002–2005 to construct a preliminary empirical model (EM). Simultaneously, we decompose the background thermospheric density from U.S. Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar Extended model into different EOFs. The decomposed EOFs are then used to fit the continuous density from EM, to develop a new nightside extended model (NEM). The preliminary EM and developed NEM are further evaluated with Challenging Minisatellite Payload (CHAMP) satellite observations. Higher correlation coefficients and smaller relative standard errors between CHAMP observations and the NEM results are obtained than those between CHAMP observations and the EM results, and the NEM results are in good agreement with the CHAMP observations in time series during both daytime and nighttime, which all prove the NEM method is effective to the reproduction and extension of GUVI original dayside observations. Furthermore, the NEM reveals two typical seasonal variation features, the semiannual variation and equinoctial asymmetry of thermospheric density. The model provides an effective tool to derive the nightside thermospheric density and explore the thermospheric intrinsic structure, and needs the further development to achieve more widespread application of the thermosphere.

Seasonal Variation of O/N₂ on Different Pressure Levels From GUVI Limb Measurements

et al. 2020

JGR Space Physics

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The ratio of O number density to N2 number density (O/N2) is an important parameter to describe thermospheric composition changes and its effects on the ionosphere. Based on Global Ultraviolet Imager (GUVI) limb measurements, we investigate the seasonal behaviors of O/N2 volume density ratio on different constant pressure levels during geomagnetically quiet periods. The global O/N2 shows the prominent annual and semiannual variations with solar activity dependence. An empirical model considering the solar activity and annual/semiannual variations can reasonably reproduce the original O/N2. The modeled O/N2 captures the hemispheric asymmetry of the annual variations in both length and magnitude. Global maps of the seasonal harmonic components of the modeled O/N2 indicate the latitudinal and altitudinal dependence of O/N2 seasonal variations. The annual component dominates over the semiannual component at mid‐latitudes, but it is smaller than the semiannual component at low latitudes. In the Northern Hemisphere, and at low geomagnetic latitudes of the Southern Hemisphere, the annual component peaks around December solstice at all altitudes, whereas at middle geomagnetic latitudes of the Southern Hemisphere, it peaks around June solstice. The semiannual component peaks at the equinoxes in almost all regions over the globe at all altitudes. The annual and semiannual amplitudes both increase with altitude. In addition, O/N2 annual variations and solar activity dependence are more influenced by the thermal expansion and contraction.