Exospheric Temperature Measured by NASA-GOLD Under Low Solar Activity
Comparison With Other Data Sets
Jaeheung Park (Korea University of Science and Technology, Korea Astronomy and Space Science Institute)
Joseph S. Evans (Computational Physics Inc.)
Richard W. Eastes (University of Colorado - Boulder)
Jerry D. Lumpe (Computational Physics Inc.)
Jose van den Ijssel (TU Delft - Aerospace Engineering)
Christoph R. Englert (Naval Research Laboratory)
Michael H. Stevens (Naval Research Laboratory)
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Abstract
Exospheric temperature is one of the key parameters in constructing thermospheric models and has been extensively studied with in situ observations and remote sensing. The Global-scale Observations of the Limb and Disk (GOLD) at a geosynchronous vantage point provides dayglow limb images for two longitude sectors, from which we can estimate the terrestrial exospheric temperature since 2018. In this paper, we investigate climatological behavior of the exospheric temperature measured by GOLD. The temperature has positive correlations with solar and geomagnetic activity and exhibits a morning-afternoon asymmetry, both of which agree with previous studies. We have found that the arithmetic sum of F10.7 (solar) and Ap (geomagnetic) indices is highly correlated with the exospheric temperature, explaining ∼64% of the day-to-day variability. Furthermore, the exospheric temperature has good correlation with thermospheric parameters (e.g., neutral temperature, O2 density, and NO emission index) sampled at various heights above ∼130 km, in spite of the well-known thermal gradient below ∼200 km. However, thermospheric temperature at altitudes around 100 km is not well correlated with the GOLD exospheric temperature. The result implies that effects other than thermospheric heating by solar Extreme Ultraviolet and geomagnetic activity take control below a threshold altitude that exists between ∼100 and ∼130 km.
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