An EOFs study of thermospheric nitric oxide flux based on TIEGCM simulations

Using eigen analysis, the hourly NO infrared radiative flux (NOF) during 2002-2015 obtained from TIEGCM simulations are decomposed into four empirical orthogonal functions (EOFs). The first mode of variability is significantly associated with Kp and F10.7, implying that geomagnetic activity and solar extreme ultraviolet flux make a strong contribution to NOF variability.

EOF 2 shows an antisymmetry between the northern and southern hemispheres and has a very strong correlation with the solar declination angle, suggesting that annual and seasonal variations of thermospheric temperature and composition play dominant roles in EOF 2. Lacking a strong correlation with solar and/or geomagnetic indices, EOF 3 may be associated with thermospheric circulation driven by the offsets between the geomagnetic and geographic poles.