O/N ₂ changes during 1--4 October 2002 storms: IMAGE SI-13 and TIMED/GUVI observations

Thermospheric O/N2 column density ratios referenced at a N2 column density of 1017 cm-2 are obtained using the IMAGE SI-13 and TIMED/GUVI far-ultraviolet (FUV) dayglow data, AURIC simulation results, and MSIS86 model. Each of the magnetic storms occurring during a 4-day period (1\textendash4 October 2002) caused significant O/N2 depletion that was detected by both of the IMAGE SI-13 and GUVI instruments. The depletion extended down to latitudes of 10\textdegree and -5\textdegree in the Northern and Southern Hemispheres, respectively. Simultaneous measurements show an excellent agreement between the SI-13 and GUVI O/N2 on both global and local scales. The IMAGE SI-13 O/N2 data provide direct optical evidence that the O/N2 depletion corotates with the Earth. The GUVI O/N2 indicate the depletion in both of the hemispheres is not symmetric owing to the seasonal effect and differences in heating and convection induced winds. Both the IMAGE SI-13 and GUVI O/N2 maps also provide a good opportunity for future modeling efforts.