# Study on the Thermospheric Density Distribution Pattern during Geomagnetic Activity
## 3 Results
### Analysis of the Temporal Distribution of Atmospheric Density during Storms  
We aim to analyze the temporal distribution of the thermospheric atmosphere density before and after a geomagnetic storm. Therefore, we obtained the measured atmospheric \begin{table}
\begin{tabular}{c c c} \hline
**Order Number** & **The Lower Limit of Error** & **The Upper Limit of Error** \\ \hline
1 & 1.84071 \(\times\) 10\({}^{-21}\) & 2.97603 \(\times\) 10\({}^{-21}\) \\
2 & 2.52995 \(\times\) 10\({}^{-23}\) & 4.09037 \(\times\) 10\({}^{-23}\) \\
3 & 7.81714 \(\times\) 10\({}^{-24}\) & 1.26386 \(\times\) 10\({}^{-23}\) \\
4 & 2.57967 \(\times\) 10\({}^{-24}\) & 4.17076 \(\times\) 10\({}^{-24}\) \\
5 & 6.23159 \(\times\) 10\({}^{-25}\) & 1.00751 \(\times\) 10\({}^{-24}\) \\ \hline \end{tabular}
\end{table} 
Table 2: Error upper and lower limits of the first five order eigenvector fields of EOF. density data of the three geomagnetic storms the day before the storm, the day of the storm, and the day after. The EOF daily spatiotemporal decomposition was performed for each data group separately, and only the first-order time coefficients after the decomposition were used. Figure 4 shows the first-order time coefficients of the day before, on, and after the three geomagnetic storms. The figures are furtherly separated into daytime and nighttime sub-figures for better presentation. Figure 4: Time coefficients of the day before, on, and after the three geomagnetic storms. (**a**) Time coefficient of the daytime area on 23 June 2015; (**b**) nighttime coefficient on 23 June 2015; (**c**) daytime time coefficient on 7 October 2015; (**d**) nighttime coefficient on 7 October 2015; (**e**) daytime time coefficient on 8 September 2017; (**f**) nighttime coefficient on 8 September 2017. Data processing shows that the atmospheric density distribution in the daytime area differs from that in the nighttime because of radiation heating. Therefore, in the following research process, the atmospheric density in the daytime and the atmospheric density in the nighttime are processed separately. That is to say, the daily data of atmospheric density will be divided into two situations: daytime and nighttime. The comparison between daytime and nighttime in Figure 4 shows the difference in the time coefficient. The EOF time coefficients of daytime and nighttime are very similar, but amplitude differences exist. In the daytime coefficients, the time coefficients of the day before the geomagnetic storm and the day after the geomagnetic storm are greater than those of the day before the geomagnetic storm, the day after the geomagnetic storm, and the day after the geomagnetic storm in the corresponding nighttime. In other words, when the thermosphere is in the daytime, its density is significantly higher than in the dark region. This phenomenon is true both before and after the geomagnetic storm. The comparison in Figure 4 also shows the time coefficient's difference before and after the geomagnetic storm. The time coefficient curve of the day before the occurrence of the geomagnetic storm (blue), the time coefficient curve of the day of the occurrence of the geomagnetic storm (red), and the time coefficient curve of the day after the occurrence of the geomagnetic storm (yellow) have obvious differences. The day's curve is the most stable before the geomagnetic storm's occurrence. The time coefficient of the day before the geomagnetic storm is similar to that during the occurrence. The difference is that the time coefficient value on the day of the occurrence peaks at the end. The peak value of the geomagnetic storm's red curve on 23 June 2015 is the steepest and most apparent. The curve after the geomagnetic storm is at the top of the three geomagnetic storm events. That is to say, the value of the first-order time coefficient of the day after the geomagnetic storm is the largest. The first-order time coefficient's peak value after the geomagnetic storm can reach 2-3 times that before the geomagnetic storm. All of them will fall back significantly.