# Evaluation of the Mid-Latitude Ionospheric trough Using GRACE Data
## 4 Conclusions  
In this paper, we presented a statistical evaluation of the main ionospheric trough in the northern and southern hemispheres from 2002 to 2015 using KBR electron density measurements from the GRACE satellite mission. Our database of MIT profiles contains 16,212 profiles for the northern hemisphere and 28,721 profiles for the southern hemisphere. The evaluation was performed using MIT parameters, such as the trough minimum position,  
Figure 20: The occurrence of the trough depending on space weather indices for the northern and southern hemispheres. width, depth, and occurrence in relation to geographical location, solar cycle, seasons, magnetic local time, and space weather indices. We obtained comprehensive results, showing that:  
1. The trough minimum location is distributed around the magnetic north and south poles, forming an ellipsoid;
2. The trough location moves poleward under low-solar-activity conditions and equatorward under high-solar-activity conditions in both hemispheres;
3. The occurrence probability of the MIT depends on solar activity. The occurrence of the trough increases with increased F10.7 values. Furthermore, the position of the MIT changes depending on solar activity, moving poleward under low-solar-activity conditions and equatorward under high-solar-activity conditions in both hemispheres; however, this dependency is more prominent in the northern hemisphere than in the southern hemisphere. The trough depth increases with increased in F10.7 values;
4. Seasonal dependency of MIT is more pronounced in the northern hemisphere than in the southern hemisphere. The MIT occurs more often in winter months (Nov-Feb) and equinoxes than in summer (May-Aug) months. The trough is deeper during local winter months in the southern hemisphere compared to summer months, whereas the trough width exhibits opposite behavior in the northern hemisphere. The MIT width varies from 8 to 10\({}^{\circ}\) in the northern hemisphere and from 5 to 7\({}^{\circ}\) in the southern hemisphere. The trough minimum moves poleward during winter months and equatorward during summer months;
5. The mean trough widths are smaller in the poleward direction, indicating a sharper slope. The mean trough width is larger in the equatorward direction, showing a less sharp slope;
6. The MIT shows a clear correlation with the SYM-H index. In the northern hemisphere, this dependence is more prominent than in the southern hemisphere. With decreasing SYM-H index values (indicating storm conditions), the trough moves equatorward narrows and deepens with decreasing SYM-H index values;
7. A comparison with the high-cadence Hp30 index shows a correlation with the MIT location, moving equatorward with increased HP30 values. In the northern hemisphere, this dependence is more prominent than in the southern hemisphere. Furthermore, the trough widens with decreasing Hp30 index values, whereas depth shows an opposite dependence, i.e., the trough deepens increasing Hp30 index values;
8. Trough occurrences increase with decreasing geomagnetic disturbance index SYM-H values;
9. MIT occurrences positively correlate with Hp30, f10.7, flow pressure, and solar wind plasma speed indices. Our study confirms previous MIT investigations and contributes new results with respect to the dependence of the MIT's on geophysical conditions. In this study, we presented, for the first time, the ellipse distribution for the northern and southern hemispheres of the mean position of the trough minimum in three seasons. We also elucidated the dependence of the MIT on the flow pressure index and high-resolution indices, such as the SYM-H and Hp30 indices. Moreover, the dependence of MIT occurrence on the space weather indices was investigated. The obtained information with respect to MIT dependency and occurrence probability can be used for MIT model validation, as well as for the development of new MIT models.