Fig. 3

The contribution of WN1–WN4 to the longitudinal structures in four seasons at three latitudes (\(15^\circ \, \text {N}\), \(25^\circ \, \text {N}\), and \(35^\circ \, \text {N}\)) from 100 to 300 km. Blue, orange, yellow and purple lines represent WN1, WN2, WN3 and WN4, respectively. a–m Represent the contribution of WN1–WN4 to the longitudinal structure at \(15^\circ \, \text {N}\), \(25^\circ \, \text {N}\) and \(35^\circ \, \text {N}\) in spring summer, autumn and winter, respectively