<p>A multiple regression model, which defines relationship between two variables, is used to perform a statistical analysis of the relationship between the stratospheric QBO and the neutral density of the D region (N<sub>n</sub>D) at altitudes of 75 km and 90 km for Singapore station. While performing the analysis, the solar maxima and solar minima epochs of the sun for 21st, 22nd and 23rd solar cycles (SCs) are taken into account. Before applying the model for the statistical analysis of the relationship, the stationary of the variables is investigated by using the unit root test. The relationship between the variables is also investigated by using the co-integration test. The relationship between N<sub>n</sub>D measured at 75 km altitude and QBO obtained at altitude of 10 hPa is observed that it is positive for solar maximum epoch at 21st and 23rd SCs and for solar minimum epoch at 21st SC and is negative at the other epochs. The relationship between N<sub>n</sub>D measured at 90 km altitude and QBO is observed to be negative at both the solar maxima expect for solar maximum of 23rd SC and the solar minima epochs. The relationship between variables is positive for both phases (east and west) of QBO. Thus, QBO leads to a statistical change in the N<sub>n</sub>D. It may also give rise to changes on the ion chemistry of the D region.</p>
Seasonal variations of nighttime D-region ionosphere in 2013 solar maximum observed from a low-latitude station
