5. Conclusions

[25]  The main results of our morphological analysis can be summarized as follows:

[26]  1. An analysis of all available N_mF2 observations over 26 Northern Hemisphere high-to-lower latitude ionosonde stations during geomagnetically quiet periods has revealed both positive and negative Q disturbances, their amplitude being comparable to moderate F2 -layer storm effects resulted from increased geomagnetic activity.

[27]  2. Positive disturbances are more numerous than negative ones at all latitudes and at any level of solar activity. Both types of Q disturbances are more numerous (by 2 times) during solar minimum. The percentage of long-duration (both negative and positive) Q disturbances increases with latitude.

[28]  3. Both types of disturbances are the most frequent in the evening and night-early morning LT sectors and they are rare during daytime.

[29]  4. Winter season (November-January) is the most preferable for negative Q disturbances. The occurrence probability is small for other seasons. The seasonal variation pattern for positive Q disturbance is more complicated and less systematic, telling us that some processes contribute to their formation and their efficiency varies with geophysical conditions.

[30]  5. Spatial variation pattern is different for positive and negative Q disturbances. The amplitude of positive disturbance increases with latitude, while it is practically latitudinal-independent for negative perturbations. Longitudinal variations of the amplitude for both types of disturbances look like a planetary wave with the minimal deviations in the American and the maximal deviations in the European sectors. The position of the extremes varies from day-to-day keeping linked to the two longitudinal sectors. In general, the American sector looks less disturbed. Large longitudinal gradients in N_mF2 are related with the front of such waves.