The occurrence and characteristics of ULF events (f ≈ 10–100 mHz) detected during the night at low latitude (L'Aquila, Italy, λ ≈ 36.3°), during quiet and moderately perturbed magnetospheric conditions, have been examined by means of a long‐term analysis between 1996 and 2012. Clearly defined events (≈8000 on each component) are typically more energetic in H than in D and basically consist of penetrating upstream waves, resonances of local field lines, and Pi2 waves. The global event occurrence shows a strong asymmetry about midnight, with a much higher wave activity before dawn than after dusk: it mostly comes from the intense penetration of upstream waves through the dawn flank of the magnetopause. D events are more frequent in summer and H events more frequent in winter, suggesting a different influence of the ionospheric modification of the downgoing signals. Between f ≈ 30 and 45 mHz, the reversal of the dominant polarization across midnight reveals tailward propagation of penetrating waves. Below f ≈ 25 mHz, intermingled with continuous Pc3 and Pc4 waves, a large fraction of events exhibit Pi2 characteristics: the dominant left‐handed polarization and the switch of the tilt angle of the major axis of the polarization ellipses are consistent with the pattern expected for waves related to the substorm current wedge. A relevant percentage of the power spectra shows a second enhancement above f ≈ 55 mHz, revealing resonance of local field lines also during the night.

A long-term analysis allowed to investigate the occurrence and characteristics of clearly defined ULF events (f ≈ 10-100 mHz) detected during daytime at low-latitude (L'Aquila, Italy; L ≈ 1.6) during quiet and moderately perturbed magnetospheric conditions. Selected events (≈30,000 on each component) typically have much greater amplitude on the H component with respect to D. They often reveal two prominent spectral peaks, one in band A (f < ≈ 45 mHz), mostly related to the transmission of upstream waves, and the other one in band B (f > ≈ 55 mHz), including resonances of local field lines and higher-frequency upstream waves. The occurrence of resonant phenomena on the D component is also clearly evidenced. The solar wind speed is confirmed as the key element for the manifestation of events; by contrast, their appearance is inhibited during extremely low solar wind densities. The events mostly manifest between dawn and early afternoon, with highest occurrence at ≈08:00-10:00 LT, as might be expected for the usual distribution of the interplanetary magnetic field orientation determining more or less favorable conditions for a foreshock region on the morning flank of the bow shock. No evidence is found for a favorite occurrence for low cone angles (θ XB < ≈ 10°); rather, they preferentially manifest for θ XB ≈ 25°-40°. The polarization pattern, much more definite in the afternoon, is consistent with the expected antisunward propagation; in the morning sector, it also suggests the possible occurrence of sunward propagating modes, mostly at f < ≈ 22 mHz. The tilt angle of the major axis of the polarization ellipses during daytime hours is oriented in the NW/SE quadrant and experiences remarkable changes at sunrise and sunset; it also shows a seasonal modulation with larger angles in the winter.

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