Characterization of short-period VLF amplitude fluctuations associated with gravity waves at low latitudes

Samanes J.; Hinostroza Caldas A.; Cueva R.Y.C.; Correia E. · Advances in Space Research (2026) · DOI: 10.1016/j.asr.2025.11.095

Resumen

We investigate the occurrence of wave-like fluctuations (WFs) in the nighttime lower ionosphere during solar minimum conditions (2008–2009) using Very Low Frequency (VLF) narrowband signals transmitted from NAA (US Cutler, Maine, f = 24 kHz) and NDK (US LaMoure, North Dakota, f = 25.2 kHz) stations and recorded at two Peruvian stations PLO (Lima) and PIU (Piura). These propagation paths span predominantly low-latitude regions and exhibit similar characteristics, as they are quasi-parallel, enabling reliable comparisons under similar geophysical and geomagnetic conditions. Statistical and wavelet spectral analysis reveal a persistent daily presence of WFs, with dominant periods between 10 and 15 min across all VLF propagation paths. The second most frequent WFs show periods shorter than 5 min and exhibit a clear seasonal pattern with enhanced activity during equinoxes. To investigate the link between WFs and Gravity Waves (GWs) activity, we analyze two case studies (August 23, 2008, and January 2, 2009), during which WFs with similar periods appear nearly simultaneously along NAA-PLO and NAA-PIU propagation paths. For these events, GWs activity in the lower and upper ionosphere was examined using atmospheric temperature profiles from the TIMED/SABER satellite and GPS-derived Total Electron Content (TEC) data, both recorded near the VLF propagation paths. The analysis of TEC data reveals GWs with periods between 10 and 17 min, consistent with those identified in the VLF signals. Temperature profiles show GWs signatures with vertical wavelengths centered at 4–6 km and 12–14 km, predominantly between 70 and 100 km altitudes that correspond to typical nighttime VLF reflection heights. These results suggest an association between the WFs observed in VLF amplitude signals and GWs activity in the ionosphere under nighttime and solar minimum conditions.

Instituciones: Universidad Nacional de Ingeniería