Investigation of VLF Radio Sounding for Studying Semi‐Diurnal Tide and Gravity Waves

• Published in: Geophysical research letters Vol. 48; no. 8
• Main Authors: Mahmoudian, Alireza, Mohebalhojeh, Ali Reza, Safari, Mohsen
• Format: Journal Article
• Language: English
• Published: 28.04.2021
• Subjects: gravity waves; radio sounding; remote sensing; Semiduirnal tides; tides
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL092949

The present paper is the investigation of the semi‐diurnal tide (SDT) and gravity waves (GW) through coupling effects on propagating Very low frequency (VLF) signal. One year of recorded VLF data is used. The first modulation of the VLF signal with SDTs and GWs is presented. The structures associated with SDT and GW are analyzed, and the daily and monthly variations are determined. Wavelet and spectrum analysis is applied to the data to determine the origin of the SDT. The corresponding period of the observed SDT is matched with solar SDT (SSDT). Seasonal variability of the SSDT in the lower ionosphere has been investigated using the VLF radio sounding for the first time. Developmental, evolution, and dissipation phases of GW with daytime and month are resolved. A plan to deploy 8 VLF stations to probe the shoreline and characterize the generation and development of SDT and GWs along the coastline is discussed. Plain Language Summary The mesosphere and lower thermosphere (MLT) has a great impact on ionospheric dynamics and electrodynamics. Atmospheric tides are one of the main drivers of MLT energetic variabilities. Atmospheric tides can be divided into lunar tides mainly generated by gravitational forcing of the moon caused in the dense lower atmosphere or solar tides generated by the absorption of solar radiation by different chemical species. The main absorption of solar radiation that occurs by water vapor in the troposphere, ozone in the stratosphere, and nitrogen and oxygen in the mesosphere excites various tidal modes in the respective regions. The lunar signal is often small in comparison with the solar tide and may also be subject to fluctuations in amplitude and phase over periods of a few days. The induced modulation of tidal winds with upper atmospheric constituents can lead to a modification in ionospheric currents, electric fields, and electron densities. The behavior of the VLF radio signal is mostly governed by the ionospheric plasma influenced by SDT and GW. The observations presented in this paper show that VLF radio sounding can be employed to study the time evolution and development of SDT in the various region providing high spatial resolution. Key Points Development of a new remote sensing technique to characterize the semidiurnal tide is proposed The first observation of the modulated Very low frequency (VLF) signal with semi‐diurnal tide (SDT) and gravity waves (GW) is provided Daily and monthly characteristics of SDT and GW in the Persian Gulf is derived