Numerical Study of Traveling Ionospheric Disturbances Generated by an Upward Propagating Gravity Wave

Abstract

Using a global atmosphere‐ionosphere coupled model, the characteristics and excitation source of traveling ionospheric disturbances (TIDs) during geomagnetically quiet periods are studied. This is the first paper concerning the simulation of TIDs generated by upward propagating gravity waves (GWs) that are spontaneously generated in the model. The dominant horizontal wavelengths of the simulated TIDs range from 700 to 1,500 km. The dominant periods and horizontal phase velocities of TIDs are 45–90 min and 250–300 m s−1, respectively. These features are the same as those of GWs in the 250–300 km height region. The phase of the electron density variations due to TIDs descends with increasing time, which is characteristic of the upward propagation of GWs. These electron density variations that are caused due to TIDs are explained by the transport processes of a neutral wind along a geomagnetic field line. These results indicate that the electron density variations respond locally to the passage of neutral wind fluctuations associated with upward propagating GWs. The GWs that excite TIDs are secondary GWs, which are generated in the mesosphere and lower thermosphere via the dissipation/breaking of tropospheric GWs. The magnitudes of TIDs at middle latitudes are larger in winter than in summer. The mechanisms of seasonal and day‐to‐day variations in TIDs that are caused due to GWs are discussed in this study.

Solar activity dependence of medium-scale traveling ionospheric disturbances using GPS receivers in Japan

“…This feature was consistent with MSTIDs in different regions (e.g., Kotake et al 2006;Otsuka et al 2011). Miyoshi et al (2018) successfully reproduced MSTIDs generated by upward propagating GWs that are spontaneously generated in the global atmosphereionosphere coupled model, and showed that the daytime MSTID was more active in winter than in summer. According to the dispersion relation for GW, the vertical wave number ( m ) of GW is expressed as where k and c are the horizontal wave number and horizontal phase speed of the gravity wave, respectively, N is the Brunt-Väisälä frequency, and H is the scale height of the neutral atmosphere.…”

Space Weather Quarterly Volume 16, Issue 4, 2019

“…However, it is not clear whether such resolutions are needed at higher levels in the thermosphere. Miyoshi et al (2018) showed that a GAIA simulation with a resolution of 1° × 1° produces fluctuations in electron density with length scales less than around 1,000 km and periods of less than around 2 hr, which are in good agreement with observations and which are not seen in a coarser resolution (2.5° × 2.5°) simulation. The fluctuations reported by Miyoshi et al are attributed to TIDs that are excited by secondary gravity waves.…”

Ionospheric response to solar extreme ultraviolet radiation variations: comparison based on CTIPe model simulations and satellite measurements

“…The model needs further improvement regarding the input of solar flux. Miyoshi et al (2018) investigated the effects of the horizontal resolution on the electron density distribution using the GAIA model. They showed that fluctuations produced in model-simulated electron density with periods of less than about 2 h and length scales of less than about 1000 km with a high horizontal resolution of 1 • × 1 • , which are in good agreement with observations.…”