Nightside Neutral Density Disturbances Collocated With Equatorial Plasma Irregularities Above 450 km: GRACE and GRACE‐FO Observations in 2002–2022

AbstractWe investigate the climatology of Neutral Density Disturbances (NDDs) collocated with Equatorial Plasma Irregularities (EPIs) at altitudes above 450 km by using 20 years of data from the Gravity Recovery and Climate Experiment (GRACE) and GRACE‐FO satellites. Electron density data are used to detect EPIs, and thermospheric neutral density measured onboard the same spacecraft serves to identify EPI‐related NDDs. A detailed analysis focused on the morphological similarity between electron and neutral densities. To examine the relationship between EPI and NDD, statistical dependences of EPIs and NDDs on season/longitude (S/L), Magnetic Latitude (MLAT), Magnetic Local Time (MLT), and solar activity have been checked. As a first step, we confirmed that the EPI climatology in GRACE satellite data is consistent with previous reports. Then, it is found that the lower the neutral density in the background upper thermosphere, the higher the probability that EPI can accompany NDDs. We suggest that the vertical plasma advection surrounding EPI can result in neutral density disturbance, of which the efficiency depends on the background neutral scale height or temperature. The colder the thermosphere, the shorter its vertical scale height (or the lower the background neutral density), which can make the plasma advection leave measurable imprints on the neutral density.