# Study of the Ionospheric Scintillation Radio Propagation Characteristics with Cosmic Observations
## 1 Introduction  
The ionosphere refers to the upper atmosphere from 60 to 1000 km above the Earth's surface. In the ionosphere, there are large amounts of free electrons and ions, and ionization is due to soft X-ray and far ultraviolet (UV) solar radiation as well as solar energetic particle precipitation. The ionosphere serves as a critical media for radio propagation [1]. Ionospheric irregularities occur when the electrons and ions are not uniformly distributed in the ionosphere. When radio signals pass through ionospheric irregularities, they can suffer from rapid fluctuations in amplitude and/or phase, which are named ionospheric scintillation [2]. Scintillation is impacted by solar activities and geomagnetic disturbances. It varies in accordance with geophysical locations and seasonal changes [3]. The Global Navigation Satellite System (GNSS) is influenced by scintillation. As discovered in previous studies, severe scintillation can lead to loss of signal locks, extreme ranging errors and deteriorated accuracy, integrity and availability [4; 5]. There are several impact factors that are responsible for the occurrence of ionospheric irregularities [6; 7]. Studies reveal that large number of ionospheric irregularities have variable patterns, such as sporadic E (Es), spread F, field-aligned irregularities (FAIs) and plasma bubbles. Ionospheric irregularities have been found in equatorial region, midlatitudes and high latitudes, due to different originations. The sporadic E layer is frequently observed from 90 to 140 km; it mostly occurs during daytime, formed in the early morning, reaching a maximum intensity at 14 LT and 20 LT for summer hemisphere [8]. The causes of E layer irregularities have been deeply investigated. [PERSON] attributed wind shear as important influential factor for the sporadic E features, while [PERSON] and [PERSON] proposed two-stream instability (TSI) and gradient-drift instability (GDI) for E layer FAIs at equator and low latitudes. It was indicated that atmosphere gravity waves, Kelvin-Helmholtz instability, Es-layer instability and GDI were all responsible for the development of mid-latitudes irregularities in E layer [9; 10; 11]. Ionospheric irregularities in the F layer are more common to study, the equatorial spread F and plasma bubbles are known to be generated by Rayleigh-Taylor instability [12; 13; 14]. Moreover, studies reveal that atmospheric gravity waves play a critical role for the seeding of irregularities, especially during low solar activity periods. The mid-latitudes ionospheric irregularities are found usually to be associated with atmospheric gravity waves and medium-scale travelling ionospheric disturbances (MSTID) [15; 16]. Its major cause is attributed to Perkins instability [7; 17; 18; 19]. In this theory, a north-south electric field is present in addition to the east-west electric field, leading to the form of rising and falling sheets of ionization. The electro-dynamical coupling between the E layer and F layer is considered important to enhance the Perkins instability growth rate [19; 20]. Geomagnetic disturbance can change the morphology of ionospheric irregularities. According to [PERSON]'s theory, geomagnetic storms can both excite and prohibit the formation of irregularities, depending on the storm commencement local time [21]. Previous studies on recent geomagnetic storms in solar cycle 24 indicate two dominant drivers for storm induced ionospheric irregularities, the prompt penetration electric field (PPEF) propagating from high latitudes [3; 22; 23] and the disturbance dynamo electric field (DDEF) formed by storm-time equatorward neutral winds and waves [6; 24]. The PPEF is eastward for southward IMF Bz until after sunset (19:00 LT and later), then its direction reverses. The DDEF is westward on daytime and eastward on nighttime, opposite to the direction of PPEF. GNSS signal propagation features under scintillation have been studied recently.