Abstract
GNSS radio occultation (RO) plays an important role in ionospheric electron density inversion and sounding of sporadic E layers. As the China's first electromagnetic satellite, China Seismo Electromagnetic Satellite (CSES) has collected the RO data from both GPS and BDS-2 satellites since March 2018. In this study, we extracted the carrier to noise density ratio (CNR) data of CSES and calculated the standard deviation of normalized CNR. A new criterion is developed to determine the Es events, that is when the mean value of the absolute value of the difference between the normalized CNR is greater than 3 times of the standard deviation. The statistics show that sporadic E layers have strong seasonal variations with highest occurrence rates in summer season at middle latitudes. It is also found that the occurrence height of Es is mainly located at 90–110 km, and the period of local time 15:00–18:00 is the high incidence period of Es. In addition, the geometric altitudes of a sporadic E layer detected in CSES radio occultation profiles and the virtual heights of a sporadic E layer obtained by the Wuhan Zuo Ling Tai (ZLT) ionosonde show four different space-time matching criterions. Our results reveal that there is a good agreement between both parameters which is reflected in the significant correlation.
Highlights
The name Sporadic E and its abbreviation Es refer to thin layers of metallic ion plasma which accumulates in the dynamo region of the Earth’s ionosphere, mostly between 100 and 125 km, where ion motion is controlled mainly by collisions with the neutrals, the ions move with the winds while electrons remain strongly magnetized (Haldoupis 2012)
The geometric altitudes of a sporadic E layer detected in China Seismo Electromagnetic Satellite (CSES) radio occultation profiles and the virtual heights of a sporadic E layer obtained by the Wuhan Zuo Ling Tai (ZLT) ionosonde show four different space-time matching criterions
The formation 25 of sporadic E layer was traditionally attributed to the “windshear theory” (Whitehead 1961; Axford 1963; Whitehead 1989), in which vertical shears in the horizontal wind play a key role in forming these layers from long-lived metallic ions through ion-neutral collisional coupling and geomagnetic Lorentz forcing, vertical shear converge metallic ions into thin sheets of enhanced electron density
Summary
The name Sporadic E and its abbreviation Es refer to thin layers of metallic ion plasma which accumulates in the dynamo region of the Earth’s ionosphere, mostly between 100 and 125 km, where ion motion is controlled mainly by collisions with the neutrals, the ions move with the winds while electrons remain strongly magnetized (Haldoupis 2012). Ionosondes provide reliable measurements on sporadic E parameters and on the altitude of each layer. Yan et al (2020) provided a comprehensive comparison of in situ electron density (Ne) and temperature (Te) measured by Langmuir probe (LAP) on board the CSES with other space-borne and ground-based observations. Their results suggested that the CSES in situ plasma parameters are reliable with a high scientific potential for investigation of geophysics and space. In this study we assessed the GRO performance of CSES in the investigating of lower ionosphere, especially the occurrence and properties of sporadic E layers on a global scale.
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