Quarterdiurnal signature in sporadic E occurrence rates and comparison with neutral wind shear

Abstract

Abstract. The GPS radio occultation (RO) technique is used to study sporadic E (Es) layer plasma irregularities of the Earth's ionosphere on a global scale using GPS signal-to-noise ratio (SNR) profiles from the COSMIC/FORMOSAT-3 satellite. The maximum deviation from the mean SNR can be attributed to the height of the Es layer. Es are generally accepted to be produced by ion convergence due to vertical wind shear in the presence of a horizontal component of the Earth's magnetic field, while the wind shear is provided mainly by the solar tides. Here we present analyses of quarterdiurnal tide (QDT) signatures in Es occurrence rates. From a local comparison with mesosphere/lower thermosphere wind shear obtained with a meteor radar at Collm (51.3∘ N, 13.0∘ E), we find that the phases of the QDT in Es agree well with those of negative vertical shear of the zonal wind for all seasons except for summer, when the QDT amplitudes are small. We also compare the global QDT Es signal with numerical model results. The global distribution of the Es occurrence rates qualitatively agrees with the modeled zonal wind shears. The results indicate that zonal wind shear is indeed an important driving mechanism for the QDT seen in Es.

Forcing mechanisms of the quarterdiurnal tide

“…We used a horizontal resolution of 2.5 • × 5.625 • for the model, which differs from the version of e.g., Lilienthal et al (2017Lilienthal et al ( , 2018, to be able to better resolve the meridional structure of the QDT. In an earlier model version with 5 • meridional resolution, essentially only one maximum in the QDT amplitudes per hemisphere was seen (Jacobi et al, 2019), while satellite observations (Azeem et al, 2016;Liu et al, 2015) show a more detailed meridional structure. Also from the linear theory including the QDT meridional structure representation by Hough modes, another result was expected, as shown by Azeem et al (2016).…”

“…MUAM is a 3-D, primitive equation, mechanistic global circulation model based on the earlier COMMA-LIM model described by Jakobs et al (1986), Fröhlich et al (2003b) and Jacobi et al (2006). Recent versions of the MUAM model are described by Lilienthal et al (2017Lilienthal et al ( , 2018, Lilienthal and Jacobi (2019), Jacobi et al (2019) and Samtleben et al (2019a, b). The model reaches from the surface at 1000 hPa to 160 km log-pressure height, with a constant scale height of H = 7 km and a vertical resolution of 2.842 km.…”

Forcing mechanisms of the migrating quarterdiurnal tide

“…The Middle and Upper Atmosphere Model (MUAM; Pogoreltsev, 2007;Pogoreltsev et al, 2007) is used to investigate the forcing mechanisms of migrating QDTs with wave number 4. MUAM is a 3-D, primitive equation, mechanistic global circulation model based on the earlier Cologne Model of the Middle Atmosphere-Leipzig Institute for Meteorology (COMMA-LIM), described by Jakobs et al (1986), Fröhlich et al (2003b) and Jacobi et al (2006). Recent versions of the MUAM model are described by Lilienthal et al (2017), Lilienthal et al (2018), Lilienthal and Jacobi (2019), Jacobi et al (2019) and Samtleben et al (2019).…”

“…The gravity wave routine, which is used in this model version, is an updated linear Lindzen-type parameterization (Lindzen, 1981;Jakobs et al, 1986), as described by Fröhlich et al (2003b) and Jacobi et al (2006). This parameterization is based on waves initialized at an altitude of 10 km that are traveling in eight directions with a phase speed between 5 and 30 ms −1 .…”

Using GNSS radio occultation data to derive critical frequencies of the ionospheric sporadic E layer in real time

“…Among these ionospheric irregularities, the sporadic E (Es) layer is of particular interest. Es is a thin layer composed of intense long-live metallic plasma at 90-130 km altitude (Plane et al 2015(Plane et al , 2018, concentrated through vertical convergence resulting from wind shear (Davis and Johnson 2005;Jacobi et al 2019). The Es layers cause approximately 8.3% interruptions of GNSS signals per occultation, which contribute more than a third to the influence of ionospheric plasma irregularities on tracking interruptions of GNSS (Yue et al 2016).…”