Investigating Spatial and Temporal Structuring of E-Region Coherent Scattering Regions Over Northern Norway

Recently, it has been shown that the Spread Spectrum Interferometric Multistatic meteor radar Observing Network radar system located in northern Norway is capable of measuring ionospheric E-region coherent scatter with spatial and temporal resolutions on the order of 1.5 km and 2 s, respectively. Four different events from June and July of 2022 are examined in the present study, where the coherent scatter measurements are used as a tracer for large-scale ionospheric phenomena such as plasma density enhancements and ionospheric electric fields. By applying a two-dimensional Fourier analysis to range-time-intensity data, we perform a multi-scale spatial and temporal investigation to determine the change in range over time of large-scale ionospheric structures (>3 km) which are compared with line-of-sight velocities of the small scale structures (∼5 m) determined from the Doppler shift of the coherent scatter. The spectral characteristics of the large-scale structures are also investigated and logarithmic spectral slopes for scale sizes of 100–10 km were found to be between −3.0 and −1.5. This agrees with much of the previous work on the spatial spectra scaling for ionospheric electric fields. This analysis aids in characterizing the source of the plasma turbulence and provides crucial information about how energy is redistributed from large to small scales in the E-region ionosphere

Simultaneous Global Ionospheric Disturbances Associated With Penetration Electric Fields During Intense and Minor Solar and Geomagnetic Disturbances

A new observational phenomenon, named Simultaneous Global Ionospheric Density Disturbance (SGD), is identified in GNSS total electron content (TEC) data during periods of three typical geospace disturbances: a Coronal Mass Ejection-driven severe disturbance event, a high-speed stream event, and a minor disturbance day with a maximum Kp of 4. SGDs occur frequently on dayside and dawn sectors, with a ∼1% TEC increase. Notably, SGDs can occur under minor solar-geomagnetic disturbances. SGDs are likely caused by penetration electric fields (PEFs) of solar-geomagnetic origin, as they are associated with Bz southward, increased auroral AL/AU, and solar wind pressure enhancements. These findings offer new insights into the nature of PEFs and their ionospheric impact while confirming some key earlier results obtained through alternative methods. Importantly, the accessibility of extensive GNSS networks, with at least 6,000 globally distributed receivers for ionospheric research, means that rich PEF information can be acquired, offering researchers numerous opportunities to investigate geospace electrodynamics

On the strength of E and F region irregularities for GNSS scintillation in the dayside polar ionosphere

We present results of the study conducted to quantify the relative contribution of different ionospheric regions to phase scintillation in Global Navigation Satellite Systems (GNSS) at the dayside high latitude ionosphere. By taking advantage of the scanning capability of the 32-m EISCAT radar in Svalbard (ESR) and its recurrent favourable location below the dayside auroral region, we developed a methodology to identify conjunctions between the radar and GNSS satellite signals in order to compare density irregularities identified by the radar with scintillation observed in GNSS signals. The analysis revealed that the dayside ionosphere contained irregularities predominantly in the F region with scintillation occurring 77% of the times. The likelihood of observing irregularities in the E region were comparatively less with a scintillation occurrence rate of 42%. The study therefore strongly suggests that the dayside F region is more structured than the E region and is the predominant source region for irregularities that cause scintillation at GNSS frequencies. The associated ionospheric conditions revealed enhanced F region electron and ion temperatures to be collocated with scintillation for majority of the times. This supports the fact that cusp/auroral dynamics play a crucial role in creating F region irregularities which can act as sources of scintillation in GNSS signals. The presented results provide a quantitative estimate of the effectiveness of irregularities and the associated ionospheric conditions in different regions of the dayside ionosphere during scintillation, which are relevant for high latitude modelling and instability studies as well as for space weather applications

Arecibo measurements of D-region electron densities during sunset and sunrise : implications for atmospheric composition

Earth’s lower ionosphere is the region where terrestrial weather and space weather come together. Here, between 60 and 100 km altitude, solar radiation governs the diurnal cycle of the ionized species. This altitude range is also the place where nanometre-sized dust particles, recondensed from ablated meteoric material, exist and interact with free electrons and ions of the ionosphere. This study reports electron density measurements from the Arecibo incoherent-scatter radar being performed during sunset and sunrise conditions. An asymmetry of the electron density is observed, with higher electron density during sunset than during sunrise. This asymmetry extends from solar zenith angles (SZAs) of 80 to 100. This D-region asymmetry can be observed between 95 and 75 km altitude. The electron density observations are compared to the one-dimensional Sodankylä Ion and Neutral Chemistry (SIC) model and a variant of the Whole Atmosphere Community Climate Model incorporating a subset SIC’s ion chemistry (WACCM-D). Both models also show a D-region sunrise–sunset asymmetry. However, WACCM-D compares slightly better to the observations than SIC, especially during sunset, when the electron density gradually fades away. An investigation of the electron density continuity equation reveals a higher electron–ion recombination rate than the fading ionization rate during sunset. The recombination reactions are not fast enough to closely match the fading ionization rate during sunset, resulting in excess electron density. At lower altitudes electron attachment to neutrals and their detachment from negative ions play a significant role in the asymmetry as well. A comparison of a specific SIC version incorporating meteoric smoke particles (MSPs) to the observations revealed no sudden changes in electron density as predicted by the model. However, the expected electron density jump (drop) during sunrise (sunset) occurs at 100◦ SZA when the radar signal is close to the noise floor, making a clear falsification of MSPs’ influence on the D region impossible