ALBERT

Description: An exceptionally strong stationary planetary wave with Zonal Wavenumber 1 led to a sudden stratospheric warming (SSW) in the Southern Hemisphere in September 2019. Ionospheric data from European Space Agency's Swarm satellite constellation mission show prominent 6‐day variations in the dayside low‐latitude region at this time, which can be attributed to forcing from the middle atmosphere by the Rossby normal mode “quasi‐6‐day wave” (Q6DW). Geopotential height measurements by the Microwave Limb Sounder aboard National Aeronautics and Space Administration's Aura satellite reveal a burst of global Q6DW activity in the mesosphere and lower thermosphere during the SSW, which is one of the strongest in the record. The Q6DW is apparently generated in the polar stratosphere at 30–40 km, where the atmosphere is unstable due to strong vertical wind shear connected with planetary wave breaking. These results suggest that an Antarctic SSW can lead to ionospheric variability through wave forcing from the middle atmosphere.

Description: Lastovicka (2021, 2023) found some differences in the dependence of yearly values foF2 on solar activity when different solar activity proxies were used. He used F10.7, F30, Mg II, solar H Lyman-α flux, sunspot numbers and He II. F30 followed by Mg II were established to be the optimum solar activity proxies, not traditionally used F10.7 and sunspot numbers, for yearly values of foF2. Here we use data of six ionospheric stations from four continents, Juliusruh, Pruhonice, Roma, Boulder, Kokubunji and Canberra, which reveal somewhat and sometimes even substantially different trends of foF2 when the effect of solar cycle is removed/reduced from foF2 data with different solar activity proxies.

Description: Long-term changes are challenging and debatable research topics because of the estimation method and the social relevance in the climate change scenario. Studies on the long-term changes in the upper atmosphere yield more attention in the last three decades. The formation of the ionosphere and sporadic-E (Es) layer is caused by the solar and lower atmospheric forcing, respectively. Ionosphere and Es-layer can be used as a tracer to estimate the lower atmospheric impact and solar forcing on the upper mesosphere and thermosphere/ionosphere. Using sixty-three and fifty-six years of continuous observations, we investigate the long-term oscillations and residual linear trends, respectively, in the E- and F-region ionosonde measured parameters (i.e. frequencies and height) over Juliusruh, Europe. The Lomb-Scargle periodogram (LSP) estimates long-term oscillations before the trend calculation. We found that the amplitude of the annual oscillation is higher than the 11-year solar cycle variation in the critical frequencies of the daytime E (foE) and Es (foEs) layers. The combination of the LSP estimated periods with their corresponding amplitudes and traditional regression analysis is used to construct a model for E- and F-region ionospheric parameters. The modeled estimates are in good agreement with the observations. The trend calculation is derived by applying a least-squares fit analysis to the residuals, subtracting the model from the observation. In the F-region, foF2, and hmF2 day (nighttime) show negative trends of -4.44±1.78 (-4.30±1.63) kHz/year and -413±47 (-574±75) m/year, respectively. In the E-region, foEs show a negative trend of -2.00±0.61 kHz/year.

Description: Sudden Stratospheric Warming (SSW) is considered one extreme of polar stratospheric dynamic variability. During this extreme circulation variability, sudden warming at the stratospheric levels is seen to occur within a few days. There is a weakening of mean flow at the stratospheric level due to the strong two-way nonlinear interactions between upward propagating planetary waves and the mean flow. Recent studies have shown that the upper atmosphere's response during a particular SSW event may differ from that observed during another SSW occurrence. More studies are required to comprehensively organize the effects of SSWs on the upper atmosphere, especially in the ionosphere. This work focuses on understanding the SSW's impact on ionosphere dynamics, especially at high and mid-latitudes combining datasets obtained from atmospheric and ionospheric measurements and modeling. The individual characteristics of an SSW event are analyzed using the meteorological parameters retrieved from the reanalysis data. The global Total Electron Content (TEC) maps and the ground magnetometer data are used to understand the ionospheric response during the SSW event. The forcing due to the atmosphere-ionosphere vertical coupling during the SSW event is studied using the Chemistry Transport Model of the Leibniz Institute of Atmospheric Physics (CTM-IAP). Ionospheric responses during these event periods are analyzed using the outputs from the CTM-IAP. The study details the plasma density variability in the ionosphere during an SSW event.