On the transformation of planetary waves of tropospheric origin into waves in radio wave absorption in the lower ionosphere

Remote sensing planetary waves in the midlatitude mesosphere using low frequency transmitter signals

“…Note that electron density and collision frequency are out of time phase bei 180 degrees. This is in accordance with the findings of Lastovicka et al (1994). Reasons for reduced electron density during periods of increased neutral density in the height range in question are: less ionization because of larger opacity and increased recombination rates.…”

“…Based on the results of Lastovicka et al (1994), Lauter et al (1984) and Taubenheim (1971) with respect to the role of electron density and collision frequency profiles during winter anomaly events we are able to quantify the variation amplitudes of these profiles by fitting them to our VLF data.…”

“…Following Lastovicka et al (1994) this takes place mainly in a height range of 65-85 km and we take this into account by modifying the electron collision frequency according to: f c (t,h) = f c (h)(1+d c cos(2π t/P )sin(π(h−65)/(85−65)) with f c (h) the undisturbed profile, d c the relative disturbance amplitude (typically d c = 0.15 − 0.3, i.e. 15-30 %) and P : planetary wave period.…”

“…These waves are strongly related to global weather (formation of cyclones, anticyclones, mid-latitude depressions) and their variability is suggested Correspondence to: E. D. Schmitter (e.d.schmitter@hs-osnabrueck.de) to be a signature of possible climatic changes (Pogoreltsev et al, 2009). Under certain conditions which for the stationary wave case are approximated by the Charney-Drazin criterion (Charney and Drazin, 1961): not too strong eastward background winds and long horizontal wavelengths) planetary waves vertically penetrate to the stratosphere and also up to the mesosphere where they can affect the ionosphere (Lastovicka et al, 1994;Borries et al, 2007;Brown and John, 1979;Haldoupis and Pancheva, 2002;Haldoupis et al, 2004). During the Northern Hemisphere winter months planetary wavenumber one is large and variable in the mesosphere and we found further hints that the D-layer winter anomaly (unusually strong absorption of radio waves in the ionosphere, not related to solar activity (Appleton and Piggott, 1954;Lauter and Schaening, 1970;Lauter et al, 1984;Taubenheim, 1971), is correlated to planetary wave activity.…”

Forcing of the ionosphere by waves from below

“…It is worth noting that even the 27-day variation in absorption is not always of direct solar origin, relatively often it seems to be related rather to a planetary wave (Pancheva et al, 1991b). Lasˇtovicˇka et al (1994a) performed model calculations that showed that the planetary waves in the neutral atmosphere were adequately transformed into planetary waves in the absorption, i.e. in the ionized component.…”