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

Abstract

Abstract. Very low and low radio frequency (VLF/LF) propagation responds sensitively to the electron density distribution in the lower ionosphere (upper mesosphere). Whereas propagation paths crossing subpolar and polar regions are frequently affected by forcing from above by particle precipitations, mid-and lowlatitude paths let forcing from below be more prominent. Our observations (2009)(2010)(2011) show, that the low frequency propagation conditions along the midlatitude path from Sicily to Germany (52 • N 8 • E) using the NSY 45.9 kHz transmitter (37 • N 14 • E) prove to be a good proxy of mesosphere planetary wave activity along the propagation path. High absorption events with VLF/LF propagation correlate to the well known winter time D-layer anomaly observed with high frequency (HF) radio waves. VLF/LF propagation calculations are presented which show that the radio signal amplitude variations can be modeled by planetary wave modulated collison frequency and electron density profiles. The other way around wave pressure amplitudes can be inferred from the VLF/LF data.

Semi-annual oscillation (SAO) of the nighttime ionospheric D region as detected through ground-based VLF receivers

“…Because the D region's formation and chemistry are tightly bound to the neutral MLT (Brasseur and Solomon, 2005), it is believed that the D region is affected by the same forcings, experiencing similar oscillations (e.g., Schmitter, 2011;Silber et al, 2013;Marshall and Snively, 2014). As far as the current authors know, there are no previous works showing the SAO dominating the natural long-term oscillations in the nighttime D region apart from the work of Toledo-Redondo et al (2012), who presented a SAO indication within the equatorial latitudes by using space-based ELF-VLF data from the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) micro-satellite.…”

“…At lower altitudes of the D region, where daytime VLF signals are reflected, we would expect chemical processes to dominate over NO dynamics, and therefore a very strong signature of solar insolation changes (which are seen mainly in the AO), together with relatively weak perturbations caused by other forcings and temperature changes, is observed (e.g., Schmitter, 2011;Silber et al, 2013). At higher altitudes within the D region, where nighttime VLF signals are reflected, dynamical processes are much more pronounced; thus oscillations, such as the SAO, which are driven by dynamical transport of important species as well as dynamical forcing (e.g., gravity and planetary waves) are much stronger and thus more easily detected.…”

“…One of these oscillations is the semi-annual oscillation (SAO). Among different parameters, the SAO can be detected in neutral atmospheric measures, e.g., the wind regime in the mesosphere-lower thermosphere (MLT) (e.g., Groves, 1972;Gregory and Manson, 1975;Lysenko et al, 1994); MLT temperatures (e.g., Groves, 1972;Takahashi et al, 1995;Taylor et al, 2005;Huang et al, 2006;Shepherd et al, 2006); and concentrations of atmospheric species, such as atomic oxygen at 80-115 km altitudes (e.g, Russell et al, 2004) and excited hydroxyl (OH * ) molecules around 87 km (e.g., Takahashi et al, 1995;Marsh et al, 2006;Shepherd et al, 2006;Gao et al, 2010). In addition, the charged part of the atmosphere (i.e., the ionosphere), experiences the SAO, which was observed and derived in and from measurements of several parameters, e.g., the ionospheric lower transition height at ∼ 180-260 km (a level where atomic and molecular ion concentrations become equal) (e.g., Lei et al, 2004); the electron and plasma density within the daytime D, E, and F regions of the ionosphere (e.g., Lauter and Nitzsche, 1967;Bremer and Singer, 1977;Forbes et al, 2000;Peters and Entzian, 2015); and also ionospheric total electron content (TEC) (e.g., Zhao et al, 2007;Opio et al, 2015).…”

Remote sensing and modeling of energetic electron precipitation into the lower ionosphere using VLF/LF radio waves and field aligned current data

“…Remote VLF/LF sensing therefore since decades proves as an inexpensive and reliable way to assess forcing processes in this layer, also with regard to auroral pre- cipitation activity (Cummer et al, 1996(Cummer et al, , 1998. During the last years we have developed a modeling scheme that allows to assess ionospheric forcing parameters from VLF/LF amplitude and phase recordings of distant Minimum Shift Keying (MSK) transmitters (Schmitter, 2010(Schmitter, , 2011(Schmitter, , 2012(Schmitter, , 2013(Schmitter, , 2014. As the amplitude of these transmissions is constant, any observed variations are caused along the propagation path.…”

“…In this paper we describe the VLF remote sensing procedure followed by the discussion of our model for the calculation of the electron density profiles, especially with regard to forcing events like electron precipitation. After the description of the VLF radio wave propagation calculations we discuss an example event: electron precipitation bursts during a moderate substorm on the 12 April 2014 (midnight-dawn) and the derivation of the precipitation energy input along a VLF propagation path in space and time from VLF data as well as using field aligned current data from the new Swarm satellite mission (launch: The NRK propagation path proceeds most of its way through the subauroral domain to the midlatitude receiver site and proves well suited to study lower ionosphere forcing from above by particle precipitation (Schmitter, 2010) and solar flares (Schmitter, 2013) as well as forcing from below by planetary wave activity (Schmitter, 2011(Schmitter, , 2012. In this paper we concentrate on forcing by energetic electron precipitation.…”