Timing of the VLF October effect in relation to mesospheric wind dynamics

<p>The seasonal variation of the daytime lower ionosphere, monitored using the propagation of Very Low Frequency (VLF) radio waves, shows an asymmetry when comparing the spring and autumn transitions. Considering the solar zenith angle variation, it can explain the spring transition but not the autumn one. The climatological variation exposes that the maximum of the VLF deviation is around the beginning of October. Thus, the deviation is called &#8220;the October effect&#8221;. This study aims to understand the possible atmospheric phenomena behind this effect. We use VLF signals transmitted from USA (NAA, f = 24 kHz), UK (GQD, f=19.6 kHz) and Iceland (NRK, f = 37.5 kHz) recorded in Northern Finland from 2011 to 2019. We compare our results with the Whole Atmosphere Community Climate Model with the thermosphere-ionosphere eXtension (WACCM-X) data. The October effect is separated into climatological earliest and latest effect according to WACCM-X climatological earliest and latest transitions from eastward to westward mean zonal winds</p>

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The numerical calculation of wave-fields, reflexion coefficients and polarizations for long radio waves in the lower ionosphere. II

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1965.0005 ◽

1965 ◽

Vol 257 (1079) ◽

pp. 243-271 ◽

Cited By ~ 32

Keyword(s):

Collision Frequency ◽

Numerical Models ◽

Low Frequency ◽

Lower Ionosphere ◽

Preceding Paper ◽

Radio Waves ◽

Very Low Frequency ◽

Cross Modulation ◽

Long Wave ◽

Ionization Structure

The characteristics of radio waves of low and very low frequency reflected from numerical models of electron density and collision frequency are calculated by the methods described in the preceding paper (Pitteway 1964). The models used are based on those found by cross-modulation experiments and approximate to those likely to be found in the ionosphere. The effects of changing the models are investigated with the object of developing methods of solving the inverse problem of deducing the ionization structure from the experimental data on long and very long wave propagation. The relations between the computed and observed characteristics are examined in a preliminary way.

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Investigation of ionosphere response to geomagnetic storms over the propagation paths of very low frequency radio waves

10.1002/essoar.10504067.1 ◽

2020 ◽

Author(s):

Victor U. J. Nwankwo ◽

Jean-Pierre Raulin ◽

Dra. Emilia Correia ◽

William F. Denig ◽

Olanike Akinola ◽

...

Keyword(s):

Geomagnetic Storms ◽

Low Frequency ◽

Radio Waves ◽

Very Low Frequency ◽

Propagation Paths

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Survey of electron density changes in the daytime ionosphere over the Arecibo observatory due to lightning and solar flares

Scientific Reports ◽

10.1038/s41598-021-89662-x ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Caitano L. da Silva ◽

Sophia D. Salazar ◽

Christiano G. M. Brum ◽

Pedrina Terra

Keyword(s):

Electron Density ◽

Solar Flares ◽

Low Frequency ◽

Lower Ionosphere ◽

Weather Conditions ◽

Optical Observations ◽

Radio Waves ◽

D Region ◽

E Region ◽

Arecibo Observatory

AbstractOptical observations of transient luminous events and remote-sensing of the lower ionosphere with low-frequency radio waves have demonstrated that thunderstorms and lightning can have substantial impacts in the nighttime ionospheric D region. However, it remains a challenge to quantify such effects in the daytime lower ionosphere. The wealth of electron density data acquired over the years by the Arecibo Observatory incoherent scatter radar (ISR) with high vertical spatial resolution (300-m in the present study), combined with its tropical location in a region of high lightning activity, indicate a potentially transformative pathway to address this issue. Through a systematic survey, we show that daytime sudden electron density changes registered by Arecibo’s ISR during thunderstorm times are on average different than the ones happening during fair weather conditions (driven by other external factors). These changes typically correspond to electron density depletions in the D and E region. The survey also shows that these disturbances are different than the ones associated with solar flares, which tend to have longer duration and most often correspond to an increase in the local electron density content.

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Strange VLF bursts in northern Scandinavia: case study of the afternoon "mushroom-like" hiss on 8 December 2013

Annales Geophysicae ◽

10.5194/angeo-33-991-2015 ◽

2015 ◽

Vol 33 (8) ◽

pp. 991-995 ◽

Cited By ~ 4

Author(s):

J. Manninen ◽

N. G. Kleimenova ◽

A. Kozlovsky ◽

I. A. Kornilov ◽

L. I. Gromova ◽

...

Keyword(s):

Low Frequency ◽

Mutual Effect ◽

Time History ◽

Lower Ionosphere ◽

Wave Interaction ◽

Recovery Phase ◽

Frequency Wave ◽

Left Hand ◽

Very Low Frequency ◽

The Right

Abstract. We investigate a non-typical very low frequency (VLF) 1–4 kHz hiss representing a sequence of separated noise bursts with a strange "mushroom-like" shape in the frequency–time domain, each one lasting several minutes. These strange afternoon VLF emissions were recorded at Kannuslehto (KAN, &varphi; = 67.74° N, λ = 26.27° E; L ∼ 5.5) in northern Finland during the late recovery phase of the small magnetic storm on 8 December 2013. The left-hand (LH) polarized 2–3 kHz "mushroom caps" were clearly separated from the right-hand (RH) polarized "mushroom stems" at the frequency of about 1.8–1.9 kHz, which could match the lower ionosphere waveguide cutoff (the first transverse resonance of the Earth–ionosphere cavity). We hypothesize that this VLF burst sequence could be a result of the modulation of the VLF hiss electron–cyclotron instability from the strong Pc5 geomagnetic pulsations observed simultaneously at ground-based stations as well as in the inner magnetosphere by the Time History of Events and Macroscale Interactions during Substorms mission probe (THEMIS-E; ThE). This assumption is confirmed by a similar modulation of the intensity of the energetic (1–10 keV) electrons simultaneously observed by the same ThE spacecraft. In addition, the data of the European Incoherent Scatter Scientific Association (EISCAT) radar at Tromsø show a similar quasi-periodicity in the ratio of the Hall-to-Pedersen conductance, which may be used as a proxy for the energetic particle precipitation enhancement. Our findings suggest that this strange mushroom-like shape of the considered VLF hiss could be a combined mutual effect of the magnetospheric ULF–VLF (ultra low frequency–very low frequency) wave interaction and the ionosphere waveguide propagation.

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