Whistler Influence on the Overall Very Low Frequency Wave Intensity in the Upper Ionosphere

Abstract

We investigate the influence of lightning‐generated whistlers on the overall intensity of electromagnetic waves measured by the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions spacecraft (2004–2010, quasi Sun‐synchronous polar orbit with an altitude of about 700 km) at frequencies below 18 kHz. Whistler occurrence rate evaluated using an onboard neural network designed for automated whistler detection is used to distinguish periods of high and low whistler occurrence rates. It is shown that especially during the night and particularly in the frequency‐geomagnetic latitude intervals with a low average wave intensity, contribution of lightning‐generated whistlers to the overall wave intensity is significant. At frequencies below 1 kHz, where all six electromagnetic wave components were measured during specific intervals, the study is accompanied by analysis of wave propagation directions. When we limit the analysis only to fractional‐hop whistlers, which propagate away from the Earth, we find a reasonable agreement with results obtained from the whole data set. This also confirms the validity of the whistler occurrence rate analysis at higher frequencies.

Low‐Latitude Whistler‐Wave Spectra and Polarization From VEFI and CINDI Payloads on C/NOFS Satellite

“…We can compare our median wave-electric-field spectral density with that observed by the survey mode on DEMETER (see nightime cases in figures 5c and 5d in Zahlava et al, 2018). They report latitude …”

“…It must be due to the moving satellite to which the raypaths must connect, slicing through plasma structures along the raypath. All three of the clusters in Figure 12 are below 100 s 1/2 phase dispersion or~8 s 1/2 group dispersion D. This is in the range classified by the cited DEMETER (Zahlava et al, 2018) study as fractional hop due to terrestrial lightning. Figure 13 shows the time-integrated phase dispersion found by the automated algorithm within the two prolific records for the magnetic inclination at the satellite (a) −44.2°and (b) −2.2°.…”

“…Figure 12 shows the time history of phase dispersions found by the automated algorithm within the two prolific records for the magnetic inclination at the satellite (a) −44.2°and (b) −2.2°. All three of the clusters in Figure 12 are below 100 s 1/2 phase dispersion or~8 s 1/2 group dispersion D. This is in the range classified by the cited DEMETER (Zahlava et al, 2018) study as fractional hop due to terrestrial lightning. We perform the search for optimal dechirps over phase dispersion, not over group dispersion D. The algorithm (Jacobson et al, 2016) can identify multiple phase dispersions simultaneously if needed.…”

“…There have already been excellent and extensive surveys of whistler-wave intensity versus latitude, employing the Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite (see, e.g., Colman & Starks, 2013;Zahlava et al, 2018). DEMETER was Sun-syncronous and observed all latitudes, including the low latitudes (±13°geographic) of C/NOFS, twice a day: once sunlit in the local morning and once in local premidnight.…”

Short‐Fractional Hop Whistler Rate Observed by the Low‐Altitude Satellite DEMETER at the End of the Solar Cycle 23

“…Whistlers are important because they induce electron precipitation from the radiation belts (see Inan et al, ; Gemelos et al, ; Bourriez et al, , and references therein). Whistlers also significantly impact the overall wave intensity in the magnetosphere (Colman & Starks, ; Němec et al, ; Záhlava et al, ). This is specially the case during nighttime when the wave attenuation in the ionosphere is lower (Cohen et al, ; Graf et al, ).…”