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.

Quasiperiodic (QP) emissions are whistler mode electromagnetic waves observed in the
inner magnetosphere that exhibit a QP time modulation of the wave intensity. We analyze 768 QP events
observed during the first 5 years of the operation of the Van Allen Probes spacecraft (September 2012
to October 2017). Multicomponent wave measurements performed in the equatorial region, where the
emissions are likely generated, are used to reveal new experimental information about their properties. We
show that the events are observed nearly exclusively inside the plasmasphere. Wave frequencies are mostly
between about 0.5 and 4 kHz. The events observed at larger radial distances and on the duskside tend to
have slightly lower frequencies than the emissions observed elsewhere. The maximum event frequencies
are limited by half of the equatorial electron gyrofrequency, suggesting the importance of wave ducting.
Modulation periods are typically between about 0.5 and 5 min, and they increase with the in situ measured
plasma number density. This increase is consistent with the main mechanisms suggested to explain the
origin of the QP modulation. Two-point measurements performed by the Van Allen Probes are used to
estimate a typical spatial extent of the emissions to about 1 RE in radial distance and 1.5 hr in magnetic local
time. Detailed wave analysis shows that the emissions are right-hand circularly polarized, and they usually
come from several different directions simultaneously. They, however, predominantly propagate at rather
low wave normal angles and away from the geomagnetic equator.

We use the measurements performed by the DEMETER (2004–010) and the Van Allen Probes
(2012–016, still operating) spacecraft to investigate the longitudinal dependence of the intensity of whistler
mode waves in the Earth’s inner magnetosphere. We show that a significant longitudinal dependence is
observed inside the plasmasphere on the nightside, primarily in the frequency range 400 Hz to 2 kHz. On
the other hand, almost no longitudinal dependence is observed on the dayside. The obtained results are
compared to the lightning occurrence rate provided by the Optical Transient Detector/Lightning Imaging
Sensor mission normalized by a factor accounting for the ionospheric attenuation. The agreement between
the two dependencies indicates that lightning-generated electromagnetic waves may be responsible for
of the observed effect, thus substantially affecting the overall wave intensity in the given frequency range.
Finally, we show that the longitudinal dependence is most pronounced for waves with oblique wave of
normal angles.

Frequency-time spectrograms measured by the Detection of Electro-Magnetic Emissions
Transmitted from Earthquake Regions (DEMETER) spacecraft (2004–2010, altitude about 700 km) at
frequencies below 20 kHz sometimes contain lightning-generated whistlers whose intensity is
significantly reduced at specific frequencies. The frequencies of the reduced intensity vary smoothly
over the event duration, forming apparent curves in frequency-time spectrograms. Events at frequencies
higher than the Earth-ionosphere waveguide cutoff frequency were explained by the interference of the
first few waveguide modes of lightning-generated spherics propagating therein (Záhlava et al., 2015,
https://doi.org/10.1002/2015JA021607. Here we present an analysis of events observed at frequencies lower
than about 1 kHz. Altogether, we analyze 263 events identified at the times when DEMETER operated in
the burst mode. The vast majority of the events (95%) took place during the nighttime, and they occurred
more frequently during spring/autumn than during winter/summer. We present an overview of event
properties. Moreover, measurements of all six electromagnetic field components performed by DEMETER
allow us to perform a detailed wave analysis. It is shown that the emissions propagate with high wave
normal angles inclined toward the Earth. We suggest that the events might be due to the wave propagation
in the ionospheric waveguide formed around the refractive index maximum at the altitude of about 105 km.

V datech družice DEMETER se podařilo nalézt nezvykle dlouho trvající událost typu QP (pozorovanou celkem na deseti půlorbitech družice), která byla současně měřena také pozemní stanicí Kannuslehto ve Finsku. Díky konjugovaným měřením těchto přístrojů bylo možné provést systematickou studii porovnávající vlastnosti této události (intenzitu elementů, časy detekce nebo modulační periodu) pozorované na družici s těmi, které byly získány z pozemního měření. Bylo ukázáno, že bez ohledu na typ měření (pozemní stanice vs. družice) zůstává struktura elementů QP události beze změny, spolu se změnou geomagnetické šířky družice se ovšem mění jejich intenzita.