Observations Of Ionospheric Disturbances Research Articles

Ionospheric storm effects over the People’s Republic of China on 14 May 2019: Results from multipath multi-frequency oblique radio sounding

Results obtained from observations of ionospheric disturbances over the People’s Republic of China during the course of the geospace storm of 14 May 2019, one of the largest storms in 2019, are presented. The Harbin Engineering University operates the multi-frequency multipath radio wave diagnostics employing software defined technology and continuously monitoring dynamic process acting in the ionosphere at oblique incidence since April 2018. The basic premise upon which this instrument operation is based is that the digital re-sampling remains coherent with radio frequency for each propagation path, which permits Doppler spectra and signal amplitudes to be calculated along each of the 14 propagation paths. UT dependences of the Doppler spectra, the main mode Doppler shifts of frequency, and signal amplitudes that were measured on the day of the ionospheric storm and on the reference days of 13 and 15 May 2019 have been analyzed. After the magnetic storm onset, the Doppler shift of frequency exhibits an abrupt –1-Hz decrease, indicating the ionospheric storm onset. In addition, quasi-periodic variations in the Doppler shift of frequency, with 5-, 15-, 20-, and 30-min periods and the amplitudes in the range from 0.05 Hz to 0.15 Hz, occur in the course of the storm. These variations are due to modulation by infrasound (5-min period oscillation) and atmospheric gravity waves (15-, 20-, and 30-min period oscillations). In the electron density, the corresponding waves have amplitudes equal to 0.7% and 4–8%, respectively.

Geomagnetic Conjugate Observations of Ionospheric Disturbances in response to North Korea Underground Nuclear Explosion on 3 September 2017

<p><strong>Abstract.</strong> We report observations of ionospheric disturbances in response to North Korea underground nuclear explosion (UNE) on 3 September 2017. By using data from IGS (International GNSS Service) stations and Swarm satellite, geomagnetic conjugate ionospheric disturbances were observed. The observational evidences showed that UNE-generated ionospheric disturbances propagated radially from the UNE epicenter with the velocity of ~<span class="thinspace"></span>280<span class="thinspace"></span>m/s. We propose that the ionospheric disturbances are results of electrodynamic process caused by LAIC (Lithosphere-Atmosphere-Ionosphere Coupling) electric field penetration. LAIC electric field can also be mapped to the conjugate hemispheres along the magnetic field line and consequently cause ionospheric disturbances in conjugate regions. The UNE-generated LAIC electric field penetration plays an important role in the ionospheric disturbances in the region of the nuclear test site nearby and the corresponding geomagnetic conjugate points.</p>

Detection of ionospheric perturbation due to a soft gamma ray repeater SGR J1550-5418 by very low frequency radio waves

We wish to report our observations of ionospheric disturbances made by incident Gamma Rays from the Soft Gamma Repeater SGR J1550-5418 which took place on 22nd of January, 2009. The observations were made by a loop antenna and a Gyrator-II type receiver which was tuned to the 500KW VTX station transmitting Very Low Frequency (VLF) signal at 18.2 kHz. We looked for signatures of sudden ionospheric disturbances (SID) which commenced within seconds of the observations reported by various satellites. We used Long Wave Propagation Capability code to compute the changes in the ionospheric parameters due to the repeated passage of the high energy radiation. We detected seventy six events in our VLF detector which appear to be associated with the SGR J1550-5418. We found that 28 of them are within three seconds of the satellite observations and 38 (fifty percent) of them are within seven seconds of the satellite observations. We also compute the evolution of the electron number density of the ionosphere due to this events and found that the ionosphere was becoming increasingly charged due to repeated bombardment of the high energy radiations. The lower ionospheric height went down significantly. We found convincing evidence that the source SGR J1550-5418 repeatedly caused ionospheric disturbances on the 22nd of January, 2009. The electron number density went up significantly at all the heights. The height of the lower ionosphere went down by about 15 km due to these repeated events.

REVIEW OF ELECTRIC AND MAGNETIC FIELDS ACCOMPANYING SEISMIC AND VOLCANIC ACTIVITY

New observations of magnetic, electric and electromagnetic field variations, possibly related to recent volcanic and seismic events, have been obtained on Mt. Unzen in Japan, Reunion Island in Indian Ocean, the Long Valley volcanic caldera in California, and for faults in China and Russia, California and several other locations. For volcanic events, contributions from different physical processes can be identified during the various eruption stages. Slow processes (weeks to months) include near-surface thermal demagnetization effects, piezomagnetic effects, and effects from rotation/displacement of magnetized material. Rapid processes (seconds to days) include piezomagnetic effects from instantaneous stress redistribution with explosive eruptions and electrokinetic effects from rupture of high pressure fluid compartments commonly encountered in volcanic regions. For seismic events, the observed coseismic offsets are instantaneous, provided care has been taken to ensure sensors are insensitive to seismic shaking and are in regions of low magnetic field gradient. Simple piezomagnetic dislocation models based on geodetically and seismically determined fault parameters generally match the observed signals in size and sign. Electrokinetic effects resulting from rupture of fluid filled compartments at hydrostatic to lithostatic pore pressures can generate transient signals in the frequency band 100 Hz to 0.01 Hz. However, large-scale fluid driven processes are not evident in near-field measurements in the epicentral region minutes to weeks before large earthquakes. The subset of ionospheric disturbances generated by trapped atmospheric pressure waves (also termed gravity waves and/or acoustic waves, traveling ionospheric disturbances or TID's) that are excited by earthquakes and volcanic eruptions are common and propagate to great distances. These are known and expected consequences of earthquakes, volcanic explosions (and other atmospheric disturbances), that must be identified and their effects removed from VLF/ULF electromagnetic field records before associating new observations of ionospheric disturbances with earthquake activity.

Observation of ionospheric disturbances following a 5‐kt chemical explosion 2. Prolonged anomalies and stratifications in the lower thermosphere after shock passage

We have observed unusual stratifications and prolonged spectral deformations of radio echoes after the passage through the E region of the shock wave produced by a 5‐kt chemical explosion. Our observations were obtained by vertical HF pulsed ionospheric sounding. At the total reflection level of the sounding waves, at a horizontal distance of 30 km from the explosion, the passage of the shock wave generated a complex structure suggesting a significant deformation of the reflecting surface. This effect was followed at the E region total reflection level (130 km) by a broadening of the Doppler spectra, persisting several tens of minutes. Two spectral peaks appear at 0.5 Hz, suggesting an amplitude modulation with a period of the order of 2 s. At lower virtual heights (94, 103, and 115 km), stratifications appear after the shock passage and move downward at velocities of the order of 23 m/s. These layers persist for several minutes. Irregularities have also been observed in the E region for over 30 min after the shock passage by a network of continuous wave HF ionospheric sounders located 250 km west of the source. The origin of these structures is discussed.

Observations of ionospheric disturbances following a 5‐kt chemical explosion: 1. Persistent oscillation in the lower thermosphere after shock passage

We have observed a 6‐min‐period oscillation persisting for an hour in the ionospheric E region following a 5‐kt chemical explosion on the ground 250 km south of the measurement site. The oscillation's phase velocity in the upper atmosphere is 0.15 km/s at an azimuth 60°W. Our observations are obtained using a time‐delayed correlation technique with multistation Doppler sounding of the overhead ionosphere. Some new aspects of the technique are described.

Doppler observations of ionospheric disturbances

Summary The Doppler shift in frequency of an ionospherically reflected radio wave can be used to study various ionospheric disturbances. In this article the experimental arrangement for measuring such a shift is described, and examples of frequency shifts associated with solar flares, geomagnetic variations and travelling disturbances are discussed.

On the Role of Joule Heating as a Source of Gravity-Wave Energy above 100 km

Abstract Observations of ionospheric disturbances by various investigators have led to the suggestion that auroral energy may be coupled to atmospheric wave motions through joule heating. A linear model of internal gravity-wave generation by joule heating in the region of the auroral electrojet (100–150 km above the earth's surface) is investigated. Heat conduction, viscosity and reflection of wave energy by atmospheric inhomogeneities are not considered. The computed value of the upward wave-energy flux from the source region is of order 0.1–1 erg cm−2 sec−1 and is of sufficient magnitude to be of importance in the energetics of the F region. Shortcomings of the present model are discussed, with emphasis on how the physical features which have been neglected might affect the present results.

Observation of ionospheric disturbances following the Alaska earthquake

The Alaska earthquake, which occurred at 5:36 P.M. local time on Friday March 27, 1964 (0336, March 28, 1964 UT), initiated a large traveling ionospheric disturbance. This disturbance undoubtedly affected many different types of ionospheric sensors; however, the data reported here are limited to ionosondes operating at College, Alaska; Adak, Alaska; Palo Alto, California; and Maui, Hawaii. The ionosonde data show indications of the perturbation in two different forms. The form depends on the distance between the observing station and the epicenter of the earthquake.