Occurrence and Variations of Middle and Low Latitude Sporadic E Layer Investigated with Longitudinal and Latitudinal Chains of Ionosondes

Abstract. Rapid radio soundings were made over Ahmedabad, a low latitude station during the period 16–20 November 1998 to study the sporadic-E layer associated with the Leonid shower activity using the KEL Aerospace digital ionosonde. Hourly ionograms for the period 11 November to 24 November were also examined during the years from 1994 to 1998. A distinct increase in sporadic-E layer occurrence is noticed on 17, 18 and 19 November from 1996 to 1998. The diurnal variations of f0Es and fbEs also show significantly enhanced values for the morning hours of 18 and 19 November 1998. The ionograms clearly show strong sporadic-E reflections at times of peak shower activity with multiple traces in the altitude range of 100–140 km in few ionograms. Sporadic-E layers with multiple structures in altitude are also seen in some of the ionograms (quarter hourly) at Thumba, situated near the magnetic equator. Few of ionograms recorded at Kodaikanal, another equatorial station, also show sporadic- E reflections in spite of the transmitter power being significantly lower. These new results highlighting the effect of intense meteor showers in the equatorial and low latitude E-region are presented.Key words. Ionosphere (equatorial ionosphere) – Radio science (ionospheric physics)

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Characteristics of double sodium layer over Haikou, China (20.0° N, 110.1° E)

Solnechno-Zemnaya Fizika ◽

10.12737/szf-52201904 ◽

2019 ◽

Vol 5 (2) ◽

pp. 30-34

Author(s):

Ян Дали ◽

Yang Dali ◽

Чжан Теминь ◽

Zhang Tiemin ◽

Ван Цзихун ◽

...

Keyword(s):

Lower Thermosphere ◽

Dye Laser ◽

Low Latitude ◽

Middle Latitudes ◽

Sodium Layer ◽

Layer Structures ◽

Low Latitudes ◽

Sporadic E Layer ◽

Mesosphere And Lower Thermosphere ◽

Sporadic E

We study the property of double sodium layer structures (DSLs) in the mesosphere and lower thermosphere (MLT) by a lidar at the low-latitude location of Haikou (20.0° N, 110.1° E), China. From April 2010 to December 2013, 21 DSLs were observed within a total of 377 observation days. DSLs were recorded at middle latitudes of Beijing and Wuhan, China, but were rarely observed at low latitudes. We analyze and discuss characteristics of DSLs such as time of occurrence, peak altitude, FWHM, duration time, etc. At the same time, the critical frequency foEs and the virtual height h'Es of the sporadic E layer Es were observed by an ionosonde over Danzhou (19.0° N, 109.3° E). We discuss such their characteristics as differences of time, differences of altitude compared to DSLs. We used an Nd:YAG laser pumped dye laser to generate the probing beam. The wavelength of the dye laser was set to 589 nm by a sodium fluorescence cell. The backscattered fluorescence photons from the sodium layer were collected by a telescope with the Φ1000 mm primary mirror.

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Recovery of Ionospheric Signals Using Fully Convolutional DenseNet and Its Challenges

Sensors ◽

10.3390/s21196482 ◽

2021 ◽

Vol 21 (19) ◽

pp. 6482

Author(s):

Merlin M. Mendoza ◽

Yu-Chi Chang ◽

Alexei V. Dmitriev ◽

Chia-Hsien Lin ◽

Lung-Chih Tsai ◽

...

Keyword(s):

Neural Network ◽

Signal To Noise Ratio ◽

Low Latitude ◽

Filtering Algorithm ◽

Low Snr ◽

Sporadic E Layer ◽

Sporadic E ◽

Ionospheric Sounding ◽

Compact Shape

The technique of active ionospheric sounding by ionosondes requires sophisticated methods for the recovery of experimental data on ionograms. In this work, we applied an advanced algorithm of deep learning for the identification and classification of signals from different ionospheric layers. We collected a dataset of 6131 manually labeled ionograms acquired from low-latitude ionosondes in Taiwan. In the ionograms, we distinguished 11 different classes of the signals according to their ionospheric layers. We developed an artificial neural network, FC-DenseNet24, based on the FC-DenseNet convolutional neural network. We also developed a double-filtering algorithm to reduce incorrectly classified signals. That made it possible to successfully recover the sporadic E layer and the F2 layer from highly noise-contaminated ionograms whose mean signal-to-noise ratio was low, SNR = 1.43. The Intersection over Union (IoU) of the recovery of these two signal classes was greater than 0.6, which was higher than the previous models reported. We also identified three factors that can lower the recovery accuracy: (1) smaller statistics of samples; (2) mixing and overlapping of different signals; (3) the compact shape of signals.

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Characteristics of double sodium layer over Haikou, China (20.0° N, 110.1° E)

Solar-Terrestrial Physics ◽

10.12737/stp-52201904 ◽

2019 ◽

Vol 5 (2) ◽

pp. 28-32

Author(s):

Ян Дали ◽

Yang Dali ◽

Чжан Теминь ◽

Zhang Tiemin ◽

Ван Цзихун ◽

...

Keyword(s):

Lower Thermosphere ◽

Dye Laser ◽

Low Latitude ◽

Middle Latitudes ◽

Sodium Layer ◽

Layer Structures ◽

Low Latitudes ◽

Sporadic E Layer ◽

Mesosphere And Lower Thermosphere ◽

Sporadic E

We study the property of double sodium layer structures (DSLs) in the mesosphere and lower thermosphere (MLT) by a lidar at the low-latitude location of Haikou (20.0° N, 110.1° E), China. From April 2010 to December 2013, 21 DSLs were observed within a total of 377 observation days. DSLs were recorded at middle latitudes of Beijing and Wuhan, China, but were rarely observed at low latitudes. We analyze and discuss characteristics of DSLs such as time of occurrence, peak altitude, FWHM, duration time, etc. At the same time, the critical frequency foEs and the virtual height h'Es of the sporadic E layer Es were observed by an ionosonde over Danzhou (19.0° N, 109.3° E). We discuss such their characteristics as differences of time, differences of altitude compared to DSLs. We used an Nd:YAG laser pumped dye laser to generate the probing beam. The wavelength of the dye laser was set to 589 nm by a sodium fluorescence cell. The backscattered fluorescence photons from the sodium layer were collected by a telescope with the Φ1000 mm primary mirror.

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