Characteristics of the E- and F-region field-aligned irregularities in middle latitudes: Initial results obtained from the Daejeon 40.8 MHz VHF radar in South Korea

Abstract. We present a summary of the statistical characteristics of echoes from ionospheric (E- and F-region) field-aligned irregularities obtained with the Piura VHF radar. This radar is located at ~ 7.0° dip latitude, just outside the equatorial electrojet (EEJ) region. Our results are based on (1) intermittent observations made between 1991 and 1999 just few days a year, and (2) continuous observations made between January 2000 and June 2001. During most of the intermittent observations, simultaneous measurements of EEJ and equatorial spread F (ESF) irregularities were performed with the Jicamarca VHF radar. From the continuous measurements, we have obtained the diurnal and seasonal characteristics of a variety of parameters (percentage of occurrence, signal-to-noise ratio and/or Doppler velocities) from the lower and upper E-region irregularities and also from F-region irregularities over Piura. For example, we have found that (1) the E-region echoes are stronger and occur more frequently during local summer (i.e. between December and March); (2) between May and June, the E-region echoes are weaker and occur less frequently; moreover, during these months, a semidiurnal wave with large amplitudes is observed in the meridional wind (> 100 ms- 1); (3) there is vertical wavelength of about 20 km in the Doppler velocity, particularly after midnight; (4) the lower (upper) E-region Doppler velocities are influenced mainly by meridional winds (equatorial F-region vertical drifts). In addition, we have observed that the seasonal and daily occurrences of Piura F-region irregularities are similar to the occurrence of topside ESF irregularities over Jicamarca. The likelihood of occurrence of F-region irregularities over Piura and, therefore, topside ESF over Jicamarca is greater when there are no E-region irregularities over Piura. On the other hand, there is more probability of observing bottomtype/bottomside ESF irregularities over Jicamarca when E-region irregularities are observed over Piura.Key words. Ionosphere (ionospheric irregularities; equatorial ionosphere; instruments and techniques)

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Statistical investigations of layer-type and clump-type plasma structures of 3-m field-aligned irregularities in nighttime sporadic E region made with Chung-Li VHF radar

Journal of Geophysical Research Atmospheres ◽

10.1029/2011ja016696 ◽

2011 ◽

Vol 116 (A12) ◽

pp. n/a-n/a ◽

Cited By ~ 10

Author(s):

C. Y. Wang ◽

Y. H. Chu ◽

C. L. Su ◽

R.-M. Kuong ◽

H.-C. Chen ◽

...

Keyword(s):

Vhf Radar ◽

E Region ◽

Sporadic E ◽

Field Aligned Irregularities

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Simultaneous VHF radar backscatter and ionosonde observations of low-latitude E region

Annales Geophysicae ◽

10.5194/angeo-23-773-2005 ◽

2005 ◽

Vol 23 (3) ◽

pp. 773-779 ◽

Cited By ~ 8

Author(s):

A. K. Patra ◽

S. Sripathi ◽

P. B. Rao ◽

K. S. V. Subbarao

Keyword(s):

Low Latitude ◽

Vhf Radar ◽

Radar Echoes ◽

First Results ◽

E Region ◽

Gradient Drift ◽

Drift Instability ◽

Relationship Of ◽

The Relationship ◽

Field Aligned Irregularities

Abstract. The first results of simultaneous observations made on the low-latitude field-aligned irregularities (FAI) using the MST radar located at Gadanki (13.5° N, 79.2° E, dip 12.5°) and the Es parameters using an ionosonde at a nearby station Sriharikota (13.7° N, 80.1° E, dip 12.6°) are presented. The observations show that while the height of the most intense radar echoes is below the virtual height of Es (h'Es) during daytime, it is found to be either below or above during nighttime. The strength of the FAI is better correlated with the top penetration frequency (ftEs) and the blanketing frequency (fbEs) during the night (r=0.4 in both cases) as compared to the day (r=0.35 and -0.04, respectively). Furthermore, the signal strength of FAI is reasonably correlated with (ftEs-fbEs) during daytime (r=0.59) while very poorly correlated during nighttime (r=0.18). While the radar observations in general appear to have characteristics close to that of mid-latitudes, the relationship of these with the Es parameters are poorer than that of mid-latitudes. The observations reported here, nevertheless, are quite consistent with the expectations based on the gradient drift instability mechanism.

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Doppler HF radar measurements of backscattered signals induced by small-scale field-aligned irregularities of subpolar f-region ionosphere

Trans Black Sea Region Symposium on Applied Electromagnetism ◽

10.1109/aem.1996.873169 ◽

2005 ◽

Author(s):

V.P. Uryadov ◽

O.M. Maksimenko ◽

X.M. Boguta

Keyword(s):

Hf Radar ◽

Small Scale ◽

F Region ◽

Scale Field ◽

Radar Measurements ◽

Backscattered Signals ◽

Field Aligned Irregularities

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Predicted and observed characteristics of small-scale field-aligned irregularities generated in the F-region by low power HF heating

Annales Geophysicae ◽

10.5194/angeo-20-647-2002 ◽

2002 ◽

Vol 20 (5) ◽

pp. 647-653 ◽

Cited By ~ 1

Author(s):

E. Kolesnikova ◽

T. R. Robinson ◽

J. A. Davies

Keyword(s):

Low Power ◽

Decay Rate ◽

Parametric Instability ◽

Small Scale ◽

F Region ◽

Scale Field ◽

Thermal Parametric Instability ◽

Hf Heating ◽

Heated Volume ◽

Field Aligned Irregularities

Abstract. Simultaneous HF scattering from the different regions of the heated volume is used to investigate characteristics of the small-scale field-aligned irregularities in the F-region. Time of growth, decay rate and saturation level for different pump powers are deduced from the observations and are compared with their behaviour predicted by the thermal parametric instability model. As a result, the estimates of the density and of the temperature modifications inside of the irregularities are obtained.Key words. Ionosphere (ionospheric irregularities)

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Multi-frequency HF radar measurements of artificial F-region field-aligned irregularities

Annales Geophysicae ◽

10.5194/angeo-22-3503-2004 ◽

2004 ◽

Vol 22 (10) ◽

pp. 3503-3511 ◽

Cited By ~ 13

Author(s):

A. Senior ◽

N. D. Borisov ◽

M. J. Kosch ◽

T. K. Yeoman ◽

F. Honary ◽

...

Keyword(s):

Wave Interaction ◽

Operating Mode ◽

Hf Radar ◽

Heating Facility ◽

F Region ◽

Density Perturbations ◽

Radar Measurements ◽

The Mean ◽

Power Measurements ◽

Field Aligned Irregularities

Abstract. We present radar backscatter power measurements using the CUTLASS HF radar at Hankasalmi, Finland from F-region field-aligned irregularities induced by HF radio pumping with the EISCAT Heating facility. A novel radar operating mode is used in which the radar frequency is rapidly swept through a number of bands, making use of the varying ionospheric refraction to probe different heights within the heated region. We obtain height profiles of backscatter power which correspond to e-folding scale lengths of around 20km for the mean-square electron density perturbations for pump wave interaction heights in the region of 240-250km in daytime conditions. The results are in agreement with previous measurements made by other techniques. We discuss some problems with the method and suggest improvements for future experiments.

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First observation of quasi-2-day oscillations in ionospheric plasma frequency at fixed heights

Annales Geophysicae ◽

10.1007/s00585-998-0609-5 ◽

1998 ◽

Vol 16 (5) ◽

pp. 609-617 ◽

Cited By ~ 15

Author(s):

D. Altadill ◽

J. G. Solé ◽

E. M. Apostolov

Keyword(s):

Ionospheric Plasma ◽

Plasma Frequency ◽

Neutral Atmosphere ◽

Middle Latitudes ◽

Ionosphere Plasma ◽

F Region ◽

Summer Half ◽

Dominant Period ◽

June July ◽

Frequency Variations

Abstract. The existence and development of the quasi-2-day oscillations in the plasma frequency variations of the F region at northern middle latitudes are investigated. A new approach to study the quasi-2-day oscillations is presented, using a methodology that allows us to do such a study at fixed heights. The hourly values of plasma frequency at fixed heights, from 170 km to 220 km at 10 km step, obtained at the Observatori de l'Ebre station (40.8°N, 0.5°E) during 1995 are used for analysis. It is found that quasi-2-day oscillations exist and persisted in the ionospheric plasma frequency variations over the entire year 1995 for all altitudes investigated. The dominant period of oscillation ranges from 42 to 56 h. The amplitude of oscillation is from 0.1 MHz to 1 MHz. The activity of the quasi-2-day oscillation is better expressed during the summer half year when several enhancements, about 15–30 days in duration, were observed. The largest enhancements of the oscillation occurred during early June, July and early August; i. e., near and after the summer solstice when the 2-day wave in the middle neutral atmosphere typically displays its largest activity in the Northern Hemisphere. The results obtained may help us understand better the possible influencing mechanisms between the 2-day wave in the middle neutral atmosphere and the ionospheric quasi-2-day oscillations.Key words. Ionosphere (Ionosphere - atmosphere interactions; Mid-latitude ionosphere; Plasma waves and instabilities)

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