Interferometry observations of low-latitude E-region irregularity patches using the Sanya VHF radar

2014 ◽  
Vol 57 (8) ◽  
pp. 1552-1561 ◽  
Author(s):  
GuoZhu Li ◽  
BaiQi Ning ◽  
LianHuan Hu
Keyword(s):  
Low Latitude ◽  
Vhf Radar ◽  
E Region

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

2005 ◽  
Vol 23 (3) ◽  
pp. 773-779 ◽  
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.

scholarly journals Morphological study of the field-aligned E-layer irregularities observed by the Gadanki VHF radar

2004 ◽  
Vol 22 (11) ◽  
pp. 3799-3804 ◽  
Author(s):  
C. J. Pan ◽  
P. B. Rao
Keyword(s):  
Geomagnetic Latitude ◽  
Spectral Width ◽  
Statistical Characteristics ◽  
Low Latitude ◽  
Vhf Radar ◽  
Lower Altitude ◽  
Radar Echoes ◽  
E Region ◽  
Sporadic E ◽  
Total Observation

Abstract. We report on the field-aligned irregularities observed in the low-latitude sporadic E-layer (Es) with the Gadanki (13.5° N, 79.2° E; geomagnetic latitude 6.3° N) VHF radar. The radar was operated intermittently for 15 days during the summer months in 1998 and 1999, for both daytime and nighttime observation. The total observation periods are 161h for the nighttime and 68h for the daytime. The observations were used to study the percentage of occurrence of the E-region echoes for both daytime and nighttime. The statistical characteristics of the mean radial velocity and spectral width are presented for three cases based on the echo occurrence characteristics and the altitude of observations (from 90 to 140km ranges), namely, the lower E-region daytime (90-110km), the lower E-region nighttime (90-105km) and the upper E-region nighttime (105-140km) echoes. The results are compared with that of Piura, a low-latitude station located at about the same geomagnetic latitude, but to the south of the equator. By comparing the behaviors of the lower E-region radar echoes of the summer months between Gadanki and Piura, we find that the lower altitude echoes below about 100km are rarely reported in Piura but commonly seen in Gadanki. Features of the nighttime echoes observed by these two radars are quite similar but daytime FAI echoes are again seldom detected by Piura.

scholarly journals First simultaneous lidar observations of sodium layers and VHF radar observations of E-region field-aligned irregularities at the low-latitude station Gadanki

2009 ◽  
Vol 27 (9) ◽  
pp. 3411-3419 ◽  
Author(s):  
S. Sridharan ◽  
A. K. Patra ◽  
N. Venkateswara Rao ◽  
G. Ramkumar
Keyword(s):  
Lower Thermosphere ◽  
Low Latitude ◽  
Vhf Radar ◽  
Neutral Winds ◽  
Zonal Winds ◽  
Tidal Phase ◽  
E Region ◽  
The Relationship ◽  
Lidar Observations ◽  
Field Aligned Irregularities

Abstract. Simultaneous observations of atmospheric sodium (Na) made by a resonance lidar and E-region field-aligned-irregularities (FAI) made by the Indian MST radar, both located at Gadanki (13.5° N, 79.2° E) and horizontal winds acquired by a SKiYMET meteor radar at Trivandrum (8.5° N, 77° E) are used to investigate the relationship among sodium layer, FAI and neutral winds in the mesosphere and lower thermosphere region. The altitudes and descent rates of higher altitude (~95 km) Na layer and FAI agree quite well. The descending structures of the higher altitude Na layer and FAI are found to be closely related to the diurnal tidal phase structure in zonal winds observed over Trivandrum. At lower altitudes, the descent rate of FAI is larger than that of Na layer and zonal tidal phase. These observations support the hypothesis that the metallic ion layers are formed by the zonal wind shear associated with tidal winds and subsequently get neutralized to manifest in the form of descending Na layers. The descending FAI echoing layers are manifestation of the instabilities setting in on the ionization layer. In the present observations, the altitudes of occurrence of Na layer and FAI echoes being low, we surmise that it is quite possible that the FAI echoes are due to the descent of already formed irregularities at higher altitudes.

The evolution of complex Es observed by multi instruments over low-latitude China

2021 ◽  
Author(s):  
Wenjie Sun ◽  
Baiqi Ning ◽  
Lianhuan Hu ◽  
Xiukuan Zhao ◽  
Guozhu Li
Keyword(s):  
High Frequency ◽  
Electron Content ◽  
Very High Frequency ◽  
Low Latitude ◽  
Radar Backscatter ◽  
Vhf Radar ◽  
Total Electron ◽  
E Region ◽  
Sporadic E ◽  
Very High

<p>Early and recent observations suggested that E-region field aligned irregularities (FAIs) related closely to the sporadic E (Es) layer of the ionosphere. The Sanya (18.3 ºN, 109.6 ºE) very high frequency (VHF) radar can operate at ionospheric irregularities mode for the detection of 3-m scale FAIs. The development of a portable digital ionosonde (PDI) which is collocated with the Sanya VHF radar can operate with temporal periods down to 1 minute, facilitating the capability of capturing the fast evolution of Es structures. But the low spatial resolution of the two kinds of instruments makes it difficult to depict the horizontal morphology of the Es structures and E-region FAIs. Since the capability of ground-based GNSS in strong Es detection was presented, it serves as a perfect supplement for the investigation of E region of the ionosphere. So comprehensive observation with multi kinds of instruments makes it possible to reveal the relationship and mechanisms of Es and E-region FAIs.</p><p>A complex daytime sporadic E (Es) case with extremely high critical frequency (foEs) was observed over the low latitude of China on 19 May 2018. Simultaneous observational results from two very high frequency (VHF) radars, two ionosondes, and multiple Global Navigation Satellite System total electron content and scintillation receivers are analyzed to investigate the evolution of the complex Es occurrence, which consisted of a relatively weak ambient Es layer (foEs < 8 MHz) and band-like strong Es structures (foEs > 17 MHz) drifting from higher latitude. The strong Es structures elongated more than 500 km in the northwest-southeast direction, drifted southwestward at a speed of ~65 m/s. VHF radar backscatter echoes were generated when the strong Es structures passed the radar field of view, with different echo patterns due to different radar and antenna configurations. No VHF radar backscatter echo was associated with the ambient Es layer.</p>

scholarly journals Enhanced incoherent scatter plasma lines

1996 ◽  
Vol 14 (12) ◽  
pp. 1462-1472 ◽  
Author(s):  
H. Nilsson ◽  
S. Kirkwood ◽  
J. Lilensten ◽  
M. Galand
Keyword(s):  
High Plasma ◽  
Collision Term ◽  
Vhf Radar ◽  
Detailed Model ◽  
Model Calculations ◽  
Incoherent Scatter ◽  
Incoherent Scatter Radars ◽  
Plasma Line ◽  
E Region ◽  
Radar Measurements

Abstract. Detailed model calculations of auroral secondary and photoelectron distributions for varying conditions have been used to calculate the theoretical enhancement of incoherent scatter plasma lines. These calculations are compared with EISCAT UHF radar measurements of enhanced plasma lines from both the E and F regions, and published EISCAT VHF radar measurements. The agreement between the calculated and observed plasma line enhancements is good. The enhancement from the superthermal distribution can explain even the very strong enhancements observed in the auroral E region during aurora, as previously shown by Kirkwood et al. The model calculations are used to predict the range of conditions when enhanced plasma lines will be seen with the existing high-latitude incoherent scatter radars, including the new EISCAT Svalbard radar. It is found that the detailed structure, i.e. the gradients in the suprathermal distribution, are most important for the plasma line enhancement. The level of superthermal flux affects the enhancement only in the region of low phase energy where the number of thermal electrons is comparable to the number of suprathermal electrons and in the region of high phase energy where the suprathermal fluxes fall to such low levels that their effect becomes small compared to the collision term. To facilitate the use of the predictions for the different radars, the expected signal- to-noise ratios (SNRs) for typical plasma line enhancements have been calculated. It is found that the high-frequency radars (Søndre Strømfjord, EISCAT UHF) should observe the highest SNR, but only for rather high plasma frequencies. The VHF radars (EISCAT VHF and Svalbard) will detect enhanced plasma lines over a wider range of frequencies, but with lower SNR.

scholarly journals A numerical model of the ionosphere, including the E-region above EISCAT

1996 ◽  
Vol 14 (2) ◽  
pp. 191-200 ◽  
Author(s):  
P.-Y. Diloy ◽  
A. Robineau ◽  
J. Lilensten ◽  
P.-L. Blelly ◽  
J. Fontanari
Keyword(s):  
Electric Field ◽  
Fluid Model ◽  
Molecular Ions ◽  
Ion Concentration ◽  
Topside Ionosphere ◽  
Ion Chemistry ◽  
Vhf Radar ◽  
Theoretical Predictions ◽  
Consistent Manner ◽  
E Region

Abstract. It has been previously demonstrated that a two-ion (O+ and H+) 8-moment time-dependent fluid model was able to reproduce correctly the ionospheric structure in the altitude range probed by the EISCAT-VHF radar. In the present study, the model is extended down to the E-region where molecular ion chemistry (NO+ and O+2, essentially) prevails over transport; EISCAT-UHF observations confirmed previous theoretical predictions that during events of intense E×B induced convection drifts, molecular ions (mainly NO+) predominate over O+ ions up to altitudes of 300 km. In addition to this extension of the model down to the E-region, the ionization and heating resulting from both solar insolation and particle precipitation is now taken into account in a consistent manner through a complete kinetic transport code. The effects of E×B induced convection drifts on the E- and F-region are presented: the balance between O+ and NO+ ions is drastically affected; the electric field acts to deplete the O+ ion concentration. The [NO+]/[O+] transition altitude varies from 190 km to 320 km as the perpendicular electric field increases from 0 to 100 mV m-1. An interesting additional by-product of the model is that it also predicts the presence of a noticeable fraction of N+ ions in the topside ionosphere in good agreement with Retarding Ion Mass Spectrometer measurements onboard Dynamic Explorer.

The first time observations of low-latitude ionospheric irregularities by VHF radar in Hainan

2012 ◽  
Vol 55 (5) ◽  
pp. 1189-1197 ◽  
Author(s):  
BaiQi Ning ◽  
LianHuan Hu ◽  
GuoZhu Li ◽  
LiBo Liu ◽  
WeiXing Wan
Keyword(s):  
Ionospheric Irregularities ◽  
Low Latitude ◽  
Vhf Radar ◽  
First Time

scholarly journals The sporadic radiant and distribution of meteors in the atmosphere as observed by VHF radar at Arctic, Antarctic and equatorial latitudes

2009 ◽  
Vol 27 (7) ◽  
pp. 2831-2841 ◽  
Author(s):  
P. T. Younger ◽  
I. Astin ◽  
D. J. Sandford ◽  
N. J. Mitchell
Keyword(s):  
Spatial Variability ◽  
Annual Cycle ◽  
High Latitude ◽  
The Arctic ◽  
Low Latitude ◽  
Vhf Radar ◽  
Ascension Island ◽  
Temporal And Spatial Variability ◽  
Temporal And Spatial ◽  
Celestial Sphere

Abstract. Results are presented of a study of the temporal and spatial variability in meteor count rate observations from three VHF meteor radars. These radar are located in the Arctic (at Esrange, 68° N), in the Antarctic (at Rothera, 68° S) and near the Equator (on Ascension Island, 8° S). It is found that for all three locations there is a strong diurnal cycle in observed hourly meteor counts and the time of maxima and minima in these counts depends on the month of the year. In addition, at high latitude there is a strong annual cycle in observed monthly-mean meteor counts, whereas for the radar at low latitude there is a semi-annual cycle. At high latitude there is also an annual cycle in the mean height at which meteors are observed. However, no such annual cycle is found in observed meteor count rates from the low latitude radar. The meteor count data from all the radars are combined to investigate the sporadic radiant distribution (i.e. the distribution of direction of arrival on the celestial sphere of sporadic meteors). This combined radiant distribution shows that there are six main source regions for meteors. The latitudinal and temporal dependence in observed meteor count rates appears to result from a combination of the sporadic radiant distribution, annual fluctuations in atmospheric density, the sensitivity of the radar to meteors from different source directions and the temporal and spatial variability in meteor fluxes.

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