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 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 Numerical simulation of mid-latitude ionospheric <i>E</i>-region based on SEEK and SEEK-2 observations

2005 ◽  
Vol 23 (7) ◽  
pp. 2377-2384 ◽  
Author(s):  
T. Yokoyama ◽  
M. Yamamoto ◽  
S. Fukao ◽  
T. Takahashi ◽  
M. Tanaka
Keyword(s):  
Numerical Simulation ◽  
Electric Field ◽  
Electric Fields ◽  
Theoretical Models ◽  
Vhf Radar ◽  
Sounding Rockets ◽  
Radar Echoes ◽  
Polarization Electric Field ◽  
E Region ◽  
Sporadic E

Abstract. Observational campaigns of the mid-latitude ionospheric E-region with sounding rockets and ground-based instruments were conducted in 1996 (SEEK) and 2002 (SEEK-2). Both of them were successfully conducted to bring important findings about the mid-latitude E-region and quasi-periodic (QP) VHF radar echoes. The observational results in the SEEK and the SEEK-2 are compared with numerical simulations and discussed in this paper. While sporadic-E (Es)-layers are actually formed by the observed neutral wind, it is difficult for the constant wind shear to produce the sharp Es-layer gradient. However, once they are formed in the lower E-region, they cannot easily be dissipated by the simple diffusive motion. The polarization electric field, calculated under the condition at the rocket launch time, shows similar amplitude and structure to the measurement around the Es-layer altitude. The structure of the plasma density and the electric field above the Es-layer observed in the SEEK-2 showed a wave-like pattern up to an altitude of 150 km. Considering a mapping of the polarization electric field generated within the Es-layers, gravity waves are the possible source of the wave-like structure of the measured electric fields and sub-peaks of the electron density above the main Es-layers. Fluctuation of the measured magnetic field is reproduced by Hall or field-aligned current driven by the polarization electric field. The current theoretical models for QP echoes and the polarization electric field are basically verified by the discussion in this paper. Keywords. Ionospheric irregularities – Mid-latitude ionosphere – Numerical simulation studies

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

&lt;p&gt;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 &amp;#186;N, 109.6 &amp;#186;E) 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.&lt;/p&gt;&lt;p&gt;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 &lt; 8 MHz) and band-like strong Es structures (foEs &gt; 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.&lt;/p&gt;

scholarly journals Some Aspects of Gyro?Splitting in the Ionosphere

1962 ◽  
Vol 15 (1) ◽  
pp. 25 ◽  
Author(s):  
GG Bowman
Keyword(s):  
Geomagnetic Latitude ◽  
Mode Propagation ◽  
E Region ◽  
Sporadic E

Ionograms for Hobart (geomagnetic latitude 52 oS.), showing x-mode propagation below the electron gyro frequency, were examined. Detailed analyses of some ionograms were made. Strong reflections for this particular propagation seem dependent on the amount of ionization, between the sporadic E level and 180 km, being reduced to a sufficiently low value. It is suggested that this can be achieved, in the sporadic E region, by the concentration of existing ionization; this concentration producing the sporadic E reflections.

scholarly journals Sporadic-E associated with the Leonid meteor shower event of November 1998 over low and equatorial latitudes

2001 ◽  
Vol 19 (1) ◽  
pp. 59-69 ◽  
Author(s):  
H. Chandra ◽  
S. Sharma ◽  
C. V. Devasia ◽  
K. S. V. Subbarao ◽  
R. Sridharan ◽  
...  
Keyword(s):  
Meteor Shower ◽  
Low Latitude ◽  
Equatorial Station ◽  
Radio Science ◽  
Ionospheric Physics ◽  
Transmitter Power ◽  
Multiple Structures ◽  
E Region ◽  
Sporadic E Layer ◽  
Sporadic E

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)

scholarly journals Statistical characteristics of PMWE observations by the EISCAT VHF radar

2013 ◽  
Vol 31 (2) ◽  
pp. 359-375 ◽  
Author(s):  
I. Strelnikova ◽  
M. Rapp
Keyword(s):  
Wind Direction ◽  
Doppler Shift ◽  
Spectral Properties ◽  
Spectral Width ◽  
Spectral Shape ◽  
The Other ◽  
Statistical Characteristics ◽  
Spectral Broadening ◽  
Vhf Radar ◽  
Large Variability

Abstract. In the present paper ~ 32.5 h of EISCAT VHF PMWE observations were analyzed with focus on spectral properties like spectral width, doppler shift and spectral shape. Examples from two days of observations with weak and strong polar mesosphere winter echo (PMWE) signals are presented and discussed in detail. These examples reveal a large variability from one case to the other. That is, some features like an observed change of vertical wind direction and spectral broadening can be very prominent in one case, but unnoticeable in the other case. However, for all observations a change of spectral shape inside the layer relative to the incoherent background is noticed.

Sign in / Sign up

Export Citation Format

Share Document