Some important factors that affect the Doppler properties of vertical m-size echoes in the low latitude E region

2005 ◽  
Author(s):  
J.-P. St.-Maurice* ◽  
R. K. Choudhary
Keyword(s):  
Low Latitude ◽  
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 Seasonal variation of low-latitude E-region plasma irregularities studied using Gadanki radar and ionosonde

2008 ◽  
Vol 26 (7) ◽  
pp. 1865-1876 ◽  
Author(s):  
D. V. Phanikumar ◽  
A. K. Patra ◽  
C. V. Devasia ◽  
G. Yellaiah
Keyword(s):  
Seasonal Variation ◽  
Seasonal Variations ◽  
Low Latitude ◽  
Plasma Irregularities ◽  
Daytime Activity ◽  
Significant Difference ◽  
E Region ◽  
Region Plasma ◽  
Present Understanding ◽  
Field Aligned Irregularities

Abstract. In this paper, we present seasonal variation of E region field-aligned irregularities (FAIs) observed using the Gadanki radar and compare them with the seasonal variation of Es observed from a nearby location SHAR. During daytime, FAIs occur maximum in summer and throughout the day, as compared to other seasons. During nighttime, FAIs occur equally in both summer and winter, and relatively less in equinoxes. Seasonal variations of Es (i.e. ftEs and fbEs) show that the daytime activity is maximum in summer and the nighttime activity is maximum in equinoxes. No relation is found between FAIs occurrence/SNR and ftEs/fbEs. FAIs occurrence, however, is found to be related well with (ftEs−fbEs). This aspect is discussed in the light of the present understanding of the mid-latitude Es-FAIs relationship. The seasonal variations of FAIs observed at Gadanki are compared in detail with those of Piura, which show a significant difference in the daytime observations. The observed difference has been discussed considering the factors governing the generation of FAIs.

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 LOW-LATITUDE E-REGION QUASI-PERIODIC ECHOES STUDIED USING LONG-TERM RADAR OBSERVATIONS OVER GADANKI

2009 ◽  
pp. 245-261
Author(s):  
N. VENKATESWARA RAO ◽  
A. K. PATRA ◽  
S. VIJAYA BHASKARA RAO
Keyword(s):  
Low Latitude ◽  
Radar Observations ◽  
E Region

scholarly journals The ionospheric responses to the 11 August 1999 solar eclipse: observations and modeling

2008 ◽  
Vol 26 (1) ◽  
pp. 107-116 ◽  
Author(s):  
H. Le ◽  
L. Liu ◽  
X. Yue ◽  
W. Wan
Keyword(s):  
Theoretical Model ◽  
Solar Radiation ◽  
Solar Eclipse ◽  
Ionospheric Disturbance ◽  
Low Latitude ◽  
Ionospheric Response ◽  
Latitude Range ◽  
Eclipse Observations ◽  
E Region ◽  
Low Latitude Ionosphere

Abstract. A total eclipse occurred on 11 August 1999 with its path of totality passing over central Europe in the latitude range 40°–50° N. The ionospheric responses to this eclipse were measured by a wide ionosonde network. On the basis of the measurements of foE, foF1, and foF2 at sixteen ionosonde stations in Europe, we statistically analyze the variations of these parameters with a function of eclipse magnitude. To model the eclipse effects more accurately, a revised eclipse factor, FR, is constructed to describe the variations of solar radiation during the solar eclipse. Then we simulate the effect of this eclipse on the ionosphere with a mid- and low-latitude ionosphere theoretical model by using the revised eclipse factor during this eclipse. Simulations are highly consistent with the observations for the response in the E-region and F1-region. Both of them show that the maximum response of the mid-latitude ionosphere to the eclipse is found in the F1-region. Except the obvious ionospheric response at low altitudes below 500 km, calculations show that there is also a small response at high altitudes up to about 2000 km. In addition, calculations show that when the eclipse takes place in the Northern Hemisphere, a small ionospheric disturbance also appeared in the conjugate hemisphere.

scholarly journals Characteristics of low latitude ionospheric E-region irregularities linked with daytime VHF scintillations measured from Varanasi

2009 ◽  
Vol 118 (6) ◽  
pp. 721-732 ◽  
Author(s):  
K. Patel ◽  
A. K. Singh ◽  
R. P. Patel ◽  
R. P. Singh
Keyword(s):  
Low Latitude ◽  
E Region
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