Statistical characteristics of VHF radar observations of low latitude E-region field-aligned irregularities over Gadanki

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

Annales Geophysicae ◽

10.5194/angeo-22-3799-2004 ◽

2004 ◽

Vol 22 (11) ◽

pp. 3799-3804 ◽

Cited By ~ 1

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.

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First VHF radar observations of tropical latitude E-region field aligned irregularities

Geophysical Research Letters ◽

10.1029/96gl02625 ◽

1996 ◽

Vol 23 (25) ◽

pp. 3683-3686 ◽

Cited By ~ 17

Author(s):

R. K. Choudhary ◽

K. K. Mahajan ◽

Sachchidanand Singh ◽

Keshav Kumar ◽

V. K. Anandan

Keyword(s):

Vhf Radar ◽

Radar Observations ◽

Tropical Latitude ◽

E Region ◽

Field Aligned Irregularities

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

Annales Geophysicae ◽

10.5194/angeo-27-3411-2009 ◽

2009 ◽

Vol 27 (9) ◽

pp. 3411-3419 ◽

Cited By ~ 5

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.

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Statistical characteristics of low-latitude ionospheric field-aligned irregularities obtained with the Piura VHF radar

Annales Geophysicae ◽

10.5194/angeo-20-1203-2002 ◽

2002 ◽

Vol 20 (8) ◽

pp. 1203-1212 ◽

Cited By ~ 25

Author(s):

J. L. Chau ◽

R. F. Woodman ◽

L. A. Flores

Keyword(s):

Signal To Noise Ratio ◽

Equatorial Electrojet ◽

Meridional Wind ◽

Statistical Characteristics ◽

Doppler Velocity ◽

Vhf Radar ◽

F Region ◽

Seasonal Characteristics ◽

E Region ◽

Field Aligned Irregularities

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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Evidence of kilometer-scale waves in the lower E region from high resolution VHF radar observations over Gadanki

Geophysical Research Letters ◽

10.1029/2001gl013340 ◽

2002 ◽

Vol 29 (10) ◽

pp. 137-1-137-4 ◽

Cited By ~ 16

Author(s):

A. K. Patra ◽

S. Sripathi ◽

V. Siva Kumar ◽

P. B. Rao

Keyword(s):

High Resolution ◽

Vhf Radar ◽

Radar Observations ◽

E Region

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Seasonal variation of low-latitude E-region plasma irregularities studied using Gadanki radar and ionosonde

Annales Geophysicae ◽

10.5194/angeo-26-1865-2008 ◽

2008 ◽

Vol 26 (7) ◽

pp. 1865-1876 ◽

Cited By ~ 7

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.

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