Low altitude quasi‐periodic radar echoes observed by the Gadanki VHF radar

Chen, Pan; Rao, P. B.

doi:10.1029/2001gl014331

Cited by 17 publications

(25 citation statements)

References 22 publications

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“…Tsunoda et al, 1999;Hysell and Burcham, 2000;Chau et al, 2002;Fukao et al, 2003). Low-altitude QP (LQP) echoes that appear below 100 km are found from Japan, India, and Puerto Rico (Rao et al, 2000;Pan and Rao, 2002;Urbina et al, 2000;Ogawa et al, 2002), also. QP structures themselves are now regarded as a general feature that appear in the E-region FAIs, although their generating mechanisms might vary by case.…”

Section: Introductionmentioning

confidence: 99%

SEEK-2 (Sporadic-<i>E</i> Experiment over Kyushu 2) − Project Outline, and Significance

et al. 2005

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Abstract. SEEK-2 (Sporadic-E Experiment over Kyushu 2)is an observation campaign to study the spatial structure of the field-aligned irregularity (FAI) and sporadic-E(E s )-layer by means of two sounding rockets and a ground-based observation network with radars and optical instruments. The experiment was successfully conducted on 3 August 2002, with successive launches of two sounding rockets from the Uchinoura Space Center (USC) of the Japan Aerospace Exploration Agency (JAXA). The timing of the experiment was carefully selected, while intense quasi-periodic (QP) echoes were observed with two radars in Tanegashima. The main E s -layer, with its double-layered structure, was observed at altitudes of 103-105 km, the presence of which was well accounted for by the ion accumulation due to neutral-wind shear. Several minor peaks were detected in the electron density profiles at altitudes of up to 130 km. The intensity of the electric field was 5-10 mV/m and showed intense fluctuations below 110 km. Wave-like variation of the electric field was seen above 110 km. From radar experiments, we found that QP echoes appeared around 105 km, which agreed well with the main E s -layer height. The QP echoes propagated to the west-northwest, with frontal structures elongated from north-northeast to south-southwest. Radar observations conduced throughout the SEEK-2 period, on the other hand, showed that frontal structures of the QP echoes were most frequently propagated to the southeast. This result was consistent with the direction of gravity-wave propagation observed with the OH imager during the same period. The rocket beacon experiment with the E s -layers revealed the spatial structure of the plasma densities. On the basis of these results and those from SEEK-1 in 1996, we examined the structures of the nighttime mid-latitude E-region. We concluded that the QP echoes reflect the horizontal structures of the main E s -layers. The source of the structures was not clearly determined from the experiments, but the candidates are gravity waves and the Kelvin-Helmholtz instability. The azimuth-dependent E s -instability may have contributed to enhance structures of the QP echoes, although this instability may not be a major source of the QP structure in SEEK-2. Polarization electric fields were induced from the E s -layer with QP echoes, mapped upward along the geomagnetic field, and played an important role in determining the structures of the whole ionospheric E-region.

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Section: Introductionmentioning

confidence: 99%

SEEK-2 (Sporadic-<i>E</i> Experiment over Kyushu 2) − Project Outline, and Significance

et al. 2005

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“…The observations on low-latitude FAI, on the other hand, have just begun. The observations on the low-latitude FAI that are available in the literature are those made by the Gadanki MST radar (13.5 • N, 79.2 • E, dip 12.5 • ), located in southern part of India (Krishna Correspondence to: A. K. Patra (patra nmrf@rediffmail.com) Murthy et al, 1998;Choudhary and Mahajan, 1999;Patra and Rao, 1999;Patra et al, 2002a,b;2004;Pan and Rao, 2002;Sripathi et al, 2003) and by the Piura VHF radar (5.2 • , 80.6 • W; 13.9 • dip angle), located in northern Peru Chau and Woodman, 1999;Chau et al, 2002). These radars are located just outside the equatorial electrojet (EEJ) region and have revealed many interesting and new features of the low-latitude E region FAI, including the general characteristics that are so different from those at either the equator or mid-latitudes (Chau et al, 2002;Patra et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

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

Patra

Sripathi²,

Rao³

et al. 2005

Ann. Geophys.

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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 E s 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 E s (h'E s ) 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 (f t E s ) and the blanketing frequency (f b E s ) 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 (f t E s -f b E s ) 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 E s 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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“…We find that 45% of the observed echoes are characterized by QP features that correspond to the nighttime LQP echoes (Pan and Rao, 2002). The occurrence ranges of the nighttime LQP echoes are slightly lower than that of the daytime LQP echoes.…”

Section: Data Presentationmentioning

confidence: 82%

“…Most of the QP radar echoes are centered at about the 110-115 km range. Lower altitude QP radar echoes are found at ranges below 100 km (Urbina et al, 2000;Pan and Rao, 2002). Continuous types of echoes are found from 24:00 to 03:00 LT at ranges between 95 and 115 km in a descending trend.…”

Section: Data Presentationmentioning

confidence: 82%

“…By summarizing the main results of the earlier observations by the Gadanki radar we find that: (1) QP echoes appeared during most of the nighttime from altitudes between 102 and 116 km, (2) the Low-altitude QP (LQP) echoes occurred both during daytime and nighttime and are confined to a slowly descending layer with a thickness of about 2-4 km in the height range of 90-100 km, and (3) two to three layered structures of continuous nature existed during both daytime and nighttime (Krishna Murthy et al, 1998; Choudhary and Mahajan; 1999; Patra and Rao, 1999;Pan and Rao;2002;Patra et al, 2002a, b).…”

Section: Data Presentationmentioning

confidence: 99%

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

Chen

Rao

2004

Ann. Geophys.

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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 161 h for the nighttime and 68 h 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 140 km ranges), namely, the lower Eregion daytime (90-110 km), the lower E-region nighttime (90-105 km) and the upper E-region nighttime (105-140 km) echoes. The results are compared with that of Piura, a lowlatitude 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 100 km 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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Low altitude quasi‐periodic radar echoes observed by the Gadanki VHF radar

Cited by 17 publications

References 22 publications

SEEK-2 (Sporadic-<i>E</i> Experiment over Kyushu 2) − Project Outline, and Significance

SEEK-2 (Sporadic-<i>E</i> Experiment over Kyushu 2) − Project Outline, and Significance

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

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

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Low altitude quasi‐periodic radar echoes observed by the Gadanki VHF radar

Cited by 17 publications

References 22 publications

SEEK-2 (Sporadic-&lt;i&gt;E&lt;/i&gt; Experiment over Kyushu 2) − Project Outline, and Significance

SEEK-2 (Sporadic-&lt;i&gt;E&lt;/i&gt; Experiment over Kyushu 2) − Project Outline, and Significance

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

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

Contact Info

Product

Resources

About

SEEK-2 (Sporadic-<i>E</i> Experiment over Kyushu 2) − Project Outline, and Significance

SEEK-2 (Sporadic-<i>E</i> Experiment over Kyushu 2) − Project Outline, and Significance