scholarly journals Concurrent observations at the magnetic equator of small-scale irregularities and large-scale depletions associated with equatorial spread F

2015 ◽  
Vol 120 (12) ◽  
pp. 10,883-10,896 ◽  
Author(s):  
Dustin A. Hickey ◽  
Carlos R. Martinis ◽  
Fabiano S. Rodrigues ◽  
Roger H. Varney ◽  
Marco A. Milla ◽  
...  
Keyword(s):  
Large Scale ◽  
Magnetic Equator ◽  
Small Scale ◽  
Equatorial Spread F ◽  
Spread F

scholarly journals Characterization of VHF radar observations associated with equatorial Spread F by narrow-band optical measurements

2004 ◽  
Vol 22 (9) ◽  
pp. 3129-3136 ◽  
Author(s):  
R. Sekar ◽  
D. Chakrabarty ◽  
R. Narayanan ◽  
S. Sripathi ◽  
A. K. Patra ◽  
...  
Keyword(s):  
Large Scale ◽  
Temporal Variations ◽  
Density Fluctuations ◽  
Optical Measurements ◽  
Small Scale ◽  
Upward Movement ◽  
Vhf Radar ◽  
Equatorial Spread F ◽  
Spread F ◽  
Airglow Intensity

Abstract. The VHF radars have been extensively used to investigate the structures and dynamics of equatorial Spread F (ESF) irregularities. However, unambiguous identification of the nature of the structures in terms of plasma depletion or enhancement requires another technique, as the return echo measured by VHF radar is proportional to the square of the electron density fluctuations. In order to address this issue, co-ordinated radar backscatter and thermospheric airglow intensity measurements were carried out during March 2003 from the MST radar site at Gadanki. Temporal variations of 630.0-nm and 777.4-nm emission intensities reveal small-scale ("micro") and large-scale ("macro") variations during the period of observation. The micro variations are absent on non-ESF nights while the macro variations are present on both ESF and non-ESF nights. In addition to the well-known anti-correlation between the base height of the F-region and the nocturnal variation of thermospheric airglow intensities, the variation of the base height of the F-layer, on occasion, is found to manifest as a bottomside wave-like structure, as seen by VHF radar on an ESF night. The micro variations in the airglow intensities are associated with large-scale irregular plasma structures and found to be in correspondence with the "plume" structures obtained by VHF radar. In addition to the commonly observed depletions with upward movement, the observation unequivocally reveals the presence of plasma enhancements which move downwards. The observation of enhancement in 777.4-nm airglow intensity, which is characterized as plasma enhancement, provides an experimental verification of the earlier prediction based on numerical modeling studies.

Evidence for a large scale electric field gradient at the onset of equatorial spread-F

1984 ◽  
Vol 46 (4) ◽  
pp. 355-362 ◽  
Author(s):  
R Raghavarao ◽  
J.N Desai ◽  
B.G Anandarao ◽  
R Narayanan ◽  
R Sekar ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Field Gradient ◽  
Field Gradient ◽  
Large Scale ◽  
Equatorial Spread F ◽  
Spread F

scholarly journals Multistation digisonde observations of equatorial spread F in South America

2004 ◽  
Vol 22 (9) ◽  
pp. 3145-3153 ◽  
Author(s):  
B. W. Reinisch ◽  
M. Abdu ◽  
I. Batista ◽  
G. S. Sales ◽  
G. Khmyrov ◽  
...  
Keyword(s):  
South America ◽  
Field Line ◽  
Magnetic Equator ◽  
Simple Correlation ◽  
Equatorial Spread F ◽  
F Region ◽  
Sporadic E Layers ◽  
Spread F ◽  
E Region ◽  
Sporadic E

Abstract. Directional ionogram and F-region drift observations were conducted at seven digisonde stations in South America during the COPEX campaign from October to December 2002. Five stations in Brazil, one in Argentina, and one in Peru, monitored the ionosphere across the continent to study the onset and development of F-region density depletions that cause equatorial spread F (ESF). New ionosonde techniques quantitatively describe the prereversal uplifting of the F layer at the magnetic equator and the eastward motion of the depletions over the stations. Three of the Brazilian stations were located along a field line with a 350-km apex over the equator to investigate the relation of the occurrence of ESF and the presence of sporadic E-layers at the two E-region intersections of the field line. No simple correlation was found.

scholarly journals NUMERICAL SIMULATIONS OF LARGE SCALE EQUATORIAL SPREAD F

1996 ◽  
Vol 45 (11) ◽  
pp. 1930
Author(s):  
HUANG CHAO-SONG ◽  
M.C.KELLEY
Keyword(s):  
Numerical Simulations ◽  
Large Scale ◽  
Equatorial Spread F ◽  
Spread F

scholarly journals The Brazil/Guará Equatorial Spread F Campaign: Results of the large scale measurements

1997 ◽  
Vol 24 (13) ◽  
pp. 1691-1694 ◽  
Author(s):  
J. LaBelle ◽  
J.-M. Jahn ◽  
R. F. Pfaff ◽  
W. E. Swartz ◽  
J. H. A. Sobral ◽  
...  
Keyword(s):  
Large Scale ◽  
Equatorial Spread F ◽  
Spread F

scholarly journals Ionogram signatures of large-scale wave structure and their relation to equatorial spread F

2012 ◽  
Vol 117 (A8) ◽  
pp. n/a-n/a ◽  
Author(s):  
Smitha V. Thampi ◽  
Roland T. Tsunoda ◽  
Lijo Jose ◽  
Tarun Kumar Pant
Keyword(s):  
Large Scale ◽  
Wave Structure ◽  
Equatorial Spread F ◽  
Spread F

First observations of large-scale wave structure and equatorial spread F using CERTO radio beacon on the C/NOFS satellite

2009 ◽  
Vol 36 (18) ◽  
Author(s):  
Smitha V. Thampi ◽  
Mamoru Yamamoto ◽  
Roland T. Tsunoda ◽  
Yuichi Otsuka ◽  
Takuya Tsugawa ◽  
...  
Keyword(s):  
Large Scale ◽  
Wave Structure ◽  
Equatorial Spread F ◽  
Spread F ◽  
Radio Beacon

scholarly journals Characteristics of mesospheric gravity waves near the magnetic equator, Brazil, during the SpreadFEx campaign

2009 ◽  
Vol 27 (2) ◽  
pp. 461-472 ◽  
Author(s):  
M. J. Taylor ◽  
P.-D. Pautet ◽  
A. F. Medeiros ◽  
R. Buriti ◽  
J. Fechine ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Magnetic Equator ◽  
Small Scale ◽  
Medium Scale ◽  
Source Regions ◽  
High Quality Image ◽  
Short Period ◽  
Spread F ◽  
Radio Measurements

Abstract. As part of the SpreadFEx campaign, coordinated optical and radio measurements were made from Brazil to investigate the occurrence and properties of equatorial Spread F, and to characterize the regional mesospheric gravity wave field. All-sky image measurements were made from two sites: Brasilia and Cariri located ~10° S of the magnetic equator and separated by ~1500 km. In particular, the observations from Brasilia provided key data in relatively close proximity to expected convective sources of the gravity waves. High-quality image measurements of the mesospheric OH emission and the thermospheric OI (630 nm) emission were made during two consecutive new moon periods (22 September to 9 November 2005) providing extensive data on the occurrence and properties of F-region depletions and regional measurements of the dominant gravity wave characteristics at each site. A total of 120 wave displays were observed, comprising 94 short-period events and 26 medium-scale gravity waves. The characteristics of the small-scale waves agreed well with previous gravity wave studies from Brazil and other sites. However, significant differences in the wave propagation headings indicate dissimilar source regions for the Brasilia and Cariri datasets. The observed medium-scale gravity wave events constitute an important new dataset to study their mesospheric properties at equatorial latitudes. These data exhibited similar propagation headings to the short-period events, suggesting they originated from the same source regions. Medium-scale waves are generally less susceptible to wind filtering effects and modeling studies utilizing these data have successfully identified localized regions of strong convection, mainly to the west of Brasilia, as their most likely sources (Vadas et al., 2009).

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