scholarly journals Thermospheric meridional wind control of equatorial spread F and evening prereversal electric field

2006 ◽  
Vol 33 (7) ◽  
Author(s):  
M. A. Abdu ◽  
K. N. Iyer ◽  
R. T. de Medeiros ◽  
I. S. Batista ◽  
J. H. A. Sobral
Keyword(s):  
Electric Field ◽  
Meridional Wind ◽  
Equatorial Spread F ◽  
Spread F

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 On the seasonal variations of the threshold height for the occurrence of equatorial spread F during solar minimum and maximum years

2007 ◽  
Vol 25 (4) ◽  
pp. 855-861 ◽  
Author(s):  
G. Manju ◽  
C. V. Devasia ◽  
R. Sridharan
Keyword(s):  
Solar Minimum ◽  
Solar Maximum ◽  
Decisive Role ◽  
Meridional Wind ◽  
Equatorial Spread F ◽  
Clear Cut ◽  
Meridional Winds ◽  
Different Seasons ◽  
Spread F ◽  
Bottom Side

Abstract. A study has been carried out on the occurrence of bottom side equatorial spread F (ESF) and its dependence on the polarity and magnitude of the thermospheric meridional wind just prior to ESF occurrence during summer, winter and equinox seasons of solar maximum (2002) and minimum years (1995), using ionosonde data of Trivandrum (8.5° N, 76.5° E, dip=0.5° N) and SHAR (13.7° N, 80.2° E, dip ~5.5° N) in the Indian longitude sector. In this study, we have examined the changes in the threshold height of the base of the F layer for the triggering of ESF, irrespective of the magnitude and polarity of the meridional winds during the above periods. The study indicates that the threshold height above which ESF triggering is entirely controlled only by the collisional R-T instability is least for summer months, with higher values for winter and equinox, during the solar minimum period, whereas for the solar maximum period the threshold height is least for winter, with higher values for summer and equinox. But the range over which the threshold height varies is very narrow (<15 km) for solar minimum in relation to the large range of variation (>50 km) in the solar maximum epoch. Further to this, the study also reveals a clear-cut increase in threshold height with solar activity for all seasons. Clear-cut seasonal variability is also observed in the threshold height, especially for solar maximum. The study quantifies the level of the base of the F layer below which neutral dynamical effects play a decisive role in the triggering of ESF during different seasons and solar epochs.

scholarly journals Wave structure and polarization electric field development in the bottomside F layer leading to postsunset equatorial spread F

2015 ◽  
Vol 120 (8) ◽  
pp. 6930-6940 ◽  
Author(s):  
M. A. Abdu ◽  
J. R. Souza ◽  
E. A. Kherani ◽  
I. S. Batista ◽  
J. W. MacDougall ◽  
...  
Keyword(s):  
Electric Field ◽  
Wave Structure ◽  
Equatorial Spread F ◽  
Field Development ◽  
Spread F ◽  
Polarization Electric Field

scholarly journals Relationships between pre-sunset electrojet strength, pre-reversal enhancement and equatorial spread-F onset

2010 ◽  
Vol 28 (2) ◽  
pp. 449-454 ◽  
Author(s):  
J. Uemoto ◽  
T. Maruyama ◽  
S. Saito ◽  
M. Ishii ◽  
R. Yoshimura
Keyword(s):  
Electric Field ◽  
Equatorial Electrojet ◽  
Layer Height ◽  
Equatorial Spread F ◽  
Magnetic Latitude ◽  
F Region ◽  
Spread F ◽  
Bottom Side ◽  
E Region ◽  
Height Increase

Abstract. The virtual height of the bottom side F-region (h'F) and equatorial spread-F (ESF) onsets at Chumphon (10.7° N, 99.4° E; 3.3° N magnetic latitude) were compared with the behaviour of equatorial electrojet (EEJ) ground strength at Phuket (8.1° N, 98.3° E; 0.1° N magnetic latitude) during the period from November 2007 to October 2008. Increase in the F-layer height and ESF onsets during the evening hours were well connected with the EEJ ground strength before sunset, namely, both the height increase and ESF onsets were suppressed when the integrated EEJ ground strength for the period from 1 to 2 h prior to sunset was negative. The finding suggests observationally that the pre-sunset E-region dynamo current and/or electric field are related to the F-region dynamics and ESF onsets around sunset.

scholarly journals Three-dimensional simulation of equatorial spread-F with meridional wind effects

2009 ◽  
Vol 27 (5) ◽  
pp. 1821-1830 ◽  
Author(s):  
J. Krall ◽  
J. D. Huba ◽  
G. Joyce ◽  
S. T. Zalesak
Keyword(s):  
Field Line ◽  
Three Dimensional ◽  
Meridional Wind ◽  
Two Dimensions ◽  
Simulation Code ◽  
Equatorial Spread F ◽  
Meridional Winds ◽  
Spread F ◽  
Field Geometry ◽  
Dimensional Simulation

Abstract. The NRL SAMI3 three-dimensional simulation code is used to examine the effect of meridional winds on the growth and suppression of equatorial spread F (ESF). The simulation geometry conforms to a dipole field geometry with field-line apex heights from 200 to 1600 km at the equator, but extends over only 4 degrees in longitude. The full SAMI3 ionosphere equations are included, providing ion dynamics both along and across the field. The potential is solved in two dimensions in the equatorial plane under a field-line equipotential approximation. By selectively including terms in the potential equation, the reduced growth predicted by Maruyama (1988) and the stabilization predicted by Zalesak and Huba (1991) are separately realized. We find that ESF is stabilized by a sufficiently large constant meridional wind (60 m/s in our example).

Equatorial Spread-F and Magnetic Activity

Nature ◽  
1958 ◽  
Vol 181 (4625) ◽  
pp. 1724-1725 ◽  
Author(s):  
A. J. LYON ◽  
N. J. SKINNER ◽  
R. W. WRIGHT
Keyword(s):  
Magnetic Activity ◽  
Equatorial Spread F ◽  
Spread F

scholarly journals Seasonal dependence of the "forecast parameter" based on the EIA characteristics for the prediction of Equatorial Spread F (ESF)

2008 ◽  
Vol 26 (7) ◽  
pp. 1751-1757 ◽  
Author(s):  
S. V. Thampi ◽  
S. Ravindran ◽  
T. K. Pant ◽  
C. V. Devasia ◽  
R. Sridharan
Keyword(s):  
Seasonal Variability ◽  
Seasonal Pattern ◽  
Onset Time ◽  
Critical Value ◽  
Latitudinal Gradients ◽  
Electron Content ◽  
Total Electron ◽  
Equatorial Spread F ◽  
Spread F ◽  
Definite Role

Abstract. In an earlier study, Thampi et al. (2006) have shown that the strength and asymmetry of Equatorial Ionization Anomaly (EIA), obtained well ahead of the onset time of Equatorial Spread F (ESF) have a definite role on the subsequent ESF activity, and a new "forecast parameter" has been identified for the prediction of ESF. This paper presents the observations of EIA strength and asymmetry from the Indian longitudes during the period from August 2005–March 2007. These observations are made using the line of sight Total Electron Content (TEC) measured by a ground-based beacon receiver located at Trivandrum (8.5° N, 77° E, 0.5° N dip lat) in India. It is seen that the seasonal variability of EIA strength and asymmetry are manifested in the latitudinal gradients obtained using the relative TEC measurements. As a consequence, the "forecast parameter" also displays a definite seasonal pattern. The seasonal variability of the EIA strength and asymmetry, and the "forecast parameter" are discussed in the present paper and a critical value for has been identified for each month/season. The likely "skill factor" of the new parameter is assessed using the data for a total of 122 days, and it is seen that when the estimated value of the "forecast parameter" exceeds the critical value, the ESF is seen to occur on more than 95% of cases.

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