scholarly journals Solar flux dependence of coherence scales in scintillation patterns produced by ESF irregularities

2005 ◽  
Vol 23 (10) ◽  
pp. 3261-3266 ◽  
Author(s):  
B. Engavale ◽  
K. Jeeva ◽  
K. U. Nair ◽  
A. Bhattacharyya
Keyword(s):  
Initial Phase ◽  
General Trend ◽  
Linear Increase ◽  
Solar Flux ◽  
Radio Waves ◽  
Spread F ◽  
Decorrelation Scale ◽  
10.7 Cm Solar Flux ◽  
East West ◽  
Scale Length

Abstract. The coherence scale length, defined as the 50% decorrelation scale length along the magnetic east-west direction, in the ground scintillation pattern obtained at a dip equatorial location, due to scattering of VHF radio waves by equatorial spread F (ESF) irregularities, is calculated, using amplitude scintillation data recorded by two spaced receivers. The average east-west drift of the ground scintillation pattern, during the pre- and post-midnight periods, also calculated from the same observations, shows an almost linear increase with 10.7-cm solar flux. In the present paper the variability of the drift is automatically taken into account in the calculation of the coherence scale length of the ground scintillation pattern. For weak scintillations, the coherence scale depends on the Fresnel scale, which varies with the height of the irregularity layer, and also on the spectral index of the irregularity power spectrum. It is found that for weak scintillations, the coherence scales are much better organized according to the 10.7-cm solar flux, during the pre-midnight period, than during the post-midnight period, with a general trend of coherence scale length increasing with 10.7-cm solar flux except for cases with F 10.7-cm solar flux <100. This indicates that, during the initial phase of ESF irregularity development, the irregularity spectrum does not have much variability while further evolution of the spatial structure in ESF irregularities is controlled by factors other than the solar flux.

scholarly journals Statistical analysis of radar observed F region irregularities from three longitudinal sectors

2013 ◽  
Vol 31 (12) ◽  
pp. 2137-2146 ◽  
Author(s):  
R. Y. C. Cueva ◽  
E. R. de Paula ◽  
A. E. Kherani
Keyword(s):  
Onset Time ◽  
Solar Flux ◽  
Christmas Island ◽  
F Region ◽  
Incoherent Scatter Radars ◽  
Declination Angle ◽  
Spread F ◽  
Occurrence Characteristics ◽  
Using Data

Abstract. Equatorial Spread F (ESF) is a manifestation of ionospheric interchange instabilities in the nighttime equatorial F region. These instabilities generate plasma density irregularities with scale sizes ranging from centimetres to thousands of kilometres. The irregularities can be detected from a variety of instruments such as digisonde, coherent and incoherent scatter radars, in situ space probes, and airglow photometers. In the present study, occurrence statistics of the ESF, based on various parameters are presented using data obtained from the VHF radars located at three longitudinally separated equatorial stations: Christmas Island (2° N, 202.6° E, 2.9° N dip latitude), São Luís (2.59° S, 315.8° E, 0.5° S dip latitude) and Jicamarca (12° S, 283.1° E, 0.6° N dip latitude). The ESF parameters presented here are the onset altitude, onset time (onset refers to first appearance of signal in the radar field of view) of the bottom-type and plume, and the peak altitude of the plume. Recent studies have used these parameters to classify the spread F occurrence characteristics. The present study reveals novel features namely, the dependence of ESF parameters on the seasonal, solar flux, declination angle and longitudinal dependence from the three radar sites. In addition, we also present an empirical model to determine the nature of these ESF parameters as a function of the solar flux which may enable us to forecast (with 30 min to 1 h tolerance) the plume occurrence at any longitude located in between São Luís and Christmas Island.

The Mid-Atlantic Ridge Near 45°N. XXIII. Analysis of Bathymetric and Magnetic Data

1975 ◽  
Vol 12 (3) ◽  
pp. 337-346 ◽  
Author(s):  
P. J. Bhattacharyya ◽  
R. D. Hyndman ◽  
M. J. Keen
Keyword(s):  
Cross Correlation ◽  
General Trend ◽  
Magnetic Data ◽  
Spreading Center ◽  
Transform Fault ◽  
Contour Maps ◽  
Regional Trends ◽  
Mid Atlantic Ridge ◽  
Lateral Displacements ◽  
East West

Bathymetric and magnetic data obtained from the Mid-Atlantic Ridge near 45°N have been analyzed numerically to determine trends, offsets and local structure. The estimates of regional trends in the data reveal that the average structural trend in this area is 17°E of north, made up of nearly north–south segments periodically offset by small right lateral displacements. The east–west offsets, not always visually manifest in contour maps of the data have been located by a cross-correlation scheme. Frequent small offsets may be the way a ridge crest accommodates to a spreading direction not perpendicular to the general trend of the crest. There is evidence for an old, now dead spreading center to the west of the median valley. This old center with an orientation of about 15°W, terminating in a right lateral transform fault has been abandoned in favor of frequent small offsets which provide smaller resistance to spreading.

scholarly journals Equatorial ionospheric zonal drift model and vertical drift statistics from UHF scintillation measurements in South America

2004 ◽  
Vol 22 (9) ◽  
pp. 3177-3193 ◽  
Author(s):  
R. E. Sheehan ◽  
C. E. Valladares
Keyword(s):  
Elevation Angle ◽  
Early Morning ◽  
Solar Flux ◽  
Drift Model ◽  
Early Evening ◽  
Vertical Drift ◽  
Wide Range ◽  
East West ◽  
Statistical Results ◽  
Ionospheric Drifts

Abstract. UHF scintillation measurements of zonal ionospheric drifts have been conducted at Ancon, Peru since 1994 using antennas spaced in the magnetic east-west direction to cross-correlate geo-synchronous satellite signals. An empirical model of average drift over a wide range of Kp and solar flux conditions was constructed from successive two-dimensional fits of drift vs. the parameters and day of year. The model exhibits the typical local time trend of maximum eastward velocity in the early evening with a gradual decrease and reversal in the early morning hours. As expected, velocities at all hours increase with the solar flux and decrease with Kp activity. It was also found that vertical drifts could contribute to the variability of drift measurements to the east of Ancon at a low elevation angle. The vertical drift at the ionospheric intersection to the east can be estimated when combined with nearly overhead observations at Ancon or a similar spaced-antenna site at Antofagasta, Chile. Comparisons on five days with nearly simultaneous measurements of vertical drift by the Julia radar at Jicamarca, Peru show varying agreement with the spaced-antenna estimates. Statistical results from 1997 to 2001 generally agree with radar and satellite studies.

Spread F echoes variability along solar flux and seasonality conditions over the 50-MHz radar on Christmas Island

2015 ◽  
Author(s):  
R. Y. C. Cueva ◽  
F. S. Rodrigues ◽  
E. R. de Paula ◽  
R. T. Tsunoda ◽  
K. M Groves ◽  
...  
Keyword(s):  
Solar Flux ◽  
Christmas Island ◽  
Spread F

Solar cycle and seasonal variations in F-region vertical drifts over Kodaikanal, India

1995 ◽  
Vol 13 (6) ◽  
pp. 633-640 ◽  
Author(s):  
K. B. Ramesh ◽  
J. H. Sastri
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Seasonal Variations ◽  
Normal Incidence ◽  
Magnetic Activity ◽  
Solar Flux ◽  
Seasonal Trend ◽  
F Region ◽  
Phase Path ◽  
10.7 Cm Solar Flux

Abstract. Measurements of the changes in phase path of F-region reflections at normal incidence at Kodaikanal (77° 28'E, 10° 14'N, dip 3°N) from February 1991 to February 1993 are used to determine the variation of the equatorial evening F-region vertical drifts (V z) with season, solar and magnetic activity. It is found that on average, at Kodaikanal, the post-sunset peak in Vz(Vzp) is higher in equinox and local winter months than in local summer. The day-to-day variability in V zp is highest in summer and lowest in winter. This seasonal trend persists even on magnetically quiet days (Ap \\leq14). Vzp is found to increase with 10.7 cm solar flux in all three seasons but tends to saturate for large flux values (>230 units) during local summer and winter months. Magnetic activity [represented by Ap as well as the time-weighted accumulations of a p and ap (τ)] does not seem to have any statistically significant effect on Vzp , except during equinoctial months of moderate solar activity, when Vzp decreases as magnetic activity increases.

The 10.7-cm Solar Flux and the 26-Month Oscillation

1966 ◽  
Vol 23 (3) ◽  
pp. 314-319 ◽  
Author(s):  
A. D. Belmont ◽  
D. G. Dartt ◽  
M. S. Ulstad
Keyword(s):  
Solar Flux ◽  
10.7 Cm Solar Flux
Sign in / Sign up

Export Citation Format

Share Document