scholarly journals Spread F echoes variability along solar flux and seasonality conditions over the 50-MHz radar on Christmas Island/ Espalhe a variabilidade dos ecos de F ao longo do fluxo solar e das condições de sazonalidade no radar de 50 MHz na Ilha Christmas

2021 ◽  
Vol 7 (9) ◽  
pp. 92880-92889
Author(s):  
Ricardo Yvan de La Cruz Cueva ◽  
Jean-Pierre Raulin ◽  
Jorge Enrique Samanes Cardenas
Keyword(s):  
Solar Flux ◽  
Christmas Island ◽  
Spread F

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.

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

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 Time and Altitude spread F echoes distribution over the Christmas Island VHF radar

2022 ◽  
Author(s):  
Ricardo Yvan de La Cruz Cueva ◽  
Eurico Rodrigues de Paula ◽  
Acácio Cunha Neto
Keyword(s):  
Solar Minimum ◽  
Solar Maximum ◽  
Equatorial Region ◽  
Peak Time ◽  
Vhf Radar ◽  
Equatorial Spread F ◽  
Plasma Drift ◽  
Christmas Island ◽  
Spread F

Abstract. The goal of this work is to study the time and altitude echoes characteristics under different solar and seasonality conditions using the VHF radar RTI images. The occurrence of equatorial spread F depends on the existence of conditions that can seed the Raileight-Taylor instability, and these conditions can change with solar flux, seasonality, longitude distributions, and day-to-day variability. So, the equatorial spread F is observed as its time and altitude occurrence. The VHF radar of Christmas Island (2.0° N, 157.4° W, 2.9° N dip latitude) has been operational in the equatorial region for some time now, allowing long-term observations. The occurrence of echoes during solar minimum conditions are observed all throughout the night since the post reversal westward electric field is weaker than the solar maximum and the possibilities for the vertical plasma drift to become positive are larger. On other hand, echoes during solar maximum will be controlled by dynamics near the time of the Pre-reversal Peak (PRE). Our results indicate peak time occurrence of echoes along this period shows a well-defined pattern, with echoes being distributed as closer to local sunset during solar maximum and around/closer midnight during solar minimum conditions, meanwhile, the peak altitude occurrence of echoes shows a slightly regular pattern with higher altitude occurrences during solar maxima and lower altitudes during solar minimum conditions.

Phenomena during the growth and decay of spread-F

1963 ◽  
Vol 25 (5) ◽  
pp. 445
Author(s):  
M.S.V. Gopala rao ◽  
B. Ramachandra rao
Keyword(s):  
Spread F

scholarly journals Investigation of Low Latitude Spread-F Triggered by Nighttime Medium-Scale Traveling Ionospheric Disturbance

2021 ◽  
Vol 13 (5) ◽  
pp. 945
Author(s):  
Zhongxin Deng ◽  
Rui Wang ◽  
Yi Liu ◽  
Tong Xu ◽  
Zhuangkai Wang ◽  
...  
Keyword(s):  
Ionospheric Disturbance ◽  
Phase Speed ◽  
Morphological Processing ◽  
Wave Number ◽  
Occurrence Rate ◽  
Electron Content ◽  
Low Latitude ◽  
Total Electron ◽  
Medium Scale ◽  
Spread F

In the current study, we investigated the mechanism of medium-scale traveling ionospheric disturbance (MSTID) triggering spread-F in the low latitude ionosphere using ionosonde observation and Global Navigation Satellite System-Total Electron Content (GNSS-TEC) measurement. We use a series of morphological processing techniques applied to ionograms to retrieve the O-wave traces automatically. The maximum entropy method (MEM) was also utilized to obtain the propagation parameters of MSTID. Although it is widely acknowledged that MSTID is normally accompanied by polarization electric fields which can trigger Rayleigh–Taylor (RT) instability and consequently excite spread-F, our statistical analysis of 13 months of MSTID and spread-F occurrence showed that there is an inverse seasonal occurrence rate between MSTID and spread-F. Thus, we assert that only MSTID with certain properties can trigger spread-F occurrence. We also note that the MSTID at night has a high possibility to trigger spread-F. We assume that this tendency is consistent with the fact that the polarization electric field caused by MSTID is generally the main source of post-midnight F-layer instability. Moreover, after thorough investigation over the azimuth, phase speed, main frequency, and wave number over the South America region, we found that the spread-F has a tendency to be triggered by nighttime MSTID, which is generally characterized by larger ΔTEC amplitudes.

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