scholarly journals The role of the F-region vertical drift on the onset time of the equatorial spread F over Ilorin, Nigeria

2019 ◽  
Vol 128 (5) ◽  
Author(s):  
O A Oladipo ◽  
J O Adeniyi ◽  
I A Adimula ◽  
A O Olawepo ◽  
A Olowookere ◽  
...  
Keyword(s):  
Onset Time ◽  
Equatorial Spread F ◽  
F Region ◽  
Vertical Drift ◽  
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.

scholarly journals Radar and satellite investigations of equatorial evening vertical drifts and spread <i>F</i>

2015 ◽  
Vol 33 (11) ◽  
pp. 1403-1412 ◽  
Author(s):  
J. M. Smith ◽  
F. S. Rodrigues ◽  
E. R. de Paula
Keyword(s):  
Local Time ◽  
Empirical Model ◽  
Sufficient Condition ◽  
Satellite Measurements ◽  
Equatorial Spread F ◽  
Annual Variability ◽  
F Region ◽  
Plasma Drifts ◽  
Spread F ◽  
Coherent Backscatter

Abstract. We analyzed pre-midnight equatorial F region observations made by the 30 MHz coherent backscatter radar of São Luis, Brazil between August 2010 and February 2012. These measurements were processed, and used to create monthly maps of the echo occurrence as a function of local time and height. The maps show the inter-annual variability associated with equatorial spread F (ESF) occurrence in the Brazilian longitude sector. We also constructed monthly curves of the evening vertical drifts, for the Brazilian sector, using measurements by the ion velocity meter (IVM) onboard the C/NOFS satellite. The IVM evening drifts show a good overall agreement with the Scherliess and Fejer (1999) empirical model. Measured and model drifts show the development of the pre-reversal enhancement (PRE) of the vertical plasma drifts during ESF season. Using joint radar and satellite measurements, we found that evening (18:00–18:30 LT) mean non-negative drifts provide a necessary but not sufficient condition for the occurrence of topside ESF echoes. Evening downward (negative) drifts preceded the absence of topside ESF irregularities.

Investigation on the role of E-F region coupling processes on the generation of nighttime MSTIDs: Case studies over northern Germany

2021 ◽  
Author(s):  
Mani Sivakandan ◽  
Jorge L Chau ◽  
Carlos Martinis ◽  
Yuichi Otsuka ◽  
Jens Mielich ◽  
...  
Keyword(s):  
Gps Tec ◽  
F Region ◽  
Perkins Instability ◽  
Sporadic E Layers ◽  
Spread F ◽  
E Region ◽  
Sporadic E ◽  
Low Latitude Ionosphere ◽  
Atmospheric Gravity

&lt;p&gt;Northwest to southeast phase fronts with southwestward moving features are commonly observed in the nighttime midlatitude ionosphere during the solstice months at low solar activity. These features are identified as nighttime MSTIDs (medium scale traveling ionospheric disturbances). Initially, they were considered to be a manifestation of neutral atmospheric gravity waves. Later on, investigations showed that the nighttime MSTIDs are electrified in nature and mostly confined to the mid and low latitude ionosphere. Although the overall characteristics of the nighttime MSTIDs are mostly well understood, the causative mechanisms are not well known. Perkins instability mechanism was believed to be the cause of nighttime MSTIDs, however, the growth rate of the instability is too small to explain the perturbations observed. Recently, model simulations and observational studies suggest that coupling between sporadic-E layers and other type of E-region instabilities, and the F region may be relevant to explain the generation of the MSTIDs.&lt;/p&gt;&lt;p&gt;In the present study simultaneous observation from OI 630 nm all-sky airglow imager, GPS-TEC, ionosonde and Meteor radars, are used to investigate the role of E and F region coupling on the generation of MSTIDs .Nighttime MSTIDs observed on three nights (14 March 2020, 23 March 2020 and 28 May 2020) in the OI 630 nm airglow images over Kuehlungsborn (54&amp;#176;07'N; 11&amp;#176;46'E, 53.79N&amp;#160; mag latitude), Germany, are presented. Simultaneous detrended GPS-TEC measurements also shows presence of MSTIDs on these nights. In addition, simultaneous ionosonde observations over Juliusruh (54&amp;#176;37.7'N 13&amp;#176;22.5'E) show spread-F in the ionograms as well as sporadic-E layer occurrence.&amp;#160; Furthermore, we also investigate the MLT region wind variations during these nights. The role of Es-layers and the interplay between the winds and Es-layers role on the generation of the MSTIDs will be discussed in detail in this presentation.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

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.

scholarly journals Fast and ultrafast Kelvin wave modulations of the equatorial evening F region vertical drift and spread F development

2015 ◽  
Vol 67 (1) ◽  
Author(s):  
Mangalathayil A Abdu ◽  
Christiano GM Brum ◽  
Paulo P Batista ◽  
Subramanian Gurubaran ◽  
Dora Pancheva ◽  
...  
Keyword(s):  
Kelvin Wave ◽  
F Region ◽  
Vertical Drift ◽  
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 Impact of disturbance electric fields in the evening on prereversal vertical drift and spread F developments in the equatorial ionosphere

2018 ◽  
Vol 36 (2) ◽  
pp. 609-620 ◽  
Author(s):  
Mangalathayil A. Abdu ◽  
Paulo A. B. Nogueira ◽  
Angela M. Santos ◽  
Jonas R. de Souza ◽  
Inez S. Batista ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Plasma Bubble ◽  
Large Variability ◽  
Plasma Drift ◽  
F Region ◽  
Vertical Drift ◽  
Spread F ◽  
The Impact ◽  
Magnetic Disturbances

Abstract. Equatorial plasma bubble/spread F irregularity occurrence can present large variability depending upon the intensity of the evening prereversal enhancement in the zonal electric field (PRE), that is, the F region vertical plasma drift, which basically drives the post-sunset irregularity development. Forcing from magnetospheric disturbances is an important source of modification and variability in the PRE vertical drift and of the associated bubble development. Although the roles of magnetospheric disturbance time penetration electric fields in the bubble irregularity development have been studied in the literature, many details regarding the nature of the interaction between the penetration electric fields and the PRE vertical drift still lack our understanding. In this paper we have analyzed data on F layer heights and vertical drifts obtained from digisondes operated in Brazil to investigate the connection between magnetic disturbances occurring during and preceding sunset and the consequent variabilities in the PRE vertical drift and associated equatorial spread F (ESF) development. The impact of the prompt penetration under-shielding eastward electric field and that of the over-shielding, and disturbance dynamo, westward electric field on the evolution of the evening PRE vertical drift and thereby on the ESF development are briefly examined. Keywords. Ionosphere (ionospheric irregularities)

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 Observational evidence for the plausible linkage of Equatorial Electrojet (EEJ) electric field variations with the post sunset F-region electrodynamics

2009 ◽  
Vol 27 (11) ◽  
pp. 4229-4238 ◽  
Author(s):  
V. Sreeja ◽  
C. V. Devasia ◽  
◽  
Keyword(s):  
Observational Study ◽  
Electric Field ◽  
Solar Maximum ◽  
Equatorial Electrojet ◽  
Observational Evidence ◽  
Related Parameter ◽  
F Region ◽  
Seasonal Characteristics ◽  
Vertical Drift ◽  
Spread F

Abstract. The paper is based on a detailed observational study of the Equatorial Spread F (ESF) events on geomagnetically quiet (Ap≤20) days of the solar maximum (2001), moderate (2004) and minimum (2006) years using the ionograms and magnetograms from the magnetic equatorial location of Trivandrum (8.5° N; 77° E; dip lat ~0.5° N) in India. The study brings out some interesting aspects of the daytime Equatorial Electrojet (EEJ) related electric field variations and the post sunset F-region electrodynamics governing the nature of seasonal characteristics of the ESF phenomena during these years. The observed results seem to indicate a plausible linkage of daytime EEJ related electric field variations with pre-reversal enhancement which in turn is related to the occurrence of ESF. These electric field variations are shown to be better represented through a parameter, termed as "E", in the context of possible coupling between the E- and F-regions of the ionosphere. The observed similarities in the gross features of the variations in the parameter "E" and the F-region vertical drift (Vz) point towards the potential usage of the EEJ related parameter "E" as an useful index for the assessment of Vz prior to the occurrence of ESF.

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