scholarly journals Preliminary Results of Observations of Aspect-sensitive Reflections from Irregularities in the F Region

1964 ◽  
Vol 17 (4) ◽  
pp. 490 ◽  
Author(s):  
Evelyn M Swenson
Keyword(s):  
Geomagnetic Latitude ◽  
Night Time ◽  
Preliminary Results ◽  
Definite Relationship ◽  
F Region ◽  
Specular Reflections ◽  
Surface Configuration ◽  
Sensitivity Range ◽  
Spread F

Night-time radio reflections from irregularities in the F. region of the ionosphere have been studied at Brisbane (geomagnetic latitude - 35.8�), at a fr-equency of 16 Mc/s. The spatial limits and behaviour of the echoes were consistent with the hypothesis of specular reflections from field-aligned columns of ionization, with observational limitations imposed by echo surface configuration, aerial sensitivity, range attenuation, and absorption. The echoes, recorded with range-azimuth display, were of many shapes, but only a U-shape tended to recur. These U-echoes were preferentially observed under conditions of magnetic disturbace. Irregularity occurrence possibly increased with latitude from 45� to55� geomagnetic latitude. No definite relationship was found between the echoesand v.l.f. noise, radio-star scintillations, spread-F, or auroras.

scholarly journals Latitude Variations of Frequency of Occurrence of "Spread-F" Satellite Traces

1957 ◽  
Vol 10 (4) ◽  
pp. 588 ◽  
Author(s):  
RWE McNicol ◽  
GG Bowman
Keyword(s):  
Relative Frequency ◽  
Frequency Of Occurrence ◽  
Night Time ◽  
F Region ◽  
Spread F ◽  
Time Spread

Night-time "spread-F" satellites, revealed as discrete extra traces of range greater than the main F-region echo on ionograms (h'f records) have been recorded by McNicol, Webster, and Bowman (1956)? as part of the spread-F phenomenon at Brisbane. This report is an investigation of the relative frequency of occurrence of such satellites at different latitudes.

scholarly journals Observations of AGW/TID propagation across the polar cap: a case study

2011 ◽  
Vol 29 (8) ◽  
pp. 1355-1363 ◽  
Author(s):  
H. T. Cai ◽  
F. Yin ◽  
S. Y. Ma ◽  
I. W. McCrea
Keyword(s):  
Large Scale ◽  
Source Region ◽  
Polar Cap ◽  
Night Time ◽  
F Region ◽  
Atmospheric Disturbances ◽  
Geomagnetic Pole ◽  
Ionization Waves ◽  
North Polar ◽  
Propagation Properties

Abstract. In this paper, we present observational evidence for the trans-polar propagation of large-scale Traveling Ionospheric Disturbances (TIDs) from their nightside source region to the dayside. On 13 February 2001, the 32 m dish of EISCAT Svalbard Radar (ESR) was directing toward the geomagnetic pole at low elevation (30°) during the interval 06:00–12:00 UT (MLT ≈ UT + 3 h), providing an excellent opportunity to monitor the ionosphere F-region over the polar cap. The TIDs were first detected by the ESR over the dayside north polar cap, propagating equatorward, and were subsequently seen by the mainland UHF radar at auroral latitudes around geomagnetic local noon. The propagation properties of the observed ionization waves suggest the presence of a moderately large-scale TIDs, propagating across the northern polar cap from the night-time auroral source during substorm conditions. Our results agree with the theoretical simulations by Balthazor and Moffett (1999) in which poleward-propagating large-scale traveling atmospheric disturbances were found to be self-consistently driven by enhancements in auroral heating.

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.

scholarly journals Coherent backscatter radar imaging in Brazil: large-scale waves in the bottomside F-region at the onset of equatorial spread <I>F</I>

2008 ◽  
Vol 26 (11) ◽  
pp. 3355-3364 ◽  
Author(s):  
F. S. Rodrigues ◽  
D. L. Hysell ◽  
E. R. de Paula
Keyword(s):  
Large Scale ◽  
Imaging Technique ◽  
Radar Imaging ◽  
Shear Instability ◽  
Wide Field ◽  
Bottom Type ◽  
F Region ◽  
Type Layer ◽  
Spread F ◽  
Coherent Backscatter

Abstract. The 30 MHz coherent backscatter radar located at the equatorial observatory in São Luís, Brazil (2.59° S, 44.21° W, −2.35° dip lat) has been upgraded to perform coherent backscatter radar imaging. The wide field-of-view of this radar makes it well suited for radar imaging studies of ionospheric irregularities. Radar imaging observations were made in support to the spread F Experiment (SpreadFEx) campaign. This paper describes the system and imaging technique and presents results from a bottom-type layer that preceded fully-developed radar plumes on 25 October 2005. The radar imaging technique was able to resolve decakilometric structures within the bottom-type layer. These structures indicate the presence of large-scale waves (~35 km) in the bottomside F-region with phases that are alternately stable and unstable to wind-driven gradient drift instabilities. The observations suggest that these waves can also cause the initial perturbation necessary to initiate the Generalized Rayleigh-Taylor instability leading to spread F. The electrodynamic conditions and the scale length of the bottom-type layer structures suggest that the waves were generated by the collisional shear instability. These results indicate that monitoring bottom-type layers may provide helpful diagnostics for spread F forecasting.

scholarly journals Studies of ionospheric F-region response in the Latin American sector during the geomagnetic storm of 21–22 January 2005

2011 ◽  
Vol 29 (5) ◽  
pp. 919-929 ◽  
Author(s):  
Y. Sahai ◽  
P. R. Fagundes ◽  
R. de Jesus ◽  
A. J. de Abreu ◽  
G. Crowley ◽  
...  
Keyword(s):  
Geomagnetic Storm ◽  
Latin American ◽  
Geomagnetic Disturbance ◽  
Equatorial Station ◽  
Phase Fluctuations ◽  
Interplanetary Magnetic Fields ◽  
F Region ◽  
Storm Sudden Commencement ◽  
Reversal Time ◽  
Spread F

Abstract. In the present investigation, we have studied the response of the ionospheric F-region in the Latin American sector during the intense geomagnetic storm of 21–22 January 2005. This geomagnetic storm has been considered "anomalous" (minimum Dst reached −105 nT at 07:00 UT on 22 January) because the main storm phase occurred during the northward excursion of the Bz component of interplanetary magnetic fields (IMFs). The monthly mean F10.7 solar flux for the month of January 2005 was 99.0 sfu. The F-region parameters observed by ionosondes at Ramey (RAM; 18.5° N, 67.1° W), Puerto Rico, Jicamarca (JIC; 12.0° S, 76.8° W), Peru, Manaus (MAN; 2.9° S, 60.0° W), and São José dos Campos (SJC; 23.2° S, 45.9° W), Brazil, during 21–22 January (geomagnetically disturbed) and 25 January (geomagnetically quiet) have been analyzed. Both JIC and MAN, the equatorial stations, show unusually rapid uplifting of the F-region peak heights (hpF2/hmF2) and a decrease in the NmF2 coincident with the time of storm sudden commencement (SSC). The observed variations in the F-region ionospheric parameters are compared with the TIMEGCM model run for 21–22 January and the model results show both similarities and differences from the observed results. Average GPS-TEC (21, 22 and 25 January) and phase fluctuations (21, 22, 25, 26 January) observed at Belem (BELE; 1.5° S, 48.5° W), Brasilia (BRAZ; 15.9° S, 47.9° W), Presidente Prudente (UEPP; 22.3° S, 51.4° W), and Porto Alegre (POAL; 30.1° S, 51.1° W), Brazil, are also presented. These GPS stations belong to the RBMC/IBGE network of Brazil. A few hours after the onset of the storm, large enhancements in the VTEC and NmF2 between about 20:00 and 24:00 UT on 21 January were observed at all the stations. However, the increase in VTEC was greatest at the near equatorial station (BELE) and enhancements in VTEC decreased with latitude. It should be pointed out that no phase fluctuations or spread-F were observed in the Latin American sector during the post-sunset pre-reversal time in the geomagnetic disturbance (21 January). The disturbance dynamo electric field possibly resulted in downward drift of the F-region plasma and inhibited the formation of spread-F.

Automatic scaling of polar ionograms

2011 ◽  
Vol 24 (1) ◽  
pp. 88-94 ◽  
Author(s):  
Carlo Scotto ◽  
Michael Pezzopane
Keyword(s):  
Automatic Scaling ◽  
Terra Nova Bay ◽  
F Region ◽  
D Region ◽  
Spread F ◽  
Terra Nova

AbstractThe Istituto Nazionale di Geosifica e Vulcanologia (INGV) software for automatic scaling of ionograms (Autoscala) was improved by introducing a system to identify D region absorption events, spread-F condition (frequency spreading in the F region), and Z-ray propagation. The algorithm was applied to a series of ionograms recorded by the AIS-INGV (Advanced Ionospheric Sounder-INGV) ionosonde installed at the Mario Zucchelli Station (74.7°S, 164.1°E), Terra Nova Bay, Antarctica. Critical cases are shown to illustrate the behaviour of the software.

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 Post midnight spread-F occurrence over Waltair (17.7° N, 83.3° E) during low and ascending phases of solar activity

2003 ◽  
Vol 21 (3) ◽  
pp. 745-750 ◽  
Author(s):  
K. Niranjan ◽  
P. S. Brahmanandam ◽  
P. Ramakrishna Rao ◽  
G. Uma ◽  
D. S. V. V. D. Prasad ◽  
...  
Keyword(s):  
Solar Activity ◽  
Atmospheric Composition ◽  
Activity Period ◽  
Sunspot Activity ◽  
Low Latitude ◽  
F Region ◽  
Composition And Structure ◽  
Spread F ◽  
Solar Activity Period ◽  
Night Airglow

Abstract. A study carried out on the occurrence of post midnight spread-F events at a low-latitude station, Waltair (17.7° N, 83.3° E), India revealed that its occurrence is maximum in the summer solstice months of the low solar activity period and decreases with an increase in the sunspot activity. The F-region virtual height variations show that 80% of these spread-F cases are associated with an increase in the F-region altitude. It is suggested with the support of the night airglow 6300 A zenith intensity data obtained with co-located ground-based night airglow photometer and electron temperature data from the Indian SROSS C2 satellite that the seasonal variation of the occurrence and probable onset times of the post midnight spread-F depend on the characteristics of the highly variable semipermanent equatorial Midnight Temperature Maximum (MTM).Key words. Ionosphere (ionospheric irregularities; ionosphere atmosphere interactions) Atmospheric composition and structure (airglow and Aurora)

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