scholarly journals Postmidnight equatorial plasma irregularities on June solstice during low solar activity – a case study

2018 ◽  
Author(s):  
Claudia M. N. Candido ◽  
Jiankui Shi ◽  
Inez S. Batista ◽  
Fabio Becker-Guedes ◽  
Emília Correia ◽  
...  
Keyword(s):  
Solar Activity ◽  
Low Latitude ◽  
Plasma Irregularities ◽  
June Solstice ◽  
Spread F ◽  
Dip Angle

Abstract. We present a case study of unusual spread-F structures observed by ionosondes at two equatorial and low latitude Brazilian stations – Sao Luis (SL: 44.2° W, 2.33° S, dip angle: −6.9°) and Fortaleza (FZ: 38.45° W, 3.9° S, dip angle: −16°). The irregularity structures observed from midnight to post-midnight hours of moderate solar activity (F10.7 

scholarly journals Postmidnight equatorial plasma irregularities on the June solstice during low solar activity – a case study

2019 ◽  
Vol 37 (4) ◽  
pp. 657-672
Author(s):  
Claudia M. N. Candido ◽  
Jiankui Shi ◽  
Inez S. Batista ◽  
Fabio Becker-Guedes ◽  
Emília Correia ◽  
...  
Keyword(s):  
Solar Activity ◽  
Low Latitude ◽  
Plasma Irregularities ◽  
Fabry Perot ◽  
June Solstice ◽  
Spread F ◽  
Plasma Depletions ◽  
Dip Angle ◽  
Layer Peak

Abstract. We present a case study of unusual spread-F structures observed by ionosondes at two equatorial and low-latitude Brazilian stations – São Luís (SL: 44.2∘ W, 2.33∘ S; dip angle: −6.9∘) and Fortaleza (FZ: 38.45∘ W, 3.9∘ S; dip angle: −16∘). The irregularity structures observed from midnight to postmidnight hours of moderate solar activity (F10.7 < 97 sfu, where 1 sfu = 10−22 W m−2 s−1) have characteristics different from typical post-sunset equatorial spread F. The spread-F traces first appeared at or above the F-layer peak and gradually became well-formed mixed spread F. They also appeared as plasma depletions in the 630.0 nm airglow emissions made by a wide-angle imager located at the nearby low-latitude station Cajazeiras (CZ: 38.56∘ W, 6.87∘ S; dip angle: −21.4∘). The irregularities appeared first over FZ and later over SL, giving evidence of an unusual westward propagation or a horizontal plasma advection. The drift-mode operation available in one of the ionosondes (a digital portable sounder, DPS-4) has enabled us to analyze the horizontal drift velocities and directions of the irregularity movement. We also analyzed the neutral wind velocity measured by a Fabry–Pérot interferometer (FPI) installed at CZ and discuss its possible role in the development of the irregularities.

Supplementary material to "Postmidnight equatorial plasma irregularities on June solstice during low solar activity – a case study"

2018 ◽  
Author(s):  
Claudia M. N. Candido ◽  
Jiankui Shi ◽  
Inez S. Batista ◽  
Fabio Becker-Guedes ◽  
Emília Correia ◽  
...  
Keyword(s):  
Solar Activity ◽  
Plasma Irregularities ◽  
June Solstice ◽  
Supplementary Material

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)

scholarly journals The statistical properties of spread F observed at Hainan station during the declining period of the 23rd solar cycle

2010 ◽  
Vol 28 (6) ◽  
pp. 1263-1271 ◽  
Author(s):  
G. J. Wang ◽  
J. K. Shi ◽  
X. Wang ◽  
S. P. Shang ◽  
G. Zherebtsov ◽  
...  
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Temporal Variations ◽  
High Solar Activity ◽  
Positive Relation ◽  
Low Latitude ◽  
23Rd Solar Cycle ◽  
Reversal Time ◽  
Spread F ◽  
Maximum Occurrence

Abstract. The temporal variations of the low latitude nighttime spread F (SF) observed by DPS-4 digisonde at low latitude Hainan station (geog. 19.5° N, 109.1° E, dip lat. 9.5° N) during the declining solar cycle 23 from March 2002 to February 2008 are studied. The spread F measured by the digisonde were classified into four types, i.e., frequency SF (FSF), range SF (RSF), mixed SF (MSF), and strong range SF (SSF). The statistical results show that MSF and SSF are the outstanding irregularities in Hainan, MSF mainly occurs during summer and low solar activity years, whereas SSF mainly occurs during equinoxes and high solar activity years. The SSF has a diurnal peak before midnight and usually appears during 20:00–02:00 LT, whereas MSF peaks nearly or after midnight and occurs during 22:00–06:00 LT. The time of maximum occurrence of SSF is later in summer than in equinoxes and this time delay can be caused by the later reversal time of the E×B drift in summer. The SunSpot Number (SSN) dependence of each type SF is different during different season. The FSF is independent of SSN during each season; RSF with SSN is positive relation during equinoxes and summer and is no relationship during the winter; MSF is significant dependence on SSN during the summer and winter, and does not relate to SSN during the equinoxes; SSF is clearly increasing with SSN during equinoxes and summer, while it is independent of SSN during the winter. The occurrence numbers of each type SF and total SF have the same trend, i.e., increasing as Kp increases from 0 to 1, and then decreasing as increasing Kp. The correlation with Kp is negative for RSF, MSF, SSF and total SF, but is vague for the FSF.

scholarly journals <i>Letter to the Editor</i>: Post-midnight onset of spread-F at Kodaikanal during the June solstice of solar minimum

1999 ◽  
Vol 17 (8) ◽  
pp. 1111-1115 ◽  
Author(s):  
J. H. Sastri
Keyword(s):  
Solar Activity ◽  
Solar Minimum ◽  
Equatorial Ionosphere ◽  
Instability Mechanism ◽  
Layer Height ◽  
Northern Summer ◽  
June Solstice ◽  
Spread F ◽  
Rayleigh Taylor Instability ◽  
Distinct Increase

Abstract. At dip equatorial stations in the Indian zone, spread-F conditions are known to develop preferentially around midnight during the June solstice (northern summer) months of low solar activity, in association with a distinct increase in F layer height. It is currently held that this onset of spread-F far away from the sunset terminator is due to the generalised Rayleigh-Taylor instability mechanism, with the gravitational and cross-field instability factors (and hence F layer height) playing important roles. We have studied the quarter-hourly ionograms of Kodaikanal (10.2°N; 77.5°E; dip 4°N) for the northern summer months (May-August) of 1994 and 1995 to ascertain the ambient ionospheric conditions against which the post-midnight onset of spread-F takes place. A data sample of 38 nights with midnight onset of spread-F and 34 nights without spread-F is used for the purpose. It is found that a conspicious increase in F layer height beginning around 2100 LT occurs on nights with spread-F as well as without spread-F. This feature is seen in the nocturnal pattern of F layer height on many individual nights as well as of average F layer height for the two categories of nights. The result strongly suggests that the F layer height does not play a pivotal role in the midnight onset of spread-F during the June solstice of solar minimum. The implications of this finding are discussed.Key words. Ionosphere (equatorial ionosphere; ionospheric irregularities)

scholarly journals Observation of seasonal asymmetry in the range spread F occurrence at different longitudes during low and moderate solar activity

2019 ◽  
Vol 37 (4) ◽  
pp. 733-745
Author(s):  
Abimbola O. Afolayan ◽  
Mandeep Jit Singh ◽  
Mardina Abdullah ◽  
Suhaila M. Buhari ◽  
Tatsuhiro Yokoyama ◽  
...  
Keyword(s):  
Solar Activity ◽  
Onset Time ◽  
Longitudinal Distribution ◽  
Low Latitude ◽  
Range Type ◽  
Seeding Effect ◽  
Spread F ◽  
Range Spread ◽  
Major Factors ◽  
Ionospheric Condition

Abstract. A comparative study of the equatorial spread F occurrence was conducted at different longitudes during 2010 and 2013 representing the low (LSA) and moderate (MSA) solar activity periods respectively. The ionogram data were recorded at low-latitude stations including Jicamarca (JIC;75.76∘ W, 8.17∘ S), Fortaleza (FZA; 38.52∘ W, 3.73∘ S), Ilorin (ILR; 7.55∘ E, 9.93∘ N), Chumphon (CPN; 88.46∘ E, 11∘ N) and Kwajalein (KWA; 167.73∘ E, 8.72∘ N). The range type spread F (RSF) occurrence was manually recorded at an hourly interval between 18:00 and 06:00 LT, and a monthly average of the RSF occurrence was estimated for each season. The longitudinal distribution of the RSF occurrence features included the observed difference in the onset time, the duration and the seasonal occurrence peak. The seasonal asymmetry in the RSF occurrence distribution was analysed in relation to the zonal drift reversal’s effect on the plasma irregularity initiation. We believe that the inconsistent equinoctial asymmetry pattern in the RSF occurrence is modulated by the seasonal/longitudinal variation of the zonal drift reversal delay during both solar epochs. Likewise, the seeding effect and the background ionospheric condition were also considered as major factors influencing the frequency of irregularity generation in these regions.

scholarly journals Climatology of Spread F over Tucumán from Massive Statistical Analysis of Autoscaled Data

Atmosphere ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 1351
Author(s):  
Carlo Scotto ◽  
Dario Sabbagh
Keyword(s):  
Solar Activity ◽  
Retrospective Studies ◽  
Temporal Evolution ◽  
Radio Signal ◽  
Low Latitude ◽  
Ionospheric Station ◽  
Spread F ◽  
Signal Path ◽  
Maximum Occurrence ◽  
Different Levels

Automatic ionogram interpretation methods developed for real-time ionospheric monitoring can be applied in retrospective studies to analyze large quantities of data. The Autoscala software, implemented for such a purpose, includes a routine for automatic detection of diffused echoes known as spread F, which appear in ionograms due to the presence of ionospheric irregularities along the radio signal path. The main objective of this routine is to reject bad quality ionograms. This new capability was used in a climatological study including a large number of ionograms recorded at the low-latitude ionospheric station of Tucumán (26.9° S, 294.6° E, magnetic latitude 15.5° S, Argentina). The study took into account different levels of geomagnetic and solar activity from 2012 to 2020. The results demonstrate the capability of Autoscala to capture the main signature characteristics of spread F and the temporal evolution of the ionosphere peak heigh hmF2, capturing the post-sunset plasma surge that precedes development of spread F. Maximum occurrence of spread F is observed in local summer, with a tendency to shift before midnight with increasing solar activity. Other new climatological details that emerged from the study are illustrated and briefly discussed, dealing with connection with geomagnetic activity, and morning hmF2 behavior after extremely marked nighttime spread F occurrence.

scholarly journals Low-latitude equinoctial spread-F occurrence at different longitude sectors under low solar activity

2013 ◽  
Vol 31 (2) ◽  
pp. 153-162 ◽  
Author(s):  
M. Pezzopane ◽  
E. Zuccheretti ◽  
P. Abadi ◽  
A. J. de Abreu ◽  
R. de Jesus ◽  
...  
Keyword(s):  
Solar Activity ◽  
Comparative Study ◽  
Continuous Wave ◽  
Physical Processes ◽  
Low Latitude ◽  
Frequency Spread ◽  
Equatorial Ionization Anomaly ◽  
Spread F ◽  
Range Spread

Abstract. We present the results of a comparative study of spread-F signatures over five low-latitude sites: Chiangmai (CGM; 18.8° N, 98.9° E, mag. Lat. 8.8° N), Thailand; Tanjungsari (TNJ; 6.9° S, 107.6° E, mag. Lat. 16.9° S), Indonesia; Palmas (PAL; 10.2° S, 311.8° E, mag. Lat. 0.9° S) and São José Dos Campos (SJC; 23.2° S, 314.1° E, mag. Lat. 14.0° S), Brazil; and Tucumán (TUC; 26.9° S, 294.6° E, mag. Lat. 16.8° S), Argentina. The investigation was based on simultaneous ionograms recorded by an FMCW (frequency-modulated continuous-wave) at CGM, an IPS-71 (digital ionosonde from KEL aerospace) at TNJ, a CADI (Canadian Advanced Digital Ionosonde) at PAL and SJC, and an AIS-INGV (Advanced Ionospheric Sounder – Istituto Nazionale di Geofisica e Vulcanologia) at TUC, during the equinoctial periods March–April (R12 = 2.0 and R12 = 2.2) and September–October (R12 = 6.1 and R12 = 7.0) 2009, for very low solar activity. Spread-F signatures were categorized into two types: the range spread-F (RSF) and the frequency spread-F (FSF). The study confirms that the dynamics and the physical processes responsible for these phenomena are actually complicated. In fact, the features that arise from the investigation are different, depending on both the longitude sector and on the hemisphere. For instance, TUC, under the southern crest of the ionospheric equatorial ionization anomaly (EIA), shows a predominance of RSF signatures, while both SJC, under the southern crest of EIA but in a different longitude sector, and CGM, under the northern crest of EIA, show a predominance of FSF signatures. Moreover, the spread-F occurrence over the longitude sector that includes CGM and TNJ is significantly lower than the spread-F occurrence over the longitude sector of PAL, SJC, and TUC.

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