scholarly journals Vertical and longitudinal electron density structures of equatorial E- and F-regions

2011 ◽  
Vol 29 (1) ◽  
pp. 81-89 ◽  
Author(s):  
P. S. Brahmanandam ◽  
Y.-H. Chu ◽  
K.-H. Wu ◽  
H.-P. Hsia ◽  
C.-L. Su ◽  
...  
Keyword(s):  
Electron Density ◽  
Phase Relation ◽  
F Region ◽  
Good Consistency ◽  
June Solstice ◽  
December Solstice ◽  
Different Seasons ◽  
E Region ◽  
First Time ◽  
Longitudinal Structures

Abstract. From global soundings of ionospheric electron density made with FORMOSAT 3/COSMIC satellites for September 2006–August 2009, day-night variations in vertical and longitudinal structures of the electron densities in equatorial E- and F-regions for different seasons are investigated for the first time. The results reveal that the wavenumber-3 and wavenumber-4 patterns dominated the nighttime (22:00–04:00 LT) F-region longitudinal structures in solstice and in equinox seasons, respectively. In daytime (08:00–18:00 LT) F-region, the wavenumber-4 patterns governed the longitudinal structures in the September equinox and December solstice, and wavenumber-3 in March equinox and June solstice respectively. A comparison of the daytime and nighttime longitudinal electron density structures indicates that they are approximately 180° out of phase with each other. It is believed that this out of phase relation is very likely the result of the opposite phase relation between daytime and nighttime nonmigrating diurnal tidal winds that modulate background E-region dynamo electric field at different places, leading to the day-night change in the locations of the equatorial plasma fountains that are responsible for the formation of the F-region longitudinal structures. Further, a good consistency between the locations of the density structures in the same seasons of the different years for both daytime and nighttime epochs has been noticed indicating that the source mechanism for these structures could be the same.

scholarly journals Morphology of quantified ionospheric range spread-F over a wide range of midlatitudes in the Australian longitudinal sector

2007 ◽  
Vol 25 (5) ◽  
pp. 1125-1130 ◽  
Author(s):  
L. A. Hajkowicz
Keyword(s):  
Distinct Pattern ◽  
F Region ◽  
Wide Range ◽  
Longitudinal Sector ◽  
June Solstice ◽  
December Solstice ◽  
Spread F ◽  
Range Spread ◽  
First Time ◽  
Latitudinal Range

Abstract. Ionograms from a standard vertical-incidence ionosonde chain (nine stations), obtained over a wide range of southern latitudes (in geom.lat. range: 23°–52° S), were digitally scanned at 5-min intervals at nighttime (18:00–06:00 LT) for 13 months (January 2004–January 2005). An important parameter of the F-region, so-called range spread-F (Sr), was for the first time quantified in km. Maximum in Sr was recorded at a sounding frequency of 1.8 MHz for each night and for each ionosonde station. A distinct pattern in the magnitude (in km) and in the percentage occurrence of the range spread-F was present in southern winter only (the June solstice). The sub-auroral region (geom. lat. ≥52° S) is characterised by consistently high spread-F (average Sr≈100 km) on 80–100 per cent of the observed nights. There is a sharp equatorward boundary in the spread-F activity in a latitudinal range: 52°–48° S followed by a midlatitude region (44°–48° S) which exhibits a peak in Sr (≈50 km) in winter only, observed on half of the nights. The midlatitude activity reaches its minimum at 42°–43° S, with Sr less than 20 km on one third of the nights. The low midlatitudes (23°–36° S) are characterised by a strong peak in Sr again in winter, centred at about 30° S (average Sr≈70 km) on 80 per cent of the nights. The pattern becomes largely absent during other seasons particularly in southern summer (the December solstice) when spread-F activity shifts to sub-auroral latitudes. The pattern in the occurrence of spread-F appears to have a global character as the enhanced spread-F activity is observed in the Japanese sector in local summer (i.e. the June solstice). It appears that the midlatitude spread-F minimum is only apparent but not real. It delineates the boundary between aurorally generated spread-F (due to travelling ionospheric disturbances, TIDs) and low midlatitude spread-F whose origin is not known.

scholarly journals Intermediate Layers responses to Geomagnetic Activity During the 2009 Deep Solar Minimum Over the Brazilian Low Latitude Sector

2021 ◽  
Author(s):  
Ângela Santos ◽  
Christiano Brum ◽  
Inez Batista ◽  
José Sobral ◽  
Mangalathayil Abdu ◽  
...  
Keyword(s):  
Geomagnetic Activity ◽  
Solar Minimum ◽  
Early Morning ◽  
Low Latitude ◽  
Seasonal Behavior ◽  
F Region ◽  
Intermediate Layers ◽  
Bottom Side ◽  
E Region ◽  
First Time

Abstract. Intermediate layers (ILs) are regions of enhanced electron density located in the ionospheric valley that extends from the peak altitude of the daytime E-region to the bottom side of the F-region. This work presents the daytime behavior of the ILs parameters (the virtual height - h’IL, and the top frequency - ftIL) over the low latitude region of Cachoeria Paulista (CP, 22.42° S; 45° W, I: −34.4°) for the deepest solar minimum of the last 500 years. In such a unique condition, this research reveals for the first time the ILs' quiet state seasonal behavior as well as its responses to moderate changes in the geomagnetic activity. The main results show that even small variations of geomagnetic activity (quantified by the planetary Kp index) are able to modify the dynamics of the ILs parameters. For the first time, it was observed that during the summer, the h’IL decrease rapidly with the increase of geomagnetic activity mainly in the early morning hours. In the following hours, a smoothed rise of the IL was found in all seasons analyzed. Regarding to frequency, it was observed that after 12:00 LT, there is a tendency of it decreased with the increase of the magnetic disturbances, being this characteristic more intense after 16:00 LT, except in the equinox, when little or no response was found during all the interval analyzed. In addition, it stands out that the annual periodicity of the ftIL was observed while the h’IL presents semiannual component.

scholarly journals Intriguing aspects of F-region plasma irregularities revealed by the Gadanki radar observations during the SAFAR campaign

2009 ◽  
Vol 27 (10) ◽  
pp. 3781-3790 ◽  
Author(s):  
A. K. Patra ◽  
D. V. Phanikumar
Keyword(s):  
Solar Activity ◽  
Electron Density ◽  
Plasma Irregularities ◽  
F Region ◽  
Mst Radar ◽  
E Region ◽  
Summer Time ◽  
Interesting Event ◽  
Region Plasma ◽  
Activity Condition

Abstract. Intriguing new results of F-region irregularities observed using the Gadanki MST radar during the SAFAR campaigns, which were conducted during the equinox and summer of 2008 that corresponds to low solar activity condition, are presented. The summer observations are first of its kind from Gadanki. Observations revealed remarkably different morphology of the F-region irregularities in summer when compared to that in equinox. In summer, the F-region irregularities were observed as horizontally stratified structures, while in equinox they were observed as plume structures. Further, the irregularities in summer commenced during the post-midnight hours in contrast to their commencement in the post-sunset hours and occurrence extending to post-midnight hours in equinox. In addition, an intriguing observation of the summer time irregularities is that they occurred when the background electron density was remarkably low as characterized by the disappearance of the F layer trace in the ionograms. An interesting event of equinox that was observed for 10 h and extended beyond the sunrise time displayed multiple plume structures having periods similar to those of the E-region velocity variations. These observations are discussed with due focus on the genesis of post-midnight F-region irregularities and their possible linkage to the E-region dynamics.

scholarly journals Letter to the editor: The ionospheric response during an interval of Pc5 ULF wave activity

2000 ◽  
Vol 18 (2) ◽  
pp. 257-261
Author(s):  
M. Lester ◽  
J. A. Davies ◽  
T. K. Yeoman
Keyword(s):  
Electron Density ◽  
Electric Fields ◽  
Wave Activity ◽  
Mhd Waves ◽  
Ion Temperature ◽  
Ionospheric Conductivity ◽  
Ulf Wave ◽  
F Region ◽  
E Region ◽  
Electric Fields And Currents

Abstract. A preliminary analysis of Pc5, ULF wave activity observed with the IMAGE magnetometer array and the EISCAT UHF radar in the post midnight sector indicates that such waves can be caused by the modulation of the ionospheric conductivity as well as the wave electric field. An observed Pc5 pulsation is divided into three separate intervals based upon the EISCAT data. In the first and third, the Pc5 waves are observed only in the measured electron density between 90 and 112 km and maxima in the electron density at these altitudes are attributed to pulsed precipitation of electrons with energies up to 40 keV which result in the height integrated Hall conductivity being pulsed between 10 and 50 S. In the second interval, the Pc5 wave is observed in the F-region ion temperature, electron density and electron temperature but not in the D and E region electron densities. The analysis suggests that the wave during this interval is a coupled Alfven and compressional mode.Key words: Ionosphere (electric fields and currents) - Magnetospheric physics (magnetosphere-ionosphere interaction; MHD waves and instabilities)

scholarly journals Tidal variations in the high-latitude E- and F-region observed by EISCAT

1996 ◽  
Vol 14 (2) ◽  
pp. 201-210 ◽  
Author(s):  
Klemens Hocke
Keyword(s):  
Electron Density ◽  
Electric Fields ◽  
Lower Thermosphere ◽  
Data Set ◽  
Density Spectrum ◽  
F Region ◽  
Temperature Oscillations ◽  
Long Time ◽  
E Region ◽  
Tidal Variations

Abstract. During the MLTCS (Mesosphere-Lower Thermosphere Coupling Study) campaign the EISCAT UHF radar was continuously operated over 7 days (30 July–5 August 1992) in the CP-1 mode. The long time series obtained of the fundamental ionospheric parameters field-aligned ion velocity (Vi), ion and electron temperature (T and Te), and electron density (Ne) are useful in investigating tidal variations in the E- and F-region since the geomagnetic activity was particularly low during the time of measurement. Maximum entropy spectra of the parameters were calculated for the relatively quiet interval from 1 August to 4 August 1992 and indicated dominant variations with harmonics of 24 hours. In the electron density spectrum especially, harmonics up to the sixth order (4-h period) are clearly visible. The phase and amplitude height profiles (100–450 km) of the diurnal, semidiurnal, and terdiurnal variations were determined by Fourier transform for a 24-h data set beginning at 12:00 UT on 3 August 1992 when the contaminating influences of electric fields were negligible. The tidal variations of the ion temperatures are compared with the corresponding variations of the neutral temperature predicted by the MSISE-90 model. A remarkable result is the dominance of terdiurnal temperature oscillations at E-region heights on 3–4 August 1992, while the measured diurnal and semidiurnal variations were negligible. The finding was confirmed by the analysis of further EISCAT data (2–3 August 1989, 2–3 July 1990, 31 March–1 April 1992) which also showed a dominant terdiurnal temperature tide in the E-region. This is different from numerous observations of tides in the E-region at mid-latitudes where the diurnal and especially the semidiurnal temperature oscillations were dominant.

scholarly journals Duskside F-region dynamo currents: its relationship with prereversal enhancement of vertical plasma drift

2010 ◽  
Vol 28 (11) ◽  
pp. 2097-2101 ◽  
Author(s):  
J. Park ◽  
H. Lühr ◽  
B. G. Fejer ◽  
K. W. Min
Keyword(s):  
Current Density ◽  
Solar Maximum ◽  
Field Observations ◽  
Longitudinal Variation ◽  
Plasma Drift ◽  
F Region ◽  
Close Relationship ◽  
E Region ◽  
Current Densities ◽  
First Time

Abstract. From magnetic field observations by CHAMP we estimate F-region dynamo current densities near the sunset terminator during solar maximum years from 2001 to 2002. The dynamo currents are compared with the pre-reversal enhancement (PRE) of vertical plasma drift as observed by ROCSAT-1. The seasonal-longitudinal variation of PRE can be largely related to the F-region dynamo current density, with the correlation coefficient reaching 0.74. The correlation can be further improved if we consider a zonal gradient of the E-region Pedersen conductivity, which also depends on season and longitude. It is widely accepted that the F-region dynamo drives PRE near sunset. For the first time, our observations provide confirmation for the close relationship between the F-region dynamo current density and PRE.

scholarly journals Variations of the peak positions in the longitudinal profile of noon-time equatorial electrojet

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Zié Tuo ◽  
Vafi Doumbia ◽  
Pierdavide Coïsson ◽  
N’Guessan Kouassi ◽  
Abdel Aziz Kassamba
Keyword(s):  
Magnetic Measurements ◽  
Equatorial Electrojet ◽  
Champ Satellite ◽  
June Solstice ◽  
December Solstice ◽  
Longitudinal Pattern ◽  
Dip Equator ◽  
Longitudinal Profiles ◽  
June July ◽  
First Time

AbstractIn this study, the seasonal variations of the EEJ longitudinal profiles were examined based on the full CHAMP satellite magnetic measurements from 2001 to 2010. A total of 7537 satellite noon-time passes across the magnetic dip-equator were analyzed. On the average, the EEJ exhibits the wave-four longitudinal pattern with four maxima located, respectively, around 170° W, 80° W, 10° W and 100° E longitudes. However, a detailed analysis of the monthly averages yielded the classification of the longitudinal profiles in two types. Profiles with three main maxima located, respectively, around 150° W, 0° and 120° E, were observed in December solstice (D) of the Lloyd seasons. In addition, a secondary maximum observed near 90° W in November, December and January, reinforces from March to October to establish the wave-four patterns of the EEJ longitudinal variation. These wave-four patterns were divided into two groups: a group of transition which includes equinox months March, April and October and May in the June solstice; and another group of well-established wave-four pattern which covers June, July, August of the June solstice and the month of September in September equinox. For the first time, the motions in the course of seasons of various maxima of the EEJ noon-time longitudinal profiles have been clearly highlighted.

scholarly journals Temporal and Spatial Dynamics of Dark Septate Endophytes in the Roots of Lycium ruthenicum in the Desert Region of Northwest China

Agronomy ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 648
Author(s):  
Li Han ◽  
Jingxin Shi ◽  
Chao He ◽  
Xueli He
Keyword(s):  
Species Diversity ◽  
Spatial Dynamics ◽  
Northwest China ◽  
Dark Septate Endophytes ◽  
Desert Ecosystems ◽  
Lycium Ruthenicum ◽  
Different Seasons ◽  
Application Potential ◽  
First Time ◽  
Hydrolyzable Nitrogen

With the intensification of desertification in northwest China, drought has become a serious environmental problem restricting plant growth and ecological restoration. Recently, dark septate endophytes (DSEs) have attracted more attention because of their ability to improve plants’ resistance to drought. Here, we investigated DSE colonization and species diversity in roots of Lycium ruthenicum collected from Anxi and Minqin, in northwest China, during July, September, and December 2019. This study aimed to evaluate the influence of seasonality and sampling sites on DSEs. In different seasons, DSE colonization varied with the phenology of L. ruthenicum. At different sites, DSE colonization significantly differed. Four isolates were reported in desert ecosystems for the first time. The results showed microsclerotial colonization was directly affected by changing seasons, while hyphal colonization and species diversity were directly affected by sampling sites. The soil organic carbon, pH, alkaline phosphatase, and alkali-hydrolyzable nitrogen were the main predictors of DSE colonization and species diversity. We conclude that DSE colonization and diversity showed significant spatial–temporal heterogeneity and were closely related to soil factors. This research provides a basis for the further understanding of the ecological functions of DSEs and their application potential for vegetative restoration and agricultural cultivation in drylands.

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