Electrodynamics of the equatorial F-region ionosphere during pre-sunrise period

Abstract. The electrodynamics of the pre-sunrise equatorial F-region is investigated using HF Doppler radar and digital ionosonde. The observations are limited to those days for which the radar probing frequency is below the foF2 value. The ionosphere observation using HF Doppler radar exhibit interesting features during pre-sunrise period similar to the post sunset pre-reversal enhancement. The most striking feature observed during pre-sunrise period is the sudden downward excursion in the vertical drift around local sunrise followed by an upward turning. Pre-sunrise observations of vertical plasma drift and the sunrise downward excursion followed by an upward turning after the ground sunrise related to the zonal electric field at the equatorial F-region are the most significant results not reported earlier.

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Impact of disturbance electric fields in the evening on prereversal vertical drift and spread F developments in the equatorial ionosphere

Annales Geophysicae ◽

10.5194/angeo-36-609-2018 ◽

2018 ◽

Vol 36 (2) ◽

pp. 609-620 ◽

Cited By ~ 5

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)

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Letter to the editor: Electric field fluctuations (25-35 min) in the midnight dip equatorial ionosphere

Annales Geophysicae ◽

10.1007/s00585-000-0252-2 ◽

2000 ◽

Vol 18 (2) ◽

pp. 252-256 ◽

Cited By ~ 4

Author(s):

J. Hanumath Sastri ◽

H. Luhr ◽

H. Tachihara ◽

T. -I. Kitamura ◽

J. V. S. V. Rao

Keyword(s):

Electric Field ◽

Electric Fields ◽

Geomagnetic Latitude ◽

Equatorial Ionosphere ◽

Plasma Drift ◽

F Region ◽

Vertical Drift ◽

Field Fluctuations ◽

Dip Equator ◽

Electric Fields And Currents

Abstract. Measurements with a HF Doppler sounder at Kodaikanal (10.2°N, 77.5°E, geomagnetic latitude 0.8°N) showed conspicuous quasi-periodic fluctuations (period 25-35 min) in F region vertical plasma drift, Vz in the interval 0047-0210 IST on the night of 23/24 December, 1991 (Ap = 14, Kp < 4-). The fluctuations in F region vertical drift are found to be coherent with variations in Bz (north-south) component of interplanetary magnetic field (IMF), in geomagnetic H/X components at high-mid latitude locations both in the sunlit and dark hemispheres and near the dayside dip equator, suggestive of DP2 origin. But the polarity of the electric field fluctuations at the midnight dip equator (eastward) is the same as the dayside equator inferred from magnetic variations, contrary to what is expected of equatorial DP2. The origin of the coherent occurrence of equatorial electric field fluctuations in the DP2 range of the same sign in the day and night hemispheres is unclear and merits further investigations.Key words: Ionosphere (electric fields and currents; equatorial ionosphere; ionosphere-magnetosphere interactions)

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Equatorial night-time F-region zonal electric fields

Annales Geophysicae ◽

10.1007/s00585-995-0871-8 ◽

1995 ◽

Vol 13 (8) ◽

pp. 871-878 ◽

Cited By ~ 3

Author(s):

S. S. Hari ◽

B. V. Krishna Murthy

Keyword(s):

Seasonal Variation ◽

Electric Field ◽

Electric Fields ◽

Night Time ◽

Equatorial Station ◽

F Region ◽

Vertical Drift ◽

Longitudinal Gradients ◽

Cycle Maximum ◽

E Region

Abstract. Night-time F-region vertical electrodynamic drifts at the magnetic equatorial station, Trivandrum are obtained for a period of 2 years, 1989 and 1990 (corresponding to solar cycle maximum epoch), using ionosonde h'F data. The seasonal variation of the vertical drift is found to be associated with the longitudinal gradients of the thermospheric zonal wind. Further, the seasonal variation of the prereversal enhancement of the vertical drift is associated with the time difference between the sunset times of the conjugate E-regions (magnetic field line linked to F-region) which is indicative of the longitudinal gradients of the conductivity (of the E-region). The vertical drifts and the causative zonal electric fields at Trivandrum are compared with those at Jicamarca and F-region zonal electric field models. It is seen that the night-time downward drift (as also the causative westward electric field) at Jicamarca is greater than that at Trivandrum. The prereversal enhancement of the drift is greater at Jicamarca than at Trivandrum during the summer and the equinoxes, whereas during the winter the opposite is the case.

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On developing a new ionospheric plasma index for Brazilian equatorial F region irregularities

Annales Geophysicae ◽

10.5194/angeo-37-807-2019 ◽

2019 ◽

Vol 37 (5) ◽

pp. 807-818 ◽

Cited By ~ 2

Author(s):

Laysa Cristina Araujo Resende ◽

Clezio Marcos Denardini ◽

Giorgio Arlan Silva Picanço ◽

Juliano Moro ◽

Diego Barros ◽

...

Keyword(s):

Magnetic Field ◽

Electric Field ◽

Space Weather ◽

Ionospheric Plasma ◽

Monitoring Program ◽

Plasma Irregularities ◽

Plasma Drift ◽

F Region ◽

Maximum Value ◽

Spread F

Abstract. F region vertical drifts (Vz) are the result of the interaction between ionospheric plasma with the zonal electric field and the Earth's magnetic field. Abrupt variations in Vz are strongly associated with the occurrence of plasma irregularities (spread F) during the nighttime periods. These irregularities are manifestations of space weather in the ionosphere's environment without necessarily requiring a solar burst. In this context, the Brazilian Space Weather Study and Monitoring Program (Embrace) of the National Institute for Space Research (INPE) has been developing different indexes to analyze these ionospheric irregularities in the Brazilian sector. Therefore, the main purpose of this work is to produce a new ionospheric scale based on the analysis of the ionospheric plasma drift velocity, named AV. It is based on the maximum value of Vz (Vzp), which in turn is calculated through its relationship with the virtual height parameter, h′F, measured by the Digisonde Portable Sounder (DPS-4D) installed in São Luís (2∘ S, 44∘ W; dip: −2.3∘). This index quantifies the time relationship between the Vz peak and the irregularity observed in the ionograms. Thus, in this study, we analyzed 7 years of data, between 2009 and 2015, divided by season in order to construct a standardized scale. The results show there is a delay of at least 15 min between the Vzp observation and the irregularity occurrence. Finally, we believe that this proposed index allows for evaluating the impacts of ionospheric phenomena in the space weather environment.

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

Annales Geophysicae ◽

10.5194/angeo-27-4229-2009 ◽

2009 ◽

Vol 27 (11) ◽

pp. 4229-4238 ◽

Cited By ~ 18

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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Response of equatorial ionosphere to episodes of asymmetric ring current activity

Annales Geophysicae ◽

10.1007/s00585-997-1316-3 ◽

1997 ◽

Vol 15 (10) ◽

pp. 1316-1323 ◽

Cited By ~ 38

Author(s):

J. H. Sastri ◽

M. A. Abdu ◽

J. H. A. Sobral

Keyword(s):

Electric Field ◽

Electric Fields ◽

Ring Current ◽

Opposite Polarity ◽

Equatorial Region ◽

Local Times ◽

High Time Resolution ◽

Plasma Drift ◽

F Region ◽

Current Events

Abstract. We present the characteristics of the response of equatorial ionospheric zonal electric field and F-region plasma density to the asymmetric ring current intensifications that occurred in succession on 16 December 1991, corresponding to the STEP/EITS-2 campaign period. The study is based on high-time- resolution (1-min) data of asymmetic ring current indices, ASY(H/D) and F-region vertical plasma drift, Vz measurements at Kodaikanal (10.25°N; 77.5°E; dip 4°), India and quarter-hourly ionosonde data of Fortaleza (4°S; 322°E; dip –9°), Brazil. It is shown that short-lived disturbances in F-layer vertical plasma drift, Vz and height (h'F/hpF2) indicative of westward and eastward electric fields prevail simultaneously in the dusk (18–21 LT) and predawn (02–05 LT) sectors, respectively, in association with the decay phase of asymmetic ring current events. Electric fields of opposite polarity do also seem to manifest at these local times, particularly in the early-morning sector in conjunction with the intensification of the asymmetric ring current. At a given location, electric field disturbances associated with individual asymmetric ring current events are thus bipolar in nature, with fields of opposite polarity during the growth and decay phases. The nature and polarity structure of the observed electric field disturbances are in agreement with the theoretical/model predictions of prompt penetration of high-latitude electric fields to the equatorial region.

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Identification of the mechanisms responsible for anomalies in the tropical lower thermosphere/ionosphere caused by the January 2009 sudden stratospheric warming

Journal of Space Weather and Space Climate ◽

10.1051/swsc/2019037 ◽

2019 ◽

Vol 9 ◽

pp. A39 ◽

Cited By ~ 1

Author(s):

Maxim V. Klimenko ◽

Vladimir V. Klimenko ◽

Fedor S. Bessarab ◽

Timofei V. Sukhodolov ◽

Pavel A. Vasilev ◽

...

Keyword(s):

Electric Field ◽

Phase Change ◽

Lower Thermosphere ◽

Upper Atmosphere ◽

Electron Content ◽

Stratospheric Warming ◽

Sudden Stratospheric Warming ◽

Low Latitude ◽

Plasma Drift ◽

Solar Tide

We apply the Entire Atmosphere GLobal (EAGLE) model to investigate the upper atmosphere response to the January 2009 sudden stratospheric warming (SSW) event. The model successfully reproduces neutral temperature and total electron content (TEC) observations. Using both model and observational data, we identify a cooling in the tropical lower thermosphere caused by the SSW. This cooling affects the zonal electric field close to the equator, leading to an enhanced vertical plasma drift. We demonstrate that along with a SSW-related wind disturbance, which is the main source to form a dynamo electric field in the ionosphere, perturbations of the ionospheric conductivity also make a significant contribution to the formation of the electric field response to SSW. The post-sunset TEC enhancement and pre-sunrise electron content reduction are revealed as a response to the 2009 SSW. We show that at post-sunset hours the SSW affects low-latitude TEC via a disturbance of the meridional electric field. We also show that the phase change of the semidiurnal migrating solar tide (SW2) in the neutral wind caused by the 2009 SSW at the altitude of the dynamo electric field generation has a crucial importance for the SW2 phase change in the zonal electric field. Such changes lead to the appearance of anomalous diurnal variability of the equatorial electromagnetic plasma drift and subsequent low-latitudinal TEC disturbances in agreement with available observations. Plain Language Summary – Entire Atmosphere GLobal model (EAGLE) interactively calculates the troposphere, stratosphere, mesosphere, thermosphere, and plasmasphere–ionosphere system states and their response to various natural and anthropogenic forcing. In this paper, we study the upper atmosphere response to the major sudden stratospheric warming that occurred in January 2009. Our results agree well with the observed evolution of the neutral temperature in the upper atmosphere and with low-latitude ionospheric disturbances over America. For the first time, we identify an SSW-related cooling in the tropical lower thermosphere that, in turn, could provide additional information for understanding the mechanisms for the generation of electric field disturbances observed at low latitudes. We show that the SSW-related vertical electromagnetic drift due to electric field disturbances is a key mechanism for interpretation of an observed anomalous diurnal development of the equatorial ionization anomaly during the 2009 SSW event. We demonstrate that the link between thermospheric winds and the ionospheric dynamo electric field during the SSW is attained through the modulation of the semidiurnal migrating solar tide.

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