Ionospheric electron content and scintillation studies at widely-spaced low-latitude stations

Abstract. Various characteristics of anomalous nighttime enhancement in ionospheric electron content (IEC) at Lunping (14.08°N geomagnetic), a station near the crest of the equatorial anomaly, have been presented by considering the IEC data for the 21st solar cycle. Out of a total of 1053 enhancements, 354 occur in pre-midnight and 699 occur in post-midnight hours, which indicates an overall dominance of post-midnight events at Lunping. The occurrence is more frequent during summer, less during the equinox and least during winter months. All the characteristics of the enhancements have seasonal dependencies and they reach their maximum values during summer months. The occurrence of the pre-midnight events show positive and post-midnight events show negative correlation with solar activity. The results have been discussed and compared with those at low-latitude stations in India and Hawaii and at the mid-latitude station, Tokyo.

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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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Investigation of Low Latitude Spread-F Triggered by Nighttime Medium-Scale Traveling Ionospheric Disturbance

Remote Sensing ◽

10.3390/rs13050945 ◽

2021 ◽

Vol 13 (5) ◽

pp. 945

Author(s):

Zhongxin Deng ◽

Rui Wang ◽

Yi Liu ◽

Tong Xu ◽

Zhuangkai Wang ◽

...

Keyword(s):

Ionospheric Disturbance ◽

Phase Speed ◽

Morphological Processing ◽

Wave Number ◽

Occurrence Rate ◽

Electron Content ◽

Low Latitude ◽

Total Electron ◽

Medium Scale ◽

Spread F

In the current study, we investigated the mechanism of medium-scale traveling ionospheric disturbance (MSTID) triggering spread-F in the low latitude ionosphere using ionosonde observation and Global Navigation Satellite System-Total Electron Content (GNSS-TEC) measurement. We use a series of morphological processing techniques applied to ionograms to retrieve the O-wave traces automatically. The maximum entropy method (MEM) was also utilized to obtain the propagation parameters of MSTID. Although it is widely acknowledged that MSTID is normally accompanied by polarization electric fields which can trigger Rayleigh–Taylor (RT) instability and consequently excite spread-F, our statistical analysis of 13 months of MSTID and spread-F occurrence showed that there is an inverse seasonal occurrence rate between MSTID and spread-F. Thus, we assert that only MSTID with certain properties can trigger spread-F occurrence. We also note that the MSTID at night has a high possibility to trigger spread-F. We assume that this tendency is consistent with the fact that the polarization electric field caused by MSTID is generally the main source of post-midnight F-layer instability. Moreover, after thorough investigation over the azimuth, phase speed, main frequency, and wave number over the South America region, we found that the spread-F has a tendency to be triggered by nighttime MSTID, which is generally characterized by larger ΔTEC amplitudes.

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Statistical study of medium-scale traveling ionospheric disturbances in low-latitude ionosphere using an automatic algorithm

Earth Planets and Space ◽

10.1186/s40623-021-01432-1 ◽

2021 ◽

Vol 73 (1) ◽

Author(s):

Pin-Hsuan Cheng ◽

Charles Lin ◽

Yuichi Otsuka ◽

Hanli Liu ◽

Panthalingal Krishanunni Rajesh ◽

...

Keyword(s):

Climate Model ◽

Geomagnetic Latitude ◽

Detection Algorithm ◽

Support Vector ◽

Electron Content ◽

Ionospheric Disturbances ◽

Low Latitude ◽

Total Electron ◽

Medium Scale ◽

Traveling Ionospheric Disturbances

AbstractThis study investigates the medium-scale traveling ionospheric disturbances (MSTIDs) statistically at the low-latitude equatorial ionization anomaly (EIA) region in the northern hemisphere. We apply the automatic detection algorithm including the three-dimensional fast Fourier transform (3-D FFT) and support vector machine (SVM) on total electron content (TEC) observations, derived from a network of ground-based global navigation satellite system (GNSS) receivers in Taiwan (14.5° N geomagnetic latitude; 32.5° inclination), to identify MSTID from other waves or irregularity features. The obtained results are analyzed statistically to examine the behavior of low-latitude MSTIDs. Statistical results indicate the following characteristics. First, the southward (equatorward) MSTIDs are observed almost every day during 0800–2100 LT in Spring and Winter. At midnight, southward MSTIDs are more discernible in Summer and majority of them are propagating from Japan to Taiwan. Second, northward (poleward) MSTIDs are more frequently detected during 1200–2100 LT in Spring and Summer with the secondary peak of occurrence between day of year (DOY) 100–140 during 0000–0300 LT. The characteristics of the MSTIDs are interpreted with additional observations from radio occultation (RO) soundings of FORMOSAT-3/COSMIC as well as modeled atmospheric waves from the high-resolution Whole Atmosphere Community Climate Model (WACCM) suggesting that the nighttime MSTIDs in Summer is likely connected to the atmospheric gravity waves (AGWs).

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Solar activity dependence of ionospheric electron content and slab thickness using different solar indices

Pure and Applied Geophysics ◽

10.1007/bf00876585 ◽

1993 ◽

Vol 140 (4) ◽

pp. 721-728 ◽

Cited By ~ 8

Author(s):

R. S. Dabas ◽

D. R. Lakshmi ◽

B. M. Reddy

Keyword(s):

Solar Activity ◽

Slab Thickness ◽

Electron Content ◽

Ionospheric Electron Content ◽

Activity Dependence

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Case study on total electron content enhancements at low latitudes during low geomagnetic activities before the storms

Annales Geophysicae ◽

10.5194/angeo-26-893-2008 ◽

2008 ◽

Vol 26 (4) ◽

pp. 893-903 ◽

Cited By ~ 27

Author(s):

◽

Keyword(s):

Total Electron Content ◽

Geomagnetic Activity ◽

Electron Content ◽

Low Latitude ◽

Total Electron ◽

Defense Meteorological Satellite Program ◽

Low Latitudes ◽

Global Ionospheric Maps ◽

Geomagnetic Activities

Abstract. Sometimes the ionospheric total electron content (TEC) is significantly enhanced during low geomagnetic activities before storms. In this article, we investigate the characteristics of those interesting TEC enhancements using regional and global TEC data. We analyzed the low-latitude TEC enhancement events that occurred around longitude 120° E on 10 February 2004, 21 January 2004, and 4 March 2001, respectively. The TEC data are derived from regional Global Positioning System (GPS) observations in the Asia/Australia sector as well as global ionospheric maps (GIMs) produced by Jet Propulsion Laboratory (JPL). Strong enhancements under low geomagnetic activity before the storms are simultaneously presented at low latitudes in the Asia/Australia sector in regional TEC and JPL GIMs. These TEC enhancements are shown to be regional events with longitudinal and latitudinal extent. The regions of TEC enhancements during these events are confined at narrow longitude ranges around longitude 120° E. The latitudinal belts of maxima of enhancements locate around the northern and southern equatorial ionization anomaly (EIA) crests, which are consistent with those low-latitude events presented by Liu et al. (2008). During the 4 March 2001 event, the total plasma density Ni observed by the Defense Meteorological Satellite Program (DMSP) spacecraft F13 at 840 km altitude are of considerably higher values on 4 March than on the previous day in the TEC enhanced regions. Some TEC enhancement events are possibly due to contributions from auroral/magnetospheric origins; while there are also quasi-periodic enhancement events not related to geomagnetic activity and associated probably with planetary wave type oscillations (e.g. the 6 January 1998 event). Further investigation is warrented to identify/separate contributions from possible sources.

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