Plasma density structures and associated irregularities in the nighttime midlatitude ionosphere are frequently observed as frontal elongated from northwest to southeast (NW‐SE) Northern Hemisphere. The coupling process between E F regions studied with a three‐dimensional numerical model, which can simulate two instability mechanisms: Perkins ‐region sporadic‐ ( s )‐layer region. fastest growth of coupled occurs when unstable conditions on NW‐SE perturbation satisfied both regions. integrated...

Abstract The equatorial zonal electric field responses to prompt penetration of eastward convection fields (PPEF) were compared at closely spaced longitudinal intervals dusk premidnight sectors during the intense geomagnetic storm 17 March 2015. At sector (Indian longitudes), a rapid uplift F layer >550 km and development plasma bubbles (EPBs) observed. These EPBs found extend up 27.13°N 25.98°S magnetic dip latitudes indicating their altitude ~1670 apex. In contrast, few degrees east in...

Abstract A new three‐dimensional high‐resolution numerical model to study equatorial plasma bubble (EPB) has been developed. The High‐Resolution Bubble (HIRB) is developed in a magnetic dipole coordinate system for the and low‐latitude ionosphere with spatial resolution of as fine 1 km. Adopting higher‐order scheme than those used existing models, HIRB capable reproducing bifurcation, pinching, turbulent structures EPB. From seeding perturbation resembling large‐scale wave structure (LSWS),...

In order to study nighttime medium‐scale traveling ionospheric disturbances (MSTIDs), we have developed a new midlatitude ionosphere electrodynamics coupling model (MIECO) which can the process between E and F regions with dipole magnetic field lines. Using model, MSTID structure is reproduced from random perturbation on an s layer by coupled Perkins sporadic‐ ( )‐layer instabilities in wide latitudinal range. A typical wavelength of ∼150 km, larger amplitude, smaller MSTID's tilt angles at...

[1] Using the 47 MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (10.36°S dip latitude), it is shown that postmidnight irregularities during solar minimum are morphologically different from those detected maximum and quite similar to observed with middle upper atmosphere (MU) radar midlatitudes (29.3°N latitude). Utilizing rapid beam-steering capability of EAR, spatial structure clearly presented for first time. It found they usually propagate westward can be categorized...

Abstract The development of equatorial plasma irregularity plumes can be well recorded by steerable backscatter radars operated at and off the magnetic equator due to fact that vertically extended plume structures are tracers magnetically north‐south aligned larger scale structures. From observations during March 2012, using two low latitude in Southeast Asia, Equatorial Atmosphere Radar (EAR) (0.2°S, 100.3°E; dip lat 10.4°S) Sanya VHF radar (18.4°N, 109.6°E; 12.8°N), characteristics over...

Abstract The occurrence rate of the equatorial plasma bubble (EPB) with season, solar activity, and geomagnetic conditions are investigated using long‐term data sets Malaysia Real‐Time Kinematics Network (MyRTKnet) from 2008 to 2013. TEC (total electron content) change index (ROTI) in 5 min was derived MyRTKnet detect EPB scale sizes around tens kilometers. Then, daily east‐west cross sections 2‐D ROTI maps were used examine features over 100°E–119°E longitudes. EPBs tend occur successively...

The relationship between sunset terminators and the onset of radar backscatter plumes associated with equatorial spread F (ESF) observed 47‐MHz Equatorial Atmosphere Radar from October 2002 to April 2004 is discussed. Almost all irregularity echoes began appear at or before time altitude apex geomagnetic field line connected area, more than half events corresponded exactly time. This tendency should be due two causes: (1) rapid change evening zonal electric (2) damping 3‐m scale...

We report simultaneous observations of medium‐scale traveling ionospheric disturbances (MSTIDs) and field‐aligned irregularities (FAIs) in the F region using two all‐sky airglow imagers middle upper atmosphere (MU) radar. MSTIDs propagating southwestward were observed simultaneously 630‐nm images over Sakata (39.0°N, 139.9°E) Shigaraki (34.9°N, 136.1°E), Japan, on night 16 June 2004. By both sites, we estimated altitude layer to be 260 km by triangulation method. During MSTID event, FAIs...

Abstract. Forces governing the three-dimensional structure of equatorial spread-F (ESF) plumes are examined using NRL SAMI3/ESF simulation code. As is case with ionization anomaly (IA), density crests within plume occur where gravitational and diffusive forces in balance. Large E×B drifts ESF place these on field lines apex heights higher than those background IA crests. poleward field-aligned ion velocities result large ion-neutral that support at altitudes crest altitudes. We show examples...

Abstract. The zonal structure of radar backscatter plumes associated with Equatorial Spread F (ESF), probably modulated by atmospheric gravity waves, has been investigated the Atmosphere Radar (EAR) in West Sumatra, Indonesia (0.20° S, 100.32° E; dip latitude 10.1° S) and FM-CW ionospheric sounders on same magnetic meridian as EAR. occurrence locations distances ESF were determined multi-beam observations drifted eastward while keeping several hundred to a thousand kilometers. Comparing...

Plasma density enhancements, or plasma blobs, and radar backscatter plumes in the nighttime equatorial F region, both of which are intriguing phenomena associated with spread (ESF), were concurrently observed for first time on 8 March 2004 along a common magnetic flux tube. The observational results strong evidence close relationship between bubbles blobs ionosphere. detected by Republic China Scientific Satellite (ROCSAT)‐1 at dip latitude ∼9°N, while 47‐MHz Equatorial Atmosphere Radar...

Abstract Using the fan sector backscatter maps of 47 MHz Equatorial Atmosphere Radar (EAR) at Kototabang (0.2°S geographic latitude, 100.3°E longitude, and 10.4°S geomagnetic latitude), Indonesia, spatial temporal evolution equatorial plasma bubbles (EPBs) were examined to classify evolutionary‐type EPBs from those which formed elsewhere drifted into field view radar. A total 535 observed during low moderate solar activity years 2010–2012, out about 210 (~39%) are evolving type remaining 325...

Abstract High‐density GPS receivers located in Southeast Asia (SEA) were utilized to study the two‐dimensional structure of ionospheric plasma irregularities equatorial region. The longitudinal and latitudinal variations tens kilometer‐scale associated with bubbles (EPBs) investigated using maps rate total electron content change index (ROTI) from 127 an average spacing about 50–100 km. ROTI measurement on 5 April 2011 revealed that 16 striations EPBs generated continuously around passage...

Abstract The effects of the St. Patrick's Day geomagnetic storms 2013 and 2015 in equatorial low‐latitude regions both hemispheres 100°E longitude sector is investigated compared with response Indian at 77°E. data from a chain ionosondes GPS/Global Navigation Satellite Systems receivers magnetic conjugate locations have been used. perturbation zonal electric field due to prompt penetration magnetospheric convective under shielded over shielding gives rise rapid fluctuations F 2 layer...

This paper presents first results of spatial structure associated with 47‐MHz coherent backscatter from the low‐latitude F region in Indonesian‐Thai longitude sector. The measurements were made Equatorial Atmosphere Radar (EAR), located on geographic equator West Sumatra, Indonesia (0.20°S, 100.32°E; dip latitude: 10.36°S). active phased‐array EAR was used to perform rapid scans over a wide azimuth sector, temporal resolution that has heretofore been unachievable. Application this unique...

[1] A detailed comparison between the observations of Communication/Navigation Outage Forecasting System (C/NOFS) satellite and 47 MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (10.36°S dip latitude) on postmidnight irregularities is presented. The zonal meridional E × B drift velocities measured by vector electric field instrument C/NOFS are consistent with westward propagation backscatter echoes line-of-sight Doppler observed EAR, respectively. plasma density depletions...

Abstract Plasma density depletions in the equatorial ionosphere, or so‐called plasma bubbles (EPBs), are generated postsunset period and tend to have a very complex spatial structure. Especially, east‐west asymmetry of EPBs has been reported by various observations. Using high‐resolution bubble (HIRB) model, which is newly developed three‐dimensional numerical model for small‐scale structuring at west wall large‐scale F layer upwelling clearly reproduced first time. It not an eastward...

Abstract Spread F on ionograms has been considered to be a phenomenon mainly occurred at nighttime. This study presented case of daytime spread observed by the ionosonde installed Puer (PUR; 22.7°N, 101.05°E; dip latitude 12.9°N), where that lasted for more than 2 h (about 08:30 LT~10:45 LT) was 14 November 2015. To investigate possible mechanism, recorded PUR and Chiang Mai (18.76°N, 98.93°E; 9.04°N) were used in this study. We found traveling ionospheric disturbances before occurrence ....

The linear growth rates of the Rayleigh-Taylor (R-T) instability in ionosphere from 2011 to 2013 were obtained with a whole atmosphere-ionosphere coupled model GAIA (ground-to-topside atmosphere and for aeronomy). effects thermospheric dynamics driven by atmospheric waves propagating below on R-T rate are included incorporating meteorological reanalysis data region 30 km altitude. daily maximum these periods compared observed occurrence days equatorial plasma bubble (EPB) determined...

We report, for the first time, simultaneous two‐dimensional observations of 630‐nm airglow depletions and radar backscatter from field‐aligned irregularities (FAI) associated with equatorial plasma bubbles. Spatial distributions were obtained by performing east‐west scans 47‐MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia. A depletion, caused a bubble, was simultaneously observed an all‐sky imager. Both depletion region appeared as band‐like structure elongated meridional...

We have studied coupling between the neutral atmosphere and ionospheric E region in midlatitude by combining two numerical simulation models. Atmospheric gravity waves generated troposphere propagate through stratosphere mesosphere can reach lower thermosphere. When a zonal wind shear that accumulate sporadic‐ ( s ) layer (eastward below westward above) is applied, accumulated strongly modulated waves, polarization electric field due to produces wave‐like patterns of plasma density upper...

A three‐dimensional numerical simulation in the nighttime midlatitude ionosphere is developed for first time and applied to Perkins instability F region. Growth of successfully reproduced under condition, results basically agree with a linear theory previous two‐dimensional studies. Northwest‐southeast (NW‐SE) alignment density perturbations generated from random seeding by applying southeastward neutral wind. The are dominant at altitudes 200–300 km where steep gradient exists, which...