Upward Drifts Research Articles

Ionospheric Super Bubbles Near Sunset and Sunrise During the 26–28 February 2023 Geomagnetic Storm

AbstractIonospheric equatorial plasma bubbles (EPBs) are usually generated around sunset over equatorial to low latitudes. In this study, super EPBs extending to middle latitudes were observed, which were freshly generated at both post‐sunset and near‐sunrise periods over East/Southeast Asia during the geomagnetic storm on 26–28 February 2023. The post‐sunset (near‐sunrise) EPB persisted ∼4 (8) hours, drifting eastward (westward) and extending up to ∼35°N. Strong L‐band scintillations, deep total electron content (TEC) depletions and significant positioning errors were caused by the post‐sunset EPB. However, the scintillations and TEC depletions linked with the near‐sunrise EPB were relatively weaker, and no apparent positioning error was caused. Before the onsets of the post‐sunset EPBs, rapid upward vertical plasma drifts of ∼60 m/s, which could be linked with storm‐time prompt penetration electric fields, were observed at magnetic equator. The upward vertical drifts could amplify the F‐region bottomside perturbation via increasing the growth rate of Rayleigh‐Taylor (R‐T) instability and lead to the generation of post‐sunset EPBs. On the other hand, before the onset of near‐sunrise EPBs, the uplift of F layer was more significant at higher latitudes than that at magnetic equator, probably indicating the presence of equatorward neutral wind. Both the equatorial F layer uplift and equatorward neutral wind could contribute to the growth of R‐T instability and favor the generation of near‐sunrise EPBs.

Generation and evolution of post-sunset equatorial plasma bubbles in East and Southeast Asia during the July 2022 geomagnetic storm

In the East and Southeast Asia, equatorial plasma bubbles (EPBs) mainly occur at post-sunset in equinoctial months. On 7–8 July 2022, a moderate geomagnetic storm occurred, with minimum Dst of −85 nT. This storm could trigger unseasonal post-sunset EPBs over the East/Southeast Asian sector. Observations from GNSS TEC/scintillation receivers, VHF coherent radar and ionosonde show that on 7 July, a few clusters of EPBs, which caused strong amplitude scintillations and significant TEC fluctuations, occurred over a wide latitude range, from low to middle latitudes up to ∼ 32°N. The EPB irregularities at middle latitudes drifted westward, with velocities of about 97 m/s. Before the generation of EPBs, apparent background ionospheric disturbances were detected. An abrupt rise of ionospheric F layer, with upward drifts of about 33 m/s was observed near sunset at low latitudes. It is suggested that the moderate geomagnetic storm was the main reason for the generation of unseasonal post-sunset EPBs. The prompt penetration of eastward electric field caused by the geomagnetic storm could lead to the abrupt rise of F layer near sunset and promote the growth of Rayleigh-Taylor instability. The background ionospheric disturbance could act as a seeding role for the unseasonal EPBs.

The Temporal Evolution of F-Region Equatorial Ionization Anomaly Owing to the 2022 Tonga Volcanic Eruption

The dynamic evolutions of the noon ionospheric Equatorial Ionization Anomaly (EIA) owing to the 2022 Tonga volcanic eruption were investigated using the ionospheric plasma measurements from the Swarm satellite, the science experiment of the Constellation Observing Systems for Meteorology, Ionosphere, and Climate (COSMIC) mission, and the thermospheric wind observations from the Ionospheric Connection Explorer (ICON). At 14.1 universal time (UT), the noon EIA was enhanced for the upward plasma drifts, when the F2-layer was significantly uplifted from 360 km to 410 km. At 15.6 UT, because of the downward drifts, the intensity of the EIA reduced, and hmF2 decreased to 270 km. At 17–18 UT, the EIA recovered and reformed, and hmF2 increased to 350 km. A two-peak structure in the plasma was observed at Swarm altitudes. The temporal evolution might be related to the vertical plasma drifts (both downward and upward) from the E-region electric field.

A numerical study of noontime bite-outs in F2-region electron density

Noontime bite-outs in ionospheric F2-region electron density in the geomagnetic equatorial, low, and middle latitudes have been reproduced in this study using the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM). The different driving mechanisms of F2-region noontime bite-outs at different latitudes were further verified by modeling simulation. In the geomagnetic equator, the upward ExB plasma drifts are the main process to produce the noontime bite-outs in ionospheric electron density. In the geomagnetic low latitudes, both the electrical fields and poleward meridional winds play a crucial role in forming the noontime bite-outs. In contrast to the case at the geomagnetic equator, a weaker fountain effect might be an favorable condition for the noontime bite-outs to occur at low latitudes. For geomagnetic middle latitudes, an upward plasma flux and poleward meridional winds are the dominated drivers in producing the noontime bite-outs. Modeling results show that a large upward plasma flux and poleward meridional winds make the noontime bite-outs to occur and observable over middle latitudes.

An Assessment of SNPP and NOAA20 VIIRS RSB Calibration Performance in NASA SIPS Reprocessed Collection-2 L1B Data Products

Two VIIRS sensors onboard the SNPP and NOAA20 satellites have been successfully operating for over 10 and 4 years, respectively, providing the worldwide user community with high-quality imagery and radiometric measurements of the land, atmosphere, cryosphere, and oceans. This study provides a temporal radiometric stability and calibration consistency assessment of the SNPP and NOAA20 VIIRS reflective solar bands using the latest NASA SIPS C2 L1B products. Several independent vicarious approaches are used to examine the stability of SNPP VIIRS and consistency of the at-sensor reflectance between the two VIIRS instruments. These approaches include observations from simultaneous nadir overpasses, the Libya-4 desert and Dome C snow/ice sites, and deep convective clouds. The impact of existing band spectral differences on the reflectance measurements is accounted for utilizing scene-specific hyperspectral observations provided by the SCIAMACHY sensor onboard the ENVISAT platform. Results indicate that both SNPP and NOAA20 VIIRS reflectances are stable within 1% over their mission periods for all bands, except for a few bands in the visible range from SNPP VIIRS that show more upward drifts at high radiances. NOAA20 VIIRS reflectances are systematically lower than SNPP by 2 to 4% for most bands, with the exception of few short wavelength bands where it is seen to be up to 7%.

Dual Sounding Rocket and C/NOFS Satellite Observations of DC Electric Fields and Plasma Density in the Equatorial E- and F-Region Ionosphere at Sunset.

E × B plasma drifts and plasma number density were measured on two NASA rockets launched simultaneously at sunset from Kwajalein Atoll with apogees of 182 and 331 km, with similar, coincident measurements gathered on the Communications/Navigation Outage Forecasting System (C/NOFS) satellite at 390 km. The combined measurements portray a highly dynamic ionosphere in a narrow range of local time and altitude, providing evidence of vortex‐like motions. Although the vertical plasma drift was upwards, its magnitude was not constant, increasing between ∼150 and 250 km altitude where the plasma density was reduced. The zonal plasma drifts displayed a shear with altitude, changing from eastward to westward flow below 270 km, coincident with the larger upward drifts and consistent with the maintenance of the vortex flow. The plasma density on the western flank was highly structured compared to the eastern flank, despite the fact that the western region corresponded to slightly earlier local times. These observations illustrate that the low latitude ionosphere at sunset must be considered as an ensemble of interconnected flows encompassing an evolving “theater,” as opposed to a background that simply unfolds linearly with respect to local time. The observations also underscore how satellites at high altitudes do not capture the highly dynamic ionosphere and thermosphere at the lower altitudes which are critical for understanding the electrodynamics system. Such motions set the stage for large scale plasma instabilities to form later in the evening, as observed by radars at Kwajalein and subsequent passes of the C/NOFS satellite.

Prompt Penetration and Substorm Effects Over Jicamarca During the September 2017 Geomagnetic Storm

AbstractWe used reanalyzed Jicamarca radar measurements to study the response of equatorial ionospheric electrodynamics and spread F during the main phase of the large September 2017 geomagnetic storm. Our observations near dusk on 7 September show very large upward drifts followed by a large short‐lived downward drift perturbation that completely suppressed the lower F region plasma irregularities and severely decreased the backscattered power from the higher altitude spread F. We suggest that this large short‐lived westward electric field perturbation is most likely of magnetospheric origin and is due to a sudden and very strong magnetic field reconfiguration. Later in the early night period, data indicate large, mostly upward, drift perturbations generally consistent with standard undershielding and overshielding electric field effects, but with amplitudes significantly larger than expected. Our analysis suggests that occurrence of storm‐time substorms is one of the major factors causing the large nighttime westward and eastward electric field perturbations observed at Jicamarca near the storm main phase. Our analysis also suggests that magnetospheric substorms play far more important roles on the electrodynamics of the equatorial nighttime ionosphere than has generally been thought.

Application of quasi-deep convective clouds method for VIIRS and MODIS TEB calibration assessments

A technique that utilizes quasi-deep convective clouds (qDCC) for the calibration assessment of the thermal emissive bands (TEB) on remote sensing instruments has been proven viable. The Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) and Suomi-National Polar-orbiting Partnership (S-NPP) and NOAA-20 (N20) Visible Infrared Imaging Radiometer Suite (VIIRS) TEB calibration uses a nonlinear algorithm with nonlinear coefficients that rely on on-orbit blackbody (BB) warm-up and cool-down operations for updates. However, a limited BB temperature range affects the calibration’s accuracy, particularly for cold scenes. The deep convective clouds (DCC) core, one of the coldest Earth scenes, is suitable for MODIS calibration assessments, more specifically, for the evaluation of the offset term’s effect in its TEB quadratic calibration function. Moreover, nighttime qDCC measurements provide the advantage of removing solar reflectance effects during daytime, thus enhancing the assessment’s accuracy for the mid-wave infrared TEB. This qDCC method is applied to the Terra MODIS and VIIRS TEB, and their stabilities are assessed using long-term qDCC trending measurements over the instruments’ missions. The measurements from bands with an 11-μm wavelength are used to identify the DCC pixels. The 11-μm bands, MODIS band 31, and VIIRS bands M15 and I5 are stable throughout the MODIS and VIIRS missions and have shown excellent calibration accuracy and noise performance. Hence, using these bands as references, a normalization method is employed to enhance the accuracy of the stability and consistency assessments. The S-NPP VIIRS TEB show stable trends over the instrument’s mission. The S-NPP-to-N20 VIIRS comparison shows that their TEB measurements are consistent over qDCC. The Terra MODIS TEB also shows stable performance—except for bands 27, 29, and 30. Terra MODIS band 30 shows a large downward trend throughout the mission, whereas bands 27 and 29 show slight, upward drifts. Finally, a calibration correction using qDCC assessments is discussed and intended to be used in a future calibration algorithm collection.

Longitudinal Variation of Postsunset Plasma Depletions From the Global‐Scale Observations of the Limb and Disk (GOLD) Mission

AbstractThe Global‐scale Observations of the Limb and Disk (GOLD) mission, launched in 2018, aims to investigate the low latitude ionosphere from a geostationary orbit at 47.5°W. It uses two identical spectrometers measuring the wavelength range from 134.0 to 163.0 nm. The configuration of the Earth's magnetic field shows that the largest offset between geographic and geomagnetic equators occurs in the longitude sectors sampled by GOLD. In an attempt to investigate the longitude dependence of the occurrence rate and time of onset of plasma bubbles, or plasma depletions, GOLD data were separated in three sectors: 65°‐55°W, 50°‐40°W, and 10°W–0°. Observations of the nighttime emissions in 135.6 nm on November 2018 and March 2019 show plasma depletions occurring very frequently at these longitudes. The growth rate of the Rayleigh‐Taylor instability was computed at these longitudes under similar low solar activity conditions, assuming an empirical model of upward plasma drifts. The time and value of the maximum growth rates obtained cannot always explain the observations. On average, the observed occurrence rate of plasma depletions is high, with a maximum of 73% (observed during November 2018 at ∼45°W). Most of the depletions observed in November at 45°W and 60°W occur within 1 h after sunset. When compared with the November 2018 observations, depletions in March 2019 occur at later times.

Anomalous Electron Temperature Increases in the Evening Equatorial Ionosphere

AbstractWe use novel radar observations at the Jicamarca Radio Observatory to study the first observations of highly enhanced plasma temperatures in the evening equatorial ionosphere. These short‐lived solstice evening events occurred following large upward plasma drifts and sharply reduced plasma densities. The electron temperatures increase during the August 5 and 6, 2011 moderate solar event reached peak values of about 1,000 K near 350 km. Smaller electron temperature increases were observed to altitudes up to about 500 km. There were also smaller concurrent ion temperature enhancements. During the very low solar flux January 20 and 21, 2020 event, a peak electron temperature increase of about 700 K occurred at an altitude of about 270 km. We also show that SAMI2‐PE simulations using the measured vertical plasma drifts reproduce the main characteristics of the measured plasma densities and temperatures up to 300 km, but not at higher altitudes. These simulations indicate that the evening anomalous plasma heating below about 300 km is due to the decrease in the electron‐ion cooling rate resulting from upward plasma drift driven decrease in the plasma density. Plasma transport and reduced cooling rate is a potential source of higher altitude heating.

Electrodynamical Coupling of the Geospace System During Solar Flares

AbstractReduced daytime upward E×B drifts and weakened fountain effects in equatorial ionosphere have been frequently observed during the initial stage of solar flares. The cause of this phenomenon, however, remains unresolved. The latest state‐of‐art whole geospace model provides an unprecedented opportunity to explore the origin of this response. We show that both prompt penetration electric fields (PPEFs) and internal changes in the wind dynamo process are responsible for the reduced upward ion drifts. Solar‐flare‐induced PPEFs are caused by a reduced high‐latitude potential as a result of flare‐enhanced ionospheric conductances which are distinct from traditional PPEFs that respond to changes in solar wind conditions or magnetosphere dynamics. The neutral wind dynamo source is mainly a reduction in the background low‐latitude eastward electric field. This reduction occurs to maintain current continuity in response to the flare enhancement of low‐latitude Cowling conductance that is relatively greater than the enhancement of the dynamo current source.

Westward Electric Fields in the Afternoon Equatorial Ionosphere During Geomagnetically Quiet Times

AbstractThe daytime average zonal electric field is well known to be eastward in the equatorial ionosphere. Geomagnetic observations have revealed that the equatorial electrojet or zonal electric field occasionally becomes westward in the afternoon sector during quiet times. We present the first analysis of the dependence of the afternoon downward plasma drifts on the season, longitude, solar activity, and lunar phase using the ROCSAT‐1 satellite observations during 1999–2004. The results show that there are ~20% of downward plasma drifts at 13–17 LT. The occurrence rate of the downward plasma drift shows a peak around January and a secondary peak in July. The occurrence rate presents a slight decrease trend with the solar activity. Especially, the occurrence rate can attain ~40–50% around 60°E in June solstice and 145–245°E in December solstice, which is nearly comparable with the occurrence rate of the upward plasma drifts in these longitudes. The downward plasma drift occurs most frequently around the full moon in the afternoon sector. The geomagnetic declination induces the hemispheric differences in the dynamo current in the conjugate regions and controls the occurrence of the westward electric fields. A wavenumber‐4 longitudinal structure also appears to be present in the occurrence rate in June–September, and the wavenumber‐4 peak coincides with the diurnal eastward tidal wind, which drives the generation of the westward electric fields.

Persistence of the Long‐Duration Daytime TEC Enhancements at Different Longitudinal Sectors During the August 2018 Geomagnetic Storm

AbstractIn this study, the ionospheric responses in the Asian‐Australian, American, and African sectors during the August 2018 geomagnetic storm were investigated based on the Beidou geostationary orbit (GEO) satellite and Massachusetts Institute of Technology (MIT) Madrigal total electron contents (TECs), combined with measurements from ionosondes, magnetometers, and Global Ultraviolet Imager (GUVI). The middle‐ and low‐latitude TECs were dominated by positive responses over the three longitudinal sectors during the storm on 26–29 August. It is unique that daytime TECs at the Asian‐Australian, American, and African sectors displayed large enhancements larger than 10 TEC units (TECu) on 27–29 August, during the recovery phase, when the ionosphere is usually dominated by plasma depletions due to the ionospheric disturbance dynamo and/or disturbed thermospheric compositions. The combination and competition of the disturbed vertical plasma drifts through the solar wind‐magnetosphere‐ionosphere (SW‐M‐I) coupling and disturbed neutral compositions contribute significantly to the daytime TEC responses at different longitudinal sectors on 26 August during the main and early recovery phases. The eastward equatorial electrojet and O/N2 during the recovery phase on 27–29 August are larger than the quiet reference, which suggest that the enhanced upward vertical plasma drifts combining with higher O/N2 make an important contribution on the daytime positive ionospheric storm during the recovery phase. The enhanced vertical plasma drifts could not be driven by the SW‐M‐I coupling or ionospheric disturbance dynamo associated with the geomagnetic storm. Further studies should be untaken to explore the dominant sources for the enhanced upward vertical drifts during the recovery phase.

The Physical Mechanisms for the Sunrise Enhancement of Equatorial Ionospheric Upward Vertical Drifts

AbstractSatellite and incoherent scatter radar observations have shown frequently a strong enhancement of upward vertical E × B drifts in the equatorial ionospheric F region near sunrise. Previous studies suggested that this enhancement is associated with the local equatorial wind dynamo, the same process used to explain the prereversal enhancement after sunset. However, this hypothesis has never been tested in a first‐principles way. In this study, we explore the physical mechanisms responsible for the sunrise enhancement of equatorial upward vertical drifts using the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model. The model well reproduces the sunrise enhancement of upward vertical drifts observed at Jicamarca on 10 June 2004. The simulation results show that large eastward zonal electric fields occur around sunrise at all latitudes but with a peak at middle latitudes. Further numerical experiments reveal that the equatorial sunrise enhancement at solar minimum is primarily driven by the E region zonal wind dynamo at middle latitudes rather than by the local dynamo effect in the equatorial region. Specifically, the intensity of the equatorial eastward electric field near sunrise is determined by the magnitudes of westward wind and its longitudinal gradient at middle latitudes and the declination of the dawn termination.

Effects of Solar Activity on Ionospheric Ion Upflow During Geomagnetic Quiet Periods: DMSP Observations

Abstract Based on the Defense Meteorological Satellite Program (DMSP) observations during Solar Cycle 23, this paper examines solar activity dependence of ionospheric bulk ion upflow events (IUEs) in the Southern Hemisphere (SH). Much previous similar work was conducted over the Northern Hemisphere (NH) with measurements from European Incoherent Scatter (EISCAT). To eliminate the influence of geomagnetic disturbance on IUEs, we pick out observations during geomagnetic quiet periods (with Kp ≤ 2+). Results show that, ion upward densities and fluxes are dramatically elevated at times of high solar activity (HSA) but ion upward drifts and occurrences are increased at times of low solar activity (LSA) in the SH, which is consistent with the situation in the NH. The ratios between HSA and LSA for these four parameters (IUEs’ density, flux, upward drift and occurrence) are ~2.71, ~1.98, ~0.76 and ~0.57, respectively. Furthermore, lower flux event takes place frequently at LSA as the background ion density is low but the upward drift is large, while higher flux event happens commonly at times of HSA accompanied by high ion density but low upward velocity. Quantitatively, an increase in unit of solar activity (characterized by P index) causes a 4.2×108 m−3 increase in ion density and a 1.2×1011 m−2·s−1 enhancement in upward flux, together with a 0.6 m·s−1 and 0.02 % decrease in ion upward velocity and uprate, respectively. The acceleration from the ambipolar electric field is thought to be a possible mechanism affecting the dependence of IUEs on solar variations. For HSA, the acceleration from the ambipolar electric field weakens, but a large number of background ions provide abundant seeds for acceleration and upflow, which maintains a high IUE flux. It is inferred that upflow events and upward drifts are inhibited by the enhanced ionospheric background density.

Variation of hmF2 and NmF2 deduced from DPS-4 over Multan (Pakistan) and their comparisons with IRI-2012 [formula omitted] IRI-2016 during the deep solar minimum between cycles 23 & 24

We report the results of ionospheric measurements from DPS-4 installed at Multan (Geog coord. 30.18°N, 71.48°E, dip 47.4°). The variations in F2-layer maximum electron density NmF2 and its peak height hmF2 are studied during the deep solar minimum between cycles 23 & 24 i.e 2008–2009 with comparisons conducted with the International Reference Ionosphere (IRI) versions 2012 & 2016. We find that the hmF2 observations peak around the pre-sunrise and sunrise hours depending on the month. Seasonally, the daytime variation of NmF2 is higher in the Equinox and Summer, while daytime hmF2 are slightly higher in the Equinox and Winter. High values of hmF2 around midnight are caused by an increase of upward drifts produced by meridional winds. The ionosphere over Multan, which lies at the verge of low and mid latitude, is affected by both E×B drifts and thermospheric winds as evident from mid-night peaks and near-sunrise dips in hmF2. The results of the comparison of the observed NmF2 and hmF2 for the year 2008–2009 with the IRI-2012 (both NmF2 and hmF2) and IRI-2016 (only hmF2) estimates indicate that for NmF2, IRI-2012 with Consultative Committee International Radio (CCIR) option produces values in better agreement with observed data. Whereas, for hmF2, IRI-2016 with both International Union of Radio Science (URSI) and CCIR SHU-2015 options, predicts well for nighttime hours throughout the year. However, the IRI-2012 with CCIR option produces better agreement with data during daytime hours. Furthermore, IRI-2012 with CCIR option gives better results during Equinox months, whereas, IRI-2016 with both URSI and CCIR SHU-2015 options predict well for Winter and Summer.

Linezolid activity against clinical Gram-positive cocci with advanced antimicrobial drug resistance in Iran.

The aim of the study was to investigate the linezolid activity against clinical Gram-positive cocci with advanced antimicrobial drug resistance. A collection of methicillin resistant Staphylococcus aureus (MRSA), vancomycin resistant enterococci (VRE), penicillin non-susceptible Streptococcus pneumoniae (PNSP), and group B streptococci (GBS) were isolated from various clinical samples. Antimicrobial susceptibility tests were done using standard methods Subsequently, we investigated linezolid antibacterial activities, the first approved oxazolidinone against isolates by the standard broth microdilution method. According to our results, MRSA and PNSP isolates were multidrug resistant, and almost half of the VRE isolates were high level gentamicin resistant (HLGR). Furthermore, resistance to linezolid was not seen among the isolates. The MIC90 values for MRSA, VRE, PNSP and GBS isolates were 4μg/ml, 2μg/ml, 1μg/ml, and 0.5μg/ml, respectively. Only 6.25% of vancomycin resistant enterococci showed intermediate susceptibility to this antibiotic. These findings indicate that linezolid has an excellent activity against clinical drug resistant Gram-positive isolates in Iran. Constant monitoring and surveillance of linezolid MIC distribution allows the researchers to assess and detect gradual upward MIC drifts.

Some drifts on posets and its application to fuzzy subalgebras

In this paper, given a poset $(X,leq)$, we introduce some drifts on a groupoid $(X,*)$ with respect to $(X,leq)$, and we obtain several properties of these drifts related to the notion of $Bin(X)$. We discuss some connections between fuzzy subalgebras and upward drifts.

TEC variations and ionospheric disturbances during the magnetic storm in March 2015 observed from continuous GPS data in the Southeast Asia region

TEC variations and ionospheric disturbances during the magnetic storm in March 2015 observed from continuous GPS data in the Southeast Asia region

Impact of midnight thermosphere dynamics on the equatorial ionospheric vertical drifts

AbstractRecent satellite and ground‐based observations have revealed the existence of upward drifts in the postmidnight equatorial ionosphere (~0–3 LT). The phenomenon has not been explained by theoretical models. Simulations using the Whole Atmosphere Model coupled with the Global Ionosphere Plasmasphere model have successfully reproduced the unusual nighttime upward drifts. The simulations and observations by the Ion Velocity Meter onboard the Communications/Navigation Outage Forecasting System also reveal substantial longitudinal dependence of the drifts. Our analysis indicates that the upward drifts are driven by thermosphere dynamics associated with the midnight temperature maximum (MTM). The MTM locally reverses the typical large‐scale zonal and meridional wind pattern, in turn affecting the nighttime F layer electrodynamics. In addition, the longitudinal variation of the drifts in different seasons depends on the magnitude and position of the MTM peak relative to the magnetic equator.