Ultra-fast Kelvin Research Articles

Ionosphere-thermosphere coupling via global-scale waves: new insights from two-years of concurrent in situ and remotely-sensed satellite observations

Growing evidence indicates that a selected group of global-scale waves from the lower atmosphere constitute a significant source of ionosphere-thermosphere (IT, 100–600 km) variability. Due to the geometry of the magnetic field lines, this IT coupling occurs mainly at low latitudes (< 30°) and is driven by waves originating in the tropical troposphere such as the diurnal eastward propagating tide with zonal wave number s = −3 (DE3) and the quasi-3-day ultra-fast Kelvin wave with s = −1 (UFKW1). In this work, over 2 years of simultaneous in situ ion densities from Ion Velocity Meters (IVMs) onboard the Ionospheric Connection Explorer (ICON) near 590 km and the Scintillation Observations and Response of the Ionosphere to Electrodynamics (SORTIE) CubeSat near 420 km, along with remotely-sensed lower (ca. 105 km) and middle (ca. 220 km) thermospheric horizontal winds from ICON’s Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) are employed to demonstrate a rich spectrum of waves coupling these IT regions. Strong DE3 and UFKW1 topside ionospheric variations are traced to lower thermospheric zonal winds, while large diurnal s = 2 (DW2) and zonally symmetric (D0) variations are traced to middle thermospheric winds generated in situ. Analyses of diurnal tides from the Climatological Tidal Model of the Thermosphere (CTMT) reveal general agreement near 105 km, with larger discrepancies near 220 km due to in situ tidal generation not captured by CTMT. This study highlights the utility of simultaneous satellite measurements for studies of IT coupling via global-scale waves.

Planetary-scale MLT waves diagnosed through multi-station methods: a review

Most experimental investigations on planetary-scale waves in the mesosphere and lower thermosphere (MLT) region are based on single-station or -satellite spectral analysis methods, which suffer from intrinsic spectral aliasing/ambiguity. To overcome the aliasing, the author has developed and utilized dual- and multi-station spectral methods in a series of recent works. These methods were implemented on meteor radar observations and surface magnetometer observations. In the implements, a variety of waves were discovered or investigated in terms of seasonal variations and responses to sudden stratospheric warming events, such as lunar and solar tides (migrating and non-migrating), Rossby wave normal modes, ultra-fast Kelvin waves, and secondary waves of wave–wave nonlinear interactions between the previous waves. The current paper illustrates these methods using synthetic data, comparatively reviews the methods and results in plain language, and proposes a new representation, termed the adjusted Feynman diagram, to summarize the nonlinear interactions and explain their implications.Graphical

The day-to-day variability in the mesosphere and lower thermosphere in low latitudes: A study using MF radar

This study presents the analysis of planetary waves (PWs) using daily mean wind velocities for four years (August 2013 to July 2017) of continuous measurements using MF radar over the low latitude Indian region Kolhapur (16.8° N; 74.2° E). The MF radar at Kolhapur was upgraded in 2013. These are the first results of PWs after the upgradation of MF radar. The seasonal and intra-seasonal variabilities of East-West (EW) traveling PWs in the MLT region have been studied. In the present work, the data was analyzed to study the waves with various periodicities (e.g. 3–4, 5–8, 15–17, and 30–60 days). The 3.5 day [Ultra-Fast Kelvin (UFK)] wave shows semiannual variability with burst like wave activity observed during the summer months and December solstice. In addition, it is observed to be stronger in the spring equinoctial period. A strong semiannual oscillation (SAO) has been observed in a 6.5-day wave with peaks near the equinoxes. Similar to SAO over the low latitude MLT region, the wave activity is stronger in April/May than in September/October. The 6.5-day waves are observed to be stronger when the background mean wind is westward. From the analysis, it has been seen that the period before and after the equinoctial period is favorable for the 6.5-day wave propagation. The 16-day wave has no significant seasonal dependence; instead, the waves spread to almost all seasons. The Madden-Julian Oscillations (MJOs) have been observed to be propagating with an average wind speed of ∼ 5 m/s when the background mean wind is eastward. The occurrence of MJO is observed during the summer and winter months. These results are the first of their kind in two aspects: first, they show the PWs with enhanced altitude coverage covering up to 110 km, and second, they show the PWs not contaminated due to equatorial electro jet influence.

Atmosphere-Ionosphere (A-I) Coupling as Viewed by ICON: Day-to-Day Variability Due to Planetary Wave (PW)-Tide Interactions.

Coincident Ionospheric Connections Explorer (ICON) measurements of neutral winds, plasma drifts and total ion densities (:=Ne, electron density) are analyzed during January 1-21, 2020 to reveal the relationship between neutral winds and ionospheric variability on a day-to-day basis. Atmosphere-ionosphere (A-I) connectivity inevitably involves a spectrum of planetary waves (PWs), tides and secondary waves due to wave-wave nonlinear interactions. To provide a definitive attribution of dynamical origins, the current study focuses on a time interval when the longitudinal wave-4 component of the E-region winds is dominated by the eastward-propagating diurnal tide with zonal wavenumber s = -3 (DE3). DE3 is identified in winds and ionospheric parameters through its characteristic dependence on local solar time and longitude as ICON's orbit precesses. Superimposed on this trend are large variations in low-latitude DE3 wave-4 zonal winds (±40 ms-1) and topside F-region equatorial vertical drifts at periods consistent with 2-days and 6-days PWs, and a ~3-day ultra-fast Kelvin wave (UFKW), coexisting during this time interval; the DE3 winds, dynamo electric fields, and drifts are modulated by these waves. Wave-4 variability in Ne is of order 25%-35%, but the origins are more complex, likely additionally reflecting transport by ~20-25 ms-1 wave-4 in-situ winds containing strong signatures of DE3 interactions with ambient diurnal Sun-synchronous winds and ion drag. These results are the first to show a direct link between day-to-day wave-4 variability in contemporaneously measured E-region neutral winds and F-region ionospheric drifts and electron densities.

Ultrafast Kelvin Wave Variations in the Surface Magnetic Field

AbstractA suite of general circulation models is used to investigate the surface magnetic perturbations due to the ionospheric currents driven by an eastward‐propagating ultrafast Kelvin wave (UFKW) packet with periods between 2 and 4 days and zonal wave number . The simulated daytime UFKW‐driven meridional magnetic perturbations dBn (∼±5 nT) (or zonal currents) between about 5° and 20° magnetic latitude in each hemisphere are opposite in sign to those equatorward of ±5° and produced by the equatorial electrojet (EEJ), with the directions on any given day determined by the phase of the UFKW as it propagates eastward with respect to the sunlit ionosphere. Since the nominal daytime Sq zonal current between ∼±30° is uniformly eastward flowing, the present results are consistent with the hypothesis that the EEJ is part of a local current vortex with oppositely directed currents near the equator versus those between 5° and 20° at low latitudes. UFKWs are a special wave type wherein meridional winds are relatively small, which leads to our finding that the EEJ dBn constitutes a simple quantitative proxy for E‐region UFKW neutral winds near the 107‐km peak height of the Hall conductivity, including the variable wave period of the UFKW packet. Numerical experiments are also performed to understand the longitude distribution of actual ground magnetometer measurements that are needed to reliably extract the UFKW dBn signal and hence the neutral winds, both of which are closely linked to plasma drifts and electron densities in the equatorial F region. Using actual magnetometer data it is moreover shown that the UFKW dBn signal is easily measurable. Therefore measurements of EEJ dBn can potentially be used to infer UFKW activity for scientific investigations focusing on coupling between the tropical troposphere and the ionosphere‐thermosphere.

Variability of the equatorial ionosphere induced by nonlinear interaction between an ultrafast Kelvin wave and the diurnal tide

The wave forcing from below allows the neutral atmosphere to drive short-term variability in the ionosphere. Recent modeling studies have shown that secondary waves originated from the nonlinear interaction of the atmospheric tides with planetary scale waves can contribute significantly to day-to-day variability of the ionosphere. In this study we used MLT neutral wind measured at São João do Cariri (7.4°S, 36.5°W) and ionospheric soundings performed by a digisonde installed at Fortaleza (3.9°S, 38.4°W) to investigate the presence and the induced variability by a secondary wave in the mesosphere-ionosphere system over the Brazilian equatorial region. We found evidences of the nonlinear interaction between a 3.5-day ultrafast Kelvin wave and the diurnal tide. The interaction produced a 1.3-day secondary wave that was found to propagate upward with maximum amplitude of 15 m/s and relatively long vertical wavelength (~44 km) in the MLT, which may allow it to penetrate into the ionosphere. In the ionosphere, we observed a common 1.3-day periodic variation in the virtual height (h'F) and critical frequency (foF2), which may be connected to the secondary wave observed in the MLT via modulation of the wind system in the E region dynamo. These findings suggest that secondary waves may impose additional variability to ionosphere.

Whole Atmosphere Model Simulations of Ultrafast Kelvin Wave Effects in the Ionosphere and Thermosphere

AbstractThis paper examines the response of the upper atmosphere to equatorial Kelvin waves with a period of ∼3 days, also known as ultrafast Kelvin waves (UFKWs). The whole atmosphere model Ground‐to‐topside model of Atmosphere and Ionosphere for Aeronomy (GAIA) is used to simulate the UFKW events in the late summer of 2010 and 2011 as well as in the boreal winter of 2012/2013. When the lower layers of the model below 30‐km altitude are constrained with meteorological data, GAIA is able to reproduce salient features of the UFKW in the mesosphere and lower thermosphere as observed by the Aura Microwave Limb Sounder. The model also reproduces ionospheric response, as validated through comparisons with total electron content data from the Gravity field and steady‐state Ocean Circulation Explorer satellite as well as with earlier observations. Model results suggest that the UFKW produces eastward‐propagating ∼3‐day variations with zonal wavenumber 1 in the equatorial zonal electric field and F region plasma density. Model results also suggest that for a ground observer, identifying ionospheric signatures of the UFKW is a challenge because of ∼3‐day variations due to other sources. This issue can be overcome by combining ground‐based measurements from different longitudes. As a demonstration, we analyze ground‐based magnetometer data from equatorial stations during the 2011 event. It is shown that wavelet spectra of the magnetic data at different longitudes are only in partial agreement, with or without a ∼3‐day peak, but a spectrum analysis based on multipoint observations reveals the presence of the UFKW.

Preliminary Evidence of Madden‐Julian Oscillation Effects on Ultrafast Tropical Waves in the Thermosphere

AbstractOver the past two decades mounting evidence demonstrated that terrestrial weather significantly influences the dynamics and mean state of the thermosphere. While important progress has been made in understanding how this coupling occurs on hourly to daily time scales, large uncertainty still exists on this effect around intraseasonal (∼30–90 days) time scales. In this work, analyses of Thermosphere Ionosphere Mesosphere Energetics Dynamics‐Sounding of the Atmosphere using Broadband Emission Radiometry temperatures near 110 km and Gravity field and steady‐state Ocean Circulation Explorer cross‐track winds near 260 km reveal prominent intraseasonal oscillations in the equatorial (±15°) zonal mean lower and middle thermosphere. Similar intraseasonal oscillations are found in the amplitudes of the diurnal eastward propagating tide with Zonal Wavenumber 3 (DE3) and the quasi‐3‐day ultrafast Kelvin wave, two prominent ultrafast tropical waves (UFTWs) excited by deep tropical tropospheric convection. Numerical simulations from the Specified‐Dynamics Whole Atmosphere Community Climate Model eXtended demonstrate a significant connection between these UFTW and the Madden‐Julian Oscillation (MJO). Compared to the boreal winter mean state, thermospheric UFTW amplitudes are larger (+5 to +12%) during MJO Phases 2–3 and smaller (−3% to −12%) during MJO Phases 6–8. Significant variations are also found with respect to the phase of the mesospheric semiannual oscillation (MSAO) and stratospheric quasi‐biannual oscillation (SQBO), with larger (±12–16%) thermospheric amplitudes during westward MSAO/SQBO phase and smaller (±3–6%) amplitudes during eastward MSAO/SQBO phase, in accordance with theoretical interpretations. This study suggests that UFTW may play a large role in coupling tropospheric intraseasonal variability to the thermosphere, raising important questions including implications for the whole atmosphere system.

Variations in the ionosphere-thermosphere system from tides, ultra-fast Kelvin waves, and their interactions

Large scale waves, such as the atmospheric tides and ultra-fast Kelvin waves (UFKW), have direct effects on the neutral wind and temperature fields of the ionosphere-thermosphere (I-T) system. In this study we examine the response of the I-T system to the atmospheric tides, one UFKW, and the secondary waves generated from their interactions using the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM). We find that forcing an UFKW at the lower boundary of the TIEGCM is all that is required for it to setup in the model. We see variations around 10% in the zonal winds that lead to similar variations in the total electron content (TEC) depending on the phase of the UFKW. From these simulations, we expect the Ionospheric Connection Explorer (ICON) mission will be able to fully capture these wave interactions by observing winds and temperatures at the mesopause and above.

The nature and origins of the day-to-day variability in Earth’s surface magnetic field

Numerical experiments are performed with the National Center for Atmospheric Research (NCAR) Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) to reveal the characteristics and origins of daytime magnetic field variations on the ground (ΔB) at planetary-wave (PW) periods (2–20 days). Simulations are performed to separate the responses to forcing in the lower atmosphere from solar-magnetospheric forcing. Lower-atmosphere forcing is specified at the 97-km lower boundary of the TIE-GCM by NCAR's Thermosphere-Ionosphere-Mesosphere Electrodynamics General Circulation Model (TIME-GCM), which itself is forced at 30 km by MERRA (Modern Era Retrospective-analysis for Research and Applications) outputs. Solar and magnetospheric inputs to the TIE-GCM are specified according to parameterizations based on F10.7 and Kp. The study focuses on latitudes 0°–65°N during October 1–31, 2009, when F10.7 (range 68–80), Kp (range 0–4), and Ap (range 0–13) are typical of quiet-time “weather”. Neutral dynamics in the dynamo region (ca. 100–150 km) during this period is dominated by winds due to PW modulated tides, where the PW include the quasi-6, 10 and 16-day westward-propagating normal modes with zonal wavenumber s = 1, and eastward-propagating ultra-fast Kelvin waves (UFKW) with s = −1 and periods between 2 and 5 days.Results and conclusions are as follows. PW-period perturbations in daytime ΔB at the ground are dominated by variability originating in the lower atmosphere. The only exception is the 45°–65° latitude regime around noon, where the ΔB variability due to lower atmospheric forcing exceeds that due to solar-magnetospheric forcing by only about 50%. Broadband zonally-symmetric oscillations also occur in ΔB due to dissipation of the tidal spectrum at PW periods in the E-region. These results raise the possibility that some level of contamination from the lower atmosphere may exist in magnetic indices such as ap, Kp, and Ap that are used as measures solar-magnetosphere-ionosphere coupling strength, under levels of geomagnetic activity similar to that characterizing October 2009. It is also found that variations in conductivities play a minor role compared with neutral winds in producing PW-period variations in ΔB, and that there is not a robust one-to-one correspondence between spectral peaks in ΔB and those in the neutral winds. Several factors contribute to this latter result, which are explained in the text.

Environmental Gating and Galvanic Effects in Single Crystals of Organic-Inorganic Halide Perovskites.

Understanding the impact of environmental gaseous on the surface of organometal halide perovskites (OMHPs) couples to the electronic and ionic transport is critically important. Here, we explore the transport behavior and origins of the gas sensitivity in MAPbBr3 single crystals (SCs) devices using impedance spectroscopy and current relaxation measurements. Strong resistive response occurs when crystals are exposed to different environments. It was shown that SC response to the environment is extremely different at the surface as compared to the bulk due to the disorder surface chemistry. The nonlinear transport properties studied using ultrafast Kelvin probe force microscopy (G-KPFM) to unravel spatio-temporal charge dynamics at SC/electrode interface. The relaxation processes observed in pulse relaxation and G-KPFM measurements along with gas sensitivity of crystals suggest the presence of a triple-phase boundary between environment, electrode, and crystal. Results indicate that the environment is a nontrivial component in the operation of OMHP devices which is reminiscent of fuel cell systems. Furthermore, the triple-phase boundary can play a significant role in the transport properties of OMHPs due to the possibility of the redox processes coupled to the concentration of bulk ionic species. Although instrumental for understanding the device characteristics of perovskites, our studies suggest a new opportunity of coupling the redox chemistry of the Br2-Br- pair that defines the bulk ionic conductivity of MAPbBr3 with the redox chemistry of gaseous (or liquid) environment via a suitable electrocatalytic system to enable new class of energy storage devices and gas sensors.

The mean zonal wind effect on the long-term variation of ultra-fast Kelvin waves in the mesosphere and lower thermosphere and in the upper stratosphere

This study investigates 14-year ultra-fast Kelvin wave (UFKW) activity in the mesosphere and lower thermosphere (MLT) and in the upper stratosphere where the mesopause semiannual oscillation (MSAO) and the stratopause semiannual oscillation (SSAO) dominate the two altitude regions, respectively. The wave properties are derived from SABER temperature data for the period from 2003 to 2016 by two-dimensional fast Fourier transform. The investigations focus on the UFKW with zonal wavenumber 1 and periods of 2.5–4.5 days. The spectra, daily variations, and seasonal variations of UFKW are investigated. The wave activity is also compared with the background zonal wind derived from the horizontal wind model 2014 (HWM14) for the MLT region and from European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis for the upper stratosphere. The results are that periods of UFKW are mainly in the range of 2.5–4.5 days, but the dominated periods change from year to year. The UFKW amplitudes increase with altitude, and the largest amplitudes occur at altitudes above 90 km. Above 95 km, the mean zonal wind is westward at all times and the amplitude of UFKW is large most of the time. In the MLT region and the upper stratosphere, the large-amplitude UFKW tend to occur in the westward phase of the MSAO and the SSAO. The seasonal variation of UFKW in the MLT region and the upper stratosphere both show a semiannual variation in which the maximum and the secondary maximum are in August and February, respectively. The correlation analysis shows that the time lags between the 90-km wave variation and lower altitude wave variations do not match the theoretical expectation of the wave upward velocity. Finally, the MSAO and the SSAO act like two filters, which modify the wave amplitude and result in different daily variations in the MLT region and in the upper stratosphere.

Ultrafast Kelvin waves in the MLT airglow and wind, and their interaction with the atmospheric tides

Abstract. Airglow and wind measurements from the Brazilian equatorial region were used to investigate the presence and the effects of the 3–4-day ultrafast Kelvin waves in the MLT. The airglow integrated intensities of the OI557.7 nm, O2b(0-1) and OH(6-2) emissions, as well as the OH rotational temperature, were measured by a multichannel photometer, and the zonal and meridional wind components between 80 and 100 km were obtained from a meteor radar. Both instruments are installed in the Brazilian equatorial region at São João do Cariri (7.4∘ S, 36.5∘ W). Data from 2005 were used in this study. The 3–4-day oscillations appear intermittently throughout the year in the airglow. They were identified in January, March, July, August and October–November observations. The amplitudes induced by the waves in the airglow range from 26 to 40 % in the OI557.7 nm, 17 to 43 % in the O2b(0-1) and 15 to 20 % in the OH(6-2) emissions. In the OH rotational temperature, the amplitudes were from 4 to 6 K. Common 3–4-day oscillations between airglow and neutral wind compatible with ultrafast Kelvin waves were observed in March, August and October–November. In these cases, the amplitudes in the zonal wind were found to be between 22 and 28 m s−1 and the vertical wavelength ranges from 44 to 62 km. Evidence of the nonlinear interaction between the ultrafast Kelvin wave and diurnal tide was observed. Keywords. Atmospheric composition and structure (airglow and aurora) – meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

Kelvin wave coupling from TIMED and GOCE: Inter/intra-annual variability and solar activity effects

The primary mechanism through which energy and momentum are transferred from the lower atmosphere to the thermosphere is through the generation and propagation of atmospheric waves. It is becoming increasingly evident that a few waves from the tropical wave spectrum preferentially propagate into the thermosphere and contribute to modify satellite drag. Two of the more prominent and well-established tropical waves are Kelvin waves: the eastward-propagating 3-day ultra-fast Kelvin wave (UFKW) and the eastward-propagating diurnal tide with zonal wave number 3 (DE3). In this work, Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperatures at 110 km and Gravity field and steady-state Ocean Circulation Explorer (GOCE) neutral densities and cross-track winds near 260 km are used to demonstrate vertical coupling in this height regime due to the UFKW and DE3. Significant inter- and intra-annual variability is found in DE3 and the UFKW, with evidence of latitudinal broadening and filtering of the latitude structures with height due to the effect of dissipation and mean winds. Additionally, anti-correlation between the vertical penetration of these waves to the middle thermosphere and solar activity level is established and explained through the effect of molecular dissipation.

Wave coupling from the lower to the middle thermosphere: Effects of mean winds and dissipation

AbstractRecent observational and modeling evidence has demonstrated that planetary waves can modulate atmospheric tides, and secondary waves arising from their nonlinear interactions are an important source of both temporal and longitude variability in the thermosphere. While significant progress has been made on understanding how this form of vertical coupling occurs, uncertainty still exists on how the horizontal structures of primary and secondary waves evolve with height and the processes responsible for this evolution, in part due to lack of global observations between 120 km and 260 km. In this work we employ a Thermosphere Ionosphere Mesosphere Electrodynamics general circulation model simulation covering all of 2009 that is forced by Modern‐Era Retrospective Analysis for Research and Applications dynamical fields, to assess the relative contribution of zonal mean winds and molecular dissipation on the vertical coupling of the eastward propagating diurnal tide with zonal wave number 3 (DE3), the 3 day ultrafast Kelvin wave, and the secondary waves arising from their nonlinear interaction. By developing and applying a new analytic formulation describing the latitudinal structure of an equatorially trapped wave subject to dissipation and background winds, we show that dissipation is the primary contributor to the broadening of the latitudinal structures with height, while asymmetries in the background wind field are responsible for the distortion of the height‐latitude structures.

Global distribution and variability of quasi 2 day waves based on the NOGAPS‐ALPHA reanalysis model

AbstractThis study presents the analysis of 14 months (January 2009 to February 2010) of continuous hourly Navy Operational Global Atmospheric Prediction System‐Advanced Level Physics High Altitude reanalysis data used for examining the quasi 2 day wave (QTDW). The global structure and seasonal variability of the eastward and westward traveling QTDWs in all meteorological fields (geopotential height, zonal and meridional wind, and temperature) have been studied. The use of hourly reanalysis data allows a comprehensive understanding of the global spatial‐temporal QTDW distribution by simultaneous separations of all tides and planetary waves. The wave characteristics (amplitudes and phases) are presented in latitude range ±80° and altitudes from 15 to 95 km. Two different types of eastward traveling waves are identified: (i) waves at middle and high latitudes with zonal wave numbers 2 and 3, which are observed in the local winters, and (ii) waves observed predominantly over the equator with zonal wave number 2, which do not have a well‐defined seasonal variability but show some enhancement between June and August. While the first type waves are seen in all meteorological fields, the second ones are not seen in the meridional wind and belong to the ultrafast Kelvin waves. Two different types of westward traveling waves have been identified as well: (i) waves at middle and high latitudes with zonal wave numbers 2, 3, and 4, which are observed mainly in summer hemisphere, and (ii) waves observed predominantly over the equator with zonal wave numbers 1, 2, and 3, enhanced predominantly at both solstices but are seen in other seasons as well. While the first type waves are seen in all meteorological fields, the second ones are observed in the meridional wind and are Rossby‐gravity normal modes.

Fast and ultrafast Kelvin wave modulations of the equatorial evening F region vertical drift and spread F development

In this paper, we investigate the role of eastward and upward propagating fast (FK) and ultrafast Kelvin (UFK) waves in the day-to-day variability of equatorial evening prereversal vertical drift and post sunset generation of spread F/plasma bubble irregularities. Meteor wind data from Cariri and Cachoeira Paulista (Brazil) and medium frequency (MF) radar wind data from Tirunelveli (India) are analyzed together with Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) temperature in the 40- to 100-km region to characterize the zonal and vertical propagations of these waves. Also analyzed are the F region evening vertical drift and spread F (ESF) development features as diagnosed by Digisonde (Lowell Digisonde International, LLC, Lowell, MA, USA) operated at Fortaleza and Sao Luis in Brazil. The SABER temperature data permitted determination of the upward propagation characteristics of the FK (E1) waves with propagation speed in the range of 4 km/day. The radar mesosphere and lower thermosphere (MLT) winds in the widely separated longitude sectors have yielded the eastward phase velocity of both the FK and UFK waves. The vertical propagation of these waves cause strong oscillation in the F region evening prereversal vertical drift, observed for the first time at both FK and UFK periodicities. A delay of a few (approximately 10) days is observed in the F region vertical drift perturbation with respect to the corresponding FK/UFK zonal wind oscillations, or temperature oscillations in the MLT region, which has permitted a direct identification of the sunset electrodynamic coupling process as being responsible for the generation of the FK/UFK-induced vertical drift oscillation. The vertical drift oscillations are found to cause significant modulation in the spread F/plasma bubble irregularity development. The overall results highlight the role of FK/UFK waves in the day-to-day variability of the ESF in its occurrence season.

Signatures of ultra fast Kelvin waves in low latitude ionospheric TEC during January 2009 stratospheric warming event

In this study, for the first time, planetary wave signatures in ionospheric Total Electron Content (TEC) retrieved from global positioning service (GPS), mesospheric wind and temperature at low latitude station has been identified during January–February 2009. Our investigations revealed that planetary waves with 3–5 days periodicity characterized as ultrafast Kelvin (UFK) waves caused by stratospheric warming event during January 2009. The UFK waves are observed to be propagated from lower atmosphere to ionosphere. The UFK perturbations during SSW event are discussed in the light of current understanding of role of non linear interaction of planetary waves to modulate low latitude ionosphere.

Ionospheric response to the ultrafast Kelvin wave in the MLT region

AbstractThe modulation of the ultrafast Kelvin wave (UFKW) on the equatorial ionosphere is investigated, using satellite neutral wind and temperature observations in the mesosphere/lower thermosphere (MLT) and ground‐based global maps of total electron content (TEC) observations. The UFKW signatures are identified in the least squares fitting spectra for MLT zonal wind, temperature, TEC, and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) electron density profiles, providing strong evidence for the neutral‐ion coupling through the UFKW. The periods of the UFKW are mostly confined within 2–5.5 days. The UFKW in zonal wind and temperature maximize in the equatorial regions, whereas the UFKW band‐pass perturbations in electron density peak at the equatorial ionization anomaly (EIA) crests with minima at the equator. The UFKW band‐pass perturbations in TEC show consistent seasonal variability with the UFKW in the MLT region, including the intraseasonal oscillations with periods of 20–70 days. The long‐term variability of the absolute UFKW band‐pass amplitudes in TEC is in‐phase with solar cycle with maximum amplitude of ~7–8 (~1–2) total electron content unit (TECU; 1 TECU = 1016 el m‐2) during solar maximum (minimum) years, while the relative amplitudes show little solar activity dependence. The COSMIC electron density profiles show that the UFKW band‐pass perturbations maximize at ~300–400 km with fountain‐like spatial distributions, indicating the modulation of the UFKW on the EIA through electrodynamics.

Study of the ultra-fast Kelvin wave with meteor radar observations over a Brazilian extra-tropical station

Characteristics of the 3.5-day ultra-fast Kelvin (UKF) wave are investigated with 4 years of meteor radar wind observations over Cachoeira Paulista (22.7°S, 45°W). The UFK signature manifests itself as discrete bursts spanning over various times of the year with generally less amplitude during fall equinox and early winter. Daily as well as seasonal mean amplitude of the UFK component is found to be considerably smaller than that observed previously from equatorial stations. Estimated vertical wavelengths of the UFK wave come out to be larger than 40km. Comparison of the present results with another Brazilian equatorial station implies latitudinal invariance of the wave as well as transient local dynamical influence to its variability. High zonal acceleration caused by momentum flux convergence due to the UFK wave just after equinoxes is believed to be responsible for driving the westerly phase of the mean zonal wind immediately after the equinoxes and hence the mesospheric semiannual oscillation to some extent. There is a clear signature of modulation of the UFK wave amplitude by various harmonics of the annual oscillation.