The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Tzuwei Fang - One of the best experts on this subject based on the ideXlab platform.
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first forecast of a sudden stratospheric warming with a coupled whole atmosphere ionosphere model idea
Journal of Geophysical Research, 2014Co-Authors: R A Akmaev, Tzuwei Fang, T J Fullerrowell, Fei Wu, Naomi MaruyamaAbstract:We present the first “weather forecast” with a coupled whole-atmosphere/ionosphere model of Integrated Dynamics in Earth's Atmosphere (IDEA) for the January 2009 Sudden Stratospheric Warming (SSW). IDEA consists of the Whole Atmosphere Model and Global Ionosphere-Plasmasphere model. A 30 day forecast is performed using the IDEA model initialized at 0000 UT on 13 January 2009, 10 days prior to the peak of the SSW. IDEA successfully predicts both the time and amplitude of the peak warming in the polar cap. This is about 2 days earlier than the National Centers for Environmental Prediction operational Global Forecast System terrestrial weather model forecast. The forecast of the semidiurnal, westward propagating, zonal wave number 2 (SW2) tide in zonal wind also shows an increase in the amplitude and a phase shift to earlier hours in the equatorial dynamo region during and after the peak warming, before recovering to their prior values about 15 days later. The SW2 amplitude and phase changes are shown to be likely due to the stratospheric ozone and/or circulation changes. The daytime upward Plasma Drift and total electron content in the equatorial American sector show a clear shift to earlier hours and enhancement during and after the peak warming, before returning to their prior conditions. These ionospheric responses compare well with other observational studies. Therefore, the predicted ionospheric response to the January 2009 SSW can be largely explained in simple terms of the amplitude and phase changes of the SW2 zonal wind in the equatorial E region.
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simulations of solar and lunar tidal variability in the mesosphere and lower thermosphere during sudden stratosphere warmings and their influence on the low latitude ionosphere
Journal of Geophysical Research, 2012Co-Authors: N M Pedatella, A D Richmond, Hanli Liu, Astrid Maute, Tzuwei FangAbstract:[1] Whole Atmosphere Community Climate Model (WACCM) simulations are used to investigate solar and lunar tide changes in the mesosphere and lower thermosphere (MLT) that occur in response to sudden stratosphere warmings (SSWs). The average tidal response is demonstrated based on 23 moderate to strong Northern Hemisphere SSWs. The migrating semidiurnal lunar tide is enhanced globally during SSWs, with the largest enhancements (∼60–70%) occurring at mid to high latitudes in the Northern Hemisphere. Enhancements in the migrating solar semidiurnal tide (SW2) also occur up to an altitude of 120 km. Above this altitude, the SW2 decreases in response to SSWs. The SW2 enhancements are 40–50%, making them smaller in a relative sense than the enhancements in the migrating semidiurnal lunar tide. Changes in nonmigrating solar tides are, on average, generally small and the only nonmigrating tides that exhibit changes greater than 20% are the diurnal tide with zonal wave number 0 (D0) and the westward propagating semidiurnal tide with zonal wave number 1 (SW1). D0 is decreased by ∼20–30% at low latitudes, while SW1 exhibits a similar magnitude enhancement at mid to high latitudes in both hemispheres. The tidal changes are attributed to a combination of changes in the zonal mean zonal winds, changes in ozone forcing of the SW2, and nonlinear planetary wave-tide interactions. We further investigate the influence of the lunar tide enhancements on generating perturbations in the low latitude ionosphere during SSWs by using the WACCM-X thermosphere to drive an ionosphere-electrodynamics model. For both solar maximum and solar minimum simulations, the changes in the equatorial vertical Plasma Drift velocity are similar to observations when the lunar tide is included in the simulations. However, when the lunar tide is removed from the simulations, the low latitude ionosphere response to SSWs is unclear and the characteristic behavior of the low latitude ionosphere perturbations that is seen in observations is no longer apparent. Our results thus indicate the importance of variability in the lunar tide during SSWs, especially for the coupling between SSWs and perturbations in the low latitude ionosphere.
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longitudinal variation of ionospheric vertical Drifts during the 2009 sudden stratospheric warming
Journal of Geophysical Research, 2012Co-Authors: Tzuwei Fang, R A Akmaev, T J Fullerrowell, Houjun Wang, Fei Wu, D N AndersonAbstract:[1] The Whole Atmospheric Model (WAM) initialized with a data assimilation scheme is capable of simulating real sudden stratospheric warming (SSW) events. The electrodynamics in the Coupled Thermosphere Ionosphere and Plasmasphere with Electrodynamics model (CTIPe) was driven by the WAM thermospheric winds in January 2009 to study the response of ionospheric Drifts during the SSW. Simulation results are compared with observations of the vertical Drift at Jicamarca and the equatorial electrojet (EEJ) in the Asian sectors. Early morning upward Drift and afternoon downward Drift are reproduced in all longitudes in the simulations, and are consistent with the available observations. Results also show that the occurrence time of the early morning upward Drift and afternoon downward Drift have significant phase differences between different longitudes. Simulations suggest that during the SSW the longitude dependence of the amplitude and phase of the equatorial vertical Plasma Drift is caused by the changing magnitudes of the migrating tides modulated by the geometry of the geomagnetic field. Some additional day-to-day variability and modulation of the phase structures at different longitudes in ionospheric vertical Drifts during the SSW are possibly produced by the short-term changes in the non-migrating tides and by planetary waves.
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response of the thermosphere and ionosphere to an ultra fast kelvin wave
Journal of Geophysical Research, 2010Co-Authors: Loren C Chang, Tzuwei Fang, S E Palo, Hanli Liu, Chin S LinAbstract:[1] Ultra Fast Kelvin (UFK) waves are eastward propagating planetary waves with periods between 3 and 5 days, which are capable of penetrating into the thermosphere and ionosphere where they may modulate phenomena occurring in this region. A sensitivity study has been conducted to examine the effect of an Ultra Fast Kelvin wave on the thermosphere and ionosphere using the NCAR Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) under June solstice solar minimum conditions. It is found that realistic ultra fast Kelvin waves with amplitudes in the MLT region of approximately 20–40 m s−1 in zonal wind fields and 10–20 K in temperature fields, can result in approximately 8–12% perturbations in hourly neutral density at 350 km, as well as hourly total electron content (TEC) perturbations of 25–50% in regions corresponding to the equatorial ionization anomalies (EIAs), with the largest relative changes resolved during the nighttime due to the lower electron densities. The electrodynamical calculations in the model were then disabled to identify the relative importance of ionospheric electrodynamics and direct wave propagation in generating the aforementioned changes. The subsequent results show that changes in thermospheric neutral density are relatively insensitive to the presence of the dynamo electric field, while UFK wave modulation of the dynamo accounts for most of the TEC perturbations due to changes of ionospheric vertical Plasma Drift.
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causal link of the wave 4 structures in Plasma density and vertical Plasma Drift in the low latitude ionosphere
Journal of Geophysical Research, 2009Co-Authors: Tzuwei Fang, A D Richmond, H Kil, George Millward, Jannyenq LiuAbstract:[1] We investigate the annual and local time variations of the wave-4 structures in the Plasma density and vertical Drift in the low-latitude F region by analyzing the measurements from the first Republic of China satellite (ROCSAT-1) and conducting simulations with the Global Ionosphere and Plasmasphere (GIP) model. The GIP model uses apex magnetic coordinates with International Geomagnetic Reference Field (IGRF) for magnetic field, neutral wind from HWM-07, and thermospheric parameters from the NRLMSISE-00 model. In order to understand how the vertical Drifts relate to the longitudinal structure of the topside ionosphere, we apply the equatorial vertical Drifts observed from ROCSAT-1 to drive the GIP model. The model well reproduces the longitudinal structure in electron density, and the magnitudes of electron density are comparable with ROCSAT-1 measurement at 600 km. The ROCSAT-1 observations of the vertical Drift and Plasma density show maximum amplitudes of their wave-4 components in July–September and minimum amplitudes in December–February. An eastward shift of the wave-4 components with increasing local time is observed in both the density and the vertical Drift. The GIP model density showed similar annual and local time variations of the wave-4 component. Since the model uses the observed equatorial vertical E × B Drift as an input, the results indicate the vertical Drifts are essential in the formation and evolution of the longitudinal wave-4 density structure. The amplitude of the eastward propagating diurnal tide (DE3) at 110 km shows similar annual and local time variations as the F region parameters, supporting the link between the DE3 tide, vertical E × B Drift, and F region Plasma density on a global scale.
N M Pedatella - One of the best experts on this subject based on the ideXlab platform.
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analysis and hindcast experiments of the 2009 sudden stratospheric warming in waccmx dart
Journal of Geophysical Research, 2018Co-Authors: Larisa Petrovna Goncharenko, J L Chau, N M Pedatella, D R Marsh, Jeffrey L Anderson, Kevin Raeder, T A SiddiquiAbstract:The ability to perform data assimilation in the Whole Atmosphere Community Climate Model eXtended version (WACCMX) is implemented using the Data Assimilation Research Testbed (DART) ensemble adjustment Kalman filter. Results are presented demonstrating that WACCMX+DART analysis fields reproduce the middle and upper atmosphere variability during the 2009 major sudden stratospheric warming (SSW) event. Compared to specified dynamics WACCMX, which constrains the meteorology by nudging toward an external reanalysis, the large‐scale dynamical variability of the stratosphere, mesosphere, and lower thermosphere is improved in WACCMX+DART. This leads to WACCMX+DART better representing the downward transport of chemical species from the mesosphere into the stratosphere following the SSW. WACCMX+DART also reproduces most aspects of the observed variability in ionosphere total electron content and equatorial vertical Plasma Drift during the SSW. Hindcast experiments initialized on 5, 10, 15, 20, and 25 January are used to assess the middle and upper atmosphere predictability in WACCMX+DART. A SSW, along with the associated middle and upper atmosphere variability, is initially predicted in the hindcast initialized on 15 January, which is ∼10 days prior to the warming. However, it is not until the hindcast initialized on 20 January that a major SSW is forecast to occur. The hindcast experiments reveal that dominant features of the total electron content can be forecasted ∼10–20 days in advance. This demonstrates that whole atmosphere models that properly account for variability in lower atmosphere forcing can potentially extend the ionosphere‐thermosphere forecast range.
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the influence of atmospheric tide and planetary wave variability during sudden stratosphere warmings on the low latitude ionosphere
Journal of Geophysical Research, 2013Co-Authors: N M Pedatella, Hanli LiuAbstract:[1] Numerical simulations are performed for a sudden stratosphere warming (SSW) under different atmospheric tide and planetary wave forcing conditions to investigate the tidal variability in the mesosphere and lower thermosphere (MLT). The influence of variability of different tides in the MLT on generating perturbations to the low latitude ionosphere is also investigated. Significant changes are found to occur in the migrating semidiurnal solar (SW2) and lunar (M2) tides as well as in the westward propagating nonmigrating semidiurnal tide with zonal wave number 1 (SW1). The changes in the zonal mean atmosphere that occur during SSWs lead to an enhancement in the SW2 and M2 tides. The vertical wavelength of the SW2 is also changed, resulting in phase variability in the SW2 at a constant altitude. Significant enhancements in the SW1 are found to occur only in the presence of additional planetary wave forcing, and this demonstrates that nonlinear planetary wave‒tide interactions lead to the enhanced SW1 during SSWs. The amplitude and phase variability of the SW2 is found to be capable of producing temporal variability in the vertical Plasma Drift velocity that is similar to the observed variability. Changes in the M2 during SSWs can contribute up to an additional ∼30% of the total ionosphere variability; however, the overall influence of the lunar tide is found to be dependent upon the phase of the moon relative to the timing of the SSW. Although the influence is relatively minor, the SW1 also contributes to the low latitude ionosphere variability during SSWs. The simulation results for the vertical Plasma Drift velocity and total electron content (TEC) further illustrate that significant longitude variability occurs in the ionosphere response to SSWs.
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simulations of solar and lunar tidal variability in the mesosphere and lower thermosphere during sudden stratosphere warmings and their influence on the low latitude ionosphere
Journal of Geophysical Research, 2012Co-Authors: N M Pedatella, A D Richmond, Hanli Liu, Astrid Maute, Tzuwei FangAbstract:[1] Whole Atmosphere Community Climate Model (WACCM) simulations are used to investigate solar and lunar tide changes in the mesosphere and lower thermosphere (MLT) that occur in response to sudden stratosphere warmings (SSWs). The average tidal response is demonstrated based on 23 moderate to strong Northern Hemisphere SSWs. The migrating semidiurnal lunar tide is enhanced globally during SSWs, with the largest enhancements (∼60–70%) occurring at mid to high latitudes in the Northern Hemisphere. Enhancements in the migrating solar semidiurnal tide (SW2) also occur up to an altitude of 120 km. Above this altitude, the SW2 decreases in response to SSWs. The SW2 enhancements are 40–50%, making them smaller in a relative sense than the enhancements in the migrating semidiurnal lunar tide. Changes in nonmigrating solar tides are, on average, generally small and the only nonmigrating tides that exhibit changes greater than 20% are the diurnal tide with zonal wave number 0 (D0) and the westward propagating semidiurnal tide with zonal wave number 1 (SW1). D0 is decreased by ∼20–30% at low latitudes, while SW1 exhibits a similar magnitude enhancement at mid to high latitudes in both hemispheres. The tidal changes are attributed to a combination of changes in the zonal mean zonal winds, changes in ozone forcing of the SW2, and nonlinear planetary wave-tide interactions. We further investigate the influence of the lunar tide enhancements on generating perturbations in the low latitude ionosphere during SSWs by using the WACCM-X thermosphere to drive an ionosphere-electrodynamics model. For both solar maximum and solar minimum simulations, the changes in the equatorial vertical Plasma Drift velocity are similar to observations when the lunar tide is included in the simulations. However, when the lunar tide is removed from the simulations, the low latitude ionosphere response to SSWs is unclear and the characteristic behavior of the low latitude ionosphere perturbations that is seen in observations is no longer apparent. Our results thus indicate the importance of variability in the lunar tide during SSWs, especially for the coupling between SSWs and perturbations in the low latitude ionosphere.
F J Rich - One of the best experts on this subject based on the ideXlab platform.
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zonal Drift of Plasma particles inside equatorial Plasma bubbles and its relation to the zonal Drift of the bubble structure
Journal of Geophysical Research, 2010Co-Authors: Chao-song Huang, O De La Beaujardiere, R F Pfaff, J M Retterer, P A Roddy, D E Hunton, F J RichAbstract:[1] It has been observed that the zonal Drift velocity of equatorial Plasma bubbles is generally eastward. However, it has not been well understood whether the zonal Drift of Plasma bubbles is the same as the ambient Plasma Drift and what process causes differences in the Drift velocities of the ambient Plasma and bubbles. In this study we analyze the ion Drift velocities measured by the Defense Meteorological Satellites Program and ROCSAT-1 satellites and the electric fields measured by the Communications/Navigation Outage Forecasting System (C/NOFS) satellite in the presence of equatorial spread F. We find that the zonal Drift velocity of the Plasma particles inside Plasma bubbles is significantly different from the ambient Plasma Drift. The relative zonal velocity of the ions inside the depletion region with respect to the ambient Plasma is generally westward. In most cases it can be as high as several hundreds of meters per second. The Plasma bubbles detected by the C/NOFS satellite in the midnight-dawn sector are still growing, and the polarization electric field inside the postmidnight bubbles is much stronger than the electric field in the ambient Plasma. We suggest that the zonal Drift velocity of the Plasma particles inside the depletion region is driven by polarization electric field. When a Plasma bubble is tilted, the E × B Drift velocity caused by the polarization electric field has an upward component and a zonal component. Because of the zonal motion of the Plasma particles inside the bubble, the eastward Drift velocity of the bubble structure is faster than the ambient Plasma Drift for a west-tilted bubble and slower than the ambient Plasma Drift for an east-tilted bubble.
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ionospheric Plasma blobs observed by oi 630 nm all sky imaging in the brazilian tropical sector during the major geomagnetic storm of april 6 7 2000
Geophysical Research Letters, 2007Co-Authors: A A Pimenta, J. A. Bittencourt, Y Sahai, F J RichAbstract:[1] This paper presents first observations of Plasma blobs (localized Plasma density enhancements) associated with large-scale Plasma density depletions (Plasma bubbles) in the nighttime low-latitude F-region during a major geomagnetic disturbance. Ground-based observations of the OI 630 nm all-sky images obtained at Cachoeira Paulista (22.7°S, 45.0°W), Brazil, in the Appleton anomaly region, showed the presence of Plasma blobs during the major geomagnetic storm of April 6–7, 2000 (ΣKp = 38 −/40+; ∣Dst∣max = 288 nT). The OI 630 nm emission images were used to map the spatial and temporal locations of Plasma blobs and bubbles in the bottomside of the F-region. The F-region parameters, presented in this work, were obtained from ionosondes operating near the same site and also at Sao Luis (2.6°S, 44.4°W), Brazil. Ionospheric Plasma blobs and bubbles zonal Drift velocities, measured by the all-sky imaging system, showed that both the Plasma blobs and the bubbles moved westward (normally the Plasma Drift is eastward during nighttime) on this magnetically disturbed night. Furthermore, the Plasma blobs showed typically east-west and north-south extensions in the range of 110–160 km and 200–450 km, respectively. It appears that the DMSP-15 satellite, orbiting at about 850 km altitude, passed through one of the blobs detected by the ground-based observations on this night while crossing the Brazilian sector. This indicates the enormous altitude extent [from about 275 km (OI 630.0 nm emission) to 850 km (DMSP satellite) altitude] of the localized Plasma density enhanced regions. In this work, we present and discuss several features related to the dynamics of the localized Plasma density enhancements and large-scale Plasma density depletions during this major geomagnetic disturbance.
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response of the equatorial ionosphere in the south atlantic region to the great magnetic storm of july 15 2000
Geophysical Research Letters, 2001Co-Authors: K M Groves, S Basu, S Y Su, F J Rich, P J Sultan, M J KeskinenAbstract:The effects of the great magnetic storm of July 15, 2000 on the equatorial ionosphere have been studied by ground-based and satellite in-situ measurements. A large westward Plasma Drift in the evening equatorial ionosphere was observed as a result of the ionospheric disturbance dynamo. In that environment, the IMF Bz turned southward and presumably caused penetration of E-fields to low latitudes. This E-field initiated the onset of 250 MHz and L-band scintillations at Ascension Island (15°W) and precipitous TEC decrease at Fortaleza, Brazil (38°W), bounding the narrow longitude region in the South Atlantic. These impulsive ionospheric effects were extremely well correlated with abrupt decreases of SYM-H (1-min resolution Dst). The DMSP in-situ measurements showed the presence of severe ion density bite-outs extending over 30° latitude in the South Atlantic Magnetic Anomaly region. The ROCSAT-1 satellite measured upward and large southward ion Drifts in the same sector.
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response of the equatorial ionosphere in the south atlantic region to the great magnetic storm of july 15 2000
Geophysical Research Letters, 2001Co-Authors: K M Groves, S Basu, F J Rich, P J Sultan, H C Yeh, M J KeskinenAbstract:The effects of the great magnetic storm of July 15, 2000 on the equatorial ionosphere have been studied by ground-based and satellite in-situ measurements. A large westward Plasma Drift in the evening equatorial ionosphere was observed as a result of the ionospheric disturbance dynamo. In that environment, the IMF Bz turned southward and presumably caused penetration of E-fields to low latitudes. This E-field initiated the onset of 250 MHz and L-band scintillations at Ascension Island (15°W) and precipitous TEC decrease at Fortaleza, Brazil (38°W), bounding the narrow longitude region in the South Atlantic. These impulsive ionospheric effects were extremely well correlated with abrupt decreases of SYM-H (1-min resolution Dst). The DMSP in-situ measurements showed the presence of severe ion density bite-outs extending over 30° latitude in the South Atlantic Magnetic Anomaly region. The ROCSAT-1 satellite measured upward and large southward ion Drifts in the same sector.
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ionospheric disturbances observed by dmsp at middle to low latitudes during the magnetic storm of june 4 6 1991
Journal of Geophysical Research, 2000Co-Authors: W J Burke, F J Rich, P J Sultan, O De La Beaujardiere, Allen G Rubin, N C Maynard, L C Gentile, C Y Huang, G R WilsonAbstract:This paper extends a recent study of electric field penetration into the inner magnetosphere observed by the Combined Release and Radiation Effects (CRRES) satellite and the Defense Meteorological Satellite Program (DMSP) satellite F8 during the magnetic storm of June 4–6, 1991, to consider its ionospheric consequences. Effects include the development of > 1 km/s subauroral ion Drift (SAID) structures, the formation of midlatitude density troughs, and the vertical transport of equatorial Plasma, bubbles. Nearly simultaneous auroral electron and Plasma Drift measurements were acquired by three DMSP satellites with F8 and F9 in one hemisphere and FlO in the other. Moderate to strong SAID structures were consistently detected for ∼10 hours during the early main phase of the storm. Weak SAIDs were encountered during ∼8 hours of the early recovery phase. DMSP data show that SAIDs with similar characteristics developed at magnetically conjugate locations and extended for at least 3 hours in local time. Simultaneous measurements show that the SAIDs spanned temporally grooving but latitudinally narrow Plasma density troughs. These observations suggest that the magnetospheric sources of SAIDs act more like voltage than current generators. Energetic electron fluxes, electric fields, and Plasma waves measured by CRRES indicate that during this storm the ring current shielding charges and SAID sources were located in regions of high Plasma density characteristic of the Plasmasphere. The sequence in which DMSP detected equatorial Plasma density irregularities is consistent with model predictions that stormtime electrodynamics at low latitudes operate on distinctive fast and slow timescales [Fejer and Schcrliess, 1997].
Hanli Liu - One of the best experts on this subject based on the ideXlab platform.
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the influence of atmospheric tide and planetary wave variability during sudden stratosphere warmings on the low latitude ionosphere
Journal of Geophysical Research, 2013Co-Authors: N M Pedatella, Hanli LiuAbstract:[1] Numerical simulations are performed for a sudden stratosphere warming (SSW) under different atmospheric tide and planetary wave forcing conditions to investigate the tidal variability in the mesosphere and lower thermosphere (MLT). The influence of variability of different tides in the MLT on generating perturbations to the low latitude ionosphere is also investigated. Significant changes are found to occur in the migrating semidiurnal solar (SW2) and lunar (M2) tides as well as in the westward propagating nonmigrating semidiurnal tide with zonal wave number 1 (SW1). The changes in the zonal mean atmosphere that occur during SSWs lead to an enhancement in the SW2 and M2 tides. The vertical wavelength of the SW2 is also changed, resulting in phase variability in the SW2 at a constant altitude. Significant enhancements in the SW1 are found to occur only in the presence of additional planetary wave forcing, and this demonstrates that nonlinear planetary wave‒tide interactions lead to the enhanced SW1 during SSWs. The amplitude and phase variability of the SW2 is found to be capable of producing temporal variability in the vertical Plasma Drift velocity that is similar to the observed variability. Changes in the M2 during SSWs can contribute up to an additional ∼30% of the total ionosphere variability; however, the overall influence of the lunar tide is found to be dependent upon the phase of the moon relative to the timing of the SSW. Although the influence is relatively minor, the SW1 also contributes to the low latitude ionosphere variability during SSWs. The simulation results for the vertical Plasma Drift velocity and total electron content (TEC) further illustrate that significant longitude variability occurs in the ionosphere response to SSWs.
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attribution of ionospheric vertical Plasma Drift perturbations to large scale waves and the dependence on solar activity
Journal of Geophysical Research, 2013Co-Authors: Hanli Liu, A D RichmondAbstract:[1] In this study, we quantify the contribution of individual large-scale waves to ionospheric electrodynamics and examine the dependence of the ionospheric perturbations on solar activity. We focus on migrating diurnal tide (DW1) plus mean winds, migrating semidiurnal tide (SW2), quasi-stationary planetary wave one (QSPW1), and nonmigrating semidiurnal westward wave one (SW1) under northern winter conditions, when QSPW1 and SW1 are climatologically strong. From thermosphere-ionosphere-mesosphere electrodynamics general circulation model simulations under solar minimum conditions, it is found that the mean winds and DW1 produce a wave two pattern in equatorial vertical E×BDrift that is upward in the morning and around dusk. The modeled SW2 also produces a wave two pattern in the ionospheric vertical Drift that is nearly a half wave cycle out of phase with that due to mean winds and DW1. SW1 can cause large vertical Drifts around dawn, while QSPW1 does not have any direct impact on the vertical Drift. Wind components of both SW2 and SW1 become large at middle to high latitudes in the E-region, and kernel functions obtained from numerical experiments reveal that they can significantly affect the equatorial ion Drift, likely through modulating the E-region wind dynamo. The most evident changes of total ionospheric vertical Drift when solar activity is increased are seen around dawn and dusk, reflecting the more dominant role of large F-region Pedersen conductivity and of the F-region dynamo under high solar activity. Therefore, the lower atmosphere driving of the ionospheric variability is more evident under solar minimum conditions, not only because variability is more identifiable in a quieter background but also because the E-region wind dynamo is more significant. These numerical experiments also demonstrate that the amplitudes, phases, and latitudinal and vertical structures of large-scale waves are important in quantifying the ionospheric responses.
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simulations of solar and lunar tidal variability in the mesosphere and lower thermosphere during sudden stratosphere warmings and their influence on the low latitude ionosphere
Journal of Geophysical Research, 2012Co-Authors: N M Pedatella, A D Richmond, Hanli Liu, Astrid Maute, Tzuwei FangAbstract:[1] Whole Atmosphere Community Climate Model (WACCM) simulations are used to investigate solar and lunar tide changes in the mesosphere and lower thermosphere (MLT) that occur in response to sudden stratosphere warmings (SSWs). The average tidal response is demonstrated based on 23 moderate to strong Northern Hemisphere SSWs. The migrating semidiurnal lunar tide is enhanced globally during SSWs, with the largest enhancements (∼60–70%) occurring at mid to high latitudes in the Northern Hemisphere. Enhancements in the migrating solar semidiurnal tide (SW2) also occur up to an altitude of 120 km. Above this altitude, the SW2 decreases in response to SSWs. The SW2 enhancements are 40–50%, making them smaller in a relative sense than the enhancements in the migrating semidiurnal lunar tide. Changes in nonmigrating solar tides are, on average, generally small and the only nonmigrating tides that exhibit changes greater than 20% are the diurnal tide with zonal wave number 0 (D0) and the westward propagating semidiurnal tide with zonal wave number 1 (SW1). D0 is decreased by ∼20–30% at low latitudes, while SW1 exhibits a similar magnitude enhancement at mid to high latitudes in both hemispheres. The tidal changes are attributed to a combination of changes in the zonal mean zonal winds, changes in ozone forcing of the SW2, and nonlinear planetary wave-tide interactions. We further investigate the influence of the lunar tide enhancements on generating perturbations in the low latitude ionosphere during SSWs by using the WACCM-X thermosphere to drive an ionosphere-electrodynamics model. For both solar maximum and solar minimum simulations, the changes in the equatorial vertical Plasma Drift velocity are similar to observations when the lunar tide is included in the simulations. However, when the lunar tide is removed from the simulations, the low latitude ionosphere response to SSWs is unclear and the characteristic behavior of the low latitude ionosphere perturbations that is seen in observations is no longer apparent. Our results thus indicate the importance of variability in the lunar tide during SSWs, especially for the coupling between SSWs and perturbations in the low latitude ionosphere.
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response of the thermosphere and ionosphere to an ultra fast kelvin wave
Journal of Geophysical Research, 2010Co-Authors: Loren C Chang, Tzuwei Fang, S E Palo, Hanli Liu, Chin S LinAbstract:[1] Ultra Fast Kelvin (UFK) waves are eastward propagating planetary waves with periods between 3 and 5 days, which are capable of penetrating into the thermosphere and ionosphere where they may modulate phenomena occurring in this region. A sensitivity study has been conducted to examine the effect of an Ultra Fast Kelvin wave on the thermosphere and ionosphere using the NCAR Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) under June solstice solar minimum conditions. It is found that realistic ultra fast Kelvin waves with amplitudes in the MLT region of approximately 20–40 m s−1 in zonal wind fields and 10–20 K in temperature fields, can result in approximately 8–12% perturbations in hourly neutral density at 350 km, as well as hourly total electron content (TEC) perturbations of 25–50% in regions corresponding to the equatorial ionization anomalies (EIAs), with the largest relative changes resolved during the nighttime due to the lower electron densities. The electrodynamical calculations in the model were then disabled to identify the relative importance of ionospheric electrodynamics and direct wave propagation in generating the aforementioned changes. The subsequent results show that changes in thermospheric neutral density are relatively insensitive to the presence of the dynamo electric field, while UFK wave modulation of the dynamo accounts for most of the TEC perturbations due to changes of ionospheric vertical Plasma Drift.
B W Reinisch - One of the best experts on this subject based on the ideXlab platform.
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ionospheric vertical Plasma Drift and electron density response during total solar eclipses at equatorial low latitude
Journal of Geophysical Research, 2015Co-Authors: B J Adekoya, V U Chukwuma, B W ReinischAbstract:The response of the vertical Plasma Drift (Vz) and the electron density (NmF2) during different solar eclipses was investigated. The diurnal values of the direct scaled measurement of F2 peak height and the one derived from M(3000) F2 data, acquired over an equatorial/low-latitude stations, have been used to determine the vertical Plasma Drift. The ionosphere during a solar eclipse is significantly affected by the E × B vertical Drift; the large depletion of electron density at low altitudes can be transported to high altitudes through the Plasma vertical Drift. The loss in ionization density during the eclipse phase decreases the electron density, which was accompanied by rapid increase in hmF2. This deviation in the NmF2 during eclipse compared to control days can be related to the increase in the loss rate due to recombination, as a result of reduction in thermal energy. However, the maximum reduction in NmF2 is not synchronous with the time of maximum totality but some minutes later. The differences in the solar epochs may contribute to the observed relative changes in the ionospheric F2 region behavior during the eclipse window. Lastly, it is very difficult to separate the influence of magnetic disturbances from solar eclipse. The deviation in NmF2 is higher during magnetic disturbed days than the quiet day. The reverse is the case for hmF2 observation. However, the NmF2 variation increases with an increase in solar activity.
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equatorial vertical Plasma Drift velocities and electron densities inferred from ground based ionosonde measurements during low solar activity
Journal of Atmospheric and Solar-Terrestrial Physics, 2013Co-Authors: B O Adebesin, J O Adeniyi, I A Adimula, B W ReinischAbstract:Abstract Average values of ionosonde hmF2 data acquired from an African equatorial station have been used to determine vertical Plasma Drift ( Vz ) measurements during period of low solar activity. Pre-noon peak was around 1000 h LT for all seasons. The peak daytime F2 Drift is higher during the equinoctial months with an average of 18.1 m/s than the solsticial months (14.7 m/s). At nighttime, Vz is characterized first by upward enhancement around 1900 h LT with a range of 0.3–8.0 m/s, then by a downward reversal. The highest enhancement was recorded in December solstice and start earliest during the March equinox. The peak reversal values are 13.3, 10.7, 9.0 and 4.2 m/s for December Solstice, September Equinox, March Equinox and June Solstice respectively. The observed simultaneous post-sunset rise in hmF2 and in vertical E × B Drift together with a sharp drop in NmF2 at all season infer that electrons moving away from the equator are at a region of low recombination loss rate. The abrupt faster Drift of the Plasma away from the equator as indicated by the pre-reversal enhancement (PRE) in upward Plasma Drift is responsible for the sharp drop in NmF2 immediately after sunset. Some past results were also confirmed in this work.
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planetary wave oscillations in mesospheric winds equatorial evening prereversal electric field and spread f
Geophysical Research Letters, 2006Co-Authors: M A Abdu, I S Batista, C G M Brum, P P Batista, A J Carrasco, B W ReinischAbstract:[1] Analysis of the MLT region winds measured by a meteor radar and the evening F region vertical Plasma Drift (prereversal zonal electric field -PRE) measured by digisondes over low latitude sites in Brazil, provide evidence of planetary wave (PW) scale oscillations of episodic nature simultaneously at mesospheric and F region heights. ∼4-day and 7-day periods are found to dominate the event analyzed. The PW scale oscillations in the PRE produces strong modulation in the equatorial spread F (ESF) irregularity processes as diagnosed by the digisondes. Considerations on the PRE development mechanism involving the E layer integrated conductivity including the effect of metallic ions and tidal winds point to the source of the PRE oscillations to be PW modulation of E region tidal winds. The PW oscillations in PRE appear to be an important source of the day-to-day variability in the ESF.
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a comparison of ionospheric vertical Drift velocities measured by digisonde and incoherent scatter radar at the magnetic equator
Journal of Atmospheric and Solar-Terrestrial Physics, 2006Co-Authors: Fernando C P Bertoni, M A Abdu, Inez S Batista, B W Reinisch, E A KheraniAbstract:Abstract Using data acquired with a Digisonde DPS-4 and an Incoherent Scatter Radar both from Jicamarca Radio Observatory, Peru, comparisons of ionospheric vertical Drift velocities derived from these two instruments are carried out in this work. They show good agreement during sunset and evening hours (around sunset, up to approximately 22 LT), and also, during the post-midnight (between 02 and 03 LT) and sunrise hours (until 08 LT), when the F-layer bottom side height is around and above 300 km, as well as during events of magnetically disturbed periods when the ionospheric Plasma Drift may be influenced by the perturbation electric fields arising from (1) direct penetration from high to low magnetic latitudes, and (2) disturbance winds dynamo action driven by Joule heating due to increased energy and momentum deposition into the high-latitude thermosphere–ionosphere system. The results of this study lend confidence to using Digisonde Drift data to study phenomena related to night-time magnetically disturbed periods.