Longitudinal variations of noontime thermospheric winds in response to IMF Bz temporal oscillations: broken mean circulation and standing feature

Abstract By using the coupled magnetosphere-thermosphere-ionosphere model, we explore the longitudinal/UT differences of the dayside neutral wind in response to the 60 min periodic oscillation of the interplanetary magnetic field (IMF) Bz. The southward propagation of the traveling atmospheric disturbances (TADs) in meridional wind stands at about 20º MLat, which is related to the geomagnetic field configuration, neutral temperature, and electron density changes. The meridional wind travels continuously from high to low latitude in the western southern hemisphere, while they are broken into pieces in the eastern southern hemisphere. The broken mean circulation that is a combined effect of TADs and simultaneous responses of the meridional winds driven by oscillating solar wind conditions is induced by the stronger roles of the ion drag than the pressure gradient. Note here that the mean circulation is the background meridional winds in the base case. The ion drag shows obvious longitudinal differences associated with the penetration of the ionospheric electric field during the oscillation of IMF Bz.

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Longitudinal variations of noontime thermospheric winds in response to IMF Bz temporal oscillations: broken mean circulation and standing feature

10.21203/rs.3.rs-46709/v2 ◽

2020 ◽

Author(s):

Kedeng Zhang ◽

Hui Wang ◽

Wenbin Wang ◽

Jing Liu ◽

Jie Gao

Keyword(s):

Southern Hemisphere ◽

Periodic Oscillation ◽

Meridional Wind ◽

Field Configuration ◽

Base Case ◽

Ionosphere Model ◽

Meridional Winds ◽

Longitudinal Variations ◽

Ionospheric Electric Field ◽

Mean Circulation

Abstract By using coupled magnetosphere-thermosphere-ionosphere model, we explore the longitudinal/UT differences of the dayside neutral wind in response to the 60 min periodic oscillation of interplanetary magnetic field (IMF) Bz. The southward propagation of the travelling atmospheric disturbances (TADs) in meridional wind stands at about 20º MLat, which is related to the geomagnetic field configuration, neutral temperature and electron density changes. The meridional wind travels continuously from high to low latitude in the western southern hemisphere, while they are broken into pieces in the eastern southern hemisphere. The broken mean circulation that is a combined effect of TADs and simultaneous responses of the meridional winds driven by oscillating solar wind conditions is induced by the stronger roles of the ion drag than the pressure gradient. Note here that the mean circulation is the background meridional winds in the base case. The ion drag shows obvious longitudinal differences associated with the penetration of the ionospheric electric field during the oscillation of IMF Bz.

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Longitudinal variations of noontime thermospheric winds in response to IMF Bz temporal oscillations: broken mean circulation and standing feature

10.21203/rs.3.rs-46709/v4 ◽

2021 ◽

Author(s):

Kedeng Zhang ◽

Hui Wang ◽

Wenbin Wang ◽

Jing Liu ◽

Jie Gao

Keyword(s):

Periodic Oscillation ◽

Meridional Wind ◽

Field Configuration ◽

Base Case ◽

Ionosphere Model ◽

Atmospheric Disturbances ◽

Meridional Winds ◽

Longitudinal Variations ◽

Ionospheric Electric Field ◽

Mean Circulation

Abstract By using the coupled magnetosphere-thermosphere-ionosphere model, we explore the longitudinal/UT dependences of the dayside neutral wind in response to the 60 min periodic oscillation of the interplanetary magnetic field (IMF) Bz. The southward propagation of the traveling atmospheric disturbances (TADs) in meridional wind stands at about 20º MLat, which is related to the geomagnetic field configuration, neutral temperature, and electron density changes. The meridional wind travels continuously from high to low latitude in the western southern hemisphere, with several sudden changes in the wave phase along the propagation direction. The broken mean circulation that is induced by the interaction between TADs and simultaneous responses of the meridional winds driven by oscillating solar wind conditions is induced by the stronger roles of the ion drag than the pressure gradient. Note here that the mean circulation is the background meridional winds in the base case with the IMF Bz setting to zero in the CMIT model. The ion drag shows obvious longitudinal differences associated with the penetration of the ionospheric electric field during the oscillation of IMF Bz.

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Longitudinal Variations of Noontime Thermospheric Winds in Response to IMF Bz Temporal Oscillations: Broken Mean Circulation and Standing Feature

10.21203/rs.3.rs-46709/v1 ◽

2020 ◽

Author(s):

Kedeng Zhang ◽

Hui Wang ◽

Wenbin Wang ◽

Jing Liu ◽

Jie Gao

Keyword(s):

Southern Hemisphere ◽

Periodic Oscillation ◽

Meridional Wind ◽

Field Configuration ◽

Low Latitude ◽

Ionosphere Model ◽

Atmospheric Disturbances ◽

Longitudinal Variations ◽

Ionospheric Electric Field ◽

Mean Circulation

Abstract By using coupled magnetosphere-thermosphere-ionosphere model, we explore the longitudinal/UT differences of the dayside neutral wind in response to the 60 min periodic oscillation of interplanetary magnetic field (IMF) Bz. The southward propagation of the travelling atmospheric disturbances (TADs) in meridional wind stands at about 20º MLat, which is related to the geomagnetic field configuration, neutral temperature and electron density changes. The meridional wind travels continuously from high to low latitude in the western southern hemisphere, while they are broken into pieces in the eastern southern hemisphere. The broken mean circulation is induced by the stronger roles of the ion drag than the pressure gradient. The ion drag shows obvious longitudinal differences associated with the penetration of the ionospheric electric field during the oscillation of IMF Bz.

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Impacts of Detoured Madden-Julian Oscillations on the South Pacific Convergence Zone

Journal of Climate ◽

10.1175/jcli-d-20-0444.1 ◽

2021 ◽

pp. 1-41

Author(s):

Lei Zhou ◽

Ruomei Ruan ◽

Raghu Murtugudde

Keyword(s):

Southern Hemisphere ◽

Rossby Waves ◽

South Pacific ◽

South Pacific Convergence Zone ◽

Boreal Winter ◽

Convergence Zone ◽

The South ◽

Maritime Continent ◽

Meridional Winds ◽

Southern Pacific Ocean

AbstractMadden-Julian Oscillations (MJOs) are a major component of tropical intraseasonal variabilities. There are two paths for MJOs across the Maritime Continent; one is a detoured route into the Southern Hemisphere and the other one is around the equator across the Maritime Continent. Here, it is shown that the detoured and non-detoured MJOs have significantly different impacts on the South Pacific convergence zone (SPCZ). The detoured MJOs trigger strong cross-equatorial meridional winds from the Northern Hemisphere into the Southern Hemisphere. The associated meridional moisture and energy transports due to the background states carried by the intraseasonal meridional winds are favorable for reinforcing the SPCZ. In contrast, the influences of non-detoured MJOs on either hemisphere or the meridional transports across the equator are much weaker. The detoured MJOs can extend their impacts to the surrounding regions by shedding Rossby waves. Due to different background vorticity during detoured MJOs in boreal winter, more ray paths of Rossby waves traverse the Maritime Continent connecting the southern Pacific Ocean and the eastern Indian Ocean, but far fewer Rossby wave paths traverse Australia. Further studies on such processes are expected to contribute to a better understanding of extreme climate and natural disasters on the rim of the southern Pacific and Indian Oceans.

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Effects of the midnight temperature maximum observed in the thermosphere–ionosphere over the northeast of Brazil

Annales Geophysicae ◽

10.5194/angeo-35-953-2017 ◽

2017 ◽

Vol 35 (4) ◽

pp. 953-963 ◽

Cited By ~ 4

Author(s):

Cosme Alexandre O. B. Figueiredo ◽

Ricardo A. Buriti ◽

Igo Paulino ◽

John W. Meriwether ◽

Jonathan J. Makela ◽

...

Keyword(s):

Relative Intensity ◽

Lower Thermosphere ◽

Meridional Wind ◽

Peak Height ◽

Neutral Wind ◽

F Region ◽

Early Evening ◽

Neutral Temperature ◽

Constant Height ◽

Meridional Winds

Abstract. The midnight temperature maximum (MTM) has been observed in the lower thermosphere by two Fabry–Pérot interferometers (FPIs) at São João do Cariri (7.4° S, 36.5° W) and Cajazeiras (6.9° S, 38.6° W) during 2011, when the solar activity was moderate and the solar flux was between 90 and 155 SFU (1 SFU  =  10−22 W m−2 Hz−1). The MTM is studied in detail using measurements of neutral temperature, wind and airglow relative intensity of OI630.0 nm (referred to as OI6300), and ionospheric parameters, such as virtual height (h′F), the peak height of the F2 region (hmF2), and critical frequency of the F region (foF2), which were measured by a Digisonde instrument (DPS) at Eusébio (3.9° S, 38.4° W; geomagnetic coordinates 7.31° S, 32.40° E for 2011). The MTM peak was observed mostly along the year, except in May, June, and August. The amplitudes of the MTM varied from 64 ± 46 K in April up to 144 ± 48 K in October. The monthly temperature average showed a phase shift in the MTM peak around 0.25 h in September to 2.5 h in December before midnight. On the other hand, in February, March, and April the MTM peak occurred around midnight. International Reference Ionosphere 2012 (IRI-2012) model was compared to the neutral temperature observations and the IRI-2012 model failed in reproducing the MTM peaks. The zonal component of neutral wind flowed eastward the whole night; regardless of the month and the magnitude of the zonal wind, it was typically within the range of 50 to 150 m s−1 during the early evening. The meridional component of the neutral wind changed its direction over the months: from November to February, the meridional wind in the early evening flowed equatorward with a magnitude between 25 and 100 m s−1; in contrast, during the winter months, the meridional wind flowed to the pole within the range of 0 to −50 m s−1. Our results indicate that the reversal (changes in equator to poleward flow) or abatement of the meridional winds is an important factor in the MTM generation. From February to April and from September to December, the h′F and the hmF2 showed an increase around 18:00–20:00 LT within a range between 300 and 550 km and reached a minimal height of about 200–300 km close to midnight; then the layer rose again by about 40 km or, sometimes, remained at constant height. Furthermore, during the winter months, the h′F and hmF2 showed a different behavior; the signature of the pre-reversal enhancement did not appear as in other months and the heights did not exceed 260 and 350 km. Our observation indicated that the midnight collapse of the F region was a consequence of the MTM in the meridional wind that was reflected in the height of the F region. Lastly, the behavior of the OI6300 showed, from February to April and from September to December, an increase in intensity around midnight or 1 h before, which was associated with the MTM, whereas, from May to August, the relative intensity was more intense in the early evening and decayed during the night.

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New results on equatorial thermospheric winds and temperatures from Ethiopia, Africa

Annales Geophysicae ◽

10.5194/angeo-35-333-2017 ◽

2017 ◽

Vol 35 (2) ◽

pp. 333-344 ◽

Cited By ~ 10

Author(s):

Fasil Tesema ◽

Rafael Mesquita ◽

John Meriwether ◽

Baylie Damtie ◽

Melessew Nigussie ◽

...

Keyword(s):

Local Time ◽

Zonal Wind ◽

Meridional Wind ◽

Local Times ◽

Maximum Speed ◽

Wind Speeds ◽

Early Evening ◽

Meridional Winds ◽

Thermospheric Winds ◽

Wind Surge

Abstract. Measurements of equatorial thermospheric winds, temperatures, and 630 nm relative intensities were obtained using an imaging Fabry–Perot interferometer (FPI), which was recently deployed at Bahir Dar University in Ethiopia (11.6° N, 37.4° E, 3.7° N magnetic). The results obtained in this study cover 6 months (53 nights of useable data) between November 2015 and April 2016. The monthly-averaged values, which include local winter and equinox seasons, show the magnitude of the maximum monthly-averaged zonal wind is typically within the range of 70 to 90 ms−1 and is eastward between 19:00 and 21:00 LT. Compared to prior studies of the equatorial thermospheric wind for this local time period, the magnitude is considerably weaker as compared to the maximum zonal wind speed observed in the Peruvian sector but comparable to Brazilian FPI results. During the early evening, the meridional wind speeds are 30 to 50 ms−1 poleward during the winter months and 10 to 25 ms−1 equatorward in the equinox months. The direction of the poleward wind during the winter months is believed to be mainly caused by the existence of the interhemispheric wind flow from the summer to winter hemispheres. An equatorial wind surge is observed later in the evening and is shifted to later local times during the winter months and to earlier local times during the equinox months. Significant night-to-night variations are also observed in the maximum speed of both zonal and meridional winds. The temperature observations show the midnight temperature maximum (MTM) to be generally present between 00:30 and 02:00 LT. The amplitude of the MTM was ∼  110 K in January 2016 with values smaller than this in the other months. The local time difference between the appearance of the MTM and a pre-midnight equatorial wind was generally 60 to 180 min. A meridional wind reversal was also observed after the appearance of the MTM (after 02:00 LT). Climatological models, HWM14 and MSIS-00, were compared to the observations and the HWM14 model generally predicted the zonal wind observations well with the exception of higher model values by 25 ms−1 in the winter months. The HWM14 model meridional wind showed generally good agreement with the observations. Finally, the MSIS-00 model overestimated the temperature by 50 to 75 K during the early evening hours of local winter months. Otherwise, the agreement was generally good, although, in line with prior studies, the model failed to reproduce the MTM peak for any of the 6 months compared with the FPI data.

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On the seasonal variations of the threshold height for the occurrence of equatorial spread F during solar minimum and maximum years

Annales Geophysicae ◽

10.5194/angeo-25-855-2007 ◽

2007 ◽

Vol 25 (4) ◽

pp. 855-861 ◽

Cited By ~ 25

Author(s):

G. Manju ◽

C. V. Devasia ◽

R. Sridharan

Keyword(s):

Solar Minimum ◽

Solar Maximum ◽

Decisive Role ◽

Meridional Wind ◽

Equatorial Spread F ◽

Clear Cut ◽

Meridional Winds ◽

Different Seasons ◽

Spread F ◽

Bottom Side

Abstract. A study has been carried out on the occurrence of bottom side equatorial spread F (ESF) and its dependence on the polarity and magnitude of the thermospheric meridional wind just prior to ESF occurrence during summer, winter and equinox seasons of solar maximum (2002) and minimum years (1995), using ionosonde data of Trivandrum (8.5° N, 76.5° E, dip=0.5° N) and SHAR (13.7° N, 80.2° E, dip ~5.5° N) in the Indian longitude sector. In this study, we have examined the changes in the threshold height of the base of the F layer for the triggering of ESF, irrespective of the magnitude and polarity of the meridional winds during the above periods. The study indicates that the threshold height above which ESF triggering is entirely controlled only by the collisional R-T instability is least for summer months, with higher values for winter and equinox, during the solar minimum period, whereas for the solar maximum period the threshold height is least for winter, with higher values for summer and equinox. But the range over which the threshold height varies is very narrow (<15 km) for solar minimum in relation to the large range of variation (>50 km) in the solar maximum epoch. Further to this, the study also reveals a clear-cut increase in threshold height with solar activity for all seasons. Clear-cut seasonal variability is also observed in the threshold height, especially for solar maximum. The study quantifies the level of the base of the F layer below which neutral dynamical effects play a decisive role in the triggering of ESF during different seasons and solar epochs.

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Intra-seasonal Oscillations (ISO) of zonal-mean meridional winds and temperatures as measured by UARS

Annales Geophysicae ◽

10.5194/angeo-23-1131-2005 ◽

2005 ◽

Vol 23 (4) ◽

pp. 1131-1137 ◽

Cited By ~ 7

Author(s):

F. T. Huang ◽

H. G. Mayr ◽

C. A. Reber

Keyword(s):

Meridional Wind ◽

Mean Flow ◽

Independent Evidence ◽

Doppler Imager ◽

Temperature Oscillations ◽

Low Latitudes ◽

Meridional Winds ◽

Flow Interactions ◽

Phase Variations ◽

Seasonal Oscillations

Abstract. Based on an empirical analysis of measurements with the High Resolution Doppler Imager (HRDI) on the UARS spacecraft in the upper mesosphere (95km), persistent and regular intra-seasonal oscillations (ISO) with periods of about 2 to 4 months have recently been reported in the zonal-mean meridional winds. Similar oscillations have also been discussed independently in a modeling study, and they were attributed to wave-mean-flow interactions. The observed and modeled meridional wind ISOs were largely confined to low latitudes. We report here on an analysis of concurrent UARS temperature measurements, which produces oscillations similar to those seen in the meridional winds. Although the temperature oscillations are observed at lower altitudes (55km), their phase variations with latitude are qualitatively consistent with the inferred properties seen in the meridional winds and thus provide independent evidence for the existence of ISOs in the mesosphere.

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Numerical modeling of the disappearance of equatorial plasma bubble by nighttime medium-scale traveling ionospheric disturbances

10.21203/rs.3.rs-102487/v2 ◽

2021 ◽

Author(s):

Min-Yang Chou ◽

Charles C. H. Lin ◽

Joseph D. Huba

Keyword(s):

Electric Fields ◽

Induce Polarization ◽

Underlying Mechanism ◽

Naval Research ◽

Ionospheric Disturbances ◽

Plasma Bubble ◽

Medium Scale ◽

Traveling Ionospheric Disturbances ◽

Ionosphere Model ◽

Meridional Winds

Abstract The Naval Research Laboratory first-principles ionosphere model SAMI3/ESF is performed to study the interaction between the nighttime medium-scale traveling ionospheric disturbances (MSTIDs) and equatorial plasma bubbles (EPBs). The synthetic dynamo currents are imposed into the potential equation to induce polarization electric fields for generating the MSTIDs. Simulations demonstrate that the MSTIDs can inhibit the upward growth of EPBs; however, MSTIDs alone are insufficient to explain the disappearance of EPBs. We found that the meridional winds likely contribute to the disappearance of MSTIDs by reducing the background electron density and polarization electric fields within the EPBs. Then, the MSTIDs transport plasma to fill the EPB depletions up via E × B drifts. Both MSTIDs and meridional winds are necessary to comprehend the underlying mechanism of EPB disappearance. We also found that the zonal and vertical E × B drifts within the MSTIDs affect the morphology of EPBs, leading to a reverse-C shape structure.

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Quasi 10-day wave modulation of equatorial ionization anomaly during the Southern Hemisphere stratospheric warming of 2002

10.5194/angeo-2019-43 ◽

2019 ◽

Author(s):

Xiaohua Mo

Keyword(s):

Southern Hemisphere ◽

Phase Relationship ◽

Periodic Oscillation ◽

Electron Content ◽

Stratospheric Warming ◽

International Gnss Service ◽

Total Electron ◽

Stratospheric Temperature ◽

Equatorial Ionization Anomaly ◽

Gps Station

Abstract. The present paper studies the perturbations in equatorial ionization anomaly (EIA) region during the Southern Hemisphere (SH) sudden stratospheric warming (SSW) of 2002, using the location of EIA crests derived from Global Positioning System (GPS) station observations and the Total Electron Content (TEC) obtained by International GNSS Service (IGS) global ionospheric TEC map (GIMs) in Asian sector. A strong quasi 10-day periodic oscillation is clearly identified in EIA region, and it has in-phase relationship between northern and southern EIA crests. An eastward phase progression of quasi 10-day wave is also seen in polar stratospheric temperature during this period, suggesting the enhanced quasi-10-day planetary wave associated with SSW produced oscillation in EIA region through modulating the equatorial fountain effect. Our results reveal some newer features of ionospheric variation that have not been reported during Northern Hemisphere (SH) SSWs.

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