scholarly journals Characterizing Unexpectedly Localized Slowing of the Thermospheric Cross‐Polar Jet of Neutral Wind Over Alaska in the Midnight Sector

2021 ◽  
Vol 126 (10) ◽  
Author(s):  
R. Itani ◽  
M. Conde
Keyword(s):  
Neutral Wind

scholarly journals On the fast movements of the thermosphere: an interpretation

2000 ◽  
Vol 18 (12) ◽  
pp. 1651-1656
Author(s):  
J. Lilensten ◽  
P. O. Amblard
Keyword(s):  
Rotation Velocity ◽  
Atmospheric Composition ◽  
Neutral Wind ◽  
Typical Size ◽  
F Region ◽  
Optical Experiment ◽  
Atmospheric Composition And Structure ◽  
Composition And Structure ◽  
Eiscat Radar

Abstract. We examine the oscillations of the meridional neutral wind in the F region as seen by the EISCAT radar. We propose an interpretation in term of eddies (tourbillons) of typical size of a few tens to a few hundreds of kilometers. The observed rotation velocity is a few hundreds of meters per second. We suggest that the tourbillons are a common feature of thermospheric movements. We propose an optical experiment to check the validity of this assumption.Key words: Atmospheric composition and structure (thermosphere · composition and chemistry) · Ionosphere (ionosphere · atmosphere interactions)

scholarly journals Extremely low equatorial ionospheric density measured by CHAMP due to strong meridional neutral wind

2021 ◽  
Author(s):  
Yaoyu Tian ◽  
Yongqiang Hao ◽  
Quanhan Li ◽  
Donghe Zhang ◽  
Zuo Xiao
Keyword(s):  
Neutral Wind

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

2017 ◽  
Vol 35 (4) ◽  
pp. 953-963 ◽  
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.

scholarly journals Variations of the 630.0 nm airglow emission with meridional neutral wind and neutral temperature around midnight

2018 ◽  
Vol 36 (5) ◽  
pp. 1471-1481
Author(s):  
Chih-Yu Chiang ◽  
Sunny Wing-Yee Tam ◽  
Tzu-Fang Chang
Keyword(s):  
Emission Rate ◽  
Local Maximum ◽  
Neutral Wind ◽  
Emission Rates ◽  
Emission Layer ◽  
Neutral Winds ◽  
Neutral Temperature ◽  
Bright Spots ◽  
Different Temperatures ◽  
Volume Emission

Abstract. The ISUAL payload onboard the FORMOSAT-2 satellite has often observed airglow bright spots around midnight at equatorial latitudes. Such features had been suggested as the signature of the thermospheric midnight temperature maximum (MTM) effect, which was associated with temperature and meridional neutral winds. This study investigates the influence of neutral temperature and meridional neutral wind on the volume emission rates of the 630.0 nm nightglow. We utilize the SAMI2 model to simulate the charged and neutral species at the 630.0 nm nightglow emission layer under different temperatures with and without the effect of neutral wind. The results show that the neutral wind is more efficient than temperature variation in affecting the nightglow emission rates. For example, based on our estimation, it would require a temperature change of 145 K to produce a change in the integrated emission rate by 9.8 km-photons cm−3 s−1, while it only needs the neutral wind velocity to change by 1.85 m−1 s−1 to cause the same change in the integrated emission rate. However, the emission rate features a local maximum in its variation with the temperature. Two kinds of tendencies can be seen regarding the temperature that corresponds to the turning point, which is named the turning temperature (Tt) in this study: firstly, Tt decreases with the emission rate for the same altitude; secondly, for approximately the same emission rate, Tt increases with the altitude.

scholarly journals Variations in the altitude of the F2 peak associated with trough-formation processes

1996 ◽  
Vol 14 (6) ◽  
pp. 628-636 ◽  
Author(s):  
R. I. Crickmore ◽  
B. Jenkins ◽  
G. J. Bailey
Keyword(s):  
Wind Velocity ◽  
Electron Concentration ◽  
Neutral Wind ◽  
Formation Processes ◽  
Production Mechanism ◽  
Causal Mechanisms ◽  
F Region ◽  
Novel Approach ◽  
Concentration Peak ◽  
Production Mechanisms

Abstract. A novel approach is described which can help to determine, from ground-based data, which of the possible production mechanisms for the mid-latitude F-region ionospheric trough is dominant during a particular event. This approach involves numerically modelling the possible causal mechanisms of the mid-latitude trough to see how each will affect the altitude of the F2-layer electron-concentration peak (hmF2), and then comparing these predictions with the observed variation of hmF2 during trough formation. The modelling work predicts that, if the neutral-wind velocity does not vary, hmF2 will remain almost constant if the trough is formed via stagnation, but will rise if it is formed as a result of high ion velocities or neutral upwelling. Observations made at Halley (76°S, 27°W, L=4.2), Antarctica, show that most frequently the only changes in hmF2 during trough formation are those expected due to variations in the neutral wind, which suggests that stagnation is the most common production mechanism. During the most geomagnetically active night studied, on which Ap varied between 18 and 32, there was a rise in hmF2 that cannot be explained by changes in the neutral wind. On this night the plasma also decayed faster, and the poleward edge of the trough was seen earlier than on other nights. These differences, together with the fact that the ion velocities remained relatively low, suggest the trough was caused by a change in neutral composition, possibly advected into the observing area.

scholarly journals Solar eclipse induced perturbations at mid-latitude during the 21 August 2017 event

2018 ◽  
Author(s):  
Bolarinwa J. Adekoya ◽  
Babatunde O. Adebesin ◽  
Timothy W. David ◽  
Stephen O. Ikubanni ◽  
Shola J. Adebiyi
Keyword(s):  
Solar Eclipse ◽  
Diffusion Processes ◽  
Data Availability ◽  
Maximum Magnitude ◽  
Neutral Wind ◽  
Iri Model ◽  
Gas Heating ◽  
Maximum Decrease ◽  
And Diffusion ◽  
Unusual Increase

Abstract. A study of the response of some ionospheric parameters and their relationship in predicting one another during the solar eclipse of 21 August 2017 is presented. Mid-latitude stations located along the eclipse path and with data availability on the GIRO database were selected. The percentage obscuration at these stations ranges between 63–100 %. The decrease in electron density during the eclipse is attributed to reduction in solar radiation and natural gas heating. The maximum magnitude of the eclipse coincided with hmF2 increase and with a lagged maximum decrease in NmF2 consistently at the stations investigated. The results revealed that the horizontal neutral wind flow is as a consequence of the changes in the thermospheric and diffusion processes. The unusual increase/decrease in the shape/thickness parameters during the eclipse period relative to the control days points to the perturbation caused by the solar eclipse. Need for IRI model to capture eclipse caused perturbation

scholarly journals Numerical Modeling of the Influence of Solar Activity on the Global Circulation in the Earth’s Mesosphere and Lower Thermosphere

2012 ◽  
Vol 2012 ◽  
pp. 1-15 ◽  
Author(s):  
Igor Mingalev ◽  
Victor Mingalev
Keyword(s):  
Solar Activity ◽  
Large Scale ◽  
Input Parameter ◽  
Lower Thermosphere ◽  
Vertical Component ◽  
Neutral Wind ◽  
Wind System ◽  
Model Calculations ◽  
Global Circulation ◽  
Mesosphere And Lower Thermosphere

The nonhydrostatic model of the global neutral wind system of the earth’s atmosphere, developed earlier in the Polar Geophysical Institute, is utilized to investigate how solar activity affects the formation of the large-scale global circulation of the mesosphere and lower thermosphere. The peculiarity of the utilized model consists in that the internal energy equation for the neutral gas is not solved in the model calculations. Instead, the global temperature field is assumed to be a given distribution, that is, the input parameter of the model. Moreover, in the model calculations, not only the horizontal components but also the vertical component of the neutral wind velocity is obtained by means of a numerical solution of a generalized Navier-Stokes equation for compressible gas, so the hydrostatic equation is not applied. The simulation results indicate that solar activity ought to influence considerably on the formation of global neutral wind system in the mesosphere and lower thermosphere. The influence is conditioned by the vertical transport of air from the lower thermosphere to the mesosphere and stratosphere. This transport may be rather different under distinct solar activity conditions.

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