scholarly journals Effects of atmospheric oscillations on the field-aligned ion motions in the polar F-region

2000 ◽  
Vol 18 (9) ◽  
pp. 1154-1163 ◽  
Author(s):  
S. Oyama ◽  
S. Nozawa ◽  
S. C. Buchert ◽  
M. Ishii ◽  
S. Watari ◽  
...  
Keyword(s):  
Momentum Transfer ◽  
Wind Velocity ◽  
Emission Rate ◽  
Weighting Function ◽  
Radar Data ◽  
Neutral Wind ◽  
Emission Layer ◽  
F Region ◽  
Wind Velocities ◽  
Eiscat Radar

Abstract. The field-aligned neutral oscillations in the F-region (altitudes between 165 and 275 km) were compared using data obtained simultaneously with two independent instruments: the European Incoherent Scatter (EISCAT) UHF radar and a scanning Fabry-Perot interferometer (FPI). During the night of February 8, 1997, simultaneous observations with these instruments were conducted at Tromsø, Norway. Theoretically, the field-aligned neutral wind velocity can be obtained from the field-aligned ion velocity and by diffusion and ambipolar diffusion velocities. We thus derived field-aligned neutral wind velocities from the plasma velocities in EISCAT radar data. They were compared with those observed with the FPI (λ=630.0 nm), which are assumed to be weighted height averages of the actual neutral wind. The weighting function is the normalized height dependent emission rate. We used two model weighting functions to derive the neutral wind from EISCAT data. One was that the neutral wind velocity observed with the FPI is velocity integrated over the entire emission layer and multiplied by the theoretical normalized emission rate. The other was that the neutral wind velocity observed with the FPI corresponds to the velocity only around an altitude where the emission rate has a peak. Differences between the two methods were identified, but not completely clarified. However, the neutral wind velocities from both instruments had peak-to-peak correspondences at oscillation periods of about 10–40 min, shorter than that for the momentum transfer from ions to neutrals, but longer than from neutrals to ions. The synchronizing motions in the neutral wind velocities suggest that the momentum transfer from neutrals to ions was thought to be dominant for the observed field-aligned oscillations rather than the transfer from ions to neutrals. It is concluded that during the observation, the plasma oscillations observed with the EISCAT radar at different altitudes in the F-region are thought to be due to the motion of neutrals.Key words: Ionosphere (Ionosphere–atmosphere interactions) – Meteorology and atmospheric dynamics (thermospheric dynamics; waves and tides)

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 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 Method for Determining Neutral Wind Velocity Vectors Using Measurements of Internal Gravity Wave Group and Phase Velocities

Atmosphere ◽  
2019 ◽  
Vol 10 (9) ◽  
pp. 546 ◽  
Author(s):  
Andrey V. Medvedev ◽  
Konstantin G. Ratovsky ◽  
Maxim V. Tolstikov ◽  
Roman V. Vasilyev ◽  
Maxim F. Artamonov
Keyword(s):  
Group Velocity ◽  
Wind Velocity ◽  
Wave Vector ◽  
Velocity Vector ◽  
Internal Gravity Waves ◽  
Vertical Wind ◽  
New Method ◽  
Neutral Wind ◽  
Wind Velocities ◽  
Wind Measurements

This study presents a new method for determining a neutral wind velocity vector. The basis of the method is measurement of the group velocities of internal gravity waves. Using the case of the Boussinesq dispersion relation, we demonstrated the ability to measure a neutral wind velocity vector using the group velocity and wave vector data. An algorithm for obtaining the group velocity vector from the wave vector spectrum is proposed. The new method was tested by comparing the obtained winter wind pattern with wind data from other sources. Testing the new method showed that it is in quantitative agreement with the Fabry–Pérot interferometer wind measurements for zonal and vertical wind velocities. The differences in meridional wind velocities are also discussed here. Of particular interest were the results related to the measurement of vertical wind velocities. We demonstrated that two independent methods gave the presence of vertical wind velocities with amplitude of ~20 m/s. Estimation of vertical wind contribution to plasma drift velocity indicated the importance of vertical wind measurements and the need to take them into account in physical and empirical models of the ionosphere and thermosphere.

scholarly journals Lower-thermospheric wind fluctuations measured with an FPI during pulsating aurora at Tromsø, Norway

2010 ◽  
Vol 28 (10) ◽  
pp. 1847-1857 ◽  
Author(s):  
S. Oyama ◽  
K. Shiokawa ◽  
J. Kurihara ◽  
T. T. Tsuda ◽  
S. Nozawa ◽  
...  
Keyword(s):  
Wind Velocity ◽  
Frictional Heating ◽  
Lower Thermosphere ◽  
Thermospheric Wind ◽  
F Region ◽  
Time Period ◽  
Fabry Perot ◽  
Eiscat Radar ◽  
Energy Dissipated ◽  
Uhf Radar

Abstract. Simultaneous observations were conducted with a Fabry-Perot Interferometer (FPI) at a wavelength of 557.7 nm, an all-sky camera at a wavelength of 557.7 nm, and the European Incoherent Scatter (EISCAT) UHF radar during the Dynamics and Energetics of the Lower Thermosphere in Aurora 2 (DELTA-2) campaign in January 2009. This paper concentrated on two events during periods of pulsating aurora. The lower-thermospheric wind velocity measured with the FPI showed obvious fluctuations in both vertical and horizontal components. Of particular interest is that the location of the fluctuations was found in a darker area that appeared within the pulsating aurora. During the same time period, the EISCAT radar observed sporadic enhancements in the F-region backscatter echo power, which suggests the presence of low-energy electron (1 keV or lower) precipitation coinciding with increase in amplitude of the electromagnetic wave (at the order of 10 Hz or higher). While we have not yet identified the dominant mechanism causing the fluctuations in FPI-derived wind velocity during the pulsating aurora, the frictional heating energy dissipated by the electric-field perturbations may be responsible for the increase in ionospheric thermal energy thus modifying the local wind dynamics in the lower thermosphere.

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

2018 ◽  
Author(s):  
Chih-Yu Chiang ◽  
Sunny Wing-Yee Tam ◽  
Tzu-Fang Chang
Keyword(s):  
Emission Rate ◽  
Local Maximum ◽  
Optical Observations ◽  
Neutral Wind ◽  
Emission Rates ◽  
Emission Layer ◽  
Neutral Winds ◽  
Neutral Temperature ◽  
Different Temperatures ◽  
Volume Emission

Abstract. Enhancements in 630.0 nm airglow around midnight at equatorial latitudes were observed by many optical observations. Such features had been suggested as the signature of 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. 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 Meridional thermospheric neutral wind at high latitude over a full solar cycle

1998 ◽  
Vol 16 (10) ◽  
pp. 1400-1409 ◽  
Author(s):  
O. Witasse ◽  
J. Lilensten ◽  
C. Lathuillere ◽  
B. Pibaret
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Universal Time ◽  
Neutral Wind ◽  
High Latitudes ◽  
Auroral Ionosphere ◽  
Neutral Winds ◽  
F Region ◽  
Eiscat Radar ◽  
Thermospheric Dynamics

Abstract. EISCAT radar experiments over a full solar cycle between January 1984 and March 1995 have been used to construct meridional neutral wind patterns in the ionospheric F region. For locally geomagnetically quiet periods the neutral winds have been binned according to season, solar activity, and universal time. The diurnal and seasonal behaviors and the effect of the solar flux are described. An empirical model of the meridional neutral wind for the high latitudes at eight altitudes in the ionospheric F region over a full solar cycle is presented. Results are compared with other recent empirical models.Key words. Auroral ionosphere · Thermospheric dynamics · EISCAT

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 Parametric design analysis of elliptical shroud profile

AIMS Energy ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 1147-1169
Author(s):  
Salih Nawaf Akour ◽  
◽  
Mahmoud Azmi Abo Mhaisen
Keyword(s):  
Wind Turbine ◽  
Wind Velocity ◽  
Parametric Design ◽  
Large Family ◽  
Design Analysis ◽  
Average Wind ◽  
Wind Velocities ◽  
Inlet Length ◽  
Commercial Software Package ◽  
Exact Shape

<abstract> <p>Parametric design analysis for Eccentric Rotated Ellipsoid (ERE) shroud profile is conducted whereas the design model is validated experimentally. A relation between shroud inlet, length and exit diameter is established, different ratios related to the wind turbine diameter are introduced, and solution for different ERE family curves that passes on the inlet, throat, and exit points is studied. The performance of the ERE shroud is studied under different wind velocities ranging from 5–10 m/s.</p> <p>The method used in creating the shroud profile is by solving the ERE curve equations to generate large family of solutions. The system is modeled as axisymmetric system utilizing commercial software package. The effect of the parameters; shroud length, exit diameter, inlet diameter, turbine position with respect to the shroud throat, and wind velocity are studied. An optimum case for each shroud length, exit diameter and location of the shroud with respect to the wind turbine throat axis are achieved.</p> <p>The simulation results show an increase in the average wind velocity by 1.63 times of the inlet velocity. This leads to a great improvement in the wind turbine output power by 4.3 times of bare turbine. One of the achieved optimum solutions for the shroud curves has been prototyped for experimental validation. The prototype has been manufactured using 3D printing technology which provides high accuracy in building the exact shape of shroud design curve. The results show very good agreement with the experimental results.</p></abstract>

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