Auroral origin of medium scale gravity waves in neutral composition and temperature

1979 ◽  
Vol 84 (A5) ◽  
pp. 1891 ◽  
Author(s):  
S. Chandra ◽  
D. Krankowsky ◽  
P. Lämmerzahl ◽  
N. W. Spencer
Keyword(s):  
Gravity Waves ◽  
Medium Scale

scholarly journals Climatology of Medium-Scale Traveling Ionospheric Disturbances (MSTIDs) Observed with GPS Networks in the North African Region

2020 ◽  
Author(s):  
Temitope Seun Oluwadare ◽  
Norbert Jakowski ◽  
Cesar E. Valladares ◽  
Andrew Oke-Ovie Akala ◽  
Oladipo E. Abe ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Occurrence Rate ◽  
Ionospheric Disturbances ◽  
North African ◽  
African Region ◽  
Atmospheric Gravity Waves ◽  
Medium Scale ◽  
Traveling Ionospheric Disturbances ◽  
The North ◽  
Atmospheric Gravity

Abstract We present for the first time the climatology of medium-scale traveling ionospheric disturbances (MSTIDs) by using Global Positioning System (GPS) receiver networks on geomagnetically quiet days (Kp ≤ 3) over the North African region during 2008-2016. The MSTIDs appear frequently as oscillating waves or wave-like structures in electron density induced by the passage of Atmospheric Gravity Waves (AGW) propagating through the neutral atmosphere and consequently, causing fluctuation in the ionospheric Total Electron Content (TEC). The TEC perturbations (dTEC) data are derived from dual frequency GPS-measurements. We have statistically analyzed the MSTIDs characteristics, occurrence rate, seasonal behavior as well as the interannual dependence. The results show a local and seasonal dependence of nighttime and daytime MSTIDs. The propagation direction is predominantly towards the South (equatorward), MSTIDs event period is (12 ≤ period ≤ 53 mins), and dominant amplitude (0.08 ≤ amp ≤ ~1.5 TECU), with a propagation velocity higher at daytime than nighttime. The amplitudes of the MSTIDs increase with solar activity. The local MSTIDs Spatio-temporal heat reveals variability in disturbance occurrence time, but seems to be dominant within the hours of (Northwest: 1200–1600 LT) and (Northeast: 1000–1400 LT) in December solstice during daytime, and around (NW: 2100–0200 LT) and (NE: 1900–0200 LT) in June solstice, but get extended to March equinox during solar maximum (2014) during the nighttime. The time series of MSTIDs regional distribution map is also generated. Atmospheric gravity waves (AGW) seems to be responsible for the daytime MSTIDs occurrence.

Forward ray-tracing for medium-scale gravity waves observed during the COPEX campaign

2012 ◽  
Vol 90-91 ◽  
pp. 117-123 ◽  
Author(s):  
I. Paulino ◽  
H. Takahashi ◽  
S.L. Vadas ◽  
C.M. Wrasse ◽  
J.H.A. Sobral ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Gravity Waves ◽  
Medium Scale

Anomalous propagation of medium scale GWs along neutral winds

2021 ◽  
Author(s):  
Jan Rusz ◽  
Jaroslav Chum ◽  
Jiří Baše
Keyword(s):  
Gravity Waves ◽  
Rest Frame ◽  
Neutral Wind ◽  
Wind Model ◽  
The Czech Republic ◽  
Neutral Winds ◽  
Medium Scale ◽  
Remote Observation ◽  
Anomalous Propagation ◽  
Predominant Direction

<p>Azimuth of medium scale gravity waves (GWs) propagation in the thermosphere/ionosphere fundamentally depends on the daytime and day of year. Previous studies show that the GWs mostly propagate against the predominant direction of neutral winds in the ionosphere. However, several cases of propagation along the wind direction have also been identified, specifically around the equinoxes. The analysis is based on remote observation of the ionosphere using multi–frequency and multipoint continuous Doppler sounding. The network consists of at least three spatially separated sounding paths (transmitter-receiver pairs) at three frequencies, situated in the western part of the Czech Republic. The apparent horizontal velocity and azimuth of GWs are derived from the time shifts observed for different measuring paths. The HWM14 neutral wind model is used for comparison of neutral winds with the observed phase speeds of GWs. Cases of anomalous propagation of GWs along the direction of neutral winds are analyzed. It is shown that the observed GW periods can be substantially shorter than the intrinsic periods in the wind-rest frame owing to Doppler shift.</p>

scholarly journals Gravity Wave Investigations over Comandante Ferraz Antarctic Station in 2017: General Characteristics, Wind Filtering and Case Study

Atmosphere ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 880
Author(s):  
Gabriel Augusto Giongo ◽  
José Valentin Bageston ◽  
Cosme Alexandre Oliveira Barros Figueiredo ◽  
Cristiano Max Wrasse ◽  
Hosik Kam ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Phase Speed ◽  
Propagation Direction ◽  
Small Scale ◽  
Wave Source ◽  
Medium Scale ◽  
Reliable Source ◽  
The Fourier Transform

This work presents the characteristics of gravity waves observed over Comandante Ferraz Antarctic Station (EACF: 62.1° S, 58.4° W). A total of 122 gravity waves were observed in 34 nights from March to October 2017, and their parameters were obtained by using the Fourier Transform spectral analysis. The majority of the observed waves presented horizontal wavelength ranging from 15 to 35 km, period from 5 to 20 min, and horizontal phase speed from 10 to 70 ± 2 m·s−1. The propagation direction showed an anisotropic condition, with the slower wave propagating mainly to the west, northwest and southeast directions, while the faster waves propagate to the east, southeast and south. Blocking diagrams for the period of April–July showed a good agreement between the wave propagation direction and the blocking positions, which are eastward oriented while the waves propagate mainly westward. A case study to investigate wave sources was conducted for the night of 20–21 July, wherein eight small-scale and one medium-scale gravity waves were identified. Reverse ray tracing model was used to investigate the gravity wave source, and the results showed that six among eight small-scale gravity waves were generated in the mesosphere. On the other hand, only two small-scale waves and the medium-scale gravity wave had likely tropospheric or stratospheric origin, however, they could not be associated with any reliable source.

scholarly journals GPS observations of medium-scale traveling ionospheric disturbances over Europe

2013 ◽  
Vol 31 (2) ◽  
pp. 163-172 ◽  
Author(s):  
Y. Otsuka ◽  
K. Suzuki ◽  
S. Nakagawa ◽  
M. Nishioka ◽  
K. Shiokawa ◽  
...  
Keyword(s):  
Electric Field ◽  
Gravity Waves ◽  
Occurrence Rate ◽  
Electron Content ◽  
Ionospheric Disturbances ◽  
Total Electron ◽  
Medium Scale ◽  
Traveling Ionospheric Disturbances ◽  
Oscillating Electric Field ◽  
Dip Angle

Abstract. Two-dimensional structures of medium-scale traveling ionospheric disturbances (MSTIDs) over Europe have been revealed, for the first time, by using maps of the total electron content (TEC) obtained from more than 800 GPS receivers of the European GPS receiver networks. From statistical analysis of the TEC maps obtained 2008, we have found that the observed MSTIDs can be categorized into two groups: daytime MSTID and nighttime MSTID. The daytime MSTID frequently occurs in winter. Its maximum occurrence rate in monthly and hourly bin exceeds 70% at lower latitudes over Europe, whereas it is approximately 45% at higher latitudes. Since most of the daytime MSTIDs propagate southward, we speculate that they could be caused by atmospheric gravity waves in the thermosphere. The nighttime MSTIDs also frequently occur in winter but most of them propagate southwestward, in a direction consistent with the theory that polarization electric fields play an important role in generating the nighttime MSTIDs. The nighttime MSTID occurrence rate shows distinct latitudinal difference: The maximum of the occurrence rate in monthly and hourly bin is approximately 50% at lower latitudes in Europe, whereas the nighttime MSTID was rarely observed at higher latitudes. We have performed model calculations of the plasma density perturbations caused by a gravity wave and an oscillating electric field to reproduce the daytime and nighttime MSTIDs, respectively. We find that TEC perturbations caused by gravity waves do not show dip angle dependencies, while those caused by the oscillating electric field have a larger amplitude at lower latitudes. These dip angle dependencies of the TEC perturbation amplitude could contribute to the latitudinal variation of the MSTID occurrence rate. Comparing with previous studies, we discuss the longitudinal difference of the nighttime MSTID occurrence rate, along with the E- and F-region coupling processes. The seasonal variation, of the nighttime MSTID occurrence rate in Europe, is not consistent with the theory that the longitudinal and seasonal variations of the nighttime MSTID occurrence could be attributed to those of the Es layer occurrence.

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