Peculiar transient phenomena observed by HF Doppler sounding on infrasound time scales

Chum, Jaroslav; Laštovička, Jan; Šindelářová, Tereza; Burešová, Dalia; Hruška, František

doi:10.1016/j.jastp.2007.06.013

Cited by 5 publications

(5 citation statements)

References 15 publications

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“…This is displayed in Figure 7, which shows a scatterplot of the analyzed events as a function of day of year and daytime. It is obvious that S‐shaped traces were mainly observed close to or after sunrise and close to or before sunset, which is consistent with the previous study [ Chum et al , 2008]. Thus, our approach based on the analysis of time differences between observation of S‐shaped traces on different sounding paths in the Doppler shift spectrograms does not make it possible to investigate propagation of GWs at arbitrary times.…”

Section: Resultssupporting

confidence: 84%

“…We have used a Doppler system developed at the Institute of Atmospheric Physics, Czech Republic. A short technical description of its first version was given by Burešová et al [2007] and Chum et al [2008]. The Doppler system has been operated at ∼3.59 MHz; thus, a Doppler shift of 1 Hz corresponds to the velocity of 41.7 m/s, assuming an approximation for simplicity.…”

Section: Measurement Setupmentioning

confidence: 99%

“…These S‐shaped traces (signatures) are believed to be formed by multipath reflection from a level of constant electron density, which has a concave shape and moves horizontally or nearly horizontally [ Davis and Baker , 1966] across a sounding region. The concave‐shaped disturbance can be caused by a GW [ Chum et al , 2008]. Provided that the curvature radius of the disturbance is less than the height of disturbance above the ground, the signals are received simultaneously along three separate paths [see Davis and Baker , 1966, Figure 5].…”

Section: Analysis Of Propagation Velocitiesmentioning

confidence: 99%

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Horizontal velocities and propagation directions of gravity waves in the ionosphere over the Czech Republic

et al. 2010

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[1] Using a five-point continuous Doppler sounding system operating at 3.59 MHz, developed at the Institute of Atmospheric Physics AS CR (IAP), we investigate propagation directions and velocities of gravity waves (GWs) at altitudes from ∼150 to ∼250 km over the western part of the Czech Republic. The velocities and directions are computed from the time delays between the observations of corresponding GWs at different reflection points that correspond to various sounding paths. We focused on the GWs that produce an S-shaped trace in Doppler shift spectrograms and are observed close to sunrise and sunset. We have selected about 100 of such events. Our results show that the analyzed GWs propagate with typical horizontal velocities from ∼100 to ∼200 m/s. The north-south component of GW velocities depends on the season, it is directed northward in the summer and southward in the winter. At the same time, the north-south component of the neutral winds calculated by the horizontal wind model HWM07 has the opposite sign. Typical observed periods of the analyzed waves range from ∼10 to ∼30 min.

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Section: Resultssupporting

confidence: 84%

Section: Measurement Setupmentioning

confidence: 99%

Section: Analysis Of Propagation Velocitiesmentioning

confidence: 99%

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Horizontal velocities and propagation directions of gravity waves in the ionosphere over the Czech Republic

et al. 2010

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“…However, all these effects were observed also on quiet days. The occurrence and origin of S-shapes in the Doppler record were discussed by Chum et al (2008). Spread and smeared signal occurred particularly in time intervals when an Es layer was present.…”

Section: Resultsmentioning

confidence: 99%

Observations of acoustic-gravity waves in the ionosphere generated by severe tropospheric weather

2009

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Atmospheric waves influence the dynamics and energetic budget of the upper atmosphere. Using the continuous HF Doppler sounder, we study the wave activity in the ionosphere during tropospheric convective storms in western and central part of the Czech Republic. The study is focused on acoustic-gravity waves in the period range 230 minutes. We discuss possible methods of distinguishing the waves emitted by meteorological sources from waves of different origin, particularly waves of geomagnetic origin. In two cases out of twenty-five analysed, we found waves in the infrasonic period range which might be generated by exceptionally intense meteorological activity in the troposphere. The results differ considerably from those previously obtained in North America. In the central part of the United States, infrasonic waves were frequently observed during convective storms. As a possible reason, we discuss different intensity and dynamics of weather systems in both regions.K e y w o r d s : acoustic-gravity waves; ionosphere; convective storms

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“…Observations of high‐frequency TIDs were made sometimes during short campaigns with rapid‐running ionosondes [e.g., Turunen and Nygrén , ; Morgan , ]. However, most of the studies were devoted to the frequency range of GWs, whereas the infrasound (acoustic waves, AWs) did not deserve noticeable attention [ Chum et al ., ], especially in the period band of 5–10 min.…”

Section: Introductionmentioning

confidence: 99%

Rapid‐run ionosonde observations of traveling ionospheric disturbances in the auroral ionosphere

2013

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[1] Since 2007, the Sodankylä Geophysical Observatory routinely performs vertical ionosphere soundings once per minute, using a frequency-modulated continuous-wave chirp at the rate of 500 kHz/s from 500 kHz to 16 MHz. We used these data to study traveling ionospheric disturbances (TIDs) during 10-16 local time. The observations were made between April 2007 and June 2012, mostly during low solar activity. The TIDs were studied in five bands of periods corresponding to the following: infrasonic (acoustic) waves and the buoyancy cutoff (periods from 5 to 10 min); small-scale gravity waves (GWs; 10-15 min); medium-scale (MS; 15-30 min) GWs; medium-large scale (MS-LS; 30-60 min) GWs; and large-scale (LS; 60-120 min) GWs. Relative contribution (with respect to LS TIDs) of the short-period (5-15 min) and MS (15-30 min) TIDs shows minima in winter and maxima in summer. These annual variations anticorrelate with variations of true height, namely, the largest relative amplitudes occur in summer, when TIDs were observed at minimal heights. We suggest that the summer increase of shorter-period TIDs is due to lowering reflection to the height where the Brunt-Väisälä period is smaller and, hence, shorter-period gravity waves exist. The summer maxima were most prominent during the 3 years of minimal solar activity (2008)(2009)(2010). In 2011, when solar activity increased, the annual variation seems less prominent. Annual variations of the longer-period (30-120 min) TIDs are essentially less significant. For all TIDs, no obvious dependences on the AE and Ap indices of magnetic activity were found.Citation: Kozlovsky, A., T. Turunen, and T. Ulich (2013), Rapid-run ionosonde observations of traveling ionospheric disturbances in the auroral ionosphere,

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Peculiar transient phenomena observed by HF Doppler sounding on infrasound time scales

Cited by 5 publications

References 15 publications

Horizontal velocities and propagation directions of gravity waves in the ionosphere over the Czech Republic

Horizontal velocities and propagation directions of gravity waves in the ionosphere over the Czech Republic

Observations of acoustic-gravity waves in the ionosphere generated by severe tropospheric weather

Rapid‐run ionosonde observations of traveling ionospheric disturbances in the auroral ionosphere

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