scholarly journals Small scale density variations of electrons and charged particles in the vicinity of polar mesosphere summer echoes

2003 ◽  
Vol 3 (4) ◽  
pp. 3469-3491
Author(s):  
M. Rapp ◽  
F.-J. Lübken ◽  
T. A. Blix
Keyword(s):  
Charged Particles ◽  
Power Spectra ◽  
Radar Signal ◽  
Small Scale ◽  
Electron Number ◽  
Vhf Radar ◽  
Air Turbulence ◽  
Half Wavelength ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes

Abstract. We present small scale variations of electron number densities and particle charge number densities measured in situ in the presence of polar mesosphere summer echoes. It turns out that the small scale fluctuations of electrons and negatively charged particles show a strong anticorrelation down to the smallest scales observed. Comparing these small scale structures with the simultaneously measured radar signal to noise profile, we find that the radar profile is well described by the power spectral density of both electrons and charged particles at the radar half wavelength (= the Bragg scale). Finally, we consider the shape of the power spectra of the observed plasma fluctuations and find that both charged particles and electrons show spectra that can be explained in terms of either neutral air turbulence acting on the distribution of a low diffusivity tracer or the fossil remnants of a formerly active turbulent region. All these results are consistent with the theoretical ideas by Rapp and Lübken (2003) suggesting that PMSE can be explained by a combination of active and fossil neutral air turbulence acting on the large and heavy charged aerosol particles which are subsequently mirrored in the electron number density distribution that becomes visible to a VHF radar when small scale fluctuations are present.

scholarly journals Small scale density variations of electrons and charged particles in the vicinity of polar mesosphere summer echoes

2003 ◽  
Vol 3 (5) ◽  
pp. 1399-1407 ◽  
Author(s):  
M. Rapp ◽  
F.-J. Lübken ◽  
T. A. Blix
Keyword(s):  
Charged Particles ◽  
Power Spectra ◽  
Radar Signal ◽  
Small Scale ◽  
Electron Number ◽  
Vhf Radar ◽  
Air Turbulence ◽  
Half Wavelength ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes

Abstract. We present small scale variations of electron number densities and particle charge number densities measured in situ in the presence of polar mesosphere summer echoes. It turns out that the small scale fluctuations of electrons and negatively charged particles show a strong anticorrelation down to the smallest scales observed. Comparing these small scale structures with the simultaneously measured radar signal to noise profile, we find that the radar profile is well described by the power spectral density of both electrons and charged particles at the radar half wavelength (=the Bragg scale). Finally, we consider the shape of the power spectra of the observed plasma fluctuations and find that both charged particles and electrons show spectra that can be explained in terms of either neutral air turbulence acting on the distribution of a low diffusivity tracer or the fossil remnants of a formerly active turbulent region. All these results are consistent with the theoretical ideas by Rapp and Lübken (2003) suggesting that PMSE can be explained by a combination of active and fossil neutral air turbulence acting on the large and heavy charged aerosol particles which are subsequently mirrored in the electron number density distribution that becomes visible to a VHF radar when small scale fluctuations are present.

scholarly journals Polar mesosphere summer echoes (PMSE): Review of observations and current understanding

2004 ◽  
Vol 4 (11/12) ◽  
pp. 2601-2633 ◽  
Author(s):  
M. Rapp ◽  
F.-J. Lübken
Keyword(s):  
Electron Number Density ◽  
Aerosol Particles ◽  
Small Scale ◽  
Number Density ◽  
Electron Number ◽  
Mesopause Region ◽  
Air Turbulence ◽  
Radar Echoes ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes

Abstract. Polar mesosphere summer echoes (PMSE) are very strong radar echoes primarily studied in the VHF wavelength range from altitudes close to the polar summer mesopause. Radar waves are scattered at irregularities in the radar refractive index which at mesopause altitudes is effectively determined by the electron number density. For efficient scatter, the electron number density must reveal structures at the radar half wavelength (Bragg condition for monostatic radars; ~3 m for typical VHF radars). The question how such small scale electron number density structures are created in the mesopause region has been a longstanding open scientific question for almost 30 years. This paper reviews experimental and theoretical milestones on the way to an advanced understanding of PMSE. Based on new experimental results from in situ observations with sounding rockets, ground based observations with radars and lidars, numerical simulations with microphysical models of the life cycle of mesospheric aerosol particles, and theoretical considerations regarding the diffusivity of electrons in the ice loaded complex plasma of the mesopause region, a consistent explanation for the generation of these radar echoes has been developed. The main idea is that mesospheric neutral air turbulence in combination with a significantly reduced electron diffusivity due to the presence of heavy charged ice aerosol particles (radii ~5–50 nm) leads to the creation of structures at spatial scales significantly smaller than the inner scale of the neutral gas turbulent velocity field itself. Importantly, owing to their very low diffusivity, the plasma structures acquire a very long lifetime, i.e., 10 min to hours in the presence of particles with radii between 10 and 50 nm. This leads to a temporal decoupling of active neutral air turbulence and the existence of small scale plasma structures and PMSE and thus readily explains observations proving the absence of neutral air turbulence at PMSE altitudes. With this explanation at hand, it becomes clear that PMSE are a suitable tool to permanently monitor the thermal and dynamical structure of the mesopause region allowing insights into important atmospheric key parameters like neutral temperatures, winds, gravity wave parameters, turbulence, solar cycle effects, and long term changes.

scholarly journals Polar mesosphere summer echoes (PMSE): review of observations and current understanding

2004 ◽  
Vol 4 (4) ◽  
pp. 4777-4876 ◽  
Author(s):  
M. Rapp ◽  
F.-J. Lübken
Keyword(s):  
Electron Number Density ◽  
Aerosol Particles ◽  
Small Scale ◽  
Number Density ◽  
Electron Number ◽  
Mesopause Region ◽  
Air Turbulence ◽  
Radar Echoes ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes

Abstract. Polar mesosphere summer echoes (PMSE) are very strong radar echoes primarily studied in the VHF wavelength range from altitudes close to the polar summer mesopause. Radar waves are scattered at irregularities in the radar refractive index which at mesopause altitudes is solely determined by the electron number density. For efficient scatter, the electron number density must reveal structures at the radar half wavelength (Bragg condition; ~3 m for typical VHF radars). The question how such small scale electron number density structures are created in the mesopause region has been a longstanding open scientific question for almost 30 years. This paper reviews experimental and theoretical milestones on the way to an advanced understanding of PMSE. Based on new experimental results from in situ observations with sounding rockets, ground based observations with radars and lidars, numerical simulations with microphysical models of the life cycle of mesospheric aerosol particles, and theoretical considerations regarding the diffusivity of electrons in the ice loaded complex plasma of the mesopause region, a consistent explanation for the generation of these radar echoes has been developed. The main idea is that mesospheric neutral air turbulence in combination with a significantly reduced electron diffusivity due to the presence of heavy charged ice aerosol particles (radii ~5–50 nm) leads to the creation of structures at spatial scales significantly smaller than the inner scale of the turbulent velocity field itself. Importantly, owing to their very low diffusivity, the plasma structures acquire a very long lifetime, i.e. 10 min to hours in the presence of particles with radii between 10 and 50 nm. This leads to a temporal decoupling of active neutral air turbulence and the existence of small scale plasma structures and PMSE and thus readily explains observations proving the absence of neutral air turbulence at PMSE altitudes. With this explanation at hand, it becomes clear that PMSE are a suitable tool to permanently monitor the thermal and dynamical structure of the mesopause region allowing insights into important atmospheric key parameters like temperatures, winds, gravity wave parameters, turbulence, solar cycle effects, and long term changes.

scholarly journals PMSE observations at three different frequencies in northern Europe during summer 1994

1996 ◽  
Vol 14 (12) ◽  
pp. 1317-1327 ◽  
Author(s):  
J. Bremer ◽  
P. Hoffmann ◽  
A. H. Manson ◽  
C. E. Meek ◽  
R. Rüster ◽  
...  
Keyword(s):  
Wind Field ◽  
Vhf Radar ◽  
Half Wavelength ◽  
Measuring Period ◽  
Spatial Differences ◽  
Strongly Connected ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes ◽  
The Common ◽  
Mf Radar

Abstract. Simultaneous observations of polar mesosphere summer echoes (PMSE) have been carried out during summer 1994 in northern Norway using three radars on different frequencies: the ALOMAR SOUSY radar at Andenes on 53.5 MHz, the EISCAT VHF radar at Tromsø on 224 MHz and the MF radar at Tromsø on 2.78 MHz. During the common measuring period in July/August 1994, PMSE could be detected at 224 and 53.5 MHz, and there are strong hints that PMSE also occur at 2.78 MHz. Reliable correlations between hourly backscattered power values indicate that the PMSE structures have zonal extensions of more than 130 km and can be detected at very different scales (half wavelength) between 0.67 (EISCAT VHF radar) and 54 m (MF radar). Using the wind values derived by the MF radar it can be shown that the mesospheric wind field influences the structure of PMSE. The diurnal variation of PMSE is strongly connected with tidal-wind components, whereas spatial differences of PMSE can partly be explained by the mean wind field.

scholarly journals Studies of polar mesosphere summer echoes by VHF radar and rocket probes

1994 ◽  
Vol 14 (9) ◽  
pp. 139-148 ◽  
Author(s):  
U.-P. Hoppe ◽  
T.A. Blix ◽  
E.V. Thrane ◽  
F.-J. Lübken ◽  
J.Y.N. Cho ◽  
...  
Keyword(s):  
Vhf Radar ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes

scholarly journals High-Range Resolution Spectral Analysis of Precipitation Through Range Imaging of the Chung-Li VHF Radar

2017 ◽  
Author(s):  
Shih-Chiao Tsai ◽  
Jenn-Shyong Chen ◽  
Yen-Hsyang Chu ◽  
Ching-Lun Su ◽  
Jui-Hsiang Chen
Keyword(s):  
Weighting Function ◽  
Power Doppler ◽  
Power Spectra ◽  
Doppler Frequency ◽  
Doppler Velocity ◽  
Small Scale ◽  
Range Imaging ◽  
Very High Frequency ◽  
Vhf Radar ◽  
Range Resolution

Abstract. Multi-frequency range imaging (RIM) has been implemented in the Chung-Li very-high-frequency (VHF) radar, located on the campus of National Central University, Taiwan, since 2008. RIM processes the echo signals with a group of closely spaced transmitting frequencies through appropriate inversion methods to obtain high-resolution distribution of echo power in the range direction. This is beneficial to the investigation of the small scale structure embedded in dynamic atmosphere. Five transmitting frequencies were employed in the radar experiment for observation of the precipitating atmosphere during the period between 21 and 23 Aug, 2013. Using the Capon and Fourier methods, the radar echoes were synthesized to retrieve the temporal signals at a smaller range step than the original range resolution defined by the pulse width, and such retrieved temporal signals were then processed in the Doppler frequency domain to identify the atmosphere and precipitation echoes. An analysis called conditional averaging was further executed for echo power, Doppler velocity, and spectral width to verify the potential capabilities of the retrieval processing in resolving small-scale precipitation and atmosphere structures. Point-by-point correction of range delay combined with compensation of range weighting function effect has been performed during the retrieval of temporal signals to improve the continuity of power spectra at gate boundaries, making the small-scale structures in the power spectra more natural and reasonable. We examined stratiform and convective precipitations and demonstrated their different structured characteristics by means of the Capon-processed results.

scholarly journals Polar mesosphere summer echoes: a comparison of simultaneous observations at three wavelengths

2007 ◽  
Vol 25 (12) ◽  
pp. 2487-2496 ◽  
Author(s):  
E. Belova ◽  
P. Dalin ◽  
S. Kirkwood
Keyword(s):  
Short Interval ◽  
Beam Width ◽  
Turbulent Energy ◽  
Energy Dissipation Rate ◽  
Theory Model ◽  
Turbulence Theory ◽  
Vhf Radar ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes ◽  
Uhf Radar

Abstract. On 5 July 2005, simultaneous observations of Polar Mesosphere Summer Echoes (PMSE) were made using the EISCAT VHF (224 MHz) and UHF (933 MHz) radars located near Tromsø, Norway and the ALWIN VHF radar (53.5 MHz) situated on Andøya, 120 km SW of the EISCAT site. During the short interval from 12:20 UT until 12:26 UT strong echoes at about 84 km altitude were detected with all three radars. The radar volume reflectivities were found to be 4×10−13 m−1, 1.5×10−14 m−1 and 1.5×10−18 m−1 for the ALWIN, EISCAT-VHF and UHF radars, respectively. We have calculated the reflectivity ratios for each pair of radars and have compared them to ratios obtained from the turbulence-theory model proposed by Hill (1978a). We have tested different values of the turbulent energy dissipation rate ε and Schmidt number Sc, which are free parameters in the model, to try to fit theoretical reflectivity ratios to the experimental ones. No single combination of the parameters ε and Sc could be found to give a good fit. Spectral widths for the EISCAT radars were estimated from the spectra computed from the autocorrelation functions obtained in the experiment. After correction for beam-width broadening, the spectral widths are about 4 m/s for the EISCAT-VHF and 1.5–2 m/s for the UHF radar. However, according to the turbulence theory, the spectral widths in m/s should be the same for both radars. We also tested an incoherent scatter (IS) model developed by Cho et al. (1998), which takes into account the presence of charged aerosols/dust at the summer mesopause. It required very different sizes of particles for the EISCAT-VHF and UHF cases, to be able to fit the experimental spectra with model spectra. This implies that the IS model cannot explain PMSE spectra, at least not for monodisperse distributions of particles.

Frequency domain interferometry of polar mesosphere summer echoes with the EISCAT VHF radar: A case study

Radio Science ◽  
1992 ◽  
Vol 27 (3) ◽  
pp. 417-428 ◽  
Author(s):  
S. J. Franke ◽  
J. Röttger ◽  
C. LaHoz ◽  
C. H. Liu
Keyword(s):  
Frequency Domain ◽  
Vhf Radar ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes

scholarly journals Frequency domain interferometry mode observations of PMSE using the EISCAT VHF radar

2000 ◽  
Vol 18 (12) ◽  
pp. 1599-1612 ◽  
Author(s):  
P. B. Chilson ◽  
S. Kirkwood ◽  
I. Häggström
Keyword(s):  
Frequency Domain ◽  
Middle Atmosphere ◽  
Lower Boundary ◽  
Doppler Velocity ◽  
Vhf Radar ◽  
Radio Science ◽  
First Results ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes ◽  
Frequency Coherence

Abstract. During the summer of 1997 investigations into the nature of polar mesosphere summer echoes (PMSE) were conducted using the European incoherent scatter (EISCAT) VHF radar in Norway. The radar was operated in a frequency domain interferometry (FDI) mode over a period of two weeks to study the frequency coherence of the returned radar signals. The operating frequencies of the radar were 224.0 and 224.6 MHz. We present the first results from the experiment by discussing two 4-h intervals of data collected over two consecutive nights. During the first of the two days an enhancement of the FDI coherence, which indicates the presence of distinct scattering layers, was found to follow the lower boundary of the PMSE. Indeed, it is not unusual to observe that the coherence values are peaked around the heights corresponding to both the lower- and upper-most boundaries of the PMSE layer and sublayers. A Kelvin-Helmholtz mechanism is offered as one possible explanation for the layering structure. Additionally, our analysis using range-time-pseudocolor plots of signal-to-noise ratios, spectrograms of Doppler velocity, and estimates of the positions of individual scattering layers is shown to be consistent with the proposition that upwardly propagating gravity waves can become steepened near the mesopause.Key words: Ionosphere (polar ionosphere) · Meteorology and Atmospheric Dynamics (middle atmosphere dynamics) · Radio Science (Interferometry)

scholarly journals The thermal and dynamical state of the atmosphere during polar mesosphere winter echoes

2005 ◽  
Vol 5 (4) ◽  
pp. 7613-7645
Author(s):  
F.-J. Lübken ◽  
B. Strelnikov ◽  
M. Rapp ◽  
W. Singer ◽  
R. Latteck ◽  
...  
Keyword(s):  
Absolute Magnitude ◽  
Quantitative Agreement ◽  
Solar Proton ◽  
Density Fluctuations ◽  
Small Scale ◽  
Vhf Radar ◽  
Model Calculations ◽  
Dynamical State ◽  
Air Turbulence ◽  
Radar Echoes

Abstract. In January 2005, a total of 18 rockets were launched from the Andøya Rocket Range in Northern Norway (69° N) into strong VHF radar echoes called 'Polar Mesosphere Winter Echoes' (PMWE). The echoes were observed in the lower and middle mesosphere during large solar proton fluxes. In general, PMWE are much more seldom compared to their summer counterparts PMSE (typical occurrence rates at 69° N are 1–3% vs. 80%, respectively). Our in-situ measurements by falling sphere, chaff, and instrumented payloads provide detailed information about the thermal and dynamical state of the atmosphere and therefore allow an unprecedented study of the background atmosphere during PMWE. There are a number of independent observations indicating that neutral air turbulence has caused PMWE. Ion density fluctuations show a turbulence spectrum within PMWE and no fluctuations outside. Temperature lapse rates close to the adiabatic gradient are observed in the vicinity of PMWE indicating persistent turbulent mixing. The spectral broadening of radar echoes is consistent with turbulent velocity fluctuations. Turbulence also explains the mean occurrence height of PMWE (~68–75 km): Viscosity increases rapidly with altitude and destroys any small scale fluctuations in the upper mesosphere, whereas electron densities are usually too low in the lower mesosphere to cause significant backscatter. The seasonal variation of echoes in the lower mesosphere is in agreement with a turbulence climatology derived from earlier sounding rocket flights. We have performed model calculations to study the absolute magnitude of backscatter from plasma fluctuations caused by neutral air turbulence. We find that volume reflectivities observed during PMWE are in quantitative agreement with theory. Apart from turbulence the most crucial requirement for PMWE is a sufficiently large number of electrons, for example produced by solar protons. We have studied the sensitivity of the radar echo strength on various parameters, most important electron number density and turbulence intensity. Our observational and theoretical considerations do not provide any evidence that charged aerosol particles are needed to explain PMWE, in contrast to the summer echoes which owe their existence to charged ice particles.

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