scholarly journals On the influence of neutral turbulence on ambipolar diffusivities deduced from meteor trail expansion

2002 ◽  
Vol 20 (11) ◽  
pp. 1857-1862 ◽  
Author(s):  
C. M. Hall
Keyword(s):  
Middle Atmosphere ◽  
Atmospheric Dynamics ◽  
Meteorology And Atmospheric Dynamics ◽  
Middle Atmosphere Dynamics ◽  
Radar Echoes ◽  
Meteor Trail ◽  
Meteor Trails

Abstract. By measuring fading times of radar echoes from underdense meteor trails, it is possible to deduce the ambipolar diffusivities of the ions responsible for these radar echoes. It could be anticipated that these diffusivities increase monotonically with height akin to neutral viscosity. In practice, this is not always the case. Here, we investigate the capability of neutral turbulence to affect the meteor trail diffusion rate.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; turbulence)

scholarly journals Unexpectedly small semidiurnal tidal wind amplitudes in the mid-latitudemesopause region during September 2002

2004 ◽  
Vol 22 (2) ◽  
pp. 701-704 ◽  
Author(s):  
D. Kürschner ◽  
Ch. Jacobi
Keyword(s):  
Phase Transition ◽  
Key Words ◽  
Central Europe ◽  
Annual Cycle ◽  
Middle Atmosphere ◽  
Atmospheric Dynamics ◽  
Mesopause Region ◽  
Meteorology And Atmospheric Dynamics ◽  
Middle Atmosphere Dynamics ◽  
Waves And Tides

Abstract. The mesopause region monthly mean winds and semidiurnal tidal amplitudes and phases over Central Europe have been measured at Collm Observatory since September 1982. The regular annual cycle of the semidiurnal tidal amplitudes show maximum values during late August and September. In contrast to that, in autumn 2002 no enhancement of the tidal amplitudes was measured, while the autumn tidal phase transition occurred unusually early. Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides; climatology)

scholarly journals <i>Letter to the Editior</i>Testing the hypothesis of the influence of neutral turbulence on the deduction of ambipolar diffusivities from meteor trail expansion

2005 ◽  
Vol 23 (3) ◽  
pp. 1071-1073 ◽  
Author(s):  
C. M. Hall ◽  
T. Aso ◽  
M. Tsutsumi ◽  
S. Nozawa ◽  
A. H. Manson ◽  
...  
Keyword(s):  
Ambient Temperature ◽  
Lower Thermosphere ◽  
Radar Echoes ◽  
Meteor Trail ◽  
Meteor Trails

Abstract. Fading times of radar echoes from underdense meteor trails in the upper mesosphere/lower thermosphere are commonly used to determine ambipolar diffusivities and hence ambient temperature. Diffusivities are generally expected to increase exponentially with height through the region from which the meteor trail echoes are obtained, viz., typically 70-110km altitude for a ~30-MHz radar. In practice, however, this is more the exception: unexpectedly large diffusivities are obtained in the lower part of the regime, and unexpectedly low values are obtained in the upper part; only in the few kilometres on either side of the maximum in echo occurrence (viz., 90km for a 30-MHz radar) does the diffusivity profile behave as expected. Hall (2002) hypothesised that neutral turbulence might be enhancing expansion of the meteor trail in the lower part of the regime. In this communication, due to results only available since the publication of Hall's suggestion, we are able to refute the hypothesis.

scholarly journals Planetary wave activity in the lower ionosphere during CRISTA I campaign in autumn 1994 (October−November)

1998 ◽  
Vol 16 (8) ◽  
pp. 1014-1023 ◽  
Author(s):  
D. Pancheva ◽  
J. Laštovička
Keyword(s):  
Planetary Wave ◽  
Middle Atmosphere ◽  
Lower Ionosphere ◽  
Wave Activity ◽  
Atmospheric Dynamics ◽  
Planetary Scale ◽  
Meteorology And Atmospheric Dynamics ◽  
Wave Numbers ◽  
Dominant Period ◽  
Waves And Tides

Abstract. On the basis of MEM spectrum analysis, the main planetary scale fluctuations formed in the lower ionosphere are studied over a period of 3–25 days during the CRISTA campaign (October-November 1994). Three dominant period bands are found: 3–5, 6–8 and 15–23 (mainly 16–18) days. For 7–8 and 16–18 day fluctuations, propagation was eastward with wave numbers K = 3 and K = 1, respectively. The magnitude of planetary wave activity in the mid-latitudes of the Northern Hemisphere during the CRISTA campaign seems to be fairly consistent with the expected undisturbed normal/climatological state of the atmosphere at altitudes of 80–100 km.Key words. Ionosphere (ionosphere-atmosphere interactions) · Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

scholarly journals Stratosphere-troposphere exchange in an extratropical cyclone, calculated with a Lagrangian method

2000 ◽  
Vol 18 (5) ◽  
pp. 573-582 ◽  
Author(s):  
M. Sigmond ◽  
J. Meloen ◽  
P. C. Siegmund
Keyword(s):  
Wind Shear ◽  
Total Ozone ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Statistical Significance ◽  
Atmospheric Dynamics ◽  
Extratropical Cyclone ◽  
Northwest Coast ◽  
Mesoscale Meteorology ◽  
Meteorology And Atmospheric Dynamics

Abstract. A Lagrangian technique is developed and applied to calculate stratosphere-troposphere exchange in an extratropical cyclone. This exchange is computed from the potential vorticity or PV along trajectories, calculated from ECMWF circulation data. Special emphasis is put on the statistical significance of the results. The computed field of the cross-tropopause flux is dominated by elongated patterns of statistically significant large downward and small upward fluxes. The downward fluxes mainly occur in the lower part of the considered tropopause folds. The upward fluxes are found near the entrance of the folds, in the tropopause ridges. The ratio between the area averaged downward and upward cross-tropopause fluxes increases with increasing strength of the cyclone. Since the largest fluxes are shown to occur in the regions with the largest wind shear, where PV-mixing is thought to cause large cross-tropopause fluxes, the results are expected to be reliable, at least in a qualitative sense. The position of a tropopause fold along the northwest coast of Africa is confirmed by total ozone observations. The results indicate that the applied Lagrangian technique is an appropriate tool for diagnosing stratosphere-troposphere exchange.Key words: Meteorology and atmospheric dynamics (general circulation; mesoscale meteorology; middle atmosphere dynamics)

scholarly journals <i>Letter to the Editor</i>: Complete maps of the aspect sensitivity of VHF atmospheric radar echoes

1999 ◽  
Vol 17 (8) ◽  
pp. 1116-1119 ◽  
Author(s):  
R. M. Worthington ◽  
R. D. Palmer ◽  
S. Fukao
Keyword(s):  
Power Distribution ◽  
Middle Atmosphere ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Vhf Radar ◽  
Meteorology And Atmospheric Dynamics ◽  
Mu Radar ◽  
Radar Echoes ◽  
Instruments And Techniques ◽  
Aspect Sensitivity

Abstract. Using the MU radar at Shigaraki, Japan (34.85°N, 136.10°E), we measure the power distribution pattern of VHF radar echoes from the mid-troposphere. The large number of radar beam-pointing directions (320) allows the mapping of echo power from 0° to 40° from zenith, and also the dependence on azimuth, which has not been achieved before at VHF wavelengths. The results show how vertical shear of the horizontal wind is associated with a definite skewing of the VHF echo power distribution, for beam angles as far as 30° or more from zenith, so that aspect sensitivity cannot be assumed negligible at any beam-pointing angle that most existing VHF radars are able to use. Consequently, the use of VHF echo power to calculate intensity of atmospheric turbulence, which assumes only isotropic backscatter at large beam zenith angles, will sometimes not be valid.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; turbulence; instruments and techniques)

scholarly journals Classification of hemispheric monthly mean stratospheric potential vorticity fields

2003 ◽  
Vol 21 (3) ◽  
pp. 805-817 ◽  
Author(s):  
R. Huth ◽  
P. O. Canziani
Keyword(s):  
Potential Vorticity ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Principal Component ◽  
Volcanic Eruptions ◽  
Atmospheric Processes ◽  
Meteorology And Atmospheric Dynamics ◽  
Stratospheric Dynamics ◽  
Northern And Southern Hemispheres

Abstract. Monthly mean NCEP reanalysis potential vorticity fields at the 650 K isentropic level over the Northern and Southern Hemispheres between 1979 and 1997 were studied using multivariate analysis tools. Principal component analysis in the T-mode was applied to demonstrate the validity of such statistical techniques for the study of stratospheric dynamics and climatology. The method, complementarily applied to both the raw and anomaly fields, was useful in determining and classifying the characteristics of winter and summer PV fields on both hemispheres, in particular, the well-known differences in the behaviour and persistence of the polar vortices. It was possible to identify such features as sudden warming events in the Northern Hemisphere and final warming dates in both hemispheres. The stratospheric impact of other atmospheric processes, such as volcanic eruptions, also identified though the results, must be viewed at this stage as tentative. An interesting change in behaviour around 1990 was detected over both hemispheres.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; general circulation; climatology)

High spatiotemporal radar observation of the polar summer mesosphere using MAARSY in a MIMO configuration

2021 ◽  
Author(s):  
Ralph Latteck ◽  
Jorge Chau ◽  
Miguel Urco ◽  
Juha Vierinen ◽  
Victor Avsarkisov
Keyword(s):  
Large Scale ◽  
Middle Atmosphere ◽  
Multiple Input Multiple Output ◽  
Horizontal Resolution ◽  
Neutral Wind ◽  
Stratified Turbulence ◽  
Turbulent Dissipation ◽  
Radar Echoes ◽  
Multiple Input ◽  
Input Multiple Output

&lt;p&gt;Atmospheric structures due to gravity waves, turbulence, Kelvin Helmholtz instabilities, etc. in the mesosphere are being studied with a varying of ground-based and satellite-based instruments. At scales less than 100 km, they are mainly studied with airglow imagers, lidars, and radars. Typical radar observations have not been able to resolve spatial and temporal ambiguities due to the strength of radar echoes, the size of the system, and/or the nature of the atmospheric irregularities. In this work we observed spatially and temporally resolved structures of PMSE with unprecedented horizontal resolution, using the improved radar imaging accuracy of the Middle Atmosphere Alomar Radar System (MAARSY) with the aid of a multiple-input multiple output (MIMO) technique. The studies are performed in both the brightness of the mesospheric echoes and their Doppler velocities. The resolutions achieved are less than 1 km in the horizontal direction, less than 300m in altitude, and less than 1 minute in time, in an area of ~15km x 15km around 85km of altitude. We present a couple of wavelike monochromatic events, one drifting with the background neutral wind, and one propagating against the neutral wind. Horizontal wavelengths, periods, and vertical and temporal coverage of the events are described and discussed. A theory of stratified turbulence is employed in the present study. In particular, it is shown that the structure that propagates with the background wind is a large-scale turbulent KHI event.&amp;#160; Some important turbulence characteristics, such as a turbulent dissipation rate, buoyancy Reynolds number, and Froude number, support our conclusion.&lt;/p&gt;

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