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 Asymmetry of atmospheric microstructure over synoptic scales

2001 ◽  
Vol 19 (8) ◽  
pp. 921-924 ◽  
Author(s):  
R. M. Worthington
Keyword(s):  
Western Europe ◽  
Lower Stratosphere ◽  
Middle Atmosphere ◽  
Radar Data ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Synoptic Scale ◽  
Wind Maximum ◽  
Vhf Radar

Abstract. Distortions are often seen in the angular distribution of echo-power from VHF wind-profiling radars, suggesting that thin stable layers, within the air flow, are distorted and tilted from horizontal. In vertical shear of the horizontal wind, the distribution of the layer tilt angles becomes skewed. A case study using six days of VHF radar data and synoptic charts above western Europe indicates that this asymmetry of atmospheric microstructure can exist throughout the troposphere and lower stratosphere, above and below the jet wind maximum, over horizontal scales of thousands of kilometres.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; synoptic-scale meteorology; turbulence).

Spatial variability of the aspect sensitivity of VHF radar echoes in the troposphere and lower stratosphere during jet stream passages

1994 ◽  
Vol 12 (8) ◽  
pp. 733-745 ◽  
Author(s):  
J. G. Yoe ◽  
P. Czechowsky ◽  
R. Rüster ◽  
G. Schmidt
Keyword(s):  
Lower Stratosphere ◽  
Radar Data ◽  
Horizontal Wind ◽  
Jet Stream ◽  
Wind Maximum ◽  
Vhf Radar ◽  
Wind Speeds ◽  
Radar Echoes ◽  
Wind Speed Maximum ◽  
Aspect Sensitivity

Abstract. The aspect sensitivity of SOUSY-VHF-radar oblique-beam echoes from the troposphere and lower stratosphere has been examined for a number of jet stream passages during the years 1990 - 1992. When the core of the jet is overhead or nearly so, vertical profiles of the aspect sensitivity display two notable features. First, the distinction between mainly isotropic and strongly aspect-sensitive echoes in the troposphere and the lower stratosphere, respectively, often reported for measurements made during calm conditions, does not necessarily prevail in the vicinity of the jet stream. Second, echoes obtained at altitudes near the height of the horizontal wind maximum are found to be more aspect sensitive for beams directed parallel to the horizontal flow or nearly so, than for other beam directions. It is demonstrated that time-averaged horizontal wind speeds estimated from the radar data, taking into account the reduced effective oblique-beam zenith angle resulting from aspect sensitivity, may exceed uncorrected wind speeds by as much as 10 m s-1 in these circumstances. Implications for wind profiling and for describing the backscattering process are discussed. Doppler spectral widths examined for one jet stream passage are found to be narrower in a beam aligned with the horizontal wind at heights near the wind speed maximum than corresponding widths measured in a beam projected at right angles to the jet. The narrowest spectra thus coincide with the most aspect-sensitive echoes, consistent with the hypothesis that such returns result from specular backscattering processes.

scholarly journals Aspect sensitivity in the VHF radar backscatters studied using simultaneous observations of Gadanki MST radar and GPS sonde

2004 ◽  
Vol 22 (11) ◽  
pp. 4013-4023 ◽  
Author(s):  
A. K. Ghosh ◽  
S. S. Das ◽  
A. K. Patra ◽  
D. N. Rao ◽  
A. R. Jain
Keyword(s):  
Vertical Shear ◽  
Horizontal Wind ◽  
Vhf Radar ◽  
Upper Troposphere ◽  
Power Difference ◽  
Mst Radar ◽  
Favorable Conditions ◽  
Tropical Station ◽  
Aspect Sensitivity

Abstract. Simultaneous observations made on four days using the MST radar and GPS-sonde at Gadanki (13.5° N, 79.2° E), a tropical station in India, are presented to address the aspect sensitivity of radar backscatters observed at different heights. The observations show that wherever stability parameter N2 is high, vertical shear of horizontal wind is low and Richardson number (Ri) is high, the aspect sensitivity is high indicating that the aspect sensitive radar backscatters are due to thermal structures in the atmosphere. Such a case can be seen very clearly in the upper troposphere and lower stratosphere. At some heights, where N2 is high, Ri is high, but shears are relatively weak, the aspect sensitivity is found to almost disappear, indicating that some amount of shear provides favorable conditions for causing aspect sensitivity. Aspect sensitivity does not occur at all where N2 is low or negative and Ri is low in spite of wind shear being either high or low, indicating that the regions are well mixed and hence turbulent. The study also shows a power difference in the symmetric beams. A case study on this aspect suggests that this asymmetry is due to the tilting of layers by the action of atmospheric waves. There is indication that these waves are generated through Kelvin-Helmholtz-instability (KHI).

scholarly journals Mesospheric turbulent velocity estimation using the Buckland Park MF radar

2001 ◽  
Vol 19 (8) ◽  
pp. 1007-1017 ◽  
Author(s):  
D. A. Holdsworth ◽  
R. A. Vincent ◽  
I. M. Reid
Keyword(s):  
Annual Variation ◽  
Middle Atmosphere ◽  
Velocity Estimation ◽  
Turbulent Velocity ◽  
Radio Science ◽  
Meteorology And Atmospheric Dynamics ◽  
Zonal Velocity ◽  
Instruments And Techniques ◽  
Full Correlation Analysis ◽  
Mf Radar

Abstract. This paper investigates turbulent velocity estimation using the full correlation analysis (FCA) of spaced antenna (SA) data, and its application to the routine FCA observations of the Buckland Park MF (BPMF) radar. The effects of transmitter beamwidths are investigated, confirming the suggestions of previous authors that wide transmit beam widths lead to an overestimation of the turbulent velocity. The annual variation of the turbulent velocity is investigated, revealing an increase in turbulent velocity with height, and equinoctal minima and solstice maxima observed below 80 km. Investigations of the turbulent velocities about the March diurnal tide maximum reveals a diurnal variation in phase with the zonal velocity. Harmonic analysis reveals this relationship exists between February and September. Descending power layers are also observed during this period. A number of mechanisms are proposed to describe these observations.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; instruments and techniques) – Radio science (instruments and techniques)

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 A statistical study of underestimates of wind speeds by VHF radar

1997 ◽  
Vol 15 (6) ◽  
pp. 805-812 ◽  
Author(s):  
L. Thomas ◽  
I. Astin ◽  
R. M. Worthington
Keyword(s):  
Statistical Treatment ◽  
Vertical Direction ◽  
Spatial Separation ◽  
Horizontal Wind ◽  
Vhf Radar ◽  
Height Range ◽  
Wind Speeds ◽  
Radar Echoes ◽  
Wind Measurements ◽  
Radar Measurements

Abstract. Comparisons are made between horizontal wind measurements carried out using a VHF-radar system at Aberystwyth (52.4°N, 4.1°W) and radiosondes launched from Aberporth, some 50 km to the south-west. The radar wind results are derived from Doppler wind measurements at zenith angles of 6° in two orthogonal planes and in the vertical direction. Measurements on a total of 398 days over a 2-year period are considered, but the major part of the study involves a statistical analysis of data collected during 75 radiosonde flights selected to minimise the spatial separation of the two sets of measurements. Whereas good agreement is found between the two sets of wind direction, radar-derived wind speeds show underestimates of 4–6% compared with radiosonde values over the height range 4–14 km. Studies of the characteristics of this discrepancy in wind speeds have concentrated on its directional dependence, the effects of the spatial separation of the two sets of measurements, and the influence of any uncertainty in the radar measurements of vertical velocities. The aspect sensitivity of radar echoes has previously been suggested as a cause of underestimates of wind speeds by VHF radar. The present statistical treatment and case-studies show that an appropriate correction can be applied using estimates of the effective radar beam angle derived from a comparison of echo powers at zenith angles of 4.2° and 8.5°.

scholarly journals Aspect sensitivity of VHF radar echoes observed in the middle and upper troposphere during the passage of a cut-off low

Radio Science ◽  
1999 ◽  
Vol 34 (3) ◽  
pp. 667-679 ◽  
Author(s):  
Bernard Campistron ◽  
Yves B. Pointin ◽  
Fabienne Lohou ◽  
Jean-Pierre Pagès
Keyword(s):  
Vhf Radar ◽  
Upper Troposphere ◽  
Radar Echoes ◽  
Aspect Sensitivity

scholarly journals Three-dimensional tracking of mid-latitude quasi-periodic E-region echoes observed with the Chung-Li VHF radar

2005 ◽  
Vol 23 (2) ◽  
pp. 393-400 ◽  
Author(s):  
C. L. Chen ◽  
C. J. Pan ◽  
J. Röttger ◽  
V. K. Anandan
Keyword(s):  
Three Dimensional ◽  
Vertical Shear ◽  
Negative Slope ◽  
Horizontal Wind ◽  
Vhf Radar ◽  
Rate Analysis ◽  
E Region ◽  
Low Altitude ◽  
Range Rate ◽  
Standard Range

Abstract. This paper presents observations of low-altitude mid-latitude E-region irregularities obtained with the 52-MHz Chung-Li VHF radar. These are carried out in the interferometer mode to investigate the behavior of these irregularities over time and space. The observations presented here show the characteristics of type-II echoes noted by a negative slope, i.e. they are approaching the radar as a function of time. The range-time-intensity (RTI) plots obtained through power spectrum analysis reveal the quasi-periodic striations, which are known as LQP (Low-altitude QP) echoes. Our interferometer analysis allows one to investigate the motion (i.e. "tracking") of the LQP echo patches in three dimensions. This method is superior to just evaluating the variations of the echo power as a function of range and time in the standard RTI-plots. By applying this method, we show that the echo patches in different striations remain at almost the same altitude when we trace the isolated echoing regions until they disappear from the radar view. We further compare the rate of change of the range (range rate dR/dt) by two techniques: one by simply measuring the varying slope of the LQP echoes from RTI plot, the other by tracking the three-dimensional locations of the LQP scatterers by using the interferometer technique. We finally prove that the changes in range as a function of time, deduced from the interferometer technique, are significantly correlated with those of the standard range rate analysis. However, the standard range rate analysis does not provide information about the correct location and the variation of the LQP irregularities. The three-dimensional analysis, which we introduced for tracking individual striations, shows that LQP echo patches are confined to between 98 and 100km altitude. This suggests that the irregularities which cause the LQP echoes drifted through the radar beam at approximately constant altitude, which we tend to attribute to a region of large-scale vertical shear of the horizontal wind.

scholarly journals Anisotropy of Doppler spectral parameters in the VHF radar observations at MU and White Sands

2001 ◽  
Vol 19 (8) ◽  
pp. 883-888 ◽  
Author(s):  
G. D. Nastrom ◽  
T. Tsuda
Keyword(s):  
Spectral Width ◽  
Meridional Plane ◽  
Spectral Parameters ◽  
Vhf Radar ◽  
Wind Speeds ◽  
Meteorology And Atmospheric Dynamics ◽  
Turbulence Effects ◽  
Instruments And Techniques ◽  
The Mean ◽  
White Sands

Abstract. Significant differences are found between the mean spectral widths from beams in the meridional plane and in the zonal plane at both the MU and the White Sands VHF radars. The spectral width in the beam directed perpendicular to the prevailing wind is greater than that in the beam parallel to the wind. The magnitudes of the differences in spectral width show a linear relationship with wind speed, with the greatest differences at the greatest wind speeds. The differences in spectral width show a positive correlation with the differences in backscattered power. The anisotropy in backscattered power is well-known and is usually attributed to aspect sensitivity effects. However, the anisotropy in spectral width does not appear to be due to the same mechanism, and while several hypotheses to account for this are considered, including finite range-volume effects, effects from the tilting of isentropic layers, and anisotropic turbulence effects, it is seen that each of these suggestions has its shortcomings.Key words. Meteorology and atmospheric dynamics (turbulence; instruments and techniques)

scholarly journals Simultaneous Observations of Cirrus Clouds with a Millimeter-Wave Radar and the MU Radar

2005 ◽  
Vol 44 (3) ◽  
pp. 313-323 ◽  
Author(s):  
Eiko Wada ◽  
Hiroyuki Hashiguchi ◽  
Masayuki K. Yamamoto ◽  
Michihiro Teshiba ◽  
Shoichiro Fukao
Keyword(s):  
Millimeter Wave ◽  
Three Dimensional ◽  
Cirrus Clouds ◽  
Vertical Shear ◽  
Dimensional Structure ◽  
Horizontal Wind ◽  
Millimeter Wave Radar ◽  
Mu Radar ◽  
Wave Radar ◽  
Radiosonde Observation

Abstract Observations of frontal cirrus clouds were conducted with the scanning millimeter-wave radar at the Shigaraki Middle and Upper Atmosphere (MU) Radar Observatory in Shiga, Japan, during 30 September–13 October 2000. The three-dimensional background winds were also observed with the very high frequency (VHF) band MU radar. Comparing the observational results of the two radars, it was found that the cirrus clouds appeared coincident with the layers of the strong vertical shear of the horizontal winds, and they developed and became thicker under the condition of the strong vertical shear of the horizontal wind and updraft. The result of the radiosonde observation indicated that Kelvin–Helmholtz instability (KHI) occurred at 8–9-km altitudes because of the strong vertical shear of the horizontal wind. The warm and moist air existed above the 8.5-km altitude, and the cold and dry air existed below the 8.5-km altitude. As a result of the airmass mixing of air above and below the 8.5-km altitudes, the cirrus clouds were formed. The updraft, which existed at 8.5–12-km altitude, caused the development of the cirrus clouds with the thickness of &gt;2 km. By using the scanning millimeter-wave radar, the three-dimensional structure of cell echoes formed by KHI for the first time were successfully observed.

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