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

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).

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Asymmetry of atmospheric microstructure over synoptic scales

Annales Geophysicae ◽

10.5194/angeo-19-921-2001 ◽

2001 ◽

Vol 19 (8) ◽

pp. 921-924 ◽

Cited By ~ 2

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).

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

Annales Geophysicae ◽

10.1007/s00585-999-1116-z ◽

1999 ◽

Vol 17 (8) ◽

pp. 1116-1119 ◽

Cited By ~ 4

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)

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Evaluation of wind profiles from the NERC MST Radar, Aberystwyth, UK

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-7-4589-2014 ◽

2014 ◽

Vol 7 (5) ◽

pp. 4589-4621

Author(s):

C. F. Lee ◽

G. Vaughan ◽

D. A. Hooper

Keyword(s):

Wind Speed ◽

Standard Error ◽

Random Error ◽

Sampling Error ◽

Weather Prediction ◽

Horizontal Wind ◽

Wind Speeds ◽

Mst Radar ◽

Wind Profiles ◽

Aspect Sensitivity

Abstract. This study quantifies the uncertainties in winds measured by the Aberystwyth Mesosphere-Stratosphere-Troposphere (MST) radar (52.4° N, 4.0° W), before and after its renovation in March 2011. 127 radiosondes provide an independent measure of winds. Differences between radiosonde and radar-measured horizontal winds are correlated with long-term averages of vertical velocities, suggesting an influence from local mountain waves. These local influences are an important consideration when using radar winds as a measure of regional conditions, particularly for numerical weather prediction. In those applications, local effects represent a source of sampling error additional to the inherent uncertainties in the measurements themselves. The radar renovation improved the SNR of measurements, with correspondingly improved altitude coverage. It also corrected an under-estimate of horizontal wind speeds attributed to beam formation problems, due to component failure pre-renovation. The standard error in radar-measured winds averaged over half-an-hour increases with wind speed and altitude, and is 0.6–2.5 m s−1 (5–20% of wind speed) for post-renovation horizontal winds. Pre-renovation values are typically 0.4 m s−1 (0.03 m s−1) larger. The standard error in radial velocities is < 0.04 m s−1. Eight weeks of special radar operation are used to investigate the effects of echo power aspect sensitivity. Corrections for echo power aspect sensitivity remove an underestimate of horizontal wind speeds, however aspect sensitivity is azimuthally anisotropic at the scale of routine observations (≈ 1 h). This anisotropy introduces additional random error into wind profiles. For winds averaged over half-an-hour, the random error is around 3.5% above 8 km, but as large as 4.5% in the mid-troposphere.

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Case study of stratospheric gravity waves of convective origin over Arctic Scandinavia – VHF radar observations and numerical modelling

Annales Geophysicae ◽

10.5194/angeo-31-239-2013 ◽

2013 ◽

Vol 31 (2) ◽

pp. 239-250 ◽

Cited By ~ 9

Author(s):

A. Réchou ◽

J. Arnault ◽

P. Dalin ◽

S. Kirkwood

Keyword(s):

Gravity Waves ◽

Barents Sea ◽

Static Stability ◽

Weather Research And Forecasting ◽

Stability Field ◽

Vhf Radar ◽

The Barents Sea ◽

Short Period ◽

Mst Radar

Abstract. Orography is a well-known source of gravity and inertia-gravity waves in the atmosphere. Other sources, such as convection, are also known to be potentially important but the large amplitude of orographic waves over Scandinavia has generally precluded the possibility to study such other sources experimentally in this region. In order to better understand the origin of stratospheric gravity waves observed by the VHF radar ESRAD (Esrange MST radar) over Kiruna, in Arctic Sweden (67.88° N, 21.10° E), observations have been compared to simulations made using the Weather Research and Forecasting model (WRF) with and without the effects of orography and clouds. This case study concerns gravity waves observed from 00:00 UTC on 18 February to 12:00 UTC on 20 February 2007. We focus on the wave signatures in the static stability field and vertical wind deduced from the simulations and from the observations as these are the parameters which are provided by the observations with the best height coverage. As is common at this site, orographic gravity waves were produced over the Scandinavian mountains and observed by the radar. However, at the same time, southward propagation of fronts in the Barents Sea created short-period waves which propagated into the stratosphere and were transported, embedded in the cyclonic winds, over the radar site.

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

Annales Geophysicae ◽

10.1007/s00585-994-0733-9 ◽

1994 ◽

Vol 12 (8) ◽

pp. 733-745 ◽

Cited By ~ 8

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.

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

Radio Science ◽

10.1029/1998rs900032 ◽

1999 ◽

Vol 34 (3) ◽

pp. 667-679 ◽

Cited By ~ 9

Author(s):

Bernard Campistron ◽

Yves B. Pointin ◽

Fabienne Lohou ◽

Jean-Pierre Pagès

Keyword(s):

Vhf Radar ◽

Upper Troposphere ◽

Radar Echoes ◽

Aspect Sensitivity

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

Annales Geophysicae ◽

10.5194/angeo-23-393-2005 ◽

2005 ◽

Vol 23 (2) ◽

pp. 393-400 ◽

Cited By ~ 4

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.

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Evaluation of wind profiles from the NERC MST radar, Aberystwyth, UK

Atmospheric Measurement Techniques ◽

10.5194/amt-7-3113-2014 ◽

2014 ◽

Vol 7 (9) ◽

pp. 3113-3126 ◽

Cited By ~ 6

Author(s):

C. F. Lee ◽

G. Vaughan ◽

D. A. Hooper

Keyword(s):

Wind Speed ◽

Sampling Error ◽

Signal To Noise Ratio ◽

Weather Prediction ◽

Horizontal Wind ◽

Mountain Waves ◽

Wind Speeds ◽

Mst Radar ◽

Wind Profiles ◽

Aspect Sensitivity

Abstract. This study quantifies the uncertainties in winds measured by the Aberystwyth Mesosphere–Stratosphere–Troposphere (MST) radar (52.4° N, 4.0° W), before and after its renovation in March 2011. A total of 127 radiosondes provide an independent measure of winds. Differences between radiosonde and radar-measured horizontal winds are correlated with long-term averages of vertical velocities, suggesting an influence from local mountain waves. These local influences are an important consideration when using radar winds as a measure of regional conditions, particularly for numerical weather prediction. For those applications, local effects represent a source of sampling error additional to the inherent uncertainties in the measurements themselves. The radar renovation improved the signal-to-noise ratio (SNR) of measurements, with a corresponding improvement in altitude coverage. It also corrected an underestimate of horizontal wind speeds attributed to beam formation problems, due to pre-renovation component failure. The root mean square error (RMSE) in radar-measured horizontal wind components, averaged over half an hour, increases with wind speed and altitude, and is 0.8–2.5 m s−1 (6–12% of wind speed) for post-renovation winds. Pre-renovation values are typically 0.1 m s−1 larger. The RMSE in radial velocities is <0.04 m s−1. Eight weeks of special radar operation are used to investigate the effects of echo power aspect sensitivity. Corrections for echo power aspect sensitivity remove an underestimate of horizontal wind speeds; however aspect sensitivity is azimuthally anisotropic at the scale of routine observations (≈1 h). This anisotropy introduces random error into wind profiles. For winds averaged over half an hour, the RMSE is around 3.5% above 8 km, but as large as 4.5% in the mid-troposphere.

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Long-term mean vertical velocity measured by MST radar at Gadanki (13.5° N, 79.2° E)

Annales Geophysicae ◽

10.5194/angeo-27-451-2009 ◽

2009 ◽

Vol 27 (2) ◽

pp. 451-459 ◽

Cited By ~ 4

Author(s):

P. V. Rao ◽

P. Vinay Kumar ◽

M. C. Ajay Kumar ◽

G. Dutta

Keyword(s):

Vertical Velocity ◽

Vertical Motion ◽

Vertical Wind ◽

Vertical Shear ◽

Horizontal Wind ◽

Direct Measurements ◽

Semidiurnal Variation ◽

Vertical Beam ◽

Tropical Station

Abstract. MST radars are capable of measuring vertical motion along a vertically directed beam. We present 8 years (1995–2003) averaged profile of vertical velocity in the troposphere and the lower stratosphere over Gadanki (13.5° N, 79.2° E), a tropical station. A downward mid-tropospheric w is observed with a reversal of sign around 10 km and a further reversal can also be seen at ~17 km. A significant diurnal and semidiurnal variation in vertical wind is observed for all heights with subsidence during the evening hours. Seasonal variability of vertical wind is also found to be quite appreciable. Vertical velocities have been derived using symmetric pairs of off-vertical beams and a comparison has been made with direct vertical beam measurements. Vertical components estimated from E-W and N-S radial velocities do not match and are also found to have discrepancy with direct measurements. Plausible causes of the discrepancy have been investigated with the help of some case studies. Vertical shear in horizontal wind, gradients in horizontal velocities and echo power imbalance may be some of the factors responsible for the observed discrepancy.

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Doppler radar spectral width broadening due to beamwidth and wind shear

Annales Geophysicae ◽

10.1007/s00585-997-0786-7 ◽

1997 ◽

Vol 15 (6) ◽

pp. 786-796 ◽

Cited By ~ 53

Author(s):

G. D. Nastrom

Keyword(s):

Wind Shear ◽

Vertical Wind Shear ◽

Spectral Width ◽

Analytic Solutions ◽

Vertical Shear ◽

Horizontal Wind ◽

Dimensional Model ◽

Spectral Broadening ◽

Vhf Radar ◽

Beam Broadening

Abstract. The spectral width observed by Doppler radars can be due to several effects including the atmospheric turbulence within the radar sample volume plus effects associated with the background flow and the radar geometry and configuration. This study re-examines simple models for the effects due to finite beamwidth and vertical shear of the horizontal wind. Analytic solutions of 1- and 2-dimensional models are presented. Comparisons of the simple 2-dimensional model with numerical integrations of a 3-dimensional model with a symmetrical Gaussian beam show that the 2-dimensional model is usually adequate. The solution of the 2-dimensional model gives a formula that can be applied easily to large data sets. Analysis of the analytic solutions of the 2-dimensional model for off-vertical beams reveals a term that has not been included in mathematical formulas for spectral broadening in the past. This term arises from the simultaneous effects of the changing geometry due to curvature within a finite beamwidth and the vertical wind shear. The magnitude of this effect can be comparable to that of the well-known effects of beam-broadening and wind shear, and since it can have either algebraic sign, it can significantly reduce (or increase) the expected spectral broadening, although under typical conditions it is smaller than the beam-broadening effect. The predictions of this simple model are found to be consistent with observations from the VHF radar at White Sands Missile Range, NM.

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