Dual Doppler Research Articles

Radar Analysis of a Tropical Convective Boundary Layer with Shallow Cumulus Clouds

A situation of fair weather cloudy convection is examined using a dual Doppler radar, environmental measurements and cloud photogrammetry. The convective layer is characterized by the interaction between the northward monsoon wind at low levels and the easterly wind above; a convective organization is found to be related to the sheer between both flows. Moreover, at the convective scale, properties of the convective layer below clouds and in clew air are considered. They show significant differences in buoyancy and entrainment effects but similar effects of the shear on variances and momentum production profiles.

Three-Dimensional Wind Field Analysis from Dual-Doppler Radar Data. Part III: The Boundary Condition: An Optimum Determination Based on a Variational Concept

The choice of the boundary condition when integrating the air mass continuity equation, is a major problem of the 3D wind field analysis from dual (or multiple) Doppler radar data. A zero vertical velocity at ground level seems the most natural boundary condition. Unfortunately, it is known that the integration processes is unstable with respect to this condition: it leads to errors amplifying exponentially with height. In order to overcome this difficulty various solutions have been proposed, the most recent ones using the variational analysis: (i) integrating from storm top level, (ii) integrating from storm top level while constraining the height integrated divergence to be as small as possible (Ziegier, 1978), and (iii) constraining the direct estimates of the 3D wind field to satisfy the continuity equation (Ray et al., 1980). The analysis proposed in this paper is also based upon a variational concept, but it differs in its principle from those previously cited. It consists in adjusting the boundary condition field at ground level in order to optimize the “mathematical regularity” of the vertical velocity field, followed by upward integration of the continuity equation. In such a formulation, the boundary condition at ground level is “floating” (i.e., not specified). However it is possible to require. as a subsidiary condition of the variational problem, that the vertical velocity at ground level fluctuate about zero with a specified variance σ02 (thus the condition W0=0 at ground level is statistically verified). The optimum choice of σ0 is established from considerations of statistical theory. It should be noted that the horizontal divergence (or coplane divergence) profile is unadjusted and that the equation of continuity is integrated upward from the optimum lower boundary condition to obtain W. An application to simulated or real data helps us to appreciate the improvements brought by the present variational approach with respect to standard methods of integration: 1) the random errors are as small as in the case of an integration from storm top level, but here the boundary condition W0=0 at ground level is statistically preserved; and 2) for the integration paths where no cannot be specified (lack of data at low level), the analysis automatically generates a boundary condition which realizes the best regularity of W with respect to the neighbouring paths. This variational analysis can be easily implemented on a computer from the program prepared for the standard integration, and it requires a short additional computation time.

Three-Dimensional Wind Field Analysis from Dual-Doppler Radar Data. Part II: Minimizing the Error due to Temporal Variation

Abstract One of the major problems in three-dimensional wind field analysis from dual (or multiple) Doppler radar data resides in the non-stationary of the observed air flow within the volume sampling time which ranges typically from 2 to 5 min. The present part II is focused on this problem. Most often, the storm moves horizontally at a speed of 5–25 m s−1.Therefore, the temporal variation for a fixed observer at ground level results from the superposition of two effects: 1) the intrinsic temporal variation (or variation seen in a frame moving with the storm) and 2) the effect of horizontal advection. The first contribution of the paper concerns the development of an algorithm for correcting for the advection effect in the case of a dual-Doppler radar observation. This algorithm, which provides a mathematically exact solution to the problem of correcting for advection, can be very easily implemented in a computer program. The second contribution deals with the errors that may arise from an accurate (or l...

A review of microwave radar observations in the dry convective planetary boundary layer

For the last two decades, radar has been used to probe the planetary boundary layer (PBL) in a number of different ways. The sensitive, high-power radars at Wallops Island, Virginia, were used to examine the refractive index structure of the PBL over hundreds of square kilometers with a resolution of several hundred meters. In these studies, fields of convective cells were documented over land and over the ocean. Vertically pointing FM-CW radars were used to observe the vertical structure of the PBL with resolution as good as 2 m. In addition, FM-CW radars, as well as conventional radars, have detected birds and insects in the PBL. Within the last seven years, dual Doppler radar was used to document the details of the velocity structure of the PBL in three dimensions. Recently, it has been shown that radar can be a useful tool for turbulence and diffusion measurements in the boundary layer.

Investigation of Clear Air Convective Structures in the PBL Using a Dual Doppler Radar and a Doppler Sodar

Abstract In August 1979, the Dual Doppler Radar (Ronsard System) and the Doppler Sodar system of CNET were simultaneously used during an experiment on clear air convection. It provided the opportunity to develop a method for the spatial study of atmospheric structures in the PBL: the mean characteristics of the flow structures at scales larger than one kilometer (wind velocity and variance profiles, one-dimensional velocity spectra) are studied. Spatial properties of the atmosphere are then investigated, showing a heterogeneity of the horizontal wind field inside the observed area. Finally, a predominant alignment of the convective cells along the same direction is found in every case.

Turbulence and waves in the optically clear planetary boundary layer resolved by dual‐Doppler radars

Dual Doppler radars provide a unique method to resolve the spatial structure of planetary boundary layer (PBL) air motions. Both the wave and turbulent fluctuations of air in the convectively unstable PBL are revealed from synthesis of the Doppler velocities of echoes (from the atmosphere's intrinsic scatterers) returned to two spaced (40 km) radars. The smaller turbulent scales follow closely the two‐thirds law‐of‐similarity theory, whereas the observed 4‐km wave is compared with those from theoretical models. Power spectra derived from Fourier space analysis of Doppler‐synthesized wind are compared to those obtained from time‐space conversion of Fourier time analysis applied to wind measurements on a 500‐m tower. It is shown that turbulent eddies move with the mean wind and maintain an identity for nearly 60 min. Larger wind variance is observed in the cross‐wind component than in the along‐wind component. Error variances are in agreement with estimates from theoretical studies. Comparisons of refractive index structure constants Cn2 deduced by radar and aircraft are within 1 dB.

Dual doppler radar observations of clear air wind perturbations in the planetary boundary layer

The National Severe Storm Laboratory's dual Doppler weather radars map clear air planetary boundary layer winds using only the intrinsic scatterers of the medium. Perturbation winds have correlation lengths of a few kilometers on this day of moderate shear and advect with the mean wind. The structure function of wind shows good agreement with the two thirds law of turbulence theory. Reflectivity has a cellular structure with weak echo interiors. Independently measured reflectivity fields have correlations as large as 0.86.

Dual Doppler Radar Coordination Using Nomograms

Abstract A simple nomogram technique to facilitate dual Doppler radar data collection is presented. Equations and nomograms are developed for relating the position of a given target relative to two radars. The results are general, but application is made to the National Severe Storms Laboratory radars at Norman and the Cimarron site 40 km northwest of Norman.

Kinematics of sea breeze storms

The paper is concerned with dual Doppler radar observations of the motion fields inside convective storms developing under sea breeze conditions in the area of Miami, Florida. At low altitudes, the storm kinematics are dominated by the eastern sea breeze inflow. At altitudes above 3 to 4 kms, the convective storm's circulation becomes increasingly important. At yet higher altitudes, there is a very strong interaction between the storm and the prevailing north westerly wind. Very strong velocity gradients are found in the upper levels of the storms which suggest a mechanism for high altitude formation of vorticity.

A dual doppler radar method for the determination of wind velocities within precipitating weather systems

A method of coordinated scanning which makes use of two Doppler radars and a procedure of data reduction are described. The two radar estimates of radial velocity of the precipitation particles are combined with the equation of mass continuity and an independent estimate of the mean particle-fall velocity. This results in a complete solution for the three components of vector air motion. Examples of air motion fields which illustrate the effectiveness of this new technique in revealing the detailed structure of the winds are shown.

A geometric analysis of the probe volume in a dual beam laser Doppler velocimeter

The probe volume of the dual beam laser Doppler velocimeter is analyzed from a geometrical standpoint. The volume is graphically reconstructed and the existence of the characteristic dual beam laser Doppler velocimeter fringes is demonstrated. The fringes are analyzed and are shown to be composed of moving tubes or pockets of coherent radiation. The composition of the light is analyzed and the extent of the coherence of the laser radiation within the light pockets is considered. The scattered light from the tubes is analyzed and the coherence enhancement of the fringe structure is shown. This information is used in an attempt to resolve the controversy as to whether the dual beam laser Doppler velocimeter is governed by a fringe counting phenomena or by a beating phenomena of light from two sources of coherent radiation of different frequencies.

A phase-locked echo tracking system for recording arterial diameter changes in vivo.

A phase-locked echo tracking system for recording arterial diameter changes in vivo.

Wind Measurement by Conventional Radar with a Dual Beam pattern

Abstract A method of measuring wind velocities by a dual beam modification to conventional (non-Doppler) radars is described. The two beams are disposed slightly to either side of the antenna bore-sight axis. This results in a double-peaked Doppler velocity (frequency) spectrum which is centered on the radial velocity component and whose peaks are spaced proportionally to the transverse velocity component. Such a dual beam Doppler radar is therefore able to measure the complete vector velocity. But the conventional radar can measure only the echo fluctuation spectrum. For any Doppler spectrum, there is a unique fluctuation spectrum, and in the case of the double peaked Doppler spectrum, the fluctuation spectrum has a secondary peak at a frequency corresponding to the peak spacing. Thus, the conventional radar can also measure the transverse velocity component. While spectrum contamination by turbulence and wind shear may cause the peaks to blend with one another, it is shown that the variance of the fluct...

Airborne Doppler Radar Navigation of Jet Transport Aircraft

Trans World Airlines will pioneer use of Doppler radar as a primary means of transport aircraft navigation over the North Atlantic. This paper summarizes flight test results using dual Doppler radar sensors and dual Doppler navigation computers on Boeing 707 long range aircraft. Test flights have been flown over TWA's North Atlantic routes for almost two years to "prove-in" the Doppler system.