Michel Chong

A multiple-Doppler synthesis and continuity adjustment technique (MUSCAT) to recover wind components from Doppler radar measurements

Abstract A new approach is presented to account for a simultaneous solution of the three wind components from at least a pair of Doppler radar observations, which could remove potential drawbacks of an iterative (nonsimultaneous) solution of Cartesian dual-Doppler analysis techniques. The multiple-Doppler synthesis and continuity adjustment technique (MUSCAT) is derived from the extended overdetermined dual-Doppler (EODD) variational formalism that contains the basis for a simultaneous (noniterative) solution of a dual- or multiple-equation system and a mass continuity equation. Necessary accommodations are discussed, including the solutions for a plane-to-plane synthesis (as in EODD) instead of a fully three-dimensional and computationally intensive analysis, owing to the three-dimensional character of the continuity equation. The evaluation of MUSCAT is carried out by first considering real data and then performing numerical tests based on simulated radar observations. The comparative study with EODD ap...

A Formulation of the Continuity Equation of MUSCAT for either Flat or Complex Terrain

Abstract The Mesoscale Alpine Programme (MAP) involved an ensemble of airborne and ground-based Doppler radars dedicated to the observation of precipitating systems over the Alps. The derivation of the three-dimensional wind fields from the multiple-Doppler synthesis and continuity adjustment technique (MUSCAT) requires that orography-induced air circulation, in particular when solving the mass continuity equation, is taken into account. A formulation of this equation in its flux form is proposed, which has the advantage of applying to either flat or complex terrain and thus eliminating the need to explicitly evaluate the vertical velocity associated with the slope wind at the surface. Pseudo-Doppler observations of a pair of ground-based radars that were operated during MAP, deduced from a modeled pre-MAP case, are used to validate the proposed solution and to investigate the performances of the Doppler wind synthesis above mountainous regions.

Three-Dimensional Wind Retrieval: Application of MUSCAT to Dual-Doppler Lidar

Abstract During the field campaign of the Terrain-induced Rotor Experiment (T-REX) in the spring of 2006, Doppler lidar measurements were taken in the complex terrain of the Californian Owens Valley for six weeks. While fast three-dimensional (3D) wind analysis from measured radial wind components is well established for dual weather radars, only the feasibility was shown for dual-Doppler lidars. A computationally inexpensive, variational analysis method developed for multiple-Doppler radar measurements over complex terrain was applied. The general flow pattern of the 19 derived 3D wind fields is slightly smoothed in time and space because of lidar scan duration and analysis algorithm. The comparison of extracted wind profiles to profiles from radiosondes and wind profiler reveals differences of wind speed and direction of less than 1.1 m s−1 and 3°, on average, with standard deviations not exceeding 2.7 m s−1 and 27°, respectively. Standard velocity–azimuth display (VAD) retrieval method provided higher ...

A Mesovortex within a Near-Equatorial Mesoscale Convective System during TOGA COARE

Abstract Airborne Doppler radar observations are used to investigate the internal structure of a midlevel mesovortex that developed within the rear part of the stratiform precipitation region of a mature-to-decaying mesoscale convective system. This system, composed of several convective elements, occurred on 13 December 1992, on the eastern side of the intensive flux array of the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment, near the equator (2°S). The mesovortex contained several features that were previously observed in other tropical and midlatitude systems. Radar observations show that the closed wind circulation at midlevels had a horizontal dimension of ∼150 km and was coincident with a marked rear inflow at the central rear of the stratiform region where a notch pattern clearly identified the rear dry air intrusion. It was associated with positive vertical vorticity (anticyclonic for the Southern Hemisphere) and could be classified as a cooling-induced vortex. Maxi...

Three-Dimensional Air Circulation in a Squall Line from Airborne Dual-Beam Doppler Radar Data: A Test of Coplane Methodology Software

Abstract The detailed structure of a tropical squall line observed in central Florida was investigated from an airborne dual-beam Doppler radar, pointing respectively fore and aft. This allowed dual-Doppler observations from a straight flight path in a way similar to the coplane sampling technique proposed for two ground-based Doppler radars and for which the authors had developed an elaborate method in order to obtain a reliable wind estimation. The application of this analysis method to the airborne dual-beam radar observations is discussed, along with the basic requirements due to the specific airborne data sampling. The retrieved three-dimensional airflow structures within the convective part of the squall line are found to be quite consistent with those previously documented from ground-based radars, such as the convective-scale downdrafts sustaining a well-marked rear-to-front flow or the convective updrafts associated with the front-to-rear flow at mid-to-upper levels and that detrain into the rear...

Extended Overdetermined Dual-Doppler Formalism in Synthesizing Airborne Doppler Radar Data

Abstract During the intensive observing period of the field phase of the Coupled Ocean–Atmosphere Response Experiment (COARE) of the Tropical Oceans and Global Atmosphere (TOGA) program, airborne Doppler radars capable of fore–aft scanning (dual-Doppler analog) were involved in aircraft missions in which highly coordinated and parallel tusks were flown (quad-Doppler analog). Pairs of observations from each radar can be used to infer the wind components through an iterative dual-equation solution, while combining them allows a direct determination. Errors from these two analysis methods are discussed, in particular those induced from geometrical considerations. Due to these geometrical limitations, neither the dual-Doppler nor the quad-Doppler approach can take advantage of the whole volume sampling. To overcome the limitations and to increase considerably the synthesis domain, the overdetermined dual-Doppler (ODD) technique is proposed in an extended version (EODD). EODD includes solutions to these proble...

Volume Scanning Strategies for 3D Wind Retrieval from Dual-Doppler Lidar Measurements

Abstract Dual-Doppler lidar volume scans for 3D wind retrieval must accommodate the conflicting goals of dense spatial coverage and short scan duration. In this work, various scanning strategies are evaluated with semisynthetic wind fields from analytical solutions and numerical simulations over flat and complex terrain using the Multiple-Doppler Synthesis and Continuity Adjustment Technique (MUSCAT) retrieval algorithm. The focus of this study is to determine how volume scan strategies affect performance of the wind retrieval algorithm. Interlaced scanning methods that take into account actual maximum measurement ranges are found to be optimal because they provide the best trade-off between retrieval accuracy, volume coverage, and scan time. A recommendation for scanning strategies is given, depending on actual measurement ranges, the variability of the wind situation, and the trade-off between spatial coverage and temporal smoothing.

A Variational Correction Method as an Alternative to Forced Rejection of Sidelobe-Contaminated Bistatic Doppler Measurements

Abstract The problem of sidelobe contamination of bistatic apparent Doppler velocity measurements involved in a bistatic Doppler radar network is examined. So far in the context of 3D wind field analysis, by combining a traditional Doppler radar with one or more bistatic receivers, identification and hence removal of regions of high degrees of contamination were necessarily crucial steps to obtaining reliable wind fields. This study proposes an alternative solution to the forced rejection of bistatic Doppler data suspected to be contaminated by sidelobe echoes, on the basis of restoring the nonmeasured “actual” (i.e., noncontaminated) bistatic Doppler velocity from both monostatic radar and bistatic receiver measurements. The correction method is based on a modeled expression of the observed bistatic apparent Doppler velocity defined as the reflectivity-weighted average of actual Doppler velocity of particles within individual volume samples, including the antenna gain pattern of both transmitting and rec...