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Thibaut Montmerle
and
Yvon Lemaître Lemaître

Abstract

The present study is devoted to a new analysis of wind measurements from dropsonding and/or radiosonding of Doppler information from multiple Doppler radar scanning and of other wind measurements (sodar, dynamical sensors on board aircraft, and instruments at ground) aimed at retrieving three-dimensional thermodynamical and dynamical fields both in clear air and in precipitating areas of mesoscale phenomena. This analysis, well suited to assimilate data from differing platforms specified at differing spatial/temporal resolutions, is based on the analytical and variational concept of the Multiple Analytical Doppler (MANDOP) analysis and thus is an extension of it. This new analysis presents many advantages, including the same as MANDOP and others well adapted for the verification or the initialization of a mesoscale cloud model. An application to simulated and to real data extracted from the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment database is presented in the paper.

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Georges Scialom
and
Yvon Lemaître

Abstract

The present study is devoted to a new analysis of the Doppler information from multiple Doppler radar scannings aimed at studying the three-dimensional wind field at mesoscale. This analysis referred to as MANDOP (for Multiple ANalytical DOPpler) is mathematically described. An application of the method to simulated and to real data is also presented in the paper, including a comparison with VAD and DVAD analyses and with observations from radiosoundings and sodar. The method consists in expanding the three wind components in terms of orthonormal functions. Physical constraints, such as the boundary condition at ground level and the continuity equation, are included in the analysis as variational constraints in order to improve the vertical component retrieval. Solving the resulting linear system provides the coefficients for the analytical expansion of the wind. Thus, the wind, as well as its derivatives and associated physical parameters (e.g., vorticity, pressure, and temperature perturbations) may be expressed with an analytical form.

The data of any number of radars (at least two) may be analyzed simultaneously without reformulating the problem. When only one radar is available, the coefficients retrieved without ambiguity are provided by the method.

Application of MANDOP analysis to real data requires that the time-induced advection problem is solved. This aspect is also addressed in the paper. The solution of this problem benefits from the analytical formulation of the wind.

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Jean-François Rysman
,
Yvon Lemaître
, and
Emmanuel Moreau

Abstract

This study describes the main patterns of rainfall distribution in the Alps–Mediterranean “Euroregion” using a ground radar and characterizes the associated processes using model output. The radar dataset spans 2009–12 with fine spatial (1 km) and temporal (5 min) resolutions. The most significant rain accumulations were observed in 2009 and 2010, and the most intense extreme events occurred in 2010. Conversely, 2012 was a dry year. Model output revealed that the wind shear, the pressure, and the meridional wind at low level were the three main factors explaining the rainfall variability between 2009 and 2012. At the monthly scale, the maximum of rain accumulation was observed in November along the coast. Results also showed that the most intense rain rates were observed during early summer and autumn in the “Pre-Alps.” The monthly variability was characterized by a displacement of extreme rain events from land to sea from late spring to winter. Correlation analyses showed that this displacement was essentially controlled by the convective available potential energy (CAPE). Rainfall showed a diurnal variability from April to August for the land areas of the Alps–Mediterranean Euroregion. The diurnal variability was significant during the spring and summer months, with maximal rain intensity between 1600 and 1800 UTC. The correlation of the rainfall with CAPE showed that this cycle was related to atmospheric instability. A secondary peak in average rain rate was observed during the early morning and was likely triggered by land breezes. The results highlighted that rainfall characteristics are extremely diverse in terms of intensity and distribution in this relatively small region.

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Olivier Caumont
,
Véronique Ducrocq
,
Guy Delrieu
,
Marielle Gosset
,
Jean-Pierre Pinty
,
Jacques Parent du Châtelet
,
Hervé Andrieu
,
Yvon Lemaître
, and
Georges Scialom

Abstract

A full radar simulator for high-resolution (1–5 km) nonhydrostatic models has been developed within the research nonhydrostatic mesoscale atmospheric (Meso-NH) model. This simulator is made up of building blocks, each of which describes a particular physical process (scattering, beam bending, etc.). For each of these blocks, several formulations have been implemented. For instance, the radar simulator offers the possibility to choose among Rayleigh, Rayleigh–Gans, Mie, or T-matrix scattering methods, and beam bending can be derived from an effective earth radius or can depend on the vertical gradient of the refractive index of air. Moreover, the radar simulator is fully consistent with the microphysical parameterizations used by the atmospheric numerical model.

Sensitivity experiments were carried out using different configurations for the simulator. They permitted the specification of an observation operator for assimilation of radar reflectivities by high-resolution nonhydrostatic numerical weather prediction systems, as well as for their validation. A study of the flash flood of 8–9 September 2002 in southeastern France, which was well documented with volumetric data from an S-band radar, serves to illustrate the capabilities of the radar simulator as a validation tool for a mesoscale model.

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Alain Joly
,
Dave Jorgensen
,
Melvyn A. Shapiro
,
Alan Thorpe
,
Pierre Bessemoulin
,
Keith A. Browning
,
Jean-Pierre Cammas
,
Jean-Pierre Chalon
,
Sidney A. Clough
,
Kerry A. Emanuel
,
Laurence Eymard
,
Robert Gall
,
Peter H. Hildebrand
,
Rolf H. Langland
,
Yvon Lemaître
,
Peter Lynch
,
James A. Moore
,
P. Ola G. Persson
,
Chris Snyder
, and
Roger M. Wakimoto

The Fronts and Atlantic Storm-Track Experiment (FASTEX) will address the life cycle of cyclones evolving over the North Atlantic Ocean in January and February 1997. The objectives of FASTEX are to improve the forecasts of end-of-storm-track cyclogenesis (primarily in the eastern Atlantic but with applicability to the Pacific) in the range 24 to 72 h, to enable the testing of theoretical ideas on cyclone formation and development, and to document the vertical and the mesoscale structure of cloud systems in mature cyclones and their relation to the dynamics. The observing system includes ships that will remain in the vicinity of the main baroclinic zone in the central Atlantic Ocean, jet aircraft that will fly and drop sondes off the east coast of North America or over the central Atlantic Ocean, turboprop aircraft that will survey mature cyclones off Ireland with dropsondes, and airborne Doppler radars, including ASTRAIA/ELDORA. Radiosounding frequency around the North Atlantic basin will be increased, as well as the number of drifting buoys. These facilities will be activated during multiple-day intensive observing periods in order to observe the same meteorological systems at several stages of their life cycle. A central archive will be developed in quasi-real time in Toulouse, France, thus allowing data to be made widely available to the scientific community.

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