4D HighResolution Analysis from Doppler Radars during IOP2a
Pierre Tabary and Georges Scialom, Centre d''etude des Environnements Terrestre et Plan'etaires, 1012 Av. de
l'Europe, 78140 V'elizy, France. tabary@cetp.ipsl.fr
Introduction
Using data from the three radars (Ronsard / CETP / France, Monte Lema / MeteoSwiss / Switzerland, SPOL / NCAR
/ USA) located in the Lago Maggiore Target Area (see Binder et al. (1999)), a fourdimensional highresolution
description of the intense convective system observed during IOP2a (1718 September 1999) has been carried out.
The retrieved fields are the 3D wind and composite reflectivity fields and the simultaneous lightning impacts.
The description runs from 17 September 1400 UTC until 18 September 1999 0200 UTC, which corresponds to
the whole lifecyle of the convective system. The resulting horizontal crosssections, every 1000 m from 1000 m
up to 11000 m above sea level, showing reflectivity (colored isolines), horizontal wind (arrows), lightning impacts
(white diamonds) and topography (black and white isolines) have been posted at the MDC where they can be
downloaded as gifformatted images.
Data used
The data used to describe the 4D structure of the IOP2asquall line are mainly the data from the French C
band Doppler Ronsard radar, Swiss Cband operational Doppler Monte Lema radar and US Sband Doppler /
polarimetric SPOL radar. The Monte Lema and the Ronsard radars performed synchronous (synchronization
time = 15 minutes) PPI's volumetric sequences, whereas the SPOL performed independent RHI's / PPI's in
specific azimuthal sectors. Prior to any further processing of the data, a preliminary phase was necessary to
crossvalidate the different data sets. The composite reflectivity shown in the crosssections is simply calculated
as the maximum of the three values measured by Ronsard / Monte Lema / SPOL, in order to minimize the
possible effects of attenuation (especially at Cband). The lightning impacts data are extracted from the high
resolution, online available ALDIS data set built up by Dr. Manfred Dorninger.
Analysis method
The method we used to retrieve the 3D wind field in precipitating areas is named MANDOP (Multiple ANalytical
DOPpler) and is extensively described in Tabary and Scialom (2000). The three wind components are expressed
in analytical form and the coefficients of expansion are retrieved through a least square fit to the radial velocity
measurements. Additional physical constraints are included in the analysis such as the anelastic continuity con
straint, the bottom freeslip boundary condition and a weak ''w=0'' constraint at the top of reflectivity echoes.
The method has been extensively tested and validated with simulated and real data in Tabary and Scialom (2000).
The description covers the period 17 September 1999 1400 UTC 18 September 1999 0200 UTC, which cor
responds to the whole lifecycle of the convective system, including initiation over the windward slopes of the
Alpine barrier, southwestnortheast organization, southeastward displacement and decay. The time window for
each analysis is 10 minutes and the frequency is 30 minutes. The analysis domain sizes are respectively 250, 250
and 12 km along the SouthNorth, WestEast and vertical axes and the corresponding grid meshes are 2, 2 and
0.5 km. Figure 1 is an illustration of a blackandwhite version of the available crosssections.
Those images can be downloaded at www.map.meteoswiss.ch. Do not hesitate to contact the authors if you need
further information or additional crosssections (e.g. vertical crosssections).
This short note is a very preliminary and condensed version of a soontobe submitted paper.
Acknowledgements: the authors would like to thank Dr. Urs Germann and Dr. Bob Rilling for their assistance
concerning the Monte Lema / SPOL radar data.
Figure 1: A blackandwhite version of the online available images corresponding to 22.35 UTC 17
September 1999 at z=1000 m asl. The topography (m) is represented by isolines of increasing thickness
every 500 m, the reflectivity field (dBZ) by greyshaded isolines every 3 DBZ, the horizontal wind (m.s
been superimposed in the
reflectivity patterns to delineate the 30 dBZregion. Also shown are some of the instruments of LMTA:
French Cband Ronsard radar (RSD), Swiss Cband Monte Lema radar (MLA), American Sband SPOL
radar (SPL), Italian Cband Spino radar (SPN), American Sband OPRA VPR (OPRA), Swiss Xband
VPR (ETHX), INSU / M'et'eoFrance UHF / VHF wind profileurs (ST), MilanoLinate sounding station
(MLT). Noticeable are the very high ligthning impact density and the strong convergence around the
reflectivity cores.
References
Binder, P., A. Rossa, P. Bougeault, J. Moore, D. Jorgensen, and M. Bollinger, 1999: MAP Implementation Plan,
version 4.1. Available upon request at MAP Data Centre, ETH Zürich, Switzerland. Tabary, P., and G. Scialom, 2001: MANDOP analysis over complex orography in the context of the MAP
Experiment, J. Atmos. Oceanic Technol., to appear.
