Due to their capabilities of measuring wind profiles in the troposphere and stratosphere with good time and height resolution, whatever the weather conditions, stratosphere-troposphere (ST) radars are well adapted to carry out atmospheric research in many fields as well as to fulfill the meteorological forecasting needs. Examples are presented from previous and future national or international campaigns planned in France. The ST radars were used first by themselves with the adjunction of radiosonde data. Then networks were built and used to get horizontal parameters. It appears that ST radar networks should naturally be included in cooperative campaigns

Crochet, M.

Petitdidier, M.

English

NASA Technical Reports Server

5.1.2
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N87-10480
SCIENTIFIC REASONS FOR A NETNORK OF ST RADARS AND COOPERATIVE CAMPAIGNS
M. Petitdidler
CRPE
4 Avenue de Neptune
94107 Saint Maur des Fosses Cedex, France
M. Crochet
LSEET
639 Boulevard des Amaris
83100 Toulon, France
INTRODU CT ION
Due to their capabilities of measuring wind profiles in the troposphere
and stratosphere with a good time and height resolution whatever are the
weather conditions, ST radars are well adapted to carry out atmospheric
research in many fields as well as to fulfill the meteorological forecasting
needs. That explains the development, all over the world, of such instruments.
The examples presented in this paper came from previous and future
national or international campaigns planned in France. The VHF ST radar
(Provence) from the LSEET participated in ALPEX 82, FRONTS 84 and MESO-GERS 84,
and a network of ST radars will take part in the FRONTS 87 campaign.
ST RADAR NE_JORK AND SCIENTIFIC CAMPAIGNS
Most of the scientific goals, which may be studied by ST radars, have been
already mentioned (LARSEN, 1983; ROPER, 1983_ FRITTS etal., 1984; GELLER,
1984). We may note:
-Even if a network of ST radars can operate by itself for dynamical
studies, complementary data are usually necessary for most scientific
investigations (radio soundings, microbarographs, precipitation radar,
satellite imeges...). Most of them are available but generally not obtained
at the same time or location.
-Even if one radar can contribute usefully to a campaign (cf FRONTS 84,
MESO-GERS 84), a minimum of 3 radars is required for most of the spat/o-
temporal investigations (horizontal extent and variations of the phenomena,
wave directions1 spectrum...).
So, the main difference between a research ST network working by itself
and integrated in a specific campaign is essentially the duration of the
experiment and the kind and number of instruments involved and working
simultaneously.
Table 1 gives a list of some scientific topics which may be studied during
specific campaigns involving the participation of other instruments in order to
get a global and detailed view of the phenomena under study. In the next sec-
tion, some examples of such campaigns are given.
These different topics impose the working characteristics of the ST radars
and their relative position and spacing in the network. The time resolution is
fixed by the expected time scales of the phenvmena under study and the height
resolution by their spatial scales and by the thickness of the turbulent layers
(10 - 300 m). In connection with sodars for boundary layer observations, the
lower altitude explored by the ST radar has to be less than 400 m; in
connection with balloons for stratospheric observations, the upper altitude has
to be higher than 12-15 km. The spacing of the radars acts as a filter in the
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horizontal scales involved. In ALPEX 82, for small horizontal scale (50 kin)
studies the spacing was about 5 kin, in FRONTS 87 for mesoscale studies, it will
be about I00 km.
PREVIOUS EXPERIFENTS
In France, some experience has been acquired during the last 3 years
concerning the integration of ST radar in scientific campaigns.
(I) During ALPEX 1982, 3 ST radars operated in the vertical mode in the
Rhone Delta (ECKLUND et al., 1983) as a result of a collaborative effort
between the Aeronomy Laboratory from NOAAand the LSEET (Toulon - France).
The main objective of the ST radar experiment was the study of short scale
gravity waves from vertical velocity measurements. These observations could
also contribute to the ALPEX objectives on Genova gulf cyclogenesis (B_UN et
al., 1985a) and local winds.
From this experiment, CARTER et al. (1984, 1985) determined the horizontal
wavelength, the phase velocity and the propagation direction of waves. Some
conclusions concerning this network are listed:
-The coherence between radar sites was very good while the coherence
between heights separated by more than 2 Pun was generally quite poor. That
does not permit a reasonable calculation of vertical wavelengths.
-With radar spacing of roughly 5 Ion, waves with horizontal wavelengths
less than I0 km could be aliased and appear to have longer wavelengths. Since
most observed waves had measured wavelengths around 10-20 km, it is possible
that some of these are eliased.
-The fact that only vertical observations were made, limited the waves
that could be detected to periods less than about 2 hr due to the weakness of
the vertical wind induced by the waves of greater periods.
(2) During FRONTS 84, in the southwest of France, a ST radar was
operating in the vertical mode during 2 months in coordination with other
instruments (RONSARD cm radar, RABelAIS mm radar, balloons, airplane, radio-
soundings, meteorological ground network .... ). The observations have been
focused in fronts and related phenomena, especially gravity waves, tropopause
breaks and coordinated observations of clouds and their surroundings by
different techniques.
Among all these instruments only the ST radar is able to provide
continuously wind profiles with a good height and time resolution whatever
the weather conditions (clouds or clear air, precipitation or not). In the
experiment FRONTS 84, the ST radar has been useful:
-Inside the storm, to extend the other radar observations at altitudes
higher than the ones observed with the precipitation radars;
-Outside the storm, to determine continuously the dynamical field and its
perturbations as a function of time and altitude;
-Due to the capability of VHF radar to get large echoes from the tropo-
pause level, to observe the behavior of the tropopause, its breaks.., and to
locate the breaks relative to the fronts (LARSEN and ROTTGER, 1982).
Sometimes, waves associated with a front have been detected. As an
example, on June 3, 1985, a wave of about 40 mln period is observed during
several hours (BRUN, personal communication).
The comparison between these different sets of data has just begun.
(3) During MES0-GERS 84, with general objectives related to the boundary
layer studies and orographic effects, the ST radar was operating in the
vertical mode down to the altitude of 1.2 km to complement and extend sodar
observations.
320
The main studies which will be carried out with the sodars and ST radar
concern gravity waves and the relationship between surface stress and
convergence or divergence effects associated with mesoscale systems.
Particularly, with ST radar, it is possible to point out if the energy is
propagating upward or downward and also to observe the entrainment effect
associated with an inversion layer when it takes place at an altitude too high
for sodars.
As the upper limit of the boundary layer has a diurnal variation and also
varies with meteorological perturbations in the altitude range of 0.5 to i kin.
it will be suitable for a ST radar to be able to observe at least down to 400
mo
In this campaign, various interesting events occurred: "Hortense"
hurricane, different kinds of frontal systems and fair weather conditions. ST
radar data are needed to interpret them in a more complete way. This variety
of phenomena is a good opportunity to estimate the contribution of ST radar to
boundary layer physics.
(4) In 1984, two campaigns involving balloon experiments and ST radars
took place. In the first one, which involved the 430-MHz radar of Arecibo, the
payload consisted of a thermistor and a sonic anemometer (THOMAS et al., 1985,
1986). In the second experiment, which involved the VHF ST radar from LSEET
during FRONTS 84, the payload consisted of a thermistor and an ionic anemometer
(DALAUDIER et al., 1985, 1986).
In these cooperative experiments, the radar observations give the temporal
variation of wind profiles and turbulent layers while balloon measurements
provide the fine structure of wind and temperature profiles. These
simultaneous in situ and remote experiments are important for a better
description of the dynamical and thermal structure of the atmosphere (DALAUDIER
et al., 1985, 1986; THOMAS et al., 1985, 1986) and also for a better
understanding of the physical mechanisms producing the clear-air radar echoes
(DALAUDIER et al., 1985, 1986).
(5) In conclusion, the preliminary results already obtained show the
interest of ST radar in cooperative campaigns for a better understanding of
some meteorological problems. Each of these experiments has been very
instructive but none was really satisfactory: only the vertical wind was
measured, only one radar was working during FRONTS 84 and }_SO-GERS 84, and
during ALPEX 82 the Rhone delta was not always documented by other techniques.
Then taking into account all of these arguments, the use of ST radar will be
optimized in other campaigns. A more comprehensive experiment is planned in
1987 with a network of 3 ST radars operating both on the vertical and horizon-
tal components of the wind.
A PLANNED EXPERI_NT - FRONTS 87
FRONTS 87 is a French - U.K. campaign which will take place in France aud
D.K. on both sides of the Channel from October to December 1987. Its
scientific goal is the study of active cold fronts in a nearly flat zone. The
objectives are:
-To acquire mesoscale data sets concerning dynamics, thermodynamics and
microphysics. The network of ST radars with a spacing of about I00 km will
provide wind vector profiles, the altitude of the tropopause, the mesoscale
flow, its horizontal gradient and divergence or convergence;
-To acquire continuous data sets in order to get the three-dimensional
structure of the front and its enviroement under some stationary assumptions.
321
The instruments participatin 8 in this campaign will be: ground-based
meteorological networks, radiosondes at 3-hr intervals, aircraft dropsondes to
produce profiles of temperature, humidity and wind, aircraft in situ
observations equipped to carry out dynamical, thermodynamical and microphysical
measurements, cm and mm radars, Doppler acoustic radars, lidar...and also
images from Meteosat and NOAA satellites.
The network of ST radars is one of the first priority of this experiment.
For this purpose and future scientific campaigns, a network of ST radars are
under study (PETITDIDIER et el., 1986).
CONCLHSION
These examples point out an evolution in the use of ST radars for
dynamical studies. At first, they have been workin 8 by themselves with the
adjunction of radiosonde data. Then networks have been built or under study
and have been used to get horizontal parameters. From now, it appears that ST
radar networks will be neturelly included in cooperative campaigns. Only
national or international scientific campaigns are able to conduct simultane-
ously all the experiments necessary to obtain an overview of a specific topic.
REFER_CES
Brun, E., M. Crochet, S. V. Venkateswaran, B. B. Belsley, and W. Ecklund
(1985a), ST radar observations of Genoa gulf cyclone durin 8 ALPEX, submitted
to J. Clim. App1. Meteorol.
Carter, D. A., B. B. Balsleyo W. L. Ecklund, M. Crochet, A. C. Riddle, and R.
Garello (1984), Tropospheric gravity waves observed by three closely spaced
ST radars, Handbook for MAP, Vol. 14, 219-228, SCOSTEP Secretariat, Dep.
Elec. Computer Eng., Univ. Ill, Urbane-Champaign.
Carter, D. A., B. B. Balsleyo W. Ecklund, M. Crochet, A. C. Riddle, and R.
Garello (1985), Tropospheric gravity waves observed by three closely spaced
ST radars, Handbook for MAP, Vol. 18, 260-263, SGOSTEP Secretariat, Dep.
Elec. Computer Eng., Univ. Ill, Urbane-Champaign.
Dalaudier, F., J. Barat, F. Bertin, E. Brun, M. Crochet, and F. Cuq (1985),
Comparison between ST radar and in situ measurements, Proc. 7th ESA Syrup.
European Rocket and Balloon Programmes, 247-251.
Dalaudier, F., J. Beret, F. Bertin, E. Brun, M. Crochet, and F. Cuq (1986),
Comparison between ST radar and in situ measurements, this volume.
Ecklund, W. L., B. B. Belsley, D. A. Carter, A. C. Riddle, M. Crochet, and R.
Garello (1983), Observations of vertical motions in the troposphere and
lower stratosphere using three closely spaced ST radars, Edmonton, Atlanta -
Canada, to be published in Radio Sci.
Fritts, D. C., M. A. Geller, B. B. Ealsley, M. L. Chanin, I. Hirota, J. R.
Holton, S. Kato, R. S. Lindzen, M. R. Schoeberl, R. A. Vincent, and R. F.
Woodman (1984), Research status and recommendations from the Alaska Workshop
on gravity waves and turbulence in the middle atmosphere - Falrbanks,
Alaska, Bull. Am. Meteorol. Soc. 65, 149-159.
Geller, M. A. (1984), Meteorological and aeroncmical requirements for MST radar
network, Handbook for MAP, Vol. 14, I-4, SCOSTEP Secretariat, Dep. Elec.
Computer Eng., Univ. Ill, Urbane-Champaign.
Larsen, M. F. (1983), The MST radar technique: Requirements for operational
weather forecasting, Handbook for MAP, Vol. 9, 3-11.
Larsen, M. F. and J. Rottger (1982), VHF and UHF Doppler radars as tools for
synoptic research, Bull. Am. Meteorol. Sot., 63, 996-1007.
Petitdidier M., V. Klaus, F. Baudin, M. Crochet, G. Penazzi, and P. Quinty
(1986), The INSU and DMN networks of ST radars, this volume.
Roper, R. G. (1983)o Metecrological and dynamical requirements for MST radar
networks, Handbook for MAP, Vol. 9, 1-2, SCOSTEP Secretariat, Dep. Elec.
Computer Eng., Univ. Ill, Urbane-Champaign.
322
Thomas, B. F., F. Eertin, M. Petitdidier, H. Teitelbaum. and R. F. Woodman
(1985), Simultaneous fine structure observation of wind and temperature
profiles by the Arecibo 430 MHz radar and in sltu measurements, Proc. 7th
ESA Symp. European Rocket and Balloon Proarammes, 381-384.
Thomas, D., F. Bertin, M. Petitdidier, H. Teitelbaum, and R. F. Woodman (1986),
Simultaneous fine structure observation of wind and temperature profiles by
the Arecibo 430 MHz radar and in situ measurements, this volume.


Scientific reasons for a network of ST radars and cooperative campaigns

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