Cut-off low monitoring by the French VHF-ST-radar network during the ESTIME campaign

Caccia, Jean-Luc; Bertin, F.; Campistron, Bernard; Klaus, V.; Pointin, Y.; Baelen, Joël Van; Wilson, Richard

doi:10.1016/s1364-6826(00)00045-6

Cited by 9 publications

(14 citation statements)

References 32 publications

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“…Other radar parameters may also be used as supplementary diagnostics of tropopause folds. These include horizontal wind shear and spectral width (Vaughan and Worthington, 2000;Reid and Vaughan, 2004), horizontal wind speeds (Rao et al, 2008) and aspect sensitivity (Caccia et al, 2000;Bertin et al, 2001). Horizontal winds from the radar are unavailable in the UTLS, so the tropopause detection algorithm used here combines radar echo power with winds from ERA-Interim (Dee et al, 2011).…”

Section: Tropopause Relation To Mesoscale Meteorologymentioning

confidence: 99%

High resolution VHF radar measurements of tropopause structure and variability at Davis, Antarctica (69° S, 78° E)

2013

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Abstract. Two years of Very High Frequency (VHF) radar echo power observations are used to examine the structure and variability of the tropopause at Davis, Antarctica. Co-located radiosonde and ozonesonde launches provide data with which to calculate the lapse-rate and chemical tropopauses. The radar tropopause, defined as the maximum vertical gradient of echo return power, can be used as a definition of the Antarctic tropopause throughout the year under all meteorological conditions. During the extended summer period of December–April (DJFMA) inclusive, radar tropopauses are (0.2 &pm; 0.4) km lower than radiosonde lapse-rate (i.e. the World Meteorological Organisation – WMO) tropopauses and during the extended winter period of June–October (JJASO) inclusive, the radar tropopauses are (0.8 &pm; 1.0) km lower. A potential vorticity tropopause is defined as the altitude of the −2 PVU surface (where 1 PVU = 106 m2 s−1 K kg−1). This is (0.3 &pm; 0.5) km lower than the radar tropopause during DJFMA and (0.5 &pm; 1.0) km lower during JJASO. The radar, potential vorticity and ozone tropopauses decrease in altitude during increasingly strong cyclonic conditions, in contrast to the radiosonde WMO tropopause which remains nearly constant. During strong JJASO cyclonic conditions, there are large (several km) differences between WMO tropopause altitudes and radar tropopause altitudes. A seasonal cycle in tropopause fold occurrence is observed, with approximately a three-fold increase during JJASO.

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Section: Tropopause Relation To Mesoscale Meteorologymentioning

confidence: 99%

High resolution VHF radar measurements of tropopause structure and variability at Davis, Antarctica (69° S, 78° E)

2013

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“…Caccia and Cammas (1998) propose a monitoring of the folds and cutoff lows, in which the air masses of stratospheric origin (with high static stability) are defined by AR > 3. This method is used in Caccia et al (2000) for analyzing three cooperative campaigns involving the French radar network and discriminate between stratospheric and tropospheric air masses.…”

Section: Detection By the Ohp Vhf St Radar And Raman Lidarmentioning

confidence: 99%

“…Three papers about the results obtained during these campaigns have already been published: the first one (Campistron et al, 1999) studies the aspect sensitivity of VHF radar echoes obtained during the passage of a cutoff low by the Lannemezan radar; the second one (Ravetta et al, 1999) compares the temperature and wind field measurements obtained in the Haute Provence Observatory in a tropopause fold with a mesoscale model; the third one (Caccia et al, 2000) assesses the monitoring of cutoff lows and tropopause folds by the aspect ratio derived from the radar measurements. The present contribution is aimed to compare during a tropopause fold event the results obtained by the VHF radar, UHF radar, ozone and temperature lidar with the European Center for Medium-Range Weather Forcasting (ECMWF) model outputs, in order to better understand: (i) the physics of the radar measurements, (ii) the mechanisms involved in the turbulence onset along the fold borders and at the tropopause level, possibly giving rise to air mass exchanges between the troposphere and the stratosphere.…”

Section: Introductionmentioning

confidence: 99%

Mixing processes in a tropopause folding observed by a network of ST radar and lidar

Bertin¹,

Campistron²,

Caccia³

et al. 2001

Ann. Geophys.

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Abstract.A campaign devoted to stratosphere-troposphere exchange mechanisms studies has been held on 4-5 March 1995, during a tropopause folding passage over western Europe. The observational network included 1 UHF and 3 VHF radar, 1 temperature lidar, and 1 ozone lidar, deployed in the south of France. The fold is associated with a strong quasi meridional jet stream running along the west side of an upper level trough forming a potential vorticity (PV ) anomaly. During this campaign, the PV anomaly is advected eastwards without major deformations, with an average velocity of about 30 km per hour. Therefore, a frozen field hypothesis has been used in order to compare the results obtained in the different sites of the network. Under this hypothesis, the same structures associated with the anomaly are observed by each radar or lidar, at the same time relative to this anomaly. The fold is put into evidence by the ozone lidar of the network and by the VHF radars when computing the aspect ratio. The turbulent activity observed by the OHP VHF radar and by the high resolution UHF PROUST radar (30 m altitude resolution) is concentrated in the wind shear regions generated by the jet stream above and below its axis. In the lower level wind shear, turbulent layers are detected within the fold and across its anticyclonic boundary, thus allowing turbulent exchanges with the tropospheric air masses. A large area of aspect ratio greater than 3 is observed in the troposphere during more than ten hours after the passage of the fold by the VHF radars. This particular signature is tentatively analyzed as the progressive dilution of air masses of stratospheric origin extruded from the fold by the turbulent processes. In the upper level wind shears, turbulent layers parallel to the wind isotachs are observed, whose thickness is often smaller than 100 m and are separated by non turbulent regions. A good correlation is found between the spatiotemporal evolution of these turbulent structures observed by the PROUST radar, and the stability structures observed at the same relative time by the temperature lidar. In addition the same turbulent structures are observed to be parallel to Correspondence to: F. Bertin (francois.bertin2@wanadoo.fr) the iso-phase lines of the wind fluctuations, observed at the same relative time by the Lannemezan radar. These characteristics are compatible with the presence of unstable inertiagravity waves, generated by the jet stream while the turbulent layers could be the signature of their saturation processes.

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“…Vaughan and Worthington (2000) reconstructed the scenario of a tropopause fold event and could detect the intrusion of the stratospheric air masses due to the stability measurements with the Aberystwyth VHF radar. Caccia et al (2000) also reported that stability measurements by ST radars are useful for the detection of cut-off low events characterized by potential vorticity anomalies.…”

Section: Stability Measurementsmentioning

confidence: 98%

“…Gage and Green, 1978;Gage et al, 1985;Tsuda et al, 1988;Chu et al, 1990;May et al, 1991), an ST radar is, therefore, a useful tool for the detection of the tropopause and fronts (e.g. recently Hooper and Thomas, 1995;Caccia and Cammas, 1998;Campistron et al, 1999;Vaughan and Worthington, 2000;Caccia et al, 2000). However, because the associated echo layers are not always aspect sensitive, the relationship between aspect sensitivity and stability is not direct.…”

Section: Stability Measurementsmentioning

confidence: 99%

Temperature sheets and aspect sensitive radar echoes

Luce

Crochet

Dalaudier³

2001

Ann. Geophys.

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Abstract. There have been years of discussion and controversy about the existence of very thin and stable temperature sheets and their relationship to the VHF radar aspect sensitivity. It is only recently that very high-resolution insitu temperature observations have brought credence to the reality and ubiquity of these structures in the free atmosphere and to their contribution to radar echo enhancements along the vertical. Indeed, measurements with very highresolution sensors are still extremely rare and rather difficult to obtain outside of the planetary boundary layer. They have only been carried out up to the lower stratosphere by Service d'Aéronomie (CNRS, France) for about 10 years. The controversy also persisted due to the volume resolution of the (Mesosphere)-Stratosphere-Troposphere VHF radars which is coarse with respect to sheet thickness, although widely sufficient for meteorological or meso-scale investigations. The contribution within the range gate of many of these structures, which are advected by the wind, and decay and grow at different instants and could be distorted either by internal gravity waves or turbulence fields, could lead to radar echoes with statistical properties similar to those produced by anisotropic turbulence. Some questions thus remain regarding the manner in which temperature sheets contribute to VHF radar echoes. In particular, the zenithal and azimuthal angular dependence of the echo power may not only be produced by diffuse reflection on stable distorted or corrugated sheets, but also by extra contributions from anisotropic turbulence occurring in the stratified atmosphere. Thus, for several years, efforts have been put forth to improve the radar height resolution in order to better describe thin structures. Frequency interferometric techniques are widely used and have been recently further developed with the implementation of high-resolution data processings. We begin by reviewing briefly some characteristics of the ST radar echoes with a particular emphasis on recent works. Their possible coupling with stable sheets is then presented and their known characteristics are described with some hypotheses concernCorrespondence to: H. Luce (luce@kurasc.kyoto-u.ac.jp) ing their generation mechanisms. Finally, measurement campaigns that took recently place or will be carried out in the near future for improving our knowledge of these small-scale structures are presented briefly.

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Cut-off low monitoring by the French VHF-ST-radar network during the ESTIME campaign

Cited by 9 publications

References 32 publications

High resolution VHF radar measurements of tropopause structure and variability at Davis, Antarctica (69° S, 78° E)

High resolution VHF radar measurements of tropopause structure and variability at Davis, Antarctica (69° S, 78° E)

Mixing processes in a tropopause folding observed by a network of ST radar and lidar

Temperature sheets and aspect sensitive radar echoes

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