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Detailed Flow, Hydrometeor and Lightning Characteristics of An Atmos. Chem. Phys., 12, 6679–6698, 2012 www.atmos-chem-phys.net/12/6679/2012/ Atmospheric doi:10.5194/acp-12-6679-2012 Chemistry © Author(s) 2012. CC Attribution 3.0 License. and Physics Detailed flow, hydrometeor and lightning characteristics of an isolated thunderstorm during COPS K. Schmidt1, M. Hagen1, H. Holler¨ 1, E. Richard2, and H. Volkert1 1Deutsches Zentrum fur¨ Luft- und Raumfahrt (DLR), Institut fur¨ Physik der Atmosphare,¨ Oberpfaffenhofen, Germany 2Laboratoire d’Aerologie,´ CNRS and Universite´ de Toulouse III, Toulouse, France Correspondence to: K. Schmidt ([email protected]) Received: 2 March 2012 – Published in Atmos. Chem. Phys. Discuss.: 16 April 2012 Revised: 5 July 2012 – Accepted: 13 July 2012 – Published: 1 August 2012 Abstract. The three-hour life-cycle of the isolated thun- gence line eventually removed the convective inhibition and derstorm on 15 July 2007 during the Convective and set deep convection in motion. A shear line in the radial ve- Orographically-induced Precipitation Study (COPS) is docu- locity relative to the Feldberg radar site shows good agree- mented in detail, with a special emphasis on the rapid devel- ment beween observation and simulation, whereas the onset opment and mature phases. Remote sensing techniques as 5- location of deep convection exhibits a horizontal discrepancy min rapid scans from geostationary satellites, combined ve- of 15 km. A quantitative schematic of the isolated thunder- locity retrievals from up to four Doppler-radars, the polari- storm synthesizes all retrieved characteristics. metric determination of hydrometeors and spatio-temporal occurrences of lightning strokes are employed to arrive at a quantification of the physical parameters of this, during the COPS period, singular event. 1 Introduction Inner cloud flow fields are available from radar multi- ple Doppler analyses at four consecutive times separated by Thunderstorms constitute an archetype of a fierce meteoro- 15 min-intervals. They contain horizontal winds of around logical event accompanied by a fleet of potential dangers, e.g. 15 m s−1 and updrafts exceeding 5 m s−1, the latter collo- severe gusts, high precipitation rates, large hail, and light- cated with lightning strokes. Reflectivity and polarimetric ning. Within thunderstorms the vertical motion – updrafts data indicate the existence of hail at the 2 km level around and downdrafts subsumed under the term convection – often 14:40. Furthermore, polarimetric and Doppler radar variables attains similar magnitudes as the horizontal wind or advec- indicate intense hydrometeor variability and turbulence cor- tion, rather than remaining two orders of magnitude smaller responding to an enhanced variance of the retrieved 3-D wind as under ordinary circumstances. In mid-latitudes, thunder- fields. Profiles of flow and hydrometeor statistics over the en- storms are often connected to dynamically active frontal tire cloud volume provide reference data for high-resolution zones of cyclones or they develop in isolation when atmo- numerical weather prediction runs in research mode. spheric conditions favour their initiation, especially on hot The study embarks from two movie-loops of geostationary summer days. The latter category exhibits a typical life cy- satellite imagery (as Supplement), which provide an intuitive cle, for which three phases can be distinguished (Cotton and distinction of six phases making up the entire life-cycle of Anthes, 1989, p. 456): the initiation of convection by sur- the thunderstorm. It concludes with a triple-image loop, jux- face heating and horizontal convergence at a variety of loca- taposing a close-up of the cloud motion as seen by Meteosat, tions becomes marked by towering cumulus clouds; the ma- simulated brightness temperature (as a proxy for clouds seen ture stage sees the merger of several cumulus elements into by the infrared satellite channel), and a perspective view on a large convective system with the formation of various hy- the model generated system of cloud cells. The simulation drometeors, the occurrence of lightning discharges compen- suggests that several updrafts fed from a low level conver- sating previous charge separations, and the onset of precipi- tation; during the dissipating phase downdrafts prevail in the Published by Copernicus Publications on behalf of the European Geosciences Union. 6680 K. Schmidt et al.: Flow, hydrometeor and lightning characteristics of a thunderstorm storm’s lower part and block convective energy being further graupel volume, updraft volume and updraft mass flux (e.g. fed into the storm. Kuhlman et al., 2006). Others relate observations of light- The quantitative documentation of a thunderstorm’s ning rate to hydrometeor content (Fehr et al., 2005; Deierling life cycle was among the objectives of the Convective et al., 2008) or to updraft motion (Deierling and Petersen, and Orographically-induced Precipitation Study (COPS; 2008). Wulfmeyer et al., 2011), which had its field phase from June During the three months of the COPS field phase it to August 2007 over an area in central Europe which cov- was only during intensive observation period (IOP) 8b on ers the region of Vosges, Rhine valley and Black Forest in 15 July 2007 that an isolated, strong and high reaching, eastern France and south-western Germany. The provision of though short-lived thunderstorm developed just east of the datasets concerning the airflow, the hydrometeor distribution crest line of the Black Forest – much in contrast to the hopes and lightning locations with an appropriate spatial and tem- of the large international team in the field that they can probe poral resolution complements previous surveys (e.g. Brown- a number of such isolated as well as very pronounced sys- ing and Ludlam, 1962; Holler,¨ 1994; Lang and Rutledge, tems, and to old popular wisdom about the peculiarity of the 2002) and constitutes an important ingredient for the ongoing region (“... but a Black Forest thunderstorm is not an ordinary development of high resolution numerical weather prediction circumstance”; Jerome, 1900, p. 168). Let us first seek an models and quantitative precipitation forecasts (e.g. Richard overview of the overall development through a movie-loop et al., 2011). obtained from satellite imagery. Multiple-Doppler-analyses integrate data from several Since the launch of the Meteosat Second Generation geo- Doppler-radars and reveal the flow components during the stationary satellite series in 2004 with its multi-channel mature phase after the onset of precipitation, i.e. when suffi- “spinning enhanced visible and infra-red imager” (SEVIRI; cient backscattering particles are available. Additionally, in- Aminou, 2002), the update rate of one image every 15 min dependent polarization measurements in two perpendicular in normal mode and every 5 min in rapid scan mode pro- planes allow the discrimination of various hydrometeors. In vides the opportunity to inspect in detail cloud motions as a pioneering study, Wakimoto and Bringi (1988) mapped a time-lapse movie-loops. From data of the experimental rapid highly dynamical thunderstorm and the induced microburst scans executed during COPS, three channel overview images on 20 July 1986 over Alabama (USA), inter alia by superpos- were produced on a stereographic weather-map-projection. ing the visual external appearance of the cloud system (pho- The COPS area’s circumference is dotted with 10◦ E as east- tos) with its internal reflectivity structure. Tuttle et al. (1989) ern boundary; it contains in its western half the Vosges and extended the analysis to polarimetric parameters and com- Black Forest mountains separated by south-north extending parisons with a two-dimensional cloud model. Frame et al. upper Rhine valley. Two loops are provided as Supplement (2009) combine Doppler- and polarimetric analyses for a su- to give an intuitive awareness of the horizontal dimensions percell thunderstorm on 23 May 2002 during the IHOP cam- and the duration of the thundercloud development as well paign, whereas Chong et al. (2000) systematically retrieved as its relation to other cloud systems during 15 July 2007: from dual-Doppler radar data orographically disturbed flows (i) an overview for western and central Europe concatenat- at the southern flank of the Alps during the special observing ing 145 images (movie1.mpg) between 06:00 and 18:00 (all period of the Mesoscale Alpine Programme in autumn 1999 times in UTC) with a nominal display speed of 14 frames including an adequate determination of the vertical motion. per second (4,200-fold speed-up), and (ii) a close up for the Also Matejka and Barthels (1998) had investigated the accu- wider COPS region consisting of 97 images between 10:00 racy of vertical motion obtained from radar measurements, and 18:00 (movie2.mpg) at half the speed (7 fps; 2,100-fold while variational refinements of the retrieval technique are speed up). more recent (Shapiro et al., 2009; Lim and Sun, 2010). Dolan These are considered as the overall features of the event, and Rutledge (2007) presented an integrative tool for the which provide the frame for the detailed data analyses of this analysis and display of multivariate radar data. As its oper- study: (i) well ahead of a frontal cloud band across France ational application in Europe is currently limited to special small cumulus clouds develop around 12:00 only over the regions (Bousquet et al., 2008), dedicated experimental cam- mountains of the Vosges, the Black Forest and the Alps; paigns, like COPS, are still necessary for principal case stud- (ii) the formation of a nearly contiguous, 100-km-long cloud ies. line over the eastern slopes of the Black Forest by 13:00; Lightning strokes are among the most spectacular meteo- (iii) the gradual enhancements of the cloud line’s southern rological phenomena of local extent and, as a physical pro- and northern portions until 14:00; (iv) the sudden vertical cess, possess a long tradition of detailed investigation (e.g. development at the middle location at 14:30, which induces Wilson, 1921).
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