EGU General Assembly Vienna 4 10 April 2011

EGU General Assembly Vienna, 4 -10 April 2011 On the observation of unusual high concentration of chain-like aggregates of small ice crystals near the top of a deep convective system during the CIRCLE-2 experiment Jean-François Gayet(1), Guillaume Mioche(1), Luca Bugliaro(2), Andreas Minikin(2), Martin Wirth(2), Andreas Dörnbrack(2), Bernhard Mayer(2) and Christophe Gourbeyre(1) 1 La. MP CNRS / Université Blaise Pascal, Aubière, France, 2 DLR, Oberpfaffenhofen, Germany During the CIRCLE-2 experiment carried out over Western Europe in May 2007, in situ and remote observations have been obtained with the DLR Falcon aircraft in cirrus clouds and convective systems. The aircraft was equipped with a unique set of instruments including the Polar Nephelometer, FSSP-300, Cloud Particle Imager (CPI) and PMS 2 D-C for the extensive in-situ cloud measurements of microphysical and optical properties and the DLR WALES Lidar (Water Vapor Lidar Experiment in Space) for nadir looking remote sensing observations. This poster illustrates results of combined observations performed near the top (-58°C) of an overshooting convective cell over Germany (26 May situation). In situ measurements reveal the occurrence of very high concentration of chain-like aggregates of small ice crystals with subsequent very large extinction and ice water content values at these altitudes. The analysis of co-located remote sensing data from both the lidar WALES and the Spinning Enhanced Visible and Infra. Red Imager (SEVIRI) aboard Meteosat Second Generation (MSG) confirms these unusual cloud properties. Outflow cirrus cloud properties observed in the vicinity of the convective cell are described for comparison purposes. Quasi co-located CALIPSO and Cloud. Sat observations are available along the Falcon track 30 min earlier the convective cell penetration. Despite this time lag, the cloud feature is nicely identified from space active remote sensing measurements. Scientific issues related to the microphysical properties and structure of deep convective are discussed with some possible insights regarding engineering issues related to the flights of commercial aircraft through areas of high ice water content. 200705261300 : 47038. 410 – 47943. 410 s 2007/05/26 12: 45 UTC 10°E CALIPSO track 12: 32 UT 50°N Pressure (h. Pa) 12 10 8 6 4 48°N 2 0 EUMETSAT MET-09 IR 108 Temperature (°C) a Concentration (l-1 mm-1) FSSP- 300 CPI 2 D-C Extinction (km-1 mm-1) Figure 1. Cloud field as observed by SEVIRI (10. 8 mm channel) on 26 May at 12: 45 UT. The CALIPSO track (12: 32 UT) is superimposed on the image with the Falcon flight track by thick line. 1 2 3 4 5 Adiabatic LWC (g/m 3) Figure 2. Temperature & Dew-point profiles measured by the Falcon (left panel). The right panel shows the calculated adiabatic LWC profile. MET-9 EUMETSAT-DLR Figure 3. False color composites of MET-9/SEVIRI observations from 26 May 2007 at 13: 00 UT. The Falcon trajectory (between 12: 45 and 13: 15 UT) is superimposed (blue line). The flight segment in red color indicates the penetration in the convective cloud. The CALIPSO track is also displayed. c. 1 c. 2 FSSP- 300 CPI d. 2 FSSP- 300 Diameter (mm) FSSP+ CPI Extinction (km-1) Diameter (mm) (Rimed long colums) Equivalent melted diameter (mm) Figure 5. (a): Composite representation of the particle size distributions from FSSP-300, CPI and 2 D-C. (b): Extinction comparison between PN and FSSP + CPI derivations. (c) and (d): Extinction and IWC size distributions measured in the outflow cirrus (c. 1, d. 1) and convective cloud (c. 2, d. 2) respectively. The results highlight a quite good consistency of microphysical parameters derivations. Conc = 6 cm -3 C 100 = 12 l -1 IWC = 0. 05 g/m 3 Deff = 80 mm Diameter (mm) Ext = 3. 1 km -1 g = 0. 773 Scattering angle (°) Conc = 54 cm -3 C 100 = 192 l -1 IWC = 0. 67 g/m 3 Deff = 57 mm Diameter (mm) Ang. Scat. coef. (mm-1 sr-1) CPI Concentration (l-1 mm-1) FSSP- 300 Ang. Scat. coef. (mm-1 sr-1) y = 1. 15 x s = 0. 98 d. 1 Concentration (l-1 mm-1) Ext = 26. 4 km -1 g = 0. 776 Scattering angle (°) Figure 6. Examples of ice crystal images measured by the CPI. Left panel: Bullet-Rosettes sampled near -45°C in the outflow cirrus. Right panel: Chainlike aggregates observed near the top of the convective cloud (11. 2 km/ 58°C). The correspondind particles size distributions and scattering phase functions with mean values of parameters are displayed on the bottom panel. Figure 4. 1 st panel: Time-series of cloud in situ parameters : Conc and C 100: Concentration of ice particles (d> 3 mm and d>100 mm, respectively); Ext: Extinction, g: Asymmetry parameter; Deff: Effective diameter; IWC: Ice water content and Z : Reflectivity factor. 2 nd panel: Attenuated backscatter ratio (at 1064 nm) from WALES lidar. 3 rd panel: Time-series of retrieved parameters along the Falcon flight from SEVIRI observations (Bugliaro et al. , ACP, 2010): Effective radius, Optical depth and IR (10. 8 mm) Brightness temperature (green curve). The air temperature measured by the Falcon is also reported (black curve). The first sequence reports outflow cirrus (1242 – 1254 UT). The overshooting convective cloud sampled near the top at 11. 2 km level (1307 – 1311 UT, see red segment on Fig. 1) is coherently described by combined observations. The high ice concentration (80 cm-3) of small ice particles (40 mm) with large extinction (40 km-1) and IWC (~ 1 g/m 3) lead to a strong lidar attenuation. SEVERI retrieved parameters confirm the occurrence of small ice crystals (compared to the outflow cirrus) with high optical thickness (40). The IR brightness temperature fits remarkably well with the in situ temperature measurements near the top of the convective cell. ● First observations of chain-like aggregate ice crystals are reported near the top (11. 2 km/ -58°C) of an overshooting convective cell in mid-latitude continental area. As reported by Connolly et al. (QJRMS, 2005) the aggregation processes result from electric field alignment of ice crystals. Supercooled droplets lofted in the updrafts are frozen by homogeneous nucleation near the -38°C level, producing high concentrations of very small primary ice particles. Indeed, theoretical adiabatic IWC values may reach 3 g/m 3 at the tropause level. Log 10 IWC = 0. 0630 Z -1. 10 s = 0. 63 Reflectivity factor (d. BZ) Particle mass (mg) (Irregular spatial) Figure 7. Relationships between equivalent melted diameter (a) and particle mass (b) according to the particle shapes (Rimed long columns and irregular spatial) assumed in IWC and Z derivations. Figure 8. IWC-Z relationships for the outflow cirrus (black symbols) and the convective cloud (red symbols). The slope differences are explained by smaller particle sizes in the convective cloud. Extrapolating the relationship for convective cloud, IWC up to 5 g/m 3 could be experienced with reflectivity factor no larger than 10 d. Bz. ● The overshooting-convective cloud properties are coherently described by combined observations. The high ice concentration (80 cm-3) of small ice particles (40 mm) with large extinction (40 km-1) and IWC (~ 1 g/m 3) lead to a strong lidar attenuation from WALES and CALIOP data. SEVIRI retrieved parameters confirm the occurrence of small ice crystals with high cloud optical thickness (40). ● Significant differences in IWC-Z relationships are found between usual outflow cirrus and the overshooting cell. Extrapolating the relationship for convective cloud, IWC up to 5 g/m 3 could be experienced with reflectivity factor no larger than 10 d. BZ. ● These observations address scientific issues related to the microphysical properties and structure of deep convective cloud and are contrary to the findings that particles larger than 50 mm control the radiative properties in convective-related clouds. These unusual observations may also provide some possible insights regarding engineering issues related to the flights of commercial aircraft through areas of high ice water content and high concentration of small ice crystals. CALIPSO 532 nm 10 12 8 b (m-1 sr-1) Log 10 (IWC) (g/m 3) (Rimed long columns) Particle mass (mg) Equivalent melted diameter (mm) (Irregular spatial) CONCLUSIONS 12 - 1. 0 - 1. 5 - 2. 0 - 2. 5 10 Reflectivity factor (d. BZ) s = 0. 75 Altitude (km) Log 10 IWC = 0. 0925 Z - 0. 11 Altitude (km) Polar Neph. Extinction (km-1) b Ice Water content (g m-3 mm-1) Diameter (mm) 8 6 4 2 Cloud. Sat 94 GHz 48. 0 48. 5 Latitude (°N) 49. 0 49. 5 Figure 9. Vertical profiles of attenuated backscatter coefficient (CALIOP on CALIPSO) and the radar reflectivity factor (CPR on Cloud. Sat) obtained 30 min before the Falcon observations carried out at 11. 2 km level (see pink segments). The observations confirm the overshooting feature of the convective cloud with low reflectivity (~5 d. BZ) near the cloud top and high b (as for WALES b is attenuated at lower altitudes indicating dense cloud with high ice particle concentration). Acknowledgements : This work was funded by the Centre National d’Etudes Spatiales (CNES) and by a grant from the CNRS/INSU. The contribution of DLR as well as large part of Falcon flight hours was funded in the framework of the DLR PAZI-2 project. We thank Prof. Schumann and Hermann Mannstein for helpful discussions. We thank the members of DLR (Deutsches Zentrum für Luft- und Raumfahrt) who organized the experiment management and aircraft operations. We acknowledge A. Schwarzenboeck and J-F Fournol (La. MP), B. Weinzierl and H. Rüba (DLR) for their active participation to the CIRCLE-2 experiment. We acknowledge NASA Langley Research Atmospheric Science Data Center, as well as ICARE Center in Lille for the CALIPSO data. 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