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Observed and modelled long-term water cloud statistics for the Murg Valley

Observed and modelled long-term water cloud statistics for the Murg Valley. Kerstin Ebell, Susanne Crewell, Ulrich Löhnert Institute for Geophysics and Meteorology, University of Cologne. 7th COPS Workshop, 27 – 29 October 2008, Strasbourg. Motivation.

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Observed and modelled long-term water cloud statistics for the Murg Valley

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  1. Observed and modelled long-term water cloud statistics for the Murg Valley Kerstin Ebell, Susanne Crewell, Ulrich Löhnert Institute for Geophysics and Meteorology, University of Cologne 7th COPS Workshop, 27 – 29 October 2008, Strasbourg

  2. Motivation 30 July 2007, Murg Valley IR sky temperature + LWP • Clouds are complex in - time/space- microphysics • Observations need to captureall characteristics see Poster by Kneifel et al. for spatio-temporal structure • Liquid water content (LWC)can not be observed by a single instrument Integrated Profiling Technique UTC 14 13 12 11 N W S E N • LWC is important- as prognostic parameter in NWP/climate models- in describing cloud radiative effects- for predicting attenuation in radio propagation problems •  due to scarsity of observations simple cloud models were developed to diagnose LWC profiles from radiosonde measurements 7th COPS Workshop, 27 – 29 October 2008, Strasbourg 7th COPS Workshop, 27 – 29 October 2008, Strasbourg 2

  3. Motivation • How are water clouds characterized in the Murg valley during April – December 2007? • „observations“ • How are they represented by models? •  Comparison to • simple cloud models • (NWP model COSMO-DE) Cloudnet Target Classification (provided by Ewan O‘Connor) Integrated Profiling Technique 7th COPS Workshop, 27 – 29 October 2008, Strasbourg

  4. Integrated Profiling Technique (IPT) – Overview • provides continuous vertical profiles of temperature, humidity and liquid water content (LWC); first attempts to derive droplet number concentration  data set of retrieved profiles available for April – December 2007! Retrieval CloudNet Target Categorization: • Each pixel is categorized in terms of the presence of liquid droplets, ice, insects or aerosol. • Discrimination between precipitating and non-precipitating clouds. • Microwave radiometers • Cloud radar • A priori information (radiosondes) Integration of measurements in the framework of optimal estimation: inversion method including - instrument characteristics (theory, error) - forward model, i.e. radiative transfer, Z- LWC-relationship - background information 7th COPS Workshop, 27 – 29 October 2008, Strasbourg

  5. RH sonde Rhcrit modad / Decker Rhcrit Salonen 06 Cloud models - overview Simple cloud models: diagnosis of clouds from radiosonde profiles • Modified adiabatic approach (Karstens et al., 1994) • Decker model (Decker et al., 1978) • modified Salonen model (Mattioli et al., 2006) General principle: • Localization of cloud base and cloud top height • Calculation of LWC: • depending on height over cloud base (Mod.ad., Salonen) • depending on cloud thickness (Decker), Min 0.05 gm-3, Max 0.2 gm-3 • Assumption: no water clouds below -20 °C 7th COPS Workshop, 27 – 29 October 2008, Strasbourg

  6. Results – Critical humidity thresholds Distribution of relative humidity (radiosonde) in cloudy pixels (April – December 2007); cloudy pixels: Cloudnet classification detects cloud droplets • detection of clouds from relative humidity profiles problematic 7th COPS Workshop, 27 – 29 October 2008, Strasbourg

  7. Results – Cloudnet and cloud models Number of clouds April-December 2007 Cloudnet classification profiles within 30 min. aftera RS ascent are taken into account for the comparison 7th COPS Workshop, 27 – 29 October 2008, Strasbourg

  8. Results – Cloud base height (lowest cloud) April-December 2007 7th COPS Workshop, 27 – 29 October 2008, Strasbourg

  9. Results – Cloud thickness distribution April-December 2007 • most frequent cloud thickness is 100-200 m • only ~17 % of clouds with thicknesses > 500 m • only ~10 % of clouds with thicknesses > 1000 m 7th COPS Workshop, 27 – 29 October 2008, Strasbourg

  10. Results - LWP For COSMO-DE evaluation more time steps and inclusion of fractional clouds needed! 7th COPS Workshop, 27 – 29 October 2008, Strasbourg

  11. Results - LWC 7th COPS Workshop, 27 – 29 October 2008, Strasbourg

  12. Summary • Derivation of liquid water, temperature and humidity profiles for nearly the whole AMF deployment (21.4.-31.12.2007) using the Integrated Profiling Technique  88110 profiles (cloudy: 33168) corresponding to 2706 hours (5 min sampling) • Most clouds are single layer, 100-200 m thick with low LWP • Simple cloud models based on RS profiles - overestimate the occurence of water clouds by ~25-35%- overestimate thin clouds (< 300 m)- overestimate of multilayer clouds and LWP • COSMO-Model evaluation is limited due to missing information on fractional cloudiness Outlook • Investigation of cloud radiative effects using IPT/Cloudnet data and single column version of the radiation code of the COSMO model • sensitivity studies, e.g. additional retrieval of number concentration 7th COPS Workshop, 27 – 29 October 2008, Strasbourg 7th COPS Workshop, 27 – 29 October 2008, Strasbourg 12

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