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 2 Motivation 30 July 2007, Murg Valley IR sky temperature + LWP N W S E N UTC 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 Clouds are complex in - time/space - microphysics Observations need to capture all 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

3 7th COPS Workshop, 27 – 29 October 2008, Strasbourg 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

4 7th COPS Workshop, 27 – 29 October 2008, Strasbourg 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! Integrated Profiling Technique (IPT) – Overview Microwave radiometers Cloud radar A priori information (radiosondes) 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. 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 Retrieval

5 7th COPS Workshop, 27 – 29 October 2008, Strasbourg 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: 1)Localization of cloud base and cloud top height 2)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 RH sonde Rh crit modad / Decker Rh crit Salonen 06

6 7th COPS Workshop, 27 – 29 October 2008, Strasbourg 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

7 7th COPS Workshop, 27 – 29 October 2008, Strasbourg Results – Cloudnet and cloud models Number of clouds Cloud occurence (%) Mod. Ad.69.4 Decker69.4 Salonen75.3 Cloudnet55.5 April-December 2007 Cloudnet classification profiles within 30 min. after a RS ascent are taken into account for the comparison

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

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

10 7th COPS Workshop, 27 – 29 October 2008, Strasbourg Results - LWP Cloud freq. (%) Mean LWP (gm -2 ) Mod. Ad Decker Salonen IPT COSMO- DE For COSMO-DE evaluation more time steps and inclusion of fractional clouds needed!

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

12 7th COPS Workshop, 27 – 29 October 2008, Strasbourg 12 7th COPS Workshop, 27 – 29 October 2008, Strasbourg Summary Derivation of liquid water, temperature and humidity profiles for nearly the whole AMF deployment ( ) using the Integrated Profiling Technique  profiles (cloudy: 33168) corresponding to 2706 hours (5 min sampling) Most clouds are single layer, 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