New observational techniques for a better understanding of clouds

Transcription

1 New observational techniques for a better understanding of clouds Ulrich Löhnert, Kerstin Ebell, Stefan Kneifel, Jan Schween, Gerrit Maschwitz... Prof. Susanne Crewell AG Integrated Remote Sensing Institute for Geophysics and Meteorology University of Cologne

2 Content The IPCC Report Radiative forcing Climate projections Clouds and radiation Cloud parameter Cloud processes Sensor synergy Ground-based remote sensing JOYCE Radiative closure Cloud radiative effect Further activities

3 Intergovernmental Panel on Climate Change (IPCC) Nobel price 2007 IPCC Fourth Assessment Report (FAR), 2007: "Warming of the climate system is unequivocal", and "Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations". Aerosols, clouds and their interaction with climate is still the most uncertain area of climate change and require multidisciplinary coordinated research efforts.

4 Carbon dioxide CO 2 Radiative Forcing RF Net change in irradiance F net (solar and terrestr.; in W m 2 ) at tropopause level F net (z) F (z) F (z) z F net (z z) F net (z) IPCC, Fig.2.3

5 Heating rates Heating rate [K /day] of one atmospheric layer results from radiation divergence z H F net (z z) F net (z) 1 F net (z) (z)c p z 30 km cloud free tropical conditions solar terrestrial μm μm Ozone water vapor CO 2 water vapor - - continuum Petty, Fig.10.6 Petty, Fig.10.8

6 Energy balance of the atmosphere solar shortwave terrestrial longwave Atmosphere has a radiation deficit compensated by turbulent fluxes of sensible and latent heat Phase transitions couple energy and water cycle KIEHL J., and K. TRENBERTH, 1997: Earth s annual global mean budget. Bull. Am. Met. Soc., 78, What is missing?

7 IPCC, Fig.2.4

8 IPCC, Fig

9 IPCC Results - Past First Assessment Report 1990 Second Assessment Report 1995 Third Assessment Report 2001

10 IPCC Results - future Plass (1956): CO 2 doubling leads to temperature change +3.6 C Manabe und Wetherald (1967) Temperaturänderung +2.3 C 2 Grad Ziel Numbers give # models, which are used to derive the uncertainty range

11 Radiative Forcing (1750 bis 2005) IPCC, Fig.2.4

12 Content The IPCC Report Radiative forcing Climate projections Clouds and radiation Cloud parameter Cloud processes Sensor synergy Ground-based remote sensing JOYCE Radiative closure Cloud radiative effect Further activities

13 From hydrometeors Why are clouds so complex? to single clouds to Einzelwolken and cloud fields to the global system

14 Cloud parameter Macro-physical Parameter cloud fraction cloud height cloud contours 3D-structure Radiative Quantities extinction coefficient [m -1 ] optical thickness z ( z') z 0 d z' transmission t = exp(- ) Micro-physical Parameter number concentration N effective radius r eff liquid water content LWC radar reflectivity Z moments of the droplet spectrum Ice- and mixed phase clouds phase shape density

15 Droplet spectra observations modelling Hawaii orographic Hawaii stratus Passat Australia continental moments of drop spectra cloud liquid water density [kg m -3 ] m(n) r n N(r)dr 0 LWC 4 3 r 3 w N(r)dr 0

16 Ice and mixed phase clouds Bergeron-Findeisen While everywhere sufficient cloud condensation nuclei for forming water droplets are available, much fewer ice nuclei exist

17 Von kleinen zu großen Teilchen m aerosols 1.0 m 10 m cloud droplets ice crystals 100 m 1.0 mm 10 mm rain drops snow turbulence mikrophysical models ~100 m numerical weather prediction (NWP) models ~10 km climate models ~100 km

18 Whats that? Increased cloud reflectivity due to increased number of small droplets (1. indirect aerosol effect)

19 Aerosol and clouds depends on aerosol composition IPCC, Fig.2.10

20 Importance of clouds in climate system Clouds? Feedbacks Aerosol Cooling H 2 O CO 2 radiative forcing [W m -2 ] Low level cloud fraction 25% 37.5% Droplet radius 8 µm 12 µm Opacity Opacity concentration 360 ppm 540 ppm Warming Clouds Radiative transfer model Fu & Liou

21 Content The IPCC Report radiative forcing climate projections Clouds and radiation Cloud parameter Cloud processes Sensor synergy Ground-based remote sensing JOYCE Radiative closure cloud radiative effect Further activities

22 Remote sensing and sensor synergy Cloud radar - radar reflektivity factor Z r 6 - Doppler-spectrum - linear depolarisation ratio LDR - influence by insects and drizzle Lidar - backscatter coefficient prop. r 2 - depolarisation information (phase!) - strong extinktion by water clouds Microwave radiometer - liquid water path LWP - temperature and humidity profiles Höhe Radar Lidar Radiometer Radar Lidar LWC -liquid water content

23 Cloud radar radar reflectivity factor :30-14:30 Doppler velocity 95 GHz GKSS Wolkenradar MIRACLE Lineare depolarisation ratio backscatter proportional r 6

24 Lidar Cloud ceilometer radar Altitude (m above ground) Aerosol Rising PBL Ice clouds Rain Fog

25 Microwave radiometry Standard atmosphere temperature profile water vapour profile liquid water path liquid water path LWP=250 gm -2 ν /GHz

26 Integrated Profiling Technique (IPT) Microwave Brightness temperatures (TB) Specifying information content Radar profile Lidar cloud base a priori LWC profile (climatology) a priori T & q profile (next radio sonde Bayesian Retrieval Measurements and retrieval are physically consistent within their uncertainty range optimal profiles of Temperature (T) Humidity (q) LWC Löhnert et al., 2001, 2004, 2008 Ebell et al., 2010

27 JOYCE Jülich ObservatorY for Cloud Evolution A cooperation of University of Cologne, Prof. A. Wahner (ICG-2) DFG priority program TR32 Live measurements at

28 JOYCE Jülich ObservatorY for Cloud Evolution Sodar Profile of wind speed and direction Lidar Ceilometer Backscatter profile, Cloud base height Mixing layer height Infrarred Spektrometer Profiles of temperature & humidity, effective radius, ice content Microwave radiometer Water vapour, Cloud water, Temperature profile Cloud Radar Cloud vertical structure Cloud water content Fall velocity Total Sky Imager Cloud fraction Rain radar Rain rate Fallvelocity. Drop size TERENO Micro Rain Radar Profiles of drop size distribution

29 Cloud radar and microwave Interruption for scanning radar reflectivity factor doppler velocity spectral width

30 IWV Spatial variability of water vapour LWP θ=57 θ=76

31 Diurnal course of IWV 5 October 2010 LWP

32 Temperature profiles

33 Content The IPCC Report radiative forcing climate projections Clouds and radiation Cloud parameter Cloud processes Sensor synergy Ground-based remote sensing JOYCE Radiative closure cloud radiative effect Further activities

34 DOE Atmospheric Radiation Measurement ARM Mobile Facility Microwave radiometer 90/150 GHz HATPRO Murgtal, Black Forest 2 April 31 Dezember 2007 Leipzig,

35 Assessment of cloud radiative effect Temperature & Humidityprofiles radio soundings remote sensing Aerosol optical thickness AOD Angström exponent single scattering albedo & asymmetry factor Surface albedo monthly direct and diffuse albedo derived from radiations measurements Water Clouds Liquid water content LWC Effective radius r eff,liq Hydrometeor- Detection Sensor combination Eis clouds Ice water content IWC Effective radius r eff,ice Radiative Transfer model RRTMG broadband irradiances Surface radiation measurements downward irradiances and clear sky estimate

36 Comparison of radiative fluxes cloud free Calculated vs observed clear-sky estimate shortwave Calculated SW flux / Wm no clouds in TSI clouds in TSI Calculated SW flux / Wm min cloud free periods largest discrepancies when categorisation misses clouds in general good agreement Observed SW flux / Wm Clear-sky SW flux estimate / Wm -2 longwave Calculated LW flux / Wm no clouds in TSI clouds in TSI Calculated LW flux / Wm Observed LW flux / Wm -2 Clear-sky LW flux estimate / Wm -2 Susanne Crewell, Summer School, Jülich 6 October ç 2010 TSI: Total sky imager 5-min averages Calculated fluxes vs. clearsky estimate SW LW Bias / Wm Stddev / Wm Explained variance

37 Comparison of radiative fluxes cloudy Calculated SW flux / Wm -2 Calculated LW flux / Wm shortwave Observed SW flux / Wm longwave clouds periods: 90% cloud fraction mean differences in shortwave and longwave smaller then 10% largest discrepancy due to non homogeneous clouds (no considered in) Mean observed Observed LW flux / Wm -2 shortwave longwave ç 5-min Mittel cos(sza) > 0.3 all clouds # of profiles 5,871 Bias Stddev Expl. variance 0.61 Mean observed Bias 6.5 Stddev 11.9 Expl. variance 0.83

38 Cloud radiative effect CRE = F NET, CLOUD - F NET,CLEAR (in Wm -2 ) Derived from surface radiation measurements clouds lead to surface warming by longwave radiation clouds lead to surface cooling by shortwave radiation

39 Summary and conclusions Clouds clouds have a strong effect on the Earths energy and water budget cloud processes are rather complex and involve scales from nm to km cloud feedbacks related to aerosols and changes in temperature and humidty are not well understood Observations better observations of clouds are urgently required sensor synergy observations and modelling need to be linked closely for further progress