Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 MW- and submm-Radiative-Transfer and Modelling of Cirrus Clouds S. Buehler, C. Emde, G. Heygster, V. O. John, T. Kuhn-Sander, K. Kunzi, M. Kuvatov, J. Miao, T.R. Sreerekha
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Part I Ø Concept of ARTS Ø Scattering Ø Iterative solution for vector radiative transfer equation (VRTE) Ø Test results Ø Summary and outlook
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 ARTS 1.0 Ø Radiative transfer model for microwave to the IR region Ø 1D Spherical Atmosphere Ø Refraction implemented Ø Absorption: JPL, HITRAN, different continuum models Ø Modular program Ø ARTS 1.0 is available for download: http://www.sat.uni-bremen.de/arts
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Model Intercomparison Ø Participating models: • ARTS • MAES (CRL, Japan) • MOLIERE (Observatoire de Bordeaux, France) • EORC (NASDA, Japan) • „Karlsruhe“ Model (Forschungszentrum Karlruhe) • MIRART (DLR) • SMOCO (CRL and FACOM, Japan) Ø Results have shown the reliability and accuracy of ARTS
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Example for test Test of radiative transfer codes, assuming a limb measurement Input for the Intercomparison: Ø Pre-calculated absorption coefficients Ø Atmospheric profiles Ø Instrumental characteristics
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Validation of ARTS Comparison between ARTS and AMSU data using radio sondes
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 3D Scattering Radiative Transfer Model Vector Radiative Transfer Equation (VRTE) Under Developments ready by mid 2003 Ø General scattering scheme Ø Polarization Ø 3D atmosphere. Atmospheric horizontal inhomogeneities have to be included for accurate scattering simulations Ø Zeeman Effect, an expression for Zeeman splitting is at present only available in a dedicated radiative transfer model
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Concept of ARTS Clear Sky RT RT Equation: � ? � Gas Absorption d I � Simulated Clear = K I B a − + Target Species : Clear Spectrum at the ds Spectral Line H 2 0, O 2 , N 2 , ....... Sensor Catalogue etc. Extinction Emission (gas) (gas) � � I I Cloudy Single Scattering Clear Properites ? Amplitude Cloudy RT Matrix for Extinction Ice Particles Absorption � RT Equation: � � d I � Phase Matrix Cloudy K I B a d n Y I ʹ = − + + ∫ Cloudy Cloudy ds 4 Particle Types: π Spheres, Cylinders, .. Emission Extinction Scattering Source (gas + particle) (gas + particle) (particle)
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Iterative Solution Method for VRTE � � � d I � Cloudy K I B a d n Y I ʹ = − + + ∫ Cloudy Cloudy ds 4 π 1. First guess radiation field in cloud box assuming clear sky field. 2. Calculate scattering integral field using clear sky field 3. Solve VRTE using the scattering integral field a First Iteration Calculate scattering integral field using the first Iteration field. 4. 5. Repeat steps 3 and 4 6. Convergence test after each iteration a final Solution
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Absorption Ø Absorption coefficients for atmospheric species are taken from catalogues (HITRAN, JPL), selected by the user Continuum absorption Ø O 2 and H 2 O, MPM and PWR T. Kuhn, H. J. Liebe, P. W. Rosenkranz Ø N 2 Quantum mechanical model and MPM A. Borysow and L. Frommhold, “Collision induced Rototranslational Absorption Spectra of -N2 Pairs for Temperatures from 50 to 300 K”, Astrophysical Journal, Vol. 311, 1986
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Example O 2 PWR H 2 O PWR z : 7.8 km p : 360 hpa T : 233 K N 2 Continuum
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Single Scattering Properties Depending on particle shape, different methods are required Ø Mie theory: spherical particles Ø T-matrix (Trasition) method: cylinders, plates, spheroids, spheres Ø DDA (Discrete Dipole Approximation): arbitrary shape Single scattering properties database Ø Amplitude matrix data for different types are stored in a database Ø From the amplitude matrix the optical properties are derived Ø All methods can be used to create files for the database
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Example solid: Extinction cross section dashed: Scattering cross section dotted: Absorption cross section Spherical particles with Radius: 500 µm 300 µm 200 µm 100 µm
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Particle Size Effects Gamma Distribution: ( 1 3 b ) / b − 1 ⎛ r ⎞ ⎛ r ⎞ u ( r ) ⎜ ⎟ exp ⎜ ⎟ = − b=1 ⎜ ⎟ ⎜ ⎟ 1 2 b r b r b ⎛ − ⎞ ⎝ ⎠ ⎝ ⎠ r eff eff ⎜ ⎟ eff b ⎝ ⎠
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Particle Aspect Ratio Effect
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Test results Setup for 1D test calculation Ø Frequency: 325 GHz - Cylindrical particles, size radius r=200 µ m (equal Ø Cloud: volume sphere) - Particle number density: 5000 m -3 - Range: 397 – 298 hpa (approximately 8 - 9.5 km) Ø Convergence limit: 0.03 K
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Example black: clear sky colour: scattered solid: p=298 hpa dotted : p=336 hpa dashed : p=397 hpa Cylindrical Particles Zenith angle 298 hpa 397 hpa
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Test for particle shape and size distribution Ø Cloud: a) Cylindrical particles, size r eff = 200 µ m (equal volume sphere) Aspect ratio ar=0.5 (Length/Diameter) b) Spherical particles, size r=200 µ m Ø Particle number density: 5000 m -3 Ø Range: 397 – 298 hpa (approximately 8 - 9.5 km) Ø Convergence limit: 0.03 K
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Example Shown is the difference 397 hpa between the case with and without scattering at different altitudes for: cylindrical particles: blue spherical particles: red 336 hpa 298 hpa
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Summary and outlook Ø ARTS 3D polarized scattering model for the microwave to the IR region is under development and is being validated, will be ready end 2003 Ø Test calculations show the expected behaviour Ø The general approach is very versatile for many applications, including limb sounding Ø The 3D geometry allows to consider many situations of importance in meteorology
Faculty 01 Institute of Environmental Physics Physics / Electrical Engineering Part II Sensor CIWSIR satellite orbit Satellite Orbit flight Flight Direction aft-view direction fore-view view from the top SSP aft-view footprints Pixel Size 45° 13 x 8 km 2 swath width flight direction Swath Width ?1400 km fore-view
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 CIWSIR Cloud Ice Water Sub-millimetre Imaging Radiometer Ø CIWSIR - Scientific Goals Ø Channel selection Ø Effect of cirrus clouds in the mm/sub-mm range - Observations Ø Effect of cirrus clouds in the mm/sub-mm range - Simulations Ø Retrieval using CIWSIR Ø Some technical Information Ø Summary
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Objectives CIWSIR is a space-born sub-mm sensor which can give daily coverage of upper tropospheric ice cloud information by providing: Ø Global and continuous observations This will support: Ø The Climatology of cirrus properties Ø Help to improve the parameterized treatment of ice clouds in models Ø better understanding of ice cloud microphysics
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 What CIWSIR Observes In the presence of cirrus clouds, the up welling radiation from lower layers of the atmosphere is reduced. In the frequency range used for CIWSIR the lower troposphere is opaque. Figure personal communication, F. Evans
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 CIWSIR Channels The clear sky radiance spectrum as measured by a satellite radiometer with the 5 CIWSIR bands
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Effect of IWP The Signal of ice clouds in the sub- mm wave spectral range is quite strong for large IWPs. This is because scattering causes brightness temperatures to go well below physical temperatures. 5 CIWSIR bands Figure personal communication, F. Evans
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Effect of IWP at CIWSIR channels Top plot: Cloud from 5 to 7 km altitude, particle radius 100 µ m. Bottom plot: Cloud from 9 to 10 km altitude, particle radius 50 µ m.
Institute of Environmental Physics EUMETSAT, 6-7 November, 2002 Effect of Size For small particles maximum signal occurs at high frequency. for larger particles the frequency of the maximum signal depend on particle size Figure personal communication, F. Evans
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