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Fog prediction in a 3D model with parameterized microphysics Mathias D. Müller 1, Matthieu Masbou 2, Andreas Bott 2, Zavisa I. Janjic 3 1) Institute of Meteorology Climatology & Remote Sensing University of Basel, Switzerland 2) Meteorological Institue, University of Bonn 3) NOAA/NCEP WSN-05 TOULOUSE, Sept. 2005
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NMM (Nonhydrostatic Mesoscale Model) dynamical framework PAFOG microphysics NMM_PAFOG Droplet number concentration Liquid water content Condensation/evaporation in the lowest 1500 m is replaced by PAFOG Janjic, Z. I., 2003: A Nonhydrostatic Model Based on a New Approach. Meteorology and Atmospheric Physics, 82, 271-285.
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PAFOG microphysics Detailed condensation/evaporation (parameterized Köhler [Sakakibara 1979, Chaumerilac et. al. 1987]) Evolving droplet population (prognostic mean diameter) Droplet size dependent sedimentation Positive definite advection scheme (Bott 1989)
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PAFOG microphysics Assumption on the droplet size distribution : Log-normal function D droplet Diameter D c,0 mean value of D σ c Standart deviation of the given droplet size distribution (σ c =0.2) where S is the Supersaturation Supersat.
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Boundary conditions for dN c 1000m PAFOG TOP 1000 m σcσc HEIGHT
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GFS NMM-22 NMM-4 NMM-2 15 UTC Nesting NMM_PAFOG GRID: 50 x 50 x 45 (+11 soil layers) dx:1 km dt: 2s (dynamics) / 10s (physics) CPU:40 min/24hr on 9 Pentium-4 (very efficient!)
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19:00 MEZ (3 hr forecast) PAFOG STANDARD 27 Nov 2004 DROPLET NUMBER CONCENTRATION LIQUID WATER CONTENT
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22:00 MEZ (6 hr forecast) STANDARD PAFOG 27 Nov 2004 DROPLET NUMBER CONCENTRATION LIQUID WATER CONTENT
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02:00 MEZ (10 hr forecast) STANDARD PAFOG 28 Nov 2004 Accurate sedimentation in PAFOG due to dN c computation. DROPLET NUMBER CONCENTRATION LIQUID WATER CONTENT
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08:00 MEZ (16 hr forecast) PAFOG STANDARD 28 Nov 2004 DROPLET NUMBER CONCENTRATION LIQUID WATER CONTENT
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10:00 MEZ (18 hr forecast) STANDARD PAFOG 28 Nov 2004 DROPLET NUMBER CONCENTRATION LIQUID WATER CONTENT
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q c at 5m height (01:00 MEZ) PAFOG STANDARD
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q c at 5m height (06:00 MEZ) PAFOG STANDARD
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Cold air pooling (05:00 MEZ)
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Cold bias problem Z.Janjic
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variational assimilation B-matrices COBEL-NOAH PAFOG Obser - vations 3D-Model runs post-processing Fog forecast period NMM-4 NMM-2 NMM-22 aLMo 3D - Forecast time 1D Ensemble prediction system www.meteoblue.ch 1D-models
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With assimilation – CASE 1 15:00 27-28 Nov 2004 observed fog
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28-29 Nov 2004 With assimilation – CASE 2 15:00
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Conclusions 3D model with detailed microphysics Promising first results Computationally very efficient and feasible in todays operational framework More cases and ‘verification’ needed Solves advection problem of 1D approach
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GRID of NMM_PAFOG 50 x 50 x 45 27 layers in the lowest 1000 m 11 soil layers Thickness(cm): 0.5 0.75 1.2 1.8 2.7 4.0 6.0 10 30 60 100
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Advection statistics 1 December 2004 – 30 April 2005, all forecasthours and levels Deviation often stronger than signal
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Fog case - Observations CASE 1CASE 2
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Assimilation example 28 Nov 2004 Zürich Kloten Airport 21 hour forecast of NMM-2
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Chaumerliac, N., Richard, E. & Pinty, J.-P. (1987), Sulfur scavenging in a mesoscale model with quasi-spectral microphysic : Two dimensional results for continental and maritime clouds, J. Geophys. Res. 92, 3114- 3126. Berry, E.X & Pranger, M. P. (1974), Equation for calculating the terminal velocities of water drops, J. Appl. Meteor. 13, 108-113. Bott, A. (1989), A positive definite advection schemme obtained by nonlinear renormalization of the advective fluxes, Monthly Weather Review 117, 1006-1015. Bott, A. & Trautmann, T. (2002), PAFOG – a new efficient forecast model of radiation fog and low-level stratiform clouds, Atmospheric Research 64, 191-203. References Janjic, Z. I., 2003: A Nonhydrostatic Model Based on a New Approach. Meteorology and Atmospheric Physics, 82, 271-285. Janjic, Z. I., J. P. Gerrity, Jr. and S. Nickovic, 2001: An Alternative Approach to Nonhydrostatic Modeling. Monthly Weather Review, 129, 1164-1178
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Sakakibara, H. (1979), A scheme for stable numerical computation of the condensation process with large time step, J. Meteorol. Soc. Japan 57, 349-353. Twomey, S. (1959), The nuclei of natural cloud formation. Part ii : The supersaturation in natural clouds and the variation of cloud droplet concentration, Geophys. Pura Appl. 43, 243-249. References
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Write in incremental Form Introduce T and U transform to eliminate B from the cost function (physical space) (Control variable space) Cost function for variational assimilation
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Error covariance matrix NMC-Method (use 3D models):
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NMC estimates of B (winter season) NMM-4 1400 UTC large model and time dependence
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