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UNIVERSITY OF ATHENS FACULTY OF PHYSICS DEP. OF APPLIED PHYSICS LAB. OF METEOROLOGY

UNIVERSITY OF ATHENS FACULTY OF PHYSICS DEP. OF APPLIED PHYSICS LAB. OF METEOROLOGY. Sensitivity tests in the ‘ dynamical ’ and ‘ thermal ’ part of the MRF-urban PBL scheme  in the MM5 model. Aggeliki Dandou, Maria Tombrou. 1. Meteorological Model MM5 (Version 3-6).

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UNIVERSITY OF ATHENS FACULTY OF PHYSICS DEP. OF APPLIED PHYSICS LAB. OF METEOROLOGY

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  1. UNIVERSITY OF ATHENS FACULTY OF PHYSICS DEP. OF APPLIED PHYSICS LAB. OF METEOROLOGY Sensitivity tests in the ‘dynamical’ and ‘thermal’ part of the MRF-urban PBLscheme  in the MM5 model Aggeliki Dandou, Maria Tombrou

  2. 1 Meteorological Model MM5 (Version 3-6) The Penn State/NCAR Mesoscale Model MM5 (Grell et al., 1994) is a terrain following numerical weather prediction model, with a multiple-nest capability, nonhydrostatic dynamics and a four-dimensional data assimilation capability. Parameterization schemes considered: • ‘simple ice’Hsie et al. (1984),for the moisture parameterization • ‘cloud-radiation scheme’ Dudhia (1989),for the radiation parameterization • ‘Grell’(1993),for the clouds parameterization • ‘Five-Layer Soil model’(Dudhia, 1996), for the soil parameterization

  3. 2 Meteorological Model MM5 (Version 3-6) PBL parameterization schemes: • MRF (Hong and Pan, 1996): high resolution non-local scheme based on Troen and Mahrt (1986) representation of counter gradient term and K profile in the well mixed PBL • MRF-urban(Dandou et al., 2005): a modified version of MRF whereby urban features were introduced both in the thermal part and the dynamical part: • MRF-not urban: a modified version of MRF, whereby the city of Athens is replaced by dry cropland and pasture surface, as the surrounding area • Anthropogenic heat:asa temporal and spatial function of the diurnal variation of the anthropogenic emissions • Heat storage:the OHM scheme (Grimmond et al., 1991) • Heat and momentum fluxes (under unstable conditions): according to Akylas et al. (2003) • Diffusion coefficients (under stable conditions): according to King et al. (2001) • Updated field for the roughness length: based on literature values in combination withsatellite detailed information on land use (spatial resolution 30 m)

  4. 3 Area of application Ground stations • National Observatory of Athens (NOA), an urban station (4 km inland from the shore), located in a park, on top of a hill (107 m asl), with urban characteristics 85% and z0=0.8 m Input data • Meteorological dataECMWF (0.5o x 0.5o) every 6 hours • Sea Surface TemperatureSST (1o x1o) every 6 hours • Marousi, a suburban station (13 km inland from the shore), inside a grove surrounded by buildings of different heights, with urban characteristics 52% and z0=0.5 m • USGS data (25 categories) (30’’ x 30’’) for topography and land use • Two-way nesting • Peiraias, an urban station at the harbor, with urban characteristics 100% and z0=1 m

  5. 4 14 September 1994 (MEDiterranean CAmpaign of PHOtochemical EvolutionMEDCAPHOT-TRACE experiment, Ziomas, 1998) Available measurements • Sensible heat flux (sonic anemometer) NOA, Marousi • Friction velocity (sonic anemometer) • Air temperature NOA, Marousi, Peiraias • Wind velocity • Landsat TM satellite image(acquisition date: 13 Joune 1993)

  6. Results 5 • Surface fluxes • Surface fluxes • Air Temperature • Diffusion coefficients • PBL height

  7. 6 • Diurnal variation of surface fluxes (MRF-urban scheme) (urban, downtown) (urban, at the harbor) (semi-urban) Q*- net all wave radiation QH-sensible heat flux QE-latent heat flux QF-anthropogenic heat ΔQs-heat storage

  8. 7 • NOA : larger values due to • Marousi: turbulence characteristics of the grove and not the surrounded built-up area • MRF: substantially higher values than the measurements • MRF-urban: in better agreement with the measurements • During the night: increase (absolute values) due to the ‘thermal’ part • During the day: decrease due to the smaller temperature gradients produced by the ‘thermal’ part and the z0 • Diurnal variation of sensible heat flux Decrease MANGE 29% Decrease MANGE 40% Model results versus measurements Measurements (Batchvarova and Gryning, 1998) Schemes intercomparison soil characteristics (bare rocks) and surface cover (olive tree plantation) temperature gradients (higher location) (Mean Absolute Normalized Gross Error) -predicted values -observed values

  9. Spatial distribution of the sensible heat flux 8 W/m2 3:00 LST MRF MRF-dyn MRF-ther MRF-urban 14:00 LST MRF MRF-dyn MRF-ther MRF-urban

  10. 9 • Max values ~0.5 m/s at both sites, although VNOA (~4 m/s) > VMAROUSI (~2 m/s), due to its higher location • Marousi: the nonhomogeneity of the surrounding buildings, interchanged with the green areas cause higher values • During the night:any comparison with the measurements is meaningless (<0.1 m/s, the model’s threshold) • During the day:decrease in the MRF-urban, closer to the measurements • Marousi: smaller decrease because the z0 did not change significantly. Higher values at noon due to the wind speed increase • Differences due to the different profile functions and z0 • During the night: increase due to the increase of instability • During the day: • Diurnal variation of friction velocity Decrease MANGE 6% Decrease MANGE 2% Measurements (Batchvarova and Gryning, 1998) Model results versus measurements Schemes intercomparison increase of z0 increase in the diffusion processes decrease in the wind speed increase of u* normalization in temperature gradients decrease of u* decrease of u*

  11. 10 • Spatial distribution of the friction velocity m/s 3:00 LST MRF MRF-dyn MRF-ther MRF-urban 14:00 LST MRF MRF-dyn MRF-ther MRF-urban

  12. Results 5 • Surface fluxes • Surface fluxes • Air Temperature • Air Temperature • Diffusion coefficients • PBL height

  13. 11 Measurements • During the night: development of an urban heat island • During the day: lower maximum values at the urban stations (NOA and Peiraias), compared to the suburban station (Marousi) • MRF-urban: decrease in the temperature amplitude wave, in better accordance with the measurements • NOA: differences with measurements due to its location on top of the hill, not resolved by the model’s spatial resolution (2 km) • During the night: increase due to the ‘thermal’ part • During the day: • Diurnal variation of air temperature (at 10 m agl) Decrease MANGE 38% Decrease MANGE 41% Decrease MANGE 53% Model results versus measurements Schemes intercomparison increase due to the ‘dynamical’ part decrease due to the ‘thermal’ part total decrease

  14. Spatial distribution of the air temperature differences (at 2m agl) 12 • Spatial distribution of the air temperature (at 2m agl) ΔΤ (oC) oC MRF-dyn - MRF MRF-ther - MRF MRF-urban- MRF MRF-urban 3:00 LST 3:00 LST 3:00 LST 3:00 LST MRF-dyn - MRF MRF-ther - MRF MRF-urban - MRF MRF-urban 14:00 LST 14:00 LST 14:00 LST 14:00 LST

  15. Results 5 • Surface fluxes • Surface fluxes • Air Temperature • Air Temperature • Diffusion coefficients • Diffusion coefficients • PBL height

  16. 13 Schemes intercomparison • During the day: • During the night: increase in the lower atmosphere due to the ‘dynamical’ and ‘thermal’ part • Diffusion coefficient profiles increase due to the ‘dynamical’ part decrease due to the ‘thermal’ part total decrease

  17. 14 • Spatial distribution of diffusion coefficients at the surface layer m2/s 3:00 LST MRF MRF-dyn MRF-ther MRF-urban 14:00 LST MRF MRF-dyn MRF-ther MRF-urban

  18. Results 5 • Surface fluxes • Surface fluxes • Air Temperature • Air Temperature • Diffusion coefficients • Diffusion coefficients • PBL height • PBL height

  19. 15 Schemes intercomparison • During the night: increase due to the ‘thermal’ part • Delay (~1 h) in max value (MRF-urban), due to the delay in the sea-breeze development • During the day: • Diurnal variation of the PBL height increase due to the ‘dynamical’ part decrease due to the ‘thermal’ part total decrease

  20. 16 • Diurnal variation of the PBL height 20-9-2002 20-9-2002 15-9-1994 Tombrou et al. (2006)

  21. 17 • Spatial distribution of the PBL height m 3:00 LST MRF MRF-dyn MRF-ther MRF-urban 14:00 LST MRF MRF-dyn MRF-ther MRF-urban

  22. Summarizing the results 18 n=77 (number of grids) t=12 (number of hours for the day and night)

  23. Spatial distribution of the wind velocity (at 10 m) 19 • Spatial distribution of the wind speed differences (at 10m) MRF-urban – MRF-not urban MRF-urban 3:00 LST 3:00 LST m/s m/s MRF-urban – MRF-not urban MRF-urban 14:00 LST 14:00 LST

  24. 20 • Vertical cross sections of the wind velocity along the sea-breeze axis MRF-urban MRF-not urban 3:00 LST 3:00 LST m/s 14:00 LST 14:00 LST 0.4 m/s 4 m/s

  25. Conclusions 21 • Both modifications play an important role and improve the model’s results • The increase in temperature and diffusion coefficients calculated by the ‘dynamical’ part is compensated by the decrease in the ‘thermal’ part, resulting in a total decrease • A decrease in turbulence and fluxes is calculated by both modifications • During the day: • A slowing in the sea-breeze front and a frictional retard concerning its penetration over the Athens city is calculated due to the increased roughness length • The total increase in temperature, diffusion coefficients, turbulence and fluxes is due to both modifications • During the night: • The maximum wind speeds calculated in the lower atmosphere is due to the urban heat island

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