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Modelling of cloud and desert dust properties over the Iberian Peninsula and Atlantic Ocean

Modelling of cloud and desert dust properties over the Iberian Peninsula and Atlantic Ocean. Fifth Meso-NH User's Meeting. Dina Santos, Maria João Costa, Ana Maria Silva e Rui Salgado. Objective.

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Modelling of cloud and desert dust properties over the Iberian Peninsula and Atlantic Ocean

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  1. Modelling of cloud and desert dust properties over the Iberian Peninsula and Atlantic Ocean Fifth Meso-NH User's Meeting Dina Santos, Maria João Costa, Ana Maria Silva e Rui Salgado

  2. Objective • To study the properties of clouds and aerosols during strong Sahara desert dust episodes, May 2006 and September 2007, using MesoNH results, over the Iberian Peninsula and Atlantic Ocean.

  3. Top of the Atmosphere - TOA Scattering & absorption of radiation Increase cloud height Heating causes cloud burn-off Increase CDNC & suppress precipitation Increase cloud lifetime

  4. MesoNH Simulations • Simulations initiated and forced by ECMWF analyses • Run in a two way nested mode, 2 nested models: • - Father: 4000 x 5000 km2 horizontal resolution:50km • - Son1: 1000 x 1000 km2 source res:10km • - Son2: 2000 x 2225 km2 study area res:10km • Simulation periods: • 26 – 29 May 2006 e 04 – 09 September 2007 • 49 stretched layers from the surface up to 24km altitude • Dust scheme activated (Dust Entrainment And Deposition - DEAD)

  5. Comparison with Satellite Images Cloud Fraction - CLDFR 28 May 1105UTC 27 May 1200UTC the total CLDFR simulated results are in agreement with the actual situation (represented by MODIS RGB images) 29 May - 1145UTC the simulated results obtained seem to overestimate the observed cloud fraction (satellite)

  6. Comparison with Satellite Images Cloud Fraction -CLDFR 07 September -1315UTC 06 September - 1410UTC the total CLDFR simulated results seem to overestimate the observed cloud fraction (satellite) 08 September – 1040UTC

  7. Comparison with Satellite Images Aerosol Optical Depth – DSTAOD2D 06 September The DSTAOD2D pattern results are in a good agreement with the actual situation 07 September

  8. Comparison with Satellite Images Aerosol Optical Depth - ODAER_NIR4 28 May 1103UTC 08 September 1055UTC The ODAER_NIR4 present lower values when compared with the correspondingvalues measured by MERIS sensor

  9. Comparison with Satellite Images Cloud Top Pressure - PRES 28 May 08 September The simulated Cloud Top Pressure values are in good agreement with the correspondingvalues measured by MERIS sensor

  10. Comparison with Ceilometer VAISALA Base Height ofConvective Cloud -CLBASCONV 27 May 28 May The simulated CLDBASCONV values agree very well with the corresponding values measured by the ceilometer

  11. Aerosol Effects DEAD scheme Clean days DEAD scheme Off

  12. Cloud Liquid Water Effective Radius-EFRADL The biggest EFRADL values are found at higher altitudes for a dusty atmosphere than the correspondent EFRADL values for a Dust Free atmosphere. For clouds below 1.5km high level dusty atmosphere EFRADL values are slightly lower than the correspondent EFRADLvalues for a Dust Free atmosphere.

  13. Aerosol Radiative Forcing Aerosol Optical Depth-DSTAOD2D 27 May 28 May Since the objective is to estimate the direct radiative forcing due to DD aerosols, the cloudy regions are not considered and the assessment of desert dust radiative forcing is therefore only made for clear sky conditions.

  14. AOD and DD Aerosol SWRF and LWRF SWF_NET LWF_NET SWF_NET_CS LWF_NET_CS Over LandRegion • On the 27 May the DD event was more effecttive. • Lower SWF values are found, at TOA and surface levels, on the 27 May compared with the corresponding values for 28 May (probably related to the fact that higher AOD values are found for 27May than the corresponding ones for the 28 May). • A cooling LW effect at surface level, is found for the 28 May, but for 27 May a warming LW effect is found(maybe related, once again, with higher AOD values found on 27May). • Nevertheless, the LWF values in altitude, for both days, have a tendency to approximate and, at the TOA, the values are very close.

  15. AOD and DD Aerosol SWRF and LWRF Over SeaRegion • On the 27 May the DD event was more effective. • For the 27 May, lower SWF values are found again compared with the corresponding values for 28 May.This difference can, once again, be related to the fact that the AOD values, on 27 May, are higher than the AOD values for 28 May. • On 27 May, for the most part, a LW warming effect is found. • On 28 May a LW cooling effect is found being more pronounced below 5km altitude.

  16. Cloud Radiative Forcing (TOA) -CRF • the TOA SWCRF for a dusty atmosphere and for a dust free atmosphere present always a negative sign, indicating a SW cooling effect at the TOA. • the TOA LWCRF for a dusty atmosphere and for a dust free atmosphere presents positive signs for all the cases, indicating then a LW warming effect at the TOA. • the TOA CRF for a dusty atmosphere presents more negative values than the TOA CRF for a dust free atmosphere,connected to the fact that the dusty clouds reflect more sunlight.

  17. Final Considerations • The main objective of this work is to study the properties of clouds and aerosols during strong DD events, in the regions of the Iberian Peninsula and Atlantic Ocean. The method uses the results obtain by the MesoNH model. • When a comparison is made by the simulated results with the measured results, it is observed that the model overestimates the total CLDFR parameter, nevertheless the pattern is, generally, in conformity with the actual situation represented by MODIS. The CLBASCONV simulated values present also a good conformity with the corresponding values measured by the ceilometer. The simulated cloud top pressurevalues present a very good concordance with the respective values measured by MERIS. • The simulated AOD, when compared qualitatively with the satellite image, presents a very good agreement, yet, when quantitatively compared, presents lower values than the corresponding values measured by the satellite. • When DD aerosols are present in the atmosphere, a SW warming effect is observed, both at TOA and surface levels, being more negative at the surface. A LW warming effect is detected when AOD higher values are found. • For clouds developing in a atmosphere where DD are present, a more negative CRF is found, comparing with the corresponding CRF values for clouds developing in a DD free atmosphere.

  18. Papers in Conferences • Santos, D., M. J. Costa, A. M. Silva and R. Salgado,2008: "Cloud microphysical characterization in the presence of a desert dust event over Portugal: a study based on atmospheric modelling and satellite remote sensing", in Remote Sensing of Clouds and the Atmosphere XIII, edited by Richard H. Picard, Adolfo Comeron, Klaus Schäfer, Aldo Amodeo, Michiel van Weele, Proc. of SPIE, Vol. 7107, 710714. • D. Santos, M. J. Costa, A.M. Silva e R. Salgado, 2009: " Modelação dos Efeitos Microfísicos e Radiativos de Poeiras do Deserto na Região da Península Ibérica ", 6º Simpósio de Meteorologia e Geofísica/10º Encuentro Luso-Español de Meteorologia,In Press. • M. J. Costa, D. Santos, R. Salgado, V. Levizzani, F. Pinelli, D. Bortoli, e A.M. Silva, 2009: ‘Modelling of orographic precipitation over Portugal and effects on the surrounding regions’, European Geosciences Union, General Assembly. • D. Santos, M. J. Costa, A. M. Silva, R. Salgado, A. Domingues e D. Bortoli, 2009: "Saharan Desert Dust Radiative Effects: A study based on atmospheric modeling ", Global Conference on Global Warming 2009. (Best Paper Award) • D. Santos, M. J. Costa, A.M. Silva e R. Salgado, 2009 : " Atmospheric modeling of Desert Dust Aerosols Effects on Clouds over the Atlantic Ocean “, 18th International Conference on Nucleation & Atmospheric Aerosols«. • Santos, D., M. J. Costa, A. M. Silva, R. Salgado and D. Bortoli, 2009: "Comparison of cloud height and depth from atmospheric modelling and ceilometer measurements", in Remote Sensing of Clouds and the Atmosphere XIV, edited by Richard H. Picard, Klaus Schäfer,Adolfo Comeron, Evgueni I. Kassianov, Christopher J. Mertens, Proc. of SPIE, Vol. 7475, 747512. • D. Santos, M. Potes, M. J. Costa, R. Salgado e A.M. Silva, 2009: "Comparison of atmospheric properties retrieved from MERIS and obtained from modelling studies ", Atmospheric Science Conference. • D. Santos, M. J. Costa, A.M. Silva e R. Salgado, 2009: ‘Modelação das propriedades das nuvens e de poeiras do deserto sobre a região da Península Ibérica e Oceano Atlântico ", IV Encontro de Pós-Graduação em Ciências Físicas e da Terra da Universidade de Évora, Évora.

  19. Future work… • These results encourage the analysis of others situations and more days are planned to be investigated and compared. Thank you! ACKNOWLEDGEMENTS The work was funded by the Portuguese FCT through grant SFRH/BD/27870/2006 and through project PTDC/CTE-ATM/65307/2006. The authors are also grateful for the suggestions and kind availability of PierreTulet and Odile Thouron!

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