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Land surface processes

Land surface processes

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Land surface processes

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  1. Land surface processes

  2. Review of last lecture • Global distribution of shallow and deep convection • Vertical structure of trade wind cumulus (shallow convection) • Vertical structure of deep convection. Four components: convective updraft, convective downdraft, mesoscale updraft, mesoscale downdraft • Differences between shallow convection and deep convection: change of T, q and h in the boundary layer • Self-suppression processes in deep convection: Overly stabilized state after deep convection • Problems in current global climate models: lack of self-suppression processes

  3. Effects of different surface types BL depth decreases Convective instability increases Deeper heat reservoir (smaller T change) Deeper water reservoir (Wetter surface) Bowen ratio decreases (More LH contribution)

  4. Effects of vegetation • Makes water/heat reservoir deeper (transport deep water • out of soil) • Enhances evaporation (leafs increase evaporation area) • Dependent on vegetation type

  5. Global distribution of different vegetation types (From Bonon et al. 2002)

  6. Vegetation feedbackVegetation in turn is affected by environmental conditions (e.g. seasons, droughts, global warming)

  7. Effects of human activities Human beings are living in the BL and affect the BL in three different ways: • Change land cover (deforestation and afforestation) • Release or cleanse pollutants (aerosols) • Release or cleanse greenhouse gases

  8. The heat island effect • Nighttime: City warmer than surrounding rural area • Daytime: City has same air temperature as rural area

  9. Causes of the heat island effect “Canyons” between buildings • Increased SW absorption caused by canyon geometry (increased area and multiple reflection) • Decreased LW loss caused by canyon geometry • Increased greenhouse effect caused by air pollution • Anthropogenic heat source • Increased sensible heat storage caused by construction materials • Decreased latent heat flux caused by change of surface type • Decrease sensible and latent heat fluxes caused by canyon geometry (reduction of wind speed)

  10. Mitigation of heat island effect • Greening the city (streets and roof top) • Change construction materials • Reduce anthropogenic heat sources

  11. Land Surface Processes in Global Climate Models

  12. Framework of National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM) Atmosphere (CAM) Land (CLM) Coupler . Sea Ice (CSIM) Ocean (POP)

  13. Community Land Model (CLM) Components • Biogeophysics • Hydrologic cycle • Biogeochemistry • Dynamic vegetation

  14. CLM Model Components: Biogeophysics

  15. CLM Model Components: Hydrological Cycle I

  16. CLM Model Components: Hydrological Cycle II

  17. CLM Water balance

  18. River Systems Simulated by CLM Dai, Qian, Trenberth and Milliman (2009), J. Climate

  19. CLM Model Components: Biogeochemistry

  20. CLM Model Components: Dynamic Vegetation

  21. DGVM Vegetation biogeography vs. Satellite

  22. Summary • Effects of different surface types: desert, city, grassland, forest, sea. Deeper heat/water reservoir, decreased Bowen ratio, thinner BL and enhanced convective instability. • Effects of vegetation: (1) makes heat/water reservoir deeper, (2) enhance evaporation, (3) grows and dies in response to environmental conditions • Heat island effect. 7 causes • Community land model (CLM). 4 components: biogeophysics, hydrological cycle, biogeochemistry, dynamical vegetation