1 / 43

7.6 Precipitation

7.6 Precipitation. Climate vs. Weather . Climatological Rainfall. This chapter looks at the processes that control the “climatological” distribution of rainfall. Climate. The average of individual weather systems (mid latitude depressions, tropical convective cells) and patterns

xaria
Download Presentation

7.6 Precipitation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 7.6 Precipitation

  2. Climate vs. Weather

  3. Climatological Rainfall • This chapter looks at the processes that control the “climatological” distribution of rainfall

  4. Climate • The average of individual weather systems (mid latitude depressions, tropical convective cells) and patterns • Weather cannot be predicted beyond a certain amount of time • Climate takes averages to predict where and when systems and patterns will tend to occur again

  5. How do we predict weather? • We can accurately predict 3-4 days in advance • Geostationary orbiting satellites gather visual wavelength data • They use this to estimate cloud albedo, water content, and in doing so the p(rain)

  6. What is rainfall climatology • Measuring, understanding, predicting rainfall distribution across different regions of Earth • These predictions are made depending on air pressure, humidity, topography, cloud type • The measurements are taken by remote sensing

  7. What causes precipitation

  8. What causes precipitation? • Moisture and energy • Ocean gives unlimited moisture (talking global average here) • Constraints are from energy

  9. Water cycle

  10. Atmospheric circulation • Large scale movement of air • The means by which thermal energy is distributed on Earth • Varies year to year but remains fairly constant

  11. Atmospheric circulation

  12. Atmospheric circulation • These are the wind belts that girdle the planet • They are grouped into three cells: Hadley, Ferrel, Polar • Most of the vertical motion occurs in Hadley

  13. Effects of warming on precipitation

  14. Effects of warming on large scale precipitation trends • Globally averaged precipitation increases with the global mean surface temperature • The change ranges from 1.5 to 3 % per degree C of warming that we see • Considerable regional variability

  15. Effects of warming on large scale precipitation trends • Increase is more dramatic in wet latitudes

  16. Effects of warming on large scale precipitation trends • Dry latitudes may see a decrease

  17. Effects of warming on large scale precipitation trends • “wet get wetter” and “dry get drier” response is evident at large scales • It is the result of a change in water vapor carried by circulations • Also, wet regions import from dry regions

  18. Effects of warming on large scale precipitation trends • At the marginal level, or local level, the precipitation response is less clear because of regional circulation shifts and model uncertainty

  19. Mitigation of effects • Especially in the dry regions • there will be a slowdown in atmospheric circulation

  20. Overall understanding • We can safely make claims about the effects of warming on ocean precipitation • Responses over warming land are iffy because certain relationships are not well understood (soil moisture precipitation feedbacks)

  21. Radiative forcing and its effects on precipitation

  22. Radiative Forcing of the Hydrological Cycle • The intensity of the hydrological cycle also depends on the radiative cooling of the troposphere

  23. Energy budget

  24. Radiative Forcing of the Hydrological Cycle • Increases in GHG concentrations reduce the radiative cooling of the troposphere

  25. Radiative Forcing of the Hydrological Cycle • When the radiative cooling of the troposphere is reduced, the rainfall rate is reduced • The strength of the circulation is also reduced • So even through even though the mean precipitation should go up by 1.5-3% per degree Celsius, the increase in GHG reduces it by about 0.5% per degree Celsius

  26. Effects of aerosol cloud interactions on precipitation • Aerosols influence cloud microphysical structure (convective intensity) • They mostly affect the atmospheric heating rate • For this reason they have mostly been studied regarding their effects on the spatial-temporal distribution of precipitation, versus global averages • Limited and ambiguous evidence

  27. convection -the atmosphere becomes unstable through heating (more than its surroundings) -significant evaporation, convective rain from convective clouds

  28. The effects of warming on extreme precipitation

  29. Warming’s effect on extreme precipitation • Precipitation from individual storms will increase with available moisture content in the atmosphere near the surface • The rate is 6-10% per degree C • But there are longer intervals between storms

  30. GCM predictions • Poor at simulating precipitation extremes • Plus predictions on warming vary • Not generally regarded as reliable re: extremes • Local temperature may not be a good proxy for assessing the effects of warming • They tend to covary with other meteorological factors • Humidity, atmospheric stability, wind direction

  31. Solar radiation management

  32. Geoengineering • Definition: broad set of methods to intentionally alter the climate system to alleviate the effects of climate change • Solar radiation management (SRM): counter the warming associated with GHG by reducing the amount of sunlight that gets absorbed • Carbon Dioxide Removal (ch. 6) • Reduce the amount of sunlight hitting the earth, or make the planet more reflective (clouds, atmosphere)

  33. Geoengineering

  34. Geoengineering • Relatively new field • Few studies look at it • Looking at SRM is limited by: • Gaps in understanding processes • Scarcity of studies

  35. Geoengineering • How to reduce sunlight reaching earth? • Solid or refractive disks in space • Dust particles in space • Feasibility is not assessed

  36. SRM methods • Increase stratospheric aerosol to produce a cooling effect, similar to an erupting volcano • Require replenishment

  37. SRM methods • Cloud brightening: boundary layer clouds cool the planet • Small changes in albedo or extent has big effects on radiation budget • Systematically introduce cloud seeds to boundary layer (Cloud condensation nuclei) • Could produce strong negative forcing • Clouds with weak precipitation are best

  38. SRM methods • Surface albedo changes: urban areas, croplands, grasslands, deserts, ocean surface • Whitening of urban areas might have effects such as -0.17 W/square meter • High uncertainty • Limited studies • Side effects for photosynthetic activity?

  39. SRM methods • Cirrus Thinning: these clouds enhance the greenhouse effect (high, thin clouds) by warming the surface • Reduce humidity in the upper troposphere

  40. Effects of SRM • Simplest SRM studies can be performed in climate model through simulations • SRM affects temperatures in the daytime only, versus GHG increases which raise temperatures regardless of the time

  41. Effects of SRM • Some uniform decrease in sunlight reaching the surface will offset mean CO2 warming • Could theoretically counteract anthropogenic climate change, cooling the Earth to preindustrial levels in 1-2 decades • Known from climate models • Data from eruptions

  42. Effects of SRM • Mount Pinatubo 1991 • 0.5 degrees C

More Related