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Landscapes and Climate

David S. Battisti University of Washington. Landscapes and Climate. The Annual Mean Precipitation Storminess and Climate Mountains -> Circulation -> Weather Extreme Precipitation Events and Climate: Can we know about them using climate models?. Landscapes and Climate.

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Landscapes and Climate

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  1. David S. Battisti University of Washington Landscapes and Climate • The Annual Mean Precipitation • Storminess and Climate • Mountains -> Circulation -> Weather • Extreme Precipitation Events and Climate: Can we know about them using climate models?

  2. Landscapes and Climate • The Annual Mean Precipitation • Today: observed vs. simulated • Precipitation in warmer climates • Precipitation: controlled by large-scale circulation or weather? • Storminess and Climate • Mountains -> Circulation -> Weather • Extreme Precipitation Events and Climate: Can we know about them using climate models?

  3. How well do Atmospheric General Circulation Models work? Typical biases in Seasonal Average Temperature (AGCMs circa 2003)

  4. How well do Atmospheric General Circulation Models work? Typical biases in Seasonal Averaged Precipitation (circa 2003)

  5. How well do Atmospheric General Circulation Models work? Temperature Sea Level Pressure Precipitation Covey et al 2000

  6. Warmer Climates and Precipitation Patterns Projected Annual Average Precipitation due to increased CO2 (“2080-2099” minus “1980-1999”) Scenario A1B Warmer climates should have less subtropical precipitation (20-35 latitude) and more tropical and high latitude precipitation, for sound dynamical reasons. Stippling is where the multimodel average change exceeds the standard deviation of the models

  7. Large-scale Circulation vs. Storm Dynamics • Cases where the large-scale circulation/forcing (e.g., Himalaya orography; land-ocean temperature contrast) drives weather? • SE Asian Monsoon, • Indonesian Monsoon, ITCZ … • South-Central US Monsoon • Cases where the large-scale circulation inextricably tied to the weather (and not directly to topography)? • Europe winter precipitation (NAO <--> storminess) • Pacific Northwest winter precipitation (midlatitude Pacific storm track re-birth; ENSO) • Don’t know: • Eastern Mediterranean and Middle East: are seasonal precip changes due to changes in storm track dynamics or to changes in the frequency of lee cyclogenesis?

  8. Climate and Landscapes • The Annual Mean Precipitation • Storm Tracks and Climate • Modern day • Glacial times • Mountains -> Circulation -> Weather • Extreme Precipitation Events and Climate: Can we know about them using climate models?

  9. Storminess and Climate • Dogma says as the equator-to-pole temperature gradient (dT/dy) increases, so should storminess increase. There is more to the story. • Counter examples abound (linked to mountains) • A modern day example: midwinter suppression of the Pacific storm track Going from November to January (increases dT/dy) and… … the Jet increases by ~20 m/s, … but storminess decreases by ~25% and the atmospheric heat transport goes down. Yin and Battisti (2005), Li et al (2005)

  10. Storminess and Climate Amplitude of Storms (e.g., eddy heat transport) Atlantic Jet Cross Section Modern Height 20N 60N 20N 60N Contours are west-to-east (zonal) wind speedTemperature is colored poleward heat flux 850mb (Km/s) 250 hPa Zonal Wind (contour in 10 m/s, starting at 30) Another counter example: In the LGM, the meridional temperature gradient increased and storminess decreased compared to today Li and Battisti 2007

  11. Landscapes and Climate • The Annual Mean Precipitation • Storminess and Climate • Mountains -> Circulation -> Weather • Major forcing of the global (NH) circulation by the: • The Andes (Location of the Pacific ITCZ) • The Rockies (Warm Europe vs. Cold NE US) • Tibetan Plateau (SE Asian Monsoon) • Mountains and storm tracks: seeding of midlatitude storms • Extreme Precipitation Events and Climate: Can we know about them using climate models?

  12. ITCZ SPCZ Cool Subtropical anticyclones 1. The Andes and the Observed Annual Mean State in the Tropical Pacific Observed annual mean state Rainfall (colors), SST (contours) and surface streamlines Why is the ITCZ in the northern hemisphere, and why is the SE Pacific cold? Note: this asymmetry is fundamental to El Nino physics, and the global climate anomalies that caused by it. Data: GPCP, NCEP OI SST, QSCAT

  13. Summary of main mechanisms

  14. There is only one ITCZ in the eastern-central Pacific and it is north of the equator … Precipitation & SST Observed Climatology Simulated Climatology: an atmospheric GCM coupled to a slab ocean. Only Andes orography is included; there is no land. … because of the mechanical affect of the Andes on the atmosphere and the resulting thermodynamic feedbacks with the ocean. Takahashi and Battisti 2006

  15. 2. The importance of mountains in wintertime Mountains No Mountains Winds, SLP and Eddy Temperature in January Seager et al 2000

  16. The importance of mountains in wintertime Change in surface air temperature due to mountains is about ~25% of the annual cycle in some places (e.g., Northeast China would be ~ 8C warmer in winter w/o the Tibetan Plateau) Seager et al 2000

  17. 3. The Asian Winter Monsoon November - March Precipitation 850 hPa Wind & Wind Speed (cm/month)

  18. 3. The Asian Winter Monsoon • Case 1: No topography • The result: two zonal bands of rainfall near the equator (ITCZs), Trade winds, subtropical Highs at 30˚ latitude, and midlatitude jets and storm tracts at about 35˚latitude.

  19. 3. The Asian Winter Monsoon • Case 2: • As in case 1, but add the Tibetan Plateau. Land temperature is fixed and adjusted at the surface lapse rate. • Hence, there is no land heating in this experiment • Orography forces a stationary wave that cools the northeastern half of China by advection of cold air from the northeast • Eg., cooling of Beijing of 8C • The Rockies have a similar affect on northeastern North America: cooling NE North America by ~9C & warming Europe by +3C (Seager et al 2000) L Cold Air Advection L L L L Jet H H H H H

  20. L L L L Jet L H H H H H H Trades Surface Flow Upper Level Flow 3. The Asian Winter Monsoon • Case 2: with Tibetan Plateau • Results: enhanced downstream jet stream & accompanying circulation that • drives enhanced trades north of the equator, pushing the ITCZ south of the equator through atmosphere-ocean feedbacks; • causes southerly winds in southern China, enhancing winter rainfall (with local orographic amplification).

  21. L H 3. The Asian Winter Monsoon … is forced mechanically by orography Precipitation & Surface Streamlines mm/day Takahashi & Battisti 2007

  22. 3. The Asian Winter Monsoon November - March Precipitation 850 hPa Wind & Wind Speed (cm/month) Convergence … is forced mechanically by orography

  23. Mountains and the seeding of midlatitude storms Frequency of cyclogenesis as diagnosed from 850mb vorticity field. Gray areas are above 1500m Mountains are a primary cause of the birth of storms in the midlatitudes S. Penny, pers. comm. 2007

  24. Mountains and the seeding of midlatitude storms Tracks of all storms that formed in the lee of mountains …with upper level forcing: 935… without upper level forcing: 696 Genesis Location S. Penny, pers. comm. 2007

  25. Atlantic Jet Cross Section Height LGM Modern 20N 60N 20N 60N Contours are west-to-east (zonal) wind speedTemperature is colored Mountains (ice sheets) and the seeding of midlatitude storms Amplitude of disturbances seeding the Atlantic storm track are weaker in the LGM A. Donohoe 2007 Li and Battisti 2007

  26. Landscapes and Climate • The Annual Mean Precipitation • Storminess and Climate • Mountains -> Circulation -> Weather • Extreme Precipitation Events and Climate: Can we know about them using climate models? • Yes • Maybe … but not yet.

  27. Extreme Precipitation Events and Climate: Can we know about them using climate models? • Yes, when changes in extreme events are due to weather that is controlled by large-scale circulation • Examples: SE Asian Monsoon, Indonesian Monsoon, The Pacific ITCZ, Hurricanes (likely intensity, not likely tracks), • At present GCM resolution, complementary downscaling (empirical/numerical) models are useful/necessary to assess changes in extreme events. • Maybe, where weather and large-scale circulation are inextricably linked … but not yet. Efforts are ongoing, but it will take time.

  28. Landscapes and Climate • The Annual Mean Precipitation • Storminess and Climate • Mountains -> Circulation -> Weather • Extreme Precipitation Events and Climate: Can we know about them using climate models? Circulation Mountains Weather ?

  29. ITCZ SPCZ Subtropical anticyclones Cool Observed annual mean state Rainfall (mm/day) and 925 mb streamlines Sea surface temperature (SST, °C) Data: GPCP, NCEP/NCAR Reanalysis, NCEP OI SST.

  30. Andes and ML Rainfall (mm/day, shaded) SST (C, contours) Mean sea level pressure (mb, shaded) 925 mb streamlines

  31. Andes, Himalayas and Rockies Rainfall (mm/day, shaded) SST (C, contours) Mean sea level pressure (mb, shaded) 925 mb streamlines

  32. Double Andes (2) Rainfall (mm/day, shaded) SST (C, contours) Mean sea level pressure (mb, shaded) 925 mb streamlines

  33. Thermocline tilt Rainfall (mm/day, shaded) SST (C, contours) Mean sea level pressure (mb, shaded) 925 mb streamlines

  34. Thermocline tilt + Seasonality Rainfall (mm/day, shaded) SST (C, contours) Mean sea level pressure (mb, shaded) 925 mb streamlines

  35. Storm Tracks and Climate Another counter example: storminess and eddy heat transport are reduced in the LGM compared to today

  36. The Indian Monsoon … is mainly thermally driven Pot. Temp. 850hPa Pot. Temp. 300hPa Heating of continental India and SE Asia is key to the “Indian monsoon”

  37. The Indian Monsoon … is mainly thermally driven May Wind 1000hPa May Precipitation m/sec mm/day

  38. The Indian Monsoon June Pot. Temp. 300hPa June Precipitation Precipitation, circulation and diabatic heating are grossly similar from month-to-month (once the Indian monsoon gets going) from June to September.

  39. The Indian Monsoon Land-Sea thermal contrast is the major driver. But is it the “hot Tibetan Plateau” or is it “the hot India/Southeast Asia plus the Himalaya wall”? The observed column averaged diabatic heating (JJA) Rodwell and Hoskins 2001 The atmosphere is heated south of the Tibetan Plateau

  40. The Indian Monsoon Does the orography drive the low level flow that fuels the monsoon heating? Low level streamfunction in summer (JJA) Mountains only Mountains plus heating Rodwell and Hoskins 2001 The summer monsoon doesn’t seem to be driven by topography

  41. The Indian Monsoon • The onset of the Indian Monsoon appears to be driven by heating over India and SE Asia • Modeling (not shown) and observations suggest the Indian monsoon is not driven by heating over the Tibetan Plateau • The Himalaya and the orography of SE Asia are important for localizing the precipitation and diabatic heating • This geometry ensures a gross similarity in monthly circulation, precipitation, etc during the monsoon season.

  42. The Asian Spring-Summer Monsoon Zonal Wind Averaged 70-100E April May June July The jet transitions from south of the plateau in April to north in July. Until the transition takes place, the downstream flow will still favor low-level convergence over south-central China.

  43. 850 hPa The Asian Spring-Summer Monsoon May wind and wind speed climatology 500 hPa The deep west-northwesterly flow into central China brings dry air that converges with moist air at lower levels arriving from the south.

  44. The Asian Spring-Summer Monsoon Wind velocity/speed at 500 hPa Zonal wind (color) and specific humidity along 95-100E May May Eq 50N

  45. Jan June The Asian Spring-Summer Monsoon • So, we expect the same (dynamically) driven monsoon but with more rainfall in spring/summer than in winter: • Higher SST -> more evaporation -> more moisture convergence -> more precipitation • More precipitation -> more land evaporation -> more precipitation (local feedback) • More precipitation -> more convergence

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