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Steven Feldstein

The link between tropical convection and the Northern Hemisphere Arctic surface air temperature change on intraseaonal and interdecadal time scales. Steven Feldstein. The Pennsylvania State University. Collaborators: Sukyoung Lee, Tingting Gong, Nat Johnson ,, Changhyun Yoo ,

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Steven Feldstein

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  1. The link between tropical convection and the Northern Hemisphere Arctic surface air temperature change on intraseaonal and interdecadal time scales Steven Feldstein The Pennsylvania State University Collaborators: Sukyoung Lee, TingtingGong, Nat Johnson,, ChanghyunYoo, David Pollard, and Tim White September 11, 2012

  2. (1) Present-day observations Warming trend is greater toward higher latitudes NOAA Global Historical Climatology Network Gridded surface air temperature Source: JISAO, University of Washington

  3. (2) Past climates (from reconstruction) Warmer climate has a smallerequator-to-pole temperature gradient Barron & Washington reconstruction data (1985, AGU) Present day Source: Hoffert & Covey (1992, Nature)

  4. (3) Future projections (from models) Multi-model mean changes in surface air temperature (°C, left) and precipitation (mm/day) A1B Scenario, 2080-2090 relative to 1980-1999 IPCC (2007)

  5. “Advances in climate modeling and reconstruction of paleoclimates from proxy data have resolved some controversies but have underscored areas where understanding of greenhouse climates remains imperfect. Latitudinal temperature gradients are particularly problematic.” from Warm Climates in Earth History (Huber et al. 2002) deficit Poleward heat flux solar surplus terrestrial deficit Poleward heat flux Baroclinic eddy heat flux = -Diffusivity x mean gradient What other mechanisms?

  6. Proposed mechanism for polar amplification: Tropical Rossby wave source, poleward wave propagation, & high-latitude adiabatic warming • CO2 warming causes tropical convective heating to be more localized • Convective heating excites Rossby waves • Rossby waves propagate poleward, transporting westerly momentum equatorward: eastward acceleration in tropics • Atmosphere adjusts toward a balanced state • Poleward heat transport by the waves westward acceleration Eastward acceleration PolewardRossby propagation X height Adiabatic warming equator pole

  7. Upper-level zonal wind of a superrotating state Inspiration of the hypothesis: Rossby waves excited by a tropical heat source cause equatorial superrotation [Saravanan 1993] latitude Wave source longitude Upper level zonal wind of normal state

  8. Upper-level zonal wind of a superrotating state Eddy heat flux of a superrotating state Inspiration of the hypothesis: Rossby waves excited by a tropical heat source cause equatorial superrotation [Saravanan 1993] Eddy heat flux of normal state Upper level zonal wind of normal state In a superrotating state, there must be a process other than baroclinic eddy heat flux that maintains the weak temperature gradient

  9. Test of the hypothesis for the Cretaceous climates • Coupled atmosphere-mixed layer ocean GCM (GENESIS) • 50-m oceanic mixed layer with diffusive heat flux • Atmospheric GCM: T31 (3.75o), 18 vertical levels • CO2: 4 X pre-industrial value 1120 ppmv • CTL run: no prescribed tropical heating • EXP run: local tropical heating – compensating cooling • Heating/cooling profile: maximum in the mid-troposhere Warm pool heating (150 W/m2) equator Compensating cooling (-50 W/m2) longitude

  10. tropical perturbation run - control run Surface temperature 250-hPa height and winds

  11. To test the hypothesis, consider thermodynamic energy equation heat flux convergence adiabatic warming radiative cooling diabatic heating temperature change heat flux convergence stationary eddies heat flux convergence transient eddies adiabatic warming

  12. Change in stationary eddy heat flux Change in stationary eddy heat flux convergence 0.3 K/day; for g = 20 day, dT ~ 6 K

  13. Change in transient eddy heat flux Change in transient eddy heat flux convergence 0.3 K/day; for g = 20 day, dT ~ 6 K

  14. change in vertical velocity (dP/dt) change in adiabatic warming 0.4 K/day; for g = 20 day, dT ~ 8 K

  15. what drives high-latitude adiabatic warming? change in stationary eddy momentum flux convergence change in vertical velocity (dP/dt) E W E W

  16. January zonal mean surface air temperature Tropical heating contrast (W/m2)

  17. Main findings of the Cretaceous modeling study • Localized tropical heating (net zero heating) can warm the Arctic. • Winter Arctic warming is driven by dynamic warming (adiabatic warming driven by stationary eddy momentum flux + stationary eddy heat flux), and possibly by downward IR (cloud cover increases). • Within the range of 0-150 W/m2, zonal mean Arctic temperature increases 0.8oC per 10 W/m2 for CO2 level of 4 X PAL (Cretaceous); • increases 0.3oC per 10 W/m2 for CO2 level of 1 X PAL (present) • Above 150 W/m2, the Arctic warming saturates • Tropical upper tropospheric zonal wind becomes more strongly super-rotating.

  18. Does localized tropical convective heating increase as the climate warms? Climatology Linear trend (1979-2002) mm/day/century

  19. Testing the hypothesis with ECMWF reanalysis (1982-2001) minus (1958-1977) Surface temperature 250-hPa streamfunction 250-hPa eddy streamfunction Convective precipitation

  20. To test the hypothesis, consider the thermodynamic energy equation heat flux convergence adiabatic warming radiative cooling diabatic heating temperature change heat flux convergence adiabatic warming diabatic heating

  21. Testing the hypothesis with ECMWF reanalysis (1982-2001) minus (1958-1977) Surface temperature Downward IR flux Direct consequence of Rossby wave dynamics Horizontal temperature advection + Adiabatic warming Surface heat flux

  22. The findings so far: Dynamical processes & downward IR radiative flux warm the Arctic Questions: 1. Are these two processes linked? 2. How does the inter-decadal time-scale Arctic warming occur through Rossby wave dynamics which takes place on intraseasonal time scales?

  23. Daily evolution associated with the 250-hPa streamfunction trend pattern 250-hPa streamfunction Downward IR flux Surface temperature

  24. Spatial correlations between trend patterns & daily patterns Tropical precip => atm circulation (Rossby waves) => IR warming, surface warming (day)

  25. Surface Air Temperature Response to Madden-Julian Oscillation MJO Phase 1 MJO Phase 5

  26. Interdecadal changes in MJO phase frequency

  27. Interdecadal changes in surface air temperature due to MJO

  28. Main findings: from (1958-1979) to (1980-2001) Tropical convective precipitation (thus heating) became more confined into the Indo-Pacific warm pool region. Winter Arctic warming is driven by dynamic warming and downward IR. This decadal time-scale Arctic warming occurs through changes in the frequency of occurrence of a small number of intraseasonal-scale teleconnection patterns. The warm pool convection leads the teleconnection patterns by 3-4 days; the teleconnection patterns lead the IR flux by 2-3 days; Interdecadal changes in the Madden-Julian Oscillation contribute toward polar amplification.

  29. Passive tracer evolution MJO phase 1 MJO phase 5

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