Shang-Ping Xie
Scripps Institution of Oceanography, UC San Diego
w/ Liu Yang, Matt Luongo, Ayumu Miyamoto, Yen-Ting Hwang, Sarah Kang
Joint low cloud/WES feedback as a conduit to tropical SST patterns
Figure 7.10 | Global mean climate feedbacks estimated in abrupt4xCO2 simulations of 29 CMIP5 models (light blue) and 49 CMIP6 models (orange), compared with those assessed in IPCC AR6 (red).
Annual stratus cloud amount
(Klein & Hartmann 1993, JC)
Global feedback vs. localized distribution
🡪 Pattern dynamics (circulation response & feedback)
Positive w/
Large uncertainty
Increased low cloud
Increased stability
Reduced SST
Low cloud-SST feedback:
Important in the subtropics
Cloud-rad effect at sfc SW (132–122°E, 20-30 °N)
JJA
Fig. 12. (a) Scatterplot of seasonal-mean stratus amount and lower tropospheric stability in major stratus regions (Klein and Hartmann 1993). (b) Scatterplot of JJA SST and shortwave CRE over the subtropical Northeast Pacific (Yang et al. 2023).
Cloud, SST, wind (JJA)
m/s
80
80
Mean SST; δSST & δWind due to stratus CRE
Miyamoto et al. (2023, J Clim)
Low cloud-SST feedback: localized
Fig. 6.12 (a) JJA changes in SST (gray shading, oC), surface downward shortwave radiation (green contours at interval of 20 W m-2; positive values for downward flux), and surface wind (m s-1; blue/red arrows for weakened/strengthened background winds) in an experiment where the low-cloud radiative effect is artificially turned off within the black box (150oW-110oW, 16oN-32oN). (b) Regression coefficients of JJA shortwave CRE (green contours every 3 W m-2 °C-1; negative dashed), SST (shading, oC) and surface wind (vectors, m s-1) onto seasonal-average SST anomaly in the black box. The thick blue contour highlights the stratus deck (mean cloud cover=0.8). (a) Miyamoto et al. (2023) and (b) adapted from Yang et al. (2023).
Obs interannual var: JJA SST, wind & SW CRE
Low cloud-SST feedback: localized
L. Yang et al. (2023, J Clim)
| Net CRE | Δq |
r | 0.48 | -0.69 |
R | 6.43 | -6.82 |
Cloud feedback & evaporative damping are comparable in strength
🡪 amplified SST variability
Remote impact on ENSO
Obs CESM Cloud locked
Equatorial SST (shading, K K-1) and surface zonal wind (m s-1 K-1) regressions against NEP SST
PMM favors a second-year ENSO event
Aerosols
How does NH cooling reach equator?
Ocean
Atmosphere
Buoyancy
Wind stress
τ’=0
Buoyancy-forced: τ’=0, interactive wind in heat flux
N PMM: low-cloud/WES
🡪 Eq Indo-Pacific: Bjerknes
SST & 850 hPa wind change
Fully coupled
Bjerknes
WES/CRE
Luongo et al. (2022, J Clim)
Response to NH solar reduction in 45-65oN (zonally uniform)
Coupled feedback:
Low-cloud/WES, Bjerknes
CESM
Obs
CESM1
Subtropical NE Pacific
CESM1 is an outlier but realistic!
Luongo et al. (2023, GRL)
L. Yang et al. (2023, J Clim)
Â
Low cloud decks are localized.
↓
Joint low cloud-WES feedback (PMM)
↓
Effective amplifier/conduit to tropics
Aerosols
WES/cloud
STC
Coupled feedback:
Bjerknes, WES, cloud …
Modes of
climate variability (ENSO…)
Patterns of
climate change
Radiative forcing
Fig. 14.22. Schematic of physical and conceptual connections between climate variability and change. They share common pattern dynamics due to coupled ocean-atmospheric feedbacks. These feedbacks manifest in unforced climate variability, offering insights into dynamic processes important for regional climate change. Climate variability drives, and climate change exacerbates, extreme events of large societal impact.
Xie, S-P, 2023: Coupled Atmosphere-Ocean Dynamics, Elsevier, 400 pages.
SST view: coupled feedback
Low cloud decks are localized.
↓
Joint low cloud-WES feedback (PMM)
↓
Effective amplifier/conduit to tropics
Aerosols
WES/cloud
STC