Drivers of the Low Cloud Response to Poleward Jet Shifts in the North Pacific in Observations and Models

TitleDrivers of the Low Cloud Response to Poleward Jet Shifts in the North Pacific in Observations and Models
Publication TypeJournal Article
Year of Publication2018
AuthorsZelinka, Mark, Grise Kevin, Klein Stephen, Zhou Chen, DeAngelis Anthony, and Christensen Matthew
JournalJournal of Climate
Abstract / Summary

The long-standing expectation that poleward shifts of the midlatitude jet under global warming will lead to poleward shifts of clouds and a positive radiative feedback on the climate system has been shown to be misguided by several recent studies. On interannual timescales, free tropospheric clouds are observed to shift along with the jet, but low clouds increase across a broad expanse of the North Pacific Ocean basin, resulting in negligible changes in total cloud fraction and top-of-atmosphere radiation. Here it is shown that this low cloud response is consistent across eight independent satellite-derived cloud products. Using multiple linear regression, it is demonstrated that the spatial pattern and magnitude of the low cloud coverage response is primarily driven by anomalous surface temperature advection. In the Eastern North Pacific, anomalous cold advection by anomalous northerly surface winds enhances sensible and latent heat fluxes from the ocean into the boundary layer, resulting in large increases in low cloud coverage. Local increases in low-level stability make a smaller contribution to this low cloud increase. Despite closely capturing the observed response of large-scale meteorology to jet shifts, global climate models largely fail to capture the observed response of clouds and radiation to interannual jet shifts because they systematically underestimate how sensitive low clouds are to surface temperature advection, and to a lesser extent, low-level stability. More realistic model simulations of cloud-radiation-jet interactions require that parameterizations more accurately capture the sensitivity of low clouds to surface temperature advection. 

URLhttps://doi.org/10.1175/JCLI-D-18-0114.1
DOI10.1175/JCLI-D-18-0114.1
Journal: Journal of Climate
Year of Publication: 2018

The long-standing expectation that poleward shifts of the midlatitude jet under global warming will lead to poleward shifts of clouds and a positive radiative feedback on the climate system has been shown to be misguided by several recent studies. On interannual timescales, free tropospheric clouds are observed to shift along with the jet, but low clouds increase across a broad expanse of the North Pacific Ocean basin, resulting in negligible changes in total cloud fraction and top-of-atmosphere radiation. Here it is shown that this low cloud response is consistent across eight independent satellite-derived cloud products. Using multiple linear regression, it is demonstrated that the spatial pattern and magnitude of the low cloud coverage response is primarily driven by anomalous surface temperature advection. In the Eastern North Pacific, anomalous cold advection by anomalous northerly surface winds enhances sensible and latent heat fluxes from the ocean into the boundary layer, resulting in large increases in low cloud coverage. Local increases in low-level stability make a smaller contribution to this low cloud increase. Despite closely capturing the observed response of large-scale meteorology to jet shifts, global climate models largely fail to capture the observed response of clouds and radiation to interannual jet shifts because they systematically underestimate how sensitive low clouds are to surface temperature advection, and to a lesser extent, low-level stability. More realistic model simulations of cloud-radiation-jet interactions require that parameterizations more accurately capture the sensitivity of low clouds to surface temperature advection. 

DOI: 10.1175/JCLI-D-18-0114.1
Citation:
Zelinka, M, K Grise, S Klein, C Zhou, A DeAngelis, and M Christensen.  2018.  "Drivers of the Low Cloud Response to Poleward Jet Shifts in the North Pacific in Observations and Models."  Journal of Climate.  https://doi.org/10.1175/JCLI-D-18-0114.1.