TY - JOUR
T1 - Midlatitude Jet Position Spread Linked to Atmospheric Convective Types
AU - Fuchs, David
AU - Sherwood, Steven C.
AU - Waugh, Darryn
AU - Dixit, Vishal
AU - England, Matthew H.
AU - Hwong, Yi-Ling
AU - Geoffroy, Olivier
PY - 2023
Y1 - 2023
N2 - Midlatitude weather is largely governed by bands of strong westerly winds known as the midlatitude jets, but what controls the jet properties, particularly their latitudes, remains poorly understood. Climate models show a spread of about 108 in their simulated present-day latitude of the Southern Hemisphere (SH) jet, and a related spread in its predicted poleward shift under global warming. We find that models with more poleward jets simulate more low-level moisture, a warmer upper troposphere, and different precipitation patterns than those with equatorward jets, potentially implicating intermodel differences in moist convection and microphysics. Accordingly, a suite of atmospheric model runs is performed where the deep or shallow convective parameterizations are individually turned off either globally or in specific latitude bands. These experiments suggest that models that produce more shallow convection in the midlatitudes tend to position the jet relatively poleward in SH summer, whereas those that favor deep convection tend to position it equatorward. This accounts for a spread 60% as large as that of the AMIP ensemble during the austral summer. Our results suggest that, in the boreal summer, similar biases appear in the Northern Hemisphere. The presence of shallow convection in the Northern Hemisphere midlatitudes reduces SH jet shift in a warmer climate in accordance to the correlation between jet positions and shift seen in this season. These results can help explain intermodel differences in the position and shift of the jet, and point to an unexpected role for atmospheric moist convection in the midlatitude circulation.
AB - Midlatitude weather is largely governed by bands of strong westerly winds known as the midlatitude jets, but what controls the jet properties, particularly their latitudes, remains poorly understood. Climate models show a spread of about 108 in their simulated present-day latitude of the Southern Hemisphere (SH) jet, and a related spread in its predicted poleward shift under global warming. We find that models with more poleward jets simulate more low-level moisture, a warmer upper troposphere, and different precipitation patterns than those with equatorward jets, potentially implicating intermodel differences in moist convection and microphysics. Accordingly, a suite of atmospheric model runs is performed where the deep or shallow convective parameterizations are individually turned off either globally or in specific latitude bands. These experiments suggest that models that produce more shallow convection in the midlatitudes tend to position the jet relatively poleward in SH summer, whereas those that favor deep convection tend to position it equatorward. This accounts for a spread 60% as large as that of the AMIP ensemble during the austral summer. Our results suggest that, in the boreal summer, similar biases appear in the Northern Hemisphere. The presence of shallow convection in the Northern Hemisphere midlatitudes reduces SH jet shift in a warmer climate in accordance to the correlation between jet positions and shift seen in this season. These results can help explain intermodel differences in the position and shift of the jet, and point to an unexpected role for atmospheric moist convection in the midlatitude circulation.
KW - Atmospheric circulation
KW - Climate change
KW - Convection
KW - Convective parameterization
KW - Convective-scale processes
KW - Jets
UR - http://www.scopus.com/inward/record.url?scp=85151060022&partnerID=8YFLogxK
UR - https://www.researchgate.net/publication/363532760_Midlatitude_jet_position_spread_linked_to_atmospheric_convective_types
U2 - 10.1175/JCLI-D-21-0992.1
DO - 10.1175/JCLI-D-21-0992.1
M3 - Article
AN - SCOPUS:85151060022
SN - 0894-8755
VL - 36
SP - 1247
EP - 1265
JO - Journal of Climate
JF - Journal of Climate
IS - 4
ER -