Abstract
The quasi-biennial oscillation (QBO) and sudden stratospheric warmings (SSWs) during the Last Glacial Maximum (LGM) are investigated in simulations using the Whole Atmosphere Community Climate Model version 6 (WACCM6). We find that the period of QBO, which is 27 months in the preindustrial and modern climate simulations, was 33 months in the LGM simulation using the proxy sea surface temperatures (SSTs) and 41 months using the model-based LGM SSTs. We show that the longer QBO period in the LGM is due to weaker wave forcing. The WACCM6 simulations of the LGM, preindustrial, and modern climates do not support previous modeling work that suggests that the QBO amplitude is smaller (larger) in a warmer (colder) climate. We find that SSWs in the LGM occurred later in the year, as compared to the preindustrial and modern climate, but that time of the final warming was similar. The difference in SSW frequency is inconclusive.
Highlights
The stratosphere during the Last Glacial Maximum (LGM) is expected to be considerably different than in the preindustrial and modern climate because of reduced CO2, CH4, and N2 O concentrations; the presence of large ice sheets in the Northern Hemisphere (NH); and lower sea surface temperature (SST) [1,2,3]
We find that the period of quasi-biennial oscillation (QBO) increases from 27 months in the preindustrial and modern climate to 33–41 months in LGM, while the stratospheric warmings (SSWs) in the LGM are found to occur later in the year
It is found that the period of QBO, which is 27 months in the preindustrial and modern climates, was 33–41 months in LGM
Summary
The stratosphere during the Last Glacial Maximum (LGM) is expected to be considerably different than in the preindustrial and modern climate because of reduced CO2 , CH4 , and N2 O concentrations; the presence of large ice sheets in the Northern Hemisphere (NH); and lower sea surface temperature (SST) [1,2,3]. Project phase 5 (CMIP5) models that are capable of simulating QBO-like variability, Kawatani and Hamilton [25] found a long-term reduction in the QBO amplitude in the lower stratosphere but their results concerning QBO period changes were inconclusive. We analyze the LGM simulations that used the prescribed SST from both model simulation and proxy data, and compare them with results of pre-industrial and modern climate simulations that used the observed SST and sea ice. We find that the period of QBO increases from 27 months in the preindustrial and modern climate to 33–41 months in LGM, while the SSWs in the LGM are found to occur later in the year. We analyze simulations of the LGM and preindustrial and modern climate constrained by observed SSTs to help broaden our perspective regarding the stratospheric response to anthropogenically induced climate changes in the future
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