Mechanisms Associated With Tropospheric Dry Static Stability Change During the Last Glacial Maximum

The processes governing tropospheric stratification alterations during the Last Glacial Maximum (LGM) are investigated using the Paleoclimate Modeling Intercomparison Project Phase 3/4 (PMIP3/PMIP4) simulations. The results demonstrate a decrease in static stability in the tropics during both December-January-February (DJF) and June-July-August (JJA), while an increase is observed in the extratropics during DJF. Further analysis reveals that the rise in static stability over high-latitude ocean is driven by shifts in surface frozen lines, whereas the increased static stability over ice sheet margins is due to the cooling effect of ice sheet slopes. The study finds that the dry static stability change in ice sheet-covered areas remains significant and robust in both PMIP3 and PMIP4. However, a weaker stabilization signal is detected in the North Atlantic in PMIP4. These findings provide valuable insights into the processes shaping tropospheric stratification during the LGM and underscore the importance of accounting for ice sheet effects in paleoclimate simulations. The Last Glacial Maximum (LGM) is a cold period in the Earth history. Here, we use numerical model data from the Paleoclimate Modeling Intercomparison Project Phase 3/4 (PMIP3/PMIP4) to investigate the atmospheric stability change during the period. The results indicate that the low latitude atmosphere was more unstable during both December-January-February (DJF) and June-July-August (JJA), whereas the midlatitude and high-latitude atmospheres were only more stable during DJF. The latter stabilization is mostly related to the sea ice activities and cold surface of ice sheet slope. During the Last Glacial Maximum (LGM), in the Northern Hemisphere (NH) static stability decreases in the tropics during both summer and winter due to weakening convection activitiesDuring the LGM, in NH winter, increase in static stability over high-latitude ocean results from the shift in frozen linesDuring the LGM, in NH winter, increase in static stability over ice sheet margins mostly results from the ice sheet slope cooling effect