5:15 PM - 6:45 PM
[MIS12-P09] Analysis of Daily-Scale Meteorological Elements Influenced by 4.2 ka Insolation Forcing Using the State-of-the-Art AOGCM MIROC6
Keywords:Milankovitch, climate model, paleoclimate, extreme weather, 4.2ka event
The 4.2 ka event, marking the boundary between the Middle and Late Holocene, is recognized as a global event characterized by drying and cooling, potentially linked to the collapse of several ancient civilizations. The causes behind the 4.2 ka event have been debated, with the specific role of the insolation forcing remaining unclear. In this study, we explored the influence of the 4.2 ka and pre-industrial (PI) insolation forcings on the climatological mean and daily temperature and precipitation. To simulate the quasi-equilibrium states under 4.2 ka and PI Milankovitch parameters, we utilized MIROC6, the state-of-the-art atmospheric-ocean general circulation model (AOGCM). We focused on the Middle East, specifically the Mesopotamian region, including Tell Leilan (37N58E), the Akkadian Empire's central city, and Muscat (23N58E), near Oman Bay, where various paleo proxies have been collected.
The results show that 4.2 ka was generally warmer (colder) and wetter (drier) in summer (winter) compared to PI. In Muscat, we observed an inverse precipitation seasonality; during 4.2 ka, rain season in summer and dry season in winter, contrasting with the PI seasonality. In Tell Leilan, the seasonal differences in temperature and precipitation were less pronounced than in Muscat; precipitation seasonality was similar in PI and 4.2 ka. Additionally, our daily-scale analysis revealed that insolation forcings changed the frequency of extreme weather events. In Muscat during summer, extreme weather events, characterized by daily mean temperatures below 30 degrees Celsius and precipitation over 20 mm/day, increased in frequency from approximately once every 20 years in PI to approximately once every 5 years in 4.2 ka. In Tel Leilan during summer, extreme precipitation and cooling events, as in Muscat, were not observed. Still, a significant negative correlation between temperatures and precipitation was exhibited. In both sites during winter, a weak and significant correlation between temperature and precipitation was exhibited, with extreme precipitation events not necessarily coinciding with extreme cooling.
Our findings demonstrate the utility of daily-scale analysis for understanding the influence of insolation forcings on climate. The divergent results between Tell Leilan and Muscat highlight the importance of considering the spatial representation of paleo proxies and potential biases in climate models when interpreting the 4.2 ka event. In future work, we will delve into the analysis of atmospheric circulations, including subtropical high pressures, winter westerly winds, and summer monsoons, to investigate further the factors influencing the climatological mean and the frequency of extreme weather events.
The results show that 4.2 ka was generally warmer (colder) and wetter (drier) in summer (winter) compared to PI. In Muscat, we observed an inverse precipitation seasonality; during 4.2 ka, rain season in summer and dry season in winter, contrasting with the PI seasonality. In Tell Leilan, the seasonal differences in temperature and precipitation were less pronounced than in Muscat; precipitation seasonality was similar in PI and 4.2 ka. Additionally, our daily-scale analysis revealed that insolation forcings changed the frequency of extreme weather events. In Muscat during summer, extreme weather events, characterized by daily mean temperatures below 30 degrees Celsius and precipitation over 20 mm/day, increased in frequency from approximately once every 20 years in PI to approximately once every 5 years in 4.2 ka. In Tel Leilan during summer, extreme precipitation and cooling events, as in Muscat, were not observed. Still, a significant negative correlation between temperatures and precipitation was exhibited. In both sites during winter, a weak and significant correlation between temperature and precipitation was exhibited, with extreme precipitation events not necessarily coinciding with extreme cooling.
Our findings demonstrate the utility of daily-scale analysis for understanding the influence of insolation forcings on climate. The divergent results between Tell Leilan and Muscat highlight the importance of considering the spatial representation of paleo proxies and potential biases in climate models when interpreting the 4.2 ka event. In future work, we will delve into the analysis of atmospheric circulations, including subtropical high pressures, winter westerly winds, and summer monsoons, to investigate further the factors influencing the climatological mean and the frequency of extreme weather events.