Last Glacial Maximum ITCZ Changes From PMIP3/4 Simulations

Abstract

The intertropical convergence zone (ITCZ) is the region near the equator where the trade winds of the Northern and Southern Hemispheres converge. It appears as a band of heavy precipitation that encircles the globe. The annual precipitation in the ITCZ accounts for 32% of the globally integrated precipitation in the current climate (Kang et al., 2018). The ITCZ has an important impact on the Earth's climate. In the tropics, the ITCZ modulates cyclone genesis and the convective initiation of the Madden-Julian Oscillation (Wang & Magnusdottir, 2006;Zelinsky et al., 2019). The ITCZ also interacts with subtropical circulations and monsoon systems through the Hadley cell (Song et al., 2018;Watt-Meyer & Frierson, 2019;Zhou et al., 2019). The onset of the boreal summer monsoon is triggered by the annual northward shift of the ITCZ (Geen et al., 2020;Linsley et al., 1994). Except for the seasonal cycle variation, extreme interannual northward shift of the ITCZ may lead to severe droughts through circulation and precipitation changes (Weller et al., 2014). Since changes in the position and structure of the ITCZ affect the tropical and extratropical climate on various time scales (Mukherjee et al., 2017), it is essen tial to understand how it responses to climate change.Previous studies have investigated how the ITCZ changes in a warming climate. Satellite observations and reanalysis data suggest that the ITCZ in the Atlantic and Pacific oceans has narrowed and strengthened in recent

Response of the Central Pacific Intertropical Convergence Zone to Northern Hemisphere Cooling During the Last Glacial Maximum and Heinrich Stadial 1

“…Using the present-day geochemically defined mean ITCZ position of 6°N-7°N as a reference, it is concluded that the annual mean ITCZ position was about 3°s outh during the LGM and 1°-3°south during HS1 relative to the present (Figure 2). The maximum 3°latitudinal shift observed in this study is much larger than the global average of <1°southward shift during the LGM and HS1 estimated by models and paleoclimate reconstructions (Atwood et al, 2020;McGee et al, 2014;Wang et al, 2023). However, these studies pointed out potential greater shift of the precipitation centroid in the central Pacific.…”

“…The maximum 3° latitudinal shift observed in this study is much larger than the global average of <1° southward shift during the LGM and HS1 estimated by models and paleoclimate reconstructions (Atwood et al., 2020; McGee et al., 2014; Wang et al., 2023). However, these studies pointed out potential greater shift of the precipitation centroid in the central Pacific.…”

The Hadley circulation in a changing climate

“…Climate model simulations of the Heinrich stadials show decreased northward OHT and an associated equatorward shift of the ITCZ, weakening of the NH monsoons, and a relatively wetter climate in the SH 236 . Similar to other cold periods, reconstructions for the last glacial maximum show a southward shift of the ITCZ 233 and reinforced northeast trade winds 105, 237 . Trade winds proxies of the HC during cold episodes are consistent with the response predicted in the section “Linking the ITCZ position with ocean heat transport, TOA flux, and SST”: cooling the NH relative to the SH shifts the ITCZ equatorward and strengthens the NH trade winds, while it weakens them in the SH 236 .…”

“…PMIP simulations of LGM ($$\sim$$21 kyr BP) clearly show that the winter solstitial HC was stronger and narrower than in preindustrial conditions 105, 108 . Literature also provides a consensus on a equatorward shift of the ITCZ 233 . During the glacials and cold episodes, such as the Younger Dryas (12.9–11.7 kyr BP) and Heinrich stadials, the complex interplay between orbital and CO 2 forcing, and ice‐sheets dynamics presumably led to an AMOC slowdown 234, 235 .…”

The Role of Wet Processes in Extratropical Thermal Stratification During the Glacial Period

“…The data set employed in this research is sourced from the Paleoclimate Modeling Intercomparison Project Phase III and Phase IV (Braconnot et al., 2011; Kageyama et al., 2021; T. Wang et al., 2023, PMIP3/PMIP4) LGM experiment and Pre‐industrial (PI) control run. A total of nine models from PMIP3 and five models from PMIP4 were included in our investigation.…”