Energetic Constraints on the Intertropical Convergence Zone Position in the Observed Seasonal Cycle From Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2)

Idealized simulations show that the approximate colocation between the ITCZ and the energy flux equator (EFE), which holds on the annual and zonal average, breaks down on subseasonal timescales, as the Hadley cell develops a shallow return flow and negative gross moist stability (GMS). Here, we explore if similar mechanisms are seen in reanalysis data. In the zonal mean, a temporal offset exists between the ITCZ and the EFE as the ITCZ is retreating from the Northern to Southern Hemisphere and the Hadley cell transports energy northward across the equator despite a northward-shifted ITCZ. At these times, the southern cell has a bottom-heavy structure, with a distorted cell boundary and northward energy transport. In the Eastern Pacific, while bottom-heavy structures exist throughout the year, the bottom heaviness is stronger in boreal fall, when GMS is negative, and SSTs are weak while their Laplacian is large and negative below the ITCZ.