Orbital forcing strongly influences the poleward shift of the spring Himalayan jet during the past millennium

Here we use the Community Earth System Model-Last Millennium Ensemble to diagnose forced trends in HJL during the past millennium. During 850-1849, there is a weak equatorward trend in winter HJL.

In contrast, the spring HJL has a relatively larger poleward trend, and increases in both variance and frequency of poleward/equatorward excursions. We demonstrate changes in orbital precession reduced the thermal gradient between tropical and subtropical Asia, shifting the spring HJL poleward. During 1850-2005, the spring HJL exhibits no trend due to compensating influences from orbital and anthropogenic greenhouse gas forcings.