Response of the low-level jet to precession and its implications for
proxies of the Indian monsoon
Abstract
The long-term variations in the South Asian monsoon have been inferred
based on the variations in the ocean productivity along the western
coast of the Arabian Sea. The variations in ocean productivity were
previously thought to be primarily influenced by the intensity of
upwelling. Here, using idealized precession experiments in fully coupled
climate models, we have shown that the area as well as the region of
maximum upwelling change with precession. When summer occurs at
perihelion (stronger summer insolation and monsoon precipitation) the
area of upwelling is narrow. In contrast, during summer at aphelion
(weaker summer insolation and monsoon precipitation), upwelling occurs
over a broader region. This is due to the effect of convective heating
over northeastern Africa and the western equatorial Indian ocean on the
width and meridional location of the low-level jet. Therefore, the
upwelling inferred from proxies does not necessarily indicate the Indian
summer monsoon strength.