Addressing Initial Eastern Equatorial Pacific Cooling

In our nuclear war simulations there is an initial cooling in the eastern equatorial Pacific. Strong radiative cooling is the main driver behind such cooling, but a local increase in the easterly trade winds may indicate a potential land breeze circulation that is driving enhanced upwelling. Nonetheless the eastern equatorial Pacific experiences the greatest cooling in the basin during the month of June (15 to 45 days after injection). To better show this evolution we construct a hovmoller plot of daily surface temperature anomalies and 850 hPa wind anomalies.

Cooling begins directly along the coast of South America, likely because those waters are very shallow and are in proximity to a moderately sized, rapidly cooling continent. Anomalous easterly winds appear along the coast soon after the black carbon injection, allowing for enhanced coastal upwelling which also contributes to this cooling signal. These easterly winds along the equator are confined to 120W-90W as westerly wind anomalies occupy much of the rest of the basin starting from July of Year 0 onward.

Ultimately, less rising air over the Western Pacific (Maritime Continent + Western Warm Pool) is far more important for the Walker Circulation than anomalous sinking air over South America. A cold South America does not have a major influence on ENSO because it does not greatly influence the Pacific Walker Circulation.