The Andes and the Southeast Pacific Cold Tongue Simulation

Current climate models significantly overestimate precipitation and temperature over the southeast Pacific. Previous studies show that the Andes influence the southeast Pacific climate, but because they are a narrow mountain range, these effects are not well represented with the smoothing in low-resolution climate models. We hypothesize that the elevation of the Andes in low-resolution climate models is too low, allowing too much airflow across the mountains. Using the Community Earth System Model (CESM) version 1.2.2 with a slab-ocean setting, we blocked the low-level airflow across the mountains by adjusting the height of the Andes. Our results show that using higher Andes in the model enhances the anticyclonic motion and increases the subsidence of air in the southeast Pacific. The evaporative cooling from the strengthened surface wind and the radiative cooling from the formation of low-level clouds lower the sea surface temperature (SST) in the southeast Pacific. The enhanced descent over the southeast Pacific inhibits precipitation. We also performed a sensitivity test, varying the elevation of the Andes from 0 to 6 km, and analyzed the resulting energy budget and climate in both hemispheres. An increase of the elevation of the Andes causes the energy flux equator (EKE) to shift northward, as a result of the decrease of the energy absorption in the Southern Hemisphere. Our research suggests that the Andes act as a barrier in maintaining the climate over the southeast Pacific Ocean, and this effect is not well represented in low-resolution climate models.

Automated summary

The study suggests that current climate models overestimate precipitation and temperature over the southeast Pacific, with the Andes playing a key role in maintaining the climate in that region. Low-resolution climate models fail to accurately represent the effects of the Andes as a barrier in the southeast Pacific Ocean.