The Impact of Large-Scale Land Surface Conditions on the South American Low-Level Jet

The South American low-level jet (SALLJ) serves as a critical mechanism for transporting water vapor from tropical latitudes to southeastern South America (SESA) and is linked to extreme precipitation in its exit region. Previous studies have shown that the SALLJ is strongly associated with the thermal low east of the Andes. This effect is particularly strong during Chaco jet events which penetrate further south than other types of SALLJ. However, few studies have investigated the connections between land surface conditions, thermal low, and the Chaco jet. In this study, we identify Chaco jet events and perform Empirical Orthogonal Function (EOF) and K-means clustering analyses on their associated 850 hPa geopotential heights. This process categorizes the Chaco jet events into two main groups: (1) a favored synoptic conditions group and (2) a quiescent synoptic conditions group. Preliminary results show that the surface sensible heat flux over the thermal low region is significantly larger in the latter group, suggesting that land surface conditions may play an important role in thermal low deepening under quiescent synoptic conditions.