Synergy between Heat and Moisture Transport in Atmospheric Rivers in the Extratropical Andes

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Abstract Atmospheric rivers (ARs) are narrow corridors of concentrated moisture and heat transport that play a vital role in driving precipitation in midlatitude regions, such as the extratropical Andes. However, the interaction between heat and moisture in ARs making landfall in the extratropical Andes remains quantitatively uncharacterized. In this study, we investigate the interaction between heat and moisture transport within 80 zonal ARs (ZARs) through concurrent heat and moisture budget analyses of events affecting the region from 1980 to 2023. Recognizing the key role of moisture-weighted mass convergence in maintaining ZARs over the ocean, our results emphasize the substantial contribution of diabatic heating—arising from microphysical processes within ZARs—in enhancing this convergence. Using the Weather Research and Forecasting (WRF) Model, we demonstrate that latent heating associated with microphysical processes within ZARs can intensify moisture-weighted mass convergence by generating diabatically induced cyclonic potential vorticity (PV). This modulation of moisture-weighted mass convergence over the open ocean by diabatic heating is shown to influence key ZAR dynamics, including low-level wind. Furthermore, we find that atmospheric column heating within ZARs—driven by both heat advection and adiabatic processes—may enhance along-ZAR moisture transport toward the continent. These findings clarify how latent heating from microphysical processes within the ZAR, together with warming from heat advection and adiabatic processes over the South Pacific, contributes to the enhancement of the ZAR structure.

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