27 Sep 2022
27 Sep 2022
Status: this preprint is currently under review for the journal CP.

On the importance of moisture conveyor belts from the tropical East Pacific for wetter conditions in the Atacama Desert during the Mid-Pliocene

Mark Reyers1, Stephanie Fiedler1, Patrick Ludwig2, Christoph Böhm1, Volker Wennrich3, and Yaping Shao1 Mark Reyers et al.
  • 1Institute for Geophysics and Meteorology, University of Cologne, Cologne, Germany
  • 2Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 3Institute for Geology and Mineralogy, University of Cologne, Cologne, Germany

Abstract. Geomorphic and sedimentologic data indicate that the climate of today’s hyper-arid Atacama Desert (Northern Chile) was more humid during the Mid-to Late Pliocene. The processes, however, leading to increased rainfall in this period are largely unknown. To uncover these processes we use both global and regional kilometre-scale model experiments for the mid-Pliocene (3.2 Ma BP). We found that the PMIP4-CMIP6 model (CESM2) and the regional model (WRF) used in our study simulate more rainfall in the Atacama Desert for the mid-Pliocene in accordance to proxy data, mainly due to stronger extreme rainfall events in winter. Case studies reveal that these extreme winter rainfall events during the mid-Pliocene are associated with strong moisture conveyer belts (MCBs) originating in the tropical East Pacific. For present-day conditions, in contrast, our simulations suggest that the moisture fluxes rather arise from the subtropical Pacific region and are much weaker. A clustering approach reveals systematic differences between the moisture fluxes in the present-day and mid-Pliocene climates, both in strength and origins. The two mid-Pliocene clusters representing tropical MCBs and occurring less than one day per year on average produce more rainfall in the hyper-arid core of the Atacama Desert south of 20° S than what is simulated for the entire present-day period. We thus conclude that MCBs are mainly responsible for enhanced rainfall during the mid-Pliocene. There is also a strong SST increase in the tropical East Pacific and along the Atacama coast for the mid-Pliocene. It suggests that a warmer ocean in combination with stronger mid-tropospheric troughs is beneficial for the development of MCBs leading to more extreme rainfall in a +3 K warmer world like in the mid-Pliocene.

Mark Reyers et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on cp-2022-72', Arthur Oldeman, 28 Sep 2022
  • RC1: 'Comment on cp-2022-72', Teresa Jordan, 30 Oct 2022
  • RC2: 'Comment on cp-2022-72', Anonymous Referee #2, 24 Nov 2022

Mark Reyers et al.

Mark Reyers et al.


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Short summary
In this study we performed high-resolution climate model simulations for the hyper-arid Atacama Desert for a time period 3.2 million years ago (mid-Pliocene). The aim is to uncover the atmospheric processes that are involved in the enhancement of strong rainfall events during this period. We find that strong upper-level moisture fluxes (so-called moisture conveyer belts) originating in the tropical East Pacific are the main driver for increased rainfall in the mid-Pliocene.