Effects of Lower Troposphere Vertical Mixing on Simulated Clouds and Precipitation Over the Amazon During the Wet Season

Author:

Hu Xiao‐Ming12ORCID,Huang Yongjie1ORCID,Xue Ming12ORCID,Martin Elinor2ORCID,Hong Yang3ORCID,Chen Mengye3ORCID,Novoa Hector Mayol4ORCID,McPherson Renee5ORCID,Perez Andres4ORCID,Morales Isaac Yanqui4ORCID,Luna Auria Julieta Flores4

Affiliation:

1. Center for Analysis and Prediction of Storms University of Oklahoma Norman OK USA

2. School of Meteorology University of Oklahoma Norman OK USA

3. School of Civil Engineering and Environmental Science University of Oklahoma Norman OK USA

4. Universidad Nacional de San Agustín de Arequipa Arequipa Peru

5. Department of Geography and Environmental Sustainability University of Oklahoma Norman OK USA

Abstract

AbstractPlanetary boundary layer (PBL) schemes parameterize unresolved turbulent mixing within the PBL and free troposphere (FT). Previous studies reported that precipitation simulation over the Amazon in South America is quite sensitive to PBL schemes and the exact relationship between the turbulent mixing and precipitation processes is, however, not disentangled. In this study, regional climate simulations over the Amazon in January–February 2019 are examined at process level to understand the precipitation sensitivity to PBL scheme. The focus is on two PBL schemes, the Yonsei University (YSU) scheme, and the asymmetric convective model v2 (ACM2) scheme, which show the largest difference in the simulated precipitation. During daytime, while the FT clouds simulated by YSU dissipate, clouds simulated by ACM2 maintain because of enhanced moisture supply due to the enhanced vertical moisture relay transport process: (a) vertical mixing within PBL transports surface moisture to the PBL top, and (b) FT mixing feeds the moisture into the FT cloud deck. Due to the thick cloud deck over Amazon simulated by ACM2, surface radiative heating is reduced and consequently the convective available potential energy is reduced. As a result, precipitation is weaker from ACM2. Two key parameters dictating the vertical mixing are identified, p, an exponent determining boundary layer mixing and λ, a scale dictating FT mixing. Sensitivity simulations with altered p, λ, and other treatments within YSU and ACM2 confirm the precipitation sensitivity. The FT mixing in the presence of clouds appears most critical to explain the sensitivity between YSU and ACM2.

Funder

Division of Atmospheric and Geospace Sciences

U.S. Department of Energy

Office of Advanced Cyberinfrastructure

National Science Foundation

Publisher

American Geophysical Union (AGU)

Subject

Space and Planetary Science,Earth and Planetary Sciences (miscellaneous),Atmospheric Science,Geophysics

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