11/16/2016

Examining the Diurnal Cycle of Convection in the Amazon

GOAmazon data provides unique opportunity for studying the complicated diurnal cycle in Amazonian convection.

The Science

The Amazon is one of the major tropical convective regions in the global climate system, providing moisture to the global hydrological cycle and energy to drive the global atmospheric circulation.  The diurnal cycle of the atmosphere is an important feature that is poorly simulated in climate models. The diurnal cycle over the Amazon basin is complex because it is affected by three types of convective systems: locally generated small convective cells with short lifetimes, coastal systems initialized at the northeast coast of Brazil by the sea breeze, and large mesoscale convective systems initiating in the Amazon basin.

The Impact

This study aims to improve understanding of the seasonal and diurnal variation of convective systems over the Amazon region and their associated large-scale structures through data collected from the GOAmazon2014/15 field campaign.  The improved understanding of the tropical cloud systems and their environments will lead to a better representation of convective processes in weather and climate models.  Additionally, the large-scale forcing datasets derived during this study are available to the science community to support high-resolution modeling of Amazonia convection.

Summary

Propagating convective systems originating far from the Amazon region are often seen in the early morning of the wet season, while they are rarely observed in the dry season.  Afternoon convective systems due to solar heating are frequently seen in both seasons.  Accordingly, in the morning, there is strong upward motion and associated heating and drying throughout the entire troposphere in the wet season, which is limited to lower levels in the dry season.  In the afternoon, both seasons exhibit weak heating and strong moistening in the boundary layer related to the vertical convergence of eddy fluxes.  A set of case studies of three typical types of convective systems occurring in Amazonia — i.e., locally occurring systems, coastal occurring systems, and basin occurring systems — is also conducted to investigate the variability of the large-scale environment with different types of convective systems.  Locally occurring systems are often seen in both seasons, will little seasonal variability.  Coastal occurring and basin occurring systems happen more in the wet season than in the dry season.  These three different types of convective systems are associated with different large-scale structures of heat and moisture budget.

Principal Investigator(s)

Shaocheng Xie
Lawrence Livermore National Laboratory
xie2@llnl.gov

Funding

This research is supported by the Biological and Environmental Research Division in the Office of Sciences of the US Department of Energy (DOE). Work at LLNL was supported by the DOE Atmospheric Radiation Measurement (ARM) program under contract  no. DE-AC52-07NA27344. Work at Stony Brook was supported by the Office of Science of the US Department of Energy and by the National Science Foundation. This paper has been authored by employees of Brookhaven Science Associates, LLC, with support from the ARM program and Atmospheric System Research Program under contract no. DE-AC02-98CH10886 with the US Department of Energy. Zhe Feng at the Pacific Northwest National Laboratory (PNNL) is supported by the US DOE, as part of the Atmospheric System Research (ASR) Program.  PNNL is operated for DOE by Battelle Memorial Institute under contract DE-AC05-76RL01830.  Work at ECMWF was supported by the US Department of Energy via the Atmospheric System Research Program under contract no. DE-SC0005259. The satellite analyses are supported by the DOE ARM and ASR program under contract, DE-SC0013896.

References

Tang S, S Xie, Y Zhang, M Zhang, C Schumacher, H Upton, M Jensen, K Johnson, M Wang, M Ahlgrimm, Z Feng, P Minnis, and M Thieman. 2016. “Large-scale vertical velocity, diabatic heating and drying profiles associated with seasonal and diurnal variations of convective systems observed in the GoAmazon2014/5 experiment.” Atmospheric Chemistry and Physics, 16(22), 10.5194/acp-16-14249-2016.