Evaluation of the Causes of Wet‐Season Dry Biases Over Amazonia in CAM5

Ma, Hsi‐Yen; Zhang, Kai; Tang, Shuaiqi; Xie, Shaocheng; Fu, Rong

doi:10.1029/2020jd033859

Cited by 9 publications

(9 citation statements)

References 85 publications

(130 reference statements)

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“…For AOD, CESM1 compares well to reanalysis in all regions, except an underestimation of AOD in SEA (see figure 1(e) for regions). These discrepancies are consistent with previous research revealing the presence of a dry bias in South America [32,33] and underestimation of AOD [34,35] in climate models when compared to observations. Additionally, while it would be ideal to further compare simulated changes to observed changes over the 20th century, this is not possible due to the lack of observations in the early 20th century in the tropics [36], so we focus on the model results to evaluate mechanisms driving long-term changes.…”

Section: Methodssupporting

confidence: 92%

Isolating the effect of biomass burning aerosol emissions on 20th century hydroclimate in South America and Southeast Asia

Magahey,

Kooperman

2023

Environ. Res. Lett.

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Biomass burning is a significant source of aerosol emissions in some regions and has a considerable impact on regional climate. Earth system model simulations indicate that increased biomass burning aerosol emissions contributed to statistically significant decreases in tropical precipitation over the 20th century. In this study, we use the Community Earth System Model version 1 Large Ensemble (CESM1-LENS) experiment to evaluate the mechanisms by which biomass burning aerosol contributed to decreased tropical precipitation, with a focus on South America and Southeast Asia. We analyze the all-but-one forcing simulations in which biomass burning aerosol emissions are held constant while other forcings (e.g., greenhouse gas concentrations) vary throughout the 20th century. This allows us to isolate the influence of biomass burning aerosol on processes that contribute to decreasing precipitation, including cloud microphysics, the radiative effects of absorbing aerosol particles, and alterations in regional circulation. We also show that the 20th century reduction in precipitation identified in the CESM1-LENS historical and biomass burning experiments is consistent across CMIP5 models with interactive aerosol schemes and the CESM2 Single-Forcing experiment. Our results demonstrate that higher concentrations of biomass burning aerosol increases the quantity of cloud condensation nuclei and cloud droplets, limiting cloud droplet size and precipitation formation. Additionally, absorbing aerosols (e.g., black carbon) contribute to a warmer cloud layer, which promotes cloud evaporation, increases atmospheric stability, and alters regional circulation patterns. Corresponding convectively coupled circulation responses, particularly over the tropical Andes, contribute to further reducing the flow of moisture and moisture convergence over tropical land. These results elucidate the processes that affect the water cycle in regions prone to biomass burning and inform our understanding of how future changes in aerosol emissions may impact tropical precipitation over the 21st century.

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Section: Methodssupporting

confidence: 92%

Isolating the effect of biomass burning aerosol emissions on 20th century hydroclimate in South America and Southeast Asia

Magahey,

Kooperman

2023

Environ. Res. Lett.

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“…6&7). Consistent with previous studies (e.g., Dai, 2006;Tang et al 2021), the major de ciency of the CMIP6 models is the too early diurnal precipitation peak, where the multi-model mean of CMIP6 models shows a diurnal phase peaking around noon (or early afternoon) instead of the late-afternoon (or early-evening) precipitation peak from the observations. The relatively poorer performance of the simulated diurnal cycle of precipitation over land/coastal land compared with that over ocean/coastal ocean could be attributed to the complex topography effects and land-atmosphere interactions which are not properly represented in the models.…”

Section: Summary and Future Worksupporting

confidence: 88%

“…Using the Cloud Archive User Service (CLAUS) data, Yang and Slingo (2001) discovered a strong diurnal signal of precipitation over the coastal regions and demonstrated that the climate model has considerable di culty in capturing the observed diurnal phase of precipitation. Generally, common climate model de ciencies in reproducing the diurnal variation of precipitation include the too often convection triggering at reduced intensity, the too early precipitation onset, and the missing of nocturnal precipitation peak (e.g., Dai, 2006;Xie et al 2019;Cui et al 2021;Ma et al 2021).…”

Section: Introductionmentioning

confidence: 99%

Diurnal cycle of precipitation over global monsoon systems in CMIP6 simulations

Tao

Xie²,

Tang³

et al. 2022

Clim Dyn

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Accurate simulation of the diurnal cycle of precipitation over different climate regimes, including global monsoon systems, is an ongoing challenge for current state-of-the-art climate models. In this study, the diurnal cycles of summertime precipitation from 21 CMIP6 historical simulations are evaluated with the NASA IMERG data via the diurnal harmonic amplitude and phase from the Fourier analysis in seven regional monsoon systems: Northern and Southern Africa monsoons, South Asia monsoon, East Asia monsoon, Australia monsoon, and North and South America monsoons. Particularly, we focus on four subregions including ocean, coastal ocean, land, and coastal land considering the different underlying physical processes. It is found that the CMIP6 historical simulations perform fairly well on reproducing the diurnal cycle of precipitation over ocean and coastal ocean, while the simulated diurnal harmonic phase and amplitude over land and coastal land show larger biases and model spread compared to biases over ocean and coastal ocean. The simulation of precipitation diurnal cycle is substantially improved in the multi-model mean of both CMIP6 historical and CMIP6 AMIP simulations compared with that of CMIP5 historical simulations. But the model bias of precipitation diurnal cycle is in general similar between CMIP6 AMIP and CMIP6 historical simulations, which suggests that the impact of the interactive ocean on the simulated diurnal precipitation averaged over a large domain is generally minor. The in uence of model resolution on the diurnal cycle is shown in mixed directions across various subregions, and signi cant improvement from the low-to high-resolution models is only notable over coastal ocean.

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“…They also fail to reproduce the observed moisture sink between 250 and 650 hPa. These discrepancies were also found in the Large‐scale Biosphere–Atmosphere experiment (LBA) conducted in southwest Amazonia (Ma et al ., 2021a), indicating that models produce too shallow afternoon convection over the broad Amazon region. The fact that models simulate Q 1 and Q 2 well at SGP but poorly at MAO also highlights the dependence of model performances at different locations.…”

Section: Model Performances On the Mean Diurnal Cycle Of Precipitationmentioning

confidence: 99%

Long‐term single‐column model intercomparison of diurnal cycle of precipitation over midlatitude and tropical land

Tang

Xie

Guo

et al. 2021

Quart J Royal Meteoro Soc

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General Circulation Models (GCMs) have for decades exhibited difficulties in modelling the diurnal cycle of precipitation (DCP). This issue can be related to inappropriate representation of the processes controlling sub-diurnal phenomena like convection. In this study, 11 single-column versions of GCMs are used to investigate the interactions between convection and environmental conditions, processes that control nocturnal convections, and the transition from shallow to deep convection on a diurnal time-scale. Long-term simulations are performed over two continental land sites: the Southern Great Plains (SGP) in the USA for 12 summer months from 2004 to 2015 and the Manacapuru site at the central Amazon (MAO) in Brazil for two full years from 2014 to 2015. The analysis is done on two regimes: afternoon convective regime and nocturnal precipitation regime. Most models produce afternoon precipitation too early, likely due to the missing transition of shallow-to-deep convection in these models. At SGP, the unified convection schemes better simulate the onset time of precipitation.At MAO, models produce the heating peak in a much lower level compared with observation, indicating too shallow convection in the models. For nocturnal precipitation, models that produce most of nocturnal precipitation all allow convection to be triggered above the boundary layer. This indicates the importance of model capability to detect elevated convection for simulating nocturnal precipitation. Sensitivity studies indicate that (a) nudging environmental variables towards observations has a minor impact on DCP, (b) unified treatment of shallow and deep convection and the capability to capture mid-level convection can help models better capture DCP, and (c) the interactions of the atmosphere with other components in the climate system (e.g. land) are also important for DCP simulations in coupled models. These results provide long-term statistical

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Evaluation of the Causes of Wet‐Season Dry Biases Over Amazonia in CAM5

Cited by 9 publications

References 85 publications

Isolating the effect of biomass burning aerosol emissions on 20th century hydroclimate in South America and Southeast Asia

Isolating the effect of biomass burning aerosol emissions on 20th century hydroclimate in South America and Southeast Asia

Diurnal cycle of precipitation over global monsoon systems in CMIP6 simulations

Long‐term single‐column model intercomparison of diurnal cycle of precipitation over midlatitude and tropical land

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