Does the threshold representation associated with the autoconversion process matter?

Guo, Huan; Liu, Yinong; Penner, Joyce E.

doi:10.5194/acp-8-1225-2008

Cited by 14 publications

(10 citation statements)

References 36 publications

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“…This is in agreement with previous studies [e.g., Wang et al ., ; Pinsky et al ., ]. The DSD broadening as shown in Figures C1 is also a result of turbulent effect [ Liu et al ., , ; Guo et al ., ; Chandrakar et al ., ].…”

Section: Resultsmentioning

confidence: 99%

Effects of environment forcing on marine boundary layer cloud‐drizzle processes

Dong

et al. 2017

JGR Atmospheres

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Determining the factors affecting drizzle formation in marine boundary layer (MBL) clouds remains a challenge for both observation and modeling communities. To investigate the roles of vertical wind shear and buoyancy (static instability) in drizzle formation, ground‐based observations from the Atmospheric Radiation Measurement Program at the Azores are analyzed for two types of conditions. The type I clouds should last for at least 5 h and more than 90% time must be nondrizzling and then followed by at least 2 h of drizzling periods, while the type II clouds are characterized by mesoscale convection cellular structures with drizzle occur every 2 to 4 h. By analyzing the boundary layer wind profiles (direction and speed), it was found that either directional or speed shear is required to promote drizzle production in the type I clouds. Observations and a recent model study both suggest that vertical wind shear helps the production of turbulent kinetic energy (TKE), stimulates turbulence within cloud layer, and enhances drizzle formation near the cloud top. The type II clouds do not require strong wind shear to produce drizzle. The small values of lower tropospheric stability (LTS) and negative Richardson number (Ri) in the type II cases suggest that boundary layer instability plays an important role in TKE production and cloud‐drizzle processes. By analyzing the relationships between LTS and wind shear for all cases and all time periods, a stronger connection was found between LTS and wind directional shear than that between LTS and wind speed shear.

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Section: Resultsmentioning

confidence: 99%

Effects of environment forcing on marine boundary layer cloud‐drizzle processes

Dong

et al. 2017

JGR Atmospheres

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“…The Acc/Aut ratio monotonically increased with increasing LWP in any schemes, but its dependence on LWP was quite different. It is noteworthy that Kessler‐type schemes underestimated the Acc/Aut ratio, and this would be primarily related to the autoconversion threshold [e.g., Guo et al , ; Golaz et al , ]. The vertical profile of the Acc/Aut ratio was also highly sensitive to a change in the autoconversion scheme, especially over the low‐level midlatitudes where the LSC makes its main contribution.…”

Section: Discussionmentioning

confidence: 99%

Evaluation of autoconversion schemes in a single model framework with satellite observations

Michibata

2015

JGR Atmospheres

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We examined the performance of autoconversion (mass transfer from cloud water to rainwater by the coalescence of cloud droplets) schemes in warm rain, which are commonly used in general circulation models. To exclude biases in the different treatment of the aerosol‐cloud‐precipitation‐radiation interaction other than that of the autoconversion process, sensitivity experiments were conducted within a single model framework using an aerosol‐climate model, MIROC‐SPRINTARS. The liquid water path (LWP) and cloud optical thickness have a particularly high sensitivity to the autoconversion schemes, and their sensitivity is of the same magnitude as model biases. In addition, the ratio of accretion to autoconversion (Acc/Aut ratio), a key parameter in the examination of the balance of microphysical conversion processes, also has a high sensitivity globally depending on the scheme used. Although the Acc/Aut ratio monotonically increases with increasing LWP, significantly lower ratio is observed in Kessler‐type schemes. Compared to satellite observations, a poor representation of cloud macrophysical structure and optically thicker low cloud are found in simulations with any autoconversion scheme. As a result of the cloud‐radiation interaction, the difference in the global mean net cloud radiative forcing (NetCRF) among the schemes reaches 10 Wm−2. The discrepancy between the observed and simulated NetCRF is especially large with a high LWP. The potential uncertainty in the parameterization of the autoconversion process is nonnegligible, and no formulation significantly improves the bias in the cloud radiative effect yet. This means that more fundamental errors are still left in other processes of the model.

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“…However, these threshold functions are not related to spectral dispersion, that is, spectral dispersion is fixed in these threshold functions, and thus the effect of spectral dispersion on the threshold function has not been applied in this study. It should be pointed out that the threshold function with spectral dispersion can effectively change the instantaneous cloud fraction, cloud fraction, and aerosol indirect effect [ Guo et al , 2008].…”

Section: Discussionmentioning

confidence: 99%

Effects of spectral dispersion on clouds and precipitation in mesoscale convective systems

Xie

Liu

2011

J. Geophys. Res.

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[1] The effects of spectral dispersion on clouds and precipitation in mesoscale convective systems have been studied by conducting 10 numerical simulations with different values of spectral dispersion (" = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0) in the clean, semipolluted, and polluted backgrounds. The simulation results show that spectral dispersion affects cloud microphysical properties markedly in each aerosol regime. With an increase in spectral dispersion, both the raindrop concentration and the rainwater content increase, while the mean radius of the raindrops diminishes substantially. Moreover, it is found that the effects of spectral dispersion on simulated precipitation differ in these three aerosol backgrounds and relative humidity. In the clean background and at relatively lower humidity, the average accumulated precipitation is reduced significantly with an increase in spectral dispersion. Precipitation varies nonmonotonically in the semipolluted background, increasing with spectral dispersion at smaller values, while decreasing at larger values. In the mean time, precipitation is continuously enhanced with increasing spectral dispersion in the polluted background. Furthermore, sensitivity tests demonstrate that the possible impacts of spectral dispersion on precipitation varies depending on the relative humidity. For instance, at high relative humidity, an increase in spectral dispersion even in a clean atmosphere leads to more precipitation. Our results could shed light on understanding the influences of aerosols on clouds and precipitation, especially the second aerosol indirect effect.Citation: Xie, X., and X. Liu (2011), Effects of spectral dispersion on clouds and precipitation in mesoscale convective systems,

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Does the threshold representation associated with the autoconversion process matter?

Cited by 14 publications

References 36 publications

Effects of environment forcing on marine boundary layer cloud‐drizzle processes

Effects of environment forcing on marine boundary layer cloud‐drizzle processes

Evaluation of autoconversion schemes in a single model framework with satellite observations

Effects of spectral dispersion on clouds and precipitation in mesoscale convective systems

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