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Numerical Simulation on the Rainout-Removal of Sulfur Dioxide and Acidification of Precipitation from Stratiform Clouds
Qin Yu,
Qin
,Yu

大气科学进展 , 1989,
Abstract: The rainout-removal of SO2 and the acidification of precipitation from stratiform clouds are simulated using a one-dimensional, time-dependent model, parameterized microphysically in which dissolution and dissociation of gaseous SO2 and H2O2, and oxidation reaction in aqueous phase are taken into account. The effects of dynamic fac-tors, including updraft flow and turbulent transport, and the concentration of gaseous SO2 and H2O2 being transported into the clouds on pH value of the precipitation, the conversion rate S(IV)-S (VI) and the wet deposition rate of SO2 are discussed.
Investigation of Cloud Seeding Interval for Precipitation Enhancement by Aircraft within Stratiform Clouds
层状云中飞机人工增雨作业间距的研究

YU Xing,DAI Jing,
余兴
,戴进

大气科学 , 2005,
Abstract: Three cloud seeding intervals frequently used in precipitation enhancement by aircraft within stratiform clouds are designed to investigate their effects on effective range by using numerical simulation. The simulated seeding lines deviate from the designed line due to transport by horizontal wind fields. The different seeding interval leads to diversified projective effective area and duration, whose tempo spatial distribution and corresponding surface position are variable. Enlargement or reduction of seeding interval does not mean to simply and synchronously amplify the effective area and duration, but amalgamation of seeding lines can extend the effective duration. Also a mathematical formula of benefit for precipitation enhancement is developed. Under the same operational conditions, the benefit of 8 km interval is 31 percent higher than that of the 20 km, and 23 percent higher than that of the 4 km. Finally, a set of mathematical expression of seeding interval is formulated for cross and parallel seeding schemes from the view of physical cause.
Cloud and aerosol effects on radiation in deep convective clouds: comparison with warm stratiform clouds  [PDF]
S. S. Lee,L. J. Donner,V. T. J. Phillips
Atmospheric Chemistry and Physics Discussions , 2008,
Abstract: Cloud and aerosol effects on radiation in two contrasting cloud types, a deep convective mesoscale cloud ensemble (MCE) and warm stratocumulus clouds, are simulated and compared. At the top of the atmosphere, 45–81% of shortwave cloud forcing (SCF) is offset by longwave cloud forcing (LCF) in the MCE, whereas warm stratiform clouds show the offset of less than ~20%. 28% of increased negative SCF is offset by increased LCF with increasing aerosols in the MCE at the top of the atmosphere. However, the stratiform clouds show the offset of just around 2–5%. Ice clouds as well as liquid clouds play an important role in the larger offset in the MCE. Hence, this study indicates effects of deep convective clouds on radiation and responses of deep convective clouds to aerosols are quite different from those of shallow clouds through the different modulation of longwave radiation; the presence of ice clouds in deep convective clouds contributes to the different modulation of longwave radiation significantly. Different cloud types, characterized by cloud depth and cloud-top height, play critical roles in those different modulations of LCF between the MCE and stratocumulus clouds. Lower cloud-top height and cloud depth lead to smaller offset of SCF by LCF and offset of increased negative SCF by increased LCF at high aerosol in stratocumulus clouds than in the MCE. Supplementary simulations show this dependence of modulation of LCF on cloud depth and cloud-top height is not limited to those two contrasting cloud types. The dependence is also simulated among different types of convective clouds, indicating the assessment of effects of varying cloud types on radiation due to climate changes can be critical to better prediction of climate.
Sensitivity of aerosol and cloud effects on radiation to cloud types: comparison between deep convective clouds and warm stratiform clouds over one-day period
S. S. Lee, L. J. Donner,V. T. J. Phillips
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2009,
Abstract: Cloud and aerosol effects on radiation in two contrasting cloud types, a deep mesoscale convective system (MCS) and warm stratocumulus clouds, are simulated and compared. At the top of the atmosphere, 45–81% of shortwave cloud forcing (SCF) is offset by longwave cloud forcing (LCF) in the MCS, whereas warm stratiform clouds show the offset of less than ~20%. 28% of increased negative SCF is offset by increased LCF with increasing aerosols in the MCS at the top of the atmosphere. However, the stratiform clouds show the offset of just around 2–5%. Ice clouds as well as liquid clouds play an important role in the larger offset in the MCS. Lower cloud-top height and cloud depth, characterizing cloud types, lead to the smaller offset of SCF by LCF and the offset of increased negative SCF by increased LCF at high aerosol in stratocumulus clouds than in the MCS. Supplementary simulations show that this dependence of modulation of LCF on cloud depth and cloud-top height is also simulated among different types of convective clouds.
A numerical study of aerosol influence on mixed-phase stratiform clouds through modulation of the liquid phase
G. de Boer, T. Hashino, G. J. Tripoli,E. W. Eloranta
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2013,
Abstract: Numerical simulations were carried out in a high-resolution two-dimensional framework to increase our understanding of aerosol indirect effects in mixed-phase stratiform clouds. Aerosol characteristics explored include insoluble particle type, soluble mass fraction, influence of aerosol-induced freezing point depression and influence of aerosol number concentration. Simulations were analyzed with a focus on the processes related to liquid phase microphysics, and ice formation was limited to droplet freezing. Of the aerosol properties investigated, aerosol insoluble mass type and its associated freezing efficiency was found to be most relevant to cloud lifetime. Secondary effects from aerosol soluble mass fraction and number concentration also alter cloud characteristics and lifetime. These alterations occur via various mechanisms, including changes to the amount of nucleated ice, influence on liquid phase precipitation and ice riming rates, and changes to liquid droplet nucleation and growth rates. Alteration of the aerosol properties in simulations with identical initial and boundary conditions results in large variability in simulated cloud thickness and lifetime, ranging from rapid and complete glaciation of liquid to the production of long-lived, thick stratiform mixed-phase cloud.
Model evaluations for winter orographic clouds with observations
XiaoFeng Lou,Dan Breed
Chinese Science Bulletin , 2011, DOI: 10.1007/s11434-010-4249-2
Abstract: The Real-Time Four-Dimensional Data Assimilation (RT-FDDA) system is used for orographic snowpack enhancement. The model has three nested domains with the grid spacing of 18, 6 and 2 km. To evaluate the simulations of winter orographic clouds and precipitation, comparisons are made between model simulations and observations to determine how the model simulates the cloud distribution, cloud height, cloud vertical profiles and snow precipitation. The simulated results of the 02:00 UTC cycling with 2-km resolution are used in the comparison. The observations include SNOTEL, ceilometer, sounding and satellite data, from the ground to air. The verification of these observations indicates that the Weather Research and Forecast (WRF) RT-FDDA system provides good simulations. It is better to use data within the forecast period of 2–16 h simulations. Although the horizontal wind component near the ground has some bias, and the simulated clouds are a little higher and have a little more coverage than observed, the simulated precipitation is a little weaker than observed. The results of the comparison show that the WRF RT-FDDA model provides good simulations and can be used in orographic cloud seeding.
Model evaluations for winter orographic clouds with observations

XiaoFeng Lou,Dan Breed,

科学通报(英文版) , 2011,
Abstract: The Real-Time Four-Dimensional Data Assimilation (RT-FDDA) system is used for orographic snowpack enhancement. The model has three nested domains with the grid spacing of 18, 6 and 2 km. To evaluate the simulations of winter orographic clouds and precipitation, comparisons are made between model simulations and observations to determine how the model simulates the cloud distribution, cloud height, cloud vertical profiles and snow precipitation. The simulated results of the 02:00 UTC cycling with 2-km resolution are used in the comparison. The observations include SNOTEL, ceilometer, sounding and satellite data, from the ground to air. The verification of these observations indicates that the Weather Research and Forecast (WRF) RT-FDDA system provides good simulations. It is better to use data within the forecast period of 2–16 h simulations. Although the horizontal wind component near the ground has some bias, and the simulated clouds are a little higher and have a little more coverage than observed, the simulated precipitation is a little weaker than observed. The results of the comparison show that the WRF RT-FDDA model provides good simulations and can be used in orographic cloud seeding.
The suppression of aerosols to the orographic precipitation in the Qinling Mountains
秦岭地区气溶胶对地形云降水的抑制作用

Dai Jin,Yu Xing,Rosenfeld Daniel and,
戴进
,余兴,Rosenfeld Daniel,

大气科学 , 2008,
Abstract: Based on the dataset of observations of precipitation,visibility and winds since 1954 at the top of Huashan Mountain,the ratio between the precipitation at Huashan Mountain and at the nearby plain stations,which is defined as the orographic enhancement factor(Ro),and the relationship between Ro and visibility,were used to quantitively study the ways that air pollution aerosols suppress orographic precipitation.Ro decreased 14%-20% gradually during the measurement period,which means that the precipitation at the top of Huashan Mountain decreased 14%-20% compared with the precipitation at the plains stations.The indicated trend of Ro matched well with the decreasing visibility and increasing aerosol,which suggests that enhanced pollution aerosols suppress the orographic precipitation.The decreasing trend of Ro is mainly caused by days of the light and moderate rain(daily precipitation less than 30 mm),but not by days with precipitation more than 30 mm,which suggested that the thin short living orographic clouds are much more susceptible to precipitation suppression by air pollution aerosols.The precipitation less than 30 mm and 5 mm,respectively,can be affected by the aerosols entering the clouds for Huashan Mountain and Xi'an stations,which suggests that the more aerosols enter the clouds,the deeper precipitation clouds will be influenced by the aerosols to suppress the precipitation.In the spring and autumn when dynamical lifting plays the leading role,the suppression of aerosol to clouds at the mountain top is stronger than that in plains,and causes about 20% decrease with a maximum of 25% in precipitation at Huashan Mountain.In the summer for the thermodynamically driven clouds,the suppression of aerosol to the clouds at the mountain top and in plains is equivalent.The variations of Ro in different wind directions show that the decreasing trend of Ro increases with the wind speed,and the decrease of orographic precipitation exceeds 30% for 240-030 wind direction and wind speed greater than 5 m/s.The quantitative analyses of Ro and visibility show that Ro decreases from about 1.8 to 1.2 when the visibility changes from 14 to 8 km,and the decrement exceeds 30%.Ro at Huashan Mountain to Huayin stations is linearly correlated with the visibility,and the regression coefficient is 0.81.Finally,a brief physical model that aerosols suppress orographic precipitation is summarized based on the results.
Data-driven exploration of orographic enhancement of precipitation
L. Foresti, M. Kanevski,A. Pozdnoukhov
Advances in Science and Research (ASR) , 2011, DOI: 10.5194/asr-6-129-2011
Abstract: This study presents a methodology to analyse orographic enhancement of precipitation using sequences of radar images and a digital elevation model. Image processing techniques are applied to extract precipitation cells from radar imagery. DEM is used to derive the topographic indices potentially relevant to orographic precipitation enhancement at different spatial scales, e.g. terrain convexity and slope exposure to mesoscale flows. Two recently developed machine learning algorithms are then used to analyse the relationship between the repeatability of precipitation patterns and the underlying topography. Spectral clustering is first used to characterize stratification of the precipitation cells according to different mesoscale flows and exposure to the crest of the Alps. At a second step, support vector machine classifiers are applied to build a computational model which discriminates persistent precipitation cells from all the others (not showing a relationship to topography) in the space of topographic conditioning factors. Upwind slopes and hill tops were found to be the topographic features leading to precipitation repeatability and persistence. Maps of orographic enhancement susceptibility can be computed for a given flow, topography and forecasted smooth precipitation fields and used to improve nowcasting models or correct windward and leeward biases in numerical weather prediction models.
Global simulations of aerosol processing in clouds
C. Hoose, U. Lohmann, R. Bennartz, B. Croft,G. Lesins
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2008,
Abstract: An explicit and detailed representation of in-droplet and in-crystal aerosol particles in stratiform clouds has been introduced in the global aerosol-climate model ECHAM5-HAM. The new scheme allows an evaluation of the cloud cycling of aerosols and an estimation of the relative contributions of nucleation and collision scavenging, as opposed to evaporation of hydrometeors in the global aerosol processing by clouds. On average an aerosol particle is cycled through stratiform clouds 0.5 times. The new scheme leads to important changes in the simulated fraction of aerosol scavenged in clouds, and consequently in the aerosol wet deposition. In general, less aerosol is scavenged into clouds with the new prognostic treatment than what is prescribed in standard ECHAM5-HAM. Aerosol concentrations, size distributions, scavenged fractions and cloud droplet concentrations are evaluated and compared to different observations. While the scavenged fraction and the aerosol number concentrations in the marine boundary layer are well represented in the new model, aerosol optical thickness, cloud droplet number concentrations in the marine boundary layer and the aerosol volume in the accumulation and coarse modes over the oceans are overestimated. Sensitivity studies suggest that a better representation of below-cloud scavenging, higher in-cloud collision coefficients, or a reduced water uptake by seasalt aerosols could reduce these biases.
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