scholarly journals Modelling the Effects of Aerosol on Mei-Yu Frontal Precipitation and Physical Processes

2019 ◽  
Vol 9 (18) ◽  
pp. 3802 ◽  
Author(s):  
Yun Zhang ◽  
Zuhang Wu ◽  
Lifeng Zhang ◽  
Yanqiong Xie ◽  
Hengchi Lei ◽  
...  
Keyword(s):  
Positive Feedback ◽  
Dynamic Effect ◽  
Summer Precipitation ◽  
Eastern Asia ◽  
Physical Processes ◽  
Frontal System ◽  
Pollution Levels ◽  
Cloud Resolving Model ◽  
Microphysical Processes ◽  
Cloud Process

The Mei-Yu front is a significantly important summer precipitation system in eastern Asia. In recent years, anthropogenic air pollution over the Yangtze-Huaihe region of China has been aggravating continuously. A cloud-resolving model coupled with an idealized frontal model is used to investigate the response of aerosols on the Mei-Yu frontal precipitation. The results indicate that increasing droplet concentrations lead to significant precipitation enhancement with the current pollution levels in Mei-Yu frontal system. Under the polluted conditions, the enhanced cold-cloud process is of great importance. Moreover, with the “towing” of active cold-cloud process, cold-cloud and warm-cloud processes developed mutually. These account for the complicated and special microphysical mechanism for aerosol impacts on Mei-Yu frontal system. Furthermore, two types of “microphysical-dynamic positive feedback loop” caused by the interactions of various physical processes and effects (direct dynamic effect, frontogenesis effect, and vapor pump effect) can be found in the Mei-Yu precipitation, which in turn reinforce the microphysical processes. The combined effect is to increase Mei-Yu front precipitation. The interaction of microphysical processes and dynamic processes, and the positive feedback loops they create are the main physical mechanisms behind the significant impacts of aerosol on Mei-Yu frontal precipitation. This may also be an important feature of climate change in eastern Asia.

scholarly journals Effects of Air Pollutants on Summer Precipitation in Different Regions of Beijing

Atmosphere ◽  
2022 ◽  
Vol 13 (1) ◽  
pp. 141
Author(s):  
Yan Yang ◽  
Wei Zhou ◽  
Qian Gao ◽  
Delong Zhao ◽  
Xiange Liu ◽  
...  
Keyword(s):  
Air Pollutants ◽  
Summer Precipitation ◽  
Weather Research And Forecasting ◽  
Mountainous Areas ◽  
Cloud Droplets ◽  
Beijing Area ◽  
Pollution Levels ◽  
Mountainous Regions ◽  
Effective Particle ◽  
Air Layers

Many studies have shown that air pollutants have complex impacts on urban precipitation. Meteorological weather station and satellite Aerosol Optical Depth (AOD) product data from the last 20 years, combined with simulation results from the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), this paper focuses on the effects of air pollutants on summer precipitation in different regions of Beijing. These results showed that air pollution intensity during the summer affected the precipitation contribution rate (PCR) of plains and mountainous regions in the Beijing area, especially in the plains. Over the past 20 years, plains PCR increased by ~10% when the AOD augmented by 0.15, whereas it decreased with lower pollution levels. In contrast, PCR in mountainous areas decreased with higher pollution levels and increased with lower pollution levels. Our analysis from model results indicated that aerosol increases reduce the effective particle size of cloud droplets and raindrops. Smaller cloud raindrops more readily transport to high air layers and participate in the generation of ice-phase substances in the clouds, increasing the total amount of cloud water in the air in a certain time, which ultimately enhanced precipitation intensity on the plains. The removal of pollutants caused by increased precipitation in the plains decreased rainfall levels in mountainous areas.

scholarly journals Millennium-length precipitation Reconstruction over South-eastern Asia: a Pseudo-Proxy Approach

2019 ◽  
Author(s):  
Stefanie Talento ◽  
Lea Schneider ◽  
Johannes Werner ◽  
Jürg Luterbacher
Keyword(s):  
Summer Precipitation ◽  
Target Area ◽  
Test Bed ◽  
Eastern Asia ◽  
Precipitation Reconstruction ◽  
Bayesian Techniques ◽  
South Eastern ◽  
Analogue Method ◽  
Hydroclimate Variability ◽  
The Difference

Abstract. Quantifying hydroclimate variability beyond the instrumental period is essential for putting current and future fluctuations into long-term perspective and to provide a test-bed for evaluating climate simulations. For South-earstern Asia such quantifications are scarce and millennium-long attempts are still missing. In this study we take a pseudo-proxy approach to evaluate the potential for generating summer precipitation reconstructions over South-eastern Asia during the past millennium. The ability of a series of novel Bayesian approaches to generate reconstructions at either annual or decadal resolutions and under diverse scenarios of pseudo-proxy records' noise is analysed and compared to the classic Analogue Method. We find that for all the algorithms and resolutions a high-density of pseudo-proxy information is a necessary but not sufficient condition for a successful reconstruction. Among the selected algorithms, the Bayesian techniques perform generally better than the Analogue Method, being the difference in abilities highest over the semi-arid areas and in the decadal-resolution framework. The superiority of the Bayesian schemes indicates that directly modelling the space and time precipitation field variability encapsulates more relevant value than just relying in similarities within a restricted pool of observational analogues, in which certain hydroclimatic regimes might be absent. Using a pseudo-proxy network with locations and noise-levels similar to the ones found in the real world, we conclude that performing a millennium-long precipitation reconstruction over South-eastern Asia is feasible as the Bayesian schemes provide skilful results over most of the target area.

scholarly journals MJO Moisture Budget during DYNAMO in a Cloud-Resolving Model

2016 ◽  
Vol 73 (6) ◽  
pp. 2257-2278 ◽  
Author(s):  
Matthew A. Janiga ◽  
Chidong Zhang
Keyword(s):  
Large Scale ◽  
Moisture Gradient ◽  
Moisture Budget ◽  
Physical Processes ◽  
Low Level ◽  
Moisture Advection ◽  
Stratiform Clouds ◽  
Cloud Resolving Model ◽  
Eddy Transport ◽  
Upper Level

Abstract Contributions by different physical processes and cloud types to the sum of the large-scale vertical moisture advection and apparent moisture sink observed by the DYNAMO field campaign northern sounding array during the passage of a Madden–Julian oscillation (MJO) event are estimated using a cloud-resolving model. The sum of these two moisture budget terms is referred to as the column-confined moisture tendency MC. Assuming diabatic balance, the contribution of different physical processes and cloud types to the large-scale vertical velocity and MC can be estimated using simulated diabatic tendencies and the domain-averaged static stability and vertical moisture gradient. Low-level moistening preceding MJO passage is captured by MC and dominated by the effects of shallow clouds. Because of the large vertical moisture gradient at this level, condensational heating in these clouds generates ascent and vertical moisture advection overwhelming the removal of water vapor by condensation. Shallow convective eddy transport also contributes to low-level moistening during this period. Eddy transport by congestus and deep convective clouds contributes to subsequent mid- and upper-level moistening, respectively, as well as low-level drying. Because the upper-level vertical moisture gradient is small, ice deposition within stratiform clouds has a net drying effect. The weak eddy transport in stratiform clouds is unable to compensate for this drying. Nonprecipitating clouds mainly modulate MC through their effects on radiation. During the enhanced phase, reduced longwave cooling results in less subsidence and drying; the opposite occurs during the suppressed phase. Large-scale horizontal advection, which is not included in MC, is responsible for much of the drying during the dissipating phase.

scholarly journals Numerical Study of Physical Processes Controlling Summer Precipitation over the Western Ghats Region

2018 ◽  
Vol 31 (8) ◽  
pp. 3099-3115 ◽  
Author(s):  
Gang Zhang ◽  
Ronald B. Smith
Keyword(s):  
Western Ghats ◽  
Arabian Sea ◽  
Numerical Study ◽  
Deep Convection ◽  
Convective Available Potential Energy ◽  
Wrf Model ◽  
Summer Precipitation ◽  
Physical Processes ◽  
Convective Rainfall ◽  
The Western Ghats

Abstract Summer precipitation over the Western Ghats and its adjacent Arabian Sea is an important component of the Indian monsoon. To advance understanding of the physical processes controlling this regional precipitation, a series of high-resolution convection-permitting simulations were conducted using the Weather Research and Forecasting (WRF) Model. Convection simulated in the WRF Model agrees with TRMM and MODIS satellite estimates. Sensitivity simulations are conducted, by altering topography, latent heating, and sea surface temperature (SST), to quantify the effects of different physical forcing factors. It is helpful to put India’s west coast rainfall systems into three categories with different causes and characteristics. 1) Offshore rainfall is controlled by incoming convective available potential energy (CAPE), the entrainment of midtropospheric dry layer in the monsoon westerlies, and the latent heat flux and SST of the Arabian Sea. It is not triggered by the Western Ghats. When offshore convection is present, it reduces both CAPE and the downwind coastal rainfall. Strong (weak) offshore rainfall is associated with high (low) SSTs in the Arabian Sea, suggested by both observations and sensitivity simulations. 2) Coastal convective rainfall is forced by the coastline roughness, diurnal heating, and the Western Ghats topography. This localized convective rainfall ends abruptly beyond the Western Ghats, producing a rain shadow to the east of the mountains. This deep convection with mixed phase microphysics is the biggest overall rain producer. 3) Orographic stratiform warm rain and drizzle dominate the local precipitation on the crest of the Western Ghats.

scholarly journals Millennium-length precipitation reconstruction over south-eastern Asia: a pseudo-proxy approach

2019 ◽  
Vol 10 (2) ◽  
pp. 347-364 ◽  
Author(s):  
Stefanie Talento ◽  
Lea Schneider ◽  
Johannes Werner ◽  
Jürg Luterbacher
Keyword(s):  
Summer Precipitation ◽  
Target Area ◽  
Test Bed ◽  
Eastern Asia ◽  
Precipitation Reconstruction ◽  
Bayesian Techniques ◽  
South Eastern ◽  
Precipitation Regimes ◽  
Analogue Method ◽  
The Difference

Abstract. Quantifying precipitation variability beyond the instrumental period is essential for putting current and future fluctuations into long-term perspective and providing a test bed for evaluating climate simulations. For south-eastern Asia such quantifications are scarce and millennium-long attempts are still missing. In this study we take a pseudo-proxy approach to evaluate the potential for generating summer precipitation reconstructions over south-eastern Asia during the past millennium. The ability of a series of novel Bayesian approaches to generate reconstructions at either annual or decadal resolutions and under diverse scenarios of pseudo-proxy records' noise is analysed and compared to the classic analogue method. We find that for all the algorithms and resolutions a high density of pseudo-proxy information is a necessary but not sufficient condition for a successful reconstruction. Among the selected algorithms, the Bayesian techniques perform generally better than the analogue method, the difference in abilities being highest over the semi-arid areas and in the decadal-resolution framework. The superiority of the Bayesian schemes indicates that directly modelling the space and time precipitation field variability is more appropriate than just relying on a pool of observational-based analogues in which certain precipitation regimes might be absent. Using a pseudo-proxy network with locations and noise levels similar to the ones found in the real world, we conclude that performing a millennium-long precipitation reconstruction over south-eastern Asia is feasible as the Bayesian schemes provide skilful results over most of the target area.

scholarly journals SALSA – a Sectional Aerosol module for Large Scale Applications

2008 ◽  
Vol 8 (9) ◽  
pp. 2469-2483 ◽  
Author(s):  
H. Kokkola ◽  
H. Korhonen ◽  
K. E. J. Lehtinen ◽  
R. Makkonen ◽  
A. Asmi ◽  
...  
Keyword(s):  
Size Distribution ◽  
Large Scale ◽  
Climate Models ◽  
Model Performance ◽  
Physical Processes ◽  
Good Consistency ◽  
Microphysical Processes ◽  
Model Setup ◽  
Aerosol Module ◽  
Physical Features

Abstract. The sectional aerosol module SALSA is introduced. The model has been designed to be implemented in large scale climate models, which require both accuracy and computational efficiency. We have used multiple methods to reduce the computational burden of different aerosol processes to optimize the model performance without losing physical features relevant to problematics of climate importance. The optimizations include limiting the chemical compounds and physical processes available in different size sections of aerosol particles; division of the size distribution into size sections using size sections of variable width depending on the sensitivity of microphysical processing to the particles sizes; the total amount of size sections to describe the size distribution is kept to the minimum; furthermore, only the relevant microphysical processes affecting each size section are calculated. The ability of the module to describe different microphysical processes was evaluated against explicit microphysical models and several microphysical models used in air quality models. The results from the current module show good consistency when compared to more explicit models. Also, the module was used to simulate a new particle formation event typical in highly polluted conditions with comparable results to more explicit model setup.

scholarly journals Models of AGN feedback

2014 ◽  
Vol 10 (S309) ◽  
pp. 182-189 ◽  
Author(s):  
Françcoise Combes
Keyword(s):  
Black Hole ◽  
Star Formation ◽  
Positive Feedback ◽  
Host Galaxy ◽  
Physical Processes ◽  
Black Hole Accretion ◽  
The Galaxy ◽  
Energy Conserving ◽  
Hole Accretion

AbstractThe physical processes responsible of sweeping up the surrounding gas in the host galaxy of an AGN, and able in some circumstances to expel it from the galaxy, are not yet well known. The various mechanisms are briefly reviewed: quasar or radio modes, either momentum-conserving outflows, energy-conserving outflows, or intermediate. They are confronted to observations, to know whether they can explain the M-sigma relation, quench the star formation or whether they can also provide some positive feedback and how the black hole accretion history is related to that of star formation.

scholarly journals Objective Diagnostics and the Madden–Julian Oscillation. Part II: Application to Moist Static Energy and Moisture Budgets

2015 ◽  
Vol 28 (19) ◽  
pp. 7786-7808 ◽  
Author(s):  
Brandon O. Wolding ◽  
Eric D. Maloney
Keyword(s):  
Temperature Gradient ◽  
Positive Feedback ◽  
Large Scale ◽  
Moist Static Energy ◽  
Intraseasonal Variations ◽  
Moisture Advection ◽  
Precipitation Anomalies ◽  
Microphysical Processes ◽  
Radiative Feedbacks ◽  
Static Energy

Abstract Processes controlling moisture variations associated with the MJO are investigated using budgets of moist static energy (MSE) and moisture. To first order, precipitation anomalies are maintained by anomalous large-scale vertical moisture advection, which can be understood through application of a weak temperature gradient balance framework to the MSE budget. Intraseasonal variations in longwave radiative cooling play a crucial role in destabilizing the MJO by enhancing intraseasonal variations in large-scale vertical moisture advection. This enhancement allows the effect of intraseasonal variations in large-scale vertical moisture advection to meet or exceed the effect of intraseasonal variations in net condensation, resulting in a positive feedback between the net effect of these processes and moisture anomalies. Intraseasonal variations in surface latent heat flux (SLHF) enhance this positive feedback, but appear to be insufficient to destabilize the MJO in the absence of radiative feedbacks. The effect an ensemble cloud population has on large-scale moisture is investigated using fields where only high-frequency variability has been removed. During the enhanced phase, approximately 85% of the moisture removed by net condensation is resupplied by the large-scale vertical moisture advection associated with apparent heating by microphysical processes and subgrid-scale vertical fluxes of dry static energy. This suggests that a relatively large increase in net condensation could be supported by a relatively small anomalous moisture source, even in the absence of radiative feedbacks. These results highlight the importance of process-oriented assessment of MJO-like variability within models, and suggest that a weak temperature gradient (WTG) balance framework may be used to identify destabilization mechanisms, thereby distinguishing between MJO-like variability of fundamentally different character.

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