scholarly journals The effects of aerosols on precipitation and dimensions of subtropical clouds; a sensitivity study using a numerical cloud model

2005 ◽  
Vol 5 (4) ◽  
pp. 7211-7245 ◽  
Author(s):  
A. Teller ◽  
Z. Levin
Keyword(s):  
Water Vapor ◽  
Climate Models ◽  
Cloud Model ◽  
Cloud Condensation Nuclei ◽  
Sensitivity Study ◽  
Meteorological Conditions ◽  
Dust Particles ◽  
Noticeable Effect ◽  
Convective Clouds ◽  
Ice Nuclei

Abstract. Numerical experiments were carried out using the Tel-Aviv University 2-D cloud model to investigate the effects of increased concentrations of Cloud Condensation Nuclei (CCN), giant CCN (GCCN) and Ice Nuclei (IN) on the development of precipitation and cloud structure in mixed-phase sub-tropical convective clouds. In order to differentiate between the contribution of the aerosols and the meteorology, all simulations were conducted with the same meteorological conditions. The results show that under the same meteorological conditions, polluted clouds (with high CCN concentrations) produce less precipitation than clean clouds (with low CCN concentrations), the initiation of precipitation is delayed and the lifetimes of the clouds are longer. GCCN enhance the total precipitation on the ground in polluted clouds but they have no noticeable effect on cleaner clouds. The increased rainfall due to GCCN is mainly a result of the increased graupel mass in the cloud, but it only partially offsets the decrease in rainfall due to pollution (increased CCN). The addition of more effective IN, such as mineral dust particles, reduces the total amount of precipitation on the ground. This reduction is more pronounced in clean clouds than in polluted ones. Polluted clouds reach higher altitudes and are wider than clean clouds and both produce wider clouds (anvils) when more IN are introduced. Since under the same vertical sounding the polluted clouds produce less rain, more water vapor is left aloft after the rain stops. In our simulations about 3.5 times more water evaporates after the rain stops from the polluted cloud as compared to the clean cloud. The implication is that much more water vapor is transported from lower levels to the mid troposphere under polluted conditions, something that should be considered in climate models.

scholarly journals The effects of aerosols on precipitation and dimensions of subtropical clouds: a sensitivity study using a numerical cloud model

2006 ◽  
Vol 6 (1) ◽  
pp. 67-80 ◽  
Author(s):  
A. Teller ◽  
Z. Levin
Keyword(s):  
Water Vapor ◽  
Climate Models ◽  
Cloud Model ◽  
Cloud Condensation Nuclei ◽  
Sensitivity Study ◽  
Meteorological Conditions ◽  
Dust Particles ◽  
Noticeable Effect ◽  
Convective Clouds ◽  
Ice Nuclei

Abstract. Numerical experiments were carried out using the Tel-Aviv University 2-D cloud model to investigate the effects of increased concentrations of Cloud Condensation Nuclei (CCN), giant CCN (GCCN) and Ice Nuclei (IN) on the development of precipitation and cloud structure in mixed-phase sub-tropical convective clouds. In order to differentiate between the contribution of the aerosols and the meteorology, all simulations were conducted with the same meteorological conditions. The results show that under the same meteorological conditions, polluted clouds (with high CCN concentrations) produce less precipitation than clean clouds (with low CCN concentrations), the initiation of precipitation is delayed and the lifetimes of the clouds are longer. GCCN enhance the total precipitation on the ground in polluted clouds but they have no noticeable effect on cleaner clouds. The increased rainfall due to GCCN is mainly a result of the increased graupel mass in the cloud, but it only partially offsets the decrease in rainfall due to pollution (increased CCN). The addition of more effective IN, such as mineral dust particles, reduces the total amount of precipitation on the ground. This reduction is more pronounced in clean clouds than in polluted ones. Polluted clouds reach higher altitudes and are wider than clean clouds and both produce wider clouds (anvils) when more IN are introduced. Since under the same vertical sounding the polluted clouds produce less rain, more water vapor is left aloft after the rain stops. In our simulations about 3.5 times more water evaporates after the rain stops from the polluted cloud as compared to the clean cloud. The implication is that much more water vapor is transported from lower levels to the mid troposphere under polluted conditions, something that should be considered in climate models.

Measurements of Saharan Dust in Convective Clouds over the Tropical Eastern Atlantic Ocean*

2015 ◽  
Vol 72 (1) ◽  
pp. 75-81 ◽  
Author(s):  
Cynthia H. Twohy
Keyword(s):  
Mineral Dust ◽  
Cloud Condensation Nuclei ◽  
Saharan Dust ◽  
Dust Particles ◽  
Tropical Storms ◽  
Liquid Droplets ◽  
Particle Type ◽  
Convective Clouds ◽  
Ice Nuclei ◽  
Eastern Atlantic Ocean

Abstract Mineral dust particles have been shown to act as cloud condensation nuclei, and they are known to interact with developing tropical storms over the Atlantic downwind of the Sahara. Once present within liquid droplets, they have the potential to act as freezing ice nuclei and further affect the microphysics, dynamics, and evolution of tropical storms. However, few measurements of mineral dust particles in tropical convective clouds exist. This study indicates that about one-third of droplets sampled in small convective clouds in the tropical eastern Atlantic contained dust particles, and dust was the dominant residual particle type sampled in ice crystals from anvil outflow. However, estimated number and mass concentrations of dust in anvil ice were small compared to the amount of dust available within the Saharan air layer itself.

scholarly journals Automated Mapping of Convective Clouds (AMCC) Thermodynamical, Microphysical, and CCN Properties from SNPP/VIIRS Satellite Data

2019 ◽  
Vol 58 (4) ◽  
pp. 887-902 ◽  
Author(s):  
Zhiguo Yue ◽  
Daniel Rosenfeld ◽  
Guihua Liu ◽  
Jin Dai ◽  
Xing Yu ◽  
...  
Keyword(s):  
Climate Models ◽  
Weather Forecasting ◽  
Meteorological Data ◽  
Cloud Condensation Nuclei ◽  
Convective Cloud ◽  
Cloud Base ◽  
Base Temperature ◽  
Cloud Drop ◽  
Automated Mapping ◽  
Convective Clouds

AbstractThe advent of the Visible Infrared Imager Radiometer Suite (VIIRS) on board the Suomi NPP (SNPP) satellite made it possible to retrieve a new class of convective cloud properties and the aerosols that they ingest. An automated mapping system of retrieval of some properties of convective cloud fields over large areas at the scale of satellite coverage was developed and is presented here. The system is named Automated Mapping of Convective Clouds (AMCC). The input is level-1 VIIRS data and meteorological gridded data. AMCC identifies the cloudy pixels of convective elements; retrieves for each pixel its temperature T and cloud drop effective radius re; calculates cloud-base temperature Tb based on the warmest cloudy pixels; calculates cloud-base height Hb and pressure Pb based on Tb and meteorological data; calculates cloud-base updraft Wb based on Hb; calculates cloud-base adiabatic cloud drop concentrations Nd,a based on the T–re relationship, Tb, and Pb; calculates cloud-base maximum vapor supersaturation S based on Nd,a and Wb; and defines Nd,a/1.3 as the cloud condensation nuclei (CCN) concentration NCCN at that S. The results are gridded 36 km × 36 km data points at nadir, which are sufficiently large to capture the properties of a field of convective clouds and also sufficiently small to capture aerosol and dynamic perturbations at this scale, such as urban and land-use features. The results of AMCC are instrumental in observing spatial covariability in clouds and CCN properties and for obtaining insights from such observations for natural and man-made causes. AMCC-generated maps are also useful for applications from numerical weather forecasting to climate models.

scholarly journals Possible Effects of Collisional Breakup on Mixed-Phase Deep Convection Simulated by a Spectral (Bin) Cloud Model

2005 ◽  
Vol 62 (6) ◽  
pp. 1917-1931 ◽  
Author(s):  
Axel Seifert ◽  
Alexander Khain ◽  
Ulrich Blahak ◽  
Klaus D. Beheng
Keyword(s):  
Cloud Model ◽  
Deep Convection ◽  
Sensitivity Study ◽  
Mixed Phase ◽  
Convective Clouds ◽  
Hebrew University ◽  
Raindrop Size ◽  
Convective Cells ◽  
Rain Rates ◽  
Rain Formation

Abstract The effects of the collisional breakup of raindrops are investigated using the Hebrew University Cloud Model (HUCM). The parameterizations, which are combined in the new breakup scheme, are those of Low and List, Beard and Ochs, as well as Brown. A sensitivity study reveals strong effects of collisional breakup on the precipitation formation in mixed-phase deep convective clouds for strong as well as for weak precipitation events. Collisional breakup reduces the number of large raindrops, increases the number of small raindrops, and, as a consequence, decreases surface rain rates and considerably reduces the speed of rain formation. In addition, it was found that including breakup can lead to a more intense triggering of secondary convective cells. But a statistical comparison with observed raindrop size distributions shows that the parameterizations might systematically overestimate collisional breakup.

scholarly journals Impact of mineral dust on cloud formation in a Saharan outflow region

2011 ◽  
Vol 11 (12) ◽  
pp. 32363-32390 ◽  
Author(s):  
L. Smoydzin ◽  
A. Teller ◽  
H. Tost ◽  
M. Fnais ◽  
J. Lelieveld
Keyword(s):  
Radiative Forcing ◽  
Mineral Dust ◽  
Eastern Mediterranean ◽  
Cloud Condensation Nuclei ◽  
Coupled Model ◽  
Cloud Formation ◽  
Dust Particles ◽  
Ice Nuclei ◽  
Outflow Region ◽  
The Impact

Abstract. We present a numerical modelling study investigating the impact of mineral dust on cloud formation over the Eastern Mediterranean for two case studies: (i) 25 September 2008 and (ii) 28/29 January 2003. On both days dust plumes crossed the Mediterranean and interacted with clouds forming along frontal systems. For our investigation we used the fully online coupled model WRF-chem. The results show that increased aerosol concentrations due to the presence of mineral dust can enhance the formation of ice crystals. This leads to slight shifts of the spatial and temporal precipitation patterns compared to scenarios where dust was not considered to act as ice nuclei. However, the total amount of precipitation did not change significantly. The only exception occurred when dust entered into an area of orographic ascent, causing glaciation of the clouds, leading to a local enhancement of rainfall. The impact of dust particles acting as giant cloud condensation nuclei on precipitation formation was found to be small. Based on our simulations the contribution of dust to the CCN population is potentially significant only for warm phase clouds. Nevertheless, the dust-induced differences in the microphysical structure of the clouds can contribute to a significant radiative forcing.

scholarly journals Surface modification of mineral dust particles by sulphuric acid processing: implications for CCN and IN abilities

2011 ◽  
Vol 11 (3) ◽  
pp. 7235-7289 ◽  
Author(s):  
P. Reitz ◽  
C. Spindler ◽  
T. F. Mentel ◽  
L. Poulain ◽  
H. Wex ◽  
...  
Keyword(s):  
Sulphuric Acid ◽  
Mineral Dust ◽  
Cloud Condensation Nuclei ◽  
Particle Surface ◽  
Surface Modifications ◽  
Dust Particles ◽  
Ammonia Vapour ◽  
Ice Nuclei ◽  
Aerosol Mass ◽  
Acid Processing

Abstract. The ability of coated mineral dust particles to act as cloud condensation nuclei (CCN) and ice nuclei (IN) was investigated at LACIS (Leipzig Aerosol Cloud Interaction Simulator) during the FROST1- and FROST2-campaigns (Freezing of dust). Sulphuric acid was condensed on the particles which afterwards were optionally humidified, treated with ammonia vapour and/or heat. By means of aerosol mass spectrometry we found evidence that processing of mineral dust particles with sulphuric acid leads to surface modifications of the particles. These surface modifications are responsible for the observed reduction of the IN activation of the particles. The observed particle mass spectra suggest that different treatments lead to different chemical reactions on the particle surface. Possible chemical reaction pathways and products are suggested and the implications on IN and CCN efficiency of the treated dust particles are discussed.

scholarly journals Simulation of Effects of Atmospheric Aerosols on Deep Turbulent Convective Clouds Using a Spectral Microphysics Mixed-Phase Cumulus Cloud Model. Part II: Sensitivity Study

2004 ◽  
Vol 61 (24) ◽  
pp. 2983-3001 ◽  
Author(s):  
A. Khain ◽  
A. Pokrovsky
Keyword(s):  
Atmospheric Aerosols ◽  
Cloud Model ◽  
Precipitation Amount ◽  
Sensitivity Study ◽  
Total Precipitation ◽  
High Concentration ◽  
Close Coupling ◽  
Convective Clouds ◽  
Warm Rain ◽  
Bulk Parameterization

Abstract Effects of different size distributions of cloud condensational nuclei (CCN) on the evolution of deep convective clouds under dry unstable continental thermodynamic conditions are investigated using the spectral microphysics Hebrew University Cloud Model (HUCM). In particular, high supercooled water content just below the level of homogeneous freezing, as well as an extremely high concentration of ice crystals above the level, observed recently by Rosenfeld and Woodley at the tops of growing clouds in Texas, were successfully reproduced. Numerical experiments indicate a significant decrease in accumulated precipitation in smoky air. The fraction of warm rain in the total precipitation amount increases with a decrease in the CCN concentration. The fraction is low in smoky continental air and is dominating in clean maritime air. As warm rain is a smaller fraction of total precipitation, the decrease in the accumulated rain amount in smoky air results mainly from the reduction of melted precipitation. It is shown that aerosols significantly influence cloud dynamics leading to the elevation of the level of precipitating particle formation. The falling down of these particles through dry air leads to a loss in precipitation. Thus, close coupling of microphysical and dynamical aerosol effects leads to the rain suppression from clouds arising in dry smoky air. The roles of freezing, CCN penetration through lateral cloud boundaries, and turbulent effects on cloud particles collisions are evaluated. Results, obtained using spectral microphysics, were compared with those obtained using two well-known schemes of bulk parameterization. The results indicate that the bulk parameterization schemes do not reproduce well the observed cloud microstructure.

scholarly journals Aerosols' influence on the interplay between condensation, evaporation and rain in warm cumulus cloud

2007 ◽  
Vol 7 (4) ◽  
pp. 12687-12714 ◽  
Author(s):  
O. Altaratz ◽  
I. Koren ◽  
T. Reisin ◽  
A. Kostinski ◽  
G. Feingold ◽  
...  
Keyword(s):  
Surface Area ◽  
Cloud Model ◽  
Volume Ratio ◽  
Meteorological Conditions ◽  
Drop Surface ◽  
Evaporation Process ◽  
Cumulus Cloud ◽  
Convective Clouds ◽  
Rain Drops ◽  
Numerical Cloud Model

Abstract. A numerical cloud model is used to study the influence of aerosol on the microphysics and dynamics of moderate-sized, coastal, convective clouds that develop under the same meteorological conditions. The results show that polluted convective clouds start their precipitation later and precipitate less than clean clouds but produce larger rain drops. The evaporation process is more significant at the margins of the polluted clouds (compared to the clean cloud) due to a higher drop surface area to volume ratio and it is mostly from small drops. It was found that the formation of larger raindrops in the polluted cloud is due to a more efficient collection process.

scholarly journals The effects of heating by transported dust layers on cloud and precipitation: a numerical study

2007 ◽  
Vol 7 (13) ◽  
pp. 3497-3505 ◽  
Author(s):  
Y. Yin ◽  
L. Chen
Keyword(s):  
Mineral Dust ◽  
Numerical Study ◽  
Cloud Model ◽  
Cloud Condensation Nuclei ◽  
Dust Particles ◽  
Cloud Base ◽  
Cloud Droplets ◽  
Cloud Optical Depth ◽  
Mineral Aerosols ◽  
Lower Cloud

Abstract. There have been numerous recent publications showing that mineral dust might be a good absorber for solar radiation in addition to its capability to act as cloud condensation nuclei (CCN) and ice forming nuclei (IFN), and could lead to reduced cloud cover and precipitation in the region where it is present. This effect is investigated using a dynamic cloud model with detailed microphysics of both warm and ice phase processes. The model is initialized using measured size distributions and concentrations of mineral dust particles. Our results show that when dust appears at the cloud-base height and below 3 km, where the temperature is warmer than −5°C, the heating induced by the presence of dust layers can inhibit the formation of cloud droplets and suppresses the development of precipitation, leading to lower cloud optical depth and albedo. On the other hand, when the dust layers are located at altitudes with temperature colder than −5°C, or above the −5°C level, mineral aerosols can act as effective ice nuclei, intensify the ice-forming processes, and may enhance the development of cloud and precipitation. It is also found that the heating effect is more pronounced in continental clouds than in maritime clouds.

scholarly journals Aerosols' influence on the interplay between condensation, evaporation and rain in warm cumulus cloud

2008 ◽  
Vol 8 (1) ◽  
pp. 15-24 ◽  
Author(s):  
O. Altaratz ◽  
I. Koren ◽  
T. Reisin ◽  
A. Kostinski ◽  
G. Feingold ◽  
...  
Keyword(s):  
Surface Area ◽  
Cloud Model ◽  
Volume Ratio ◽  
Meteorological Conditions ◽  
Drop Surface ◽  
Evaporation Process ◽  
Cumulus Cloud ◽  
Convective Clouds ◽  
Rain Drops ◽  
Numerical Cloud Model

Abstract. A numerical cloud model is used to study the influence of aerosol on the microphysics and dynamics of moderate-sized, coastal, convective clouds that develop under the same meteorological conditions. The results show that polluted convective clouds start their precipitation later and precipitate less than clean clouds but produce larger rain drops. The evaporation process is more significant at the margins of the polluted clouds (compared to the clean cloud) due to a higher drop surface area to volume ratio and it is mostly from small drops. It was found that the formation of larger raindrops in the polluted cloud is due to a more efficient collection process.

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