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 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.

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 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 Disaggregative Invariance of Daily Precipitation

1997 ◽  
Vol 36 (6) ◽  
pp. 721-734 ◽  
Author(s):  
Roman Krzysztofowicz ◽  
Thomas A. Pomroy
Keyword(s):  
Empirical Evidence ◽  
Diurnal Cycle ◽  
Daily Precipitation ◽  
Precipitation Amount ◽  
Total Precipitation ◽  
Stochastic Independence ◽  
Precipitation Forecasting ◽  
Precipitation Timing ◽  
Temporal Disaggregation ◽  
Precipitation Records

Abstract Disaggregative invariance refers to stochastic independence between the total precipitation amount and its temporal disaggregation. This property is investigated herein for areal average and point precipitation amounts accumulated over a 24-h period and disaggregated into four 6-h subperiods. Statistical analyses of precipitation records from 1948 to 1993 offer convincing empirical evidence against the disaggregative invariance and in favor of the conditional disaggregative invariance, which arises when the total amount and its temporal disaggregation are conditioned on the timing of precipitation within the diurnal cycle. The property of conditional disaggregative invariance allows the modeler or the forecaster to decompose the problem of quantitative precipitation forecasting into three tasks: (i) forecasting the precipitation timing; (ii) forecasting the total amount, conditional on timing; and (iii) forecasting the temporal disaggregation, conditional on timing. Tasks (ii) and (iii) can be performed independently of one another, and this offers a formidable advantage for applications.

The Long Term Spatial-temporal Distribution of Aerosol Optical Depth and Its Associated Atmospheric Circulation Over Southeast Africa.

2021 ◽  
Author(s):  
Matthews Nyasulu ◽  
Md. Mozammel Haque ◽  
Bathsheba Musonda ◽  
Cao Fang
Keyword(s):  
Human Health ◽  
Atmospheric Circulation ◽  
Atmospheric Aerosols ◽  
Crop Residues ◽  
Temporal Distribution ◽  
Western Coast ◽  
High Concentration ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol

Abstract Recent studies have revealed significant impacts of increased concentration of anthropogenic aerosols in the atmosphere to both climate and human health. Southeast Africa is one of the regions where studies related to atmospheric aerosols remain scant, causing high uncertainty in predicting and understanding the impacts of these aerosols to both climate and human health. The present study therefore has investigated the long term spatial-temporal distribution of atmospheric aerosols, trends, its relationship with cloud properties and the associated atmospheric circulation over the region. High concentration of aerosol has been detected during the dry months of September to November (SON) while low during March to May (MAM) and June-July (JJA) seasons in most areas. Highest 550 was recorded in areas with low elevation such as over Lake Malawi, Zambezi valley and along the western coast of the Indian Ocean. The average of the detected concentration is however low as compared to highly polluted regions of the globe. Statistical analyses revealed insignificant change of AOD550 in most areas between 2002 and 2020 time period. The study has also revealed seasonality of aerosol distribution highly influenced by changes in atmospheric circulation. Burning of biomass during dry months such bush fires and burning of crop residues remain the major source of anthropogenic aerosol concentration over Southeast Africa hence needs to be controlled.

scholarly journals Statistical analysis of daily precipitation in the Bydgoszcz region

2018 ◽  
Vol 23 ◽  
pp. 00004
Author(s):  
Waldemar Bojar ◽  
Leszek Knopik ◽  
Renata Kuśmierek-Tomaszewska ◽  
Jacek Żarski ◽  
Wojciech Żarski
Keyword(s):  
Statistical Analysis ◽  
Gamma Distribution ◽  
Daily Precipitation ◽  
Precipitation Amount ◽  
City Centre ◽  
Total Precipitation ◽  
Precipitation Frequency ◽  
Potential Variation ◽  
The City ◽  
Daily Total

The aim of the research has been to provide a statistical analysis of precipitation in the Bydgoszcz region based on the results of the measurements taken at the Experiment Station of the UTP University of Science and Technology in Bydgoszcz, located at Mochle, about 20 km away from the city centre. The paper analyses the daily total precipitation throughout 43 years (1971—2013). The analysis demonstrated a high dependence of the indicators studied on the month, confirming the annual pattern typical for the transitional climate of the temperate zone. In general, it shows an advantage of the amount and variation, and less considerably — the daily precipitation frequency in summer months, as compared with the winter months. The distribution of the probability of the daily precipitation amount for each month turned out to be compliant with gamma distribution, which allows for a potential variation in the future.

scholarly journals Impact of upstream moisture structure on a back-building convective precipitation system in south-eastern France during HyMeX IOP13

2018 ◽  
Vol 18 (23) ◽  
pp. 16845-16862 ◽  
Author(s):  
Keun-Ok Lee ◽  
Cyrille Flamant ◽  
Fanny Duffourg ◽  
Véronique Ducrocq ◽  
Jean-Pierre Chaboureau
Keyword(s):  
Moisture Content ◽  
Precipitation Amount ◽  
Lower Troposphere ◽  
Precipitation Event ◽  
Total Precipitation ◽  
Mountainous Region ◽  
Southern France ◽  
South Eastern ◽  
Sensitivity Experiments ◽  
Observation Period

Abstract. The present study examines the impact of the environmental moisture structure in the lower troposphere (below 2 km above sea level, a.s.l.) on the precipitation development, observed in southern France during Intensive Observation Period (IOP) 13 of the first Special Observation Period of the Hydrological cycle in the Mediterranean Experiment (HyMeX SOP-1), through a series of sensitivity experiments using the non-hydrostatic mesoscale atmospheric numerical model (Meso-NH). The control simulation (CNTL) and all the other 12 sensitivity experiments examined in this study succeed in reproducing a heavy precipitation event (HPE) in the coastal mountainous region of Var in south-eastern France as observed. The sensitivity experiments are designed to investigate the response of the HPE to the variability of the water vapour content upstream in the moist marine atmospheric boundary layer (MABL) and the drier air above. The comparisons between CNTL and the 12 sensitivity experiments show how the life cycle of precipitation associated with the HPE, but also the upstream flow (over the sea), is modified, even for moisture content changes of only 1 g kg−1 below 2 km a.s.l. Within the low-level wind convergence between southerlies and south-westerlies, a small increase of moisture content in the MABL prolongs moderate precipitation (≥5 mm in 15 min) and enlarges the area of weak precipitation (≥1 mm in 15 min). The moistening in the 1–2 km a.s.l. layer, just above the MABL, prolongs the duration of moderate precipitation, for a similar total precipitation amount as in CNTL. The drier MABL and 1–2 km a.s.l. layer shorten the lifetime of precipitation and reduce the total precipitation amount with respect to CNTL. We also found that the moisture in the MABL has a stronger impact on producing enhanced precipitation (both in terms of amount and intensity) than the moisture just above (1–2 km a.s.l.). Also, it is worth noting that adding moisture in the MABL does not necessarily lead to enhanced precipitation amount. In moistening the MABL, the duration of moderate precipitation increases with increasing moisture as does the area covered by weak precipitation, while the area covered by the intense precipitation (≥30 mm) decreases. Despite a simplified moisture-profile modification approach, this study suggests that moisture structure in the lower troposphere is key for accurate prediction at short-term range of the timing and location of precipitation in the coastal mountainous region in southern France.

scholarly journals Precipitation Characteristics in Eighteen Coupled Climate Models

2006 ◽  
Vol 19 (18) ◽  
pp. 4605-4630 ◽  
Author(s):  
Aiguo Dai
Keyword(s):  
Climate Models ◽  
Global Climate Model ◽  
Precipitation Amount ◽  
Total Precipitation ◽  
Coupled Models ◽  
Central Pacific ◽  
Coupled Climate Models ◽  
Low Latitudes ◽  
Stratiform Precipitation ◽  
Precipitation Ratio

Abstract Monthly and 3-hourly precipitation data from twentieth-century climate simulations by the newest generation of 18 coupled climate system models are analyzed and compared with available observations. The characteristics examined include the mean spatial patterns, intraseasonal-to-interannual and ENSO-related variability, convective versus stratiform precipitation ratio, precipitation frequency and intensity for different precipitation categories, and diurnal cycle. Although most models reproduce the observed broad patterns of precipitation amount and year-to-year variability, models without flux corrections still show an unrealistic double-ITCZ pattern over the tropical Pacific, whereas the flux-corrected models, especially the Meteorological Research Institute (MRI) Coupled Global Climate Model (CGCM; version 2.3.2a), produce realistic rainfall patterns at low latitudes. As in previous generations of coupled models, the rainfall double ITCZs are related to westward expansion of the cold tongue of sea surface temperature (SST) that is observed only over the equatorial eastern Pacific but extends to the central Pacific in the models. The partitioning of the total variance of precipitation among intraseasonal, seasonal, and longer time scales is generally reproduced by the models, except over the western Pacific where the models fail to capture the large intraseasonal variations. Most models produce too much convective (over 95% of total precipitation) and too little stratiform precipitation over most of the low latitudes, in contrast to 45%–65% in convective form in the Tropical Rainfall Measuring Mission (TRMM) satellite observations. The biases in the convective versus stratiform precipitation ratio are linked to the unrealistically strong coupling of tropical convection to local SST, which results in a positive correlation between the standard deviation of Niño-3.4 SST and the local convective-to-total precipitation ratio among the models. The models reproduce the percentage of the contribution (to total precipitation) and frequency for moderate precipitation (10–20 mm day−1), but underestimate the contribution and frequency for heavy (>20 mm day−1) and overestimate them for light (<10 mm day−1) precipitation. The newest generation of coupled models still rains too frequently, mostly within the 1–10 mm day−1 category. Precipitation intensity over the storm tracks around the eastern coasts of Asia and North America is comparable to that in the ITCZ (10–12 mm day−1) in the TRMM data, but it is much weaker in the models. The diurnal analysis suggests that warm-season convection still starts too early in these new models and occurs too frequently at reduced intensity in some of the models. The results show that considerable improvements in precipitation simulations are still desirable for the latest generation of the world’s coupled climate models.

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