scholarly journals Preconditioning, aerosols, and radiation control the temperature of glaciation in Amazonian clouds

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Alexandre L. Correia ◽  
Elisa T. Sena ◽  
Maria A. F. Silva Dias ◽  
Ilan Koren
Keyword(s):  
Water Cycle ◽  
Deep Convection ◽  
Convective Cloud ◽  
Convective Clouds ◽  
Radiation Control ◽  
Cloud Models ◽  
Radiation Fluxes ◽  
Cloud Development ◽  
Fundamental Phenomenon ◽  
Heat Budgets

AbstractGlaciation in clouds is a fundamental phenomenon in determining Earth’s radiation fluxes, sensible and latent heat budgets in the atmosphere, the water cycle, cloud development and lifetime. Nevertheless, the main mechanisms that govern the temperature of glaciation in clouds have not been fully identified. Here we present an analysis of 15 years (2000-2014) of satellite, sunphotometer, and reanalysis datasets over the Amazon. We find that the temperature of glaciation in convective clouds is controlled by preconditioning dynamics, natural and anthropic aerosols, and radiation. In a moist atmospheric column, prone to deep convection, increasing the amount of aerosols leads to a delay in the onset of glaciation, reducing the glaciation temperature. For a dry column, radiative extinction by biomass burning smoke leads to atmospheric stabilization and an increase in the glaciation temperature. Our results offer observational benchmarks that can help a more precise description of glaciation in convective cloud models.

scholarly journals Potential impact of aerosols on convective clouds revealed by Himawari-8 observations over different terrain types in eastern China

2021 ◽  
Vol 21 (8) ◽  
pp. 6199-6220
Author(s):  
Tianmeng Chen ◽  
Zhanqing Li ◽  
Ralph A. Kahn ◽  
Chuanfeng Zhao ◽  
Daniel Rosenfeld ◽  
...  
Keyword(s):  
Water Cycle ◽  
Eastern China ◽  
Convective Cloud ◽  
Northern China ◽  
Cloud Data ◽  
Convective Clouds ◽  
Cloud Properties ◽  
Cloud Development ◽  
Potential Impact ◽  
The Impact

Abstract. Convective clouds are common and play a major role in Earth's water cycle and energy balance; they may even develop into storms and cause severe rainfall events. To understand the convective cloud development process, this study investigates the impact of aerosols on convective clouds by considering the influence of both topography and diurnal variation in radiation. By combining texture analysis, clustering, and thresholding methods, we identify all convective clouds in two warm seasons (May–September, 2016/17) in eastern China based on Himawari-8 Level 1 data. Having large diurnally resolved cloud data together with surface meteorological and environmental measurements, we investigate convective cloud properties and their variation, stratified by elevation and diurnal change. We then analyze the potential impact of aerosol on convective clouds under different meteorological conditions and topographies. In general, convective clouds tend to occur preferentially under polluted conditions in the morning, which reverses in the afternoon. Convective cloud fraction first increases then decreases with aerosol loading, which may contribute to this phenomenon. Topography and diurnal meteorological variations may affect the strength of aerosol microphysical and radiative effects. Updraft is always stronger along the windward slopes of mountains and plateaus, especially in northern China. The prevailing southerly wind near the foothills of mountains and plateaus is likely to contribute to this windward strengthening of updraft and to bring more pollutant into the mountains, thereby strengthening the microphysical effect, invigorating convective clouds. By comparison, over plain, aerosols decrease surface heating and suppress convection by blocking solar radiation reaching the surface.

scholarly journals Potential impact of aerosols on convective clouds revealed by Himawari-8 observations over different terrain types in eastern China

2020 ◽  
Author(s):  
Tianmeng Chen ◽  
Zhanqing Li ◽  
Ralph A. Kahn ◽  
Chuanfeng Zhao ◽  
Daniel Rosenfeld ◽  
...  
Keyword(s):  
Water Cycle ◽  
Eastern China ◽  
Convective Cloud ◽  
Northern China ◽  
Cloud Data ◽  
Convective Clouds ◽  
Cloud Properties ◽  
Cloud Development ◽  
Potential Impact ◽  
The Impact

Abstract. Convective clouds are common and play a major role in Earth's water cycle and energy balance; they may even develop into storms and cause severe rainfall events. To understand the convective cloud development process, this study investigates the impact of aerosols on convective clouds by considering the influence of both topography and diurnal variation of radiation. By combining texture analysis, clustering and thresholding methods, we identify all convective clouds in two warm seasons (May–September, 2016–2017) in eastern China based on Himawari-8 Level 1 data. Having a large diurnally resolved cloud data together with surface meteorological and environmental measurements, we investigate convective cloud properties and their variation, stratified by elevation and diurnal change. We then analyze the potential impact of aerosol on convective clouds under different meteorological conditions and topographies. In general, convective clouds tend to occur preferentially under polluted conditions in the morning, which reverses in the afternoon. Convective cloud fraction first increase then decrease with aerosol loading, which may contribute to this phenomenon. Topography and diurnal meteorological variations may affect the strength of aerosol microphysical and radiative effects. Updraft is always stronger along the windward slopes of mountains and plateaus, especially in northern China. The prevailing southerly wind near the foothills of mountains and plateaus is likely to contribute to this windward strengthening of updraft and to bring more pollutant into the mountains, thereby strengthening the microphysical effect, invigorating convective clouds. By comparison, over plain, aerosol decreases surface heating and suppresses convection by blocking solar radiation reaching the surface.

An Evaluation of the Proposed Mechanism of the Adaptive Infrared Iris Hypothesis Using TRMM VIRS and PR Measurements

2005 ◽  
Vol 18 (20) ◽  
pp. 4185-4194 ◽  
Author(s):  
Anita D. Rapp ◽  
Christian Kummerow ◽  
Wesley Berg ◽  
Brian Griffith
Keyword(s):  
Surface Temperature ◽  
Deep Convection ◽  
Cloud Amount ◽  
Tropical Rainfall Measuring Mission ◽  
Convective Cloud ◽  
Sea Surface ◽  
Central Pacific ◽  
Convective Clouds ◽  
Brightness Temperatures ◽  
Surface Rainfall

Abstract Significant controversy surrounds the adaptive infrared iris hypothesis put forth by Lindzen et al., whereby tropical anvil cirrus detrainment is hypothesized to decrease with increasing sea surface temperature (SST). This dependence would act as an iris, allowing more infrared radiation to escape into space and inhibiting changes in the surface temperature. This hypothesis assumes that increased precipitation efficiency in regions of higher sea surface temperatures will reduce cirrus detrainment. Tropical Rainfall Measuring Mission (TRMM) satellite measurements are used here to investigate the adaptive infrared iris hypothesis. Pixel-level Visible and Infrared Scanner (VIRS) 10.8-μm brightness temperature data and precipitation radar (PR) rain-rate data from TRMM are collocated and matched to determine individual convective cloud boundaries. Each cloudy pixel is then matched to the underlying SST. This study examines single- and multicore convective clouds separately to directly determine if a relationship exists between the size of convective clouds, their precipitation, and the underlying SSTs. In doing so, this study addresses some of the criticisms of the Lindzen et al. study by eliminating their more controversial method of relating bulk changes of cloud amount and SST across a large domain in the Tropics. The current analysis does not show any significant SST dependence of the ratio of cloud area to surface rainfall for deep convection in the tropical western and central Pacific. Results do, however, suggest that SST plays an important role in the ratio of cloud area and surface rainfall for warm rain processes. For clouds with brightness temperatures between 270 and 280 K, a net decrease in cloud area normalized by rainfall of 5% per degree SST was found.

scholarly journals Secondary Ice Formation in Idealised Deep Convection—Source of Primary Ice and Impact on Glaciation

Atmosphere ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 542
Author(s):  
Annette K. Miltenberger ◽  
Tim Lüttmer ◽  
Christoph Siewert
Keyword(s):  
Deep Convection ◽  
Three Dimensional ◽  
Convective Cloud ◽  
Cloud Formation ◽  
Ice Formation ◽  
Ice Crystal ◽  
Lagrangian Analysis ◽  
Vertical Coupling ◽  
Convective Clouds ◽  
Ice Production

Secondary ice production via rime-splintering is considered to be an important process for rapid glaciation and high ice crystal numbers observed in mixed-phase convective clouds. An open question is how rime-splintering is triggered in the relatively short time between cloud formation and observations of high ice crystal numbers. We use idealised simulations of a deep convective cloud system to investigate the thermodynamic and cloud microphysical evolution of air parcels, in which the model predicts secondary ice formation. The Lagrangian analysis suggests that the “in-situ” formation of rimers either by growth of primary ice or rain freezing does not play a major role in triggering secondary ice formation. Instead, rimers are predominantly imported into air parcels through sedimentation form higher altitudes. While ice nucleating particles (INPs) initiating heterogeneous freezing of cloud droplets at temperatures warmer than −10 °C have no discernible impact of the occurrence of secondary ice formation, in a scenario with rain freezing secondary ice production is initiated slightly earlier in the cloud evolution and at slightly different places, although with no major impact on the abundance or spatial distribution of secondary ice in the cloud as a whole. These results suggest that for interpreting and analysing observational data and model experiments regarding cloud glaciation and ice formation it is vital to consider the complex vertical coupling of cloud microphysical processes in deep convective clouds via three-dimensional transport and sedimentation.

scholarly journals The Formation of Wider and Deeper Clouds as a Result of Cold-Pool Dynamics

2014 ◽  
Vol 71 (8) ◽  
pp. 2842-2858 ◽  
Author(s):  
Linda Schlemmer ◽  
Cathy Hohenegger
Keyword(s):  
Deep Convection ◽  
Gravity Current ◽  
Cold Pool ◽  
Peak Time ◽  
Entrainment Rate ◽  
Convective Clouds ◽  
Cold Pools ◽  
Cloud Resolving Model ◽  
Cloud Development ◽  
Rain Formation

Abstract This study investigates how precipitation-driven cold pools aid the formation of wider clouds that are essential for a transition from shallow to deep convection. In connection with a temperature depression and a depletion of moisture inside developing cold pools, an accumulation of moisture in moist patches around the cold pools is observed. Convective clouds are formed on top of these moist patches. Larger moist patches form with time supporting more and larger clouds. Moreover, enhanced vertical lifting along the leading edges of the gravity current triggered by the cold pool is found. The interplay of moisture aggregation and lifting eventually promotes the formation of wider clouds that are less affected by entrainment and become deeper. These mechanisms are corroborated in a series of cloud-resolving model simulations representing different atmospheric environments. A positive feedback is observed in that, in an atmosphere in which cloud and rain formation is facilitated, stronger downdrafts will form. These stronger downdrafts lead to a stronger modification of the moisture field, which in turn favors further cloud development. This effect is not only observed in the transition phase but also active in prolonging the peak time of precipitation in the later stages of the diurnal cycle. These findings are used to propose a simple way for incorporating the effect of cold pools on cloud sizes and thereby entrainment rate into parameterization schemes for convection. Comparison of this parameterization to the cloud-resolving modeling output gives promising results.

Transport of isoprene and its oxidation products by deep convective clouds in the Amazon

2021 ◽  
Author(s):  
Roman Bardakov ◽  
Joel Thornton ◽  
Ilona Riipinen ◽  
Radovan Krejci ◽  
Annica Ekman
Keyword(s):  
Deep Convection ◽  
Convective Cloud ◽  
Particle Growth ◽  
Lightning Activity ◽  
Oxidation Products ◽  
Gas Uptake ◽  
Convective Clouds ◽  
Ice Particles ◽  
Volatile Oxidation Products ◽  
Deep Convective Clouds

<p>Transport of organic trace gases by deep convective clouds plays an important role for new particle formation (NPF) and particle growth in the upper atmosphere. Isoprene accounts for a major fraction of the global volatile organic vapor emissions and a significant fraction is emitted in the Amazon. We examined transport and chemical processing of isoprene and its oxidation products in a deep convective cloud over the Amazon using a box model. Trajectories of individual air parcels of the cloud derived from a large eddy simulation are used as input to the model. Our results show that there exist two main pathways for NPF from isoprene associated with deep convection. The first one is when the gas transport occurs through a cloud with low lightning activity and with efficient gas uptake of low-volatile oxidation products by ice particles. Some of the isoprene will reach the cloud outflow where it is further aged and produces low volatile species capable of forming and growing new particles. The second way is via transport through clouds with high lightning activity and with low gas uptake by ice. For this case, low volatile oxidation products will reach the immediate outflow in concentrations close to the values observed in the boundary layer. The efficiency of gas condensation on ice particles is still uncertain and further research in this direction is needed.</p>

scholarly journals Resolving both entrainment-mixing and number of activated CCN in deep convective clouds

2011 ◽  
Vol 11 (3) ◽  
pp. 9673-9703 ◽  
Author(s):  
E. Freud ◽  
D. Rosenfeld ◽  
D. Axisa ◽  
J. R. Kulkarni
Keyword(s):  
Droplet Size ◽  
Cloud Droplet ◽  
Convective Cloud ◽  
Ambient Air ◽  
Droplet Evaporation ◽  
Radiative Properties ◽  
Cloud Base ◽  
Droplet Growth ◽  
Convective Clouds ◽  
Cloud Models

Abstract. The number concentration of activated CCN (Na) is the most fundamental microphysical property of a convective cloud. It determines the rate of droplet growth with cloud depth and conversion into precipitation-sized particles and affects the radiative properties of the clouds. However, measuring Na is not always possible, even in the cores of the convective clouds, because entrainment of sub-saturated ambient air deeper into the cloud lowers the concentrations by dilution and may cause partial or total droplet evaporation, depending on whether the mixing is homogeneous or extreme inhomogeneous, respectively. Here we describe a methodology to derive Na based on the rate of cloud droplet effective radius (Re) growth with cloud depth and with respect to the cloud mixing with the entrained ambient air. We use the slope of the tight linear relationship between the adiabatic water and Re3 to derive an upper limit for Na assuming extreme inhomogeneous mixing. Then we tune Na down to find the theoretical relative humidity that the entrained ambient air would have for each horizontal cloud penetration, in case of homogeneous mixing. This allows us to evaluate both the entrainment and mixing process in the vertical dimension in addition to getting a better estimation for Na. We found that the derived Na from the entire profile data is highly correlated with the independent CCN measurements from below cloud base. Moreover, it was found that mixing of sub-saturated ambient air into the cloud is inclined towards the extreme inhomogeneous limit, i.e. that the time scale of droplet evaporation is significantly smaller than that for turbulent mixing. This means that ambient air that entrains the cloud is pre-moistened by total evaporation of cloud droplets before it mixes deeper into the clouds where it can hardly change the droplet size distribution, hence Re remains close to its adiabatic value at any given cloud depth. However, the tendency towards the extreme inhomogeneous mixing appeared to slightly decrease with altitude, possibly due to enhanced turbulence and larger cloud drops aloft. Quantifying these effects, based on more examples from other projects and high resolution cloud models is essential for improving our understanding of the interactions between the cloud and its environment. These interactions may play an important role in cloud dynamics and microphysics, by affecting cloud depth and droplet size spectra, for example, and may therefore influence the cloud precipitation formation processes.

scholarly journals Resolving both entrainment-mixing and number of activated CCN in deep convective clouds

2011 ◽  
Vol 11 (24) ◽  
pp. 12887-12900 ◽  
Author(s):  
E. Freud ◽  
D. Rosenfeld ◽  
J. R. Kulkarni
Keyword(s):  
Droplet Size ◽  
Cloud Droplet ◽  
Convective Cloud ◽  
Ambient Air ◽  
Droplet Evaporation ◽  
Radiative Properties ◽  
Cloud Base ◽  
Droplet Growth ◽  
Convective Clouds ◽  
Cloud Models

Abstract. The number concentration of activated CCN (Na) is the most fundamental microphysical property of a convective cloud. It determines the rate of droplet growth with cloud depth and conversion into precipitation-sized particles and affects the radiative properties of the clouds. However, measuring Na is not always possible, even in the cores of the convective clouds, because entrainment of sub-saturated ambient air deeper into the cloud lowers the concentrations by dilution and may cause partial or total droplet evaporation, depending on whether the mixing is homogeneous or extreme inhomogeneous, respectively. Here we describe a methodology to derive Na based on the rate of cloud droplet effective radius (Re) growth with cloud depth and with respect to the cloud mixing with the entrained ambient air. We use the slope of the tight linear relationship between the adiabatic liquid water mixing ratio and Re3 (or Rv3) to derive an upper limit for Na assuming extreme inhomogeneous mixing. Then we tune Na down to find the theoretical relative humidity that the entrained ambient air would have for each horizontal cloud penetration, in case of homogeneous mixing. This allows us to evaluate both the entrainment and mixing process in the vertical dimension in addition to getting a better estimation for Na. We found that the derived Na from the entire profile data is highly correlated with the independent CCN measurements from below cloud base. Moreover, it was found that mixing of sub-saturated ambient air into the cloud at scales of ~100 m and above is inclined towards the extreme inhomogeneous limit, i.e. that the time scale of droplet evaporation is significantly smaller than that for turbulent mixing. This means that ambient air that entrains the cloud is pre-moistened by total evaporation of cloud droplets before it mixes deeper into the clouds where it can hardly change the droplet size distribution, hence Re remains close to its adiabatic value at any given cloud depth. However, the tendency towards the extreme inhomogeneous mixing appeared to slightly decrease with altitude, possibly due to enhanced turbulence and larger cloud drops aloft. Quantifying these effects, based on more examples from other projects and high resolution cloud models is essential for improving our understanding of the interactions between the cloud and its environment. These interactions may play an important role in cloud dynamics and microphysics, by affecting cloud depth and droplet size spectra, for example, and may therefore influence the cloud precipitation formation processes.

scholarly journals Diurnal variation of upper tropospheric humidity and its relations to convective activities over tropical Africa

2007 ◽  
Vol 7 (1) ◽  
pp. 351-381 ◽  
Author(s):  
E. S. Chung ◽  
B. J. Sohn ◽  
J. Schmetz ◽  
M. Koenig
Keyword(s):  
Diurnal Variation ◽  
Deep Convection ◽  
Time Lag ◽  
Convective Cloud ◽  
Diurnal Variations ◽  
Tropical Africa ◽  
High Cloud ◽  
Convective Clouds ◽  
Lagrangian Framework ◽  
Upper Tropospheric Humidity

Abstract. Diurnal variations of upper tropospheric humidity (UTH) as well as middle tropospheric humidity (MTH) were examined in conjunction with the diurnal cycle of convection over tropical Africa and the adjacent tropical Atlantic Ocean using Meteosat-8 measurements. Cloud and humidity features were also tracked to document the diurnal variations of humidity and clouds in the Lagrangian framework. A distinct diurnal variation of UTH (and MTH) is noted over regions where tropical deep convective cloud systems are commonly observed. The amplitude of the UTH diurnal variation is larger over land, while its variations over convectively inactive subtropical regions are much smaller. The diurnal variation of UTH tends to peak during nighttime over land, lagging deep convection and high cloud whose maxima occurred in the late afternoon and the evening, respectively. The time lag between the maximum UTH and deep convection/high cloud maxima over the ocean appears to be longer in comparison to that found over land. It was also indicated that both the UTH (and MTH) and the cirrus anvil cloud show a variation which is in phase, implying that moistening of the upper troposphere is closely linked to process of development and dissipation of deep convective clouds.

scholarly journals Thermal structure of intense convective clouds derived from GPS radio occultations

2012 ◽  
Vol 12 (12) ◽  
pp. 5309-5318 ◽  
Author(s):  
R. Biondi ◽  
W. J. Randel ◽  
S.-P. Ho ◽  
T. Neubert ◽  
S. Syndergaard
Keyword(s):  
Thermal Structure ◽  
Deep Convection ◽  
Lapse Rate ◽  
Orthogonal Polarization ◽  
Cold Temperatures ◽  
Temperature Lapse Rate ◽  
Convective Systems ◽  
Convective Clouds ◽  
Strong Inversion ◽  
Cloud Tops

Abstract. Thermal structure associated with deep convective clouds is investigated using Global Positioning System (GPS) radio occultation measurements. GPS data are insensitive to the presence of clouds, and provide high vertical resolution and high accuracy measurements to identify associated temperature behavior. Deep convective systems are identified using International Satellite Cloud Climatology Project (ISCCP) satellite data, and cloud tops are accurately measured using Cloud-Aerosol Lidar with Orthogonal Polarization (CALIPSO) lidar observations; we focus on 53 cases of near-coincident GPS occultations with CALIPSO profiles over deep convection. Results show a sharp spike in GPS bending angle highly correlated to the top of the clouds, corresponding to anomalously cold temperatures within the clouds. Above the clouds the temperatures return to background conditions, and there is a strong inversion at cloud top. For cloud tops below 14 km, the temperature lapse rate within the cloud often approaches a moist adiabat, consistent with rapid undiluted ascent within the convective systems.

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