scholarly journals Robust relations between CCN and the vertical evolution of cloud drop size distribution in deep convective clouds

2008 ◽  
Vol 8 (6) ◽  
pp. 1661-1675 ◽  
Author(s):  
E. Freud ◽  
D. Rosenfeld ◽  
M. O. Andreae ◽  
A. A. Costa ◽  
P. Artaxo
Keyword(s):  
Amazon Basin ◽  
Drop Size ◽  
Cloud Condensation Nuclei ◽  
Liquid Water Content ◽  
Cloud Drop ◽  
Cloud Droplets ◽  
Freezing Level ◽  
Convective Clouds ◽  
Warm Rain ◽  
Drop Size Distributions

Abstract. In-situ measurements in convective clouds (up to the freezing level) over the Amazon basin show that smoke from deforestation fires prevents clouds from precipitating until they acquire a vertical development of at least 4 km, compared to only 1–2 km in clean clouds. The average cloud depth required for the onset of warm rain increased by ~350 m for each additional 100 cloud condensation nuclei per cm3 at a super-saturation of 0.5% (CCN0.5%). In polluted clouds, the diameter of modal liquid water content grows much slower with cloud depth (at least by a factor of ~2), due to the large number of droplets that compete for available water and to the suppressed coalescence processes. Contrary to what other studies have suggested, we did not observe this effect to reach saturation at 3000 or more accumulation mode particles per cm3. The CCN0.5% concentration was found to be a very good predictor for the cloud depth required for the onset of warm precipitation and other microphysical factors, leaving only a secondary role for the updraft velocities in determining the cloud drop size distributions. The effective radius of the cloud droplets (re) was found to be a quite robust parameter for a given environment and cloud depth, showing only a small effect of partial droplet evaporation from the cloud's mixing with its drier environment. This supports one of the basic assumptions of satellite analysis of cloud microphysical processes: the ability to look at different cloud top heights in the same region and regard their re as if they had been measured inside one well developed cloud. The dependence of re on the adiabatic fraction decreased higher in the clouds, especially for cleaner conditions, and disappeared at re≥~10 μm. We propose that droplet coalescence, which is at its peak when warm rain is formed in the cloud at re=~10 μm, continues to be significant during the cloud's mixing with the entrained air, cancelling out the decrease in re due to evaporation.

scholarly journals Robust relations between CCN and the vertical evolution of cloud drop size distribution in deep convective clouds

2005 ◽  
Vol 5 (5) ◽  
pp. 10155-10195 ◽  
Author(s):  
E. Freud ◽  
D. Rosenfeld ◽  
M. O. Andreae ◽  
A. A. Costa ◽  
P. Artaxo
Keyword(s):  
Amazon Basin ◽  
Drop Size ◽  
Cloud Condensation Nuclei ◽  
Liquid Water Content ◽  
Cloud Drop ◽  
Cloud Droplets ◽  
Freezing Level ◽  
Convective Clouds ◽  
Warm Rain ◽  
Drop Size Distributions

Abstract. In-situ measurements in convective clouds (up to the freezing level) over the Amazon basin show that smoke from deforestation fires prevents clouds from precipitating until they acquire a vertical development of at least 4 km, compared to only 1–2 km in clean clouds. The average cloud depth required for the onset of warm rain increased by ~350 m for each additional 100 cloud condensation nuclei per cm3 at a super-saturation of 0.5% (CCN0.5%). In polluted clouds, the diameter of modal liquid water content grows much slower with cloud depth (at least by a factor of ~2), due to the large number of droplets that compete for available water and to the suppressed coalescence processes. Contrary to what other studies have suggested, we did not observe this effect to reach saturation at 3000 or more accumulation mode particles per cm3. The CCN0.5% concentration was found to be a very good predictor for the cloud depth required for the onset of warm precipitation and other microphysical factors, leaving only a secondary role for the updraft velocities in determining the cloud drop size distributions. The effective radius of the cloud droplets (re) was found to be a quite robust parameter for a given environment and cloud depth, showing only a small effect of partial droplet evaporation from the cloud's mixing with its drier environment. This supports one of the basic assumptions of satellite analysis of cloud microphysical processes: the ability to look at different cloud top heights in the same region and regard their re as if they had been measured inside one well developed cloud. The dependence of re on the adiabatic fraction decreased higher in the clouds, especially for cleaner conditions, and disappeared at re≥~10 µm. We propose that droplet coalescence, which is at its peak when warm rain is formed in the cloud at re~10 µm, continues to be significant during the cloud's mixing with the entrained air, canceling out the decrease in re due to evaporation.

scholarly journals Linear relationship between effective radius and precipitation water content near the top of convective clouds

2021 ◽  
Author(s):  
Ramon Campos Braga ◽  
Daniel Rosenfeld ◽  
Ovid O. Krüger ◽  
Barbara Ervens ◽  
Bruna A. Holanda ◽  
...  
Keyword(s):  
Linear Relationship ◽  
Water Content ◽  
Amazon Basin ◽  
Hydrological Cycle ◽  
Cloud Condensation Nuclei ◽  
Effective Radius ◽  
Convective Clouds ◽  
Warm Rain ◽  
Precipitation Water ◽  
Cloud Tops

Abstract. Quantifying the precipitation within clouds is a crucial challenge to improve our current understanding of the Earth’s hydrological cycle. We have investigated the relationship between the effective radius of droplets and ice particles (re) and precipitation water content (PWC) measured by cloud probes near the top of growing convective cumuli. The data for this study were collected by aircraft measurements in clean and polluted conditions over the Amazon Basin and over the western tropical Atlantic in September 2014. Our results indicate a threshold of re ∼ 13 μm for warm rain initiation in convective clouds, which is in agreement with previous studies. In clouds over the Atlantic Ocean, warm rain starts at smaller re, likely linked to the enhancement of coalescence of drops formed on giant cloud condensation nuclei. In cloud passes where precipitation starts as ice hydrometeors, the threshold of re is also shifted to values smaller than 13 μm when coalescence processes are suppressed and precipitating particles are formed by accretion. We found a statistically significant linear relationship between PWC and re for measurements at cloud tops, with a correlation coefficient of ∼0.94. The tight relationship between re and PWC was established only when particles with sizes large enough to precipitate (drizzle and raindrops) are included in calculating re. Our results emphasize for the first time that re is a key parameter to determine both initiation and amount of precipitation at the top of convective clouds.

scholarly journals Linear relationship between effective radius and precipitation water content near the top of convective clouds: measurement results from ACRIDICON–CHUVA campaign

2021 ◽  
Vol 21 (18) ◽  
pp. 14079-14088
Author(s):  
Ramon Campos Braga ◽  
Daniel Rosenfeld ◽  
Ovid O. Krüger ◽  
Barbara Ervens ◽  
Bruna A. Holanda ◽  
...  
Keyword(s):  
Linear Relationship ◽  
Water Content ◽  
Amazon Basin ◽  
Hydrological Cycle ◽  
Cloud Condensation Nuclei ◽  
Effective Radius ◽  
Convective Clouds ◽  
Warm Rain ◽  
Precipitation Water ◽  
Cloud Tops

Abstract. Quantifying the precipitation within clouds is a crucial challenge to improve our current understanding of the Earth's hydrological cycle. We have investigated the relationship between the effective radius of droplets and ice particles (re) and precipitation water content (PWC) measured by cloud probes near the top of growing convective cumuli. The data for this study were collected during the ACRIDICON–CHUVA campaign on the HALO research aircraft in clean and polluted conditions over the Amazon Basin and over the western tropical Atlantic in September 2014. Our results indicate a threshold of re∼13 µm for warm rain initiation in convective clouds, which is in agreement with previous studies. In clouds over the Atlantic Ocean, warm rain starts at smaller re, likely linked to the enhancement of coalescence of drops formed on giant cloud condensation nuclei. In cloud passes where precipitation starts as ice hydrometeors, the threshold of re is also shifted to values smaller than 13 µm when coalescence processes are suppressed and precipitating particles are formed by accretion. We found a statistically significant linear relationship between PWC and re for measurements at cloud tops, with a correlation coefficient of ∼0.94. The tight relationship between re and PWC was established only when particles with sizes large enough to precipitate (drizzle and raindrops) are included in calculating re. Our results emphasize for the first time that re is a key parameter to determine both initiation and amount of precipitation at the top of convective clouds.

scholarly journals Modeling the relation between CCN and the vertical evolution of cloud drop size distribution in convective clouds with parcel model

2007 ◽  
Vol 22 (3) ◽  
pp. 313-321
Author(s):  
Gérson Paiva Almeida ◽  
Rômulo Rodrigues dos Santos
Keyword(s):  
Size Distribution ◽  
Drop Size ◽  
Liquid Water Content ◽  
Drop Size Distribution ◽  
Amazon Forest ◽  
Polluted Environment ◽  
Cloud Drop ◽  
Microphysical Process ◽  
Warm Rain ◽  
Rain Formation

In this work we use values of effective radius of cloud drop size distribution and modal radius of liquid water content generated with a parcel model with detailed treatment of liquid phase microphysical process to evaluate the warm rain formation suppression over the Amazon due to the presence of aerosols generated by forest burning. Four cases based on observations are simulated: a clean marine environment as the one observed close to Fortaleza; a clean environment as the ones observed over the apparently unpolluted Amazon forest; a environment observed during the intense burning season in the polluted part of the Amazon; and the same polluted environment observed during the transition season from dry to wet. It is shown that the model reproduces quantitatively some of the observed features of clouds in different environments. The model indicated that in very polluted environment the warm rain formation process can be completely suppressed. Nevertheless, in certain situations the formation of warm rain can still be achieved and significant amount of rainwater can be formed.

scholarly journals Raindrop Size Distribution and Rain Characteristics during the 2013 Great Colorado Flood

2015 ◽  
Vol 17 (1) ◽  
pp. 53-72 ◽  
Author(s):  
Katja Friedrich ◽  
Evan A. Kalina ◽  
Joshua Aikins ◽  
Matthias Steiner ◽  
David Gochis ◽  
...  
Keyword(s):  
Drop Size ◽  
Doppler Radar ◽  
Liquid Water Content ◽  
Size Distributions ◽  
Intense Rainfall ◽  
Wind Fields ◽  
Raindrop Size Distribution ◽  
Median Volume ◽  
Drop Size Distributions ◽  
Analysis System

Abstract Drop size distributions observed by four Particle Size Velocity (PARSIVEL) disdrometers during the 2013 Great Colorado Flood are used to diagnose rain characteristics during intensive rainfall episodes. The analysis focuses on 30 h of intense rainfall in the vicinity of Boulder, Colorado, from 2200 UTC 11 September to 0400 UTC 13 September 2013. Rainfall rates R, median volume diameters D0, reflectivity Z, drop size distributions (DSDs), and gamma DSD parameters were derived and compared between the foothills and adjacent plains locations. Rainfall throughout the entire event was characterized by a large number of small- to medium-sized raindrops (diameters smaller than 1.5 mm) resulting in small values of Z (<40 dBZ), differential reflectivity Zdr (<1.3 dB), specific differential phase Kdp (<1° km−1), and D0 (<1 mm). In addition, high liquid water content was present throughout the entire event. Raindrops observed in the plains were generally larger than those in the foothills. DSDs observed in the foothills were characterized by a large concentration of small-sized drops (d < 1 mm). Heavy rainfall rates with slightly larger drops were observed during the first intense rainfall episode (0000–0800 UTC 12 September) and were associated with areas of enhanced low-level convergence and vertical velocity according to the wind fields derived from the Variational Doppler Radar Analysis System. The disdrometer-derived Z–R relationships reflect how unusual the DSDs were during the 2013 Great Colorado Flood. As a result, Z–R relations commonly used by the operational NEXRAD strongly underestimated rainfall rates by up to 43%.

scholarly journals Distance-Scaled Water Concentrations versus Mass-Median Drop Size, Temperature, and Altitude in Supercooled Clouds

2008 ◽  
Vol 65 (7) ◽  
pp. 2087-2106 ◽  
Author(s):  
Richard K. Jeck
Keyword(s):  
Stable Condition ◽  
Liquid Water Content ◽  
Common Reference ◽  
Freezing Level ◽  
Convective Clouds ◽  
Stratiform Clouds ◽  
Median Diameter ◽  
Droplet Sizes ◽  
New Statistics ◽  
Mass Median

Abstract About 28 000 nautical miles (n mi) of select in-flight measurements of liquid water content (LWC), droplet sizes, temperature, and other variables in supercooled clouds from a variety of research projects over portions of North America, Europe, and the northern oceans have been compiled into a computerized database for obtaining new statistics on the ranges, frequency of occurrence, and interrelationships of the variables. The LWCs are averaged over uniform cloud intervals of variable length. LWC probabilities are then generated as a function of averaging distance, temperature, droplet mass-median diameter (MMD), altitude, and freezing-level height. These variously scaled LWCs (different averaging intervals from 1 s to 200 n mi) are easily accommodated by distance-based graphing (LWC versus averaging distance). These graphs provide realistic LWCs for modeling, and they can serve as a common reference for comparing LWC measurements over any averaging scale. Maximum recorded LWCs are about 1.6 g m−3 in stratiform clouds and about 5 g m−3 in convective clouds, both over short (<0.5 km) distances. A sharp MMD mode near 15 μm appears to be a stable condition in which the LWCs can be the largest and extend the farthest. The larger the MMD above the mode, the shorter its spatial extent will be, the rarer its occurrence, and the lower the maximum LWC that can be present.

scholarly journals The evolution of cloud microphysics upon aerosol interaction at the summit of Mt. Tai, China

2019 ◽  
Author(s):  
Jiarong Li ◽  
Chao Zhu ◽  
Hui Chen ◽  
Defeng Zhao ◽  
Likun Xue ◽  
...  
Keyword(s):  
Climate Models ◽  
Cloud Condensation Nuclei ◽  
Liquid Water Content ◽  
Cloud Microphysics ◽  
Life Cycles ◽  
Cloud Droplets ◽  
Climate Effect ◽  
Local Climate ◽  
The North ◽  
Microphysical Properties

Abstract. The influence of aerosols, both natural and anthropogenic, remains a major area of uncertainty when predicting the properties and behaviour of clouds and their influence on climate. In an attempt to understand better the microphysical properties of cloud droplets, the aerosol-cloud interactions, and the corresponding climate effect during cloud life cycles in the North China Plain, an intensive observation took place from 17 June to 30 July 2018 at the summit of Mt. Tai. Cloud microphysical parameters were monitored simultaneously with number concentrations of cloud condensation nuclei (NCCN) at different supersaturations, PM2.5 mass concentrations, particle size distributions and meteorological parameters. Number concentrations of cloud droplets (NC), liquid water content (LWC) and effective radius of cloud droplets (reff) show large variations among 40 cloud events observed during the campaign. Perturbations of aerosols will significantly increase the NC of cloud droplets and shift cloud droplets toward smaller size ranges. Clouds in clean days are more susceptible to the change in concentrations of particle number (NP). LWC shows positive correlation with reff. As NC increases, reff changes from a trimodal distribution to a unimodal distribution. By assuming a cloud thickness of 100 m, we find that the albedo can increase 36.4 % if the cloud gets to be disturbed by aerosols. This may induce a cooling effect on the local climate system. Our results contribute more information about regional cloud microphysics and will help to reduce the uncertainties in climate models when predicting climate responses to cloud-aerosol interactions.

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.

Investigation of Hydrometeors Using a C-band Poloarimetric Radar and In-situ Measurements during IMFRE in Central China

2020 ◽  
Author(s):  
Bin Wang ◽  
Xiquan Dong ◽  
Zhikang Fu ◽  
Lingli Zhou
Keyword(s):  
Supercooled Liquid ◽  
Central China ◽  
Size Distributions ◽  
Cloud Droplets ◽  
Freezing Level ◽  
Rain Drop ◽  
Dominant Process ◽  
Drop Size Distributions ◽  
First Time

<p>This study uses C-band polarimetric radar (C-POL) measurements to classify the hydrometeors and retrieve rain drop size distributions (DSDs) during the IMFRE (Investigative Monsoon Frontal Rainfall Experiment) field campaign in central China.  Three types of precipitation in a Meiyu frontal heavy rainfall case are classified to further investigate the microphysical characteristics and processes based on C-POL observations and classified hydrometeors. When raindrops fall from the freezing level, collision–coalescence plays an equally important role as break-up and/or evaporation in stratiform regions, but is the dominant process for convective-related precipitation and is an attribute of intensive precipitation. There are more supercooled liquid water droplets above the freezing level in convective cores due to strong updrafts, which can bring more cloud droplets into the upper levels to help the formation of graupel and hail. To the best of our knowledge, this work is the first time that C-POL-classified hydrometeors and rain-parameter retrievals have been validated against in-situ aircraft and surface disdrometer measurements over the middle reaches of the Yangtze River Valley in central China, which will pave the way for future studies related to Meiyu frontal rainfall systems.</p>

scholarly journals The scientific basis for a satellite mission to retrieve CCN concentrations and their impacts on convective clouds

2012 ◽  
Vol 5 (8) ◽  
pp. 2039-2055 ◽  
Author(s):  
D. Rosenfeld ◽  
E. Williams ◽  
M. O. Andreae ◽  
E. Freud ◽  
U. Pöschl ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Cloud Condensation Nuclei ◽  
Scientific Basis ◽  
Cloud Base ◽  
Satellite Measurements ◽  
Satellite Mission ◽  
Cloud Drop ◽  
Aerosol Radiative Forcing ◽  
Convective Clouds ◽  
Synchronous Orbit

Abstract. The cloud-mediated aerosol radiative forcing is widely recognized as the main source of uncertainty in our knowledge of the anthropogenic forcing on climate. The current challenges for improving our understanding are (1) global measurements of cloud condensation nuclei (CCN) in the cloudy boundary layer from space, and (2) disentangling the effects of aerosols from the thermodynamic and meteorological effects on the clouds. Here, we present a new conceptual framework to help us overcome these two challenges, using relatively simple passive satellite measurements in the visible and infared (IR). The idea is to use the clouds themselves as natural CCN chambers by retrieving simultaneously the number of activated aerosols at cloud base, Na, and the cloud base updraft speed. The Na is obtained by analyzing the distribution of cloud drop effective radius in convective elements as a function of distance above cloud base. The cloud base updraft velocities are estimated by double stereoscopic viewing and tracking of the evolution of cloud surface features just above cloud base. In order to resolve the vertical dimension of the clouds, the field of view will be 100 m for the microphysical retrievals, and 50 m for the stereoscopic measurements. The viewing geometry will be eastward and 30 degrees off nadir, with the Sun in the back at 30 degrees off zenith westward, requiring a Sun-synchronous orbit at 14 LST. Measuring simultaneously the thermodynamic environment, the vertical motions of the clouds, their microstructure and the CCN concentration will allow separating the dynamics from the CCN effects. This concept is being applied in the proposed satellite mission named Clouds, Hazards and Aerosols Survey for Earth Researchers (CHASER).

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