scholarly journals Microphysical Characteristics of Frozen Droplet Aggregates from Deep Convective Clouds

2018 ◽  
Author(s):  
Junshik Um ◽  
Greg M. McFarquhar ◽  
Jeffrey L. Stith ◽  
Chang Hoon Jung ◽  
Seoung Soo Lee ◽  
...  
Keyword(s):  
National Science Foundation ◽  
Ice Crystals ◽  
Maximum Dimension ◽  
Cloud Particle ◽  
Atmospheric Research ◽  
Convective Clouds ◽  
National Science ◽  
Deep Convective Clouds

Abstract. During the 2012 Deep Convective Clouds and Chemistry (DC3) experiment the National Science Foundation/National Center for Atmospheric Research Gulfstream-V (G-V) aircraft sampled the upper anvils of two storms that developed in eastern Colorado on 6 June 2012. A cloud particle imager (CPI) mounted on the G-V aircraft recorded images of ice crystals at altitudes of 12.0–12.4 km and T = −61– −55 °C. A total of 22,393 CPI crystal images were analyzed, all with maximum dimension Dmax 

scholarly journals Microphysical characteristics of frozen droplet aggregates from deep convective clouds

2018 ◽  
Vol 18 (23) ◽  
pp. 16915-16930
Author(s):  
Junshik Um ◽  
Greg M. McFarquhar ◽  
Jeffrey L. Stith ◽  
Chang Hoon Jung ◽  
Seoung Soo Lee ◽  
...  
Keyword(s):  
Relative Position ◽  
Linear Chain ◽  
Morphological Characteristics ◽  
Ice Crystals ◽  
Frequency Of Occurrence ◽  
Fall Velocity ◽  
Cloud Particle ◽  
Aggregation Index ◽  
Convective Clouds ◽  
Deep Convective Clouds

Abstract. During the 2012 Deep Convective Clouds and Chemistry (DC3) experiment the National Science Foundation/National Center for Atmospheric Research Gulfstream V (GV) aircraft sampled the upper anvils of two storms that developed in eastern Colorado on 6 June 2012. A cloud particle imager (CPI) mounted on the GV aircraft recorded images of ice crystals at altitudes of 12.0 to 12.4 km and temperatures (T) from −61 to −55 ∘C. A total of 22 393 CPI crystal images were analyzed, all with maximum dimension (Dmax⁡)<433 µm and with an average Dmax⁡ of 80.7±45.4 µm. The occurrence of well-defined pristine crystals (e.g., columns and plates) was less than 0.04 % by number. Single frozen droplets and frozen droplet aggregates (FDAs) were the dominant habits with fractions of 73.0 % (by number) and 46.3 % (by projected area), respectively. The relative frequency of occurrence of single frozen droplets and FDAs depended on temperature and position within the anvil cloud. A new algorithm that uses the circle Hough transform technique was developed to automatically identify the number, size, and relative position of element frozen droplets within FDAs. Of the FDAs, 42.0 % had two element frozen droplets with an average of 4.7±5.0 element frozen droplets. The frequency of occurrence gradually decreased with the number of element frozen droplets. Based on the number, size, and relative position of the element frozen droplets within the FDAs, possible three-dimensional (3-D) realizations of FDAs were generated and characterized by two different shape parameters, the aggregation index (AI) and the fractal dimension (Df), that describe 3-D shapes and link to scattering properties with an assumption of spherical shape of element frozen droplets. The AI of FDAs decreased with an increase in the number of element frozen droplets, with larger FDAs with more element frozen droplets having more compact shapes. The Df of FDAs was about 1.20–1.43 smaller than that of black carbon (BC) aggregates (1.53–1.85) determined in previous studies. Such a smaller Df of FDAs indicates that FDAs have more linear chain-like branched shapes than the compact shapes of BC aggregates. Determined morphological characteristics of FDAs along with the proposed reconstructed 3-D representations of FDAs in this study have important implications for improving the calculations of the microphysical (e.g., fall velocity) and radiative (e.g., asymmetry parameter) properties of ice crystals in upper anvil clouds.

scholarly journals Vertical distribution of the phase state of particles in tropical deep-convective clouds as derived from cloud-side reflected solar radiation measurements

2017 ◽  
Author(s):  
Evelyn Jäkel ◽  
Manfred Wendisch ◽  
Trismono C. Krisna ◽  
Florian Ewald ◽  
Tobias Kölling ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Phase State ◽  
Lower Boundary ◽  
Mixed Phase ◽  
Vertical Position ◽  
Cloud Particle ◽  
Phase Layer ◽  
Spectral Reflectivity ◽  
Convective Clouds ◽  
Deep Convective Clouds

Abstract. Vertical profiles of the cloud particle phase state in tropical deep-convective clouds (DCCs) were investigated using airborne solar radiation data collected by the German research aircraft HALO during the ACRIDICON-CHUVA campaign, which was conducted over the Brazilian Amazon in September 2014. A phase discrimination retrieval based on imaging spec-troradiometer measurements of cloud side spectral reflectivity was applied to DCCs under different aerosol conditions. From the retrieval results the height of the mixed phase layer of the DCCs was determined. The retrieved profiles were compared with in situ measurements and satellite observations. It was found that the depth and vertical position of the mixed phase layer can vary up to 900 m for one single cloud scene. In particular, this variation is attributed to the different stages of cloud development in one scene. Clouds of mature or decaying stage are affected by falling ice particles resulting in lower levels of fully glaciated cloud layers compared to growing clouds. Comparing polluted and moderate aerosol conditions revealed a shift of the lower boundary of the mixed phase layer from 5.6 ± 0.2 km (269 K) [moderate] to 6.2 ± 0.3 km (267 K) [polluted], and of the upper boundary from 6.8 ± 0.2 km (263 K) [moderate] to 7.4 ± 0.4 km (259 K) [polluted], as would be expected from theory.

scholarly journals Vertical distribution of the particle phase in tropical deep convective clouds as derived from cloud-side reflected solar radiation measurements

2017 ◽  
Vol 17 (14) ◽  
pp. 9049-9066 ◽  
Author(s):  
Evelyn Jäkel ◽  
Manfred Wendisch ◽  
Trismono C. Krisna ◽  
Florian Ewald ◽  
Tobias Kölling ◽  
...  
Keyword(s):  
Lower Boundary ◽  
Mixed Phase ◽  
Vertical Position ◽  
Particle Phase ◽  
Spectral Radiation ◽  
Cloud Particle ◽  
Phase Layer ◽  
Spectral Reflectivity ◽  
Convective Clouds ◽  
Deep Convective Clouds

Abstract. Vertical profiles of cloud particle phase in tropical deep convective clouds (DCCs) were investigated using airborne solar spectral radiation data collected by the German High Altitude and Long Range Research Aircraft (HALO) during the ACRIDICON-CHUVA campaign, which was conducted over the Brazilian rainforest in September 2014. A phase discrimination retrieval based on imaging spectroradiometer measurements of DCC side spectral reflectivity was applied to clouds formed in different aerosol conditions. From the retrieval results the height of the mixed-phase layer of the DCCs was determined. The retrieved profiles were compared with in situ measurements and satellite observations. It was found that the depth and vertical position of the mixed-phase layer can vary up to 900 m for one single cloud scene. This variability is attributed to the different stages of cloud development in a scene. Clouds of mature or decaying stage are affected by falling ice particles resulting in lower levels of fully glaciated cloud layers compared to growing clouds. Comparing polluted and moderate aerosol conditions revealed a shift of the lower boundary of the mixed-phase layer from 5.6 ± 0.2 km (269 K; moderate) to 6.2 ± 0.3 km (267 K; polluted), and of the upper boundary from 6.8 ± 0.2 km (263 K; moderate) to 7.4 ± 0.4 km (259 K; polluted), as would be expected from theory.

scholarly journals A NOTE ON THE CISK MECHANISM IN THE TROPICS AND ITS ROLE IN DISTURBANCE FORMATION AND MAINTENANCE.

1975 ◽  
Vol 15 (2) ◽  
pp. 89-101
Author(s):  
JOANNE SIMPSON
Keyword(s):  
Boundary Layer ◽  
Research Program ◽  
National Science Foundation ◽  
Atmospheric Research ◽  
National Science ◽  
The Tropics

El concepto de CISK o "inestabilidad condicional de segunda clase" ha sido desarrollado para explicar el crecimiento de los sistemas de cúmulos y la intensificación de los disturbios tropicales hasta alcanzar de calibre de tormentas o huracanes. Se ha postulado al CISK como base para la parametrizacion de los procesos de cúmulo en modelos de gran escala. Su investigación tuvo importancia en el diseño y el análisis planeando del experimento GATE de 1974. La médula del concepto de CISK incluye convergencia friccionalmente inducida en una capa fronteriza de Ekman, que se supone intensifica la convección, la cual a su vez estimula la convergencia de la capa fronteriza. Muchos modelos CISK hacen equivaler la capa de fricción Ekman con la capa inferior a la base de los cúmulos, en los trópicos. Este trabajo corrige este error mostrando que la capa fronteriza de fricción en los trópicos se extiende hasta la parte más elevada de los cúmulos. Varios diferentes tipos de interacciones de escalas en los trópicos se examinan. Se presentan aquí sugestiones específicas para ampliar el concepto CISK en relación a la agudización de las tormentas tropicales y a la parametrización de los procesos de los cúmulos. 1 Research partly supported by the Global Atmospheric Research Program, National Science Foundation and the U. S. GATE Project Office, National Oceanic and Atmospheric Administration. Grant No. OCD74-21701, entitled "Cloud populations and their interaction with the boundary layer during GATE".

scholarly journals Non-Monotonic Dependencies of Cloud Microphysics and Precipitation on Aerosol Loading in Deep Convective Clouds: A Case Study Using the WRF Model with Bin Microphysics

Atmosphere ◽  
2018 ◽  
Vol 9 (11) ◽  
pp. 434 ◽  
Author(s):  
Ye-Lim Jeon ◽  
Sungju Moon ◽  
Hyunho Lee ◽  
Jong-Jin Baik ◽  
Jambajamts Lkhamjav
Keyword(s):  
Precipitation Amount ◽  
Cloud Microphysics ◽  
Ice Crystals ◽  
Precipitation Event ◽  
Cold Pool ◽  
Convective Clouds ◽  
Aerosol Loading ◽  
Optimal Value ◽  
Deep Convective Clouds ◽  
Bin Microphysics

Aerosol-cloud-precipitation interactions in deep convective clouds are investigated through numerical simulations of a heavy precipitation event over South Korea on 15–16 July 2017. The Weather Research and Forecasting model with a bin microphysics scheme is used, and various aerosol number concentrations in the range N0 = 50–12,800 cm−3 are considered. Precipitation amount changes non-monotonically with increasing aerosol loading, with a maximum near a moderate aerosol loading (N0 = 800 cm−3). Up to this optimal value, an increase in aerosol number concentration results in a greater quantity of small droplets formed by nucleation, increasing the number of ice crystals. Ice crystals grow into snow particles through deposition and riming, leading to enhanced melting and precipitation. Beyond the optimal value, a greater aerosol loading enhances generation of ice crystals while the overall growth of ice hydrometeors through deposition stagnates. Subsequently, the riming rate decreases because of the smaller size of snow particles and supercooled drops, leading to a decrease in ice melting and a slight suppression of precipitation. As aerosol loading increases, cold pool and low-level convergence strengthen monotonically, but cloud development is more strongly affected by latent heating and convection within the system that is non-monotonically reinforced.

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