Details
| Original language | English |
|---|---|
| Pages (from-to) | 2125-2142 |
| Number of pages | 18 |
| Journal | Journal of the Atmospheric Sciences |
| Volume | 74 |
| Issue number | 7 |
| Publication status | Published - 1 Jul 2017 |
Abstract
The mechanism of raindrop formation in a shallow cumulus cloud is investigated using a Lagrangian cloud model (LCM). The analysis is focused on how and under which conditions a cloud droplet grows to a raindrop by tracking the history of individual Lagrangian droplets. It is found that the rapid collisional growth, leading to raindrop formation, is triggered when single droplets with a radius of 20 μm appear in the region near the cloud top, characterized by large liquid water content, strong turbulence, large mean droplet size, broad drop size distribution (DSD), and high supersaturations. Raindrop formation easily occurs when turbulence-induced collision enhancement (TICE) is considered, with or without any extra broadening of the DSD by another mechanism (such as entrainment and mixing). In contrast, when TICE is not considered, raindrop formation is severely delayed if no other broadening mechanism is active. The reason for the difference is clarified by the additional analysis of idealized box simulations of the collisional growth process for different DSDs in varied turbulent environments. It is found that TICE does not accelerate the timing of the raindrop formation for individual droplets, but it enhances the collisional growth rate significantly afterward by providing a greater number of large droplets for collision. Higher droplet concentrations increase the time for raindrop formation and decrease precipitation but intensify the effect of TICE.
Keywords
- Cloud microphysics, Cumulus clouds, Large eddy simulations, Turbulence
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Atmospheric Science
Cite this
- Standard
- Harvard
- Apa
- Vancouver
- BibTeX
- RIS
In: Journal of the Atmospheric Sciences, Vol. 74, No. 7, 01.07.2017, p. 2125-2142.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - The Route to Raindrop Formation in a Shallow Cumulus Cloud Simulated by a Lagrangian Cloud Model
AU - Hoffmann, Fabian
AU - Noh, Yign
AU - Raasch, Siegfried
N1 - Publisher Copyright: © 2017 American Meteorological Society. Copyright: Copyright 2017 Elsevier B.V., All rights reserved.
PY - 2017/7/1
Y1 - 2017/7/1
N2 - The mechanism of raindrop formation in a shallow cumulus cloud is investigated using a Lagrangian cloud model (LCM). The analysis is focused on how and under which conditions a cloud droplet grows to a raindrop by tracking the history of individual Lagrangian droplets. It is found that the rapid collisional growth, leading to raindrop formation, is triggered when single droplets with a radius of 20 μm appear in the region near the cloud top, characterized by large liquid water content, strong turbulence, large mean droplet size, broad drop size distribution (DSD), and high supersaturations. Raindrop formation easily occurs when turbulence-induced collision enhancement (TICE) is considered, with or without any extra broadening of the DSD by another mechanism (such as entrainment and mixing). In contrast, when TICE is not considered, raindrop formation is severely delayed if no other broadening mechanism is active. The reason for the difference is clarified by the additional analysis of idealized box simulations of the collisional growth process for different DSDs in varied turbulent environments. It is found that TICE does not accelerate the timing of the raindrop formation for individual droplets, but it enhances the collisional growth rate significantly afterward by providing a greater number of large droplets for collision. Higher droplet concentrations increase the time for raindrop formation and decrease precipitation but intensify the effect of TICE.
AB - The mechanism of raindrop formation in a shallow cumulus cloud is investigated using a Lagrangian cloud model (LCM). The analysis is focused on how and under which conditions a cloud droplet grows to a raindrop by tracking the history of individual Lagrangian droplets. It is found that the rapid collisional growth, leading to raindrop formation, is triggered when single droplets with a radius of 20 μm appear in the region near the cloud top, characterized by large liquid water content, strong turbulence, large mean droplet size, broad drop size distribution (DSD), and high supersaturations. Raindrop formation easily occurs when turbulence-induced collision enhancement (TICE) is considered, with or without any extra broadening of the DSD by another mechanism (such as entrainment and mixing). In contrast, when TICE is not considered, raindrop formation is severely delayed if no other broadening mechanism is active. The reason for the difference is clarified by the additional analysis of idealized box simulations of the collisional growth process for different DSDs in varied turbulent environments. It is found that TICE does not accelerate the timing of the raindrop formation for individual droplets, but it enhances the collisional growth rate significantly afterward by providing a greater number of large droplets for collision. Higher droplet concentrations increase the time for raindrop formation and decrease precipitation but intensify the effect of TICE.
KW - Cloud microphysics
KW - Cumulus clouds
KW - Large eddy simulations
KW - Turbulence
UR - http://www.scopus.com/inward/record.url?scp=85023161748&partnerID=8YFLogxK
U2 - 10.1175/JAS-D-16-0220.1
DO - 10.1175/JAS-D-16-0220.1
M3 - Article
AN - SCOPUS:85023161748
VL - 74
SP - 2125
EP - 2142
JO - Journal of the Atmospheric Sciences
JF - Journal of the Atmospheric Sciences
SN - 0022-4928
IS - 7
ER -