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Title: On Which Microphysical Time Scales to Use in Studies of Entrainment-Mixing Mechanisms in Clouds

Journal Article · · Journal of Geophysical Research: Atmospheres
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [4]; ORCiD logo [5];  [3];  [3];  [3]
  1. Nanjing Univ. of Information Science and Technology (China). Key Lab. of Meteorological Disaster. Joint International Research Lab. of Climate and Environment Change (ILCEC). Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD). Key Lab. for Aerosol-Cloud-Precipitation of China Meteorological Administration; Tsinghua Univ., Beijing (China). Ministry of Education Key Lab. for Earth System Modeling. Dept. for Earth System Science
  2. Brookhaven National Lab. (BNL), Upton, NY (United States). Environmental and Climate Sciences Dept.
  3. Nanjing Univ. of Information Science and Technology (China). Key Lab. of Meteorological Disaster. Joint International Research Lab. of Climate and Environment Change (ILCEC). Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters (CIC-FEMD). Key Lab. for Aerosol-Cloud-Precipitation of China Meteorological Administration
  4. Yonsei Univ., Seoul (Korea, Republic of). Dept. of Atmospheric Sciences
  5. Univ. of Utah, Salt Lake City, UT (United States). Dept. of Atmospheric Sciences
+ Show Author Affiliations

The commonly used time scales in entrainment-mixing studies are examined in this paper to seek the most appropriate one, based on aircraft observations of cumulus clouds from the RACORO campaign and numerical simulations with the Explicit Mixing Parcel Model. The time scales include: τevap, the time for droplet complete evaporation; τphase, the time for saturation ratio deficit (S) to reach 1/e of its initial value; τsatu, the time for S to reach -0.5%; τreact, the time for complete droplet evaporation or S to reach -0.5%. It is found that the proper time scale to use depends on the specific objectives of entrainment-mixing studies. First, if the focus is on the variations of liquid water content (LWC) and S, then τreact for saturation, τsatu and τphase are almost equivalently appropriate, because they all represent the rate of dry air reaching saturation or of LWC decrease. Second, if one focuses on the variations of droplet size and number concentration, τreact for complete evaporation and τevap are proper because they characterize how fast droplets evaporate and whether number concentration decreases. Moreover, τreact for complete evaporation and τevap are always positively correlated with homogeneous mixing degree (ψ), thus the two time scales, especially τevap, are recommended for developing parameterizations. However, ψ and the other time scales can be negatively, positively, or not correlated, depending on the dominant factors of the entrained air (i.e., relative humidity or aerosols). Third and finally, all time scales are proportional to each other under certain microphysical and thermodynamic conditions.

Research Organization:
Brookhaven National Lab. (BNL), Upton, NY (United States); Nanjing Univ. of Information Science and Technology (China); Yonsei Univ., Seoul (Korea, Republic of)
Sponsoring Organization:
333 High-level Talents Training Project in Jiangsu (China); China Meteorological Administration; Korea Meteorological Administration (KMA); National Key Research and Development Program of China; National Natural Science Foundation of China (NSFC); Natural Science Foundation of Jiangsu Province (China); Six Talent Peak Project in Jiangsu (China); USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Grant/Contract Number:
SC0012704
OSTI ID:
1430845
Report Number(s):
BNL--203380-2018-JAAM
Journal Information:
Journal of Geophysical Research: Atmospheres, Journal Name: Journal of Geophysical Research: Atmospheres Journal Issue: 7 Vol. 123; ISSN 2169-897X
Publisher:
American Geophysical UnionCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (2)

Scale Dependence of Cloud Microphysical Response to Turbulent Entrainment and Mixing journal November 2018
Aerosol–cloud closure study on cloud optical properties using remotely piloted aircraft measurements during a BACCHUS field campaign in Cyprus journal January 2019

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54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
clouds
entrainment-mixing
observation
simulation
time scales