Premium
Observational Relationship Between Entrainment Rate and Environmental Relative Humidity and Implications for Convection Parameterization
Author(s) -
Lu Chunsong,
Sun Cheng,
Liu Yangang,
Zhang Guang J.,
Lin Yanluan,
Gao Wenhua,
Niu Shengjie,
Yin Yan,
Qiu Yujun,
Jin Lianji
Publication year - 2018
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2018gl080264
Subject(s) - entrainment (biomusicology) , buoyancy , environmental science , relative humidity , atmospheric sciences , convection , neutral buoyancy , cloud physics , meteorology , humidity , radiative transfer , climatology , cloud computing , mechanics , geology , physics , quantum mechanics , computer science , operating system , rhythm , acoustics
Entrainment rate is a critical but highly uncertain quantity in convective parameterizations; especially, the effects of environmental relative humidity on entrainment rate are controversial, or even opposite, in different studies. Analysis of aircraft observations of cumuli from the Routine AAF (Atmospheric Radiation Measurement [ARM] Aerial Facility) Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations (RACORO) and Rain in Cumulus over the Ocean (RICO) field campaigns shows that entrainment rate is positively correlated with relative humidity. Physical analysis shows that higher relative humidity promotes entrainment by reducing buoyancy in the cloud cores and by weakening downdrafts near the cloud cores. The reduced buoyancy in the cloud cores and weakened downdrafts surrounding the cores further reduce updrafts in the cloud cores; the cloud cores with smaller updrafts are more significantly affected by their environment, resulting in larger entrainment rate. The relationship between entrainment rate and relative humidity is consistent with the buoyancy sorting concept widely used in convection parameterizations. The results provide reliable in situ observations to improve parameterizations of entrainment rate.