TY - JOUR
T1 - A climatology of marine boundary layer cloud and drizzle properties derived from ground-based observations over the azores
AU - WU, PENG
AU - DONG, XIQUAN
AU - XI, BAIKE
N1 - Publisher Copyright:
© 2020 American Meteorological Society.
Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.
PY - 2020/12/1
Y1 - 2020/12/1
N2 - In this study, more than 4 years of ground-based observations and retrievals were collected and analyzed to investigate the seasonal and diurnal variations of single-layered MBL (with three subsets: nondrizzling, virga, and rain) cloud and drizzle properties, as well as their vertical and horizontal variations. The annual mean drizzle frequency was ;55%, with ;70% in winter and ;45% in summer. The cloud-top (cloud-base) height for rain clouds was the highest (lowest), resulting in the deepest cloud layer, i.e., 0.8 km, which is 4 (2) times that of nondrizzling (virga) clouds. The retrieved cloud-droplet effective radii rc were the largest (smallest) for rain (nondrizzling) clouds, and the nighttime values were greater than the daytime values. Drizzle number concentration Nd and liquid water content LWCd were three orders and one order lower, respectively, than their cloud counterparts. The rc andLWCc increased from the cloud base to zi '0.75 by condensational growth, while drizzle median radii rd increased from the cloud top downward the cloud base by collision- coalescence. The adiabaticity values monotonically increased from the cloud top to the cloud base with maxima of ;0.7 (0.3) for nondrizzling (rain) clouds. The drizzling process decreases the adiabaticity by 0.25 to 0.4, and the cloud-top entrainment mixing impacts as deep as upper 40% of the cloud layers. Cloud and drizzle homogeneities decreased with increased horizontal sampling lengths. Cloud homogeneity increases with increasing cloud fraction. These results can serve as baselines for studying MBL cloud-to-rain conversion and growth processes over the Azores.
AB - In this study, more than 4 years of ground-based observations and retrievals were collected and analyzed to investigate the seasonal and diurnal variations of single-layered MBL (with three subsets: nondrizzling, virga, and rain) cloud and drizzle properties, as well as their vertical and horizontal variations. The annual mean drizzle frequency was ;55%, with ;70% in winter and ;45% in summer. The cloud-top (cloud-base) height for rain clouds was the highest (lowest), resulting in the deepest cloud layer, i.e., 0.8 km, which is 4 (2) times that of nondrizzling (virga) clouds. The retrieved cloud-droplet effective radii rc were the largest (smallest) for rain (nondrizzling) clouds, and the nighttime values were greater than the daytime values. Drizzle number concentration Nd and liquid water content LWCd were three orders and one order lower, respectively, than their cloud counterparts. The rc andLWCc increased from the cloud base to zi '0.75 by condensational growth, while drizzle median radii rd increased from the cloud top downward the cloud base by collision- coalescence. The adiabaticity values monotonically increased from the cloud top to the cloud base with maxima of ;0.7 (0.3) for nondrizzling (rain) clouds. The drizzling process decreases the adiabaticity by 0.25 to 0.4, and the cloud-top entrainment mixing impacts as deep as upper 40% of the cloud layers. Cloud and drizzle homogeneities decreased with increased horizontal sampling lengths. Cloud homogeneity increases with increasing cloud fraction. These results can serve as baselines for studying MBL cloud-to-rain conversion and growth processes over the Azores.
KW - Cloud retrieval
KW - Clouds
KW - Databases
KW - Drizzle
KW - Marine boundary layer
KW - Surface observations
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U2 - 10.1175/JCLI-D-20-0272.1
DO - 10.1175/JCLI-D-20-0272.1
M3 - Article
AN - SCOPUS:85095705460
VL - 33
SP - 10133
EP - 10148
JO - Journal of Climate
JF - Journal of Climate
SN - 0894-8755
IS - 23
ER -