Abstract
Observations from the Atmospheric Radiation Measurement Program (ARM) site at Manus Island in the western Pacific and (re)analysis products are used to investigate moistening by shallow cumulus clouds and by the circulation in large-scale convective events. Large-scale convective events are defined as rainfall anomalies larger than one standard deviation for a minimum of three consecutive days over a 10° × 10° domain centered at Manus. These events are categorized into two groups: Madden-Julian oscillation (MJO) events, with eastward propagation, and non-MJO events, without propagation. Shallow cumulus clouds are identified as continuous time-height echoes from 1-min cloud radar observations with their tops below the freezing level and their bases within the boundary layer. Daily moistening tendencies of shallow clouds, estimated from differences between their mean liquid water content and precipitation over their presumed life spans, and those of physical processes and advection from (re)analysis products are compared with local moistening tendencies from soundings. Increases in low-level moisture before rainfall peaks of MJO and non-MJO events are evident in both observations and reanalyses. Before and after the rainfall peaks of these events, precipitating and nonprecipitating shallow clouds exist all the time, but their occurrence fluctuates randomly. Their contributions to moisture tendencies through evaporation of condensed water are evident. These clouds provide perpetual background moistening to the lower troposphere but do not cause the observed increase in low-level moisture leading to rainfall peaks. Such moisture increase is mainly caused by anomalous nonlinear zonal advection.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 4797-4820 |
| Number of pages | 24 |
| Journal | Journal of the Atmospheric Sciences |
| Volume | 72 |
| Issue number | 12 |
| DOIs | |
| State | Published - Dec 1 2015 |
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Keywords
- Atm/Ocean Structure/ Phenomena
- Clouds
- Cumulus clouds
- Madden-Julian oscillation
ASJC Scopus subject areas
- Atmospheric Science
Cite this
The role of shallow cloud moistening in MJO and Non-MJO convective events over the ARM manus site. / Zermeño-Díaz, David M.; Zhang, Chidong; Kollias, Pavlos; Kalesse, Heike.
In: Journal of the Atmospheric Sciences, Vol. 72, No. 12, 01.12.2015, p. 4797-4820.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - The role of shallow cloud moistening in MJO and Non-MJO convective events over the ARM manus site
AU - Zermeño-Díaz, David M.
AU - Zhang, Chidong
AU - Kollias, Pavlos
AU - Kalesse, Heike
PY - 2015/12/1
Y1 - 2015/12/1
N2 - Observations from the Atmospheric Radiation Measurement Program (ARM) site at Manus Island in the western Pacific and (re)analysis products are used to investigate moistening by shallow cumulus clouds and by the circulation in large-scale convective events. Large-scale convective events are defined as rainfall anomalies larger than one standard deviation for a minimum of three consecutive days over a 10° × 10° domain centered at Manus. These events are categorized into two groups: Madden-Julian oscillation (MJO) events, with eastward propagation, and non-MJO events, without propagation. Shallow cumulus clouds are identified as continuous time-height echoes from 1-min cloud radar observations with their tops below the freezing level and their bases within the boundary layer. Daily moistening tendencies of shallow clouds, estimated from differences between their mean liquid water content and precipitation over their presumed life spans, and those of physical processes and advection from (re)analysis products are compared with local moistening tendencies from soundings. Increases in low-level moisture before rainfall peaks of MJO and non-MJO events are evident in both observations and reanalyses. Before and after the rainfall peaks of these events, precipitating and nonprecipitating shallow clouds exist all the time, but their occurrence fluctuates randomly. Their contributions to moisture tendencies through evaporation of condensed water are evident. These clouds provide perpetual background moistening to the lower troposphere but do not cause the observed increase in low-level moisture leading to rainfall peaks. Such moisture increase is mainly caused by anomalous nonlinear zonal advection.
AB - Observations from the Atmospheric Radiation Measurement Program (ARM) site at Manus Island in the western Pacific and (re)analysis products are used to investigate moistening by shallow cumulus clouds and by the circulation in large-scale convective events. Large-scale convective events are defined as rainfall anomalies larger than one standard deviation for a minimum of three consecutive days over a 10° × 10° domain centered at Manus. These events are categorized into two groups: Madden-Julian oscillation (MJO) events, with eastward propagation, and non-MJO events, without propagation. Shallow cumulus clouds are identified as continuous time-height echoes from 1-min cloud radar observations with their tops below the freezing level and their bases within the boundary layer. Daily moistening tendencies of shallow clouds, estimated from differences between their mean liquid water content and precipitation over their presumed life spans, and those of physical processes and advection from (re)analysis products are compared with local moistening tendencies from soundings. Increases in low-level moisture before rainfall peaks of MJO and non-MJO events are evident in both observations and reanalyses. Before and after the rainfall peaks of these events, precipitating and nonprecipitating shallow clouds exist all the time, but their occurrence fluctuates randomly. Their contributions to moisture tendencies through evaporation of condensed water are evident. These clouds provide perpetual background moistening to the lower troposphere but do not cause the observed increase in low-level moisture leading to rainfall peaks. Such moisture increase is mainly caused by anomalous nonlinear zonal advection.
KW - Atm/Ocean Structure/ Phenomena
KW - Clouds
KW - Cumulus clouds
KW - Madden-Julian oscillation
UR - http://www.scopus.com/inward/record.url?scp=84950275991&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84950275991&partnerID=8YFLogxK
U2 - 10.1175/JAS-D-14-0322.1
DO - 10.1175/JAS-D-14-0322.1
M3 - Article
VL - 72
SP - 4797
EP - 4820
JO - Journals of the Atmospheric Sciences
JF - Journals of the Atmospheric Sciences
SN - 0022-4928
IS - 12
ER -