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Sensitivity of Numerical Simulations of EASM* to
Different Convection Schemes
Haoming Chen, Tianjun Zhou, Rucong Yu, LASG, Institute of Atmospheric Physics, Chinese Academy of SciencesLASG, Institute of Atmospheric Physics, Chinese Academy of Sciences
Richard Neale, Jim Hack National Center for Atmospheric ResearchNational Center for Atmospheric Research
University Allied Workshop University Allied Workshop (1-3 July, (1-3 July, 2008)2008)
* EASM : East Asian Summer Monsoon
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Outline
Introduction Introduction
Model and Data DescriptionModel and Data Description
Results Results
Climatological mean pattern
Seasonal Variation
Summary and Discussion Summary and Discussion
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Introduction
The huge Asian summer monsoon system can be divided into two subsystems: the Indian summer monsoon (ISM) and the East Asian summer monsoon (EASM) systems;
EASM is a hybrid type of tropical and subtropical monsoon
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Introduction
Simulation of the Asian summer monsoon and its variability has proved to be one of the most challenging issues for
general circulation models (Kang et al., 2002; Wang et al., 2004; Meehl et al., 2006).
The CAM model has been widely used for the climate research, but its performance in EASM has not been fully evaluated.
The coupling of convective processes with the large-scale dynamics is crucial for modeling the distribution of precipitation (Zhang, 2005) . The simulation of EASM rainfall and circulations are sensitive to convection schemes (Huang
et al., 2001) .
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Questions
1) Can the new version NCAR CAM3.5 reasonably reproduce the climatic features of EASM?
2) What are the influences of different convection schemes on EASM simulations?
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CAM3.5 and Experiments
ExperimentConvective
Scheme Integration Time References
CNTLZhang and McFarlane
1977.01 - 2003.12Zhang and McFarlane
(1995)
NR Neale and Richter 1977.01 - 2002.12
Wu Wu and Zhang 1977.01 - 2000.12 Wu et al.(2007)
Zhang Revised Zhang 1978.01 - 1999.12 Zhang et al. (2002)
CAM3.5 is the recently improved version AGCM in NCAR Finite-Volume dynamical core; Horizontal resolution is about 2.5°longitude by 1.9°latitude with 26 vertical levels; Changes to convection and cloud processes, land model and chemistry modules compared to CAM3; Three revised convection schemes are applied, and four AMIP-type experiments are performed.
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Climatological mean pattern
RainfallRainfall
Meridional Meridional Monsoon Monsoon
CellCell
EASM ClimatologyEASM Climatology
Horizontal Horizontal CirculationCirculation
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JJA Mean Precipitation
Two major rainfall belts:
★ tropical monsoon trough
★ subtropical Meiyu /Baiyu/ Changma front
None of the schemes realistically reproduce the observed Meiyu rain band; the simulated tropical rainfall are relatively weak
The revised schemes improve the rainfall simulation, but the details depend on schemes
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Taylor Diagram
The three revised schemes improve the precipitation simulation;
The NR scheme simulates more realistic rainfall in EASM and its tropical rainfall belt;
The subtropical rainfall simulated by Wu scheme are most reasonable.Total Precip. (90-140Total Precip. (90-140°°E, 0-45E, 0-45°°N)N)
Tropical Precip (90-140Tropical Precip (90-140°°E, 5-15E, 5-15°°N)N)
Subtropical Precip. (90-140Subtropical Precip. (90-140°°E, 25-35E, 25-35°°N)N)
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100 hPa Wind and Geopotential Height
Tibetan High
★ Subtropical Westerly
★ Tropical Easterly Jet
The simulated High
shift westward; the
westerly and easterly
are stronger;
The circulation are
generally similar in
different schemes
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500 hPa Wind and Geopotential Height
A strong anticyclone dominates the subtropical western Pacific
The simulated WPSH is stronger than the reanalysis and extends about 20° westward and its ridge shift more than 5° north
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Water Vapor Transport
Three main branches of water vapor transport:
southwesterly from ISMsouthwesterly from ISM southeasterly from southeasterly from
western Pacific western Pacific cross-equator flow cross-equator flow
straddling 105straddling 105°°E-150E-150°°EE
The southwesterly transport is too weak in the model, whereas the southeasterly transport extends northward.
Vertically integration from 1000 – 100 hPa
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Meridional Monsoon Cell
The normal Hadley cell is replaced by a meridional monsoon cell;
The model simulates weak monsoon cell, which is closely related to rainfall biases in the model
Averaged over 90 -140 °E
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Seasonal Variation
Abrupt Jump
•WPSH ridge•Rainfall belt
Zonal averaged rainfall
Seasonal March
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Zonal Averaged Rainfall
The major rainfall advances toward the north since March, Mei-Yu /Baiyu/ Changma begins along the Yangtze River valley in June; heavy rainfall withdraw southward in August;
The model can reproduce the poleward progress and southward withdraw; the subtropical rainfall shifts northward
Averaged over 110°E~125°E
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North Jump of WPSH Ridge and Rainfall BeltNorth Jump of WPSH Ridge and Rainfall BeltW
PS
H R
idg
eW
PS
H R
idg
eR
ain
fall
Bel
tR
ain
fall
Bel
t
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DiscussionDiscussion
Strong temperature gradient in both the meridional and zonal directions;
Zonal “+ - +” pattern in temperature difference fields greatly reduce the meridional thermal contrast.
Temp. averaged between 200 - 500 hPaTemp. averaged between 200 - 500 hPa
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Summary
The CAM3.5 model can realistically reproduce the main circulation of EASM, but the precipitation simulated is poor, especially in the subtropical Meiyu/Baiyu/Changma rainfall belt, which is closely related to the biases of the monsoon circulation in subtropical region;
The model can capture the southward advance and northward withdraw of the main rain belts, as well as the two north jump of WPSH, but failed to represent the north jump of rainfall belt;
The three revised schemes generally improve the model performance in EASM, and the simulation of EASM rainfall depends on convection schemes, but the circulation is less sensitive to different schemes
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