Low-Level Wind Variability over the Indochina Peninsula during Boreal Winter
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Transcript of Low-Level Wind Variability over the Indochina Peninsula during Boreal Winter
Low-Level Wind Variability over the Indochina Peninsula during Boreal Winter
2012 1st Journal Conference on Environmental Science and Development (2012 1st JCESD)
Sirapong Sooktawee, Usa Humphries, Atsamon Limsakul, and Prungchan Wongwises
Introduction
� The flooding in southern Thailand probably resulted from the Asian Winter Monsoon (S. Limjirakan and A. Limsakul, 2011).
� Winter monsoon is a one of major climate features influencing the Indochina peninsula, but less of studies than studies focussing on summer monsoon.
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than studies focussing on summer monsoon.
� During winter season, East Asian Winter Monsoon (EAWM) is important climate feature.
� Low-level wind (850 hPa) can be used to represent winter monsoon (He J., et al., 2007)
The 2012 1st Journal Conference on Environmental Science and Development
Study Domain
� The study area representing Indochina peninsula (IDP) is a domain of 5-30°N, 90-110°E
� The domain consists of Cambodia, Laos,
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Cambodia, Laos, Myanmar, Thailand,
Viet Nam, and some territory of Malaysia.
The 2012 1st Journal Conference on Environmental Science and Development
KH: Cambodia, LA: Laos, MM: Myanmar, MY: Malaysia, TH: Thailand, and VN: Viet Nam
Data of the Study� Monthly Japanese 25-year reanalysis (JRA-25) data (Dec-Jan-Feb) with 1.25°×
1.25° horizontal resolution of 32 years (1979-2010) at 850 hPa level was used for analysis of the study.
� National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data with 2.5°× 2.5°horizontal resolution (1957-2010) was used to ensure representativeness of JRA-25 data set.
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The 2012 1st Journal Conference on Environmental Science and Development
JRA-25 NCEP/NCAR
Boreal winter climatology of low-level wind (850 hPa wind)
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Methodology
� Vector Empirical Orthogonal Function (VEOF)
is used to decompose orthogonal modes in
terms of time and space.
Hardy et al. (1978) succeeded to decompose surface wind
from observation representing mesoscale region.
Wu et al. (2006), (2008) apply the method to distinct modes
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Wu et al. (2006), (2008) apply the method to distinct modes
of monsoon.
� Pearson correlation was used to investigate
relation of temporal variation to East Asian
winter monsoon (EAWM) indices.
The 2012 1st Journal Conference on Environmental Science and Development
Procedure of Analysis
Construct a data matrix
Determine anomalies of zonal ( ) and meridional ( )winds
Form a complex number from and
u′ v′
u′ v′
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The 2012 1st Journal Conference on Environmental Science and Development
Analyze by VEOF
Eigenvectors(Spatial pattern)
Principal components (PCs)(Temporal variation)
Real part Imaginary part Real part Imaginary part
Modes of Low-Level Wind
• The first eigenvector (VEOF1) and the second eigenvector (VEOF2) accounting for 46.58% and 13.77% of variance, respectively, that is 60.35% of the total.
Real part (zonal) of PC1
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The 2012 1st Journal Conference on Environmental Science and Development
Imaginary part (meridional) of PC1
Positive phase Negative phase
Mean Low-Level Wind Fields
The circulation during boreal winter in 1998 (negative phases) exhibits stronger southwesterlies over northern part of Thailand, Laos, and Viet Nam than the circulation (positive phases) in 1999
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The 2012 1st Journal Conference on Environmental Science and Development
a positive phase year (1999)a negative phase year (1998)
Composite Analysis for Anomalies
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The 2012 1st Journal Conference on Environmental Science and Development
positive phase negative phase
Relation between PC1 and EAWM
Correlation coefficients show weak correlations to EAWM indices
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The 2012 1st Journal Conference on Environmental Science and Development
Conclusions
� VEOF can use to decompose variability of winter monsoon over the
IDP.
� From composite analysis, positive (negative) phase of anomalous
zonal and meridional wind show strengthening on northeasterlies
(southwesterlies) perhaps related to more (less) influence of EAWM
on the Indochina peninsular.
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The 2012 1st Journal Conference on Environmental Science and Development
� The variability of winter monsoon over the IDP shows interannual
variation.
� The correlation coefficients of PC1s to TII and TAI indices are weak.
� Influences of other climate modes on the Indochina peninsula and mechanism are required to investigate further.
Acknowledgements
� The Japan Meteorological Agency (JMA) and the Central Research Institute of
Electric Power Industry (CRIEPI)
� Assoc. Prof. Dr. Lin Wang, Institute of Atmospheric Physics, Chinese Academy of
Sciences and his group
� The Physical Sciences Division (PSD) of the Earth System Research Laboratory
(ESRL), the National Oceanic and Atmospheric Administration (NOAA)
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The 2012 1st Journal Conference on Environmental Science and Development
� The National Center for Atmospheric Research (NCAR)
� The Joint Graduate School of Energy and Environment (JGSEE) and the Center of
Excellence on Energy Technology and Environment (CEE)
Thank You for Your Attention