Low-Level Wind Variability over the Indochina Peninsula during Boreal Winter
1. 2012 1st Journal Conference on Environmental Science and Development (2012 1st JCESD)
Low-Level Wind Variability over
the Indochina Peninsula during Boreal Winter
Sirapong Sooktawee, Usa Humphries, Atsamon Limsakul,
and Prungchan Wongwises
2. 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.
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)
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The 2012 1st Journal Conference on Environmental Science and Development
3. 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,
Myanmar, Thailand,
Viet Nam, and some
territory of Malaysia.
KH: Cambodia, LA: Laos, MM: Myanmar, MY: Malaysia,
TH: Thailand, and VN: Viet Nam
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4. 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.
JRA-25 NCEP/NCAR
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6. 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
of monsoon.
Pearson correlation was used to investigate
relation of temporal variation to East Asian
winter monsoon (EAWM) indices.
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7. Procedure of Analysis
Determine anomalies of zonal ( u′) and meridional (v′ )winds
Form a complex number from u′ and v′
Construct a data matrix
Analyze by VEOF
Eigenvectors Principal components (PCs)
(Spatial pattern) (Temporal variation)
Real part Imaginary part Real part Imaginary part
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The 2012 1st Journal Conference on Environmental Science and Development
8. 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
Imaginary part (meridional) of PC1
Positive phase Negative phase
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The 2012 1st Journal Conference on Environmental Science and Development
9. 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
a negative phase year (1998) a positive phase year (1999)
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The 2012 1st Journal Conference on Environmental Science and Development
10. Composite Analysis for Anomalies
positive phase negative phase
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The 2012 1st Journal Conference on Environmental Science and Development
11. Relation between PC1 and EAWM
Correlation coefficients show weak
correlations to EAWM indices
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12. 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.
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.
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13. 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)
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
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