Application of a RegCM3 to
weather/climate change in
Southeast Asia
Wan-Ru Huang
Department of Earth Sciences, National Taiwan Normal University
TWPGFS Workshop 7-8 May 2014
Contents
Part I:
Regional Climate Simulations of Summer Diurnal
Rainfall Variations over East Asia and Southeast
China (Huang et al. 2013, Climate Dynamics, 40:
1625-1642)
Part II:
Dynamical Downscaling Forecasts of Western North
Pacific Tropical Cyclone Genesis and Landfall (Huang
and Chan 2014, Climate Dynamics, 40: 2227-2237).
Progression of the RegCM system
Convective and Cumulus Schemes of RegCM3:
1) MIT-Emanuel Scheme (EMU)
2) Grell scheme with Fritsch-Chappell closure (GFC)
3) Grell scheme with Arakawa-Schubert closure (GAS)
4) Anthes-Kuo scheme (AK)
Objective of Part I study:
As there are four available cumulus schemes, we
want to find out which one is better in simulating
the sub-daily variations (including S1 & S2) of
rainfall in the Southeast China.
Statistical Analyses
Obs
S1(P)
Phase
S2(P)
Amp. Phase
Amp.
models
EMU1
GFC1
GAS1



AK1



17
Huang et al. (2010)
Summary of Part I Study
• The modified EMU scheme is better than other
scheme on the simulation of Asian summer monsoon
system.
• EMU & GFC perform better than GAS and AK scheme
on the simulation of diurnal rainfall over SEC.
• Use of the “right” scheme is important in the
application of the regional climate model in seasonal
prediction or long-term projection of future rainfall
and its variability.
Part II: application of RegCM3 on TC genesis
 Au-Yeung and Chan (2012): the RegCM3 driven by the
ERA40 reanalysis can reasonably represent the TC
genesis over the WNP basin.
Question raised from past studies
 The ability of the RegCM3 in simulating the landfalling
TCs is not examined by Au-Yeung and Chan (2012) .
 Chan and Xu (2009): the temporal evolution of the total
number of WNP-TC genesis from the observations is
positively correlated to the total number of WNP-TC
making landfall in East Asia.
Likely, the capability of the RegCM3 in simulating TC
genesis can be extended to produce reasonable seasonal
forecasts of landfalling TCs in East Asia.
Objective of current study
To verify above hypothesis by using a real-time global climate
model forecast as boundary conditions for the RegCM3.
The selection of input forecast data
Kim et al. (2012) employed a hybrid statistical–dynamical
prediction method using the real-time global forecast data
provided by the NCEP CFS (National Centers for Environmental
Prediction Climate Forecast System) to predict the track of the
seasonal TC activity and were able to generate skillful seasonal
predictions of TC activity.
Likely, the NCEP CFS hindcast data can serve as boundary
conditions for the RegCM3 in making reasonable seasonal
predictions of landfalling TCs in East Asia.
Design of experiments
Exp1:
forcing the RegCM3 with the NCEP CFS reanalysis to investigate
the ability of the model in generating a good climatology of TC
activity in spatial and temporal scales.
to ensure that the RegCM3 can be used in
the next step
Exp2:
forcing the RegCM3 with the NCEP CFS version 2 hindcast data
to examine its ability on the seasonal prediction of TC genesis
and landfall.
We examine TC genesis prior to TC landfall because a model performing
well on the simulation of characteristics of TC genesis has a better
chance to produce a reasonable seasonal forecast of TC landfalling
activity (Liu and Chan, 2003).
Selection of TC genesis and tracks
Observations:
 Data from the Joint Typhoon Warning Center (JTWC)
 Only the records with wind speeds  25 knots and genesis
location within the region bounded by 0o-40oN, 100oE-170oW
is considered.
Model simulations:
 Methods for the identification of TC genesis and tracks follow
Au-Yeung and Chan (2012) :
(1)local maximum relative vorticity at 850 hPa  1  10-4 s-1;
(2)temperature at 300 hPa must be 1oC higher than the average
temperature within 15o latitude radius from the TC center;
(3)TC lifetime must be at least 2 days; and
(4)genesis location must occur over the ocean.
Other model Setups
Domain Area:
-75oE to 170oW, 10oS to 45oN
Resolution:
- 20 vertical levels
- 50 km horizontal resolution
This resolution is sufficient to simulate accurately the distribution
of precipitation over East Asia (Gao et al. 2006) and to depict
properly the TC genesis over WNP (Au-Yeung and Chan 2012).
All lateral boundary conditions are provided every 6 h via
a relaxation method with a 15-grid buffer zone
Exp1: TC genesis-spatial similarity
significant at the 95% confidence interval
Spatial correlation coefficient for
(a) and (b) ~ 0.93; significant at
the 95% confidence interval
Exp1: TC genesis-temporal similarity
Exp1: TC genesis-temporal similarity
Tcorr ~ 0.8 higher than Tcorr = 0.65 in AYC12
Exp2: TC genesis-spatial similarity
significant at the 95% confidence interval
Scorr (a and b) ~ 0.87; significant
at 95% confidence interval
Exp2: TC genesis-temporal similarity
 Total number of WNP-TCs generated
during May to October estimated from
Exp2 (~ 22.54 cases per MJJASO
season) is very close to the observed
one (~ 22.36 cases per MJJASO season)
 This implies that Exp2 performs
better in predicting WNP-TC
numbers on a seasonal timescale
(e.g. the entire MJJASO season) than
a monthly timescale
Exp2: TC genesis-temporal similarity
 Tcorr ~ 0.63; significant at
the 95% confidence
interval
 Note also that the apparent
decreasing trend in the
observed annual number of
TC genesis is well captured
by the model hindcast as
well
Exp2: TC genesis-more examination
Scorr~0.72
 The selection of warm and cold years
is based on the ERSST.v3b sea surface
temperature anomalies (SSTA)
averaged over the Niño 3.4 region
(5oN-5oS, 120o-170oW) provided by the
National Weather Service Climate
Prediction Centre.
Scorr~0.78
 A year with the value of SSTA
averaged from May to October larger
than 0.8 (smaller than -0.8) standard
deviation is identified as a warm (cold)
year (e.g. Chan 2000).
Scorr~0.67
 In warm ENSO years, the mean genesis
location of TCs (a) tends to shift
southeastward
Cases per MJJASO
per decade
Four groups of TC landfall
Chan and Xu (2009)
1) South TCs (STC) – TC landfall in South China, Vietnam and the Philippines
2) Middle TCs (MTC) – TC landfall in East China
3) North TCs (NTC) – TC landfall in the Korean peninsula and Japan
4) All TC (ATC) – the total number of landfalling TCs in Asia
Four groups of TC landfall
 The skill of RegCM3 in the forecasts of landfalling TCs is
higher over the Southeast Asian region than over the
other sub-regions of East Asia.
Possible causes
 Note that the RegCM3 used in the present work was
modified to a better simulation for the summer monsoon
circulation change over the Southeast Asian regions
(Chan et al. 2004).
 As the large-scale conditions of flow are one of the major
factors affecting the number of landfalling TCs (Goh and
Chan 2010), it is likely that the current setup of RegCM3,
which is more suitable for the seasonal forecasts of
circulation change over the Southeast Asian region,
might not be the best for the perdition of TC making
landfalls in the other regions.
Exp2 vs. CFS2: statistical evidence
Exp2 vs. CFS2: statistical evidence
 The use of RegCM3 driven by the CFS2 gives a better
forecast skill than the use of CFS2 alone for the
prediction of WNP-TCs making landfall in East Asia.
Summary of Part II Study
The use of a dynamical downscaling method
for the global forecast data by RegCM3
would likely lead to a higher forecast skill of
regional TC landfalls in most of the East
Asian region.
Thank you!
SST (2014 CFSv2 – climatology); MJJASO
oC
Fig. 1
The difference of sea surface temperature between 2014 MJJASO (CFSv2)
and climatology.
Fig. 2
Similar to Fig. 1, but for the MJJASO (a) climatology and 2014 TC predicted by (b) CFSv2
and (c) RegCM. The difference between (b), (c) and (a) is shown in (d), (e).
Fig. 3 Month to month evolution of TC genesis number obtained from climatology of JTWC
(blue bar), 2014 CFSv2 (red line), and 2014 RegCM (green dotted line) for (a) March 1st
run and (b) April 1st run.
(a) Selected domain for STC, MTC and NTC
NTC
MTC
STC
AMJJAS
Cases per MJJASO
Cases per AMJJAS
(b) Number of TC landfalls
MJJASO
MJJASO climatology from JTWC (Huang and Chan 2013)
CFSv2
RegCM
Fig. 4
In (a), the boxes mark the different groups of landfalling TCs (STC –
south TCs, MTC – middle TCs, and NTC – north TCs) studied in the
report, following Chan and Xu (2009). (b) is the number of AMJJAS and
MJJASO TCs making landfall in the identified regions estimated from
CFSv2 (red solid line) and RegCM (green dotted line). In (b), the
climatology of MJJASO TC landfalls extracted from Huang and Chan
(2013) is also added for comparison.