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Figure 1. Precipitation rate (mm day -1 ) for summer
(JJA) 1998 from (a) the CMAP data as observation
and (b) the simulation by the HadGEM3-RA
There are coherent bias patterns in the simulated East Asian
summer monsoon of 1998 and 1997 (not shown). The
HadGEM3-RA overestimates precipitation over most of the
region and underestimates over the centre of model domain.
There are warm biases over north China, Manchuria, and
northern continent and small cold biases over south China
and Japan. In 500 hPa geopotential height, there is a
negative bias over the centre of model domain and positive
biases near the north and west lateral boundaries. Biases of
sea level pressure are negative over the centre and positive
near the lateral boundaries of the domain. In the lower
troposphere there are south-westerly biases near the southern
boundary and dry biases over most of the domain. In vertical
profiles of the biases of air temperature and specific
humidity, there are distinct warm and dry biases within
lower troposphere, with maximum warming and drying at
850 hPa. In contrast, there are warm and wet upper
tropospheric biases with a maximum at 300 hPa.
These coherent bias patterns seem to indicate the following
mechanism; strong south-westerlies in the south of the
domain supply warm and moist air and that enhances
convective activity over south China and northwest Pacific
Ocean. Active convection transports moisture from lower to
upper levels. At the same time, cyclonic flow related to the
active convections leads to reduced moisture supply into
north of the region of convection. Therefore, precipitation is
underestimated over the centre of model domain, such as the
Korean Peninsula region.
Figure 2. Differences of summer precipitation rate
(mm day -1 ) from 1998 to 1997, obtained from (a) the
observation and (b) the simulation.
4. Concluding remarks and future works
It is found that the HadGEM3-RA reproduces well
extreme seasonal timescale climatic events of the East
Asian monsoon, such as flooding in China and Japan
during summer of 1998, and is able to capture the
interannual variation between the East Asian monsoon
seasons of 1997 and 1998. However, the HadGEM3-RA
exhibits systematic errors, such as wet bias in
precipitation, warm bias in surface air temperature, and
strong south-westerly bias near southern and eastern
lateral boundaries.
To improve model performance, we will conduct
sensitivity experiments to physics and simulation domain
size. After sensitivity experiments on seasonal scale, we
will conduct a multi-annual climatological simulation.
References
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Mawson, A. Staniforth, A. A. White, and N. Wood, A
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Meteor. Soc., 131, 1759–1782. 2005.
Martin, G. M., M. A. Ringer, V. D. Pope, A. Jones, C.
Dearden, and T. J. Hinton, The physical properties of
the atmosphere in the new Hadley Centre Global
Environmental Model (HadGEM1). Part I: Model
description and global climatology. J. Climate, 19,
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