There are many regional activities upon the Asian-Australian monsoon studies. Some of them have been well coordinated within the CLIVAR and other international scientific frameworks (e.g., GEWEX and IGBP). Some have not.
The follows are those reported at the 4th CLIVAR/AAMP meeting, 29-31 August 2001, University of Reading, which highlight the recent approaches in the different nations towards the common target - the variability and predictability of the monsoons. They are from:
Information of the regional advances is helpful for the Panel and will be updated from time to time. It may be submitted to the Panel members or the ICPO.
Neville Nicholls
Bureau of Meteorology Research Centre, Melbourne
The APN Network for Climate Extremes is a group of scientists in the Asia Pacific region who are collaborating to enhance the capability of nations in the region to monitor and analyse trends and variations in extreme climate events. The Network is supported by the Asia Pacific Network for Global Change Research and involves participants from seventeen countries in the Asia Pacific region: Australia, Cambodia, China, Fiji, French Polynesia, Indonesia, Japan, Malaysia, Myanmar, New Caledonia, New Zealand, Papua New Guinea, Philippines, Samoa, Solomon Islands, Thailand, and Vietnam. Three workshops have been held, hosted by BMRC in Melbourne, and a paper published. An interesting result is that the number of extreme hot days and nights has increased throughout the region over the past 40 years, while the number of cold extremes has decreased. Further details are available at the Network's website: http://www.bom.gov.au/bmrc/csr/apn/index.html.
Analysis and Interpretation of ocean thermal structure: Susan Wijffels and Gary Meyers (CSIRO Marine Research) are documenting variability of mass, temperature and salinity transport of Indonesian throughflow (ITF) and its relationship to winds over the Pacific and Indian Oceans. A key result is that heave of the thermocline along the northern side of ITF (i.e. Indonesian coast) affects SST by upwelling, and this is driven by winds over the Indian Ocean. Ming Feng, Susan Wijffels and Gary Meyers are analysing the large scale propagating features seen in altimeter and XBT data. Tara Ansell (a PhD student at Melbourne University) is using XBT data and ocean-model results to identify the mechanisms that cause SST variability in the eastern and western poles of the Indian Ocean Dipole.
BMRC is studying the coherence and predictability of seasonal rainfall in the maritime continent. Seasonal variations appear to be predictable during the dry season in this region, but not generally during the wet season (e.g., 'Spatial coherence and predictability of Indonesian wet season rainfall', Haylock & McBride, J. Climate, in press). Further evidence of this seasonal/spatial variation in predictability emerged at the Third Workshop on Regional Climate Prediction and Applications - Tropical Pacific Islands and Rim (University of Oklahoma, April-June 2001). Contact: John McBride, BMRC.
BMRC continues investigations of the possible
effects of Indian Ocean sea surface temperatures on the climate of Australia
and the surrounding region. This work indicates that an Indian Ocean Dipole,
independent of the El Niño - Southern Oscillation, is rare. Most
'dipole-like' behaviour of the Indian Ocean appears to be a response to
the El Niño - Southern Oscillation. A paper discussing some of this
work was presented at the AMS Annual Meeting in January, and an article
has been submitted to CLIVAR-Exchanges. Contact: Neville Nicholls, BMRC.
The Regional Model Intercomparison Project (RMIP), is an intercomparison of regional models over a large Asian domain (about 50E-150E and 5N-60N), run for an 18-month period (March 1997 to August 1998) at a resolution of about 60 km. Eleven models have run the simulations with lateral boundary forcing supplied by NCEP reanalyses. John McGregor and Jack Katzfey (CSIRO Atmospheric Research) have submitted 2 runs, one for DARLAM and one for the CSIRO conformal-cubic (C-C) model (using a stretched global grid). RMIP is an APN project. Results are being analysed by Congbin Fu's group at IAP in Beijing. An interesting result is that most, but not all, models have a tendency to shift the East Asia monsoonal rainfall too far northwards.
Stuart Godfrey, Rui-Jin Hu and Andreas Schiller (CSIRO Marine Research) are exploring the dynamics and thermodynamics of the Indian Ocean in their global MOM model, to better understand what sets long-term mean surface heat fluxes and SST variations within it. They find that mixing within the Somali Current, down to depths of 1000m or so, sets the depth and temperature distribution of the entire Indian Ocean north of the Indonesian Throughflow at 7°S. This in turn sets the depth distribution of the zonal Indonesian Throughflow jet via geostrophy, which then supplies the western boundary current feeding the Somali Current. Hence mixing events in the Somali Current determine the long-term mean heat transport and surface heat flux into the northern Indian Ocean, rather than the other way round. This may have implications for the design of an ocean monitoring system for climate, in the Indian Ocean.
Coupled model of Indian-Pacific Ocean: Jaci Brown
and Stuart Godfrey (CSIRO Marine Research) are working on extending the
Kleeman intermediate coupled model of the Pacific Ocean to include the
Indian Ocean.
BMRC is enhancing its empirical studies of intraseasonal oscillations, with the aim of attempting to predict these, especially with statistical methods. The approach is to use real-time filtering of OLR data to monitor and predict the convective variations of the Madden-Julian oscillation and various convectively coupled equatorial waves, based on the "climatological" spectral peaks of a long record of satellite-observed data. More information is available at http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/maproom.html
Andreas Schiller and Stuart Godfrey (CSIRO Marine Research) have explored intraseasonal SST variability in their ocean GCM. Good simulations are achieved, in which surface heat flux variations are found (as in simpler models) to be the dominant term. However, entrainment through the mixed layer base contributes locally; barrier-layer formation occurs before onset of strong winds; and different processes control intraseasonal dynamics in different events.
Relation of Indian Ocean Variability to Australian
Winter Rain: Tara Ansell and Stuart Godfrey (CSIRO Marine Research) have
examined moisture flux towards Australia and rainfall onto Australia during
intraseasonal oscillation events, using a composite provided by Peter Webster.
5-10 days after a maximum of rainfall over the equatorial Bay of Bengal,
a 'northwest cloudband' develops with strong moisture fluxes from south
of Sumatra extending over Australia; strong rain develops, as a composite
average. There is a statistically significant relation (correlation coefficient
0.61) between number of ISOs each northern summer, and the Indian Ocean
Dipole Index (IODI). There are about four Northwest Cloud Bands each winter
that are not associated with an ISO event for every one that is; but the
unrelated ISOs bring less rain to Australia. Composites of the cloud bands
that are not related to ISO events are also associated with strong patterns
over the equatorial Indian Ocean 6 days earlier, but the associated wind
patterns are qualitatively different from ISOs.
Several collaborative projects focussed on the application of seasonal climate predictions for agriculture, health, and environmental management, have commenced. Some of the agricultural projects (e.g., in Pakistan, India) are organised through the START CLIMAG program (contact: Holger Meinke, Department of Primary Industry, Queensland). The effects of the El Niño - Southern Oscillation on marine animals (dugongs) and birds are being studied (contact: Neville Nicholls, BMRC).
A pilot project titled "Capturing the Benefits of Seasonal Forecasts in agricultural management" has been carried out under the Australian Centre for International Agricultural Research. This 3-year program involved field sites in Matopos Zimbabwe (grazing management), Tamil Nadu India (farm decision making), and Mataram Indonesia (Water and Crop management). The lead scientists in Australia are drawn from the Queensland Department of Primary Industries, the Queensland Department of Natural Resources and the Bureau of Meteorology Research Centre (contact J. McBride, BMRC).
Oceans to Farms: This multi-disciplinary project
is a study of the way seasonal climate forecasts can best be used to manage
farming and farm-related industries. A lagged statistical relationship
is established between ocean surface temperatures and variables such as
plant growth and rainfall. The forecast system is tailored for specific
regions, industries and decision points in the farming cycle. Different
management strategies are tested using 100 years of historical data. A
key result is that it is often better to predict plant growth rather than
rainfall. Another key result is that skill at predicting rainfall or growth
is only one factor in farm management decision-making; the same forecast
can end up with very different usefulness in different contexts. The economic
and conservation value of this forecast system has been studied in most
detail for the northern Queensland extensive grazing industry. This experiment
indicates that production increases of 16% are possible at the same time
as a 12% reduction in soil loss, given appropriate management strategies
based on the forecast. These benefits exceed those obtained using a forecast
based on the Southern Oscillation Index (SOI). Somewhat surprisingly, the
ocean-based forecasts also perform slightly better than a perfect knowledge
of seasonal rainfall totals. This is because rainfall distribution is important,
and predicting an index of plant growth takes this into account. Contact:
Pater McIntosh, CSIRO Marine Research.
The Darwin Climate Monitoring and Research Station (DCMRS), a cooperative network run by the BMRC and the Northern Territory Regional Office of the Bureau of Meteorology, provides a basis for research activities in a tropical monsoon environment, including support for TRMM and the Atmospheric Radiation Measurement (ARM) program of the US Dept of Energy. The DCMRS undertakes climatological observations and research relevant to the systematic measurement of tropical rainfall, cloud properties and their impact on radiation in the monsoon environment. Emphasis is on providing ground truth data for TRMM and ARM, and process studies including special observing projects on the four-dimensional structure, dynamics and microphysical properties of tropical convection and associated radiation. (Contact: Tom Keenan, BMRC).
Indian Ocean Sustained Observations - XBT Network: The lines IX1, 12, 22, 29 and PX2 (Banda Sea) were started in 1983-1986. The lines are now operational (i.e. long-term maintenance assured in an appropriation budget) under direction of the Joint Australian (CMR/BMRC) Facility for Ocean Observing Systems (JAFOOS). JAFOOS also operates the WOCE Upper Ocean Thermal Data Assembly Centre, where all Indian Ocean XBT data are assembled annually and given scientific quality control following published standards and procedures. The assembled data sets are available now for 1990-97. JAFOOS and International Pacific Research Centre (IPRC) are jointly proposing to use the WOCE procedure to QC all T(Z) data in the Indian Ocean for the 20th century. The panel is requested to consider and endorse the idea in principle, pending review of the final draft of the proposal. Contact: Gary Meyers, CSIRO Marine Research).
Argo network: Australia has initiated an Argo float network to collect temperature and salinity profiles to a depth of 2000m. Initially 10 floats were placed in the eastern Indian Ocean between NW Australia and Indonesia. Resources are available to maintain and extend the array southward to the SW corner of Australia and about 1000 km offshore. Contact: Neville Smith, BMRC.
Hui-Jun Wang
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing
Further research foci:
Leading Scientists:
Prof. Ding Yihui
National Climate Centre, China Meteorological
Administration
46 Baishiqiao Road, Haidian, Beijing 100081 China
Fax: 86-10-62176804, E-mail: yhding@public.bta.net.cn
Prof. Chongyin LI
Institute of Atmospheric Physics, Chinese Academy
of Sciences
Qi Jia Huo Zi, Beijing 100029 China
Fax: 86-10-62562347, E-mail: lcy@lasgsgi4.iap.ac.cn
Research foci:
Leading Scientist
Prof. Ronghui Huang
Institute of Atmospheric Physics, Chinese Academy
of Sciences
Zhong Guan Cun, Beijing 100080 China
E-mail: hrh@lasg.iap.ac.cn
Subtropical anticyclone (SA) belt affects
the motion of weather system, moisture transport, as well as the persistent
anomalies of the weather and climate in subtropical regions. The structure,
activity, and their relationship with the weather and climate in China
and the East Asian monsoon have long been studied. However, there is lack
of systematic knowledge on its variation mechanism. Of weather and climate
dynamics, the dynamics of subtropical anticyclone is a challenge to scientists.
The project launched comprehensive studies of
the mechanism of the SA variation through data diagnosis, numerical modelling
and theoretical analysis. Many significant achievements have been gained
and the insight into the configuration and formation mechanism of subtropical
anticyclone has been renewed.
Leading Scientist
Prof. Guoxiong Wu
Institute of Atmospheric Physics, Chinese Academy
of Sciences
Qi Jia Huo Zi, Beijing 100029 China
E-mail: gxwu@lasg.iap.ac.cn
Aims:
Leading scientist:
Prof. Zeng Qing-Cun
Institute of Atmospheric Physics, Chinese Academy
of Sciences
Zhong Guan Cun, Beijing 100080 China
E-mail: zengqc@lasg.iap.ac.cn
Aims:
Leading scientist:
Prof. Ronghui Huang
Institute of Atmospheric Physics, Chinese Academy
of Sciences,
PO Box 2718, Beijing 10080 CHINA
Fax: +86-10-6256-0390, Email: hrh@lasg.iap.ac.cn
By applying the definition of Zeng and Zhang
(1992), the seasonality of the global wind field is analysed by Xue and
Zeng (1999). They found that in the lower troposphere, in addition to the
classic tropical monsoon regions, there are regions with maximum of seasonality
in the subtropics and in high latitudes respectively, due to seasonal migration
of the subtropical highs and seasonal variation of storm tracks of the
westerlies. These regions can be called the subtropical and temperate-frigid
monsoon region respectively. The subtropical monsoon tends to approach
the tropical one with height and eventually the tropical monsoon and subtropical
monsoon merge into a whole planetary monsoon system in the upper troposphere.
In the stratosphere, seasonality is much larger than that in the troposphere,
and there is a well-defined belt with very large seasonality in each hemisphere
caused by the opposite circulation between summer and winter and by the
establishment and collapse of the night jet. In general, the baroclinic
structure of seasonal variation of the atmospheric general circulation
reflects the interaction between the lower levels and higher levels of
the atmosphere or between the troposphere and the stratosphere.
Seasonality of the large-scale monsoon may generally
be attributed to that of the zonal wind because the atmospheric general
circulation is dominated by its zonal components. In some regions such
as East Asian monsoon region, however, the meridional wind plays an important
role in seasonal variation of East Asian monsoon, hence the monsoon intensity
index defined by Webster and Yang (1992) is not well suitable for East
Asian monsoon. In order to accurately depict the intensity change of East
Asian monsoon, it is evident that the zonal and the meridional wind components
must be considered simultaneously.
The result also shows that interannual variation
of the atmospheric general circulation is closely related to seasonal variation
of monsoon in monsoon regions. In the tropical Pacific, however, interannual
variation caused by the external factors such as SST anomalies associated
with ENSO cycle is possibly larger than that caused by the internally seasonal
variation in the atmosphere.
Based on the similar method, Xue and Zeng (2001)
defined an index to express the abruptness of the seasonal variation of
atmospheric circulation. They find that such abruptness is generally larger
in the monsoon regions than in the global average. In terms of the vertical
structure, the upper troposphere is of larger abruptness in the seasonal
variation.
References:
Zeng, Qing-Cun, and Bang-Lin Zhang, 1992: On
the seasonal variation of the atmospheric general circulation and monsoon.
Chinese J. Atmos. Sci., 22, 505-813. (in Chinese).
Xue, Feng, and Qing-Cun Zeng, 1999: Diagnostic
study on seasonality and interannual variability of wind field. Adv. Atmos.
Sci., 16, 537-543.
Xue, Feng, and Qing-Cun Zeng, 2001: The seasonal
abruptness of the general circulation as revealed from the data analysis.
Chinese J. Atmos. Sci., in press.
Sun and Sun (1995) analysed the atmospheric
circulation in the composed flood years and drought years in the Yangtze
River and Huai River valleys. They revealed that the preceding winter monsoon
circulation in East Asia is anomalous for the drought years. The anomalies
of the preceding winter circulation include the larger meridionality of
the 500 hPa geopotential height over the Eurasia, the stronger East Asian
trough, frequent cold serge activities, stronger cross-equatorial flow,
and stronger convective activities around the Philippines. While the preceding
winter circulation anomalies for the flood years are almost opposite to
those for the draught years.
Gong et al. (2001) analysed the connection between
Arctic Oscillation (AO) and variability of East Asian monsoon. Two indices
are chosen to describe the winter monsoon. One is the intensity of the
Siberian High, defined as the average sea-level pressure (SLP) over the
centre region, and the other is the temperature of Eastern China, averaged
over 76 surface stations. These are two closely related components, correlated
at -0.62 for the period 1951-99. Temperature drops by 0.64 degrees Celsius
in association with a one standard deviation increase in Siberian high
intensity. It is find that there are significant out-of-phase relationships
between AO and the East Asian winter monsoon. The correlation coefficient
between AO and Siberian High intensity index is ?0.48 for period 1958-98.
AO is also significantly correlated with the temperature of eastern China
at 0.34. However, when the linear trend is removed, the correlation is
no longer significant. But the strong correlation between AO and Siberian
high and temperature are still significant. These results reveal that the
impact of AO influences the East Asian winter monsoon through the impact
on the Siberian high. Negative phase of the AO is concurrent with a stronger
East Asian trough and an anomalous anticyclonic flow over Urals at the
middle troposphere (500 hPa). Both the AO and the Eurasian pattern play
important roles in the changes of the Siberian High and/or East Asian monsoon.
They account for 13% and 36% of the variance in the Siberian High respectively.
The Asian winter monsoon (AWM) response to global
warming was investigated trough a long-term integration of the transient
greenhouse warming with the ECHAM4/OPYC3 CGCM (Hu et al., 2000). The physics
of the response was studied through analyses of the impact of global warming
on the variation of the ocean and land contrast near the ground over the
Asian and western Pacific region and the east Asian trough and jet stream
in the middle and upper troposphere. Forcing of transient eddy activity
on the zonal circulation over the Asian and western Pacific region was
also analysed. It is found that in the global warming scenario the winter
northeasterlies along the Pacific coast of Eurasian continent weaken systematically
and significantly, and intensity of the AWM reduces evidently, but the
AWM variances on the interannual and interdecadal scales are not affected
much by global warming. It is suggested that global warming makes the climate
over the most part of Asia be milder with enhanced moisture in winter.
In the global warming scenario the contrast of the sea-level pressure and
the near-surface temperature between the Asian continent and the Pacific
ocean becomes significantly smaller, northward and eastward shifts and
weakening of the east Asian trough and jet stream in the middle and upper
troposphere are found. As a consequence, the cold air in the AWM originated
from the East Asian trough and high latitudes is less powerful. In addition,
feedback of the transient activity also makes a considerable contribution
to the higher-latitude shift of the jet stream over the North Pacific in
the global warming scenario.
References:
Sun, Shu-Qing, and Bo-Min Sun, 1995: The anomalous
East Asian winter monsoon circulation and the flood and drought in the
Yangtze River and Huaihe River Valleys, Acta Meteorologica Sinica, 53,
440-450.
Gong, Dao-yi, Shao-Wu Wang, and Jin-Hong Zhu,
2001: East Asian winter monsoon and Arctic oscillation. Geophys. Res. Lett.,
28, 2073-2076.
Hu, Zeng-Zhen, L. Bengtsson, and K. Arpe, 2000:
Impacts of global warming on the Asian winter monsoon in a coupled GCM.
J. Geophys. Res., 105, 4607-4624.
Zhang et al. (2000) found that there exists
bimodality in the longitude location of the SAH. According to the two regions
where the SAH prefers to stay, the SAH is classified into the Tibetan Mode
(TM) and the Iranian Model (IM), respectively. The studies on the maintenance
mechanism both from circulation structure and thermal structure manifest
the different features of the TM and IM. The diagnosis based on the thermodynamic
equation further reveals that the TM is closely related to the diabatic
heating of the Tibetan Plateau whereas the IM is more associated with the
adiabatic heating in the free atmosphere, as well as the diabatic heating
near the surface.
The composite corresponding to the two modes
shows that the bimodality has strong impacts on the large area climate
anomalies in Asia. In the TM case, the abnormal warm centre appears over
the Tibetan Plateau region accompanied by enhanced northerly airflow in
the middle-high latitudes and southerly airflow in the subtropics, forming
a convergence zone near 30oN and resulting in more precipitation in the
areas extending from the Tibetan Plateau to the Yangtze River Valley, to
the south of Japan, as well as in South China Sea and the surrounding areas.
As to the IM case, opposite anomaly patterns are detected in the surface
air temperature, lower troposphere circulation, and precipitation.
Zhang et al. (2001) also analysed the long-term
variability of SAH. From late 1970s, the alternation of the SAH bimodality
in its longitude location takes on a more low-frequency variability. More
TM cases appear in 1980s and more IM cases in 1990s. The detrended time
series of the SAH intensity index shows that the signals with large variability
mainly happen on the decadal scale. There is a remarkable phase transition
occurring in late 1970s. The interannual variability is weak, especially
before the mid-1980s.
References:
Zhang, Q., G.X. Wu and Y. F. Qian, 2001: Long-term
variability of the South Asia High and its relation to tropospheric geopotential
height and global SST. (Submitted to Theoretical and Applied Climatology.)
Zhang, Q., G.X. Wu and Y. F. Qian, 2000: The
bimodality of the 100hPa South Asia High and its association on the climate
anomaly over Asia in summer. (Submitted to Journal of the Meteorologocal
Society of Japan.)
As revealed by Wang (2001a), the transition
of the global atmospheric circulation in the end of 1970Ės can clearly
be detected in the atmospheric temperature, wind velocity, and so on. Wavelet
analysis reveals that the temporal scale of this change is larger than
20 years. The global annual mean free air temperature undergoes a transition
in the end of 1970Ės to a warmer period at all the pressure levels below
200 hPa, with the reverse change at levels near 50 hPa. As for the spatial
pattern of the transition, the mid-latitudes Asia has its clear speciality
where the change of air temperature is opposite to that of the global average
at levels below 200 hPa. The Asian and African summer monsoon circulation
becomes weaker after this transition. The trade wind over the tropical
eastern Pacific in summer and winter is weakened after 1970Ės, and, accordingly,
the SST over the Nino3 region increased at the same time. The summer precipitation
in some parts of China undergoes a transition as well, especially over
the Yangtze, Yellow, and Huai River valleys.
The instability in the relationship between the
East Asian summer monsoon and the ENSO cycle in the long-term variation
was studied by Wang (2001b). By instability, we mean that high inter-relation
exists in some periods but low inter-relation may appear in some other
periods. It is revealed that the interannual variation of the summer atmospheric
circulation during the Îhigh correlationĖ periods (HCP) is significantly
different from that during the Îlow correlationĖ periods (LCP). Larger
interannual variability is found during HCP for trade wind over the south
eastern Pacific, the low-level air temperature over the tropical eastern
pacific, the subtropical high pressure systems in the two hemispheres,
and so on. The correlation between summer rainfall over China and ENSO
is different as well between HCP and LCP.
References:
Wang Hui-Jun, 2001a, The Weakening of the Asian
Monsoon Circulation after the End of 1970Ės, Adv. Atmos. Sci.,18, 376-386.
Wang Hui-Jun, 2001b: The Discontinuity in the
East Asian Summer monsoon-ENSO Relations, Adv. Atmos. Sci., (in press).
The dynamics of the mobile interface between
the mid-latitude westerly and the tropical easterly is developed. A complete
form of vorticity equation is deduced to study the interactions among each
climate subsystems. The "Thermal adaptation" theory is established to reveal
the atmospheric responses to external thermal forcing. Based upon theoretical
study and numerical simulation, vertical inhomogeneous heating and spherical
effect are proved to be the basic factors determining the configuration
of subtropical anticyclone. The mechanisms of land surface sensible heating
and deep convective condensation heating in forming each of the isolated
SA are revealed. Horizontal inhomogeneous heating is proved to be a key
factor in connecting the anomaly of the subtropical anticyclone to the
anomaly of circulation in mid-high latitudes. "Two-stage thermal adaptation"
theory is constructed and the "Lindzen-Nigam" theory is extended to investigate
the mechanism of how the tropical SSTA in Indian Ocean affects the abnormality
of the subtropical anticyclone. This then provides a new method for short-term
climate predictions.
The relationship between the abnormal strength
of the subtropical anticyclone over the western Pacific and the anomalies
in tropical and western Pacific general circulations, as well as sea surface
temperature has been established in this study. The activities of the SA
over the western Pacific in different time-scales ranging from decadal,
annual, seasonal, intra- seasonal and 5-10-day period have been discovered.
The influences of such persistent anomalies on the weather and climate
over the basins of Yangtze River and Huaihe River are also studied.
The aforementioned results have rectified parts
of the traditional knowledge about the SA formation. It has been proved
that vertically sinking motion cannot be used to explain the formation
of subtropical anticyclones in the upper and middle troposphere. The forming
mechanism of the SA over the eastern Pacific is different from that over
the western Pacific. These two anticyclones cannot be regarded as one unit
system. The relationship between summer precipitation over China and the
SA over the western Pacific is a kind of interaction, instead of cause
and effect. Therefore it was concluded that forecasting the anomaly
of summer climate must consider the anomalies of external heating sources.
2.6.1 Hindcast experiment of 1998 flood in
China by the AGCM
Sets of numerical hindcast experiments were carried
out to study the excessive rain happened over China in 1998 by using an
atmospheric general circulation model (Wang et al., 2000). The monthly
sea surface temperatures for 1998 were prescribed as the model boundary
conditions. The initial atmospheric conditions for each of the 30 member
simulations were obtained from the daily reanalysis data for 00 UTC from
April 1 to April 30, 1998. The initial conditions for snow mass, soil temperature,
and soil wetness was prescribed as those of the model climatology. The
CCSR/NIES model could reproduce a reasonable degree of outlook of the summer
climate anomalies over East Asia including the rain over China in 1998
given the observed monthly SSTs and the initial atmospheric conditions
in April. The simulated anomalies in JJA geopotential height at 500 hPa
agree well with observations over Eurasia and the tropical western Pacific.
The stronger wind over 850 hPa for JJA is reasonably reproduced. The model
also captures the weakness of Indian monsoon and the negative precipitation
anomaly over the tropical western Pacific. The simulated subtropical high
over the South China Sea is also realistic.
Discrepancies between the ensemble simulation
and the observation can be found in several aspects. One of them is the
overestimation of wind anomalies at 850 hPa and the OLR anomalies over
the tropical western Pacific. The model simulates a northward shift of
heavy rain area over China compared to the observation, and it fails to
simulate the negative anomaly in JJA GH5 over the Berling Sea along the
date line.
This research suggests that the initial atmospheric
anomalies in April may have strong impacts on the simulated Eurasia flow
pattern and the precipitation anomalies over the East Asia in the subsequent
summer. However, studies of such impacts in other years would be necessary
to confirm the above results. At the same time, the study on physical processes
responsible for possible relationship between winter (or spring) and summer
conditions over Eurasia is required.
The result shows that the enhancement of the
western Pacific high-pressure system as well as the related change of the
flow pattern at 850 hPa over the western Pacific and East Asia were caused
mainly by the global SST anomalies. But, which part of the SST anomalies
played the key role in this regard remains unknown, and may become clear
through more diagnostic analysis and numerical experiments.
Since the year 1998 was a special year both in
SST anomalies and in atmospheric anomalies over East Asia, hindcast studies
for other years would be much valuable.
2.6.2 ENSO prediction system based on CGCM
Zhou and Zeng (2001) developed an ENSO prediction
system based on the coupled atmosphere-ocean GCM developed in Institute
of Atmospheric Physics, Chinese Academy of Sciences. The modelĖs climate
drift was removed by using a statistic method to correct the atmospheric
variables at air-sea interface, and the climate variations in interannual
scales are simulated consistent with ENSO cycle in many aspects.
An initialisation scheme was designed for inducing
climate anomalies by using SST anomalies in the tropical Pacific at the
background of the model climatology. The numerical experiment showed that
the initialisation was successful in creating interannual variability that
was needed in ENSO predictions.
The forecast system was tested by performing
a series of 24-month hindcast experiments, one per month for the period
of November 1981 to December 1997. The system was found to produce generally
good hindcasts of SST anomalies in the eastern tropical Pacific. The correlations
of SST anomaly in Nino3 region exceed 0.54 up to 15 months in advance though
they are lower than the persistence in the first few months. The rsm errors
are less than 0.9oC for the same forecast length.
Further analyses show that the system is more
skilful in predicting SST anomalies in the 1980s and less in the 1990s.
This is a common discrepancy in most other dynamical forecast systems.
The model skills are also seasonal-dependent, lower for the predictions
starting from later autumn to winter and higher for those from spring to
autumn in a year-time forecast length, especially from July to September
the system performs very higher skills with anomaly correlations exceeding
0.6 up to about one and half years. It is encouraging that the prediction,
beginning from March, persists 8 months long with the correlation exceeding
0.6. This is operationally useful in predictions of summer rainfall in
China (Lin et al., 1999, 2000).
The results from this study are encouraging,
but there are also many aspects to be improved. The initial conditions
created by using the SST anomalies in the tropical Pacific are less accurate
in the anomalous structure of the ocean thermocline in which the memory
of the coupled system for the ENSO variability is contained. We are developing
a data assimilation system similar to that of Derber and Rosati (1989),
which is obviously an efficient way for inserting ocean subsurface data
into the coupled system to created more accurate initial conditions that
are physically in balance with the model through some appropriate modification.
There are deficiencies in the present coupled model. The amplitude of the
simulated interannual variability is smaller than the observation, which
is presented in most coupled general circulation models. The reasons are
not well known. One of the possible reasons is the coarse modelsĖ resolution,
especially that the horizontal resolution in the ocean model is not higher
enough in simulating the Kelvin wave well in the tropical waveguide which
is regarded as the control mechanism in the ENSO evolution. Another possible
reason is maybe from the coupling scheme and/or the two-component modelĖs
performance themselves, such as physical parameterisation, the limited
tropical region of the ocean model and so on, which suppress and/or modify
the feedback between atmosphere and ocean. They are currently improving
the modelĖs simulations for both climatology and climate variation by increasing
the modelĖs resolution and modifying the coupling techniques. Another obvious
deficiency is the lower skills in the 1990Ės predictions. Most coupled
forecast systems based on dynamical frames show the similar performance.
The development of ENSO in the earlier 1990s is different from that in
the 1980s and this period is sometimes referred as an irregular developing
period. Some researches indicated that the longer-than-interannual time
scale variability (e.g. decadal variation) maybe plays an important role,
which is regarded as the interaction between tropics and extratropics (Zhang
et al, 1999). The coupled model applied in this forecast system is failing
in simulating this long-term variation because the modelĖs ocean is restricted
in the tropical Pacific belt. In theory, therefore, the application of
a global ocean model instead of the tropical one is maybe a good way to
improve the forecasts, but the other difficulties caused by the global
simulation could prevent the system achieving this improvement.
2.6.3 Prediction of monsoon rainfall anomalies
by AGCM
Early in 1989, the experimental extraseasonal
predictions of summer monsoon rainfall anomaly by GCMs had been carried
out in the Institute of Atmospheric Physics, Chinese Academy of Sciences
((IAP/CAS), and the prediction result was shown to be encouraging (Zeng
et al., 1990). Since then, many efforts have been taken for the establishment
and improvement of the IAP Prediction System for Short-term Climate Anomaly
(PSSCA) as summarized by Zeng et. al. (1997). After its establishment,
IAP PSSCA has been applied to the semi-operational real time climate prediction
from 1989 to 1997 (Yuan et al., 1996; Zeng et al., 1997), verifications
show that IAP PSSCA can well predict the large positive and negative anomalies
of summer rainfall resulting in disastrous climate events, such as the
severe flooding in the Huai and Yangtze River regions in 1991, and the
severe drought in the Huai and Yangtze River regions in 1994. Generally
speaking, the prediction skill for IAP PSSCA is relatively large over Eastern
part of China and Southern China, which maybe ascribed to the relative
high seasonal predictability over these regions (Wang, et al. 1997).
In 1998, an improved version of the IAP prediction
system was achieved, with major improvements in the better representation
of land surface processes, the establishment and incorporation of ENSO
prediction system, and the improvement of correction system etc. (Lin et
al., 1998; Zhou et al., 1998). The real-time prediction results are shown
to be promising, for example, the positive rainfall anomalies over Yangtze
River Valley and Northeast China during the summer of 1998, the positive
rainfall anomalies over Southern China and the drought over most part of
North China during the summer of 1999 have all been quite well predicted
by the IAP seasonal prediction system.
References:
Zeng Qingcun et al., 1990: Experiments in numerical
extra-seasonal prediction of climate anomalies, Chinese Journal of Atmospheric
Sciences, 14(1),10-25 (In Chinese with English abstract).
Yuang Chongguang, Li Xu and Zeng Qingcun, 1996:
Summary on the research of extraseasonal numerical prediction of climate
anomalies, Climatic and Environmental Research, Vol.1, No.2, 150-159 (In
Chinese with English abstract).
Zeng Qingcun, et al., 1997: Seasonal and Extraseasonal
Prediction of summer monsoon precipitation by GCMs, Advance in Atmospheric
Sciences, Vol.14, 163-176.
Wang Hui-Jun et al., 1997: The interannual variability
and predictability in a global climate model, Advance in Atmospheric Sciences,
14, 554-562.
Lin Zhaohui et al., An improved short-term climate
prediction system and its application to the Extraseasonal prediction of
rainfall anomaly in China for 1998, Climatic and Environmental Research,
No.4, Vol.3, 1998,339-348.
Zhou Guangqing et al., A coupled Ocean-Atmospheric
General Circulation Model for ENSO prediction and 1997/1998 ENSO Forecast,
Climatic and Environmental Research, No.4, Vol.3, 1998,
Wang Hui-Jun, et al., 2000, Ensemble Hindcast
Experiments for the Flood Period over China in 1998 by Use of the CCSR/NIES
Atmospheric General Circulation Model, J. Meteorol. Soc. Japan, 78(4),
357-365.
Zhou GQ and QC Zeng, 2001: Predictions of ENSO
with a coupled atmosphere-ocean general circulation model, Adv. Atmos.
Sci., 18, 587-603.
Rupa Kumar Kolli
Indian Institute of Tropical Meteorology, Pune
Debasis Sengupta
Indian Institute of Science, Bangalore
Considering the fact that the monsoons have
a predominant influence on the society and national economy of India, monsoon
variability and prediction have been the major focus of climate research
in the country, in almost all the major centres of meteorological and allied
studies. These centres, through their individual endeavours as well as
national and international collaborative efforts, have contributed significantly
to the understanding of monsoon variability on different spatio-temporal
scales. In this context, the CLIVAR Asian-Australian Monsoon Panel
(AAMP), which held its first meeting in India, is widely considered by
the Indian groups as an effective platform to discuss the outstanding scientific
issues related to regional aspects of the monsoons from a global perspective
and draw up well-coordinated research initiatives in monsoon modelling
as well as observational programmes. In recent years, one of the
major highlights of climate research in India has been the Indian Climate
Research Programme (ICRP) established by the Department of Science &
Technology, Government of India, under which a wide variety of research
projects related to monsoon variability are supported. The Indian research
groups also actively participate in the international programmes like the
WCRP, IGBP, START, etc. In addition to these initiatives, India also has
active bilateral collaborative research programmes on monsoon-related aspects
with many countries, e.g., USA, UK, France, China, Russia, Japan, Brazil,
etc. A synthesis of the regional consequences of global change in India
was completed recently under the aegis of IGBP/START, with the participation
of scientists representing several major groups from South Asia.
In the following paragraphs, an attempt is made to provide a brief overview
of the recent activities in India, related to monsoon research.
The following are the major organizations/institutes/centres/departments in India, which have active research groups working on various aspects of monsoon variability and prediction:
Indian Institute of Tropical Meteorology (IITM),
Pune
India Meteorological Department (IMD)
National Centre for Medium Range Weather Forecasting
(NCMRWF), New Delhi
Centre for Atmospheric & Oceanic Sciences
(CAOS), Indian Institute of Science (IISc), Bangalore
Centre for Mathematical Modelling and Computer
Simulation (C-MMACS), Bangalore;
National Institute of Oceanography (NIO), Goa
Naval Physical and Oceanographic Laboratory (NPOL),
Cochin
Space Application Centre (SAC), Ahmedabad
Centre for Atmospheric Sciences, Indian Institute
of Technology, (IITD), New Delhi
Department of Science and Technology (DST), New
Delhi
Department of Ocean Development (DOD), New Delhi
Physical Research Laboratory (PRL), Ahmedabad
National Remote Sensing Agency (NRSA), Hyderabad
Department of Meteorology & Oceanography,
Andhra University (AU), Visakhapatnam
Department of Atmospheric Sciences, Cochin University
of Science & Technology, Kochi
Department of Geophysics, Banaras Hindu University,
Varanasi
Department of Physics, University of Pune
ICRP, as formulated in its Science Plan in 1996, is a multi-agency programme coordinated by the Department of Science and Technology, which is focussed on the following major objectives:
Understanding the physical processes responsible for variability on subseasonal, seasonal, interannual and decadal time scales of the monsoon, the oceans (specifically the Indian Seas and the equatorial Indian Ocean) and the coupled atmosphere-ocean-land system.
Study of the space-time variation of the monsoons from subseasonal, interannual to decadal scales for assessing the feasibility for climate prediction and development of methods for prediction.
Study of change in climate and its variability (on centennial and longer time scales) generated by natural and anthropogenic factors.
Investigation of the links between climate variability and critical resources such as agricultural productivity to provide a basis for deriving agricultural strategies for maximising the sustainable yield in the presence of climate variability and for realistic assessment of impact of climate change.
ICRP addresses the above objectives in three components, viz., (i) Monsoon Variability (MONVAR), (ii) Past Climates and Climate Change (PCCC) and (iii) Climate and Agriculture (CLIMAG). A majority of the activities under ICRP are directly relevant to AAMP interests.
A major highlight of the activities spearheaded
by the ICRP is the observational programme Bay of Bengal Monsoon Field
Experiment (BOBMEX) already completed and the Arabian Sea Monsoon Experiment
(ARMEX) which is in the final phase of planning. BOBMEX was successfully
carried out during July 16 through August 31, 1999. Two research vessels
and two deep ocean buoys were used as special observation platforms, with
simultaneous additional observational support from the coastal network.
Analysis of BOBMEX data is in progress and some results have already been
published. Under ARMEX, monsoon convection off the west coast of
India will be studied in Phase I. Phase II will focus on the pre-monsoon
southeastern Arabian Sea warm pool and its relationship with monsoon onset.
India has a long history of instrumental records of climatic data, with a large number of well-distributed observatories (557 surface, 35 RS/RW, 65 PB, 199 Agromet, 45 radiation, 5000 rainfall stations, etc.). Some of these observatories have surface data extending back to more than 130 years. Special scientific expeditions sent to Antarctica have taken systematic meteorological observations including vertical ozone profiling from the Indian stations. Satellite based observation and derived data are also available from INSAT. Marine meteorological data and data from special oceanographic cruises are also archived. The climate data are archived at the National Data Centre of IMD.
NIO has a long-term observational programme in the Indian seas. XBT observations are being carried out along 4 shipping routes, viz., Chennai-Port Blair, Kolkata-Port Blair, Bombay-Mauritius and Chennai-Singapore. The Bay of Bengal XBT lines will be enhanced to include met parameters, chlorophyll and phytoplankton. DOD has an ongoing programme on ocean observation systems to continuously monitor meteorological and oceanographic parameters from drifting and moored buoys. This programme is expected to be enhanced substantially in the next few years.
IITM organized a special Land Surface Processes Experiment (LASPEX) during 1997-99, in which a large amount of surface and upper air data have been collected for 2 years at five experimental sites in the Sabarmati river basin of Gujarat.
IMD has recently started a National Climate Centre (NCC) at Pune, for climate monitoring and diagnostics services. NCC brings out monthly and seasonal 'Climate Diagnostics Bulletin of India', and other publications related to extreme climatic events and special climatological reports.
IITM has developed long-period homogeneous monthly
rainfall data sets on sub-divisional/regional/all-India scale. These
data sets for the period 1871-1999 are available for download on http://www.tropmet.res.in.
Regional-mean monthly surface-air temperature data are also available at
the same web site for the period 1901-90.
The major institutes in the country extensively
dealing with modelling studies are IITM, NCMRWF, IITD, IISc, SAC, NIO,
CMMACS, AU, etc. These groups are involved in a variety of modelling
activities related to the monsoons. Extensive sensitivity studies
and experimental seasonal forecasts have been made at IITM using the COLA
and UKMO atmospheric general circulation models (GCMs). IITM participated
in the CLIVAR Asian-Australian Monsoon AGCM Inter-comparison Project to
study the impact of 1997-98 El Nino on the Asian monsoon. Different
groups have also been involved in model output diagnostics for validation
of monsoon simulations in atmospheric as well as coupled GCMs. Attempts
have been made to develop future scenarios for the monsoon using model
data from climate change experiments. Major programmes of work have
now been undertaken to use high-resolution regional climate models for
climate change scenario development for impact assessments. Several groups
have used basin scale ocean models to understand intraseasonal to interannual
variability of circulation and SST of the Indian Ocean.
IMD has been issuing operational seasonal
forecasts since 1988, of the Indian summer monsoon rainfall over the country
as a whole. The forecast is mainly based on a "power regression"
model based on 16 parameters. In the year 2000, the model was updated
by replacing four out of the 16 parameters. Prominent among the dropped
predictors was the April 500 hPa ridge location. IMD also issues
seasonal forecasts for a few homogenous monsoon regions, viz., northwest
India, peninsula, and northeast India. Experimental long-range forecasts
have also been attempted by some groups in the country, based on empirical
techniques, neural networks and GCMs.
The following are some of the major areas relevant to monsoon research, in which the various groups in the country are engaged:
Modelling studies will continue to be a major focus of monsoon research in the country, with the primary objectives (i) validating the monsoon simulations and identifying the biases, (ii) sensitivity studies of various regional/global forcings; (iii) model output diagnostics of monsoon processes; and (iv) future climatic scenario development. The coming years will also see a greater emphasis on the role of the Indian Ocean and the adjacent Indian seas in monsoon variability, by means of special observational studies. Development of long-period homogeneous observational data products on monsoon rainfall and related parameters with a higher spatial and temporal resolution will be actively pursued.
Yukio Masumoto
Department of Earth and Planetary Sciences, University of Tokyo, Tokyo
The Frontier Research System for Global Change (FRSGC) is investigating the atmosphere-ocean circulations and their variability associated with the Asian-Australian monsoon using atmospheric and/or oceanic GCMs and coupled GCMs. The Japan Meteorological Agency (JMA) also investigates the large-scale and the regional-scale variability in the atmospheric circulations and the predictability of the variability using the observed data and the numerical models. The intraseasonal variability in the tropical regions of the Indo-Pacific area, the seasonal variations in the Asian-Australian monsoon regions, and the interannual variations associated with the ENSO and the Indian Ocean Dipole Mode are the main targets of the research.
The Frontier Observational Research System for Global Change (FORSGC) is conducting intensive field observations in the Asia/Eurasian region and the Indian and the Pacific Oceans to investigate the atmosphere-ocean-land interactions associated with the climate variability in the Indo-Pacific sector. The atmosphere-land observations include (a) deployment of the in-situ automatic flux measurements network in the Eurasian continent, (b) Doppler radars, the wind profiler system, radiosonde observations in the eastern Asia (Meiyu or Baiu frontal zone) and the western tropical Pacific (the warm water pool region), and (c) the comprehensive network of the radiosonde observations, GPS water vapour measurements, and stable isotope hydrological measurements in the Asia/Pacific monsoon region as well as Aerosonde observations in the western tropical Pacific Ocean. The ocean observations are (a) ADCP mooring at 90E on the equator from November 2000 for at least 4 years, (b) about 10 ARGO floats deployment per year in the Indian Ocean and more in the Pacific Ocean, (c) several surface drifter deployments. In addition, the FORSGC and the JMA and the Fishery Agency jointly maintain three VOS XBT/XCTD lines in the Indian Ocean and the western tropical Pacific Ocean as well as several other XBT observations in the Indian Ocean by the voluntary ships. The Japan Marine Science and Technology Centre (JAMSTEC) is maintaining the TRITON buoys in the western tropical Pacific ocean and is planning to deploy two TRITON buoys in the tropical eastern Indian Ocean in October 2001. The R/V Mirai of JAMSTEC goes to the eastern Indian Ocean once a year.
There are other individual research activities on the A-A monsoons by the scientists in the universities. The above FRSGC and FORSGC projects are carrying out under the strong cooperation with the university scientists.
In-Sik Kang
Department of Atmospheric Sciences, Seoul National University, Seoul
Korea reports two sets of monsoon-related activities at the 2001 Asian-Australian Monsoon Panel. The first is the Asia-Pacific Economic Cooperation (APEC) Climate Network (APCN) initiated by Korea Meteorological Administration, and the second is the activities of new institute, the Climate Environment System Research Centre (CES) established in Seoul National University, September 2000. The objective of the APCN is to establish a climate network in the Asian-Pacific region and to produce experimental multi-model ensemble prediction for APEC member countries. It is expected that the APCN will gather the dynamical seasonal prediction products from Australia, Canada, China, Japan, Korea, Russia, USA, and Chinese Taipei to produce the multi-model ensemble seasonal prediction and disseminate the climate prediction information to APEC member countries. The APCN will particularly focus on the prediction of Asian summer Monsoon, which controls the regional climate over the Pacific-Asian sector.
The CES is a Korean national science centre endorsed by the Ministry of Science and Technology and financially supported by the Korean Science and Engineering Foundation for 9 years. The objective of the CES is to provide the tool of integrated prediction system for regional climate and atmospheric environment. The CES consists of three research groups: The process study group, atmospheric environment group, and the climate modelling and prediction group. The CES is a kind of virtual institute with a core facility at Seoul National University, which support twenty professors from six domestic universities. The CES will play as a Korean national focal point of various international climate programs, particularly WCRP/CLIVAR. It is particularly mentioned that the CES has been coordinating the Cyber Institute of Pacific-Asian Climate System (CIPACS) to promote international cooperative researches in the regional climate problems, particularly the East Asian Monsoon variability. At present, the scientists participating in the CIPACS are from various institutes in the Asia-Pacific region such as NASA, the University of Tokyo, Institute of Atmospheric Physics (IAP, China), The National Taiwan University, the University of Hawaii/IPRC, and others, and the CES provides a central facility for the CIPACS.
William K. M. Lau
Climate and Radiation Branch, NASA/GSFC, Greenbelt MD 20771
The Asian-Australian Monsoon (AAM) is an integral component of the earthĖs climate system, involving complex interactions of the atmosphere, the hydrosphere and the biosphere. Monsoon rainfall sustains life for more than 60% of the world population. The re-distribution of AAM heat sources and sinks may alter the large- scale circulation thus affecting weather and climate in regions far away from the AAM. Disruption in agricultural and industrial production, property damage and fatality, and spreading of diseases caused by AAM droughts and floods not only have devastating effects in monsoon countries, but also pose serious threats on the global economy, with possible security implications for the USA and other highly industrialized countries of the world. Understanding and improving the predictions of the monsoon are therefore extremely important and should be considered high- priority research with immediate benefit for mankind.
Recent studies have revealed that aspects of global climate change may be rooted in rising sea surface temperature and increased deep convection in the Indo-Pacific region. It is likely that a major impediment to making reliable projections of global warming may lie in our inability to understand and model the global re-distribution of AAM heat sources and sinks in global change scenarios. Therefore developing a strong AAM research program is paramount in meeting one of major goal of CLIVAR: to identify and understand the major patterns of climate variability on seasonal and long time scales, including climate change and evaluate their predictability and to improve their predictions.
Currently, CLIVAR has focused on natural variability of the coupled ocean-atmosphere system, while GEWEX has been devoted to interactions of the land and the atmosphere. Both programs are now poised to explore and exploit the predictability and predictions of components of the climate systems that involve full ocean-atmosphere-land-biosphere interactions. The AAM is therefore at the core of CLIVAR and GEWEX. US scientists have traditionally exerted strong leadership in international AAM research. However, this leadership will soon be forfeited unless an organized AAM research effort is put into place in the US. Given the importance of AAM in climate research and its linkages to various components of the US CLIVAR program, it is imperative that a coherent US strategy for studying the AAM be developed and integrated into the US CLIVAR program.
In this document, we present a 5-year research plan for the AAM under the US CLIVAR program. The AAM research plan is developed with the following overarching goal: To understand and predict AA-monsoon variability and its interaction with other parts of the EarthĖs climate system
The AAM research plan is discussed in terms of five components: empirical studies, modelling, process studies including field campaigns, long-term observations, and data initiatives. A summary of recommendations includes:
- Conduct empirical diagnostic studies to better understand monsoon-ocean processes in the Indian and western Pacific Oceans, monsoon-land processes over Eurasia and maritime continent, intraseasonal oscillations and global teleconnections associated with the redistribution of AAM heat sources and sinks.
- Carry out model intercomparison experiments using a hierarchy of models, especially coupled models, to explore physical mechanisms and predictability associated with slow changing boundary conditions at the ocean and land interfaces, and possible role of intraseasonal oscillations. Coordinate efforts in improving model physical representation of monsoon processes.
- Begin planning of a coupled ocean-atmosphere process study involving a field campaign in the tropical eastern Indian Ocean within the next 5 years in conjunction with related national and international programs.
- Design an observational network for long-term monitoring of the Indian Ocean in close cooperation with international CLIVAR and relevant global observation systems.
- Support a data mining effort to collect, standardize, archive and distribute historical data from all monsoon regions to provide comprehensive and research quality data to the scientific community.
Linkages of the US AAM research to international monsoon research especially to ongoing CLIVAR and GEWEX activities are emphasized. The research plan presented here is expected to be a dynamic one. The AAMWG will continue to work with the US CLIVAR panel to further develop and modify the research plan as the need arises.