Atmospheric Sciences [A]

A33A  CC:8  Wednesday  1330h

Asian-Australian Monsoon: Interannual Variability


Presiding: M C Wheeler, Australian Bureau of Meteorology; H H Hendon, Australian Bureau of Meteorology

A33A-01 INVITED

Level and Source of Predictability of Seasonal Rainfall Anomalies In Malaysia

* Tangang, F (tangang@ukm.my), National University of Malaysia, School of Environmental and Natural Resource Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi Selangor, Bangi, 43600, Malaysia
Juneng, L (juneng@ukm.my), National University of Malaysia, School of Environmental and Natural Resource Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi Selangor, Bangi, 43600, Malaysia

The establishment of a long-range seasonal forecasting system for seasonal precipitation anomaly in Malaysia is of practical relevance. This paper describes a development of a forecast model for seasonal precipitation anomaly in Malaysia based on the canonical correlation analysis technique (CCA). Based on ~50 years of data, the predictive skills of five predictor fields i.e., the precipitation itself, local sea surface temperature (SST), quasi- global SST, sea level pressure and northern 700 hPa geopotential height to predict seasonal anomalous rainfall in Malaysia were investigated. The sequence of four consecutive 3-month predictor fields was used to capture the evolutionary features in the predictor fields. The skills were measured based on correlation coefficient values between observed and predicted precipitation anomalies, estimated in hindcast mode using the one-year-out version of the cross-validation technique. Based on a series of experiment, it was found that the model with quasi-SST predictor alone produced the most favorable results. However the skills showed seasonal and spatial variations with higher skills were found during the Northern Hemisphere winter season and concentrated over East Malaysian region (northern Borneo). The averaged skills for 5 months lead time for this region were between 0.3-0.5 with much lower skills ( < 0.3) for Peninsular Malaysia. Interestingly, these patterns of predictability were very much El Nino-Southern Oscillation (ENSO) -related.


A33A-02

Real-time Monitoring and Forecast Experiments of the Asian-Austrian Monsoons at the NOAA Climate Prediction Center

* Zhang, Q (Qin.Zhang@noaa.gov), NOAA Climate Prediction Center, 5200 Auth Road, Room 800, Camp Springs, MD 20746, United States
Yang, S (Song.Yang@noaa.gov), NOAA Climate Prediction Center, 5200 Auth Road, Room 800, Camp Springs, MD 20746, United States
Chelliah, M (Muthuvel.Chelliah@noaa.gov), NOAA Climate Prediction Center, 5200 Auth Road, Room 800, Camp Springs, MD 20746, United States

Variability of the Asian-Australian monsoon (AAM) system affects not only the weather and climate over Asia and Australia but also the global climate. Prediction of the AAM on seasonal and intraseasonal timescales is a challenge for both research and operational communities. Developing objective tools to assist seasonal and intraseasoanl monsoon prediction is one of the goals of AAM monitoring and forecast experiments. Real-time monitoring and forecast of AAM have been conducted at the NOAA Climate Prediction Center (CPC) where various products have been developed to monitor the global monsoon systems. Seasonal, monthly, and weekly means and anomalies of different variables including precipitation, outgoing longwave radiation, 800-hPa and 200-hPa winds, sea surface temperature, 2-m temperature, soil moisture, and 200-hPa velocity potential are derived from the NCEP reanalysis-2 and other data sources. Accumulated and anomalous rainfalls over the lands averaged in 5x5 degree longitude-latitude boxes are calculated from the CPC United precipitation daily data. Several commonly-used dynamical monsoon indices have been chosen to monitor and forecast the different monsoon components of the AAM system. The Webster-Yang monsoon index measures the variability of large- scale features of the Asian monsoon circulation. The South Asia monsoon index focuses better on the monsoons over India and the Bay of Bengal. Meanwhile, the dynamical Indian monsoon index is a good indictor for the change in the atmospheric circulation associated with the Indian monsoon system. The East Asian-Northwestern Pacific monsoon index not only monitors and forecasts the interannual variability of the East Asian monsoon but also depicts the intraseasonal evolution of the monsoon. The Australian monsoon index reflects the variability of the monsoon rainfall over northern Australia very well. The two-week predictions of these monsoon indices at CPC, which is updated daily, are based on the ensemble means of 20 members of the NCEP Global Forecast System. Monthly-seasonal forecasts, updated three times a month, are derived from the NCEP coupled Climate Forecast System. Combinations of these predictions and the regression patterns of winds and precipitation against the indices yield useful weeks-month range outlooks of the AAM.

http://www.cpc.noaa.gov/products/Global_Monsoons/Global-Monsoon.shtml


A33A-03

Active and Break Periods of the Australian Monsoon

* Hakeem, S H (h.shaik@bom.gov.au), Australian Bureau of Meteorology, PO Box 40050 Casuarina, Darwin, NT 0810, Australia
Cleland, S J (s.cleland@bom.gov.au), Australian Bureau of Meteorology, PO Box 40050 Casuarina, Darwin, NT 0810, Australia

Several criteria to define or identify the onset, active or break periods of the monsoon over the region have been proposed by a number of researchers. The methods adopted in the past range from using rainfall only; wind only; wind and rainfall; wind, rainfall and cloudiness; and westward propagating large scale disturbances. Four operational techniques of monsoon monitoring have been developed in the Darwin Regional Specialized Meteorological Centre. Two methods use the rainfall only criteria and look into the onset of wet season rainfall/monsoon rainfall. The other two methods are based purely on wind data. The techniques developed in this study are modified versions of the original research presentations by the respective authors. Modifications were warranted to reflect the changes to the observational network since then and to also calculate and make the results available on a near real time basis. These techniques are in trial for the past 3 years in Darwin. Except for one technique that provides only the date of onset, the other techniques could be used to monitor the progress of monsoon through the season. The techniques were used to obtain onset, active periods of monsoon for a period of 20 years. The number of active bursts, the frequency of active and break periods in relation to the ENSO state are presented. All the three techniques used in the study are in agreement with the active and inactive periods, though there was a little disagreement on the onset and cessation date of the active convection. In general, the active periods range from ten days to one day. During 2006-07 and 2007-08 seasons, there were six active periods ranging from 10- day to one-day spells.


A33A-04

Interannual Variability in the Seasonal Northward Shift of the Baiu Front

* Tomita, T (tomita@sci.kumamoto-u.ac.jp), Graduate School of Science and Technology / Kumamoto Univ., Kurokami 2-39-1, Kumamoto, 860-8555, Japan
* Tomita, T (tomita@sci.kumamoto-u.ac.jp), FRCGC / JAMSTEC, Kanazawa-ku, Showa-machi 3173-25, Yokohama, 236-0001, Japan
Nonaka, M (nona@jamstec.go.jp), FRCGC / JAMSTEC, Kanazawa-ku, Showa-machi 3173-25, Yokohama, 236-0001, Japan
Yamaura, T (info@spherewind.com), Graduate School of Science and Technology / Kumamoto Univ., Kurokami 2-39-1, Kumamoto, 860-8555, Japan

The Baiu (Japanese)/Mei-yu (Chinese)/Changma (Korean) front moves northward from May to July in the East Asia-North Pacific sector. The seasonal march exhibits an interannual tendency, that is, the polarity of Baiu precipitation anomalies turnabout from May to June and keep it from June to July. The turnabout in the anomaly field occurs in the seasonal northward shift of the mean Baiu front over the surface divergence anomalies that are maintained by the tropical sea surface temperature anomalies (SSTAs) due to the El Niño/Southern Oscillation. The deep mixed layer depth (MLD) in the western tropical Pacific is responsible for the persistence of the SSTAs there and further the surface divergence anomalies in the western North Pacific. When the MLD is deep, the ocean with large thermal and dynamical inertia can affect the atmosphere, while when the MLD is shallow, the atmosphere oppositely changes the temperature anomalies in the shallow surface oceanic mixed layer. Thus, the air-sea correlation is changed from May to June to the north of 20˚N. The interannual tendency in the seasonal northward shift of the Baiu front would contribute to raise the predictability of the Baiu front, that is, the early summer climate in East Asia.


A33A-05

The Monsoon as an Antisymmetric Response to Convective Heating

* McBride, J L (J.mcbride@bom.gov.au), Centre for Australian Weather and Climate Research, 700 Collins St Docklands, Melbourne, Vic 3001, Australia
Williams, M (Mark.Williams@bom.gov.au), Bureau of Meteorology, 1010 Latrobe St Docklands, Melbourne, Vic 3001, Australia
Prabowo, M R (m.prabowo@bmg.go.id), Akademi Meteorologi dan Geofisika, Jl. Perhubungan I No. 5 Komplek Meteo DEPHUB, Tangerang, 15221, Indonesia

It was demonstrated by Gill in the 1980's that the large scale lower tropospheric structure of the monsoon can be interpreted as a dynamical response of equatorially trapped waves to latent heat release. The structure of the response is such that heating symmetric with respect to the equator excites waves that have a symmetric response in the zonal component of the wind and antisymmetric in the meridional component. Conversely antisymmetric heating excites a response antisymmetric in zonal wind and symmetric in meridional wind. The Outgoing Longwave radiation fields and the low level wind (from operational numerical weather prediction analyses) have been decomposed into these symmetric and antisymmetric structures over a period of seven complete years. Examining the annual cycle it is demonstrated that the structure of the northern hemisphere summer monsoon is dominated by the Rossby wave n=2 response to the antisymmetric heating by convection in the Summer Hemisphere. The Southern Summer monsoon over the maritime continent has structural components of both the symmetric and the antisymmetric equatorial waves. Interannual variability is examined over the maritime continent for a 25 year period. It is found that the antisymmetric heating follows a regular annual cycle with little interannual variability. The variability associated with ENSO is reflected in the symmetric heating and so in the response in the symmetric component of the zonal wind field. A conceptual framework emerges whereby the monsoon component of the circulation is defined in terms of an annual cycle of antisymmetric heating and zonal wind. It is shown that this definition is useful in defining monsoonal flow regimes. It is also shown this framework is useful in understanding the response of the monsoon regime to ENSO.


A33A-06

Analyze of climate change In Java as impact global warming

* makmur, e (erwin_makmur@yahoo.com), Indonesia Meteorological and Geophysical Agency, Jl. Angkasa 1 no. 2, Jakarta, Indonesia
tamto, S (sttsw@yahoo.com), Indonesia Meteorological and Geophysical Agency, Jl. Angkasa 1 no. 2, Jakarta, Indonesia

Meteorological and Geophysical Agency (BMG) of Indonesia releases two kinds of Seasonal Forecasts every year namely Dry Season Forecast which is released every early March and Rainy Season Forecast which is released every early September. Based on classified monthly average rainfall distribution pattern, BMG identifies whole Indonesia region as follows : Area which has noticeable difference between the dry and rainy seasons according to the seasonal criteria, namely Seasonal Area (SA). Area which has no clear difference between the dry and rainy seasons according to the seasonal criteria, namely Non Seasonal Area (Non SA). Onset of Dry Season is determined based on the cumulative rainfall within 10 (ten) days is less than 50 millimeters successively. The onset of dry season is probably earlier, equal, or late than normal. Onset of Rainy Season is determined based on the cumulative rainfall is equal or more than 50 millimeters successively. The onset of rainy season is probably occur earlier, equal, or late than normal. Dasarian are time period for ten days. It is divided into 3 (three) "dasarian", i.e. : 1st "dasarian" from 1st date until 10th date, 2nd "dasarian" from 11th date until 20th date and 3rd "dasarian" from 21st date until the end of the month. The Cumulative Rainfall Respectives to Normal is comparison of cumulative rainfall during particularly period (one rainy season period or one dry season period) and normal, It is divided into 3 (three) categories, i.e. : Above Normal (AN) if the cumulative rainfall is greater than 115% toward the average Normal (N) if the cumulative rainfall is between 85% and 115% toward the average Below Normal (BN) if the cumulative rainfall is smaller than 85% toward the average Climate condition in Indonesia depends on the atmosphere dynamics condition such as monsoon circulation and the sea surface temperature over Indonesia pool, it is also influenced by regional and global climate phenomenon Based on normal data (average 1950 2000), we analyze that area over the Java island have changed for long period of season (dry and wet season), the onset of season, and cumulative rainfall within particularly period.