scholarly journals A CGCM Study on the Northward Propagation of Tropical Intraseasonal Oscillation over the Asian Summer Monsoon Regions

2010 ◽  
Vol 21 (2) ◽  
pp. 299 ◽  
Author(s):  
Shu-Ping Weng ◽  
Jin-Yi Yu
Keyword(s):  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Intraseasonal Oscillation ◽  
Northward Propagation ◽  
Asian Summer ◽  
Tropical Intraseasonal Oscillation

scholarly journals Subseasonal Variability Associated with Asian Summer Monsoon Simulated by 14 IPCC AR4 Coupled GCMs

2008 ◽  
Vol 21 (18) ◽  
pp. 4541-4567 ◽  
Author(s):  
Jia-Lin Lin ◽  
Klaus M. Weickman ◽  
George N. Kiladis ◽  
Brian E. Mapes ◽  
Siegfried D. Schubert ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
General Circulation ◽  
Asian Summer Monsoon ◽  
Intraseasonal Oscillation ◽  
Climate Simulation ◽  
Boreal Summer ◽  
Subseasonal Variability ◽  
Wide Range ◽  
Northward Propagation ◽  
Asian Summer

Abstract This study evaluates the subseasonal variability associated with the Asian summer monsoon in 14 coupled general circulation models (GCMs) participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). Eight years of each model’s twentieth-century climate simulation are analyzed. The authors focus on the three major components of Asian summer monsoon: the Indian summer monsoon (ISM), the western North Pacific summer monsoon (WNPSM), and the East Asian summer monsoon (EASM), together with the two dominant subseasonal modes: the eastward- and northward-propagating boreal summer intraseasonal oscillation (BSIO) and the westward-propagating 12–24-day mode. The results show that current state-of-the-art GCMs still have difficulties and display a wide range of skill in simulating the subseasonal variability associated with Asian summer monsoon. During boreal summer (May–October), most of the models produce reasonable seasonal-mean precipitation over the ISM region, but excessive precipitation over the WNPSM region and insufficient precipitation over the EASM region. In other words, models concentrate their rain too close to the equator in the western Pacific. Most of the models simulate overly weak total subseasonal (2–128 day) variance, as well as too little variance for BSIO and the 12–24-day mode. Only 4–5 models produce spectral peaks in the BSIO and 12–24-day frequency bands; instead, most of the models display too red a spectrum, that is, an overly strong persistence of precipitation. For the seven models with three-dimensional data available, five reproduce the preconditioning of moisture in BSIO but often with a too late starting time, and only three simulate the phase lead of low-level convergence. Interestingly, although models often have difficulty in simulating the eastward propagation of BSIO, they tend to simulate well the northward propagation of BSIO, together with the westward propagation of the 12–24-day mode. The northward propagation in these models is thus not simply a NW–SE-tilted tail protruding off of an eastward-moving deep-tropical intraseasonal oscillation.

Intraseasonal Forecasting of the Asian Summer Monsoon in Four Operational and Research Models*

2013 ◽  
Vol 26 (12) ◽  
pp. 4186-4203 ◽  
Author(s):  
Xiouhua Fu ◽  
June-Yi Lee ◽  
Bin Wang ◽  
Wanqiu Wang ◽  
Frederic Vitart
Keyword(s):  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Intraseasonal Oscillation ◽  
Monsoon Trough ◽  
Prediction Skill ◽  
Boreal Summer ◽  
International Programs ◽  
Anomaly Correlation Coefficient ◽  
Asian Summer ◽  
The University

Abstract The boreal summer intraseasonal oscillation (BSISO) is a dominant tropical mode with a period of 30–60 days, which offers an opportunity for intraseasonal forecasting of the Asian summer monsoon. The present study provides a preliminary, yet up-to-date, assessment of the prediction skill of the BSISO in four state-of-the-art models: the ECMWF model, the University of Hawaii (UH) model, the NCEP Climate Forecast System, version 2 (CFSv2), and version 1 for the 2008 summer (CFSv1), which is a common year of two international programs: the Year of Tropical Convection (YOTC) and Asian Monsoon Years (AMY). The mean prediction skill over the global tropics and Southeast Asia for first three models reaches about 1–2 (3) weeks for BSISO-related rainfall (850-hPa zonal wind), measured as the lead time when the spatial anomaly correlation coefficient drops to 0.5. The skill of CFSv1 is consistently lower than the other three. The strengths and weaknesses of the CFSv2, UH, and ECMWF models in forecasting the BSISO for this specific year are further revealed. The ECMWF and UH have relatively better performance for northward-propagating BSISO when the initial convection is near the equator, although they suffer from an early false BSISO onset when initial convection is in the off-equatorial monsoon trough. However, CFSv2 does not have a false onset problem when the initial convection is in monsoon trough, but it does have a problem with very slow northward propagation. After combining the forecasts of CFSv2 and UH into an equal-weighted multimodel ensemble, the resultant skill is slightly better than that of individual models. An empirical model shows a comparable skill with the dynamical models. A combined dynamical–empirical ensemble advances the intraseasonal forecast skill of BSISO-related rainfall to three weeks.

scholarly journals Real-time multivariate indices for the boreal summer intraseasonal oscillation over the Asian summer monsoon region

2012 ◽  
Vol 40 (1-2) ◽  
pp. 493-509 ◽  
Author(s):  
June-Yi Lee ◽  
Bin Wang ◽  
Matthew C. Wheeler ◽  
Xiouhua Fu ◽  
Duane E. Waliser ◽  
...  
Keyword(s):  
Real Time ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Intraseasonal Oscillation ◽  
Boreal Summer ◽  
Monsoon Region ◽  
Boreal Summer Intraseasonal Oscillation ◽  
Asian Summer ◽  
Summer Monsoon Region

scholarly journals The First Transition of the Asian Summer Monsoon, Intraseasonal Oscillation, and Taiwan Mei-yu

2008 ◽  
Vol 21 (7) ◽  
pp. 1552-1568 ◽  
Author(s):  
Chih-wen Hung ◽  
Huang-Hsiung Hsu
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Intraseasonal Oscillation ◽  
Eastern Africa ◽  
Monsoon Circulation ◽  
Close Monitoring ◽  
Maritime Continent ◽  
The Indian Ocean ◽  
Asian Summer

Abstract This study reveals the close relationship between the first transition of the Asian summer monsoon (ASM), the tropical intraseasonal oscillation (TISO), and the mei-yu in Taiwan, which occurs climatologically between mid-May and mid-June. For about half of the years in 1958–2002, the first transition of the Asian summer monsoon can be classified as a sharp onset, which is characterized by an abrupt reversal of the monsoon flow from northeasterly to southwesterly. The evolution of the large-scale monsoon circulation and convection in the sharp-onset years is characterized by an eastward-propagating TISO from eastern Africa and the western Indian Ocean to the Maritime Continent. Upon the arrival of the TISO in the Maritime Continent, a sharp onset of the ASM occurs, and a channel supplying moist air in the lower troposphere is well established across the Indian Ocean to the South China Sea (SCS). This channel consists of the Somali jet, transporting the moisture from the Southern Hemisphere to the Northern Hemisphere, and the southwesterly monsoon, delivering the moisture across the Indian Ocean to the SCS and the western North Pacific. This efficient and persistent transport of moisture to the SCS and surrounding areas presumably provides a favorable condition for the maintenance of the mei-yu front and the development of convective systems. This also marks the onset of the Taiwan mei-yu season. Because a strong TISO signal, which tends to occur concurrently with the sharp onset of the ASM, is often observed prior to the onset of the first transition and Taiwan mei-yu, a close monitoring of the TISO can be informative for the weather forecasters in Taiwan to project the initiation of the Taiwan mei-yu.

scholarly journals Predictability Studies of the Intraseasonal Oscillation with the ECHAM5 GCM

2005 ◽  
Vol 62 (9) ◽  
pp. 3320-3336 ◽  
Author(s):  
Stefan Liess ◽  
Duane E. Waliser ◽  
Siegfried D. Schubert
Keyword(s):  
Summer Monsoon ◽  
Zonal Wind ◽  
Asian Summer Monsoon ◽  
Intraseasonal Oscillation ◽  
Empirical Orthogonal Functions ◽  
Breeding Method ◽  
Potential Predictability ◽  
Control Simulation ◽  
Upper Limit ◽  
Asian Summer

Abstract Our ability to predict active and break periods of the Asian summer monsoon is intimately tied to our ability to predict the intraseasonal oscillation (ISO). The present study analyzes the upper limit of potential predictability of the northern summer ISO, as it is simulated by the ECHAM5 atmospheric general circulation model forced with climatological SSTs. The leading extended empirical orthogonal functions of precipitation, computed from a 10-yr control simulation, are used to define four different phases of the ISO. Fourteen-member ensembles of 90-day hindcasts are run for each phase of the three strongest ISO events identified in the 10-yr control run. Initial conditions for each ensemble are created from the control simulation using a breeding method. The signal-to-noise ratio is analyzed over a region that covers the core of the Asian summer monsoon activity. Over Southeast Asia, the upper limit for predictability of precipitation and 200-hPa zonal wind is about 27 and 33 days, respectively. Over India, values of more than 15 days occur for both variables. A spatial analysis of the different phases of the ISO reveals that the predictability follows the eastward- and northward-propagating ISO during the active and break phases of the monsoon. Precipitation reveals increased predictability at the end of the convective phase. Analogous, 200-hPa zonal wind shows strongest predictability during low and easterly anomalies. This potential predictability is considerably higher than for numerical forecasts of typical weather variations, particularly for the Tropics, indicating that useful forecasts of monsoon active and break events may be possible with lead times of more than two weeks for precipitation and the dynamics. A closer look at the breeding method used here to initialize the hindcasts shows the importance of appropriate ensemble experiment designs.

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