scholarly journals Long-Term Variations of Broad-Scale Asian Summer Monsoon Circulation and Possible Causes

2013 ◽  
Vol 26 (22) ◽  
pp. 8947-8961 ◽  
Author(s):  
Zhiyan Zuo ◽  
Song Yang ◽  
Renhe Zhang ◽  
Pinping Jiang ◽  
Li Zhang ◽  
...  
Keyword(s):  
Global Warming ◽  
Indian Ocean ◽  
Interannual Variability ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Vertical Shear ◽  
Tropospheric Temperature ◽  
The Indian Ocean ◽  
Asian Summer ◽  
Broad Scale

Abstract The widely applied Webster–Yang index (WYI), which measures the broad-scale dynamical features of the Asian summer monsoon (ASM), has experienced robust interannual and interdecadal variations and a decreasing tendency, with apparent shifts in 1972. The WYI exhibits moderate variability and frequent positive phases before 1972, intensive interannual variability during 1972–98, and an obvious decreasing tendency and mainly negative phase afterward. The vertical shear easterly anomalies over the tropics/subtropics and the anomalous vertical shear anticyclonic circulation over Eurasia (Eu) are the background for the decreasing WYI, associated with reduced summer precipitation around the Bay of Bengal and Sumatra. On interdecadal time scales, the negative (positive) Atlantic multidecadal oscillation (AMO) is characterized by cooling (warming) in Eurasian tropospheric temperature (TT) via the North Atlantic Oscillation. Global warming manipulates the increasing tendency and the interannual variability of TT over the Indian Ocean (IO). The mutual effects of AMO on Eurasian TT and global warming on Indian Ocean TT correspond to the similar decreasing tendency and interdecadal shift of the difference in TT between Eurasia and the Indian Ocean (EuTT − IOTT) with those of the ASM. Thus, the AMO and global warming seem to cause the interdecadal variability of ASM. Although the interannual relationship between Niño-3 SST and ASM weakens recently as a result of the weakening tendency of ASM, the Niño-3 SST still plays an important role in ASM variability via EuTT − IOTT anomalies. In addition, the WYI in the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis shows a larger decreasing tendency for 1999–2010 compared to other reanalysis products, a plausible reason for the inconsistent variations between land–sea thermal contrast and the NCEP–NCAR WYI during that period.

scholarly journals Delivery of halogenated very short-lived substances from the West Indian Ocean to the stratosphere during Asian summer monsoon

2017 ◽  
Author(s):  
Alina Fiehn ◽  
Birgit Quack ◽  
Helmke Hepach ◽  
Steffen Fuhlbrügge ◽  
Susann Tegtmeier ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Summer Monsoon ◽  
Asian Monsoon ◽  
Asian Summer Monsoon ◽  
Source Region ◽  
West Indian ◽  
The West ◽  
West Indian Ocean ◽  
Asian Summer

Abstract. Halogenated very short-lived substances (VSLS) are naturally produced in the ocean and emitted to the atmosphere. When transported to the stratosphere, these compounds can have a significant influence on the ozone layer and climate. During a research cruise on RV Sonne in the subtropical and tropical West Indian Ocean in July and August 2014, we measured the VSLS, methyl iodide (CH3I) and for the first time bromoform (CHBr3) and dibromomethane (CH2Br2), in surface seawater and the marine atmosphere to derive their emission strengths. Using the Lagrangian transport model Flexpart with ERA-Interim meteorological fields, we calculated the direct contribution of observed VSLS emissions to the stratospheric halogen burden during Asian summer monsoon. Furthermore, we compare the in situ calculations with the interannual variability of transport from a larger area of the West Indian Ocean surface to the stratosphere for July 2000–2015. We found that the West Indian Ocean is a strong source region for CHBr3 (910 pmol m−2 h−1), very strong for CH2Br2 (930 pmol m−2 h−1), and average for CH3I (460 pmol m−2 h−1). The atmospheric transport from the tropical West Indian Ocean surface to the stratosphere experiences two main pathways. On very short timescales, especially relevant for the shortest-lived compound CH3I (3.5 days lifetime), convection above the Indian Ocean lifts oceanic air masses and VSLS towards the tropopause. On a longer timescale, the Asian summer monsoon circulation transports oceanic VSLS towards India and Bay of Bengal, where they are lifted with the monsoon convection and reach stratospheric levels in the southeastern part of the Asian monsoon anticyclone. This transport pathway is more important for the longer-lived brominated compounds (17 and 150 days lifetime for CHBr3 and CH2Br2). The entrainment of CHBr3 and CH3I from the West Indian Ocean to the stratosphere during Asian summer monsoon is less than from previous cruises in the tropical West Pacific Ocean during boreal autumn/early winter, but higher than from the tropical Atlantic during boreal summer. In contrast, the projected CH2Br2 entrainment was very high because of the high emissions during the West Indian Ocean cruise. The 16-year July time series shows highest interannual variability for the short-lived CH3I and lowest for the long-lived CH2Br2. During this time period, a small increase of VSLS entrainment from the West Indian Ocean through the Asian monsoon to the stratosphere is found. Overall, this study confirms that the subtropical and tropical West Indian Ocean is an important source region of halogenated VSLS, especially CH2Br2, to the troposphere and stratosphere during the Asian summer monsoon.

scholarly journals Re-Examination of the Decadal Change in the Relationship between the East Asian Summer Monsoon and Indian Ocean SST

Atmosphere ◽  
2018 ◽  
Vol 9 (10) ◽  
pp. 395 ◽  
Author(s):  
Seogyeong Kim ◽  
Kyung-Ja Ha ◽  
Ruiqiang Ding ◽  
Jiangping Li
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Southern Oscillation ◽  
Asian Summer Monsoon ◽  
Low Frequency ◽  
Decadal Change ◽  
Remote Forcing ◽  
The Indian Ocean ◽  
Asian Summer ◽  
The Relationship

This study examines the decadal change in the relationship between two major Indian Ocean (IO) sea surface temperature patterns, namely the Indian Ocean dipole (IOD) and northern IO and the East Asia summer monsoon (EASM) in the early 2000s. In 1991–1999, the former epoch, the interannual variability of EASM was associated with the IOD-like pattern in the original paper and its relationship weakened in 2000–2016. There are two possible causes for this decadal change; stronger land-sea thermal contrast as a local forcing in latter epoch, which may result in the weakening of the relationship between the IO and the EASM. In addition, the influence of El Niño-southern Oscillation (ENSO) on the western North Pacific subtropical high (WNPSH) could be changed depending on the frequency of ENSO. In the 2000s, the intensity of the low frequency (LF)-type ENSO (42–86 months period) events was weaker compared to the former epoch but that of quasi-biennial (QB)-type ENSO (16–36 months period) remained persistent. This could explain that the QB-type ENSO is remote forcing that modulates the change in the relationship between the tropical IO patterns and EASM in the 2000s.

scholarly journals Impact of the Indian Ocean SST basin mode on the Asian summer monsoon

2007 ◽  
Vol 34 (2) ◽  
Author(s):  
Jianling Yang ◽  
Qinyu Liu ◽  
Shang-Ping Xie ◽  
Zhengyu Liu ◽  
Lixin Wu
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Basin Mode ◽  
The Indian Ocean ◽  
Asian Summer

scholarly journals Parametric Sensitivity Analysis for the Asian Summer Monsoon Precipitation Simulation in the Beijing Climate Center AGCM, Version 2.1

2015 ◽  
Vol 28 (14) ◽  
pp. 5622-5644 ◽  
Author(s):  
Ben Yang ◽  
Yaocun Zhang ◽  
Yun Qian ◽  
Tongwen Wu ◽  
Anning Huang ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Western Pacific ◽  
Evaporation Coefficient ◽  
Precipitation Climatology ◽  
Simulated Precipitation ◽  
Asian Summer ◽  
Precipitation Anomalies

Abstract In this study, the authors apply an efficient sampling approach and conduct a large number of simulations to explore the sensitivity of the simulated Asian summer monsoon (ASM) precipitation, including the climatological state and interannual variability, to eight parameters related to the cloud and precipitation processes in the Beijing Climate Center AGCM, version 2.1 (BCC_AGCM2.1). The results herein show that BCC_AGCM2.1 has large biases in simulating the ASM precipitation. The precipitation efficiency and evaporation coefficient for deep convection are the most sensitive parameters in simulating the ASM precipitation. With optimal parameter values, the simulated precipitation climatology could be remarkably improved, including increased precipitation over the equatorial Indian Ocean, suppressed precipitation over the Philippine Sea, and more realistic mei-yu distribution over eastern China. The ASM precipitation interannual variability is further analyzed, with a focus on the ENSO impacts. It is shown that simulations with better ASM precipitation climatology can also produce more realistic precipitation anomalies during El Niño–decaying summer. In the low-skill experiments for precipitation climatology, the ENSO-induced precipitation anomalies are most significant over continents (vs over ocean in observations) in the South Asian monsoon region. More realistic results are derived from the higher-skill experiments with stronger anomalies over the Indian Ocean and weaker anomalies over India and the western Pacific Ocean, favoring more evident easterly anomalies forced by the tropical Indian Ocean warming and stronger Indian Ocean–western Pacific teleconnection as observed. The model results reveal a strong connection between the simulated ASM precipitation climatological state and interannual variability in BCC_AGCM2.1 when key parameters are perturbed.

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.

Linking Observations of the Asian Monsoon to the Indian Ocean SST: Possible Roles of Indian Ocean Basin Mode and Dipole Mode

2010 ◽  
Vol 23 (21) ◽  
pp. 5889-5902 ◽  
Author(s):  
Jianling Yang ◽  
Qinyu Liu ◽  
Zhengyu Liu
Keyword(s):  
Indian Ocean ◽  
Atmospheric Circulation ◽  
Summer Monsoon ◽  
Asian Monsoon ◽  
Asian Summer Monsoon ◽  
Ocean Basin ◽  
Indian Ocean Basin Mode ◽  
Basin Mode ◽  
The Indian Ocean ◽  
Asian Summer

Abstract The authors investigate the relationship between sea surface temperature (SST) in the tropical Indian Ocean (TIO) and the seasonal atmosphere circulation in the Asian monsoon region (AMR) using the maximum covariance analyses (MCAs). The results show that the Asian monsoon circulation is significantly correlated with two dominant SST anomaly (SSTA) modes: the Indian Ocean Basin mode (IOB) and the Indian Ocean dipole mode (IOD). The peak SSTA of the IOB appears in spring and has a much stronger relationship with the Asian summer monsoon than the peak of the IOD does, whereas the peak SSTA for the IOD appears in fall and shows a stronger link to the Asian winter monsoon than to the Asian summer monsoon. In addition, the IOB in spring has a relatively stronger link with the atmospheric circulation in summer than in other seasons. The large-scale atmospheric circulation and SSTA patterns of the covariability of the first two dominant MCA modes are described. For the first MCA mode, a warm IOB, persists from spring to summer, and the atmospheric circulation is enhanced by the establishment of the climatological summer monsoon. The increased evaporative moisture associated with the warm IOB is transported to South Asia by the climatological summer monsoon, which increases the moisture convergence toward this region, leading to a significant increase in summer monsoon precipitation. For the second MCA mode, a positive IOD possibly corresponds to a weaker Indian winter monsoon and more precipitation over the southwestern and eastern equatorial TIO.

scholarly journals Relative Roles of Land–Sea Distribution and Orography in Asian Monsoon Intensity

2009 ◽  
Vol 66 (9) ◽  
pp. 2714-2729 ◽  
Author(s):  
Zhongfeng Xu ◽  
Congbin Fu ◽  
Yongfu Qian
Keyword(s):  
Indian Ocean ◽  
South Asian ◽  
Summer Monsoon ◽  
Large Scale ◽  
Asian Monsoon ◽  
Asian Summer Monsoon ◽  
Monsoon Circulation ◽  
Eurasian Continent ◽  
The Indian Ocean ◽  
Asian Summer

Abstract The relative impacts of various land–sea distributions (LSDs) and mountains on Asian monsoon extent and intensity are assessed using a series of AGCM simulations. The air–sea coupling effects are not considered in this study. All simulations were integrated with zonal mean SST, globally uniform vegetation, soil color, and, except several simulations, soil texture. The results show that the LSD plays a more fundamental role than orography in determining the extent of Asian and African monsoons. The tropical zonal LSD and Asian mountains both play a crucial role for establishing summer monsoon convection over the South Asian region. The monsoon circulation index (MCI1) defined by the difference of zonal wind between 850 and 200 hPa is used to measure the intensity of the South Asian summer monsoon. The large-scale meridional land–sea thermal contrast between the Eurasian continent and the Indian Ocean only induces a 1.8 m s−1 increase of MCI1. The presence of the Indian subcontinent and Indochina peninsula (Asian mountains), however, induces a 6.6 (7.4) m s−1 increase of MCI1 associated with the release of latent heat of condensation. Clearly, the tropical subcontinental-scale zonal LSD and the Asian mountains almost equally contribute to the increase of MCI1 and play a more important role than the large-scale meridional LSD between the Eurasian continent and the Indian Ocean. Possible mechanisms of how the tropical subcontinental-scale zonal LSD and Asian mountains impact the Asian summer monsoon circulation and precipitation are also discussed.

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