The Asian summer monsoon response to the La Niña event of 2010

2012 ◽  
Vol 19 (2) ◽  
pp. 216-225 ◽  
Author(s):  
Milind Mujumdar ◽  
B. Preethi ◽  
T. P. Sabin ◽  
Karumuri Ashok ◽  
Sajjad Saeed ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
La Niña ◽  
La Nina ◽  
Asian Summer ◽  
La Nina Event

scholarly journals Influence of Asian Summer Monsoon Anticyclone on the Trace gases and Aerosols over Indian region

2019 ◽  
Author(s):  
Ghouse Basha ◽  
M. Venkat Ratnam ◽  
Pangaluru Kishore ◽  
S. Ravindrababu ◽  
Isabella Velicogna
Keyword(s):  
Summer Monsoon ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Asian Summer Monsoon ◽  
Monsoon Season ◽  
Trace Gases ◽  
La Niña ◽  
La Nina ◽  
Asian Summer

Abstract. The Asian Summer Monsoon Anticyclone (ASMA) persisting during monsoon season in the upper troposphere and lower stratosphere (UTLS) region play an important role in confining the trace gases and aerosols for a longer period thus affects regional and global climate. Our understanding on these trace gases and aerosols variability in the ASMA is limited. In this study, the effect of the ASMA on the trace gases (Water Vapour (WV), Ozone (O3), Carbon Monoxide (CO)) and aerosols (Attenuated Scattering Ratio (ASR)) obtained from long-term (2006–2016) satellite measurements is investigated. Since the ASMA is present in the UTLS region, its influence on the tropopause characteristics is also explored. Higher tropopause altitude, WV, CO and ASR confining to the ASMA region is observed, whereas tropopause temperatures and O3 are found low. There exists large inter-annual variation in the ASMA and hence its effect on these trace gases and aerosols are also seen clearly. A significant relationship is also observed between the phases of Quasi-Biannual Oscillation (QBO) and El Niño Southern Oscillation (ENSO) on the trace gases and ASR, including the tropopause when measurements in the ASMA region are subject to multivariate regression analysis. Further, the influence of the Indian summer monsoon (ISM) activity on the ASMA trace gases and aerosols is studied with respect to active and break spells of monsoon, strong and weak monsoon years, strong La Niña, El Niño years. Results show a significant increase in WV, CO and decrease in O3 during the active phase of the ISM, strong monsoon years and strong La Niña years in the ASMA. Enhancement in the ASR values during the strong monsoon years and strong La Niña years is observed. Thus, it is prudent to conclude that the dynamics of the ASMA play an important role in the confinement of several trace gases and aerosols and suggested to consider the activity of summer monsoon while dealing with them at sub-seasonal scales.

scholarly journals Asian summer monsoon anticyclone: trends and variability

2020 ◽  
Vol 20 (11) ◽  
pp. 6789-6801 ◽  
Author(s):  
Ghouse Basha ◽  
M. Venkat Ratnam ◽  
Pangaluru Kishore
Keyword(s):  
Tibetan Plateau ◽  
Summer Monsoon ◽  
Decadal Variability ◽  
Asian Summer Monsoon ◽  
Active Phase ◽  
Reanalysis Data ◽  
La Niña ◽  
The Tibetan Plateau ◽  
La Nina ◽  
Asian Summer

Abstract. The Asian summer monsoon anticyclone (ASMA) has been a topic of intensive research in recent times regarding its variability in dynamics, chemistry and radiation. This work explores the spatial variability and the trends of the ASMA using observational and reanalysis data sets. Our analysis indicates that the spatial extent and magnitude of the ASMA is greater during July and August than in June and September. The decadal variability of the anticyclone is very large at the edges of the anticyclone compared with the core region. Significant decadal variability is observed in the northeastern and southwestern parts of the ASMA with reference to the 1951–1960 period. The strength of the ASMA shows a drastic increase in zonal wind anomalies in terms of temporal variation. Furthermore, our results show that the extent of the anticyclone is greater during the active phase of the monsoon, strong monsoon years, and La Niña events. Significant warming with strong westerlies is observed exactly over the Tibetan Plateau from the surface to the tropopause during the abovementioned periods. Our results support the existence of transport process over the Tibetan Plateau and the Indian region during active, strong monsoon years and during strong La Niña years. Therefore, it is recommended that the different phases of the monsoon be taken into account when interpreting the variability of pollutants and trace gases in the anticyclone.

scholarly journals Asian Summer Monsoon Anticyclone: Trends and Variability

2019 ◽  
Author(s):  
Ghouse Basha ◽  
M. Venkat Ratnam ◽  
Pangaluru Kishore
Keyword(s):  
Tibetan Plateau ◽  
Summer Monsoon ◽  
Decadal Variability ◽  
Asian Summer Monsoon ◽  
Active Phase ◽  
La Niña ◽  
The Tibetan Plateau ◽  
La Nina ◽  
Asian Summer

Abstract. The Asian Summer Monsoon (ASM) dynamics act as a pathway for the transport of trace gases and pollutants both vertically (through convection) and horizontally (through low-level jet and tropical easterly jet). These pollutants will be trapped in the anticyclone present during the same period in the upper troposphere and lower stratosphere (UTLS). Since the anticyclone extends from the Middle East to East Asia, trapped pollutants are expected to make a large radiative forcing to the background atmosphere. Thus, it is essential to understand the anticyclone features in detail and its relation to long-term oscillations. This work explores the spatial variability and the trends of the Asian Summer Monsoon Anticyclone (ASMA) using observational and reanalysis data sets. Emphasis is made to investigate the temporal, spatial, and long-term trends of ASMA. Our analysis indicates that the spatial extent and magnitude of ASMA is greater during July and August compared to June and September. The decadal variability of the anticyclone is very large at the edges of anticyclone than at the core region. Significant deviations in the northeast and southwest parts of ASMA are also observed in the decadal variability with reference to 1951−1960 period. The strength of the ASMA shows a drastic increase from the easterlies to the westerlies in terms of temporal variation. Further, our results show that the extent of anticyclone is greater during the active phase of the monsoon, strong monsoon years, and during La Niña events. Significant warming with strong westerlies is observed exactly over the Tibetan Plateau during the active phase of the monsoon, strong monsoon years, and during La Niña events. Over the Tibetan Plateau, there is strong elevated heating from the surface to the tropopause, which is observed with strong westerlies during active and strong monsoon years. Our results support the transport process over Tibetan Plateau and the Indian region during active, strong monsoon years and during strong La Niña years. It is suggested to consider different phases of monsoon while interpreting the pollutants/trace gases in the anticyclone.

scholarly journals Influence of Indian Summer Monsoon on Tropopause, Trace Gases and Aerosols in Asian Summer Monsoon Anticyclone Observed by COSMIC, MLS and CALIPSO

2021 ◽  
Vol 13 (17) ◽  
pp. 3486
Author(s):  
Ghouse Basha ◽  
M. Venkat Ratnam ◽  
Jonathan H. Jiang ◽  
Pangaluru Kishore ◽  
Saginela Ravindra Babu
Keyword(s):  
Summer Monsoon ◽  
Significant Role ◽  
Indian Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Global Climate ◽  
Trace Gases ◽  
La Niña ◽  
Upper Troposphere ◽  
La Nina ◽  
Asian Summer

The existence of the Asian Summer Monsoon Anticyclone (ASMA) during the summer in the northern hemisphere, upper troposphere and lower stratosphere (UTLS) region plays a significant role in confining the trace gases and aerosols for a long duration, thus affecting regional and global climate. Though several studies have been carried out, our understanding of the trace gases and aerosols variability in the ASMA is limited during different phases of the Indian monsoon. This work quantifies the role of Indian Summer Monsoon (ISM) activity on the tropopause, trace gases (Water Vapor (WV), Ozone (O3), Carbon Monoxide (CO)) and aerosols (Attenuated Scattering Ratio (ASR)) obtained from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC), Microwave Limb Sounder (MLS), Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite observations, respectively, during the period 2006–2016. Enhancement in the tropopause altitude, WV, CO, ASR and low tropopause temperatures, O3 in the ASMA region is clearly noticed during peak monsoon months (July and August) with large inter-annual variability. Further, a significant increase in the WV and CO, and decrease in O3 during the active phase of the ISM, strong monsoon years and strong La Niña years in the ASMA is noticed. An enhancement in the ASR values during the strong monsoon years and strong La Niña years is also observed. In addition, our results showed that the presence of deep convection spreading from India land regions to the Bay of Bengal with strong updrafts can transport the trace gases and aerosols to the upper troposphere during active spells, strong monsoon years and La Niña years when compared to their counterparts. Observations show that the ASMA is very sensitive to active spells, strong monsoon years and La Niña years compared to break spells, weak monsoon years and El Niño years. It is concluded that the dynamics play a significant role in constraining several trace gases and aerosols in the ASMA and suggested considering the activity of the summer monsoon while dealing with them at sub-seasonal scales.

scholarly journals The Zonal Oscillation and the Driving Mechanisms of the Extreme Western North Pacific Subtropical High and Its Impacts on East Asian Summer Precipitation

2019 ◽  
Vol 32 (10) ◽  
pp. 3025-3050 ◽  
Author(s):  
Tat Fan Cheng ◽  
Mengqian Lu ◽  
Lun Dai
Keyword(s):  
Summer Monsoon ◽  
El Niño ◽  
North Pacific ◽  
Western North Pacific ◽  
El Nino ◽  
La Niña ◽  
Positive Phase ◽  
La Nina ◽  
Asian Summer ◽  
Zonal Oscillation

Abstract This paper scrutinizes the zonal oscillation of the western North Pacific subtropical high (WNPSH) via diagnosing its two extreme phases, which are defined by the top 10% strongest (positive phase) and the weakest (negative phase) WNPSH index (WNPSHI) days during summers in 1979–2016. Key findings include the following: a tripole pattern consisting of intensified (weakened) precipitation over the Maritime Continent and the East Asian summer monsoon regions, and suppressed (strengthened) precipitation over the western North Pacific summer monsoon region during positive (negative) WNPSH phases; a westward movement of WNPSH-induced precipitation anomalies that subsequently affects eastern China, Japan, and the Korean Peninsula at different time lags; an OLR–vorticity pattern explained by atmospheric responses to thermal sources is suggested to drive the oscillation; and the competitive interaction of local air–sea feedbacks, especially during the positive phase. In addition, moderate-to-strong positive correlations between the WNPSHI and the Niño-3.4 index are found on 1–2-, 2–3-, and 3–6-yr time scales; both exhibit decadal shifts to a higher-frequency mode, suggesting the intensification of both the zonal WNPSH oscillation and the ENSO under the changing climate and their close interdecadal association. A nonlinear quasi-biennial WNPSH–ENSO relationship is identified: the positive (negative) WNPSH phase sometimes occurs during 1) a decaying El Niño (La Niña) in the preceding summer/autumn, and/or 2) a developing La Niña (El Niño) in the current summer/autumn. A full ENSO transition from moderate-to-strong El Niño to La Niña is often seen during the positive phase, offering potential in predicting ENSO events and extreme WNPSH phases and thereby the summer monsoon rainfall in East Asia.

scholarly journals El Niño Southern Oscillation influence on the Asian summer monsoon anticyclone

2018 ◽  
Author(s):  
Xiaolu Yan ◽  
Paul Konopka ◽  
Felix Ploeger ◽  
Mengchu Tao ◽  
Rolf Müller ◽  
...  
Keyword(s):  
Atmospheric Circulation ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Asian Summer Monsoon ◽  
La Niña ◽  
Tropical Tropopause ◽  
La Nina ◽  
Asian Summer ◽  
The Impact

Abstract. We analyze the influence of the El Niño Southern Oscillation (ENSO) on the atmospheric circulation and the mean ozone distribution in the tropical and sub-tropical UTLS region. In particular, we focus on the impact of ENSO on the onset of the Asian summer monsoon (ASM) anticyclone. Using the Multivariate ENSO Index, we define climatologies (composites) of atmospheric circulation and composition in the months following El Niño and La Niña (boreal) winters and investigate how ENSO-related flow anomalies propagate into spring and summer. To quantify differences in the divergent and non-divergent part of the flow, the velocity potential (VP) and the stream function (SF) respectively, are calculated from the ERA-Interim reanalysis around the tropical tropopause (potential temperature level θ=380 K). While VP quantifies the well-known ENSO anomalies of the Walker circulation, SF can be used to study the impact of ENSO on the formation of the ASM anticyclone which turns out to be slightly weaker after El Niño than after La Niña winters. In addition, stratospheric intrusions around the eastern flank of the anticyclone into the Tropical Tropopause Layer (TTL) are weaker in the months after strong El Niño events due to more zonally symmetric subtropical jets than after La Niña winters. By using satellite (MLS), in-situ (SHADOZ) observations and model simulations (CLaMS) of ozone, we discuss ENSO-induced differences around the tropical tropopause. Ozone composites show more zonally symmetric features with less in-mixed ozone from the stratosphere into the TTL during and after strong El Niño events and even during the formation of the ASM anticyclone. The difference between El Niño and La Niña composites becomes statistically insignificant in late summer.

Asymmetric relationship between ENSO and the tropical Indian Ocean summer SST anomalies

2021 ◽  
pp. 1-51
Author(s):  
Xiangbai Wu ◽  
Gen Li ◽  
Wenping Jiang ◽  
Shang-Min Long ◽  
Bo Lu
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
Rossby Wave ◽  
El Niño ◽  
El Nino ◽  
Asian Summer Monsoon ◽  
Sst Cooling ◽  
La Nina ◽  
Asian Summer ◽  
Sst Anomalies

AbstractDuring the summer following El Niño, a basin-wide sea surface temperature (SST) warming takes place over the tropical Indian Ocean (TIO), exerting profound influences on the Asian summer monsoon. This is an important source of seasonal predictability for the Asian summer monsoon. Based on observations, however, the present study finds that the relationship between El Niño-Southern Oscillation (ENSO) and the TIO SST anomalies during the decaying summer is asymmetric with a much weaker relationship between La Niña and the TIO SST anomalies relative to El Niño. The analyses show that this asymmetric relationship can be explained by the asymmetries in initial TIO SST, oceanic Rossby wave in the southern Indian Ocean and ENSO decaying rate. In contrast to El Niño events, La Niña events tend to have a stronger initial TIO warming and a less peak intensity with a weaker oceanic Rossby wave response in the southern Indian Ocean. On the other hand, La Niña events tend to decay more slowly with the persistent SST cooling over the central equatorial Pacific in the following summer. The equatorial Pacific SST cooling would induce an anomalous anticyclone via a Gill-type Rossby wave response, weakening the positive feedback between the anomalous cyclone spanning the tropical Northwest Pacific and North Indian oceans and the TIO summer basin-wide SST cooling. These results have important implications for the climate predictability of the Indian Ocean and Asian summer monsoon.

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