scholarly journals Structure, dynamics, and trace gases variability within the Asian summer monsoon anticyclone in extreme El Niño of 2015–16

2020 ◽  
Author(s):  
Saginela Ravindra Babu ◽  
Madineni Venkat Ratnam ◽  
Ghouse Basha ◽  
Shantanu Kumar Pani ◽  
Neng-Huei Lin
Keyword(s):  
Summer Monsoon ◽  
El Niño ◽  
El Nino ◽  
Asian Summer Monsoon ◽  
Trace Gases ◽  
Northeastern Asia ◽  
Structure Dynamics ◽  
Asian Summer ◽  
Extreme El Niño

Abstract. In this work, the detailed changes in the structure, dynamics and trace gases within the Asian summer monsoon anticyclone (ASMA) during extreme El Niño of 2015–16 is delineated by using Aura Microwave Limb Sounder (MLS) measurements, COSMIC Radio Occultation (RO) temperature, and NCEP reanalysis products. We have considered the individual months of July and August 2015 for the present study. The results show that the ASMA structure was quite different in 2015 as compared to the long-term (2005–2014) mean. In July, the spatial extension of the ASMA shows larger than the long-term mean in all the regions except over northeastern Asia, where, it exhibits a strong southward shift in its position. The ASMA splits into two and western Pacific mode is evident in August. Interestingly, the subtropical westerly jet (STJ) shifted southward from its normal position over northeastern Asia as resulted mid latitude air moved southward in 2015. Intense Rossby wave breaking events along with STJ are also found in July 2015. Due to these dynamical changes in the ASMA, pronounced changes in the ASMA tracers are noticed in 2015 compared to the long-term mean. A 30 % (20 %) decrease in carbon monoxide (water vapor) at 100 hPa is observed in July over most of the ASMA region, whereas in August the drop is strongly concentrated in the edges of the ASMA. Prominent increase of O3 (> 40 %) at 100 hPa is clearly evident within the ASMA in July, whereas in August the increase is strongly located (even at 121 hPa) over the western edges of the ASMA. Further, the temperature around the tropopause shows significant positive anomalies (~ 5 K) within the ASMA in 2015. Overall, warming of the tropopause region due to the increased O3 weakens the anticyclone and further supported the weaker ASMA in 2015 reported by previous studies.

scholarly journals Structure, dynamics, and trace gas variability within the Asian summer monsoon anticyclone in the extreme El Niño of 2015–2016

2021 ◽  
Vol 21 (7) ◽  
pp. 5533-5547
Author(s):  
Saginela Ravindra Babu ◽  
Madineni Venkat Ratnam ◽  
Ghouse Basha ◽  
Shantanu Kumar Pani ◽  
Neng-Huei Lin
Keyword(s):  
Summer Monsoon ◽  
El Niño ◽  
El Nino ◽  
Asian Summer Monsoon ◽  
Trace Gases ◽  
Northeastern Asia ◽  
Structure Dynamics ◽  
Asian Summer ◽  
Extreme El Niño

Abstract. A weak El Niño during 2014–2015 boreal winter developed as a strong boreal summer event in 2015 which continued and even enhanced during the following winter. In this work, the detailed changes in the structure, dynamics, and trace gases within the Asian summer monsoon anticyclone (ASMA) during the extreme El Niño of 2015–2016 is delineated by using Aura Microwave Limb Sounder (MLS) measurements, COSMIC radio occultation (RO) temperature, and National Centers for Environmental Prediction (NCEP) reanalysis products. Our analysis concentrates only on the summer months of July and August 2015 when the Niño 3.4 index started to exceed values of 1.5. The results show that the ASMA structure was quite different in summer 2015 as compared to the long-term (2005–2014) mean. In July, the spatial extension of the ASMA is greater than the long-term mean in all the regions except over northeastern Asia, where it exhibits a strong southward shift in its position. The ASMA splits into two, and the western Pacific mode is evident in August. Interestingly, the subtropical westerly jet (STJ) shifted southward from its normal position over northeastern Asia, and as a result midlatitude air moved southward in 2015. Intense Rossby wave breaking events along with STJ are also found in July 2015. Due to these dynamical changes in the ASMA, pronounced changes in the ASMA tracers are noticed in 2015 compared to the long-term mean. A 30 % (20 %) decrease in carbon monoxide (water vapor) at 100 hPa is observed in July over most of the ASMA region, whereas in August the drop is strongly concentrated at the edges of the ASMA. A prominent increase in O3 (> 40 %) at 100 hPa is clearly evident within the ASMA in July, whereas in August the increase is strongly located (even at 121 hPa) over the western edges of the ASMA. Further, the temperature around the tropopause shows significant positive anomalies (∼ 5 K) within the ASMA in 2015. The present results clearly reveal the El-Niño-induced dynamical changes caused significant changes in the trace gases within the ASMA in summer 2015.

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 Variation in the Asian monsoon intensity and dry–wet conditions since the Little Ice Age in central China revealed by an aragonite stalagmite

2014 ◽  
Vol 10 (5) ◽  
pp. 1803-1816 ◽  
Author(s):  
J.-J. Yin ◽  
D.-X. Yuan ◽  
H.-C. Li ◽  
H. Cheng ◽  
T.-Y. Li ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
El Niño ◽  
El Nino ◽  
Asian Summer Monsoon ◽  
Eastern China ◽  
Central China ◽  
Solar Irradiation ◽  
Mountain Area ◽  
Monsoon Intensity ◽  
Asian Summer

Abstract. This paper focuses on the climate variability in central China since AD 1300, involving: (1) a well-dated, 1.5-year resolution stalagmite δ18O record from Lianhua Cave, central China (2) links of the δ18O record with regional dry–wet conditions, monsoon intensity, and temperature over eastern China (3) correlations among drought events in the Lianhua record, solar irradiation, and ENSO (El Niño–Southern Oscillation) variation. We present a highly precise, 230Th / U-dated, 1.5-year resolution δ18O record of an aragonite stalagmite (LHD1) collected from Lianhua Cave in the Wuling Mountain area of central China. The comparison of the δ18O record with the local instrumental record and historical documents indicates that (1) the stalagmite δ18O record reveals variations in the summer monsoon intensity and dry–wet conditions in the Wuling Mountain area. (2) A stronger East Asian summer monsoon (EASM) enhances the tropical monsoon trough controlled by ITCZ (Intertropical Convergence Zone), which produces higher spring quarter rainfall and isotopically light monsoonal moisture in the central China. (3) The summer quarter/spring quarter rainfall ratio in central China can be a potential indicator of the EASM strength: a lower ratio corresponds to stronger EASM and higher spring rainfall. The ratio changed from <1 to >1 after 1950, reflecting that the summer quarter rainfall of the study area became dominant under stronger influence of the Northwestern Pacific High. Eastern China temperatures varied with the solar activity, showing higher temperatures under stronger solar irradiation, which produced stronger summer monsoons. During Maunder, Dalton and 1900 sunspot minima, more severe drought events occurred, indicating a weakening of the summer monsoon when solar activity decreased on decadal timescales. On an interannual timescale, dry conditions in the study area prevailed under El Niño conditions, which is also supported by the spectrum analysis. Hence, our record illustrates the linkage of Asian summer monsoon precipitation to solar irradiation and ENSO: wetter conditions in the study area under stronger summer monsoon during warm periods, and vice versa. During cold periods, the Walker Circulation will shift toward the central Pacific under El Niño conditions, resulting in a further weakening of Asian summer monsoons.

scholarly journals Two Types of Strong Northeast Asian Summer Monsoon

2009 ◽  
Vol 22 (16) ◽  
pp. 4406-4417 ◽  
Author(s):  
Jung-Eun Kim ◽  
Sang-Wook Yeh ◽  
Song-You Hong
Keyword(s):  
Indian Ocean ◽  
Summer Monsoon ◽  
El Niño ◽  
El Nino ◽  
Asian Summer Monsoon ◽  
Striking Difference ◽  
Convective System ◽  
Asian Summer ◽  
Northeast Asian ◽  
Preceding Winter

Abstract The characteristics of a strong northeast Asian summer monsoon (NEASM) with and without (A and B type, respectively) a basinwide warming in the Indian Ocean during the preceding winter are examined for the period of 1979–2006. In the case of the A type, strong El Niño–like sea surface temperature (SST) decays very rapidly from the preceding winter (December–February) to the following summer (June–August), which may be due to a feedback process of the warm Indian Ocean. In addition, the A-type strong NEASM is more associated with a weak western North Pacific summer monsoon than the B-type strong NEASM. On the other hand, for the B type an El Niño–like SST during the preceding winter is a persistent influence into the following summer. A striking difference can be found in the atmospheric teleconnection pattern from the tropics to the midlatitudes over the Indo-Pacific region, that is, the Pacific–Japan-like pattern versus a pronounced Rossby wave train pattern. This may result from the difference in location of the maximum center of rainfall anomalies over the tropical northwestern Pacific between the two types of strong NEASM. The authors argue that Indian Ocean basin warming plays a role in modifying the convective system over the subtropical western Pacific, resulting in changes in atmospheric teleconnections between the two types of strong NEASM. The weak NEASM, in which the anomalous rainfall pattern resembles that of the A-type strong NEASM except for the sign, is also discussed.

A Model Study of the Air–Sea Interaction Associated with the Climatological Aspects and Interannual Variability of the South Asian Summer Monsoon Development

2012 ◽  
Vol 25 (3) ◽  
pp. 839-857 ◽  
Author(s):  
Ngar-Cheung Lau ◽  
Mary Jo Nath
Keyword(s):  
South Asian ◽  
Summer Monsoon ◽  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Asian Summer Monsoon ◽  
Function Analysis ◽  
South Asian Summer Monsoon ◽  
The South ◽  
Asian Summer

Abstract The climatological characteristics and interannual variations of the development of the South Asian summer monsoon (SASM) in early summer are studied using output from a 200-yr simulation of a coupled atmosphere–ocean general circulation model (CM2.1). Some of the model results are compared with corresponding observations. Climatological charts of the model and observational data at pentadal intervals indicate that both the precipitation and SST signals exhibit a tendency to migrate northward. Enhanced monsoonal precipitation at a given site is accompanied by a reduction in incoming shortwave radiation and intensification of upward latent heat flux, and by oceanic cooling. An extended empirical orthogonal function analysis is used to identify the dates for initiation of the northward march of SASM in individual summers. It is noted that early monsoon development prevails after the mature phase of La Niña events, whereas delayed development occurs after El Niño. Sensitivity experiments based on the atmospheric component of CM2.1 indicate that the effects of SST forcings in the tropical Pacific (TPAC) and Indian Ocean (IO) on monsoon development are opposite to each other. During El Niño events, the atmospheric response to remote TPAC forcing tends to suppress or postpone monsoon development over South Asia. Conversely, the warm SST anomalies in IO, which are generated by the “atmospheric bridge” mechanism in El Niño episodes, lead to accelerated monsoon development. The net result of these two competing effects is an evolution scenario with a timing that is intermediate between the response to TPAC forcing only and the response to IO forcing only.

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