The remote response of the South Asian Monsoon to reduced dust emissions and Sahara greening during the middle Holocene

Abstract. Previous studies based on multiple paleoclimate archives suggested a prominent intensification of the South Asian Monsoon (SAM) during the mid-Holocene (MH, ∼6000 years before present). The main forcing that contributed to this intensification is related to changes in the Earth's orbital parameters. Nonetheless, other key factors likely played important roles, including remote changes in vegetation cover and airborne dust emission. In particular, northern Africa also experienced much wetter conditions and a more mesic landscape than today during the MH (the so-called African Humid Period), leading to a large decrease in airborne dust globally. However, most modeling studies investigating the SAM changes during the Holocene overlooked the potential impacts of the vegetation and dust emission changes that took place over northern Africa. Here, we use a set of simulations for the MH climate, in which vegetation over the Sahara and reduced dust concentrations are considered. Our results show that SAM rainfall is strongly affected by Saharan vegetation and dust concentrations, with a large increase in particular over northwestern India and a lengthening of the monsoon season. We propose that this remote influence is mediated by anomalies in Indian Ocean sea surface temperatures and may have shaped the evolution of the SAM during the termination of the African Humid Period.

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The remote response of the South Asian Monsoon to reduced dust emissions and Sahara greening during the middle Holocene

10.5194/cp-2020-142 ◽

2020 ◽

Author(s):

Francesco S. R. Pausata ◽

Gabriele Messori ◽

Jayoung Yun ◽

Chetankumar A. Jalihal ◽

Massimo A. Bollasina ◽

...

Keyword(s):

South Asian ◽

Asian Monsoon ◽

Monsoon Season ◽

Dust Emission ◽

Northern Africa ◽

South Asian Monsoon ◽

The South ◽

Airborne Dust ◽

Orbital Parameters ◽

Humid Period

Abstract. Previous studies based on multiple paleoclimate archives suggested a prominent intensification of the South Asian Monsoon (SAM) during the mid-Holocene (MH, ~ 6000 years before present day). The main forcing that contributed to this intensification is related to changes in the Earth’s orbital parameters. However, other key factors likely played important roles, including remote changes in vegetation cover and airborne dust emission. In particular, northern Africa also experienced much wetter conditions and a more mesic landscape than today during the MH (the so-called African Humid Period), leading to a large decrease in airborne dust globally. However, most modelling studies investigating the SAM changes during the Holocene overlooked the potential impacts of the vegetation and dust emission changes that took place over northern Africa. Here, we use a set of simulations for the MH climate, in which vegetation over the Sahara and reduced dust concentrations are considered. Our results show that SAM rainfall is strongly affected by Saharan vegetation and dust concentrations, with a large increase in particular over northwestern India and a lengthening of the monsoon season. We propose that this remote influence is mediated by anomalies in Indian Ocean sea-surface temperatures and may have shaped the evolution of the SAM during the termination of the African Humid Period.

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Synoptic Preconditions for Extreme Flooding during the Summer Asian Monsoon in the Mumbai Area

Journal of Hydrometeorology ◽

10.1175/jhm-d-13-039.1 ◽

2014 ◽

Vol 15 (1) ◽

pp. 229-242 ◽

Cited By ~ 2

Author(s):

Marco Lomazzi ◽

Dara Entekhabi ◽

Joaquim G. Pinto ◽

Giorgio Roth ◽

Roberto Rudari

Keyword(s):

Time Series ◽

South Asian ◽

Asian Monsoon ◽

Indian Subcontinent ◽

Monsoon Season ◽

Value Added ◽

South Asian Monsoon ◽

Flood Events ◽

The South ◽

Synoptic Conditions

Abstract The summer monsoon season is an important hydrometeorological feature of the Indian subcontinent and it has significant socioeconomic impacts. This study is aimed at understanding the processes associated with the occurrence of catastrophic flood events. The study has two novel features that add to the existing body of knowledge about the South Asian monsoon: 1) it combines traditional hydrometeorological observations (rain gauge measurements) with unconventional data (media and state historical records of reported flooding) to produce value-added century-long time series of potential flood events and 2) it identifies the larger regional synoptic conditions leading to days with flood potential in the time series. The promise of mining unconventional data to extend hydrometeorological records is demonstrated in this study. The synoptic evolution of flooding events in the western-central coast of India and the densely populated Mumbai area are shown to correspond to active monsoon periods with embedded low pressure centers and have far-upstream influences from the western edge of the Indian Ocean basin. The coastal processes along the Arabian Peninsula where the currents interact with the continental shelf are found to be key features of extremes during the South Asian monsoon.

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Lower tropospheric ozone over India and its linkage to the South Asian monsoon

10.5194/acp-2017-906 ◽

2017 ◽

Cited By ~ 1

Author(s):

Xiao Lu ◽

Lin Zhang ◽

Xiong Liu ◽

Meng Gao ◽

Yuanhong Zhao ◽

...

Keyword(s):

South Asian ◽

Summer Monsoon ◽

Tropospheric Ozone ◽

Asian Monsoon ◽

Monsoon Season ◽

Meteorological Conditions ◽

South Asian Monsoon ◽

Summer Monsoon Season ◽

The South

Abstract. Lower tropospheric (surface to 600 hPa) ozone over India poses serious risks to local human and crops, and potentially affects global ozone distribution through frequent deep convection in tropical regions. Our current understanding of processes controlling seasonal to long-term variations in lower tropospheric ozone over this region is rather limited due to spatially and temporally sparse observations. Here we present an integrated process analysis of the seasonal cycle, interannual variability, and long-term trends of lower tropospheric ozone over India and its linkage to the South Asian Monsoon using the Ozone Monitoring Instrument (OMI) satellite observations for years 2006–2014 interpreted with a global chemical transport model (GEOS-Chem) simulation for 1990–2010. OMI observed lower tropospheric ozone over India averaged for 2006–2010 show the highest concentrations (54.1 ppbv) in the pre-summer monsoon season (May) and the lowest concentrations (40.5 ppbv) in the summer monsoon season (August). Process analyses in GEOS-Chem show that hot and dry meteorological conditions and active biomass burning together contribute to 5.8 Tg more ozone produced in the lower troposphere of India in May than January. The onset of the summer monsoon brings ozone-unfavorable meteorological conditions and strong upward transport, all lead to large decreases in the lower tropospheric ozone burden. Interannually, we find that both OMI and GEOS-Chem indicate strong interannual positive correlations (r = 0.55–0.58) between ozone and surface temperature in pre-summer monsoon seasons, with larger correlations found in high NOx emission regions reflecting NOx-limited production conditions. Summer monsoon seasonal mean ozone levels are strongly controlled by monsoon strengths. Lower ozone concentrations are found in stronger monsoon seasons mainly due to less ozone net chemical production. Furthermore, model simulations over 1990–2010 estimate a mean annual trend of 0.19 ± 0.07 (p-value

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Lower tropospheric ozone over India and its linkage to the South Asian monsoon

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-3101-2018 ◽

2018 ◽

Vol 18 (5) ◽

pp. 3101-3118 ◽

Cited By ~ 17

Author(s):

Xiao Lu ◽

Lin Zhang ◽

Xiong Liu ◽

Meng Gao ◽

Yuanhong Zhao ◽

...

Keyword(s):

South Asian ◽

Summer Monsoon ◽

Tropospheric Ozone ◽

Asian Monsoon ◽

Monsoon Season ◽

Meteorological Conditions ◽

South Asian Monsoon ◽

Summer Monsoon Season ◽

The South

Abstract. Lower tropospheric (surface to 600 hPa) ozone over India poses serious risks to both human health and crops, and potentially affects global ozone distribution through frequent deep convection in tropical regions. Our current understanding of the processes controlling seasonal and long-term variations in lower tropospheric ozone over this region is rather limited due to spatially and temporally sparse observations. Here we present an integrated process analysis of the seasonal cycle, interannual variability, and long-term trends of lower tropospheric ozone over India and its linkage to the South Asian monsoon using the Ozone Monitoring Instrument (OMI) satellite observations for years 2006–2014 interpreted with a global chemical transport model (GEOS-Chem) simulation for 1990–2010. OMI observed lower tropospheric ozone over India averaged for 2006–2010, showing the highest concentrations (54.1 ppbv) in the pre-summer monsoon season (May) and the lowest concentrations (40.5 ppbv) in the summer monsoon season (August). Process analyses in GEOS-Chem show that hot and dry meteorological conditions and active biomass burning together contribute to 5.8 Tg more ozone being produced in the lower troposphere in India in May than January. The onset of the summer monsoon brings ozone-unfavorable meteorological conditions and strong upward transport, which all lead to large decreases in the lower tropospheric ozone burden. Interannually, we find that both OMI and GEOS-Chem indicate strong positive correlations (r=0.55–0.58) between ozone and surface temperature in pre-summer monsoon seasons, with larger correlations found in high NOx emission regions reflecting NOx-limited production conditions. Summer monsoon seasonal mean ozone levels are strongly controlled by monsoon strengths. Lower ozone concentrations are found in stronger monsoon seasons mainly due to less ozone net chemical production. Furthermore, model simulations over 1990–2010 estimate a mean annual trend of 0.19 ± 0.07 (p value < 0.01) ppbv yr−1 in Indian lower tropospheric ozone over this period, which are mainly driven by increases in anthropogenic emissions with a small contribution (about 7 %) from global methane concentration increases.

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