Interannual variability of moisture source over southern Indian Ocean during boreal summer and its relationship with local SST

2012 ◽  
Vol 33 (3) ◽  
pp. 556-567 ◽  
Author(s):  
Yunting Qiao ◽  
Renguang Wu ◽  
Wei Huang ◽  
Maoqiu Jian
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Southern Indian Ocean ◽  
Boreal Summer ◽  
Moisture Source

scholarly journals A Tropospheric ozone maximum over the equatorial southern Indian Ocean

2012 ◽  
Vol 12 (1) ◽  
pp. 1979-2024
Author(s):  
L. Zhang ◽  
Q. B. Li ◽  
L. T. Murray ◽  
M. Luo ◽  
H. Liu ◽  
...  
Keyword(s):  
Indian Ocean ◽  
South America ◽  
Interannual Variability ◽  
Tropospheric Ozone ◽  
Three Dimensional ◽  
Central Africa ◽  
Tropospheric Chemistry ◽  
Southern Indian Ocean ◽  
Three Dimensional Model ◽  
Dynamic Factors

Abstract. We examine the distribution of tropical tropospheric ozone (O3) from the Microwave Limb Sounder (MLS) and the Tropospheric Emission Spectrometer (TES) by using a global three-dimensional model of tropospheric chemistry (GEOS-Chem). MLS and TES observations of tropospheric O3 during 2005 to 2009 reveal a distinct, persistent O3 maximum, both in mixing ratio and tropospheric column, in May over the Equatorial Southern Indian Ocean (ESIO). The maximum is most pronounced in 2006 and 2008 and less evident in the other three years. This feature is also consistent with the total column O3 observations from the Ozone Mapping Instrument (OMI) and the Atmospheric Infrared Sounder (AIRS). Model results reproduce the observed May O3 maximum and the associated interannual variability. The origin of the maximum reflects a complex interplay of chemical and dynamic factors. The O3 maximum is dominated by the O3 production driven by lightning nitrogen oxides (NOx) emissions, which accounts for 62% of the tropospheric column O3 in May 2006. We find the contribution from biomass burning, soil, anthropogenic and biogenic sources to the O3 maximum are rather small. The O3 productions in the lightning outflow from Central Africa and South America both peak in May and are directly responsible for the O3 maximum over the western ESIO. The lightning outflow from Equatorial Asia dominates over the eastern ESIO. The interannual variability of the O3 maximum is driven largely by the anomalous anti-cyclones over the southern Indian Ocean in May of 2006 and 2008. The lightning outflow from Central Africa and South America is effectively entrained by the anti-cyclones followed by northward transport to the ESIO.

scholarly journals Positive Indian Ocean Dipole events prevent anoxia along coast of India

2016 ◽  
Author(s):  
V. Parvathi ◽  
I. Suresh ◽  
Matthieu Lengaigne ◽  
Christian Ethé ◽  
Jérôme Vialard ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Indian Ocean Dipole ◽  
Boreal Summer ◽  
Low Oxygen ◽  
Easterly Wind ◽  
Positive Indian Ocean Dipole ◽  
Subsurface Waters ◽  
Anoxic Events ◽  
The Indian Ocean

Abstract. The seasonal upwelling along the west coast of India (WCI) brings nutrient-rich, oxygen-poor subsurface waters to the continental shelf, leading to very low oxygen concentrations at shallow depths during late boreal summer and fall. This yearly-recurring coastal hypoxia is sometimes more severe, leading to coastal anoxia that has strong impacts on the living resources. In the present study, we analyze a 1/4°-resolution coupled physical-biogeochemical regional oceanic simulation over the 1960–2012 period to investigate the physical processes influencing oxycline interannual variability off the WCI. Our analysis indicates a tight relationship between the oxycline and thermocline variations along the WCI at both seasonal and interannual timescales, thereby revealing a strong physical control of the WCI oxycline variability. As in observations, our model exhibits a shallow oxycline/thermocline along the WCI during fall that combines with interannual variability to create a window of opportunity for coastal anoxic events at this time of the year. We further demonstrate that boreal fall WCI oxycline fluctuations are strongly related to the Indian Ocean Dipole (IOD), with an asymmetric influence of positive and negative IOD phases. Positive IODs are associated with easterly wind anomalies near the southern tip of India. These winds force downwelling coastal Kelvin waves that propagate along the WCI and deepen the thermocline and oxycline there, thus preventing the occurrence of coastal anoxia. On the other hand, negative IOD events are associated with WCI thermocline and oxycline anomalies of opposite sign, but of smaller amplitude, and are hence a necessary, but not sufficient condition for coastal anoxia. As the IODs generally start developing in summer, these findings suggest some predictability to the occurrence of WCI coastal anoxia a couple of months ahead.

scholarly journals Interannual Variability of Equatorial Eastern Indian Ocean Upwelling: Local versus Remote Forcing

2016 ◽  
Vol 46 (3) ◽  
pp. 789-807 ◽  
Author(s):  
Gengxin Chen ◽  
Weiqing Han ◽  
Yuanlong Li ◽  
Dongxiao Wang
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Southern Oscillation ◽  
Equatorial Indian Ocean ◽  
Eastern Indian Ocean ◽  
Boreal Summer ◽  
Thermocline Depth ◽  
Remote Forcing ◽  
Local Forcing ◽  
The Mean

AbstractThe equatorial eastern Indian Ocean (EIO) upwelling occurs in the Indian Ocean warm pool, differing from the equatorial Pacific and Atlantic upwelling that occurs in the cold tongue. By analyzing observations and performing ocean model experiments, this paper quantifies the remote versus local forcing in causing interannual variability of the equatorial EIO upwelling from 2001 to 2011 and elucidates the associated processes. For all seasons, interannual variability of thermocline depth in the EIO, as an indicator of upwelling, is dominated by remote forcing from equatorial Indian Ocean winds, which drive Kelvin waves that propagate along the equator and subsequently along the Sumatra–Java coasts. Upwelling has prominent signatures in sea surface temperature (SST) and chlorophyll-a concentration but only in boreal summer–fall (May–October). Local forcing plays a larger role than remote forcing in producing interannual SST anomaly (SSTA). During boreal summer–fall, when the mean thermocline is relatively shallow, SSTA is primarily driven by the upwelling process, with comparable contributions from remote and local forcing effects. In contrast, during boreal winter–spring (November–April), when the mean thermocline is relatively deep, SSTA is controlled by surface heat flux and decoupled from thermocline variability. Advection affects interannual SSTA in all cases. The remote and local winds that drive the interannual variability of the equatorial EIO upwelling are closely associated with Indian Ocean dipole events and to a lesser degree with El Niño–Southern Oscillation.

scholarly journals A tropospheric ozone maximum over the equatorial Southern Indian Ocean

2012 ◽  
Vol 12 (9) ◽  
pp. 4279-4296 ◽  
Author(s):  
L. Zhang ◽  
Q. B. Li ◽  
L. T. Murray ◽  
M. Luo ◽  
H. Liu ◽  
...  
Keyword(s):  
Indian Ocean ◽  
South America ◽  
Interannual Variability ◽  
Tropospheric Ozone ◽  
Three Dimensional ◽  
Central Africa ◽  
Tropospheric Chemistry ◽  
Southern Indian Ocean ◽  
Three Dimensional Model ◽  
Dynamic Factors

Abstract. We examine the distribution of tropical tropospheric ozone (O3) from the Microwave Limb Sounder (MLS) and the Tropospheric Emission Spectrometer (TES) by using a global three-dimensional model of tropospheric chemistry (GEOS-Chem). MLS and TES observations of tropospheric O3 during 2005 to 2009 reveal a distinct, persistent O3 maximum, both in mixing ratio and tropospheric column, in May over the Equatorial Southern Indian Ocean (ESIO). The maximum is most pronounced in 2006 and 2008 and less evident in the other three years. This feature is also consistent with the total column O3 observations from the Ozone Mapping Instrument (OMI) and the Atmospheric Infrared Sounder (AIRS). Model results reproduce the observed May O3 maximum and the associated interannual variability. The origin of the maximum reflects a complex interplay of chemical and dynamic factors. The O3 maximum is dominated by the O3 production driven by lightning nitrogen oxides (NOx) emissions, which accounts for 62% of the tropospheric column O3 in May 2006. We find the contribution from biomass burning, soil, anthropogenic and biogenic sources to the O3 maximum are rather small. The O3 productions in the lightning outflow from Central Africa and South America both peak in May and are directly responsible for the O3 maximum over the western ESIO. The lightning outflow from Equatorial Asia dominates over the eastern ESIO. The interannual variability of the O3 maximum is driven largely by the anomalous anti-cyclones over the southern Indian Ocean in May 2006 and 2008. The lightning outflow from Central Africa and South America is effectively entrained by the anti-cyclones followed by northward transport to the ESIO.

Mechanisms for the Interannual Variability in the Tropical Indian Ocean. Part I: The Role of Remote Forcing from the Tropical Pacific

2007 ◽  
Vol 20 (13) ◽  
pp. 2917-2936 ◽  
Author(s):  
Bohua Huang ◽  
J. Shukla
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Low Frequency ◽  
Tropical Indian Ocean ◽  
Boreal Summer ◽  
Remote Forcing ◽  
The Indian Ocean ◽  
Frequency Fluctuations ◽  
Southwestern Indian Ocean ◽  
Sst Anomalies

Abstract A series of experiments are conducted using a coupled ocean–atmosphere general circulation model in regional coupled mode, which permits active air–sea interaction only within the Indian Ocean to the north of 30°S, with sea surface temperatures (SSTs) prescribed over the rest of the world oceans. In this paper, an ensemble of nine simulations has been analyzed with the observed SST anomalies for 1950–98 prescribed over the uncoupled region. The purpose of this study is to determine the major patterns of interannual variability in the tropical Indian Ocean that could be related to the global low-frequency fluctuations and to understand the physical links between the remote forcing and the regional coupled variations. The ensemble coupled simulations with prescribed SST outside the Indian Ocean are able to reproduce a considerable amount of observed variability in the tropical Indian Ocean during 1950–98. The first EOF modes of the simulated upper-ocean heat content and SST anomalies show structures that are quite consistent with those from the historical upper oceanic temperature and SST analyses. The dominant pattern of response is associated with an oceanic dynamical adjustment of the thermocline depth in the southwestern Indian Ocean. In general, a deepening of the thermocline in the southwest is usually accompanied by the enhanced upwelling and thermocline shoaling centered near the Sumatra coast. Further analysis shows that the leading external forcing is from the El Niño–Southern Oscillation (ENSO), which induces an anomalous fluctuation of the atmospheric anticyclones on both sides of the equator over the Indian Ocean, starting from the evolving stage of an El Niño event in boreal summer. Apart from weakening the Indian monsoon, the surface equatorial easterly anomalies associated with this circulation pattern first induce equatorial and coastal upwelling anomalies near the Sumatra coast from summer to fall, which enhance the equatorial zonal SST gradient and stimulate intense air–sea feedback in the equatorial ocean. Moreover, the persistent anticyclonic wind curl over the southern tropical Indian Ocean, reinforced by the equatorial air–sea coupling, forces substantial thermocline change centered at the thermocline ridge in the southwestern Indian Ocean for seasons. The significant thermocline change has profound and long-lasting influences on the SST fluctuations in the Indian Ocean. It should be noted that the ENSO forcing is not the only way that this kind of basinwide Indian Ocean fluctuations can be generated. As will be shown in the second part of this study, similar low-frequency fluctuations can also be generated by processes within the Indian and western Pacific region without ENSO influence. The unique feature of the ENSO influence is that, because of the high persistence of the atmospheric remote forcing from boreal summer to winter, the life span of the thermocline anomalies in the southwestern Indian Ocean is generally longer than that generated by regional coupled processes.

scholarly journals Role of Oceanic and Land Moisture Sources and Transport in the Seasonal and Interannual Variability of Summer Monsoon in India

2017 ◽  
Vol 30 (5) ◽  
pp. 1839-1859 ◽  
Author(s):  
Amey Pathak ◽  
Subimal Ghosh ◽  
J. Alejandro Martinez ◽  
Francina Dominguez ◽  
Praveen Kumar
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Summer Monsoon ◽  
Monsoon Season ◽  
Initial Period ◽  
Western Indian Ocean ◽  
Moisture Flux ◽  
Moisture Source ◽  
Moisture Sources ◽  
Moisture Supply

Abstract Three key issues of moisture supply and Indian summer monsoon rainfall (ISMR) variability are discussed in the present work: identification of the oceanic and terrestrial sources of moisture; the extent to which each source affects the ISMR; and their individual contributions to the interannual variability of ISMR. The modified Dynamic Recycling Model, based on a Lagrangian trajectory approach, is used to estimate the relative contributions from 27 terrestrial and oceanic moisture source regions to the monsoon during 1979–2013. ERA-Interim data are used for the study. The results show that the ISMR is strongly influenced by the land–ocean–atmosphere interactions, and a significant fraction of atmospheric moisture to the ISMR comes from five main moisture sources: the western Indian Ocean (WIO), central Indian Ocean (CIO), upper Indian Ocean (UIO), Ganges basin (GB), and Red Sea and the neighboring gulf (RDG). The moisture flux from WIO is very high during the initial period of monsoon seasons. From the mid-monsoon season, the contribution from this moisture source decays and land sources through evapotranspiration (ET) become more active. Early decay of moisture contributions from the WIO and the GB is observed during weak monsoon years. El Niño years are associated with low contributions of moisture from all sources, whereas warm Indian Ocean years are associated with low moisture flux from the major sources except WIO. ISMR is characterized by the prolonged and increasing moisture supply from WIO during the first half of the monsoon along with contributions from GB during the end of season. The results are consistent across several reanalyses (CFSR, ERA-Interim, and MERRA).

scholarly journals Interannual variability of atmospheric dimethylsulfide in the southern Indian Ocean

2000 ◽  
Vol 105 (D21) ◽  
pp. 26369-26377 ◽  
Author(s):  
J. Sciare ◽  
N. Mihalopoulos ◽  
F. J. Dentener
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Southern Indian Ocean
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