Factors controlling January–April rainfall over southern India and Sri Lanka

Vialard, Jérôme; Terray, Pascal; Duvel, Jean-Philippe; Nanjundiah, Ravi S.; Shenoi, S. S. C.; Shankar, D.

doi:10.1007/s00382-010-0970-4

Cited by 15 publications

(23 citation statements)

References 44 publications

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“…In contrast, the horizontal advection term shows a weaker variability (between −0.15 and 0.15°C d −1 ) and is not significantly correlated with the SST tendency. In line with the previous studies [e.g., Roxy and Tanimoto , ; Vialard et al ., ], this analysis confirms that the atmospheric forcing is, by and large, the main driver of the SST evolution at this location, though the horizontal advection can also play a role as in early 2013 (see Figure c). Figures d–f allow us to investigate further the main component of the atmospheric heat flux responsible for these atmospheric fluctuations.…”

Section: Driving Processessupporting

confidence: 71%

Surface layer temperature inversion in the Bay of Bengal: Main characteristics and related mechanisms

et al. 2016

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Surface layer temperature inversion (SLTI), a warm layer sandwiched between surface and subsurface colder waters, has been reported to frequently occur in conjunction with barrier layers in the Bay of Bengal (BoB), with potentially commensurable impacts on climate and postmonsoon tropical cyclones. Lack of systematic measurements from the BoB in the past prevented a thorough investigation of the SLTI spatiotemporal variability, their formation mechanisms, and their contribution to the surface temperature variations. The present study benefits from the recent Research Moored Array for African‐Asian‐Australian Monsoon Analysis and Prediction (RAMA) buoys located in BoB along 90°E at 4°N, 8°N, 12°N, and 15°N over the 2006–2014 period. Analysis of data from these RAMA buoys indicates that SLTI forms after the summer monsoon and becomes fully developed during winter (December–February). SLTI exhibits a strong geographical dependency, with more frequent (80% times during winter) and intense inversions (amplitude, ΔT ∼ 0.7°C) occurring only in the northern BoB compared to central and southern Bay. SLTI also exhibits large interannual and intraseasonal variations, with intraseasonal amplitude significantly larger (ΔT ∼ 0.44°C) than the interannual amplitude (∼0.26°C). Heat budget analysis of the mixed layer reveals that the net surface heat loss is the most dominant process controlling the formation and maintenance of SLTI. However, there are instances of episodic advection of cold, low‐saline waters over warm‐saline waters leading to the formation of SLTI as in 2012–2013. Vertical processes contribute significantly to the mixed layer heat budget during winter, by warming the surface layer through entrainment and vertical diffusion.

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Section: Driving Processessupporting

confidence: 71%

Surface layer temperature inversion in the Bay of Bengal: Main characteristics and related mechanisms

et al. 2016

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“…The resulting high pressure over the Arabian Peninsula and low pressure under the Intertropical Convergence Zone (ITCZ) around 10°S drive the Indian Winter Monsoon (IWM), characterized by northeasterly winds over the AS (Figure a). While IWM contributes significantly to the annual precipitation over the Himalayan region (e.g., Dimri et al, ) and the southeastern India and Sri Lanka (e.g., Rajeevan et al, ; Vialard et al, ), most of the rainfall occurs over the ocean around 10°S, thereby forming only a small fraction of the annual rainfall over India. Nonetheless, the winter monsoon has its most important implications for the biogeochemistry and ecosystems of the northern IO (e.g., Smith & Madhupratap, ).…”

Section: Introductionmentioning

confidence: 99%

Robust Projected Weakening of Winter Monsoon Winds Over the Arabian Sea Under Climate Change

Parvathi

Suresh

Lengaigne

et al. 2017

Geophysical Research Letters

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The response of the Indian winter monsoon to climate change has received considerably less attention than that of the summer monsoon. We show here that all Coupled Model Intercomparison Project Phase 5 (CMIP5) models display a consistent reduction (of 6.5% for Representative Concentration Pathways 8.5 and 3.5% for 4.5, on an average) of the winter monsoon winds over the Arabian Sea at the end of 21st century. This projected reduction weakens but remains robust when corrected for overestimated winter Arabian Sea winds in CMIP5. This weakening is driven by a reduction in the interhemispheric sea level pressure gradient resulting from enhanced warming of the dry Arabian Peninsula relative to the southern Indian Ocean. The wind weakening reduces winter oceanic heat losses to the atmosphere and deepening of convective mixed layer in the northern Arabian Sea and hence can potentially inhibit the seasonal chlorophyll bloom that contributes substantially to the Arabian Sea annual productivity.

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“…Most of these have focused on the summer monsoon, because of its implications for rainfall patterns and water supply in countries downstream of the summer monsoon 13,[15][16][17] ; and especially because of its consequences for coastal upwelling, biological productivity and fisheries in countries bordering the AS 3 . In contrast, the response of the boreal winter component of the monsoon cycle to global warming has received far less attention, despite knowledge that it has a significant impact on annual precipitation patterns over the HTP region and over southeast India and Sri Lanka 18 , and on winter convective mixing, responsible for sustaining the large phytoplankton blooms of winter, which contribute significantly to enhancing the rich fisheries potential of the AS 4,5,12,19 .…”

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Ecosystem state change in the Arabian Sea fuelled by the recent loss of snow over the Himalayan-Tibetan Plateau region

Goés

Tian

Gomes

et al. 2020

Sci Rep

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The recent trend of global warming has exerted a disproportionately strong influence on the Eurasian land surface, causing a steady decline in snow cover extent over the Himalayan-tibetan plateau region. Here we show that this loss of snow is undermining winter convective mixing and causing stratification of the upper layer of the Arabian Sea at a much faster rate than predicted by global climate models. over the past four decades, the Arabian Sea has also experienced a profound loss of inorganic nitrate. in all probability, this is due to increased denitrification caused by the expansion of the permanent oxygen minimum zone and consequent changes in nutrient stoichiometries. these exceptional changes appear to be creating a niche particularly favorable to the mixotroph, Noctiluca scintillans which has recently replaced diatoms as the dominant winter, bloom forming organism. Although Noctiluca blooms are non-toxic, they can cause fish mortality by exacerbating oxygen deficiency and ammonification of seawater. As a consequence, their continued range expansion represents a significant and growing threat for regional fisheries and the welfare of coastal populations dependent on the Arabian Sea for sustenance. The Arabian Sea (AS) is a unique, low-latitude oceanic ecosystem because it is influenced by monsoonal winds that reverse their direction seasonally 1. These reversing winds cause dynamic shifts in surface currents and alterations in the pycnocline, which help fertilize its normally nutrient-depleted surface layers. However, the mechanisms that drive water-column mixing, the upward transport of nutrients and the consequent upsurge of phytoplankton biomass during the summer (Jun.-Sep.) and the winter (Nov.-Feb.) monsoons are different 2-6. During the summer monsoon, nutrient enrichment is via coastal upwelling, which begins when the adjacent land mass becomes warmer relative to the AS, and low pressure develops over the Arabian Peninsula 3,7,8. During this time of the year, strong topographically-steered southwesterly winds blowing over the AS form a low-level atmospheric jet called the Findlater Jet 9. This jet induces a northeastwardly flow of the surface currents, leading to strong upwelling of deep, nutrient-rich waters, causing large phytoplankton blooms along the coasts of Somalia, Yemen, and Oman 3,5,6,10,11. In contrast, during winter, when the Eurasian continent cools, nutrient enrichment is via deep penetrative convective mixing as a result of excessive heat loss from the AS surface layer caused by cold and dry northeasterly winds blowing from the snow-covered Himalayan-Tibetan Plateau (HTP) 4,5. The erosion of the thermocline, and entrainment of deep (100-150 m) nutrient-rich waters into the surface layer of the AS, begins as early as Dec., and has a major influence on winter phytoplankton blooms observable as far south as 14°N 4,11,12 .

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Factors controlling January–April rainfall over southern India and Sri Lanka

Cited by 15 publications

References 44 publications

Surface layer temperature inversion in the Bay of Bengal: Main characteristics and related mechanisms

Surface layer temperature inversion in the Bay of Bengal: Main characteristics and related mechanisms

Robust Projected Weakening of Winter Monsoon Winds Over the Arabian Sea Under Climate Change

Ecosystem state change in the Arabian Sea fuelled by the recent loss of snow over the Himalayan-Tibetan Plateau region

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