Decreasing intensity of monsoon low-frequency intraseasonal variability over India

Karmakar, Nirupam; Chakraborty, Arindam; Nanjundiah, Ravi S.

doi:10.1088/1748-9326/10/5/054018

Cited by 37 publications

(54 citation statements)

References 35 publications

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“…In the Indian monsoon region, the growth of vegetation is mainly controlled by precipitation [6,7], which has experienced significant changes in intensity and frequency over the past half-century [8][9][10]; these changes will certainly cause shifts in vegetation phenology, such as a significant advance in the start of growing season (SOS) in northern parts (e.g., Punjab, Haryana) of India [11]. Therefore, accurate depictions of vegetation phenology in the Indian monsoon region are urgently needed.…”

Section: Introductionmentioning

confidence: 99%

Determining the Start of the Growing Season from MODIS Data in the Indian Monsoon Region: Identifying Available Data in the Rainy Season and Modeling the Varied Vegetation Growth Trajectories

Shang

Liu

et al. 2018

Remote Sensing

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Abstract:In the Indian monsoon region, frequent cloud cover in the rainy season results in less valid satellite observations during the vegetation growth period, making it difficult to extract land surface phenology (LSP). Even worse, many valid but humid observations were misidentified as clouds in the MODIS cloud mask, causing severe gaps in the LSP product. Using a refined cloud detection approach to separate clear-sky and cloudy observations, this study found that potentially valid observations during the vegetation growth period could be identified. Furthermore, the varied vegetation growth trajectories cannot be well-fitted by a global curve-fitting approach, but can be modelled by using the locally adjusted cubic-spline capping approach, which performed well for any seasonal patterns. Applying this approach, the start of growing season (SOS) was determined with 9.18% of vegetation growth amplitude between the maximum and minimum NDVI to generate the SOS product (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016). The valid percentage of this regional product largely increased from 29.30% to 69.76% compared with the MCD12Q2 product, and its reliability was approximate to that of deciduous broadleaf forest in North America and Europe. This product could serve as a basis for understanding the response of terrestrial ecosystems to the changing Indian monsoon.

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Section: Introductionmentioning

confidence: 99%

Determining the Start of the Growing Season from MODIS Data in the Indian Monsoon Region: Identifying Available Data in the Rainy Season and Modeling the Varied Vegetation Growth Trajectories

Shang

Liu

et al. 2018

Remote Sensing

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“…However, demise dates are strongly associated with the HF‐ISO phases across entire India and demise of the ISM occurs mostly in phase 7 of HF‐ISO except some grid points over northeast India (Figure h). Onset of monsoon rainfall occurring in unfavorable phases of LF‐ISO over the eastern India coincide with the fact that most of the low‐pressure systems that develop over the BoB, in unfavorable LF‐ISO phases in many cases, propagate toward this region and cause substantial amount of rainfall during May–early June (Goswami et al, ; Karmakar et al, , ). This may mark the onset of the ISM rainfall over these regions just before the low‐level westerlies strongly establishes over the domain.…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, we do not consider data over these regions in any of our analysis. Many earlier studies also neglected these regions to study monsoon variability (Karmakar et al, 2015;Krishnamurthy & Shukla, 2007). We also use National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis-1 (Kalnay et al, 1996) data sets to understand large-scale atmospheric patterns during onset/demise of the ISM.…”

Section: Data Set and Methodologymentioning

confidence: 99%

The Relation of Intraseasonal Variations With Local Onset and Demise of the Indian Summer Monsoon

Karmakar

Misra

2019

JGR Atmospheres

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Two of the most important hydroclimatic features of the Indian summer monsoon (ISM) rainfall are its onset/demise and intraseasonal oscillations (ISOs) manifested by the active‐break cycles. In this study, we aim to understand the quantitative association between these two phenomena. An objective definition of local onset/demise of the ISM based on more than a century‐long India Meteorological Department rain gauge observation is taken into consideration. Using multichannel singular spectrum analysis we isolate northward‐propagating low‐frequency (20–60 days; LF‐ISO) and northwestward propagating high‐frequency (10–20 days; HF‐ISO) ISOs from the daily ISM rainfall. Our results suggest that a large number of local onset (59%) and demise (62%) events occur during positive developing phases and positive decaying phases of two ISOs, respectively, with phase locking between LF‐ISO and HF‐ISO being particularly important. Local onset is largely associated with favorable phases of ISOs across India except for LF‐ISO over eastern India and HF‐ISO over western Ghats and central India (CI). We find that local demise is more coherent with the ISO phases, especially with HF‐ISO across the domain. We performed a case study to understand large‐scale association with the onset of the ISM over CI. In 44 of total 58 cases (1948–2005), when CI onset occurred during favorable LF‐ISO or HF‐ISO phase, they are either linked with a northward propagation of convection from the equator in LF‐ISO time scale (28 cases) or westward propagating structures from the western Pacific in HF‐ISO time scale (27 cases).

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“…The reduction in seasonal mean rainfall over India in recent decades (Naidu et al ., ) is also associated with an increase in localized heavy precipitation events (Karmakar et al ., ). It was also found that the amplitude of intraseasonal variability in rainfall during summer is weakening over India (Karmakar et al ., ). In contrast to the literature that suggests a weakening of ISMR in recent decades, a few studies conclude that, in spite of global warming, there is no clear evidence that the strength or variability of ISMR has exhibited any long‐term trend (Kripalani et al ., ; Goswami et al ., ; Kumar et al ., ; Guhathakurta and Revadekar, ).…”

Section: Introductionmentioning

confidence: 99%

Influence of global sea‐surface temperature on ultra‐low‐frequency variability in Indian summer monsoon rainfall

Karmakar

Chakraborty

Nanjundiah

2020

Quart J Royal Meteoro Soc

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A multidecadal or ultra‐low‐frequency mode of variability in Indian summer monsoon rainfall (ISMR) with a spectral peak at nearly 67 years is identified using a nonparametric approach, namely, singular spectrum analysis. Not only does this mode modulate the seasonal mean rainfall over India, but also frequent occurrences of excess or below normal rainfall over India are favored by the phases of this mode. We show that 80% of all droughts occur during the negative phase of this mode, compared with 60% of all floods during its positive phase. Although the existence of this mode was reported in many previous studies, proper understanding of its exact nature and driving mechanism, and how it relates to global sea‐surface temperature (SST), is still not clear. Here, we show that the 67‐year variability in ISMR is associated with a SST mode of similar periodicity, which primarily exhibits a hemispheric SST difference, with the strongest signals over the northern Pacific and Atlantic. The positive phase of this SST mode induces low surface pressure over the northern Arabian Sea. Changes in surface pressure over the northern Arabian Sea govern changes in ISMR. The bridge between the SST mode and central Asian circulation is possibly established through the North Pacific Oscillation. The positive phase of this mode enhances the meridional temperature gradient over India, which acts to strengthen the tropical easterly jet, and subsequently the low‐level westerly jet over India. These lead to a negative surface pressure anomaly over the Indian subcontinent and an associated anomalous cyclonic circulation. The environment thus created is conducive to increased seasonal mean monsoon rainfall over India. The phase of the SST mode is remarkably similar to, and leading by 2–3 years, that of the multidecadal mode in ISMR up to the 1990s. However, the relationship weakens after the early 1990s.

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Decreasing intensity of monsoon low-frequency intraseasonal variability over India

Cited by 37 publications

References 35 publications

Determining the Start of the Growing Season from MODIS Data in the Indian Monsoon Region: Identifying Available Data in the Rainy Season and Modeling the Varied Vegetation Growth Trajectories

Determining the Start of the Growing Season from MODIS Data in the Indian Monsoon Region: Identifying Available Data in the Rainy Season and Modeling the Varied Vegetation Growth Trajectories

The Relation of Intraseasonal Variations With Local Onset and Demise of the Indian Summer Monsoon

Influence of global sea‐surface temperature on ultra‐low‐frequency variability in Indian summer monsoon rainfall

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