Variability of monsoon inversion over the Arabian Sea and its impact on rainfall

Dwivedi, Sanjeev; Viswanadhapalli, Yesubabu; Ratnam, M. Venkat; Dasari, Hari Prasad; Langodan, Sabique; Raj, Sarath; Hoteit, Ibrahim

doi:10.1002/joc.6896

Cited by 17 publications

(13 citation statements)

References 75 publications

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“…This is reasonable as the prevailing anomalous northeasterly winds reduce the advection of cold maritime air at low levels, while enhanced easterly winds in the middle troposphere prevent the advection of warm, desert air from the northwest at middle levels, effectively reducing the strength of inversion. Indeed, this is consistent with the noted decrease and increase in strength of inversion in this region during the active and break phases of the Indian monsoon, respectively (Narayanan and Rao, 1981;Dwivedi et al, 2021). In fact, the reduction in strength of inversion was also noted by Miller and Keshavamurty (1968) in their original study of a MTC.…”

Section: Rainy Day Compositessupporting

confidence: 83%

Classification of Middle Tropospheric Systems over the Arabian Sea and Western India

Kushwaha¹,

Sukhatme²,

Nanjundiah³

2022

Preprint

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The formation of Middle Tropospheric Cyclones (MTCs) that are responsible for a large portion of annual precipitation and extreme rainfall events over western India is studied using an unsupervised machine learning algorithm and cyclone tracking. Both approaches reveal four dominant weather patterns that lead to the genesis of these systems; specifically, re-intensification of westward moving synoptic systems from Bay of Bengal (Type 1, 51%), in-situ formation with a coexisting cyclonic system over the Bay of Bengal that precedes (Type 2a, 31%) or follows (Type 2b, 10%) genesis in the Arabian Sea, and finally in-situ genesis within a northwestward propagating cyclonic anomaly from the south Bay of Bengal (Type 2c, 8%). Thus, a large fraction of rainy middle tropospheric synoptic systems in this region form in association with cyclonic activity in the Bay of Bengal. The four variants identified also show a marked dependence on large-scale environmental features with Type 1 and Type 2a formation primarily occurring in phases 4 and 5, and Type 2b and Type 2c in phases 3 and 4 of the Boreal Summer Intraseasonal Oscillation. Further, while insitu formation with a Bay of Bengal cyclonic anomaly (Type 2a and 2b) mostly occurs in June, downstream development is more likely in the core of the monsoon season. Out of all categories, Type 2a is associated with the highest rain rate (60 mm/day) and points towards the dynamical interaction between a low pressure system over the Bay of Bengal and the development of MTCs over western India and the northeast Arabian Sea. This classification, identification of precursors, connection with cyclonic activity over the Bay of Bengal and dependence on large-scale environment provides an avenue for better understanding and prediction of rain-bearing MTCs over western India.

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Section: Rainy Day Compositessupporting

confidence: 83%

Classification of Middle Tropospheric Systems over the Arabian Sea and Western India

Kushwaha¹,

Sukhatme²,

Nanjundiah³

2022

Preprint

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“…To enhance the land sea contrast in the downscaled simulations and to represent precisely the lower boundary conditions, the low‐resolution SST fields from ERA‐Interim data are replaced with time‐varying high‐resolution SST obtained from the RTG‐HR (Gemmill et al ., 2007). The complete details on the model initialization and physical parameterization utilized in this study are discussed in the studied of Viswanadhapalli et al ., 2019a and Dwivedi et al ., 2021.…”

Section: Model Configuration Data and Methodologymentioning

confidence: 99%

Evaluation of Weather Research and Forecasting model downscaled rainfall and its variability over India

Kumar

Viswanadhapalli

Naidu

et al. 2021

Intl Journal of Climatology

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Long‐term variations in the frequencies of different rainfall events during summer monsoon season (June through September) are analysed over a period of 38‐years (1980–2017) using the simulations of weather research and forecasting (WRF) model evaluated against the India Meteorological Department (IMD). Further, we have divided the study period into two sub‐periods such as before (1980–1998), and after the mega ENSO event (1999–2017). Our analysis suggests the WRF exhibits good skill in capturing the increased trends in the frequency of heavy and very heavy (extreme) rainfall events during the recent epoch (1999–2017).We have assessed the skill of WRF in capturing the observed probability distributions of daily rain rates over different sub‐regions of India. Our results depict that the downscaled products of WRF captured well the extreme rainfall as observed in IMD, signifying that this dynamically downscaled model with continuous 36‐hr re‐initialization makes it suitable to simulate extreme rainfall events compared to light rainfall event. However, our analysis reports that there is a slight overestimation in WRF rainfall and fails in capturing the light rainfall events compared to IMD. The overestimation of rainfall by WRF possibly be due to increased pressure gradients and enhances the convection in the upper streams and associated rainfall. Our study emphasizes that the variability in summer monsoon rainfall during the recent period is due to the changes in the monsoon circulations, particularly monsoon low‐level jet that leads to alter the moisture budget in terms of moisture convergence and transport. Moreover, the variability in frequencies of rainfall events are analysed for strong La Niña/El Niño years and observed an increase in extremes over major part of India during strong La Niña except over parts of Central India and NEI where strong El Niño dominates; which is well captured by the WRF model.

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“…The monsoon low-level jet (MLLJ), a southwesterly wind-flow confined to a narrow region over the western Arabian Sea, is a prime indicator of the ISM circulation (Joseph and Raman, 1966;Findlater, 1969). The MLLJ originates from cross-equatorial flow and acts as an important driver for transporting moisture toward the Indian region, controlling the monsoon inversion layers over the west central Arabian Sea (Dwivedi et al, 2016(Dwivedi et al, , 2021. The MLLJ further feeds moisture to the monsoon depressions formed over the Bay of Bengal (BoB) (Nagar et al, 2009;Walker et al, 2015) and modulate the rainfall over India (Roxy et al, 2017;Viswanadhapalli et al, 2020).…”

Section: Monsoon Circulationmentioning

confidence: 99%

“…This also influences the exchange of moisture and energy between the ocean surfaces (Narayanan and Rao, 1981). The difference in temperature between the pressure levels of 850 and 950 hPa [ T = T 850hPa -T 950hPa )] is used here to identify the MI (Dwivedi et al, 2016(Dwivedi et al, , 2021 for all WRF downscaling experiments during the three studied monsoon seasons and is compared with that of ERA5 (Figure 8). Muraleedharan et al (2013) revealed that higher (lower) MI values over the western Arabian Sea are associated with the active (break) phases of the ISM.…”

Section: Monsoon Inversion Over the Arabian Seamentioning

confidence: 99%

“…Muraleedharan et al (2013) revealed that higher (lower) MI values over the western Arabian Sea are associated with the active (break) phases of the ISM. Dwivedi et al (2016Dwivedi et al ( , 2021 reported that the strengthening of the MI is associated with a weak or a drought monsoon season. The analysis of MI as resulting from ERA5 suggests that the seasonal mean of MI is stronger over the west-central Arabian Sea during the drought season (Figure 8).…”

Section: Monsoon Inversion Over the Arabian Seamentioning

confidence: 99%

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Enhanced Simulation of the Indian Summer Monsoon Rainfall Using Regional Climate Modeling and Continuous Data Assimilation

et al. 2022

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This study assesses a Continuous Data Assimilation (CDA) dynamical-downscaling algorithm for enhancing the simulation of the Indian summer monsoon (ISM) system. CDA is a mathematically rigorous technique that has been recently introduced to constrain the large-scale features of high-resolution atmospheric models with coarse spatial scale data. It is similar to spectral nudging but does not require any spectral decomposition for scales separation. This is expected to be particularly relevant for ISM, which involves various interactions between large-scale circulations and regional physical processes. Along with a control simulation, several downscaling simulations were conducted with the Weather Research and Forecasting (WRF) model configured over the Indian monsoon region at 10 km horizontal resolution using CDA, spectral (retaining different wavenumbers) and grid nudging for three contrasting ISM rainfall seasons: normal (2016), excess (2013), and drought (2009). The simulations are nested within the global NCEP Final Analysis data available at 1 × 1° horizontal resolution. The model outputs are evaluated against the India Meteorological Department (IMD) gridded precipitation and the fifth generation ECMWF atmospheric reanalysis (ERA-5). Compared to grid and spectral nudging, the simulations using CDA produce enhanced ISM features over the Indian subcontinent including the low-level jet, tropical easterly jet, easterly wind shear, and rainfall distributions for all investigated ISM seasons. The major ISM processes, in particular the monsoon inversion over the Arabian Sea, tropospheric temperature gradients and moist static energy over central India, and zonal wind shear over the monsoon region, are all better simulated with CDA. Spectral nudging outputs are found to be sensitive to the choice of the wavenumber, requiring careful tuning to provide robust simulations of the ISM system. In contrast, control and grid nudging generally fail to well-reproduce some of the main ISM features.

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Variability of monsoon inversion over the Arabian Sea and its impact on rainfall

Cited by 17 publications

References 75 publications

Classification of Middle Tropospheric Systems over the Arabian Sea and Western India

Classification of Middle Tropospheric Systems over the Arabian Sea and Western India

Evaluation of Weather Research and Forecasting model downscaled rainfall and its variability over India

Enhanced Simulation of the Indian Summer Monsoon Rainfall Using Regional Climate Modeling and Continuous Data Assimilation

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