The four regional varieties of<scp>South Asian</scp>monsoon low‐pressure systems and their modulation by tropical intraseasonal variability

Deoras, Akshay; Hunt, Kieran M. R.; Turner, Andrew

doi:10.1002/wea.3997

Cited by 10 publications

(27 citation statements)

References 33 publications

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“…Type 2b system formation peaks during phases 3 & 4 of the BSISO, during which the maximum convection and cyclonic vorticity enhancement occur over the south-central Arabian Sea and west equatorial India Ocean. This is in accord with the recent work by Deoras et al (2021); Hunt et al (2021) which suggests that LPS formation in the Arabian Sea and rainfall is usually enhanced during phases 2 − 4 of the BSISO. Finally, Type 2c formation also peaks at phase 3 of BSISO, when the convection over the equatorial Indian ocean is enhanced and migrates northward (Kikuchi et al, 2012).…”

Section: Modulation By Intra-seasonal Oscillationssupporting

confidence: 93%

“…This is not surprising because, during these phases, convection and cyclonic vorticity are enhanced over the north Bay of Bengal, which supports the formation of cyclonic systems (Karmakar and Misra, 2020;Diaz and Boos, 2021). Since Type 1 systems over the Arabian Sea are a result of downstream development of Bay of Bengal lows, their frequency is expected to be directly modulated by cyclonic activity over East India and Bay of Bengal, thereby dependent on ISO phases which control low-pressure center formation over the Bay of Bengal (Deoras et al, 2021;Karmakar et al, 2021). Type 2a systems genesis also occurs during all phases of the ISO but shows peak activity during phase 5, followed by phase 4.…”

Section: Modulation By Intra-seasonal Oscillationsmentioning

confidence: 87%

“…During Phases 6 through 8, convection weakens, representing the dry or break phase over the Indian subcontinent. Several authors have suggested that the BSISO phase and amplitude modulate various meteorological phenomena including the onset of monsoon, formation of cyclones, and monsoon lows (Wheeler and Hendon, 2004;Karmakar et al, 2021;Hunt et al, 2021;Deoras et al, 2021). Thus, it is worth exploring whether the BSISO also influences the formation of synoptic systems in the Arabian Sea and western India.…”

Section: Datamentioning

confidence: 99%

“…These systems show vorticity and wind maxima in the lower troposphere with closed isobars around the center, usually have a vertically upright structure and primarily move west or northwest from the Bay of Bengal to the Indian landmass (Godbole, 1977;Krishnamurthy and Ajayamohan, 2010;Boos et al, 2015). The genesis of these low-pressure systems (LPSs) has received enormous attention in the last few decades, and various mechanisms for their formation have been proposed (Krishnamurti et al, 1977;Shukla, 1978;Goswami et al, 1980;Adames and Ming, 2018;Meera et al, 2019;Diaz and Boos, 2019a,b); further, recent work has brought forth the role of Intraseasonal Oscillations (ISOs) in creating a favorable environment for the genesis of these systems (Karmakar et al, 2021;Deoras et al, 2021). In fact, during the summer monsoon, LPSs over the Bay of Bengal have been classified as being born in-situ or associated with downstream development of South China Sea disturbances (Krishnamurti et al, 1977;Chen and Weng, 1999;Meera et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

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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: Modulation By Intra-seasonal Oscillationssupporting

confidence: 93%

Section: Modulation By Intra-seasonal Oscillationsmentioning

confidence: 87%

Section: Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Kushwaha¹,

Sukhatme²,

Nanjundiah³

2022

Preprint

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“…The monsoon low‐pressure systems (LPSs) are synoptic‐scale vortices embedded in the large‐scale South Asian summer monsoon circulation. These precipitating vortices produce more than half of the summer monsoon rainfall over Central India (Deoras et al., 2021; Hunt & Fletcher, 2019; Krishnamurthy & Ajayamohan, 2010; Praveen et al., 2015; Thomas et al., 2021). The weak cyclonic vortices that form over the Bay of Bengal (BoB) during the summer monsoon season (June to September) were reported more than a century ago (e.g., Blanford (1890); Eliot (1884)).…”

Section: Introductionmentioning

confidence: 99%

A Dynamical Linkage Between Western North Pacific Tropical Cyclones and Indian Monsoon Low‐Pressure Systems

Srujan

Sandeep

Suhas

et al. 2022

Geophysical Research Letters

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The relatively weak tropical storms, known as low‐pressure systems (LPSs), contribute as much as 60% of the seasonal precipitation over the hugely populated central India. More than a third of LPSs are formed by the downstream amplification of the westward propagating disturbances from the Pacific. Here, we show that the downstream LPS genesis is associated with the tropical cyclones (TCs) in the Western North Pacific (WNP). Four major clusters of landfalling TCs that have a relatively lesser degree of recurvature account for about 83% of the downstream LPS genesis. Causality in the fluctuations of the sea level pressure over the Bay of Bengal (BoB) prior to the initiation of LPSs is attributed to the Rossby wave activity over WNP through transfer entropy analysis. Our results suggest a potential for the prediction of the downstream synoptic activity over the BoB at least seven days ahead.

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The structure of strong Indian monsoon low‐pressure systems in subseasonal‐to‐seasonal prediction models

Deoras

Turner

Hunt

2022

Quart J Royal Meteoro Soc

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The structure of strong Indian monsoon low‐pressure systems (LPSs) up to forecast lead times of 15 days in 11 models of the Subseasonal‐to‐Seasonal (S2S) Prediction Project is analysed. Strong LPS (SLPS) tracks are obtained from a catalogue of LPSs tracked in all ensemble members of the S2S models during a common reforecast period of June–September 1999–2010. SLPSs, which have a minimum intensity equal to at least the upper‐quartile intensity of all LPSs, are then composited to generate horizontal and vertical structures of several dynamic and thermodynamic fields. The evolution of fields with forecast lead time and during LPS lifecycle is analysed. Furthermore, the simulation of the lower‐tropospheric monsoon circulation, precipitation biases, and the precipitation contribution of LPSs are analysed. All S2S models and the multimodel mean simulate the lower‐tropospheric monsoon circulation, but prominent dry biases are observed in the Australian Bureau of Meteorology and Environment and Climate Change Canada models. The precipitation contribution of LPSs to the summer mean precipitation is smaller in all S2S models than in tracks derived from ERA‐Interim reanalysis. The location and amplitude of the lower‐tropospheric cold core and the location of maximum precipitation are not well simulated by many models, particularly by the Hydrometeorological Centre of Russia model, in which the cold core is missing altogether. The structure of relative vorticity anomaly in all S2S models and the multimodel mean is shallower and weaker than in ERA‐Interim and MERRA‐2 reanalyses. Though the cold core intensifies through the LPS lifecycle in all models, the warm core features a midlife maximum, except in models such as Australian Bureau of Meteorology and China Meteorological Administration. These results demonstrate the potential for S2S models at simulating the structure of SLPSs, benefiting stakeholders that use S2S models for forecasting.

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The four regional varieties ofSouth Asianmonsoon low‐pressure systems and their modulation by tropical intraseasonal variability

Cited by 10 publications

References 33 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

A Dynamical Linkage Between Western North Pacific Tropical Cyclones and Indian Monsoon Low‐Pressure Systems

The structure of strong Indian monsoon low‐pressure systems in subseasonal‐to‐seasonal prediction models

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