Role of synoptic-scale forcing in cyclogenesis over the Bay of Bengal

Akter, Nasreen; Tsuboki, Kazuhisa

doi:10.1007/s00382-014-2077-9

Cited by 27 publications

(32 citation statements)

References 31 publications

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“…In the last 21 years (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019)(2020), a total of 18 cyclones occurred during premonsoon with the maximum TC frequency in May (61%) and the minimum in March (6%). The frequencies of premonsoon TCs is almost half that in the postmonsoon season (October-December) due to the presence of a stable layer over the northern BoB; this inhibits the development of TCs even though the monsoon trough is located in the northernmost region of the Bay (Akter and Tsuboki 2014). The larger values (> 50 J kg − 1 ) of convective inhibition (CIN) shown in Fig.…”

Section: Synoptic-scale Dryline and Premonsoon Cyclonesmentioning

confidence: 90%

Tropical Cyclogenesis Associated with Premonsoon Climatological Dryline over the Bay of Bengal

Akter

2021

Preprint

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Tropical cyclones of the Bay of Bengal (BoB) that formed near the synoptic-scale dryline usually intensified over a short distance (~600-800 km) within 3 days and caused severe destruction after landfall. High-resolution simulations of very severe cyclonic storms in association with dryline indicate that the meridional shear aids in the development of a group of linear convective cells that mature as an east-west oriented quasi-linear convective system (QLCS) within the boundary between the dry-moist air masses. The leading edge deep convections are supported by low-level moist southwesterly inflow; however, the typical mid-level mesoscale convective vortex (MCV) associated with these QLCS is unremarkable due to a very narrow trailing stratiform region within the QLCS. Supercells are likely to be organized within the QLCS due to extremely unstable atmospheric conditions resulting from a strong vertical shear of 27-39 m s−1 between 0-6 km and large convective available potential energy of >3000 J kg−1. The vertical shear veering with height causes several numbers of low-level mesovortices having diameters less than 10 km at the leading edge in the different convective stages of the QLCS. The dryline aloft in the BoB produces horizontal positive shear vorticity of the order 10–5 s−1 with higher values in the levels 850-600 hPa. The advection of intense cloud-scale cyclonic vortices (~10–3 s−1) assists and enhances a cyclonic vortex to the rear side of the QLCS that performs as an MCV for cyclogenesis over the BoB.

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Section: Synoptic-scale Dryline and Premonsoon Cyclonesmentioning

confidence: 90%

Tropical Cyclogenesis Associated with Premonsoon Climatological Dryline over the Bay of Bengal

Akter

2021

Preprint

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“…Low‐to‐mid‐level RH in the NIO is also usually moderate, with average value over 70% from the pre‐ to post‐monsoon season. It was discussed in Akter and Tsuboki () that during pre‐monsoon the westerlies over India would bring dry air from the continent into BoB that lowers the potential for convection development, however, the southwesterlies from the equatorial region bring in abundant moisture such that RH is maintained high in BoB. At the same time, MSE is quite zonally uniform in the NIO (not shown).…”

Section: The Active Tc Seasons In As and Bobmentioning

confidence: 99%

Comparison between the active tropical cyclone seasons over the Arabian Sea and Bay of Bengal

Sattar

Cheung

2019

Intl Journal of Climatology

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Climatologically, tropical cyclone (TC) activity in the North Indian Ocean (NIO) is asymmetric between the Arabian Sea (AS) and Bay of Bengal (BoB) basin. For the 172 TCs formed over NIO during 1983–2015, only 56 formed over AS and the rest (116) over BoB. During the period, AS was very active in a few years (but with quiet BoB season), and the opposite occurred in some others. It is found that this contrast occurred mostly during the post‐monsoon season of October–December. The meteorological and climate factors that accounted for these contrasting AS and BoB TC seasons are analysed. While climate variability such as the El Niño Southern Oscillation and Indian Ocean Dipole have known influences to NIO TC activity, results reveal that no single climate mode can well explain the TC development concentrating on AS or BoB only. Instead, it is found that variability of the northeast monsoon is an important factor responsible for the difference between the two basins. Excess moisture is available over the AS due to anomalous low‐level flow from the equatorial IO in the years in which there are more TCs in that basin, and dryer condition is over the BoB. In these years, there is likely excess northeast monsoon rainfall. The relationship is opposite between post‐monsoon BoB TC activity and the northeast monsoon. Nevertheless, the anomalous flow during active AS TC seasons is similar to that occurs during positive Indian Ocean Dipole, and thus this climate variability may be responsible for redistributing the moisture content in the NIO.

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“…The along‐dryline topography is mostly plains, with a few discontinuous mountain ranges (Eastern Ghat) that have average heights of less than 1000 m. The 20‐year averaged low‐level streamline with moisture flux in the figure indicates that the convergence zone forms during the premonsoon when the dry northwesterly and moist southwesterly winds congregate. Dry air masses (specific humidity <7 g kg −1 ) to the west of the convergence zone are approaching from arid regions in Southwest Asia and Western India, whereas moist air masses (specific humidity >18 g kg −1 ) to the east of the convergence zone are approaching from the BoB (Akter and Tsuboki, ). The potential temperature is found more than 32 °C, and the maximum horizontal wind speed is approximately 6 m s −1 in the west of the convergence zone.…”

Section: Premonsoon Indian Drylinementioning

confidence: 99%

“…The Indian dryline is directly responsible for the formation of severe thunderstorms in the premonsoon. However, Akter and Tsuboki () noticed that the dryline environment supports the reduction of tropical cyclone activity over the adjacent ocean, i.e. in the Bay of Bengal (BoB).…”

Section: Introductionmentioning

confidence: 99%

Climatology of the premonsoon Indian dryline

Akter

Tsuboki

2016

Intl Journal of Climatology

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A northeast‐ to southwest‐oriented surface dryline with a dew point gradient of 1 °C per 10 km develops along the eastern Indian coast during the entire premonsoon season. Deep, hot, dry air of up to 500 hPa moves from arid regions in Southwest Asia and Western India to the Bay of Bengal (BoB), and warm, shallow, moist air from the BoB penetrates below the dry air, forming an inclined moisture gradient aloft to the east and reaching the surface to the west. The slope of the gradient depends on the vertically increased southwesterly wind over the BoB, which gradually intensifies from March to May. Diurnal low‐level temperature variations over the land cause periodic movements of the dry‐moist air convergence zone at the surface in the zonal direction. During the premonsoon, the average east–west diurnal oscillation of the surface dryline is approximately 100 km, and the eastward movement is almost three times faster than the westward movement.

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Role of synoptic-scale forcing in cyclogenesis over the Bay of Bengal

Cited by 27 publications

References 31 publications

Tropical Cyclogenesis Associated with Premonsoon Climatological Dryline over the Bay of Bengal

Tropical Cyclogenesis Associated with Premonsoon Climatological Dryline over the Bay of Bengal

Comparison between the active tropical cyclone seasons over the Arabian Sea and Bay of Bengal

Climatology of the premonsoon Indian dryline

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