Genesis of the monsoon trough boundary layer experiment (MONTBLEX)

Sikka, D. R.; Narasimha, R.

doi:10.1007/bf02839270

Cited by 28 publications

(6 citation statements)

References 35 publications

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“…Lightning frequency also drops during periods of strong monsoon when moist winds from the BoB prevail. Stull 1988; and later [78] observed that "the introduction of moisture and buoyant forces into the atmospheric boundary layer is directly influenced by the atmospheric forcing such as frictional drag, solar heating and moisture inflow which begin the thermal convection at the surface level" [78]. Our study supports the analysis made by Romatschke, et al [64] and Choudhury, et al…”

Section: Discussionsupporting

confidence: 85%

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An inclusive study of lightning at various temporal resolutions over North East India using hi-res satellite data

Mahanta,

Saha,

Choudhury

2023

112

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Average lightning flash rate density (LFD) values for North East India (NEI) are analyzed for the 16-years (1998–2013) period based on high resolution TRMM LIS data. The number of lightning flash strokes are most active from March to October with the highest number of lightning strokes happening during the months of April and May, with the monsoon months witnessing the maximum spatial density shifting to the plains area. After October, LFD begin to decrease across the entire region. The highest LFD with a value of 56.65 flashes km-2 year-1, observed along an escarpment in the southern parts of Meghalaya plateau. The minimum is found in the semiarid high altitude districts along the Tibetan border in north with a value of 0.74 flashes km-2 year-1. We observed considerable Convective Available Potential Energy (CAPE) with moderately high LFD during the monsoon season, indicating the importance of these quantities in monsoon convections over this region. The low-level wind flow has a significant impact on the LFD distributions during the entire year. The Himalayas to the North and Bay of Bengal to the south enhance local convergence and convection resulting in lightning. Results of this study can be used in relation to lightning safety standards.

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Section: Discussionsupporting

confidence: 85%

“…Over the north-eastern part of South Asia a total of 90,859 estimated flashes occurred for the entire period. However only 88% (78,941) of the total flashes occurred over NEI and the remaining occurred over parts of Bangladesh, Bhutan and Myanmar bordering NEI. Next we aggregated the data in daily matrices for further analysis.…”

Section: Analysis Methodsmentioning

confidence: 99%

An inclusive study of lightning at various temporal resolutions over North East India using hi-res satellite data

Mahanta,

Saha,

Choudhury

2023

112

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“…For example, most monsoon depressions, which account for almost all extreme rainfall events (rainfall >100 mm day −1 ) over central India, form over the warm waters of the northern BOB and move westward or northwestward along the IMT 16 , 17 . The dynamic and thermodynamic conditions differ over the eastern and western flanks of the IMT 18 . Nevertheless, the variation of the IMT over the BOB is not well considered by the existing monsoon indices.…”

Section: Introductionmentioning

confidence: 99%

A predictable prospect of the South Asian summer monsoon

et al. 2022

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Prediction of the South Asian summer monsoon (SASM) has remained a challenge for both scientific research and operational climate prediction for decades. By identifying two dominant modes of the SASM, here we show that the unsatisfactory prediction may be due to the fact that the existing SASM indices are mostly related to the less predictable second mode. The first mode, in fact, is highly predictable. It is physically linked to the variation of the Indian monsoon trough coupled with large rainfall anomalies over core monsoon zone and the northern Bay of Bengal. An index is constructed as a physical proxy of this first mode, which can be well predicted one season in advance, with an overall skill of 0.698 for 1979–2020. This result suggests a predictable prospect of the SASM, and we recommend the new index for real-time monitoring and prediction of the SASM.

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“…But during wet situations the jet is found to be better organized; its axis is around the 950 hPa level, and the velocities are between 4 and 8 m/s both morning and evening (figures 8a and b). It is well known that a low level jet occurs over peninsular India during the monsoons (Joseph and Raman 1966;Rao 1976), as an extension of the Findlater jet (Findlater 1969) over the Arabian Sea; this jet, usually located around 15~ is generally observed at central and southern stations south of 20~ Although the presence of such a jet at latitudes beyond 20~ does not appear to have been studied, it is possible to interpret the data, such as from figure 3 in Sikka and Narasimha (1995), as indicating a westerly jet over Jodhpur, especially during a break in the monsoon. There was no classical 'break' in 1990 (Srivastav 1995); at any rate it is generally considered that at the latitude of Jodhpur such a jet, even if present, will be weak.…”

Section: Radiosonde Datamentioning

confidence: 99%

Thermal and wind structure of the monsoon trough boundary layer

Rajkumar

Narasimha

Singal

et al. 1996

Proc. Indian Acad. Sci. (Earth Planet Sci.)

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Radiosonde data from Jodhpur, taken at 0530, 1730 and around ll00hrlST during MONTBLEX 1990, reveal that the distribution of virtual potential temperature 0~ below about 500 hPa has a structure characterized by up to three layers each of approximately constant gradient. We are thus led to introduce a characterization of the observed thermal structure through a sequence of the symbols N, S and U, standing respectively for neutral, stable or unstable con&tlons in the different layers, beginning with the one closest to the ground. It is found that, of the 29 combinations possible, only the seven classes, S, SS', SNS', NS, NSS', USS' and UNS are observed, where S' stands for a stable layer with a different gradient of 0, than in the layer S. It is also found that, in 90 %0 of the launches at 0530 hr, 48 %0 of the launches at 1730 hr and 69% of the launches around 1100 hr, the first radiosonde layer near the ground is stable; the classical mixed layer was found in only 11%0 of the data set analysed, and, if present on other occasions, must have been less than 250m in height, the first level at which radiosonde data are avadable. Supplementing the above data, sodar echograms, available during 82% of the time between June and August 1990, suggest a stable layer up to a few tens of metres 48%o of the time. A comparative study of the radiosonde data at Ranch1 shows that the frequent prevalence of stability near the surface at Jodhpur cannot be attributed entirely to the large scale subsidence known to be characteristic of the Rajasthan area. Further, data at Jodhpur reveal a weak low level jet at heights generally ranging from 400 to 900 m with wind speeds of 6 to 15m/s. Based on these results, it is conjectured that the lowest layers in the atmosphere during the monsoons, especially with heavy clouding or rain, may frequently be closer to the classical nocturnal boundary layer than to the standard convective mixed layer, although often with shallow plumes that penetrate such a stable layer during daytime.

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Genesis of the monsoon trough boundary layer experiment (MONTBLEX)

Cited by 28 publications

References 35 publications

An inclusive study of lightning at various temporal resolutions over North East India using hi-res satellite data

An inclusive study of lightning at various temporal resolutions over North East India using hi-res satellite data

A predictable prospect of the South Asian summer monsoon

Thermal and wind structure of the monsoon trough boundary layer

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