scholarly journals Influence of upper level troughs and ridges on the formation of post-monsoon cyclones in the Bay of Bengal

MAUSAM ◽  
2021 ◽  
Vol 10 (1) ◽  
pp. 7-24
Author(s):  
S. N. SEN
Keyword(s):  
Tropical Cyclones ◽  
Cross Sections ◽  
Bay Of Bengal ◽  
Middle Latitude ◽  
Northeast India ◽  
Contributory Factor ◽  
The South ◽  
Minimum Requirement ◽  
Post Monsoon ◽  
Upper Level

The upper air conditions at the formative stages of several depressions and cyclones in the Indian seas were studied by Desai and Rao in the light of Riehl model for the formation of tropical cyclones. The recent introduction of twice daily radiosonde-rawin ascents at some stations in India provided additional facilities for similar studies in this area. The available upper air conditions associated with the formation of two post-monsoon cyclones of 1955 in the Bay of Bengal  were accordingly studied with the idea of finding how far Riehl's theory of tropical cyclones could be applied in these cases.   The present study of the post-monsoon cyclones of 1955 reveals that two radiosonde ascents a day from a reasonable network of stations should be minimum requirement for studies of this kind, Time cross-sections showing 24-hour changes of heights at intervals of 12 hours are presented to illustrate the sequence of movement of upper troughs and ridges. As postulated by Riehl, the formation of both the cyclones was apparently associated with the passage of troughs in the westerlies across northeast India, i.e., to the north of the area of cyclogenesis. But the upper air data from the available network of stations were too inadequate for drawing any definite conclusion as to whether the initial mass divergence at upper level was caused by the southward extension of the westerly trough and the superposition of its forward portion over the surface incipient low, or by the in-phase superposition of the upper trough in the westerlies with the upper tropospheric vortices moving across the Bay of pour Bengal, Dynamical development to the south of a confluent trough in the westerlies is suggested as a possible , contributory factor for the cyclogenesis in the south Bay of Bengal.   The influence of the middle-latitude trough on the recurvature of one of the cyclones while out at sea and of 453474 another similar cyclone of October 1949 which had recurved only after crossing the coast, and the unexpected weakening of the former while out at sea, have been discussed.

scholarly journals Modulation of environmental conditions on the significant difference in the super cyclone formation rate during the pre- and post-monsoon seasons over the Bay of Bengal

2021 ◽  
Author(s):  
Zhi Li ◽  
Yuhuan Xue ◽  
Yue Fang ◽  
Kuiping Li
Keyword(s):  
Bay Of Bengal ◽  
Monsoon Season ◽  
Formation Rate ◽  
Specific Humidity ◽  
Global Maximum ◽  
Tropical Ocean ◽  
Post Monsoon ◽  
Significant Difference ◽  
Post Monsoon Season ◽  
Upper Level

AbstractUnlike other tropical ocean basins, the Bay of Bengal (BoB) has two tropical cyclone (TC) seasons: a pre-monsoon season (Pre-MS) and a post-monsoon season (Post-MS). More interestingly, during the period from 1981 to 2016, the global maximum and minimum formation rates of super cyclones (SCs, categories 4 and 5) occurred in the Pre-MS and Post-MS, respectively, in the BoB. Methods including Butterworth filter, box difference index analysis and quantitative diagnosis were utilized herein to detect what and how background environmental factors cause significantly different SC formation rates between the Pre- and Post-MS. Diagnosis results revealed that the vertical temperature difference (VTD) mainly determines whether TCs can develop into SCs during the Post-MS, similar to Pre-MS. It’s in agreement with previous studies demonstrating that the VTD is controlled by the low-level temperature during the Post-MS but is determined by the upper-level temperature during the Pre-MS. The results also revealed that the background sea surface temperature is much higher in the Pre-MS than in the Post-MS and forces higher 1000 hPa-level air temperature. Additionally, there is higher saturated specific humidity (qs) due to the higher temperature in the Pre-MS. The differences in the bottom-level temperature and qs cooperate to predominantly contribute to the significant difference in Vpot2, which could denote the maximum potential intensity of TC, eventually leading to the remarkably different SC formation rates between the Pre- and Post-MS in the BoB.

scholarly journals Climatology of Energetics of cyclones over Indian Seas

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Somenath Dutta ◽  
Geena Sandhu ◽  
Sanjay G Narkhedkar ◽  
Sunitha Devi
Keyword(s):  
Tropical Cyclones ◽  
Bay Of Bengal ◽  
Arabian Sea ◽  
Monsoon Season ◽  
Recent Decade ◽  
Reanalysis Data ◽  
Monsoon Period ◽  
Post Monsoon ◽  
Post Monsoon Season ◽  
Indian Seas

The study discusses the energetic aspects of tropical cyclones formed over Arabian Sea (AS) and Bay of Bengal (BOB) during the period from 1991 till 2013 and aims at bringing out climatology of the energetics of tropical cyclones over Indian Seas. Total 88 cyclones that developed over the Indian Seas during the recent decade of 1991-2013 have been studied. These intense systems are categorized on the basis of their formation region and season of formation. It is seen that during the study period, the frequency of formation of cyclones over BOB is twice that over AS which is consistent with the climatology of the regions. Further, it is noticed that over both the regions, they are more frequently formed in the post monsoon period compared to pre monsoon. The trend analysis of the frequency of cyclones forming over both basins, season wise shows that the overall trend for both basins is of just decreasing type. However, for Arabian Sea; the decreasing trend is more apparent in the post monsoon season, whereas in the case of the Bay of Bengal the decreasing trend is more evident in the pre monsoon season. Various energy terms, their generation and conversion terms have been computed using NCEP/NCAR reanalysis data. Day to day quantitative analysis of these parameters is studied critically during various stages of the cyclones. The composites of these categorized systems are formed and studied. The formative, intensification and dissipation stages showed variations in their energy terms.

scholarly journals EI- Nino and tropical storm tracks over Bay of Bengal during post monsoon season

MAUSAM ◽  
2021 ◽  
Vol 42 (3) ◽  
pp. 257-260
Author(s):  
AKHILESH GUPTA ◽  
A. MUTHUCHAMI
Keyword(s):  
Tropical Cyclones ◽  
Bay Of Bengal ◽  
Tamil Nadu ◽  
Andhra Pradesh ◽  
Southern Oscillation ◽  
Monsoon Season ◽  
Post Monsoon ◽  
Post Monsoon Season ◽  
Cent Level

The role of EI-Nino in modulating tropical cyclone motion over Bay of Bengal during post monsoon season has been examined. Storms which formed during the years 1901-1987 have been classified into recuriving or those of which crossing north of 17° N and non-recurving or those of which crossing south of 17° N the east coast of India. It has been found that in most of the cases (87 %) during EI-Nino years, the tropical cyclones which formed over Bay of Bengal crossed south of 17° N, i.e. south Andhra Pradesh Tamil Nadu coast, whereas tropical cyclones, ed during the year prior to the EI-Nino years [El- Nino (-1 ) year] are seen crossing mostly (in 79% of cases) either h of 17°N or recurving m northeastward direction. In other years this kind of behaviour is not generally onseerved. The correlation between southern oscillation indices and the fractional values of storms crossing south of 170 N for the period 1901-1987 (n=87) is found to be ---0.63 which is significant at 1 per cent level.

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