Bimodal Character of Cyclone Climatology in the Bay of Bengal Modulated by Monsoon Seasonal Cycle*

2013 ◽  
Vol 26 (3) ◽  
pp. 1033-1046 ◽  
Author(s):  
Zhi Li ◽  
Weidong Yu ◽  
Tim Li ◽  
V. S. N. Murty ◽  
Fredolin Tangang
Keyword(s):  
Relative Humidity ◽  
Bay Of Bengal ◽  
Heat Content ◽  
Environmental Parameters ◽  
Vertical Shear ◽  
Boreal Summer ◽  
Humidity Effect ◽  
Conventional View ◽  
The Difference ◽  
Relative Humidity Effect

Abstract The annual cycle of tropical cyclone (TC) frequency over the Bay of Bengal (BoB) exhibits a notable bimodal character, different from a single peak in other basins. The causes of this peculiar feature were investigated through the diagnosis of a genesis potential index (GPI) with the use of the NCEP Reanalysis I dataset during the period 1981–2009. A methodology was developed to quantitatively assess the relative contributions of four environmental parameters. Different from a conventional view that the seasonal change of vertical shear causes the bimodal feature, it was found that the strengthened vertical shear alone from boreal spring to summer cannot overcome the relative humidity effect. It is the combined effect of vertical shear, vorticity, and SST that leads to the GPI minimum in boreal summer. It is noted that TC frequency in October–November is higher than that in April–May, which is primarily attributed to the difference of mean relative humidity between the two periods. In contrast, more supercyclones (category 4 or above) occur in April–May than in October–November. It is argued that greater ocean heat content, the first branch of northward-propagating intraseasonal oscillations (ISOs) associated with the monsoon onset over the BoB, and stronger ISO intensity in April–May are favorable environmental conditions for cyclone intensification.

Seasonal and Intraseasonal Modulation of Tropical Cyclogenesis Environment over the Bay of Bengal during the Extended Summer Monsoon

2012 ◽  
Vol 25 (8) ◽  
pp. 2914-2930 ◽  
Author(s):  
Wataru Yanase ◽  
Masaki Satoh ◽  
Hiroshi Taniguchi ◽  
Hatsuki Fujinami
Keyword(s):  
Relative Humidity ◽  
Summer Monsoon ◽  
Bay Of Bengal ◽  
Monsoon Season ◽  
Intraseasonal Oscillation ◽  
Vertical Shear ◽  
Boreal Summer ◽  
Tropical Cyclogenesis ◽  
Composite Analysis ◽  
Absolute Vorticity

Abstract The environmental field of tropical cyclogenesis over the Bay of Bengal is analyzed for the extended summer monsoon season (approximately May–November) using best-track and reanalysis data. Genesis potential index (GPI) is used to assess four possible environmental factors responsible for tropical cyclogenesis: lower-tropospheric absolute vorticity, vertical shear, potential intensity, and midtropospheric relative humidity. The climatological cyclogenesis is active within high GPI in the premonsoon (~May) and postmonsoon seasons (approximately October–November), which is attributed to weak vertical shear. The genesis of intense tropical cyclone is suppressed within the low GPI in the mature monsoon (approximately June–September), which is due to the strong vertical shear. In addition to the climatological seasonal transition, the authors’ composite analysis based on tropical cyclogenesis identified a high GPI signal moving northward with a periodicity of approximately 30–40 days, which is associated with boreal summer intraseasonal oscillation (BSISO). In a composite analysis based on the BSISO phase, the active cyclogenesis occurs in the high GPI phase of BSISO. It is revealed that the high GPI of BSISO is attributed to high relative humidity and large absolute vorticity. Furthermore, in the mature monsoon season, when the vertical shear is climatologically strong, tropical cyclogenesis particularly favors the phase of BSISO that reduces vertical shear effectively. Thus, the combination of seasonal and intraseasonal effects is important for the tropical cyclogenesis, rather than the independent effects.

scholarly journals Mechanisms of the Northward Movement of Submonthly Scale Vortices over the Bay of Bengal during the Boreal Summer

2006 ◽  
Vol 134 (8) ◽  
pp. 2251-2265 ◽  
Author(s):  
Satoru Yokoi ◽  
Takehiko Satomura
Keyword(s):  
Bay Of Bengal ◽  
Lower Troposphere ◽  
Meridional Wind ◽  
Relative Vorticity ◽  
Vertical Shear ◽  
Boreal Summer ◽  
Meridional Component ◽  
Upper Troposphere ◽  
Budget Analysis ◽  
Vorticity Anomaly

Abstract Mechanisms of the northward movement of submonthly scale vortices over the Bay of Bengal during the boreal summer (May–September) are studied with the use of a vorticity budget analysis applied to the ECMWF 40-yr Re-Analysis (ERA-40) data. To quantitatively evaluate the contribution from each term that constitutes the vorticity anomaly equation to the movement of the vortices, a vector measure, termed the forcing vector (FV), is used in the present study. Because the axis of the submonthly scale relative vorticity anomaly does not tilt meridionally below the 200-hPa level, the mechanisms of the northward movement of a composite submonthly scale vortex integrated from the surface to the 100-hPa level [the barotropic component (BTC)] are studied. The barotropic vortex moves northwestward, with northward speeds of 0.9° day−1. The meridional component of the FV (MFV), which represents the contribution to the meridional component of the movement, reveals that the primary and secondary terms that contribute to the northward movement are the advection of the vortex by the environmental meridional wind, and the tilting effect of the environmental horizontal vorticity vector by the vertical pressure velocity anomaly associated with the vortex, respectively. The former term works mainly in the lower troposphere, while the latter operates in the middle and upper troposphere. The first baroclinic component (FBCC) of the vortex in the troposphere also moves northwestward with almost the same northward speed as the BTC. Mechanisms of the northward movement of the FBCC are also clarified in the present study through examination of the MFV. The primary contributing term is the same as that of the BTC, while the tilting term hinders the northward movement of the FBCC. For the FBCC, the secondary contributing term is the advection of the planetary vorticity by the meridional wind anomaly associated with the horizontal convergence and divergence anomalies in the lower and upper troposphere, respectively. The present study also discusses the phase relation between the BTC and the FBCC from the viewpoint of their northward movement in an environment of easterly vertical shear.

Thermogravimetric study of sequential carbonation and decarbonation processes over Na2ZrO3 at low temperatures (30–80 °C): relative humidity effect

RSC Advances ◽  
2016 ◽  
Vol 6 (71) ◽  
pp. 66579-66588 ◽  
Author(s):  
J. Arturo Mendoza-Nieto ◽  
Heriberto Pfeiffer
Keyword(s):  
Solid State ◽  
Relative Humidity ◽  
Low Temperature ◽  
Low Temperatures ◽  
Humidity Effect ◽  
Temperature Range ◽  
Thermogravimetric Study ◽  
Relative Humidity Effect

Na2ZrO3 was synthetized via solid-state and tested in a low temperature range (30–80 °C) for carbonation and decarbonation processes using RH values between 0 and 80%. Results confirm that it is possible to accomplish successively at least 8 cycles.

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