Role of warm ocean conditions and the MJO in the genesis and intensification of extremely severe cyclone Fani

AbstractCyclone Fani, in April 2019, was the strongest pre-monsoon cyclone to form in the Bay of Bengal after 1994. It underwent rapid intensification and intensified quickly to an extremely severe cyclone. It maintained a wind speed of ≥ 51 m s−1 (≥ 100 knots) for a record time period of 36 h. The total lifespan of the cyclone was double than the climatological lifespan. Also, the duration of the cyclone in its extremely severe phase and the accumulated cyclone energy were significantly larger than the climatological records for the pre-monsoon season. In the current study, we investigate the ocean-atmospheric conditions that led to its genesis, rapid intensification and long lifespan. Our analysis shows that the Madden Julian Oscillation and anomalous high sea surface temperatures provided conducive dynamic and thermodynamic conditions for the genesis of cyclone Fani, despite forming very close to the equator where cyclogenesis is generally unlikely. Further, favourable ocean subsurface conditions and the presence of a warm core eddy in the region led to its rapid intensification to an extremely severe cyclone. A large area of warm ocean surface and subsurface temperatures aided the cyclone to maintain very high wind speed for a record time period. The vital role of the ocean surface and the subsurface in the genesis and the intensification highlights the need to efficiently incorporate ocean initial conditions (surface and sub-surface) and ocean–atmosphere coupling in the operational cyclone forecasting framework.

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Role of Surface Enthalpy Fluxes in Idealized Simulations of Tropical Depression Spinup

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-17-0119.1 ◽

2018 ◽

Vol 75 (6) ◽

pp. 1811-1831 ◽

Cited By ~ 7

Author(s):

Varun S. Murthy ◽

William R. Boos

Keyword(s):

Wind Speed ◽

Initial Conditions ◽

Early Stage ◽

Three Dimensional ◽

Surface Fluxes ◽

Tropical Cyclogenesis ◽

Radial Gradient ◽

Tropical Depression ◽

Surface Enthalpy

AbstractAn idealized, three-dimensional, cloud-system-resolving model is used to investigate the influence of surface enthalpy flux variations on tropical depression (TD) spinup, an early stage of tropical cyclogenesis in which the role of surface fluxes remains incompletely understood. A range of simulations supports the hypothesis that a negative radial gradient of surface enthalpy flux outside the storm center is necessary for TD spinup but can arise from multiple mechanisms. The negative radial gradient is typically created by the wind speed dependence of surface enthalpy fluxes, consistent with some previous theories for tropical cyclone intensification. However, when surface enthalpy fluxes are prescribed to be independent of wind speed, spinup still occurs, albeit more slowly, with the negative radial gradient of surface enthalpy flux maintained by an enhanced air–sea thermodynamic disequilibrium beneath the cold core of the incipient vortex. Surface enthalpy flux variations seem more important for intensification than initial conditions. For example, a vortex forms and intensifies even from a state of rest when the center of the domain is initialized to be nearly saturated with water vapor, but this intensification is modest in amplitude and transient, lasting less than 12 h, without interactive surface enthalpy flux. Sustained spinup on time scales longer than a day does not occur when surface enthalpy fluxes are horizontally homogeneous or constant, even when fixed at the high value of 200 W m−2. In the ensemble of simulations presented here, the vortex intensification rate scales linearly with the storm-scale surface enthalpy flux anomaly relative to the undisturbed environment.

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Numerical Simulations of the Role of Land Surface Conditions in the Evolution and Structure of Summertime Thunderstorms over a Flat Highland

Monthly Weather Review ◽

10.1175/2007mwr2053.1 ◽

2008 ◽

Vol 136 (1) ◽

pp. 173-188 ◽

Cited By ~ 20

Author(s):

Hiroyuki Yamada

Keyword(s):

Numerical Simulations ◽

Land Surface ◽

Initial Conditions ◽

Precipitation Process ◽

Atmospheric Conditions ◽

Surface Conditions ◽

Central Tibetan Plateau ◽

Vegetation Activity ◽

Cloud Evolution

Abstract Numerical simulations of summertime thunderstorms over a flat highland (4700 m MSL), assuming the central Tibetan Plateau, were conducted with the use of a cloud-resolving nonhydrostatic model. This study was aimed at clarifying the role of land surface conditions, such as soil moisture and vegetation activity, in the evolution and structure of airmass thunderstorms over the plateau. Two simulations with cyclic lateral boundaries and different surfaces of a dry or wet land were initialized using a unique vertical atmospheric profile at dawn. These initial conditions assume the real atmospheric conditions in two periods of the 1998 summer monsoon, which are characterized by a dry or wet surface. The results of the two experiments were used to examine the contrasting features between the two experiments arising from the different surface conditions. The simulations reproduced differences in the convective structure, the conditions of the subcloud layer, and the evaporation rate of precipitation within this layer. These resulted from different surface-heating processes and were supported by the observational evidence clarified in a previous study. Moreover, the simulations also reproduced the cell broadening occurring in both the boundary and cloud layers and different precipitation processes dependent on the updraft strength. The evidence was partly supported by additional analyses of observational data. This study, therefore, demonstrates a significant effect of the plateau surface upon the cloud evolution and the precipitation process.

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Role of total-totals stability index in forecasting of thunderstorm/non-thunderstorm days over Kolkata during pre-monsoon season

MAUSAM ◽

10.54302/mausam.v58i3.1333 ◽

2021 ◽

Vol 58 (3) ◽

pp. 369-374

Author(s):

MEDHA KHOLE ◽

H. R. BISWAS

Keyword(s):

Monsoon Season ◽

Stability Index ◽

Threshold Value ◽

Thunderstorm Activity ◽

Radiosonde Data ◽

Atmospheric Conditions ◽

Probability Of Occurrence ◽

Index Value

The thunderstorm activity over Kolkata during pre-monsoon months (March, April and May) has been studied using the radiosonde data of Kolkata (Dumdum). The objective of the study is to examine the utility of Total-Totals Index (TTI) in forecasting occurrence/non-occurrence of thunderstorm over Kolkata. The investigation reveals that Total-Totals Index can be preliminarily used as a predictor to differentiate thunderstorm and non-thunderstorm days. The probability of occurrence of thunderstorm is higher when Total-Totals Index value is higher. While the exact prediction of thunderstorm in all the cases, using the TTI alone, is obviously not possible as TTI alone does not describe the total atmospheric conditions. However, a significant forecast can be furnished by using a threshold value of Total-Totals Index.

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Evidence for surface organic matter modulation of air-sea CO<sub>2</sub> gas exchange

Biogeosciences Discussions ◽

10.5194/bgd-5-4209-2008 ◽

2008 ◽

Vol 5 (6) ◽

pp. 4209-4233

Author(s):

M. Ll. Calleja ◽

C. M. Duarte ◽

Y. T. Prairie ◽

S. Agustí ◽

G. J. Herndl

Keyword(s):

Organic Matter ◽

Wind Speed ◽

Gas Exchange ◽

Ocean Surface ◽

Co2 Exchange ◽

Gas Transfer ◽

Co2 Fluxes ◽

Transfer Velocity ◽

Gas Transfer Velocity

Abstract. Air-sea CO2 exchange depends on the air-sea CO2 gradient and the gas transfer velocity (k), computed as a simple function of wind speed. Large discrepancies among relationships predicting k from wind suggest that other processes may also contribute significantly to modulate CO2 exchange. Here we report, on the basis of the relationship between the measured gas transfer velocity and the ocean surface organic carbon concentration at the ocean surface, a significant role of surface organic matter in suppressing air-sea gas exchange, at low and intermediate winds, in the open ocean. The potential role of total surface organic matter concentration (TOC) on gas transfer velocity (k) was evaluated by direct measurements of air-sea CO2 fluxes at different wind speeds and locations in the open ocean. According to the results obtained, high surface organic matter contents may lead to lower air-sea CO2 fluxes, for a given air-sea CO2 partial pressure gradient and wind speed below 5 m s−1, compared to that observed at low organic matter contents. We found the bias in calculated gas fluxes resulting from neglecting TOC to co-vary geographically and seasonally with marine productivity. These findings suggest that consideration of the role of organic matter in modulating air-sea CO2 exchange can improve flux estimates and help avoid possible bias associated to variability in surface organic concentration across the ocean.

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Estimation of Ocean Surface Wind Speed and Direction From Polarimetric Radiometry Data

10.21236/ada533831 ◽

2008 ◽

Author(s):

David R. Lyzenga

Keyword(s):

Wind Speed ◽

Surface Wind ◽

Ocean Surface ◽

Surface Wind Speed ◽

Ocean Surface Wind

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Recurrence Characteristics Analysis of Near-Surface Wind Speed Signal with Different Sampling Frequencies

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.599-601.1605 ◽

2014 ◽

Vol 599-601 ◽

pp. 1605-1609 ◽

Cited By ~ 1

Author(s):

Ming Zeng ◽

Zhan Xie Wu ◽

Qing Hao Meng ◽

Jing Hai Li ◽

Shu Gen Ma

Keyword(s):

Wind Speed ◽

Surface Wind ◽

Surface Wind Speed ◽

Recurrence Plot ◽

Sampling Frequency ◽

Near Surface ◽

Gas Leakage ◽

Time Period ◽

Characteristics Analysis ◽

Quantification Analysis

The wind is the main factor to influence the propagation of gas in the atmosphere. Therefore, the wind signal obtained by anemometer will provide us valuable clues for searching gas leakage sources. In this paper, the Recurrence Plot (RP) and Recurrence Quantification Analysis (RQA) are applied to analyze the influence of recurrence characteristics of the wind speed time series under the condition of the same place, the same time period and with the sampling frequency of 1hz, 2hz, 4.2hz, 5hz, 8.3hz, 12.5hz and 16.7hz respectively. Research results show that when the sampling frequency is higher than 5hz, the trends of recurrence nature of different groups are basically unchanged. However, when the sampling frequency is set below 5hz, the original trend of recurrence nature is destroyed, because the recurrence characteristic curves obtained using different sampling frequencies appear cross or overlapping phenomena. The above results indicate that the anemometer will not be able to fully capture the detailed information in wind field when its sampling frequency is lower than 5hz. The recurrence characteristics analysis of the wind speed signals provides an important basis for the optimal selection of anemometer.

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Dust Production around Carbon-Rich Stars: The Role of Metallicity

Universe ◽

10.3390/universe7070233 ◽

2021 ◽

Vol 7 (7) ◽

pp. 233

Author(s):

Ambra Nanni ◽

Sergio Cristallo ◽

Jacco Th. van Loon ◽

Martin A. T. Groenewegen

Keyword(s):

Wind Speed ◽

Galactic Halo ◽

Magellanic Clouds ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Circumstellar Envelopes ◽

Chemical Enrichment ◽

Wide Range ◽

The Universe

Background: Most of the stars in the Universe will end their evolution by losing their envelope during the thermally pulsing asymptotic giant branch (TP-AGB) phase, enriching the interstellar medium of galaxies with heavy elements, partially condensed into dust grains formed in their extended circumstellar envelopes. Among these stars, carbon-rich TP-AGB stars (C-stars) are particularly relevant for the chemical enrichment of galaxies. We here investigated the role of the metallicity in the dust formation process from a theoretical viewpoint. Methods: We coupled an up-to-date description of dust growth and dust-driven wind, which included the time-averaged effect of shocks, with FRUITY stellar evolutionary tracks. We compared our predictions with observations of C-stars in our Galaxy, in the Magellanic Clouds (LMC and SMC) and in the Galactic Halo, characterised by metallicity between solar and 1/10 of solar. Results: Our models explained the variation of the gas and dust content around C-stars derived from the IRS Spitzer spectra. The wind speed of the C-stars at varying metallicity was well reproduced by our description. We predicted the wind speed at metallicity down to 1/10 of solar in a wide range of mass-loss rates.

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Possible Role of High-Dose Barbiturates and Early Administration of Parenteral Ketogenic Diet for Reducing Development of Chronic Epilepsy in Febrile Infection-Related Epilepsy Syndrome: A Case Report

Neuropediatrics ◽

10.1055/s-0040-1716903 ◽

2020 ◽

Author(s):

Shimpei Baba ◽

Tohru Okanishi ◽

Koichi Ohsugi ◽

Rika Suzumura ◽

Keiko Niimi ◽

...

Keyword(s):

Continuous Infusion ◽

Ketogenic Diet ◽

Epilepsy Syndrome ◽

High Dose ◽

Early Administration ◽

Chronic Epilepsy ◽

Time Period ◽

Irreversible Brain Damage ◽

Electroencephalogram Eeg

AbstractWe describe the efficacy of high-dose barbiturates and early administration of a parenteral ketogenic diet (KD) as initial treatments for acute status epilepticus (SE) in an 8-year-old girl with febrile infection-related epilepsy syndrome (FIRES). The patient was admitted to our hospital with refractory focal SE. Abundant epileptic discharges over the left frontal region were observed on electroencephalogram (EEG). Treatment with continuous infusion of thiamylal for 4 hours, increased incrementally to 40 mg/kg/h, successfully ended the clinical SE, and induced a burst-suppression coma. The infusion rate was then gradually decreased to 4 mg/kg/h over the next 12 hours. Parenteral KD was administered from days 6 to 21 of illness. Continuous infusion of thiamylal was switched to midazolam on day 10 without causing seizures or EEG exacerbations. The patient has remained seizure free in the 15 months since hospital discharge. The effectiveness of KD for the treatment of FIRES has attracted attention amongst clinicians, but KD treatment may need to last for 2 to 4 days before it can stop SE, a time period that could cause irreversible brain damage. Considering the severity of SE in our patient and the dose of barbiturates needed to treat it, we consider this case to have had a good clinical outcome. The results suggest that rapid termination of seizure using high-dose barbiturates in conjunction with early administration of parenteral KD could reduce the development of chronic epilepsy in patients with FIRES.

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