Rainfall estimation of landfalling tropical cyclones over Indian coasts through satellite imagery

One of the most significant impacts of landfalling tropical cyclones is caused by the copiousrainfall associated with it. The main emphasis of present study is to provide some guidance to the operational forecastersfor indicating the possible rainfall over the areas likely to be affected by the cyclones after landfall. Study of 14 pastlandfalling cyclones reveals that the maximum rainfall occurred in the first forward quadrant of tropical cyclonemovement, followed by the second quadrant and the areas near the track of the cyclones. Isohyetal analysis of 24 hoursrainfall for each cyclone reveals that occurrence of heavy rainfall is generally confined up to 150 kms radius from thestorm centre and rainfall is found to generally extend up to 300 kms with gradual decrease in amount. The rainfallreceiving areas are mostly covered with convective clouds with cloud top temperatures of -80 to -60 ºC, prior to and afterthe landfall of the systems. In 93% of tropical cyclones out of the 14 cases studied, 70 % convection lay to the right of thetrack. To examine the rainfall asymmetry due to asymmetry in distribution of convection, cloud top temperatures derivedfrom satellite infrared imagery data have been taken as the proxy of strong convection. It is also revealed in the study thatthe slow moving tropical cyclones cause heavy rain rather than fast moving tropical cyclones. The Bay of Bengalcyclones which crossed coast as cyclonic storm and very severe cyclonic storm caused 71.4% rainfall within the range 0-10 cm, 22.8% rainfall in the range 11-20 cm and 4.3% rainfall within the range 21-30 cm in the area of radius of 300 kmsfrom the centre of the cyclonic storms. For the Arabian Sea tropical cyclones, in general, about 70% rainfall occurredwithin the range 16-25 cm in 24 hours.

Preferred intra-seasonal circulation patterns of the Indian summer monsoon and active-break cycles

Intra-Seasonal circulation regimes are identified from a cluster analysis of 5-day mean anomaly fields of 850 hPa horizontal winds from the ERA-Interim reanalysis for the boreal summer season (June–Sept. for 1979–2018) over the region (50°–100° E; 5° S–35° N). The k-means method was applied to the leading 6 principal components yielding k clusters. The degree of clustering is significant compared to synthetic data sets for any value of $$k > 3$$ k > 3 . The circulation is most likely to stay in the same cluster from one pentad to the next; significant transitions (with 95% confidence level) form a cycle. The similarity between the cycle depicted from 4 or 5 clusters and the active-break cycle, as well as the 45-day oscillation, is established by composites of 850 hPa winds, 200 hPa divergence, 500 hPa vorticity and vertical pressure velocity, precipitable water, diabatic heating and rainfall over India: Strong convection over the subtropical Indian Ocean moves to the central Bay of Bengal and central India, subsequently to the northern Bay of Bengal and west Bengal, and then further north into the Himalayas. We also find preferred transitions in which the convection moves equatorward from central India. The number of complete cycles found in 40 summers is 7 in the 4-cluster analysis. The number of times the system undergoes four (three) consecutive legs of the cycle is 16 (31). For 5 clusters only 3 complete cycles are found. sequences of five, four and three consecutive legs occur 10, 11 and 28 times, respectively.

Numerical Study of the Action of Convection on the Volume and Length of the Flammable Zone Formed by Hydrogen Emissions from the Vent Masts Installed on an International Ship

International ships carrying liquefied fuel are strongly recommended to install vent masts to control the pressure of cargo tanks in the event of an emergency. However, the gas emitted from a vent mast may be hazardous for the crew of the ship. In the present study, the volume and length of the flammable zone (FZ) created by the emitted gas above the ship was examined. Various scenarios comprising four parameters, namely, relative wind speed, arrangement of vent masts, combination of emissions among four vent masts, and direction of emission from the vent-mast outlet were considered. The results showed that the convection acts on the volume and length of an FZ. The volume of an FZ increases when there is a reduction in convection reaching the FZ and when strong convection brings hydrogen from a nearby FZ. The length of the FZ is also related to convection. An FZ is elongated if the center of a vortex is located inside the FZ, because this vortex traps hydrogen inside the FZ. The length of an FZ decreases if the center of the vortex is located outside the FZ, as such a vortex brings more fresh air into the FZ.

Influence of convection on the upper tropospheric O₃ and NO_x budget in southeastern China

Thunderstorms can significantly influence the air composition via strong updraft and lightning nitrogen oxides (LNOx). In this study, the ozonesondes and TROPOMI nitrogen dioxide (NO2) observations for two cases are combined with model to investigate the effects of typical strong convection on vertical redistribution of air pollutants in Nanjing, southeastern China. The ozonesonde observations show higher O3 and water vapor mixing ratios in the upper troposphere (UT) after convection, indicating the strong updraft transporting lower-level airmass into the UT, and the possible downward O3-rich air near the top of UT over the convective period. During the whole convection life cycle, the UT O3 production is driven by the chemistry (> 87 %) and reduced by the LNOx (−40 %). Sensitivity tests demonstrate that neglecting LNOx in standard TROPOMI NO2 products causes overestimated air mass factors over fresh lightning regions and the opposite for outflow and aged lightning areas. Therefore, a new high-resolution retrieval algorithm is applied to estimate the LNOx production efficiency. Our work shows the demand for high-resolution modeling and satellite observations on LNOx emissions of both active and dissipated convection, especially small-scale storms.

Numerical Study of Natural Convection of Biological Nanofluid Flow Prepared from Tea Leaves under the Effect of Magnetic Field

The heat transfer of a biological nanofluid (N/F) in a rectangular cavity with two hot triangular blades is examined in this work. The properties used for nanoparticles (N/Ps) are derived from a N/P prepared naturally from tea leaves. Silver N/Ps are distributed in a 50–50 water/ethylene glycol solution. The cavity’s bottom wall is extremely hot, while the upper wall is extremely cold. The side walls are insulated, and the enclosure is surrounded by a horizontal magnetic field (M/F). The equations are solved using the control volume technique and the SIMPLE algorithm. Finally, the Nu is determined by changing the dimensions of the blade, the Rayleigh number (Ra), and the Hartmann number (Ha). Finally, a correlation is expressed for the Nu in the range of parameter changes. The results demonstrate that an increment in the Ra from 103 to 105 enhances the Nu more than 2.5 times in the absence of an M/F. An enhancement in the strength of the M/F, especially at the Ra of 105, leads to a dramatic reduction in the Nu. An increase in the height of the triangular blade intensifies the amount of Nu in weak and strong convection. The enlargement of the base of the triangular blade first enhances and then decreases as the Nu. The addition of 5% silver biological N/Ps to the fluid enhances the Nu by 13.7% in the absence of an M/F for high Ras.

Two-dimensional simulation of frost formation on the NACA0012 airfoil under strong convection by using the p-VOF method

A newly developed frosting simulation method, p-VOF method, is applied to simulate the dynamic frost formation on the NACA0012 airfoil under strong convection. The p-VOF method is a pseudo VOF method of the multiphase flow simulation with phase change. By solving a simplified mass conservation equation explicitly instead of the original volume fraction equations in CFD software, the efficiency and robustness of calculation are greatly improved. This progress makes it possible to predict a long-time frost formation. The p-VOF method was successfully applied to the simulation of dynamic frosting on the two-dimensional NACA0012 airfoil under strong convection conditions with constant frost physical properties. The simulation result shows that the average thickness of the frost layer increases, and the frost bulges and flow separation appear earlier, when the airfoil surface temperature decreases or the air humidity increases. The frost bulges and flow separation appear earlier, when the air velocity is faster, the growth rate of the frost layer at the early stage is greater, but the final frost layer is thinner.

Preferred Intra-seasonal Circulation Patterns of the Indian Summer Monsoon and Active-Break Cycles

Intra-Seasonal circulation regimes are identified from a cluster analysis of 5-day mean (pentad) anomaly fields of 850 hPa horizontal winds (u,v)from the ERA-Interim reanalysis for the boreal summer season (120 days starting 01June for the years 1979 - 2018) over the broad Indian region (50 o -100 o E; 5 o S - 35 o N). The anomalies are formed with respect to a parabolic (in time) seasonal cycle computed separately for each year, thus filtering out periods of greater than 240 days. The k-means method was applied in the phase space of the leading 6 (12) principal component modes, which explain 65% (78%) of the space-time variance, yielding k clusters. The degree of clustering is significant when compared to synthetic data sets for any value of k > 3. The transition matrices for k=4 and k=5 establish that the system is most likely to stay in the same cluster from one pentad to the next, but that the significant transitions (with 95% confidence level using a modified bootstrap method) form a cycle. The similarity between the cycle as depicted from 4 or 5 clusters is established by composites of 850 hPa (u,v,), 200 hPa divergence, 500 hPa vorticity and vertical pressure velocity, and daily rainfall over India: Strong convection (with large positive divergence and vorticity) over the subtropical Indian Ocean, moves to the central Bay of Bengal and over central India, then subsequently to the northern Bay of Bengal and west Bengal, and then further north into the Himalayas. The Indian rainfall composites show a similar cycle. The phases in which strong convection is seen over central and northern India are seen for about 60% of the time for both k=4 and k=5 analyses. However the 4 cluster analysis also shows a preferred transition in which the convection moves equatorward from central India. The number of complete cycles (including a return to the starting cluster) found in the 40 years of data is 7 in the 4-cluster analysis, while the number of times the system undergoes four (three) consecutive legs of the cycle is 16 (31). Fewer instances of complete cycles are found for 5 clusters (only 3), but sequences of five, four and three consecutive legs occur 10, 11 and 28 times respectively. Composites of the tropics-wide vertically integrated diabatic heating (estimated from ERA5 reanalyses) reproduce the characteristics of the boreal summer intra-seasonal oscillation, with northwest-to-southeast oriented bands of heating moving northward from the tropical Indian Ocean into the subtropics. This depiction of the active-break cycle is particularly useful for diagnosing the cycle in short-range forecasts: as long as pentad anomalies can be formed, they can be assigned to one of the observed clusters described in this paper without the need for further time-filtering.

Two-Dimensional Simulation of Frost Formation on the NACA0012 Airfoil under Strong Convection by Using the P-VOF Method

A newly developed frosting simulation method, pseudo-VOF (p-VOF) method, has applied to simulate the dynamic frost formation on the NACA0012 airfoil under strong convection. The p-VOF method is a pseudo volume of fraction simulation method of the multiphase flow with phase change. By solving a simplified mass conservation equation explicitly instead of the original volume fraction equations in CFD software, the efficiency and robustness of calculation are greatly improved. This progress makes it possible to predict a long-time frost formation. The p-VOF method was successfully applied to the simulation of dynamic frosting on the two-dimensional NACA0012 airfoil under strong convection conditions with constant frost physical properties. The simulation result shows that the average thickness of the frost layer increases, and the frost bulges and flow separation appear earlier, when the airfoil surface temperature decreases or the air humidity increases. The frost bulges and flow separation appear earlier, when the air velocity is faster, the growth rate of the frost layer at the early stage is greater, but the final frost layer is thinner.

Numerical Simulation Of Thermodiffusion Subjected To Different Gravity Fields

In this work, a typical thermodiffusion experiment on a binary mixture is simulated numerically using a two-dimensional computational fluid dynamics (CFD) code. Three scenarios for gravity have been studied: residual, pure oscillatory, and microgravity micro-accelerations. It was found that less separation of mixture components in the presence of strong gravity fields is due to the formation of buoyancy-driven flows. For the case of pure oscillatory gravity, the effects of the frequency and amplitude are discussed in detail. A critical vibrational Rayleigh number is proposed above which the diffusion process is highly affected by the external excitation. For the case of the microgravity environment, quasi-steady accelerations and g-jitter, both of which are found on the International Space Station, have been considered. Results show g-jitter has a minimal effect on the thermodiffusion experiment. The effects of the residual gravity field were also found to be insignificant in stimulating a strong convection flow.