Severe Typhoon Research Articles

Changes in the hydrodynamic characteristics of the upper layer of the South China Sea during the period of super typhoon Rammasun (2014)

Severe typhoon Rammasun (2014) was strengthened (super typhoon) in the east of the Leizhou Peninsula before moving into the Beibu Gulf. This study used the empirical orthogonal function (EOF) method to analyze the spatiotemporal variations in the sea surface wind (SSW), surface level anomaly (SLA), sea surface temperature (SST), mixed layer depth (MLD) and precipitation of the SCS. The study found that this typhoon had a significant influence on the SSW, SLA, SST, MLD and precipitation changes. During the typhoon Rammasun, the spatial distribution of precipitation showed obvious ‘left-hand-side intensification’ relative to the typhoon track. However, the SST decreased rapidly, and cooling showed a clear ‘right-hand-side intensification’, and two cyclonic eddies in the southwestward were observed from the mode of EOF-1 of the SLA. The spatiotemporal variations of SST, MLD, SLA, SSW and precipitation during the period of super typhoon Rammasun were excellently reflected by the EOF method. The variabilities of SST, MLD, SLA, SSW and precipitation in the SCS during the typhoon period and the relationship between the variabilities were further analyzed.

Extreme storm surge induced coastal inundation in Yangtze Estuary regions

Coastal inundation induced by the storm surge belongs to one of the major natural hazards in Shanghai and other regions around the Yangtze Estuary. The worst scenarios of coupling the extreme storm and the sea level rise are presented to assess the storm surge hazard in the Yangtze Estuary. The numerical model MIKE 21 FM is adopted to implement the numerical study, which includes wind, current, tide and wave. The storm surge induced by typhoon 9711 is simulated, and the measurements of six tide gauges are used to validate the numerical model. To identify the worst case scenario of severe typhoon (9711) and super typhoon (5612), we propose seven typhoon tracks through the Yangtze Estuary and fourteen scenarios of landfall time for each typhoon track, which generates 196 cases. Finally, based on the worst case scenario and the relative sea level rise in the range of 0 m to 0.7 m, the coastal inundation maps of Pudong New District and Changxing Island are provided and discussed.

Aircraft Observations of Turbulence Characteristics in the Tropical Cyclone Boundary Layer

The Hong Kong Observatory conducted six flights in the atmospheric boundary layer of five tropical cyclones: tropical storm Jebi (1309), typhoon Kalmaegi (1415), severe tropical storm Linfa (1510), typhoon Mujigae (1522), and severe typhoon Nida (1604). Three-dimensional wind data with a 20-Hz sampling rate are available for a height range of 500–670 m, with the mean wind speed from these low-level flights ranging from 10 to 62 m s−1. The turbulent momentum flux and turbulence kinetic energy (e) are measured using the eddy-correlation method, while horizontal scales of turbulent eddies, vertical eddy diffusivity (K), and the vertical turbulent mixing length scale are estimated indirectly. The dependence of the momentum flux, e, K, and the vertical mixing length on wind speed and height are compared with previous studies. Both the momentum flux and turbulent kinetic energy increase with the wind speed, although the rate of increase is smaller for higher wind speeds. It is also found that K increases with wind speed according to a power law up to 40 m s−1 before levelling off, while the vertical mixing length is nearly constant at 100 m. The results serve as a reference for evaluating and improving the turbulent parametrizion in tropical-cyclone models, while the observed large turbulent mixing near the top of the inflow layer of the eyewall region should not be neglected in numerical models.

Study on Wind Simulations Using Deep Learning Techniques during Typhoons: A Case Study of Northern Taiwan

A scheme for wind-speed simulation during typhoons in Taiwan is highly desirable, considering the effects of the powerful winds accompanying the severe typhoons. The developed combination of deep learning (DL) algorithms with a weather-forecasting numerical model can be used to determine wind speed in a rapid simulation process. Here, the Weather Research and Forecasting (WRF) numerical model was employed as the numerical simulation-based model for precomputing solutions to determine the wind velocity at arbitrary positions where the wind cannot be measured. The deep neural network (DNN) was used for constructing the DL-based wind-velocity simulation model. The experimental area of Northern Taiwan was used for the simulation. Regarding the complex typhoon system, the collected data comprised the typhoon tracks, FNL (Final) Operational Global Analysis Data for the WRF model, typhoon characteristics, and ground weather data. This study included 47 typhoon events that occurred over 2000–2017. Three measures were used to analyze the models for identifying optimal performance levels: Mean absolute error, root mean squared error, and correlation coefficient. This study compared observations with the WRF numerical model and DNN model. The results revealed that (1) simulations by using the WRF-based models were satisfactorily consistent with the observed data and (2) simulations by using the DNN model were considerably consistent with those of the WRF-based model. Consequently, the proposed DNN combined with WRF model can be effectively used in simulations of wind velocity at arbitrary positions of study area.

Examination of Surface Wind Asymmetry in Tropical Cyclones over the Northwest Pacific Ocean Using SMAP Observations

Tropical cyclone (TC) surface wind asymmetry is investigated by using wind data acquired from an L-band passive microwave radiometer onboard the NASA Soil Moisture Active Passive (SMAP) satellite between 2015 and 2017 over the Northwest Pacific (NWP) Ocean. The azimuthal asymmetry degree is defined as the factor by which the maximum surface wind speed is greater than the mean wind speed at the radius of the maximum wind (RMW). We examined storm motion and environmental wind shear effects on the degree of TC surface wind asymmetry under different intensity conditions. Results show that the surface wind asymmetry degree significantly decreases with increasing TC intensity, but increases with increasing TC translation speed, for tropical storm and super typhoon strength TCs; whereas no such relationship is found for typhoon and severe typhoon strength TCs. However, the degree of surface wind asymmetry increases with increasing wind shear magnitude for all TC intensity categories. The relative strength between the storm translation speed and the wind shear magnitude has the potential to affect the location of the maximum wind speed. Moreover, the maximum degree of wind asymmetry is found when the direction of the TC motion is nearly equal to the direction of the wind shear.

Tropical Cyclone Surface Pressure Field Estimation Using Satellite Passive Microwave Observations over the Oceans

AbstractThe real time and accurate estimation of tropical cyclone (TC) surface pressure fields is highly desired in TC forecasting and analysis. Using satellite passive microwave observations over the oceans, the retrieval of TC surface pressure fields was investigated in this study, and a new retrieval algorithm was developed. This algorithm uses brightness temperatures (TBs) and TB anomalies together to accurately estimate TC surface pressure fields. Considering the relative superiority of 118‐GHz radiometers in spatial resolution, this study not only used the measurements of 60‐GHz radiometer Advanced Technology Microwave Sounder (ATMS) but also the 118‐GHz radiometer Microwave Humidity and Temperature Sounder (MWHTS). The TC measurements from July 2015 to September 2018 and the corresponding Global Data Assimilation System (GDAS) Final (FNL) analysis data were used to develop and test the retrieval algorithm. The testing results show that the proposed method can estimate the surface pressure fields of a TC's core area (within a 2° radius from the center) with an accuracy of better than 4.0, 5.0, and 8.0 hPa for tropical depressions and tropical storms, typhoons or hurricanes, and severe typhoons or major hurricanes, respectively. In addition, an in situ comparison demonstrates that the accuracy of the retrieved central pressure is better than 6.0, 8.0, and 10.0 hPa for tropical depressions and tropical storms, typhoons or hurricanes, and severe typhoons or major hurricanes, respectively.

The risk of typhoon and storm surge along the coast of Vietnam

The history (1951–2016) and the risk of typhoon and storm surge in coastal areas of Vietnam are analyzed and evaluated based on the observation data, results of statistical and numerical models. The Monte Carlo method was used to construct a bogus typhoon. A coupled numerical model of Surge, Wave and Tide (called SuWAT) was used for simulation of storm surge. The results show that in the period of 1951–2016 there were many typhoons which landed and induced high storm surge on the coast of the North and the North of Center of Vietnam. During one thousand years, there have been 4,678 typhoons entering the coastal zone from Quang Ninh to Ca Mau. In particular, the most severe typhoon in coastal area from Quang Ninh to Thanh Hoa is at level 16 (Beaufort scale), Nghe An - Quang Tri at level 16, Quang Binh - Phu Yen at level 17, Binh Dinh - Ninh Thuan at level 15 and Binh Thuan - Ca Mau at level 13. The coastal areas with highly vulnerable storm surge are provinces from Quang Ninh to Hai Phong (4.5 m), Thanh Hoa to Nghe An (4.0 m), Quang Tri (5.0 m). The results of this study are the basis for the preparation to cope with strong/super typhoon in the coast of Vietnam.

The Gap Rock Lighthouse: construction and typhoon damage.

This paper focuses on the Gap Rock lighthouse, a legendary maritime infrastructure built 130 years ago in the Chinese territory and an early example of joint venture among the Qing Dynasty, the British Empire and the Hong Kong Colonial Government over a course of two decades. Based on 4 years of cross-territorial archival and field research as well as in-depth interviews with descendants of two key stakeholders, the origin of this lasting legacy on the sea is traced, followed by a detailed account of its challenging processes of planning, design and construction, and of the considerable damage to the compound by a severe typhoon in 1893. A qualitative analysis of the key contributing factors of the damage was conducted by taking into consideration the Island's unique topography and the historical records of territorial weather reports. A re-construction of the typhoon impact on the Lighthouse is presented to explain the possible mistakes in its siting and design that eventually caused the severe damage. This serves as a reminder of the significance of a thorough geographical investigation for any infrastructure for all construction professionals in the face of climatic change. This article is part of the theme issue 'Environmental loading of heritage structures'.

Rapid Assessment of a Typhoon Disaster Based on NPP-VIIRS DNB Daily Data: The Case of an Urban Agglomeration along Western Taiwan Straits, China

Rapid assessment of natural disasters is essential for disaster analysis and spatially explicit strategic decisions of post-disaster reconstruction but requires timely available data. The recent daily data of the National Polar-Orbiting Partnership Visible Infrared Imaging Radiometer Suite (NPP-VIIRS) day/night band (DNB) provide new opportunities to detect and evaluate natural disasters. Here, we introduce an application of NPP-VIIRS DNB daily data for rapidly assessing the damage of a severe typhoon that struck the urban agglomerations along the western Taiwan Straits in China. Our research explored the methods of rapid identification and extraction of the areas based on changes in nighttime light (NTL) after the typhoon disaster by using a statistical radiation-normalization method. We analyzed the correlations of NTL image derivatives with human population, population density, and gross domestic product (GDP). The strong correlations were found between NTL image light density and population density (R2 = 0.83) and between the total nighttime light intensity and GDP (R2 = 0.96) at the prefecture level. In addition, we examined the interrelationships between changes in NTL images and the areas affected by the typhoon and proposed a method to predict the affected population. Finally, the affected area and the affected population in the study area could be rapidly retrieved based on the proposed remote sensing method. The overall accuracy was 83.2% for the detection of the affected population after disaster and the recovery rate of the affected area was 86.9% in the third week after the typhoon. This research demonstrates that the NTL image-based change detection method is simple and effective, and further explains that the NPP-VIIRS DNB daily data are useful for rapidly assessing affected areas and affected populations after typhoon disasters, and for timely quantifying the degree of recovery at a large spatial scale.

The Prevalence of Posttraumatic Stress Disorder Among Survivors After a Typhoon or Hurricane: A Systematic Review and Meta-Analysis.

Posttraumatic stress disorder (PTSD) is a psychological disorder, which could be caused by traumatic events. The prevalence of PTSD among survivors after a typhoon or hurricane varied widely. Therefore, this study aimed to determine a combined prevalence of PTSD among survivors after a typhoon or hurricane. A systematic search of literature was performed in the 3 English databases: PubMed (National Library of Medicine, Bethesda, MD), ISI Web of Science (Thomson Reuters, New York, NY), and Embase (Elsevier, Amsterdam, Netherlands). Also, a similar search was performed in the 2 Chinese databases such as Chinese National Knowledge Infrastructure and WanFang. Loney et al.'s criteria were used to evaluate the quality of the selected articles for this study. The combined prevalence of PTSD among the study population was estimated using the Freeman-Tukey double arcsine transformation method. Subgroup analyses and a meta-regression analysis were carried out to explore the origin of heterogeneity. Thirty-nine eligible articles were included in this study. They comprised 43 123 typhoon and hurricane survivors of which 9373 were diagnosed with PTSD. The combined prevalence of PTSD among this population was 17.81%. Subgroup analyses revealed that the combined prevalence of PTSD related to typhoon and hurricane Categories 5, 4, and 2 showing a corresponding decreasing tendency. About 18% of people who experienced a severe typhoon or hurricane develop PTSD with the prevalence decreasing with reduced severity of the typhoon or hurricane.

Typhoon Mangkhut Case Study: Household and Community Typhoon Preparedness in Hong Kong, a Densely Populated Urban City

Introduction:As a subtropical urbanized city in Southeast Asia, Hong Kong is prone to frequent typhoons. With an increasing number of severe typhoons, usual preparedness measures should be explored to assess their adequacy to safeguard health and wellbeing. Typhoon Mangkhut (2018) serves as an example of the successes and limitations of community preparedness for a severe typhoon.Aim:To explore how Hong Kong residents prepared for Typhoon Mangkhut and whether their usual preparedness measures provided enough protection.Methods:A population-based randomized telephone survey of Hong Kong residents (n=521) was conducted soon after Typhoon Mangkhut’s landing. Only residents aged 18 or above and understood Cantonese were included. Socio-demographic factors, types of typhoon and general preparedness, risk perception, and impacts from the typhoon were asked. Descriptive characteristics and univariate analysis were used to describe the patterns and associations.Results:8.6% of respondents felt their home was at high risk of danger during typhoons although 33.4% reported some form of impact from Mangkhut. Over 70% reported doing at least one typhoon specific preparedness measure. Among those who practiced at least one typhoon specific preparedness measure, 37.2% (p=0.002) were affected by the typhoon.Discussion:Despite the high adaptation of preparedness measures, warranted by the frequent typhoons, Hong Kong residents were not adequately prepared for a severe typhoon. While the early warning system and evacuation of flood-prone areas mitigated some of the impact, unexpected effects such as flying air conditioners, roadblocks affecting employment, swaying buildings, and loss of power supply were not accounted for. Future preparedness for natural disasters which will become more extreme due to climate change and needs to account for unforeseen risks.

Diel vertical migration of zooplankton and micronekton on the northern slope of the South China Sea observed by a moored ADCP

Acoustic Doppler current profiler (ADCP) echoes can be transformed into mean volume backscattering strength (MVBS), which is positively proportional to the biomass of zooplankton and micronekton. A mooring with an upward-looking 75-kHz ADCP was deployed on the northern slope of the South China Sea to monitor diel vertical migration (DVM) and vertical distributions of zooplankton and micronekton under general conditions and extreme conditions such as typhoons. DVM occurs throughout the year, with the maximum migrating speed reaching 9.0 cm s−1. It had some cyclic variation, which was in response to marine environment and astronomical influence. Light initiates the ascents and descents of the migrators, and migration intensity may be proportional to the solar altitude. Neap-spring tidal cycle and full moon phase influences are prominent, and the peak at 112 d may be driven by variation of currents. In addition, 270 m is the demarcation between upward and downward migrations; some organisms living below this layer, especially zooplankton and micronekton, migrate to the surface to obtain nutrients and energy; other marine mesopelagic organisms also survive in this manner. Super and severe typhoons reduced vertical migration, having less influence on the deep scattering layer. As Super Typhoon Rammasun passed by the mooring station, current speed increases and temperature decreases were synchronous with changes in the deep scattering layer; the migrators swam downward to evade the influence of a higher-speed current rather than swam upward to compensate for the decrease of temperature.

Bayesian Nonparametric Modeling of Structural Health Indicators under Severe Typhoons and Its Application to Modeling Modal Frequency

AbstractStructural health indicators, such as modal frequencies, have been commonly utilized to interpret the health condition of monitored structures. This study modeled the relationship between s...

The contribution of super typhoons to tropical cyclone activity in response to ENSO

Western North Pacific tropical cyclone (TC) activity is known to have a significant response to El Niño and Southern Oscillation (ENSO). Among the TC intensity classifications, “super typhoon”, is widely used as a symbolic word for warning people about the potential for experiencing the most severe typhoon. This study quantifies the contribution of super typhoons to TC activity in response to ENSO, where the Southern Oscillation Index (SOI) is used to indicate the internal variation of ENSO. It is found that the number and the genesis location of non-super typhoons are little influenced by ENSO, and the changes are mostly by the addition of super typhoons. Historical levels of El Niño and La Niña span from −2σ to +2σ of the SOI. Over this range of SOI values, the mean response is 5.6 super typhoons (7.1 for El Niño and 1.5 for La Niña) which nearly matches the mean response overall of 6 storms (24.6 for El Niño and 18.6 for La Niña). The spatial distribution of TC genesis locations for different ENSO conditions does not completely explain these results.

Impact of typhoon periphery on high ozone and high aerosol pollution in the Pearl River Delta region

This paper analyzes observation data in the Pearl River Delta (PRD) region from 2012 to 2013, and explores the impact of typhoon periphery on high ozone and high aerosol pollution episodes (double high episodes). Observation analysis show that severe tropical storms to severe typhoons are mainly located in the range of 10°N-30°N, 116°E-135°E when double high episodes occur. Meanwhile, obvious high temperature, low humidity, low wind speed, high actinic flux, high aerosol optical depth (AOD), and high single scattering albedo (SSA) can be observed in double high episodes.The diurnal cycle of the PM2.5 is significant in double high episodes, and the average peak concentration in the afternoon can exceed 90 μg/m3. The diurnal cycle of PM2.5 in non–double high episodes is not significant, and the average value is about 34–39 μg/m3. The ozone peak concentration in double high episodes is 81–103 ppbv, which is about 27–40 ppbv higher than that of non–double high episodes. High correlation can be found between the aerosol and ozone diurnal cycles in double high episodes, and r2 reaches 0.76. In double high episodes, black carbon, nitrate, and sea salt decrease while sulfate, ammonium, secondary organic carbon, and total PM2.5 significantly increase in the afternoon. The growth of PM2.5 in double high episodes is mainly contributed by scattered fine particles from photochemical processes and transmission. The mechanisms that control the double high episodes in the PRD are described below. Ozone and aerosol begin to accumulate under unfavorable meteorological conditions. Via local photochemical processes and external transport, the scattered aerosol increases and leads to an increase in multiple scattering and actinic radiation, which is in turn more favorable for photochemical reaction and further increases the ozone concentration. Meanwhile, high oxidizability promotes the formation of scattered aerosol, creating positive feedback. In addition, the scattered aerosol increases backscattering, which increases the photolysis rate and ozone concentration in the middle and upper boundary layer. Meanwhile, downdraft and turbulence transports high-concentration ozone to the ground.

Analysis and Prediction of Tropical Storm Pakhar at National Center for Hydro-Meteorological Forecasting of Viet Nam

ABSTRACT Tropical Storm Pakhar appeared as a low pressure system over the South China Sea on March 26, 2012. It then became a tropical storm a few days later on March 29, 2012. Pakhar was really an abnormal tropical storm activated over the South China Sea in March which seldom appeared at that time. The movement of Pakhar was not very complicated because it mainly moved under the steering lines of subtropical high pressure systems. However, its intensity was still a problem for many typhoon centers, especially when Pakhar experienced a rapid intensification within 12 hours at 00Z on March 30. At that time NCHMF and JRTD (Japan) warned it as a tropical storm, while BABJ (China) and JTWC (US navy) warned as severe tropical storm and typhoon respectively. Pakhar decreased quickly when approached the onshore areas of Viet Nam. At 08Z on 1 April, upon analyzing the radar data at NhaBe station and the half-hourly observations along the coastline, NCHMF downgraded Pakhar into a tropical depression, while other typhoon centers maintained Pakhar’s intensity as a tropical storm untill 00Z on 2 April.

Application of different wind field models and wave boundary layer model to typhoon waves numerical simulation in WAVEWATCH III model

Taking severe typhoon Kalmaegi (2014) as an example, which is chosen due to its good availability of observations from mulitplatforms, the application ability of different wind field models and wave boundary layer model (WBLM) are investigated simultaneously in WAVEWATCH III model (WW3). First, based on the comparisons between measurements of two in situ buoys and model results, a better-quality wind forcing from WRF’s output stands out slightly compared with other two constructed wind fields during the time segment of “During-TY”. Second, the comparisons of simulated results by using different drag coefficient schemes between WBLM and the original parameterisation formula in ST2 package are further implemented. The good performance of drag coefficient from WBLM under high-wind conditions, which is embedded into ST2 wind-input source function, is also verified by several data set of field observations. As a result, on the basis of the observations from buoy-based and radar altimeter measurements (RAs), the values of significant wave height () from simulation with WBLM are weaker at high sea state areas () compared with that from the ST2 scheme, which coincide with the general knowledge that the amount of momentum exchange at the air-sea interface plays a vital role in the development of typhoon waves. Limited by less frequently sampled collocated measurements under high-wind conditions, the effectiveness of improvement for typhoon waves simulation using WBLM in WW3 requires more validation cases in future work.

On Tropical Cyclone Activity Over the Western North Pacific in 2012

ABSTRACT Tropical cyclone (TC) activity over the western North Pacific (WNP) in 2012 is summarized and the associated large-scale environmental conditions are discussed. In total 25 named storms formed in the WNP basin in 2012, among them were 3 tropical storms (TSs), 7 severe TSs, 4 typhoons, 6 severe typhoons, and 5 super typhoons. TC activity was close to a 30-year average but above the average active level of recent years since 2005. Total number of TCs formed in the South China Sea (SCS) in 2012 was below normal, with only 40% of the climatological mean. Overall, TC genesis over the WNP was characterized by four active periods. During each period TCs took distinct prevailing tracks. The periodic characteristics in TC genesis were attributed to the activity of the intraseasonal oscillation (ISO), while those in TC tracks were related to the large-scale dynamical and thermodynamic conditions induced by the enhanced WNP monsoon activity and the weak El Nino conditions.

“Convective Hot Tower” Signatures and Rapid Intensification of Severe Typhoon Vicente (1208)

ABSTRACT Severe typhoon vicente (1208) was the first tropical cyclone that necessitated the issuance of No. 10 Hurricane Signal in Hong Kong since Typhoon York back in 1999. Hurricane force winds were recorded over the southwestern part of Hong Kong during the passage of vicente. In the evening on 23 July 2012, “convective hot towers” appeared on the eyewall of Vicente and were captured on both radar imagery and lightning location map. The corresponding cloud top overshot 15 km up to the top of the troposphere, accompanied by cloud-to-ground lightning. Such observations signified that the associated updraft turned violent at the locations of convective hot towers. Shortly afterwards, Vicente intensified rapidly to a severe typhoon over the South China Sea to the south-southwest of Hong Kong around midnight, reaching its peak intensity with an estimated maximum sustained wind of 155 km/h near its centre. It is the first time in the century-long tropical cyclone history of Hong Kong that the signature of “con-vective hot towers” in a rapidly intensifying typhoon can be observed in details by multiple remote-sensing platforms. This paper serves to document such rare observational evidence and share the main results as a checklist for reference by operational forecasters when monitoring proximate typhoons for signs of rapid intensification.

An Objective Tropical Cyclone Intensity Estimation Model Based on Digital IR Satellite Images

ABSTRACT An objective tropical cyclone (TC) intensity estimation model is proposed based on the statistical relationship between TC intensity and its inner-core convection, plus the persistence of TC intensity. In the model, the inner-core convection is described by several parameters retrieved from digital infrared (IR) satellite images, including the number of convective cores (Num), their distance to the TC center, and their blackbody temperature (TBB), among others. The persistence of TC intensity is embodied by the TC intensity six hours previous (V6h). The model was set up by the stepwise regression technique using a five-year dataset (2006-2010) and was tested using an independent dataset covering 2011-2012, with V6h from the best-track dataset. Selected factors of the model included V6h, Num, Lat (TC center latitude), Lon (TC center longitude), DISmin (minimum distance between convective cores and TC center), and TBBdif (difference between the maximum and minimum TBB value of convective cores). Results showed that, for independent samples during 2011-2012, the MAE (mean absolute error) and RMSE (root-mean-square error) of Vmax estimation were 1.8 m s− 1 and 2.4 m s− 1, respectively. In order to make the model totally independent from the best-track dataset, the model estimation from six hours previous was used as the V6h for a second independent test covering 2011-2012. The results showed that the model had an MAE and RMSE of 5.4 m s− 1 and 7.3 m s− 1, respectively. Large errors were found for strong TCs (Severe Typhoon or Super Typhoon). The error statistics of the proposed model are comparable to published statistics on the widely used Dvorak technique or its objective versions, implying its potential to be used as an alternative tool for TC intensity estimation in either real-time operation or post-season best-track analyses.