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Tropical Cyclone Research and Review  
  Tropical Cyclone Research and Review--2017, 6 (3-4)   Published: 2017-12-15
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A Diagnostic from Vertical Wind Profiles for Detecting Extreme Rainfall

Jeff Callaghan
Tropical Cyclone Research and Review. 2017, 6 (3-4): 41;  doi: 10.6057/2017TCRRh3.01
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The damage and loss of life from fresh water flooding as Tropical Cyclones move inland and towards higher latitudes rivals the losses at the point of landfall. This makes it extremely important to understand the structure of these systems as some such events produce much less damaging rainfall. Extreme rainfall and major flooding events are studied around the Globe to examine the likely structure of weather systems which produce extreme rainfall. An extensive search for rare radio-sonde data has been carried out near where extreme rainfall and flooding has been reported. In almost every case atmospheric moisture content is high and the low-level wind direction turns anti-cyclonically with increasing height up to 500 hPa. The rare exception to the rule is when tropical thunderstorms generate extreme rainfall. This study extends previous work in Eastern Australia by showing that the link between turning winds and rainfall exists in both the tropics and temperate zones, and the link applies in cases of extreme rainfall and associated major flooding.

 Asymmetric Inner Core Convection Leading to Tropical Cyclone Intensification

Jeff Callaghan
Tropical Cyclone Research and Review. 2017, 6 (3-4): 55;  doi: 10.6057/2017TCRRh3.02
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One of the predictors used to forecast the rapid intensification of Tropical Cyclones (RI) is the symmetry of inner core convection which used infrared (IR) satellite imagery in the determination of this structure. This has led Forecasters and Researchers to conclude the symmetry of inner core convection was an important factor in RI. However we showed here using examples of RI that IR satellite imagery was not always a good guide to determine symmetry of inner core convection especially in the early stages of RI. However it has been previously shown that the heat released in these highly asymmetric convective bands may be transformed into the kinetic energy of the quasi-symmetric wind field and the available potential energy associated with the warm core. One of the most rapid RI cases had asymmetric inner core convection early in a six hour period where the Central Pressure dropped 29hPa and the sustained wind speed increased by 55knots(28.3ms-1). In other cases, where there was available inner core data, the inner core convection developed in a region where microwave imagery indicated asymmetric inner core convection. The convection was located where Dropsonde winds and Doppler radar winds from reconnaissance aircraft indicated a warm air advection pattern in that the winds turned anticyclonically with height in the lowest 5km of the atmosphere. Updrafts from this strong convection near the eye become upward extending centres of cyclonic vorticity and may also produce warming in the eye with adjacent broad subsiding currents. It was shown that models could not forecast the RI of severe tropical cyclone Marcia as recently as February 2015. In this case convection was formed more vigorously on the western flank under the influence of a warm air advection wind pattern and convection remained mostly on this western side as RI proceeded. This process needs to be understood on its influence on the models failing to forecast RI. Rare Doppler wind of Hurricane Hermine showed the wind structure as a band a convection on the storm’s eastern flank rapidly transformed into circular bands of convection as warm air advection winds increased around the inner core.

Evolution of thermodynamic structures during rapid growth and decay of extremely severe cyclonic storm CHAPALA (2015)

Tropical Cyclone Research and Review. 2017, 6 (3-4): 67;  doi: 10.6057/2017TCRRh3.05
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The structure and evolution of inner-core convective bursts and their differences associated with rapid intensification (RI) and rapid decay (RD) of tropical cyclone CHAPALA are examined. The inception of RI was associated with substantial increase of convective heating and its vertical extent in the inner core. Increase in diabatic heating was of the order of 12-21 oC, particularly in the middle and upper troposphere. Latent heat release produced a diabatically generated potential vorticity (PV) in vertical column. The immediate cause of RI was a significant increase of moisture flux from surface to 500 hPa. This was accomplished primarily by updrafts of the order of 6-12 Pa s-1, representing the strong vertical motion distribution inside the warm core convective zone. The episode of deep convective bursts transpired during the period of RI. The evolving flow became highly symmetric and dominated by deep convective axisymmetric vortex structures. The RD coincided with the significant weakening in updraft of moisture flux consequently decrease of diabatic heating in the middle and upper troposphere and dissipation of upper and lower PV.

Some Special Characteristics of Track and Intensity of Typhoons over the Western North Pacific

Tarasha Khurana, S. K. Bhattacharya, S. D. Kotal
Tropical Cyclone Research and Review. 2017, 6 (3-4): 82;  doi: 10.6057/2017TCRRh3.03
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Joint Typhoon Warning Center (JTWC) Best Track data from 1995 to 2014 are processed to examine some specific patterns and trends shown by Typhoons over the Western North Pacific. With a multivariate dataset of 588 TC cases in hand, we carry out a sub-domain analysis by dividing the Western North Pacific region into domains of 2°x2° and find the preferred regions of genesis, favourable direction of movement, steep recurvature, rapid intensification, and rapid decay. The region from longitude 132°E to 134°E and latitude 16°N to 18°N showed the highest number of cases (19) for rapid intensification (RI) and a general pattern is found that the RI systems occurred mostly in the later half of the year with a negative Pacific Decadal Oscillation (PDO) index. Similarly, the domain from longitude 114°E to 116°E and latitude 26°N to 28°N had the highest probability of 0.857 for rapid decay. The probabilities of recurvature for each sub-domain were calculated for angles 30°, 45°, 60°, 90°, 120° and 150°. The sub-domain around longitude 118°E and latitude 12°N had the steepest recurve of 168.69°. It also had a high probability of 0.714 for a recurvature of greater than 90°. The most taken direction of movement of typhoons around the Western North Pacific were analysed in different ways and along the 16 points of compass, the direction from 270° to 292.5° was found to be the most preferred direction of movement.

A Challenge of the Experiment on Typhoon Intensity Change in Coastal Area

Xiaotu Lei, Waikin Wong, Clarence Fong
Tropical Cyclone Research and Review. 2017, 6 (3-4): 94;  doi: 10.6057/2017TCRRh3.04
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The Experiment on Typhoon Intensity Change in Coastal Area (EXOTICCA) was proposed by the China Meteorological Administration (CMA) and Hong Kong Observatory (HKO) and endorsed by the ESCAP/WMO Typhoon Committee (TC). The major goals and objectives of the EXOTICCA are: 1) to conduct the field
campaigns on the intensity and structural characteristics of the target offshore and landfall tropical cyclones by employing integrated and novel observation techniques, and 2) to conduct demonstration research on the utilization of the synergized field observation data with the aim of deepening the understanding of the mechanism of structure and intensity changes, to improve the relevant capability of operational analysis, numerical weather prediction (NWP) models forecast, reliable storm surge and flooding and associated risk assessment. The Organizational structure and implementation schedule etc. are also introduced in this paper.

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