Kevin K. W. Cheung

Large-Scale Environmental Parameters Associated with Tropical Cyclone Formations in the Western North Pacific

Abstract The local environmental conditions associated with 405 tropical cyclone (TC) formations in the western North Pacific during 1990–2001 are examined in this study. Six large-scale parameters are obtained and computed from the NCEP reanalyses with 2.5° latitude resolution. These include the sea surface temperature, 200–850-hPa vertical and meridional zonal shear, 500–700-hPa average relative humidity, convective available potential energy, and 200-hPa divergence. It is found that these parameters show quite consistent values in almost all the cases examined, and near-Gaussian distributions are found for them. The mean values of these distributions are 28.9°C, −3.2 m s−1, −2.3 m s−1, 61.8%, 1184.1 J kg−1, and 5.2 × 10−6 s−1 for the above six domain-averaged parameters, respectively. Based on these distributions of values, a formation potential area is defined as a location that possesses these environmental parameters, all within the thresholds (one standard deviation from the mean value found above)...

Initial Maintenance of Tropical Cyclone Size in the Western North Pacific

A tropical cyclone (TC) size parameter, which is defined here as the radius of 15 m s 21 near-surface wind speed (R15), is calculated for 145 TCs in the western North Pacific during 2000‐05 based on QuikSCAT oceanic winds. For the 73 TCs that intensified to typhoon intensity during their lifetimes, the 33% and 67% respective percentiles of R15 at tropical storm intensity and at typhoon intensity are used to categorize small, medium, and large TCs. Whereas many of the small TCs form from an easterly wave synoptic pattern, the monsoon-related formation patterns are favorable for forming medium to large TCs. Most of these 73 TCs stay in the same size category during intensification, which implies specific physical mechanisms for maintaining TC size in the basin. The 18 persistently large TCs from the tropical storm to the typhoon stage mostly havenorthwestward or north-northwestward tracks, while the 16 persistently small TCs either move westward‐ northwestward in lower latitudes or develop at higher latitudes with various track types. For the large TCs, strong low-level southwesterly winds exist in the outer core region south of the TC center throughout the intensification period. The small TCs are more influenced by the subtropical high during intensification. The conclusion is that it is the low-level environment that determines the difference between large and small size storms during the early intensification period in the western North Pacific.

An automated partnering monitoring system—Partnering Temperature Index

Partnering has become an important approach for construction project management and there exists a wide range of tools to facilitate the implementation of partnering in construction projects. However, there is a lack of attention in terms of the assessment of partnering efforts. Appropriate actions can be taken if there is a systematic approach to monitor the status of partnering performance. In this connection, a Partnering Temperature Index (PTI) to measure the partnering status is proposed. By making use of the Internet technology and database, PTI can be monitored on-line, hence saving much time and expense if collection and retrieval of data are performed manually. As such, an Internet based automated partnering monitoring tool, named the Partnering Temperature Index Automation Suite is developed. The Internet based PTI Automation Suite enables data input by the project participants at any time and place and the project administrator can perform data analysis on-line. Graphical presentations of data are also built in to assist management to identify problem areas. The PTI Automation Suite can be extended to incorporate other key performance indicators to serve as a total project management tool.

Tropical Cyclone Formations in the South China Sea Associated with the Mei-Yu Front

Abstract This study examines the 119 tropical cyclone (TC) formations in the South China Sea (SCS) during 1972–2002, and in particular the 20 in May and June. Eleven of these storms are associated with the weak baroclinic environment of a mei-yu front, while the remaining nine are nonfrontal. Seven of the 11 initial disturbances originated over land and have a highly similar evolution. Comparison of the frontal and nonfrontal formation shows that a nonfrontal formation usually occurs at a lower latitude, is more barotropic, develops faster, and possibly intensifies into a stronger TC. Six nonformation cases in the SCS are also identified that have similar low-level disturbances near the western end of a mei-yu front but did not develop further. In the nonformation cases, both the northeasterlies north of the front and the monsoonal southwesterlies are intermittent and weaker in magnitude so that the vorticity in the northern SCS does not spin up to tropical depression intensity. Because of the influence o...

Mesoscale features associated with tropical cyclone formations in the western North Pacific

Abstract The mesoscale features of 124 tropical cyclone formations in the western North Pacific Ocean during 1999–2004 are investigated through large-scale analyses, satellite infrared brightness temperature (TB), and Quick Scatterometer (QuikSCAT) oceanic wind data. Based on low-level wind flow and surge direction, the formation cases are classified into six synoptic patterns: easterly wave (EW), northeasterly flow (NE), coexistence of northeasterly and southwesterly flow (NE–SW), southwesterly flow (SW), monsoon confluence (MC), and monsoon shear (MS). Then the general convection characteristics and mesoscale convective system (MCS) activities associated with these formation cases are studied under this classification scheme. Convection processes in the EW cases are distinguished from the monsoon-related formations in that the convection is less deep and closer to the formation center. Five characteristic temporal evolutions of the deep convection are identified: (i) single convection event, (ii) two co...

Numerical Study of the Rainfall Event due to the Interaction of Typhoon Babs (1998) and the Northeasterly Monsoon

Abstract A heavy rainfall event in the Taiwan area associated with the interaction between Typhoon Babs (1998) and the East Asia winter monsoon is studied. Typhoon Babs is a case in point demonstrating the often-observed phenomenon that heavy rainfall can be induced in the eastern and/or northeastern region of Taiwan. Such heavy rainfall was caused by the joint convergent flow associated with the outer circulation of typhoons and the strengthening northeasterly monsoon in late typhoon season, even though Babs remained distant from Taiwan when it moved through the island of Luzon in the Philippines and stayed over the South China Sea. This heavy rainfall event is simulated in this study using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) with three nested domains and a highest horizontal resolution of 6.67 km. The control experiments with Kain–Fritsch cumulus parameterization perform well in terms of both simulated track and int...

Tropical Cyclone Formations over the Western North Pacific in the Navy Operational Global Atmospheric Prediction System Forecasts

Abstract A set of criteria is developed to identify tropical cyclone (TC) formations in the Navy Operational Global Atmospheric Prediction System (NOGAPS) analyses and forecast fields. Then the NOGAPS forecasts of TC formations from 1997 to 1999 are verified relative to a formation time defined to be the first warning issued by the Joint Typhoon Warning Center. During these three years, the spatial distributions of TC formations were strongly affected by an El Nino–Southern Oscillation event. The successful NOGAPS predictions of formation within a maximum separation threshold of 4° latitude are about 70%–80% for 24-h forecasts, and drop to about 20%–30% for 120-h forecasts. The success rate is higher for formations in the South China Sea and between 160°E and 180° but is generally lower between 120° and 160°E. The composite 850-hPa large-scale flow for the formations between 120° and 160°E is similar to a monsoon confluence region with marked cross-equatorial flow. Therefore, it is concluded that the skil...

A review of ensemble forecasting techniques with a focus on tropical cyclone forecasting

This paper presents a general review of ensemble forecasting techniques, with a focus on short-range and tropical cyclone predictions. The basic ideas and terminology of ensemble forecasting are introduced, and using four measures to evaluate an ensemble (ensemble mean forecast, consistency, spread versus skill, and inclusiveness), various potential utilities (e.g. dynamical probabilistic forecasts) are illustrated. Since the perturbation methodologies designed for medium-range forecasts of mid-latitude synoptic-scale systems –singular vectors, bred modes, and so on –are already quite mature, they are only briefly described here. The general problems encountered in applying ensemble forecasting techniques to short-range and tropical cyclone forecasts are diagnosed, and some recent studies on these topics reviewed. In general, the perturbation methodologies used for short-range ensembles to date can have a skill comparable to or slightly higher than their corresponding high-resolution control forecast. However, the complicated problem of the relationship between initial condition errors and model deficiencies persists. A similar situation also applies to ensembles designed for tropical cyclone forecasting. An additional difficulty is the different error characteristics encountered in the tropics, mainly the result of the strong convection in the area and the mutual interaction with the ocean. Studies from several research groups use quite different perturbation methodologies, but the results are encouraging. Most of them performed ensemble forecasting of tropical cyclone motion, but extensions to tropical cyclone intensity forecasts are also being developed. Copyright

Ensemble Forecasting of Tropical Cyclone Motion Using a Barotropic Model. Part I: Perturbations of the Environment

Abstract The technique of ensemble forecasting is applied to the problem of tropical cyclone motion prediction. Three methods of generating perturbations for the environmental flow, Monte Carlo forecast (MCF), lagged-average forecast (LAF), and the breeding of growing modes (BGM), are tested with a barotropic model using 66 cases from the Tropical Cyclone Motion (TCM-90) Experiment. For the MCF, the ensemble mean forecast is almost identical to that without any perturbation. The other two methodologies are verified both under the perfect model assumption and using the best tracks. On average, in about half of the cases improvement in forecast can be demonstrated in the former verification. A high degree of correlation (with linear correlation coefficient >0.9) is also found between the spread of the ensemble and the root-mean-square forecast error. In the best-track verification, improvement in forecasts can also be obtained in 36% (42%) of all the cases using the LAF (BGM) technique. The spread-skill cor...

A web-based performance assessment system for environmental protection: WePass

In response to the increasing public concern over the effects of construction waste on the environment, a performance assessment system has been designed to provide an instant, online assessment of how well a construction site performs environmentally, e.g. measuring the level of pollution generated from a construction site. Through the use of both Internet and database technologies, it is possible to collect and present data that are essential for environmental management online. To achieve this, a set of environmental performance parameters was derived through a postal questionnaire survey and interviews with experts in the field. A conceptual framework was developed, of which the key components were: template, knowledge base, output data and benchmark group. In combination, these factors provide a system that enables speedy assessment and effective management of environmental performance on construction sites, hence prompt decisions can be made and corrective actions can be taken before potential hazards turn into real disasters.