I. Introduction to DOTSTAR
Since a large number of typhoons have caused great devastation over the years, typhoon research is of utmost importance to Taiwan and its people. In August 2002, the NSC approved funding for typhoon research over the next three years, and the grant-aided "Priority Typhoon Research" project is directed by Prof. Chun-Chieh Wu of the Department of Atmospheric Sciences, National Taiwan University. The project includes the "Dropsonde Observation for Typhoon Surveillance near the TAiwan Region" (DOTSTAR), involving interdepartmental as well as international efforts from Taiwan and the US, aims to perform GPS dropwindsonde airborne observation of typhoons. It is hoped that this project and DOTSTAR will shed light on the theory of typhoon dynamics, enhance the accuracy of typhoon track forecasts, put Taiwan at the forefront of international typhoon research, and make a significant contribution to the study of typhoons in the northwestern Pacific and East Asia region.
This research project will be the first time during the last 16 years that an aircraft is used in the northwestern Pacific region to deploy dropwindsondes observing typhoon structure. The results of the project will enable Taiwan to formulate future airborne observation strategies, facilitate adaptive observation of typhoons, and improve the capability of data assimilation. The project is therefore considered a pioneering step forward in basic researches and typhoon forecasting.
The project will employ an ASTRA aircraft and the Airborne Vertical Atmosphere Profiling System (AVAPS). With the aforementioned equipment, dropswindsondes will be released directly into typhoons from an altitude of 43,000 feet, and observations will be executed for five hours during each flight. Data will be collected on proper atmospheric conditions in key areas around the typhoons, and the acquired information will be extremely useful in forecasting and academic research. The DOTSTAR have conducted 64 surveillance flight missions for 49 typhoons since 2003 typhoon season (see detail at Updated Summary of Progress). It is expected that major breakthroughs will be made in typhoon forecasting and research.
II. Objectives of DOTSTAR
- A pilot study to perform the dropsonde surveillance to enhance the observations of the atmosphere around typhoons that may affect the Taiwan area.
- To evaluate how the dropsonde data influence the model's track prediction, and to study the optimum observation strategies for improving typhoon forecasts.
- To provide excellent guide for future observation strategies.
- To validate the remote sensing data around typhoons and to help explore the typhoon dynamics and theories.
- To improve the adaptive observation strategy and data assimilation, which are at the forefront of typhoon forecast and research.
- To promote the international status of Taiwan in the tropical cyclone research field and to play the leading role of typhoon research in the northwestern Pacific and East Asia region.
- The pioneering aircraft-surveillance of typhoons in the northweatern Pacific in East Asia.
- An interdepartmental project with National Science Council (NSC), National Taiwan University (NTU), Central Weather Bureau (CWB), National Central University (NCU), Private Chinese Culture University (PCCU), Civil Aeronautics Administration (CAA), and Aerospace Industrial Development Corporation (AIDC).
- International collaboration with National Oceanic and Atmospheric Administration (NOAA)/ Hurrican Research Division (HRD), National Centers of Environmental Prediction (NCEP), Geophsical Fluid Dynamics Laboratory (GFDL), National Center for Atmospheric Research (NCAR), Massachusetts Institute of Technology (MIT), Naval Research Laboratory (NRL), Japan Meteorological Agency (JMA)/ Meteorological Research Institute (MRI).
- International research collaboration and memo of technical exchange (NTU, CWB, and NOAA/HRD)
- An international project with foresightedness and mainly led by researchers in Taiwan, with strong collaboration with researches at HRD.
IV. Why do we conduct the DOTSTAR project ?
In 1982, the Hurricane Research Division and other organizations of the National Oceanic and Atmospheric Administration (NOAA) began to investigate possible improvements to numerical tropical cyclone (TC) track forecasts that could result from enhancing numerical weather prediction (NWP) model initial conditions in the data-sparse TC environment. The hypothesis was that the assimilation of dropwindsonde observations from aircraft into the models could improve TC track forecasts. Dropwindsondes measure vertical profiles of wind, temperature, pressure and humidity during their fall from an aircraft to the ocean surface and transmit the data to the aircraft. A crew member processes the data, puts it in a standard format, and sends it to the Global Telecommunications System. From 1982 to 1996, the crews of the NOAA WP-3D (P-3) aircraft operated by the Aircraft Operations Center, obtained nineteen sets of such observations. These data have helped to significantly reduce TC track forecast errors in the National Meteorological Center (now the National Centers for Environmental Prediction [NCEP]) global model, the Geophysical Fluid Dynamics Laboratory (GFDL) hurricane model, and the HRD barotropic VICBAR model (Burpee et al. 1996).
This accomplishment led to the development of a new generation of Global Positioning System dropwindsondes, and NOAA acquired a high-altitude jet aircraft, the Gulfstream-IV-SP (G-IV), as a dedicated operational platform to obtain measurements throughout the depth of the troposphere. Because of its speed, the G-IV covers a larger area of the TC environment than does one of the P-3 aircraft and also can fly much higher than a P-3. The G-IV is primarily used in the Atlantic basin for storms that threaten the coastal areas of the continental US and can be deployed for storms that threaten US interests in the Caribbean, and for storms in the Eastern and Central North Pacific that threaten southern California and Hawaii.
Since 1982, NCEP has extensively advanced its NWP modeling system. This has allowed them to take advantage of observations from new satellites and dropwindsondes to improve data assimilation techniques, the modeling of physical processes, use of ensembles to characterize the analyses/forecast uncertainty, and increased forecast system resolution (from 200 km to 55 km). These advancements allowed incremental improvements to the analyses of the large-scale tropical circulation and the TC environment. Commensurate with these changes was NOAA investment in high speed computing to support the development of NCEP state-of-the art global and the GFDL hurricane models.
To optimize the use of the G-IV dropwindsonde observations, HRD has developed targeting techniques to identify locations where additional observations have an enhanced likelihood of improving the NCEP global model TC track forecasts (Aberson 2003). The strategy employs estimates of initial condition uncertainty and potential error growth from NCEP's operational global ensemble forecasting system and a sampling strategy that ensures adequate sampling of the prospective target regions. During 2002, eighteen of these targeting missions were conducted, mainly in major Hurricanes Isidore and Lili. The data collected during these missions improved the one- and two-day NCEP global model track forecasts by an average of 13% and longer-range forecasts by up to 32%. During the last three years, the data have improved the critical 36 to 60 h global model track forecasts by about 20%; these are important times for finalizing any decision to issue warnings of a TC threat to the public. Further, some evidence suggests that the G-IV data produce even better track forecasts for the strong or rapidly intensifying storms.
With the support of an additional flight crew to cover a second daily mission, NOAA for the first time conducted two surveillance missions per day during the 2002 season. The second missions led to even larger improvements than seen in the general sample. For example, the second surveillance mission on 19 September in Hurricane Isidore led to track forecast improvements between 45% and 80% through three days; these are much larger than the average improvements in those cases in which a second daily mission was not tasked. Similar results were obtained in the second daily missions during Hurricane Lili.
When a TC makes landfall, successful evacuations and damage mitigation measures, based on the most accurate track and intensity forecasts possible, can reduce property damage and the loss of lives. Recently, each mile of coastline in a hurricane warning has been estimated to cost an average of about $1 million dollars to evacuate, not including preparation costs or loss of business. Further value is realized with the ability to avoid unnecessary warnings and costly preparations when a TC comes close to, but does not directly impact the coastline. The cost of one G-IV flight is currently about $40,000.
Based on the mentioned potential value of GPS dropsonde data and the successful experience of the U. S., we consider it necessary to execute a pilot study on the surveillance of typhoons to gather and test new data for typhoons near Taiwan. This research will integrate the Taiwan academy and CWB, collaborating with NCEP, HRD, FNMOS in the U. S.. It is an international project with foresightedness and mainly led by researchers in Taiwan. The accomplishment of typhoon research and forecast by the surveillance aircraft in northwestern Pacific region in this project will be a significant guidance for future observation strategies. The project is beneficial for improving the adaptive observation strategies and data assimilation, which plays an important role in typhoon forecast and research.
In addition, the whole plan is performed respectively in two directions: one is the aircraft surveillance, which includes the aircraft operation, communication and dropsonde-released equipment, data receiving, data debugging/analysis, adaptive observation and the decision of flight route and so on. The other is the research component, which includes the receiving, analysis and assimilation of the dropsonde data, as well as the evaluation of impact of the dropsonde data on typhoon forecast and research. The whole research involves numerous scientific and technical details and makes great progress now. The research achievements have been published in international journal.