Baek-Jo Kim Hyo-Sang Chung Chun-Ho Cho Jeong-Hoon Kim Meteorological Research Institute Korea Meteorological Administration Korea Vaisala AUTOSONDE supporting severe weather observations Structural Features of Typhoon RUSA’s Center Revealed At the Korea Meteorological Administration, the Center for Severe Weather Monitoring and Observation runs a major project to obtain and study dense observation data for severe weather conditions. The project relies on high-tech equip- ment for its observation needs. At Haenam Weather Observa- tory, a Vaisala AUTOSONDE Automatic Sounding System is used for high-resolution upper air weather observation data. Figure 1. The Korea Meteorological Administration’s Haenam Weather Observatory is located on the south coast of Korea. 4 162/2003 he Center for Severe mission of KEOP-2002 is to pro- Figure 2. Typhoon Weather Monitoring and duce spatial and temporal high- RUSA’s route Observation, established resolution upper-air observation across the Korean T coast. by the Meteorological Research data over the southwestern part Institute at the Korea Meteorol- of the Korean peninsula. The ogical Administration, is located dense observation data is used to at the Haenam Weather Obser- study the structure of severe vatory (34° 33’N, 126°N 35’E). weather phenomena, their for- The objective of its principal mation and development. The project, called the Korea En- project utilizes a portable rawin- hanced Observing Period sonde system and the AUTO- (KEOP), is to produce dense ob- SONDE, as well as the upper-air servation data for severe weather observation network of the Ko- conditions, such as heavy rain- rea Meteorological Administra- fall and typhoons, which occur tion (KMA). during the summer. The project uses intensive field-based experi- Frequent observations ments deploying sophisticated To enhance the utilization and meteorological equipment. The application of the AUTOSON- intensive observation data analy- DE and to assess its steadfastness Weather Monitoring and Obser- sis and studies of its application against maximum wind speeds vation was able to delineate and will provide better understand- of over 20 m/s, valuable three- analyze the characteristics of the ing of the structure and develop- hour upper-air observations vertical atmospheric structure ment of various severe weather were made from 09 UTC on Au- around typhoon RUSA’s center. phenomena, as well as improve gust 29th to 21 UTC on Septem- Several studies had previous- the short-term forecasts of severe ber 1st, 2002. During this peri- ly been conducted in other weather events. od, at 06 UTC on August 31st, countries to analyze the atmos- As the Center aims to apply 2002, the Center was able to pheric vertical structure around high-tech meteorological equip- capture typhoon RUSA - which a typhoon’s center, using wind ment to intense field-based ex- had caused unprecedented dam- profilers and dropwindsondes periments, the Meteorological age to lives and property in Ko- (Sato, 1992; May, 1993; Research Institute initiated the rea - as it approached the Korean Willoughby, 1998). However, purchase of a Vaisala AUTO- peninsula and hit a southern such studies in Korea remain SONDE in 2000. The AUTO- coastal region near the Haenam very limited due to the difficulty SONDE’s operation has been Weather Observatory. The ty- of maintaining effective three- stable and, since mid-January phoon was the most powerful hour upper-air sounding obser- 2001, the system has provided hurricane to strike the Korean vation capability in high winds Figure 3. The Vaisala severe weather condition data Peninsula since Typhoon Sarah and heavy precipitation. More- AUTOSONDE Automatic Sounding System installed at for research purposes, on such in 1959. Wind speeds reached over, only a few of the observed Haenam Weather Observatory. phenomena as heavy rainfall up to 120 miles (200 kilometers) structured typhoons had hit the and typhoons. per hour, and up to 36 inches of Korean peninsula. Consequent- rain poured on some parts of ly, the unique research done on Observation details High-resolution South Korea over a two-day peri- typhoon RUSA is very meaning- The time-altitude cross-sections upper-air data od. Using the temporal high-res- ful in enhancing our perspec- of various meteorological ele- The AUTOSONDE was espe- olution upper-air observation tives and understanding of the ments (temperature, relative hu- cially successful in the KEOP- data obtained by the AUTO- structure of this severe weather midity, equivalent potential 2002 project in 2002. The main SONDE, the Center for Severe system. temperature and wind vec- ➤ 162/2003 5 Figure 2. Time-altitude cross-sections of (a) temperature, (b) relative humidity, (c) equivalent potential temperature, and (d) wind vector, observed by the AUTOSONDE from 09 UTC August 29th to 21 UTC September 1st 2002. a) tor), using the data from the 21 balloons, in order to save costs UTC AUTOSONDE upper-air by reducing the amount of gas observation, are shown in figure needed in the process. 4. The red typhoon symbol on the bottom of the graph indi- Findings of the study cates the time when the typhoon In figure 4a, it can be seen how RUSA hit the southern coastal the lower level temperatures region of Korea. The time of the started to gradually decrease typhoon was determined by while the higher level tempera- considering the position of the tures increased as the typhoon typhoon’s center, obtained from approached the Korean peninsu- the best track of typhoon RUSA la. The interface height of the issued by RSMC (Regional Spe- decreasing and increasing tem- cialized Meteorological Center) perature regimes was about 2.5 of Tokyo, the shortest distance km. The decrease in lower level between the typhoon and the temperatures could be partly ex- Haenam Weather Observatory, plained by the adiabatic expan- b) and the lowest surface pressure sion of air parcels under where at the observatory. The blank the pressure was lower than in parts of the figure indicate that the studied environment, and no observation data were ob- on the cooling effect induced by tained due to the strong surface precipitation. winds after the typhoon passed. Relative humidity was char- The more expensive helium was acterized by high humidity asso- generally selected for balloon ciated with cloud band ahead of filling gas instead of the normal the typhoon, low humidity de- hydrogen, for maximum safety rived from the temperature in- during the intensive observation crease caused by adiabatic com- campaign. In this particular AU- pression around the typhoon TOSONDE observation (shown center, and the effect of the syn- below), 200-gram weather bal- optic weather system after the ty- loons were used instead of the phoon had passed (fig. 4b). A regular 800-gram or 1,000-gram high equivalent potential tem- c) d) 6 162/2003 Figure 5. Relationship between azimuthal velocity and Haenam rainfall (left panel), and the structure of typhoon RUSA’s eye and associations with convective cloud systems (right panel), analyzed by high-resolution upper- air soundings from AUTOSONDE and the corresponding satellite images. perature at the typhoon passage From the tangential velocity there was no rain and the sky Acknowledgements time appeared due to the in- computed from the AUTO- was clear Haenam. This study is partly supported by crease in the amount of cloud at SONDE, four maximum tan- METRI’s principal project, the “Korea Enhanced Observing Period (KEOP)”. regions where it was relatively gential velocity areas could be Conclusions warmer than in the studied envir- seen at altitudes of 3 to 4 km. Looking at the analyses done in References onment (fig. 4c). The easterlies These corresponded with the this project, it can be said that May, P. T., and Greg J. Holland, 1993: before the typhoon were abrupt- rainfall peaks at Haenam. The the Vaisala AUTOSONDE Wind profiler observations of Tropical ly changed to westerlies after the satellite images showed that the played an important role in get- Storm Flo at Saipan, Wea, and, Fore- typhoon passed (fig. 4d). first maximum tangential veloci- ting useful data from typhoon casting, 9, 410-426. The change in wind speed, ty - at 07 UTC on August 30th - RUSA. By providing sufficient shown at altitudes of 2 to 3 km, was influenced by the second three-hour upper-air observa- Sato, K., 1992: Small-scale wind distur- bances by the MU Radar during the was relatively small compared to cloud band formed ahead of the tions in conditions where maxi- passage of typhoon Kelly, J. Atmos. the change in wind direction. In typhoon. The second area was at mum wind speeds were 20 m/s, Sci., 50, 518-537. addition, there was a divergent 00 UTC on August 31st, just be- the AUTOSONDE helped clari- region at above 8 km. From the fore the typhoon passed, when fy the structure, formation, and Willoughby, H. E., 1998: Tropical cyclone temporal high-resolution upper- there was strong cyclonic and development mechanism of the Eye Thermodynamics, Mon. Wea. air observation data obtained convergent circulation in the ty- typhoon. ● Rev., 126, 3053-3067. with the AUTOSONDE, the phoon’s inner eyewall. The third warming core associated with velocity was located at the eye- the adiabatic compression of air wall of the ill-organized typhoon parcels and low humidities at center (see fig. 5). mid to high levels could be seen. The maximum rainfall at Weak wind speeds which charac- Haenam normally occurs when terized the typhoon center could a strong cyclonic circulation, as- also be seen, since the observa- sociated with the outer eyewall tion site at Haenam was located of the typhoon, appeared at the Figure 6. Dr Kim was in charge of the KEOP within the unstructured and observation site. However, due project at the Korea widened typhoon center after it to the influence of the unstruc- Meteorological had hit the peninsula.