Satellite image of tropical cyclone Saola and Damrey observed by FY-2E at 21:00 on August, 2012 (Beijing Time). Source: National Satellite Meteorological Center
China has seen an unusual typhoon season in 2012. From 1 January to 31 October 2012, totally 23 tropical cyclones (TCs, including tropical storms, severe tropical storms, typhoons, severe typhoons and super typhoons) formed over the western North Pacific Ocean and the South China Sea and 7 of them made their landfalls on China’s coastal areas. They were severe tropical storm Doksuri (1206), typhoon Vicente (1208), severe typhoon Saola (1209), typhoon Damrey (1210), severe typhoon Haikui (1211)，typhoon Kai-tak (1213) and severe typhoon TembinE (1214).
The Characteristics of tropical cyclones in 2012
1) Stronger landing TCs than normal
Until 31 October, 23 TCs formed over the Western North Pacific and the South China Sea. The total TC number is nearly the same as the average (22.9). Among those, 7 TCs made their landfall over China’s coastal areas. The number of landing TC is slightly over historical average (6.6). Six of seven landing TCs made their landfalls in the form of typhoon or with higher intensity. Among them, Severe Typhoon Saola (1209), Severe Typhoon Haikui (1211) and Severe Typhoon Tembin (1214) made their landfalls with maximum surface wind speed around 42~45m/s. And the averaged intensity of all landing TCs is 38.1m/s, stronger than the average (31.4 m/s).
2) High frequency of landing activities in August
In August, 5 TCs made their landfall over China’s coastal areas (1209 Saola, 1210 Damrey, 1211 Haikui, 1213 Kai-Tak and 1214 Tembin). This number also broke the historical record in August, just as the same month in 1994 and 1995. Particularly two tropical cyclones Saola and Damrey made their landfalls on 2 August 2012 within only 10 hours in between, which was the earliest in record. Few days later, KAI-TAK made its landfall in Zhejiang Province. In one-week period, 3 TCs hit China’s coastal areas.
3) Extensive areas affected by strong rainfall and winds
In 2012, the coastal regions hit by TC landfalls extend from the Southeast to the Northeast part of China with a large spread of latitude. The TCs landing on the Southern China coast have higher frequency, while those landing on the Eastern China coast have strong intensity. Damrey (1210) and Bolaven (1215) brought severe rainfall and gale winds in the north part of China, while normally only one tropical cyclone in every two years would impact that region in every two years. Damrey (1210) became the strongest TC landing to the north of the Yangtze River since 1949.There are 18 provinces/regions in China have been affected by strong rainfall related to TC landfalls.
4) Binary tropical cyclones (more than usual)
There were much clearly more 「binary typhoon」 activities in 2012 than usual, and there were totally 10 individual typhoons that had formed into 5 binary typhoon processes, i.e. Saola and Damrey; Tembin and Bolaven; Jelawat and Ewiniar; Mallksi and Gae Mi; Prapiroo and Maria.
5) Offshore intensification
Among all TCs which either landed on or affected China in 2012, five typhoons were featured with offshore intensifications, and they were Vicente(1208), Damrey (1210), Haikui (1211), Kai-Tak (1213) and Son-Tinh (1223) respectively.
Operational Forecast
From the perspective of TC track forecasts in the past 5 years, there is a tendency that the errors of the official typhoon track forecasts are decreasing year by year. In 2012, the deviations of 24-, 48- and 72-hour typhoon track forecasts were 94 km, 163 km and 232 km respectively, which were obviously less than the multi-year mean values, especially, the 24-hour forecast error was less than 100 km for the first time.
Meteorological Services and Cross-sector Response
In 2012, totally 7 typhoons landed on China, six of which reached typhoon intensity. China Meteorological Administration initiated Meteorological Disaster Emergency Response plans respectively. Among these, the Category II emergency response was initiated for Vicente (1208), Saola(1209), Damrey (1210) and Kai-Tak (1213). In response to typhoon Haikui (1211), China Meteorological Administration (CMA) firstly initiated red warning in the past five years. Others, CMA issued Category III Emergency Responses respectively to address typhoon Tembin and Bolaven.
Satellite image of severe typhoon Haikui observed by FY-3B at 13:40 on August 6. Source: National Satellite Meteorological Centre.
In response to typhoon Haikui (1211), CMA had initiated the category I emergency response plan on August 7, which was the first time in the past five years, and sent workgroup to Shandong, Zhejiang and Shanghai to guide the meteorological service.
According to the typhoon track and landing forecasts provided by meteorological departments, local civil affairs departments at all levels can timely activate early-warning response system and made emergency transfer and relocation of 5,620,000 person-times, which effectively reduced casualties. At the central level, the China National Committee for Disaster Reduction and the Ministry of Civil Affairs activated early-warning response system for seven times and dispatched a number of working groups to inspect relief material reserves and shelters and guide local governments to cope with possible impacts of typhoon.
Observers in Dachen Island in Zhejiang made observations in a harsh conditions with coming severe typhoon Haikui.
A large number of vessels orderly returned to harbor, Taizhou, Zhejiang Province.
Statistical Chart of Person-times of Emergency Transfer and Relocation in Provinces Affected by Typhoons in 2012.
Satellite Observation and CMAcast
FY-2F geostationary satellite rapid range scanning plays important role in TCs detection and analysis.
A new geostationary satellite (FY-2F, the seventh of FY-2 series) was launched from the Xichang Satellite Launch Centre on 13 January 2012. FY-2F has more flexible and higher temporal resolution for specific regions to be scanned. Using FY-2F satellite data, the targeted TCs and convective weather systems can be tracked and monitored continuously. FY-2F provides the multi-temporal observations and in-orbit backup with FY-2D and FY-2E. Together, they will play an important role in natural disaster monitoring, prevention and preparedness.
Based on the satellite imagery which is used to determine TC centres, FY-2F cloud animations are very useful, especially for asymmetrical TC structures (e.g. Doksuri). Because they have six minutes interval and can show more continuous TC structure evolutions. At the same time, a new improved calibration method was used in FY-2F infrared channels, which can make the brightness temperature and some retrieved products more reliable for TC applications. For example, TBB products reflect evolution of meso-scale TC internal convections and it is a useful tool for accurate TC intensity analysis by using DVORAK objective methods.
Satellite Weather Analysis Platform (SWAP) application in TC forecasting
Since 2012, Satellite Weather Analysis Platform (SWAP) has already been used for TC prediction in the National and Provincial Meteorological Services, including the National Meteorological Centre, Guangdong Province, Shanghai Municipality, and Zhejiang Province, etc. This platform provides a useful tool for all forecasters, and satellite data can be easily localized. It will become one of the important tools for TC prediction and relevant services work.
Increased comprehensive applications of geostationary and polar orbiting satellites have improved applications.
FY-3B polar orbiting satellites has several advantages in monitoring TC internal thermal structure, raining band structure, heavy precipitation range and cloud asymmetrical structure, with MWTS (Microwave Temperature Sounder), MWHS (Microwave Humidity Sounder) and MWRI (Microwave Radiation Imager). While, using FY-2D/E/F geostationary satellite, some products like Quantitative Precipitation Estimation and Cloud Classification can be derived. In 2012, taking their respective advantages, new products were developed and applied to TC analyses.
CMAcast, which is a newly established DVB-S2 standard satellite data broadcast system of CMA, has become its formal operation since 1 June 2012. The CMAcast is an integrated satellite data-broadcasting system in conformance to the DVB-S2 standard, substituting for the present satellite data-broadcasting systems (PCVSAT, DVB-S and FENGYUNcast) which already have 2400, 700 and 200 users respectively. The CMAcast is the major component of the national meteorological data dissemination system, continuously broadcasting the real-time observational data and products crucial for the weather forecasts and related services to more than 2500 users. It is also the most effective way to share the various meteorological data and products with the public user communities in China. At present, the daily broadcast data volume is more than 210 GB, including the territorial and international observation data, the CMA T639 NWP products, the satellite observation products of FY2D/E and FY3A/B, EUMETSAT satellite products, etc.
Development in GRAPES_TYM and GZTCM
GRAPES-TYM passed the quasi-operational test in July of 2012. It is mainly used to forecast typhoon tracks, intensity, wind and rainfall brought about by typhoon in the western North Pacific and the South China Sea. This model runs twice per day when typhoon develops, with a forecast time validity of 72h. Its horizontal resolution is 0.15 degree and vertical resolution 31 layers. The track forecast of GRAPES-TYM is a slightly better than T213 Global Typhoon Track Prediction System, while its typhoon intensity and rainfall forecasts are significantly better than T213.
In 2012, the Guangzhou Tropical Cyclone Model (GZTCM) was running smoothly at the Guangzhou Institute of Tropical and Marine Meteorology under CMA. A non-hydrostatic semi-Lagrange model with a limited area, GZTCM has a horizontal resolution of 0.36 degree, 55 vertical layers (updated from the former version with 31 layers) and a time step of 200 seconds. With this model, 5-day conventional weather forecasts, 72-h typhoon track forecasts and 72-h typhoon intensity (pressure at TC centre) and high wind forecasts are issued. Assessments of real-time forecasts are made for reference in operational forecasts.
Editor Zhang Yong