Yonagunijima
Yonagunijima is an island located in the westernmost territory of Japan, only about 110 km from Taiwan (Figures 7.1.1.9 and 7.1.1.10). It is an island stretching east-west, with a coast line of about 27.5 km and an area of about 28.9 km2. The station is located near the north coast of the island, surrounded by grasslands and sugarcane fields. It is situated on the east end of the community, with a prevailing wind direction of north-northeast to northeast, or south, and westerly winds are rare; thus, it is unaffected by the pollution sources concentrated in the area to the west including Taiwan. Therefore, the station is considered to meet the conditions required for a GAW Regional Station representing the Nansei Islands. Table 7.1.1.4 lists the observation parameters and systems used at the station.
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Fig. 7.1.1.9 Location map of Yonagunijima station. |
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Fig. 7.1.1.10 Location view of Yonagunijima station. |
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Table 7.1.1.4 Observation parameters, frequency and instruments at Yonagunijima station. |
| Parameter | Start of observation | Frequency | Instrument |
|---|---|---|---|
| CO2 | January 1997 | Continuous | Non-dispersive Infrared Analyzer (NDIR) HORIBA, Ltd. VIA510R |
| January 2008 | Continuous | Non-dispersive Infrared Analyzer (NDIR) LI-COR Biosciences, Inc. LI-7000 |
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| CH4 | January 1998 | Continuous | Non-dispersive Infrared Analyzer (NDIR) HORIBA, Ltd. GA360-S |
| January 2008 | Continuous | Gas Chromatograph with FID Round Science Inc. RGC-1 |
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| CO | January 1998 | Continuous | Non-dispersive Infrared Analyzer (NDIR) HORIBA, Ltd. GA360-S |
| January 2008 | Continuous | Gas Chromatograph with RGD Round Science Inc. TRA-1 |
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| O3 | January 1997 | Continuous | UV Ozone Monitor EBARA JITSUGYO CO.,LTD. EG-2001F |
| January 2008 | Continuous | UV Ozone Monitor Thermo Fisher Scientific Inc. 49i |
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| Aerosol optical depth | January 1998 | Three time per day | Sunphotometer EKO INSTRUMENTS CO., LTD. MS-110 |
| April 2007 | Continuous | Sunphotometer PMOD/WRC PFR |
The climate of Yonagunijima Island is affected by the high pressure system of the Asian continent in winter and by the Pacific high in summer. The annual mean temperature in a normal year is 23.6°C in Yonagunijima: the monthly mean temperatures from May through October in a normal year exceed 25°C, and the monthly mean temperatures for January and February are about 18°C, with some days being below 15°C. Compared with Minamitorishima, which lies at about the same latitude as Yonagunijima, the temperature in winter is about 4°C lower, while the temperature in summer is about the same, indicating that Yonagunijima has a larger annual temperature variation. The annual precipitation in a normal year is about 2360 mm, which is primarily provided by winter monsoons, fronts in the rainy season, and typhoons. During the period when the island is under the influence of high pressure system of the Asian continent, north-northeast to northeast winds prevail; on the other hand, during the period when it is under the influence of the Pacific high, southern winds prevail. The maximum wind speed exceeds 10 m/s on more than half the total days of the winter period. During the winter period, there are many cloudy and rainy days.
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Fig. 7.1.1.11 Daily mean, daily maximum and minimum temperatures, and daily precipitation amounts at Yonagunijima station in 2009. |
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Fig. 7.1.1.12 Monthly and annual wind roses at Yonagunijima station in 2009. |
Ryori | Minamitorishima | Yonagunijima | Syowa | Ground-base Meteorological Observation