基于MTSAT卫星遥感监测的浙江省及周边海区大雾分布特征

Distribution characteristics of the fog derived from the MTSAT satellite data in Zhejiang Province and its adjacent sea area

中文关键词:  卫星遥感  大雾  MTSAT  气候分布  季节变化

英文关键词:Remote sensing  Fog  MTSAT  Climatological distribution  Seasonal variation

中文摘要:

      利用日本静止气象卫星MTSAT逐时资料,综合地面气象观测数据,对浙江省及其周边海区陆地和海上2008—2012年的大雾进行了专题信息提取,并给出了浙江省陆域、周边海域0.05°×0.05°网格点的小时尺度的遥感大雾产品,结果表明:(1)基于MTSAT卫星观测数据,采用分级判识太阳高度角阈值和归一化大雾指数的方法,构建的浙江及其周边地区陆地和海上遥感大雾监测模型,大雾判识精度总体超过75%,基本满足使用需求。(2)浙江省陆域近5年大雾年平均累计为411.7 h,约占全年的4.7%,基本呈南多北少,山区多平原少的格局,其中浙江南部高山区、舟山和温州部分海岛及西部山区为大雾多发区,且大雾季节分布为冬秋季较多,春夏季较少,22时至09时是浙江省陆域大雾的高发时段,10时以后大雾逐渐消散,至后半夜、凌晨前后,大雾频次逐渐增多。(3)研究区海雾主要发生在大陆近海,呈现由近海向外海减少的空间格局,东海海域年大雾累计为311.7 h,以东海西南部地区大雾出现最多,浙江省沿海大雾的高发区位于温州海域及钱塘江口。研究区海域大雾具有明显的季节特征,主要表现为春季较多,夏季次之,秋冬季较少的分布格局,且海上主要受平流雾影响,大雾不易消散,持续时间较长。从各海区大雾发生频次从高到低依次为:东海东南部、台湾以东洋面、东海中东部、黄海西南部、东海中西部、台湾海峡、东海西北部、黄海东南部、东海西南部和东海东北部。

英文摘要:

      Fog is a common weather phenomenon, and is also a hazardous weather which is one of main causes of sea and air traffic accidents. So far, the climatological distribution of fog was still a lack of detailed understanding in Zhejiang and its adjacent sea regions. The spatial and temporal distribution of fog acquired from the long time series, is beneficial to monitor the fog formation, evolution and dissipation, and it is significant to the fog distribution and forecast. The fog information of Zhejiang Province and its adjacent sea regions was acquired by using the MTSAT geostationary satellite and weather stations whose data covered the period ranging from 2008 to 2012. Moreover, the fog products on hour scales with 0.05 °× 0.05 ° grid resolution were worked out. The results showed that the method of fog identification which classified the threshold of solar altitude with the Normalized Fog Index (NDFI) of the MTSAT data is well suitable for the fog monitoring in the study area. The accuracy of fog identification was nearly 75% that could meet the operational using demand. In the Zhejiang land, the average annual cumulative hour of fog occurrence were about 411.7 h which accounts for 4.7% of the whole year time. The spatial distribution of fog in the Zhejiang land shows that fog occurring frequency in the south area was more than that in the north area, and the frequency in the mountainous area was higher than that in the plain. The south and west mountains, some islands of Zhoushan and Wenzhou were the high-risk areas of the Zhejiang land. In time scale, the fog of the Zhejiang land was more in autumn and winter and less in spring and summer, and the time ranging from 22:00 BT to 09:00 BT was the peak of fog occurring. The spatial distribution of fog in the sea surrounding Zhejiang indicated that sea fog mainly occurs in the coastal area, presenting the pattern in which the fog occurring frequency was decreasing from coastal to offshore. The average annual cumulative hour of fog occurrence in the East China Sea (ECS) were about 311.7 h, and fog occurring frequency was the highest in the southwest of the area. Sea fog of Zhejiang more often occurs in the Wenzhou coastal zone and the Qiantang River estuary, and it had a distinct seasonal characteristic that more fogs in spring and summer, less fogs in autumn and winter. Comparing to land fog, sea fog was not easy to dissipate and can last a longer time because it is the advection fog. Arranging the sea zones by fog occurring frequency, the descending sequence was the southeastern part of ECS, the oceans east of Taiwan, Mideastern part of ECS, southwestern part of Yellow Sea, the midwestern part of ECS, and Taiwan, northwestern part of ECS, southwestern part of Yellow Sea and northeastern part of ECS.