On the Northward Ageostrophic Winds Associated with a Tropical Cyclone
On the Northward Ageostrophic Winds Associated with a Tropical Cyclone
复制标题
与热带气旋相关的北转地转风
DOI：
10.2151/sola.2019-040
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发表时间：
2019
期刊：
影响因子：
1.9
通讯作者：
Kazuo Saito
中科院分区：
文献类型：
--
作者：
Kazuo Saito
It is well known that northward winds are often observed at southern coastal areas of Japan when a developed tropical cyclone is located off the south coast of Japan. These northward winds have been frequently referred to the northward emission of warm and humid air from the typhoon which cause pre-typhoon rainfalls, but their mechanism has not been clarified. In this paper, we show that the northward wind can be explained by the ageostrophic wind components dynamically induced by acceleration vector round the tropical cyclone. On 7 October 2009, when a developed typhoon (T0918 Melor) approached Japan, distinct northward winds were observed at aerological observations over western Japan. Using numerical simulations with the Japan Meteorological Agency nonhydrostatic model, we reproduced the observed northward wind and their mechanism were examined by numerical experiments. The origin of the northward winds is explained by the ageostrophic winds dynamically induced by the acceleration vectors. When a typhoon approaches a baroclinic zone from south, north eastward ageostrophic winds are induced by southeastward acceleration vectors. Other possible causes (diabatic heating and orographic effect) are examined by sensitivity experiments. Diabatic heating by moist process acts to enhance the ageostrophic winds but the role is not primary. Orography has little effect on the observed ageostrophic wind. Non-axisymmetric features of the upper level divergence flow of a tropical cyclone near a baroclinic zone can also be elucidated by the similar mechanism of the ageostrophic winds. (Citation: Saito, K., 2019: On the northward ageostrophic winds associated with a tropical cyclone. SOLA, 15, 222−227, doi:10.2151/sola.2019-040.)
