LARGE-SCALE COMMON FEATURES OF SUBTROPICAL CONVERGENCE ZONES (THE BAIU FRONTAL ZONE, THE SPCZ, AND THE SACZ) .2. CONDITIONS OF THE CIRCULATIONS FOR GENERATING THE STCZS
LARGE-SCALE COMMON FEATURES OF SUBTROPICAL CONVERGENCE ZONES (THE BAIU FRONTAL ZONE, THE SPCZ, AND THE SACZ) .2. CONDITIONS OF THE CIRCULATIONS FOR GENERATING THE STCZS
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DOI：
10.2151/jmsj1965.71.5_581
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发表时间：
1993-10-01
影响因子：
3.1
通讯作者：
KODAMA, YM
中科院分区：
文献类型：
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作者：
KODAMA, YM
白宇/梅雨锋带（BFZ）、南太平洋辐合带（SPCZ）和南大西洋辐合带（SACZ）是副热带的重要辐合带。这些区域（以下简称亚热带辐合带；STCZ）是重要的副热带锋区，具有较强的水汽辐合、等效位温场锋生和对流不稳定的产生。为了阐明特定区域形成STCZ的原因，我们对全球副热带地区与STCZ周围的大尺度环流进行了比较。此外，还比较了STCZ活跃期和非活动期的STCZ周围大尺度环流。当满足以下两个条件时，STCZ出现： (1)副热带纬度(30-35度)有副热带急流；(2)副热带高压西缘盛行低空向极地气流。不满足一两个条件的地区，副热带地区无降水或仅有弱降水区。当满足（不满足）这两个条件时，STCZ 会增强（减弱）。此外，在副热带其他地方，如果同时满足这两个条件，即使时间很短，也会暂时出现类似STCZ的显着降水区。极地流对于副热带水汽的强烈辐合、等效位温场的锋生和对流不稳定的产生是副热带锋区特征所不可缺少的。向极地流是在副热带高压区和副热带高压区形成的低热区之间的东向气压梯度中形成的。季风对流和大陆上的陆地表面加热是形成低热的重要热源。
The Baiu/Meiyu frontal zone (BFZ), the South Pacific convergence zone (SPCZ), and the South Atlantic convergence zone (SACZ) are significant convergence zones in the sub-tropics. These zones (hereafter Sub-Tropical Convergence Zones; STCZs) are significant sub-tropical frontal zones characterized with strong moisture convergence, frontogenesis in equivalent potential temperature fields, and generation of convective instability.To clarify the reasons why the STCZs form in the specific areas, we investigated large-scale circulations in the sub-tropics globally compared with those around the STCZs. Moreover, the large-scale circulations around the STCZs were compared between active and inactive periods of the STCZs.The STCZs appeared where the following two conditions were quasi-stationarily satisfied; (1) sub-tropical jets flow in the sub-tropical latitudes (30-degrees-35-degrees) and (2) low-level poleward flows prevail along the western peripheries of the sub-tropical highs. Over the areas where one or two of the conditions were not satisfied, no, or only weak, precipitation areas appear in the sub-tropics. The STCZs were intensified (weakened) when the two conditions were satisfied (not satisfied). Moreover, significant precipitation zones similar to the STCZs also temporarily appeared elsewhere in the sub-tropics, if the two conditions were satisfied there even for a short period.The poleward flows were indispensable for the strong moisture convergence, the frontogenesis in equivalent potential temperature fields, and the generation of convective instability, in the sub-tropics, which are the characteristics of the sub-tropical frontal zones. The poleward flows were formed geostrophically in the eastward pressure gradient between the sub-tropical highs and heat lows developed in the high-pressure-zones in the sub-tropics. Monsoon convections and land-surface heating over the continents were important as heat sources to form the heat lows.