In Situ Evidence of Low-Level Atmospheric Responses to the Oyashio Front in Early Spring
In Situ Evidence of Low-Level Atmospheric Responses to the Oyashio Front in Early Spring
复制标题
DOI：
10.2151/jmsj.2019-024
复制
发表时间：
2019
影响因子：
3.1
通讯作者：
Y. Kawai;H. Nishikawa;E. Oka
中科院分区：
文献类型：
--
作者：
Y. Kawai;H. Nishikawa;E. Oka
以前的模拟研究表明，亚北极太平洋的Oyashio锋面在中尺度上对大气有重大影响；然而，据作者所知，还没有在该地区的大气中捕捉到海洋印记的现场观测。我们利用2013年4月在俄亥俄州锋面周围发射的103个无线电探空仪，通过连续的地面气象学和Ceileter观测，提供了大气层对Oyashio锋面响应的现场证据。合成廓线显示，1000m以下的低层大气在Oyashio锋面的冷侧是静态稳定的，但在暖侧是不稳定和混合的。在温暖一侧的大气中，相对湿度在1000米左右的高度急剧下降，这表明平均云顶在这个高度。冷区云底高度出现频率在50-100m之间最高，暖区云底高度分布在较高海拔。与北风相比，南风条件下锋面大气边界层和云底高度的差异更为明显。在宽度约400 km的局地海面温度最低值以上，海洋混合层深度达到局地最大值的地方，在海拔1000m以下观测到一个大的水平大气温度梯度，这个水平梯度对应着1.2hpa的海平面气压(SLP)异常，与在黑潮延伸区观测到的SLP异常相当。此外，我们还发现，狭窄的温暖海洋飘流润湿了上面的大气，影响了向下的长波辐射。在4月5日位于146.4°E和147.0°E之间的宽流光上，西半部和东半部的近地表大气特性有很大的不同。
Previous modeling studies have indicated that the Oyashio front in the subarctic Pacific Ocean significantly affects the atmosphere on mesoto basin scales; however, there were no in situ observations that captured oceanic imprints on the atmosphere in this region as far as the authors know. We present in situ evidence of atmospheric responses to the Oyashio front by using a total of 103 radiosondes launched around the Oyashio front in April 2013 with continuous surface meteorology and ceilometer observations. Composite profiles showed that the lowlevel atmosphere below 1000 m was statically stable on the cold side of the Oyashio front, but unstable and mixed on the warm side. In the atmosphere on the warm side, the relative humidity dropped sharply at an altitude of around 1000 m, an indication that the mean cloud top was at this altitude. While the frequency of cloud base height peaked at 50 – 100 m in the cold areas, cloud bases were distributed at higher altitudes in the warm areas. These differences in the atmospheric boundary layer and cloud base heights across the front were clearer under conditions of southerly winds compared with those of northerly winds. Above a local sea surface temperature minimum with a width of approximately 400 km, where the ocean mixed layer depth is known to reach a local maximum, a large horizontal air temperature gradient was observed below an altitude of 1000 m. This horizontal gradient corresponded to a sea level pressure (SLP) anomaly of 1.2 hPa, comparable to observations of SLP anomalies in the Kuroshio Extension region. Furthermore, we found that narrow warm ocean streamers moistened the overlying atmosphere, affecting downward longwave radiation. Over the wide streamer located between 146.4°E and 147.0°E on 5 April, the near-surface atmospheric properties were largely different over the western half and the eastern half.