Synoptic Climatology of Rain-on-Snow Events in Alaska
Synoptic Climatology of Rain-on-Snow Events in Alaska
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DOI：
10.1175/mwr-d-19-0311.1
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发表时间：
2019-03
影响因子：
3.2
通讯作者：
A. Crawford;K. Alley;A. Cooke;M. Serreze
中科院分区：
文献类型：
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作者：
A. Crawford;K. Alley;A. Cooke;M. Serreze
当雨雪（ROS）事件在积雪中冻结时，雨水会对高纬度有蹄类种群产生不利影响，形成冰层，阻碍冬季饲料的获取。在极端情况下，活性氧事件会导致大规模死亡。活性氧事件与暖湿空气平流有关，与温带气旋有关。然而，这些条件在许多冬季降水事件中是常见的，挑战了我们对ROS事件发生的特定条件的理解。本研究使用现代研究与应用回顾性分析第2版（MERRA-2）来区分阿拉斯加的ROS事件与降水事件，其中只有雪落在预先存在的积雪上[雪对雪（SOS）]。在北坡和科泽布湾，产生ros和sos的风暴路径没有明显区别。然而，在内陆、西南部和安克雷奇，产生ros的风暴的路径往往比产生sos的风暴更靠北和更靠西。产生ROS的风暴的西北移动与ROS事件期间阿拉斯加湾东部对流层上层反气旋的位置有关。产生ros的风暴并不比产生sos的风暴更强烈，但它们与大气阻塞的关联导致风暴东侧的压力梯度更强，从而导致温度和可降水量正异常的平流更强。在几个地点，阿拉斯加湾东部的海平面压力在ROS事件发生前几天也明显高于SOS事件发生前，这进一步表明大气阻塞是ROS事件的促进因素和潜在预测因素。
Rain-on-snow (ROS) events can have adverse impacts on high-latitude ungulate populations when rain freezes in the snowpack, forming ice layers that block access to winter forage. In extreme cases, ROS events have led to mass die-offs. ROS events are linked to advection of warm and moist air, associated with extratropical cyclones. However, these conditions are common to many winter precipitation events, challenging our understanding of the particular conditions under which ROS events occur. This study uses the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) to differentiate ROS events in Alaska from precipitation events in which only snow falls on a preexisting snowpack [snow-on-snow (SOS)]. Over the North Slope and Kotzebue Sound, no clear difference exists between the tracks of ROS-producing and SOS-producing storms. However, in the interior, southwest, and Anchorage, tracks of ROS-producing storms tend to be farther north and west than for SOS-producing storms. The northwest shift of ROS-producing storms is linked to the position of upper-tropospheric anticyclones in the eastern Gulf of Alaska during ROS events. ROS-producing storms are no more intense than SOS-producing storms, but their association with atmospheric blocking leads to stronger pressure gradients on the east side of storms and thereby stronger advection of positive anomalies in temperature and precipitable water. For several sites, sea level pressure in the eastern Gulf of Alaska is also significantly higher a few days prior to ROS events than prior to SOS events, further implicating atmospheric blocking as a facilitator and potential predictor of ROS events.