Impact of snow initialization on sub-seasonal forecasts
Impact of snow initialization on sub-seasonal forecasts
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DOI：
10.1007/s00382-013-1782-0
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发表时间：
2013-10-01
期刊：
影响因子：
4.6
通讯作者：
Benestad, R. E.
中科院分区：
文献类型：
--
作者：
Orsolini, Y. J.;Senan, R.;Benestad, R. E.
近年来，积雪对冬季大气遥相关的影响重新受到关注，部分原因是其对季节可预测性的潜在影响。许多观测和模型研究表明，秋季欧亚积雪尤其影响北太平洋和北大西洋的环流模式。我们与欧洲中期天气预报中心 (ECMWF) 集合预报系统进行了一系列大气-海洋耦合模拟，以研究精确降雪初始化的影响。 2004-2009 年，从 10 月 15 日到 12 月 1 日，每 15 天开始对两个月的集合预报，要么根据重新分析对降雪变量进行实际初始化，要么使用来自备用秋季日期和年份的“扰乱”降雪初始条件。最初，在前 15 天，较厚的积雪降低了欧亚大陆和北美大陆的表面温度。如果提前30天，由于西伯利亚高压的加强和向西扩展，它会导致北极和欧亚大陆高纬度地区变暖。它还导致欧亚大陆中纬度地区变冷，并降低北极上空的海平面压力。这种“温暖的北极-寒冷的大陆”差异意味着，通过更现实的降雪初始化对近地表温度的预测与重新分析更加一致，减少了北极的寒冷模型偏差和中纬度地区的温暖模型偏差。针对不同的提前期，估计了实际降雪初始化对雪深和近地表温度预报技能的影响。在前 15 天对积雪覆盖的土地的预报技能略有提高之后，我们还发现北极和北太平洋部分地区的预报技能在长达 30 天的提前时间内有所提高，这可以归因于陆地上实际的降雪初始化。
The influence of the snowpack on wintertime atmospheric teleconnections has received renewed attention in recent years, partially for its potential impact on seasonal predictability. Many observational and model studies have indicated that the autumn Eurasian snow cover in particular, influences circulation patterns over the North Pacific and North Atlantic. We have performed a suite of coupled atmosphere-ocean simulations with the European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble forecast system to investigate the impact of accurate snow initialisation. Pairs of 2-month ensemble forecasts were started every 15 days from the 15th of October through the 1st of December in the years 2004-2009, with either realistic initialization of snow variables based on re-analyses, or else with "scrambled" snow initial conditions from an alternate autumn date and year. Initially, in the first 15 days, the presence of a thicker snowpack cools surface temperature over the continental land masses of Eurasia and North America. At a longer lead of 30-day, it causes a warming over the Arctic and the high latitudes of Eurasia due to an intensification and westward expansion of the Siberian High. It also causes a cooling over the mid-latitudes of Eurasia, and lowers sea level pressures over the Arctic. This "warm Arctic-cold continent" difference means that the forecasts of near-surface temperature with the more realistic snow initialization are in closer agreement with re-analyses, reducing a cold model bias over the Arctic and a warm model bias over mid-latitudes. The impact of realistic snow initialization upon the forecast skill in snow depth and near-surface temperature is estimated for various lead times. Following a modest skill improvement in the first 15 days over snow-covered land, we also find a forecast skill improvement up to the 30-day lead time over parts of the Arctic and the Northern Pacific, which can be attributed to the realistic snow initialization over the land masses.