LAUSR

In the last three decades, rapid surface warming is observed in the land areas of northern high latitudes during boreal summer months. Although the warming trend is thought to be driven by early snowmelt, the exact causes, especially its relationship with atmospheric circulation changes, remain a subject of debate. By analyzing ERA-Interim data, this study examines the possible factors for rapid subarctic warming. It is found that more than half of the warming trend over the entire subarctic and 80% over northern Canada and eastern Siberia (regions with maximum amplification) can be explained by enhanced downward infrared radiation (IR). Downward IR is largely driven by horizontal atmospheric moisture flux convergence and warm-air advection. The positive trend in geopotential height over the Greenland region is key for moisture flux convergence over northern Canada and eastern Siberia through changes in the storm tracks. An enhanced summertime blocking activity in the Greenland region seems responsible for the positive trend in geopotential heights.