The Arctic summer circulation and the maintenance of Boreal-forest rainbets

The boreal forests grows by rainfall along these forests (named hereafter as the boreal-forest rainfall). It is hypothesized that the boreal-forest rainbelts are maintained by the convergence of water vapor flux associated with transient disturbances such as individual meso and synoptic scale storms (denoted as °µminor storm tracks°¨ to distinguish major storm tracks in the North Pacific and North Atlantic). In order to substantiate this hypothesis, the structure of the Arctic summer circulation and the Arctic transient activity are explored with the NCEP reanalysis data.

The Arctic summer circulation is characterized by three Arctic ridges over the Barent Sea, New-Siberian Islands, and Alaska-the Beaufort Sea. These ridges are coupled, respectively, with the eastward extension of the North Atlantic anticyclone, the East Siberian monsoon, and the narrow Alaska Pacific-coast trough line. A clear transition of the circulation structure emerges from the barotropic stationary eddies (associated with the Barent Sea ridge) to the East Siberian monsoon low (associated with the New-Siberian islands ridge), and from the narrow Alaska Pacific-coast trough to the merging of the east-Canadian Arctic trough and the North-Atlantic circulation. Jet stream-like high-speed westerlies along the three aforementioned ridges appear in the Arctic seaboard of the Eurasian and North American continents. The strong baroclinic zones coupled with these jet stream-like westerlies maintain the Arctic transient activity indicated by frontal activity, cyclone frequency, and variance of transient variables. The coincidence of convergence of the transient water vapor flux with these baroclinic zones and the boreal-forest rainbelts substantiate the aforementioned maintenance of the hypothesis for the boreal-forest rainbelts.