The Effect of Boreal Late Autumn Snow Cover over Western and Central China on the Northern Hemisphere Wintertime Blocking Frequency

Abstract

The impact of snow cover in western and central China during late autumn on wintertime blocking occurrence is investigated using reanalysis data. The study results show that wintertime atmospheric circulations affected by late autumn snow cover anomalies form favorable conditions for increased blocking frequency (BF), especially in the North Pacific and North Atlantic. Evidence is also presented that the stratosphere–troposphere interactions are the key mechanism of the lag response of wintertime North Pacific and North Atlantic BFs to the late autumn snow cover. That is, positive anomalous snow cover can induce a dipole anomaly in the geopotential height field over the lower stratosphere, due to the decrease of the 300–1000-hPa thickness and the concurrent variation between the East Asian plateau jet and the polar front jet. The associated positive geopotential height anomalies are located over northwestern Eurasia. Meanwhile, western and central China shows remarkably negative geopotential height anomalies. Also, the corresponding atmospheric circulation in the lower stratosphere increases the Eliassen–Palm flux that propagates into the stratosphere through the constructive interference between the forced and climatological waves. The upward wave activity fluxes collapse the polar vortex in the stratosphere, resulting in the downward propagation of the geopotential and wind anomalies from the stratosphere. Consequently, the decreased zonal wind speed in the upper layer of the blocking region forms conditions favorable for wintertime blocking.

Possible relationship between heatwaves in Korea and the summer blocking frequency in the Sea of Okhotsk

“…This index is based on the method proposed in Tibaldi and Molteni (1990) and used in many previous studies (e.g. You and Ahn, 2012; Park and Ahn, 2014; Choi and Ahn, 2017; Lee and Ahn, 2017). The daily blocking index was calculated using the daily averaged 500 hPa geopotential height obtained from R‐2.…”

Intraseasonal Snow Cover Variations Over Western Siberia and Associated Atmospheric Processes

“…Jeong et al () stated that the increase in the Eurasian snow cover contributes to the strengthening of the Siberian high on decadal time scale. The interannual variations of the intensity of the Arctic Oscillation (North Atlantic Oscillation [NAO]) and the blocking are associated with the snow cover anomalies over Eurasia (Choi & Ahn, ; Cohen et al, ; Kim et al, ; Xu et al, ). On intraseasonal time scale, snow cover variations over the Tibetan Plateau are influenced by the Madden‐Julian Oscillation (Li et al, ) and affect the East Asian atmospheric circulation through snow thermodynamic effects (Li et al, ).…”

Impacts of Autumnal Eurasian Snow Cover on Predominant Modes of Boreal Winter Surface Air Temperature Over Eurasia

“…Xu et al () indicated that the planetary waves with zonal wave number 1 operate in connecting the October snow cover in northern Eurasia with the warm Arctic‐cold Eurasia pattern during the subsequent January through the mechanism of the troposphere‐stratosphere coupling. Choi and Ahn () revealed that more late autumn snow cover over western and central China is conductive to the occurrence of blocking, particularly over the North Pacific and North Atlantic. It is indicated that the troposphere‐stratosphere interaction is the key to these processes.…”