Influence of Tibetan Plateau snow cover on East Asian atmospheric circulation at medium-range time scales

Abstract

The responses of atmospheric variability to Tibetan Plateau (TP) snow cover (TPSC) at seasonal, interannual and decadal time scales have been extensively investigated. However, the atmospheric response to faster subseasonal variability of TPSC has been largely ignored. Here, we show that the subseasonal variability of TPSC, as revealed by daily data, is closely related to the subsequent East Asian atmospheric circulation at medium-range time scales (approximately 3-8 days later) during wintertime. TPSC acts as an elevated cooling source in the middle troposphere during wintertime and rapidly modulates the land surface thermal conditions over the TP. When TPSC is high, the upper-level geopotential height is lower, and the East Asia upper-level westerly jet stream is stronger. This finding improves our understanding of the influence of TPSC at multiple time scales. Furthermore, our work highlights the need to understand how atmospheric variability is rapidly modulated by fast snow cover changes.

Fig. 1

Standard deviation and climatology of wintertime Tibetan Plateau snow cover based on daily data. a Standard deviation of the 120-day high-pass filtered anomalous probability of snow-cover occurrence over the Tibetan Plateau (TP) during wintertime. b Climatological probability of snow-cover occurrence over the TP during wintertime. The unit is %. The black oval and text strings in a mark western TP, central TP and eastern TP from left to right. Gray areas indicate areas with altitudes less than 3000 m. The map of TP was created by using topographic data from Global Relief Model data of ETOPO1 (doi:10.7289/V5C8276M)

Fig. 2

Response of the regional upper-level zonal wind to the subseasonal variability of Tibetan Plateau snow cover in observations. Shadings show the composite of the 300-hPa zonal wind with respect to the Tibetan Plateau snow cover index at lag a 1−2 days, b 3−4 days, c 5−6 days, and d 7−8 days. The unit is m s⁻¹. The purple contour marks the regions of the Tibetan Plateau with altitudes higher than 3000 m. Stippled regions mark composites with significance at the 99% level (two-side Student’s t test; see Methods). A lag of n in the left title of each plot indicates that the 300-hPa zonal wind lags the Tibetan Plateau snow cover index by n days. The right title of each plot indicates the East Asia upper-level westerly jet stream index for each plot. The black contours show the climatological mean of the wintertime 300-hPa zonal wind. The contour interval is 10 m s⁻¹. Contours with negative values are not shown. The zero contour is plotted with a bold black line. The magenta dashed rectangle in a shows the subdomain of the East Asia upper-level westerly jet stream core region (28–38°N, 120–160°E). The map of Tibetan Plateau was created by using topographic data from Global Relief Model data of ETOPO1 (doi:10.7289/V5C8276M)

Fig. 3

Response of the regional upper-level zonal wind to the subseasonal variability of Tibetan Plateau snow cover in numerical experiments. Responses of the 300-hPa zonal wind to Tibetan Plateau snow cover at lag a 1−2 days, b 3−4 days, c 5−6 days, and d 7−8 days. The unit is m s⁻¹. The purple contour marks the regions of the Tibetan Plateau with altitudes higher than 3000 m. A lag of n in the title of each plot indicates the days by which the 300-hPa zonal wind lags the initial date of the model. The right title of each plot indicates the East Asia upper-level westerly jet stream index for each plot. The map of Tibetan Plateau was created by using topographic data from Global Relief Model data of ETOPO1 (doi:10.7289/V5C8276M)

Fig. 4

The East Asia upper-level westerly jet stream index and Tibetan Plateau snow cover index from observations and numerical experiments. a The response of the East Asia upper-level westerly jet stream index to the subseasonal variability of Tibetan Plateau snow cover. b The persistence of the Tibetan Plateau snow cover index. The x-axis represents the number of days lagging the start of each event for the composites or the model initial date. The black line and blue line represent the reanalysis/analysis composites and numerical experiments, respectively. The light blue shading represents the range of the East Asia upper-level westerly jet stream index or Tibetan Plateau snow cover index between the 25th and 75th percentile of the numerical experiment ensembles. The unit is m s⁻¹ or %

Fig. 5

Response of the vertical profile of atmospheric temperature and circulation to the subseasonal variability of Tibetan Plateau snow cover in the numerical experiments. a Temperature responses over the Tibetan Plateau at lag = 1–2 day (averaged between 85 and 105°N; units: K). Gray areas indicate the mean terrain elevation. b As a, but for geopotential height (unit: m). c Geopotential height response over the western Pacific Ocean at lag = 5‒6 days (averaged between 120 and 150°N; units: m). d As c, but for zonal wind (shading; unit: m s⁻¹). The black contours in d show the climatological mean of the wintertime zonal wind. Contour interval is 10 m s⁻¹. Contours with negative values are not shown. The zero contour is plotted with a bold black line