Table 1.
Classification of Palmer Drought Severity Index (PDSI).
Figure 1.
Time series of autumn (September–November) Palmer Drought Severity Index (PDSI) averaged for 61 weather observation stations in Korea (bar graph) and the result (t-value) of statistical change-point analysis (solid line).
Figure 2.
Differences in (a) precipitable water, (b) precipitation, and (c) PDSI between 1998–2013 and 1974–1997. Units are kg m−2 for precipitable water and ms−1 for precipitation.
Figure 3.
Same as in Fig. 2, but for (a) 850 hPa, (b) 500 hPa, and (c) 200 hPa stream flows. Shaded areas are significant at the 95% confidence level.
Figure 4.
(a) spatial distribution of correlation coefficient between autumn PDSI in Korea and geopotential height at 850 hPa, (b) time series of autumn PDSI in Korea (solid line) and geopotential height averaged over 50°S–30°S and 50°–100°E in (a) (dotted line), and (c) the result of statistical change-point analysis on geopotential height averaged over 50°S–30°S and 50°–100°E.
Figure 5.
Same as in Fig. 2, but for air temperature. Shaded areas are significant at the 95% confidence level.
Figure 6.
Same as in Fig. 2, but for specific humidity.
Figure 7.
Spatial distribution of western North Pacific subtropical high (WNPSH) in 1998–2013 (solid line) and 1974–1997 (dashed line). Here, the WNPSH is defined as areas that geopotential height at 500 hPa is >5870 gpm.
Figure 8.
Composite differences of latitude–pressure cross section of (a) vertical velocity (contours) and meridional circulations (vectors), (b) air temperature, and (c) specific humidity averaged along 125°–135°E between 1998–2013 and 1974–1997 for September–November. The values of vertical velocity are multiplied by −100. Bold arrows and shaded areas are significant at the 90% confidence level. Contour intervals are 0.7−2 hPa s−1 for vertical velocity, 0.2 °C for air temperature, and 0.2 g kg−1 for specific humidity, respectively.
Figure 9.
Spatial distributions of (a) jet streak in 1998–2013 (solid line) and 1974–1997 (dashed line) and (b) difference in 200 hPa zonal wind between 1998–2013 and 1974–1997 for September–November. Contour interval in (b) is 1 ms−1. Shaded areas in (b) are significant at the 95% confidence level.
Figure 10.
Same as in Fig. 2, but for sea surface temperature.
Figure 11.
Same as in Fig. 2, but for (a) water equivalent of accumulated snow depth (WEASD) and (b) ground heat net flux (GFLUX). Units are kg m−2 in (a) and W m−2 in (b).
Figure 12.
(a) Differences in the mean TC passage frequencies (TCPF) between 1998–2013 and 1974–1997 for September–November within each 5°×5° latitude-longitude grid box. Small solid rectangles indicate that the differences are significant at the 95% confidence level and (b) time series of TCPF (dot with closed circle) around Korea (25°–40°N and 120°–135°E) (dashed line in (a)) and its result on statistical change-point analysis (dotted line).
Figure 13.
Same as in Fig. 2, but for (a) 850 hPa velocity potential and divergent wind) and (b) 200 hPa velocity potential and divergent wind. Shaded areas denote negative anomalies. Contour interval is 2 m2s−110−6.
Figure 14.
Time series of autumn (September–November) Palmer Drought Severity Index (PDSI) in Korea (thick solid line), model (thick dashed line), and the result (t-value) of statistical change-point analysis on model (thick grey line).
Figure 15.
Schematic illustration of anomalous atmospheric circulation patterns related to the weakening of autumn drought in Korea since 1998.