The Change of Seasonal Trend Appeared in Wintertime Daily Mean Temperature of Seoul, Korea Byong Ik Park* 1941 1970 1971 2000 1 1 2 12 27 1 20 1 21 2 9 1970 1971 Abstract This study aims to investigate the change of seasonal trend appeared in the daily normals of wintertime daily mean temperature of Seoul for 1941~1970 and 1971~2000 and the factors to affect it. The lowest temperature in wintertime is appeared in the period of the first and second ten-days of January in the daily normals for 1941~1970 and in the third ten-days of January and the first ten-days of February for 1971~2000. This means seasonal trend was changed. This change is due to the fact average temperature from 27 December to 20 January is rising much more than the wintertime mean temperature and average temperature from 21 January to 9 February less than that for two daily normals. This features are notable after 1971. The Siberian high and norther wind around the Korean Peninsula are weakened remarkably recently, so mean temperature of Seoul from 27 December to 20 January is warming much more. On the other hand, the Siberian high from 21 January to 9 February is weakened and the Aleutian low is strengthened recently and northerly is not change obviously, so temperature of Seoul is not warming so much. : seasonal trend, change of seasonal trend, Siberian high, Aleutian low (Assistant Professor, Department of Geography Education, Seoul National University), fbipark@snu.ac.kr 152
100 0 74 IPCC 2007 1999 40 50 12 0 23 10 (Jung et al., 2002) 0 07 10 3 12 (Rho, 1973; Lee, 1978; Cho et al., 1988; Ryoo et al., 1993; Ha et al., 2004; Seo et al., 2010) (Lee and Kang, 1997; Kim et al., 1999; Kim et al., 2000; Choi et al., 2003; Choi et al., 2003) (Jung et al., 2002; Ryoo et al., 2004; Choi et al., 2008) (Jung et al., 2002; Choi et al., 2008) 1 (seasonal cycle) (annual cycle) 1940 (Thomson, 1995) 1954 2007 (Stine et al., 2009) (Thomson, 1995) (Stine et al., 2009) (Stine et al., 2009) (Choi et al., 2006; Kwon et al., 2007 1955 2003 10 2 98 1 85 1 13 (Qian et al., 2011) 1941 1970 30 Lee 1979 1 (Lee, 1979) 1941 1970 1 (Lee, 1979) 1973 2004 (Choi et al., 2006) 1 1941 1970 1971 2000 153
1941 1 1 2010 12 31 9 (SLP) 925hPa NCEP/NCAR (reanalysis data) 2 1948 2010 2 5 30 1941 1970 1971 2000 8 1 7 31 365 (harmonic analysis) (harmonic wave) (Lee, 1969; Wilks, 2006) n/2 2 kt y t y C k cos n k k=1 n/2 2 kt 2 kt y A k cos B k sin n n k=1 n t 1 2 n y t t y C k k k k A k, B k C k A 2 k B 2 k 1/2 k B k A k tan 1, A k >0 B k A k tan 1, A k <0, A 2 k 0 1 k n/k 365 1 1 2 3 120 (Lee, 1969; Murakami and Matsumoto, 1994; Wang and LinHo, 2002) Lee(1979) 3 Choi et al.(2006) 7 Wang and LinHo(2002) (mm/day) 1 12 1 36 3) 11 1 3 31 1941 1970 1971 2000 (Figure 1) 154
1941 2010 1941 1970 4 5 925hPa (v925) 6) SLP v925 1941 1970 1971 2010 2 SLP 925hPa Figure 1 1941 1970 1971 2000 1 36 1 1 2 Figure 1. Daily normals of daily mean temperature of Seoul for 1941~1970 (thin solid line), 1971~2000 (thick solid line) and synthesized waves of 1~36 harmonics for each daily normal. Thin and thick dashed lines are synthesized waves for normals of 1941~1970 and 1971~2000 respectively. In this paper the synthesized waves are regarded as the seasonal trend. The harmonic waves are computed for 1 years from 1 Aug. to 31 Jul. 155
Table 1. Average wintertime (1 Nov.~31 Mar.) warming of daily normals for 1971~2000 with comparison to those for 1941~1970 and major periods with more/less warming than average for 10 stations of Korea. Station Average warming( C) Period with more warming than average Period with less warming than average Gangneung Seoul Incheon Ulleungdo Daegu Jeonju Gwangju Busan Mokpo Jeju 0 77 1 25 0 80 0 54 1 20 0 44 0 72 0 71 0 37 0 56 12 25 1 18 12 27 1 20 12 26 1 20 12 25 1 20 12 28 1 20 12 28 1 23 12 29 1 22 12 26 1 19 12 28 1 23 12 27 1 22 1 19 2 9 1 21 2 9 1 21 2 3 1 21 2 10 1 21 2 2 1 24 2 3 1 23 2 10 1 20 2 3 1 24 2 9 1 23 2 10 Figure 2. Temperature differences between two daily normals (solid line) and synthesized harmonics (dashed line) for 1941~1970 and 1971~2000. Linear solid line denote average of temperature differences of synthesized harmonics for the period from 1 Nov. to 31 Mar. and two linear dashed lines show average 1 standard deviation. Figure 2 Figure 2 11 1 3 31 1 25 (SD) Figure 2 12 27 1 20 156
11 1 21 2 9 1 1 2 12 27 1 20 (Pre-period) 1 21 2 9 (Post-period) Table 1 10 1 36 12 27 1 20 1 20 2 10 10 1941 1970 1940 12 2010 2 Figure 3 Figure 3 5 Figure 4 Figure 3 5 5 0 Figure 4 1970 0 1 25 1970 Figure 3. Changes of average departure of pre-period (12/27~1/20, Pre_AV) and post-period (1/21~2/9, Post_AV) from the daily normals of 1941~1970 for Seoul. The pre-period and post-period of Seoul are referred to Table 1. Closed circles and squares are Pre_AV and Post_AV respectively. Thin solid line and dashed line are moving averages with 5 term of Pre_AV (Pre_MA5) and Post_AV (Post_MA5) respectively. Thin and thick linear lines are simple regression line of Pre_AV and Post_AV respectively. 157
Figure 4. Change of difference of Pre_MA5 and Post_MA5. Closed circle is difference of Pre_MA5 and Post MA5, solid line is moving average with 5 term of the difference, lines with closed square mark are averages of the difference for 1941~1970 (low average) and 1971~2010 (large average). Abbreviations are referred to Figure 3. 14 12 1 2 28 (Ryoo et al., 2004) 1985 1986 1986 1987 11 1 3 31 1989 (Kang, 1988; Ryoo et al., 2002 925hPa Figure 5 1949 2010 0 6 0 4 (Zhang et al., 1997; Kim et al., 2005) 158
Figure 5 90 110 E 52 5 60 N Figure 6 0 039 0 831 0 05 Figure 6 12 2 Figure 5. Distributions of the correlation coefficients between the time series of Pre_AV (upper panel) and Post_AV (lower panel) and the corresponding period average of sea level pressure (SLP) for 1949~2010. Negative values are denoted by dotted lines. The subarea in the upper panel is indicated by thick solid line to compute areal average SLP (see Figure 6). 159
(Kim et al., 2005) 12 1 2 0 0331 0 0473 0 0641 0 066 2 10 0 7hPa 0 0075 Kim et al.(2005) 2 Kim et al.(2005) 1 2 20 Figure 7 925hPa (v925) (Kang, 1988; Ryoo et al., 2002 Figure 6. Time series of the areal averages of pre-period (solid line, Pre_SLP) and post-period (dashed line, Post_SLP) mean SLP and simple regression lines for Pre_SLP (thick dashed line) and Post_SLP (thin dashed line). The target area is denoted in Figure 5 and lower and upper regression line equations are computed for pre_slp and Post_SLP respectively. The regression of Pre_SLP is significant at the 0.05 level. 160
Figure 8 120 130 E 30 40 N v925 0 008 0 247 v925 0 01 0 0197 10 0 2ms 1 10 0 1ms 1 Figure 7. Same as Figure 5, except for v925 (north-south wind speed at 925hPa surface). 161
1970 (Figure 4) 1949 1970 1971 2010 925hPa 1970 Figure 9 (Figure 9a, c) 1970 (Figure 9b, d) 1970 1971 (Kang, 1988; Ryoo et al., 2002 Figure 10 1970 925hPa (Figure 10a) 1970 Figure 8. Same as Figure 6, except for v925. The target area is indicated in Figure 7. The regression of Pre_V925 is significant at the 0.01 level. 162
(Figure 10b) 1970 (Figure 10a, b) 4hPa 7hPa Figure 9. (a) Long term mean (LTM) SLP and 925hPa wind vector of pre-period for 1949~1970, (b) difference between pre-period LTM and post-period LTM of SLP and wind vector for 1949~1970, (c), (d) same as (a), (b) except for 1971~2000 respectively. Thick solid line denotes the Tibet Plateau. 163
Figure 10. Difference between LTMs of SLP and wind vector over 1971~2000 and 1949~1970 for pre-period (a) and post-period (b). Thick solid line denotes the Tibet Plateau. 925hPa 1941 1970 1971 2000 1 36 925hPa 1 1 2 12 27 1 20 11 1 3 31 1 21 2 9 9 1941 2010 1941 1970 1941 1970 0 1971 1 25 1970 164
925hPa (v925) v925 v925 1970 925hPa 1970 1971 1970 1971 1941 1970 1971 2000 1 1 2 1) Lee(1979) 0 5 2) (reanalysis data) NOAA Earth System Research Laboratory Physical Sciences Division(PSD) http://www.esrl.noaa.gov/psd/ (download) (Thanks for data) 3) Lee(1979) 1 12 12 30 7 (Kim and Roh, 2010) (Kim and Roh, 2010 Fig. 11; Lee, 1971, 1985) 10 12 10 36 4) 30 1981 2010 1941 2010 1941 1970 5) 1 1 2009 11 2010 3 165
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