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- Hindawi Publishing Corporation
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- Copyright © 2020 Haiwen Liu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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- 10.1155/2020/9031796
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Abstract
Hindawi Advances in Meteorology Volume 2020, Article ID 9031796, 10 pages https://doi.org/10.1155/2020/9031796 Research Article Why the Increasing Trend of Summer Rainfall over North China Has Halted since the Mid-1990s 1 1 1 1 2 Haiwen Liu , Jiarui Miao, Kaijun Wu , Mengxing Du , Yuxiang Zhu , and Shaoyu Hou Department of Aviation Meteorology, Civil Aviation University of China, Tianjin 300300, China CMA Training Center, China Meteorological Administration, Beijing 100081, China College of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu 610225, China Correspondence should be addressed to Kaijun Wu; kjwu@cauc.edu.cn Received 3 October 2019; Revised 12 December 2019; Accepted 21 December 2019; Published 27 January 2020 Academic Editor: Anthony R. Lupo Copyright © 2020 Haiwen Liu et al. +is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Previous studies indicate that the summer (July-August) rainfall over North China has decreased since the mid-1970s due to the weakening of East Asian summer monsoon (EASM). However, this study firstly discovers the new evidences that the summer rainfall over North China had a significant increasing tendency during 1979–1996; since 1997, this increasing tendency has halted while more summer droughts occurred over North China. One important cause for the halted increasing tendency over North China is the interdecadal decrease of the westerly water vapor transport during 1997–2016 in addition to the weakened EASM. +e decrease of the westerly water vapor transport during 1997–2016 was due to the interdecadal warming over Lake Baikal. +e interdecadal warming in the upper troposphere at 200 hPa forced the weakening of the upper-level zonal winds since 1997, which resulted in the anomalous descending flow over the north side of North China and the halted precipitation trend in North China. investigated [10, 12–14], for example, the thermal contrast 1. Introduction between the land and ocean by the large-scale temperature North China, a highly populated region, is located in variations [2, 22], the sea surface temperature (SST) vari- northern China [1]. +e summer (July-August) mean ations in the equatorial central and eastern Pacific [5], the rainfall over North China has exhibited strong interdecadal role of the air-sea interaction in the middle latitudes [23], the variability [2–8]. North China experienced a relatively wet Arctic sea-ice variations in winter [24], the North Atlantic period from the 1950s to 1964 and a dry period since the end Oscillation (NAO) and North Pacific Oscillation (NPO) of 1970s [9, 10] when the droughts have greatly affected local variation [25], the interdecadal change of EASM [12], the agriculture, industry, and even the drinking water [11]. western Pacific subtropical high (WPSH) over the sub- Except the interdecadal shift of summer rainfall over eastern tropical regions of East Asia [4, 26], the interdecadal cooling China in the late 1970s [10, 12–14], another decadal shift in the upper troposphere and lower stratosphere over East over East Asia in the mid-1990s has also been investigated Asia [27], the Pacific decadal oscillation (PDO) [28–30], and [15–19]. For example, Chen et al. [20] found that southern the thermal effect of black carbon aerosols over Asia [31]. China summer rainfall experienced a remarkable increase in Although the consensuses on the interdecadal summer the early 1990s. Wu et al. [21] discovered a pronounced drought over North China have been made in the mentioned interdecadal change in summer rainfall over southern China studies above, along with the development of the updated around 1992/93, with persistent negative anomalies during rainfall data with higher spatial resolutions, how did the 1979–1992 and positive anomalies during 1993–2002. summer rainfall over North China change in the recent Many possible causes of the interdecadal shift of the decades is still of great concern in the climate research eastern China rainfall pattern in the late 1970s are community. It is well known that there are four vapor inflow 2 Advances in Meteorology The North China region corridors, the southwest corridor, the South China Sea, the 50°N southeast corridor, and northwest corridor, from the mid- latitude westerlies to China [32, 33]. In addition to the great importance of the summer monsoon water vapor transport 45°N to North China [34], which boundary is also crucial to the moisture budget over North China associated with inter- decadal variations of the summer rainfall there? To address 40°N these issues, this study will investigate a new interdecadal characteristic of the summer rainfall over North China using the latest precipitation data and analyze the possible causes. +e organization of the paper is as follows. +e datasets 35°N and methodology are described in Section 2. Section 3 presents the interdecadal variability of summer rainfall over North China between the periods of 1979–1996 and 30°N 1997–2016 and further analyzes the interdecadal variations 100°E 105°E 110°E 115°E 120°E 125°E 130°E 135°E of atmospheric circulation, water vapor budget, and surface 0 m 1000 m 2000 m 3000 m 4000 m 5000 m 6000 m air temperature (SAT). A summary is given in Section 4. Figure 1: Locations of the 17 weather stations (blue circles) in ° ° North China and the region of North China (35 N–41 N, 2. Datasets and Methods ° ° 110 E–122 E, blue rectangle). +e shading represents the surface elevation surrounding North China in meters. +e existing criteria of the precipitation in North China [9], the averaged summer (July-August) precipitation of the 17 gauge-based stations chosen from 160 stations in China detect the trend and abrupt point of the time series [40, 41]. from 1951 to 2016, are used to reveal the interdecadal +e statistical significance of the composite analysis and trend variability of summer rainfall over North China. +e 17 analysis is tested using Student’s t-test [42]. meteorological stations are Chengde, Beijing, Tianjin, Shi- +e water vapor transport (M) via each boundary is jiazhuang, Dezhou, Xingtai, Anyang, Yantai, Qingdao, calculated by Weifang, Jinan, Linyi, Heze, Zhengzhou, Changzhi, Taiyuan and Linfen, which are widely used to represent rainfall over M � Q × n dl. (1) North China [9] and mostly located within the domain ° ° ° ° (35 N–41 N, 110 N–122 E) in Figure 1. Q is vertical integral of water vapor flux, while L is To further demonstrate the robustness of the inter- boundary line and dl is the unit boundary length. n is the decadal variability of the summer rainfall over North China, inward-pointing normal vector of the boundaries of the the full data monthly product version 2018 of Global Pre- target region [43]. +e net budget of the regional water vapor cipitation Climatology Centre (GPCC) is also used. +e transport is calculated by each boundary. +e positive re- ° ° GPCC with a spatial resolution of 1.0 ×1.0 is derived from gional water vapor budget indicates the net atmospheric quality-controlled station data from 1979 to 2016 and is water vapor flux from outside and the abundant precipitable widely used in the study of the interdecadal variation of local water within the region. or regional rainfall [35–37]. To investigate the interdecadal variations of the summer rainfall over North China using two types of the precipi- 3. Results tation data, two indexes of summer precipitation over North 3.1. Interdecadal Variability of Summer Rainfall over North China (ISPNC) are defined. One index is the normalized 17- station averaged summer precipitation, referred to as the China. Figure 2(a) shows time series of ISPNC during 1979–2016. Obviously, summer rainfall of North China had ISPNC [9]. +e other one is the normalized regional av- ° ° ° ° eraged summer precipitation in 35 N–41 N, 110 N–122 E an increasing tendency from 1979 to 1996. With the rate of 0.101/year, the tendency during 1979–1996 passed the sig- using GPCC data, defined as ISPNC . GPCC nificance test at the 95% confidence level, suggesting that To investigate the interdecadal variabilities of the atmo- summer rainfall of North China had a significant increasing spheric circulation, the European Centre for Medium-Range tendency during the period. +is interdecadal characteristic Weather Forecasts (ECMWF) Interim Re-Analysis (ERA- ° ° is very different from the previous studies [2–8], which Interim) is used [38]. +e gridded (0.75 × 0.75 ) monthly mainly focused on the interdecadal decrease of the summer ERA-Interim data during 1979–2016 are applied in this study. Variables include horizontal winds in 850 hPa, geopotential rainfall in North China since the mid-1980s [5, 6, 9]. Few studies discover that there was an obviously increasing height in 500 hPa, 2 m surface air temperature (SAT), and vertical integral of water vapor flux. To verify the interdecadal tendency during 1979–1996. Unfortunately, the increasing tendency has halted since 1997. +en North China entered variabilities of the atmospheric circulation, the monthly JRA- 55 data during 1979–2013 are also used [39]. Two re-analysis the drought period, with several persistent droughts ac- companied by severe effects on industry and agriculture over datasets are highly consistent. For brevity, we only show the North China [5, 44]. ERA-Interim results. Mann-Kendall (M-K) method is used to Advances in Meteorology 3 –2 Mean = 0.05 Trend = 0.101/Year (98%) Mean = −0.04 1980 1985 1990 1995 2000 2005 2010 2015 (a) UB UF –5 1980 1985 1990 1995 2000 2005 2010 2015 (b) Figure 2: (a) +e time series of ISPNC during 1979–2016. +e horizontal dashed lines indicate the interdecadal mean, while solid line from 1979 to 1996 indicates the interdecadal trend, and the vertical dashed lines indicate the interdecadal shift points. (b) +e Mann-Kendall test of ISPNC (green dotted line shows backward statistic rank series, and blue dotted line shows forward statistic rank series). Two black lines show 95% confidence level. +e time series of ISPNC in Figure 3(a) also show summer rainfall variation since 1997 has been different from GPCC similar increasing tendency during 1979–1996 with the the so-called pattern of southern flood and northern drought trend rate of 0.094/year, which also reaches the 95% con- since the end of 1970s [26, 27, 46, 47]. fidence level according to Student’s t-test. +is increasing tendency has also halted since 1997. So the gauge-based 3.2. ,e Interdecadal Variability of the Atmospheric station precipitation data and the grid precipitation data of GPCC both show that summer rainfall over North China Circulation. East Asia is dominated by a typical monsoon climate [45, 48]. +e summer precipitation change over had an obvious increasing tendency during 1979–1996 and has halted since 1997. eastern China, affected by the EASM greatly, is very sig- nificant on the interannual and interdecadal timescales [10]. To further investigate the interdecadal shift of the To further study the causes of drier North China, Figure 5(a) summer rainfall over North China, Mann-Kendall test method was used to detect the abrupt point of ISPNC shows the difference of the 850 hPa wind during 1997–2016 in with respect to the period of 1979–1996. As Figure 5(a) Figure 2(b). +ere is a cross point between the backward statistic rank series and forward statistic rank series, sug- shows, North China is dominated by the anomalous northerly wind from Lake Baikal, which suggests that the gesting that summer rainfall over North China experienced a distinct interdecadal change around 1996. Since 1997, there EASM is weaker in 1997–2016 compared with 1979–1996. Weaker summer monsoon favors the less precipitation over have been more droughts occurring in North China. A severe drought attacking North China in 2014 also indicated North China [12, 44]. Meanwhile, an anomalous anticyclonic circulation that North China has become drier in recent years [44]. ° ° Figure 3(b) further verifies the interdecadal shift of the dominates the region of Lake Baikal (40 N–60 N, ° ° 80 E–120 E) significantly. +e anticyclonic circulation sys- summer rainfall over North China using grid precipitation data of GPCC. tem over Lake Baikal is also vital for the variation of summer +e differences of summer rainfall by 1997–2016 mean rainfall over North China [8, 49]. +e anomalous easterly minus 1979–1996 mean over Northeast Asia further verify flow and northerly flow from the anomalous anticyclone are the interdecadal variability of summer rainfall over North closely associated with the water vapor flux anomaly over North China. In Figure 5(b), an anomalous anticyclonic China in Figure 4. Whether using gauge-based station data or using the grid precipitation data of GPCC, the significant center of the water vapor flux is also observed over Lake Baikal. North China is dominated by the anomalous negative summer rainfall differences are both found over North China, which is statistically significant at the 95% northeast water vapor flux. +e difference of water vapor flux over Lake Baikal and North China during two periods is confidence level by Student’s t-test. Meanwhile, the main wetter regions are located in the Huaihe River valley, which significant and reaches the 95% confidence level. Obviously, the anomalous northeast water vapor flux from Lake Baikal suggests that the wetter belt has moved northwards from southern China [45]. Meanwhile, the spatial pattern of is beneficial to the interdecadal drought over North China. –60 –20 –40 –40 –20 –40 –20 –40 –80 –40 –40 –40 –40 –60 –40 –40 –20 –60 –20 –20 –20 –60 4 Advances in Meteorology Mean = 0.16 –2 Trend = 0.094/Year (95%) Mean = –0.15 1980 1985 1990 1995 2000 2005 2010 2015 (a) UB UF –2 –4 1980 1985 1990 1995 2000 2005 2010 2015 (b) Figure 3: (a) Same as Figure 2(a) but for the ISPNC . (b) Same as Figure 2(b) but for the ISPNC . GPCC GPCC 50°N 50°N –40 45°N 45°N 40°N 40°N 35°N 35°N 30°N 30°N 100°E 105°E 110°E 115°E 120°E 125°E 130°E 135°E 100°E 105°E 110°E 115°E 120°E 125°E 130°E 135°E (a) (b) Figure 4: Difference of summer rainfall by 1997–2016 mean minus 1979–1996 mean for (a) 160 stations and (b) GPCC. +e shading indicates statistically significant difference at the 95% confidence level based on Student’s t-test. +e box shows North China. To further investigate which boundary of water vapor difference of water vapor budget over North China is transport is critical for interdecadal drought over North negative (-2.25 ×10 kg/s). Numerous studies focused on the China, the water vapor transports via four boundaries are fact that weaker summer monsoon flow is responsible for calculated. As shown in Figure 6, the anomalous input water less water vapor transport via south boundary and less vapor transports are via east and north boundary, which is summer rainfall in North China [34]. +is study further consistent with the fact that North China is dominated by points that water vapor transport via west boundary is also the northeast flow and northeast water vapor flux in Fig- important for the less summer rainfall in North China. +e ure 5. +e interdecadal differences of the water vapor water vapor transport via the west boundary is crucial for the transport via the east boundary and north boundary are summer rainfall over eastern China [32, 33]. In the JRA-55 6 6 input 9.14 ×10 kg/s and 21.70 ×10 kg/s, and the inter- data, the differences of water vapor transport via four decadal differences of the water vapor transport via the west boundaries of North China have same directions with those boundary and south boundary are output 14.62 ×10 kg/s in ERA-Interim data but there is a weak positive difference and 18.47 ×10 kg/s, respectively. of net water vapor budget, which is not consistent with the Because the sum of output water vapor transport is results in ERA-Interim data. +e weak positive difference of greater than the sum of input water vapor transport, the water vapor budget is against the fact of less rainfall over –20 –20 –60 –40 –60 –40 –40 –40 –20 –20 –20 –60 –20 –20 –60 –20 –80 –20 –20 –40 –20 –100 –20 –20 –40 –40 –20 –80 –20 –60 –60 –20 –40 –20 –20 –20 –40 –40 60 Advances in Meteorology 5 70°N 70°N 60°N 60°N 50°N 50°N Lake Baikal Lake Baikal 40°N 40°N NC NC 30°N 30°N 20°N 20°N 60°E 70°E 80°E 90°E 100°E 110°E 120°E 130°E 140°E 150°E 60°E 70°E 80°E 90°E 100°E 110°E 120°E 130°E 140°E 150°E (a) (b) Figure 5: +e difference by 1997–2016 mean minus 1979–1996 mean for (a) 850 hPa horizontal winds (units: m/s) and (b) vertical integral of water vapor flux (unit: kg/m/s). Shaded areas are statistically significant at the 95% confidence level according to Student’s t-test. +e red box ° ° ° ° shows North China. +e green box shows the region of Lake Baikal (40 N–60 N, 80 E–120 E). +e white region outlines surface pressure lower than 850 hPa. ERA (1997–2016 minus 1979–1996) Unit: kg/s 21.70 × 10 –2.25 × 10 6 6 14.62 × 10 9.14 × 10 18.47 × 10 (35.25N–40.5°N, 110.25E–121.5°E) Figure 6: Difference of water vapor budget via each boundary of North China by 1997–2016 mean minus 1979–1996 mean (unit: kg/s). Dark arrows indicate the direction of horizontal water vapor transport difference across each boundary. Number in box indicates the difference of water vapor budget for North China. North China. +e reason for the weak positive difference of the northwest of North China during 1997–2016, compared water vapor budget over North China in JRA-55 data is with 1979–1996, suggests the interdecadal weakening of the worthy of further study. 200 hPa zonal winds. +e strength of the upper-level zonal +ere are also obvious interdecadal variations in low and winds has great contribution to the precipitation over North middle troposphere. As Figure 7(a) shows, the anomalous China [50, 51]. +e anomalous descending motion over positive geopotential height at 500 hPa is observed over Lake North China in Figure 9 further demonstrates the weakened Baikal. +e anomalous positive geopotential height benefits pumping role of the 200 hPa zonal winds over North China. the anomalous northerly wind in eastern China. +e +e interdecadal weakening of ascending motion and anomalous positive geopotential height at 500 hPa is asso- interdecadal reduction of the water vapor flux over North China result in the interdecadal reduction of precipitation ciated with the interdecadal warming over Lake Baikal. +e interdecadal warming over Lake Baikal happens not only in over North China. the surface in Figure 7(b) but also in 200 hPa in Figure 8(a). +e interdecadal warming in 200 hPa reduces the meridional contrast of air temperature nearby Lake Baikal. +ereby, the 3.3. ,e Possible Mechanism of the Interdecadal Variability of Summer Rainfall over North China. +e interdecadal negative difference of zonal wind exists around 40 N, sug- gesting the weakening 200 hPa zonal winds in the inter- warming of Lake Baikal has a significant impact on the summer rainfall over North China [8, 48, 52], which is also decadal time scales. As Figure 8(b) shows, the northward and westward movement of the 200 hPa zonal winds center over confirmed in Figure 7(b). To discover the abrupt point of the 0.4 –14 0.2 –0.2 0.4 0.2 –0.2 0.4 0.8 0.6 0.6 0.6 –0.6 0.2 0.4 0.2 0. 2 0.8 0.4 –4 −1.5 1.5 – 16 –16 –2 1.6 0.6 0.4 –0.2 0.2 –0.2 0.5 2.5 0.2 0.6 0.8 0.6 0.6 –22 −1 0.4 1.6 0.4 0.5 0.6 –0.4 −2 0.8 0.2 −0.5 0.6 0.8 0.6 1.4 –14 –20 –1 8 −1 –2 0.4 0.2 −1 −1.5 2.5 0 .2 −1 0.6 –0.4 –12 −1.5 –0.2 0.8 1.2 −1.5 0.8 −2 −1.5 1.2 0.6 0.8 1.6 –10 0.5 0.4 0.2 −0.5 1.4 −3 1.6 0.2 0.2 0.5 0.6 0. 4 1.2 –8 1.8 1.5 2.5 −2 6 Advances in Meteorology 70°N 70°N 60°N 60°N Lake Baikal 50°N 50°N Lake Baikal 40°N 40°N NC NC 0.4 30°N 30°N –0.2 20°N 20°N 60°E 70°E 80°E 90°E 100°E 110°E 120°E 130°E 140°E 150°E 60°E 70°E 80°E 90°E 100°E 110°E 120°E 130°E 140°E 150°E (a) (b) Figure 7: Same as Figure 5 but for (a) 500 hPa geopotential height (unit: gpm) and (b) SAT (unit: C). 70°N 70°N 60°N 60°N Lake Baikal Lake Baikal 50°N 50°N 0.5 40°N 40°N −3.5 NC 30°N 30°N 20°N 20°N 60°E 70°E 80°E 90°E 100°E 110°E 120°E 130°E 140°E 150°E 60°E 70°E 80°E 90°E 100°E 110°E 120°E 130°E 140°E 150°E −30 −25 −20 −15 −10 −5 0 5 10 15 20 25 30 −1 −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.8 1 (a) (b) Figure 8: (a) Same as Figure 5 but for 200 hPa zonal winds (contours, unit: m/s) and temperature (shading, unit: C). +e difference of temperature in blue box with black dots is statistically significant at the 95% confidence level according to Student’s t-test. +e difference of zonal winds with black cross is statistically significant at the 95% confidence level according to Student’s t-test. (b) 200 hPa zonal winds (unit: m/s) in JA of 1979–1996 mean (black contours) and 1997–2016 mean (white contours). +e shading is the climatic mean of 200 hPa zonal winds during 1979–2016. +e black box shows North China. +e green box shows the region of Lake Baikal. warming of Lake Baikal, the standardized time series of the since the mid-1990s. +e negative correlation existing be- ° ° averaged summer SAT over Lake Baikal (40 N–60 N, tween the SATover Lake Baikal and the summer rainfall over ° ° 80 E–120 E) is shown in Figure 10(a). +e feature of the North China [49] suggests that the interdecadal warming of interdecadal and interannual variability of SAT over Lake Lake Baikal contributes to the interdecadal less summer Baikal is apparent. Mann-Kendall test method is used to rainfall over North China. +e interdecadal warming of Lake investigate accurate abrupt point of the SATover Lake Baikal Baikal is observed not only in the lower troposphere in in Figure 10(b). +e abrupt year of the SAT over Lake Baikal Figure 7(b) but also in the upper troposphere in Figure 8(a). +e interdecadal warming of Lake Baikal results in not only is close to the abrupt year of the summer rainfall over North China. the anomalous anticyclonic circulation and anomalous +e SAT over Lake Baikal and the summer rainfall over positive geopotential height over Lake Baikal in the lower and North China have experienced the interdecadal changes middle troposphere but also the weakening of the zonal wind 1.2 0.8 −1 0.4 −1.5 –6 −1 0.8 0.5 1.5 3.5 −2.5 −1.5 −0.5 –0.4 −1.5 −4 1.5 −2 0.5 −0.5 1.4 1.8 −3 −1 −1 1.5 −0.5 1.5 −0.5 0.5 0.8 −0.5 −5 −2.5 0.5 –4 –2 0.4 −3.5 −2.5 −2 −0.5 0.5 1.5 −0.5 0.4 0.6 0.8 −0.5 −4.5 −3 −2.5 −1 0.5 −3 −0.5 0.4 0.6 1.8 −1 −1.5 –0.2 2.2 2.5 0 0.6 −2.5 0.6 0.8 0.6 0.5 0.2 0.2 −2 −1.5 0.6 −0.5 −1 0.2 –6 0.8 0.2 0.4 0.6 0.4 0.4 1.2 –8 0.6 0.2 0.4 0.8 –10 1.6 0.2 0.5 1.4 −1.5 0.2 −2 0.4 0.2 0.6 −0.5 0.2 0.6 –12 0.6 0.8 −1 0.6 −1 0.6 0.4 –2 1.2 −1.5 0.2 –1 8 0.4 0.4 0.2 0.4 0.8 –4 0.4 0.6 1.5 0.2 0.8 0.8 0.4 0.8 0.2 0.8 0.2 1 1.5 −1 0.5 0.5 −0.5 −1 −0.5 3.5 −1 0.5 Advances in Meteorology 7 20°N 30°N 40°N 50°N 60°N Figure 9: Latitude-height cross section of difference of vertical velocity along 116.25 E in JA by 1997–2016 mean minus 1979–1996 mean (unit: − 2 10 Pa/s). Shaded areas are statistically significant at the 95% confidence level according to Student’s t-test. +e red line shows North China. Trend = 0.069/year (96%) –1 –2 Mean = –0.74 Mean = 0.6 1980 1985 1990 1995 2000 2005 2010 2015 (a) UB UF –2 1980 1985 1990 1995 2000 2005 2010 2015 (b) Figure 10: (a) Same as Figure 2(a) but for the summer SAT over Lake Baikal. (b) Same as Figure 2(b) but for the summer SAT over Lake Baikal. in the upper troposphere. Obviously, the anomalous anti- variations of the summer rainfall over North China since the cyclonic circulation over Lake Baikal is beneficial to less water mid-1990s are firstly discovered in this paper. +e possible vapor transport from the monsoon flow and the westerlies. causes such as the interdecadal variations of the atmospheric Meanwhile, the weakening of the zonal wind in the upper circulation and the water vapor budget are discussed. +e major troposphere favors the weakening of the ascending motion mechanisms are shown in Figure 11 and summarized as follows. and further results in the weakening of the pumping effects of Summer rainfall over North China had an increasing the zonal winds in the upper troposphere. +e interdecadal tendency during 1979–1996; since 1997, this increasing weakening of the ascending motion and interdecadal re- tendency has halted, and more summer droughts occurred duction of the water vapor transport to North China directly over North China. lead to the interdecadal drought over North China. +e SAT over Lake Baikal and the summer rainfall over North China have had interdecadal abrupt since the mid- 1990s. +e interdecadal warming of Lake Baikal is beneficial 4. Summary and Discussion to the interdecadal less summer rainfall over North China. +e intense interdecadal warming of Lake Baikal results Using the 17-station rainfall and the new GPCC full data in not only the anomalous anticyclonic circulation and monthly product precipitation data sets, the interdecadal −0.5 1.5 −0.5 −1 −0.5 2.5 −1 0.5 −1.5 −1 −0.5 −0.5 0.5 −0.5 −1.5 1. 5 −1.5 − 1. 5 0.5 0.5 −1 0.5 1.5 −2 60°N 50°N 40°N 30°N 20°N 60°N 60° E 50°N 40°N 30°N 20°N 60°E 70°E 70°E Weakened Upper-level jet stream 80°E 80°E 90°E 90°E 100°E 100°E 8 Advances in Meteorology 1997–2016 minus 1979–1996 200 hPa Anomalous descending flows 850 hPa Lake Baikal Anomalous anticyclone Drier North China Figure 11: Schematic diagram of mechanism for the halt of the increasing trend of summer rainfall over North China since the mid-1990s. anomalous positive geopotential height over Lake Baikal in Conflicts of Interest the lower and middle troposphere, but also the weakening of +e authors declare that they have no conflicts of interest. the zonal wind in the upper troposphere. +e anomalous anticyclonic circulation in the lower troposphere over Lake Acknowledgments Baikal results in less water vapor transport from the mon- soon flow and the westerly flow. +e weakening of the zonal +is work is supported by the Strategic Priority Research wind in the upper troposphere favors the weakening of the Program of Chinese Academy of Sciences (XDA20100304), ascending motion and the pumping effects of the zonal the State Key Program of the National Natural Science winds in the upper troposphere. +e interdecadal weakening Foundation of China (41475051, 41875111), the Starting of the ascending motion and the less interdecadal water Foundation of the Civil Aviation University of China vapor transport result in the interdecadal drought in North (2016QD05X), and the Research Foundation of the Civil China. 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Advances in Meteorology – Hindawi Publishing Corporation
Published: Jan 27, 2020