Title: Correlation of surface sensible heat flux in the arid region of northwestern China with the northern boundary of the East Asian summer monsoon and Chinese summer precipitation
Abstract: Journal of Geophysical Research: AtmospheresVolume 116, Issue D19 Climate and DynamicsFree Access Correlation of surface sensible heat flux in the arid region of northwestern China with the northern boundary of the East Asian summer monsoon and Chinese summer precipitation Hui Wang, Hui Wang [email protected] Key Laboratory of Meteorological Disaster of Ministry of Education, Nanjing University of Information Science and Technology, Nanjing, ChinaSearch for more papers by this authorDongliang Li, Dongliang Li Key Laboratory of Meteorological Disaster of Ministry of Education, Nanjing University of Information Science and Technology, Nanjing, ChinaSearch for more papers by this author Hui Wang, Hui Wang [email protected] Key Laboratory of Meteorological Disaster of Ministry of Education, Nanjing University of Information Science and Technology, Nanjing, ChinaSearch for more papers by this authorDongliang Li, Dongliang Li Key Laboratory of Meteorological Disaster of Ministry of Education, Nanjing University of Information Science and Technology, Nanjing, ChinaSearch for more papers by this author First published: 13 October 2011 https://doi.org/10.1029/2011JD015696Citations: 7AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract [1] Northwestern (NW) China is the typical arid region of central Asia, and its surface sensible heat (SSH) anomaly significantly affects the Chinese climate and the atmospheric circulation of East Asia. In this study, we investigated the relationship between the SSH flux in the NW arid region of China and the northern boundary of the East Asian summer monsoon (EASM) and Chinese summer rainfall using a climatic diagnosis analysis method. Then the causes of formation were analyzed from the changes of the transfer of water vapor, geopotential height field, and the upper- and lower-level atmospheric circulation fields, and so on. It is found that during years of unusually weak (strong) SSH flux, the northern boundary of the EASM shifts northward (southward) than in normal years. There is an interplay between the SSH in the NW arid region of China and the precipitation in the northern boundary zone of the EASM: In the early stage of the monsoon, the SSH inhibits the latter precipitation, and during the peak of the monsoon, the precipitation suppresses the SSH. The teleconnection wave train structure of the geopotential height field at 500 hPa and the upper- lower-level atmospheric circulation fields above the Eurasian continent exhibit profound changes when summer SSH fluxes are unusually weak and strong. These changes are accompanied by significant alterations to the vertical velocity field and the water vapor field above northern China. The combination of these changes thereby contributes to the unusually southward shift of the northern boundary of the EASM. Key Points Negative correlation between SSH of NW China and northern boundary of EA monsoon There is interplay between SSH of NW China and EA summer monsoon precipitation 1. Introduction [2] China is located in the East Asian (EA) monsoon region. The beginning of the rainy season in eastern China corresponds to the onset of the summer monsoon; the summer monsoon precipitation develops northward and reaches its northernmost boundary (the Hetao, Northern China, and northeastern (NE) China) after mid-July. Subsequently, the rain belt retreats southward along with the monsoon. The evolution and progression of the summer monsoon have a profound influence on some crucial weather and climate phenomena, including regional precipitation, drought, flood, and northern sandstorms in China. Since the EA summer monsoon (EASM) shows annual fluctuations and exhibits an unstable northern boundary, a monsoon boundary zone with high annual variability in precipitation ranges from the upper Yellow River to northern China [Xu and Qian, 2003]. Previous studies of the influence of the EASM on Chinese climate have primarily focused on the major precipitation regions, including southern China and the Yangtze–Huaihe River basin [Guo, 1983; Shi et al., 1996; Huang and Yan, 1999; Huang et al., 1999a], but ignored rainfall in the northern monsoon boundary region. There are two major climatic systems that influence the northern boundary zone of the EASM: the northern arid climatic system and the southern monsoon climatic system. This boundary zone has an annual precipitation of 200–450 mm [Shi, 1996], so the impact of the change in precipitation on vegetation is more significant, and the presence (absence) of summer monsoon rainfall will bring wet (dry) climate conditions in this region. This monsoon boundary zone is not only semiarid but also a climatically sensitive and ecologically vulnerable zone [Ou and Qian, 2006]. In addition, this area is prone to natural disasters [Shi et al., 1994; Huang and Zhou, 2002]. Hence, it is scientifically and practically important to study the boundary zone of the EASM. [3] The monsoon is an atmospheric consequence of seasonal variation in land-sea thermal differences, and, as such, it is strongly influenced by the thermal situation on land. Many studies have indicated that thermal abnormalities in the Qinghai-Tibet Plateau have a significant impact on the formation and evolution of the Asian summer monsoon [Nitta, 1983; Luo and Yanai, 1984; Huang, 1984, 1985; Yanai et al., 1992; Molnar et al., 1993; Wu and Zhang, 1998] and lead to aberrant atmospheric circulation in the Northern Hemisphere as well as irregular climatic patterns in China [Zhao and Chen, 2001a, 2001b; Li et al., 2001; Liu et al., 2002; Duan et al., 2003; Zhao et al., 2003; Ning and Qian, 2006; Zhao and Qian, 2007, 2009; Tang and Yu, 2008]. Northwestern (NW) China is the typical arid zone of central Asia and is characterized in the summer by extremely strong surface sensible heat (SSH); the strength of SSH even surpasses that of some plateau areas. The studies by Huang et al. [2006] and Zhou and Huang [2008] have indicated that an annual variation in the SSH on Chinese NW arid and semiarid areas during the spring and summer is one of the major factors contributing to annual fluctuations in climatic hazards, including drought and flood. Gao et al. [2008] used numerical experiments to reveal that unusual SSH in the NW arid regions significantly affects summer rainfall in China. Unfortunately, not much work on the SSH flux in vast arid areas in China and its influences have been carried out. We analyze the relations between and the causes of the aberrant SSH on arid regions of NW China and the northern boundary of the EASM and summer precipitation in China. We wish to provide a theoretical basis for drought and flood predictions during the flood season and the environmental protection in the farming-grazing transitional belt in China. 2. Examination of the Influence of SSH Flux on NW Arid Regions [4] The monthly surface thermal transfer coefficients of 84 meteorological stations in the arid region of NW China are calculated with the aid of the normalized difference vegetation index (NDVI) data from 1982 to 2006 observed by National Oceanic and Atmospheric Administration (NOAA) remote sensing satellites and Ch − INDV parametric relational expressions rather than taking Ch as fixed value [Wang and Li, 2010]; then the monthly SSH fluxes are calculated using the bulk transfer method with the observations from the meteorological stations [Wang and Li, 2011]. Monthly precipitation data were collected from 743 weather stations in China. Rain belt classification data were obtained from the National Climate Center of China. The data concerning the northern boundary of the EASM were provided by Huang et al. [2009]. 2.1. Relation to the Northern Boundary of the EASM [5] Important achievements have been made in studies of the definition of northern boundary of the EASM and the variations in its position [Tang et al., 2006, 2009; Jiang et al., 2006; Hu and Qian, 2007; Huang et al., 2009]. However, differences in data collection methods and representations have led to large discrepancies in the proposed northern boundary of the summer monsoon. Using the standard of soaking rainfall (i.e., total precipitation of 20 mm during a continuous rainfall) by Huang et al. [2009], this paper defines the northern boundary zone of the summer monsoon and the northern limit of the boundary zone as the locations where there are six times the amount of soaking rainfall and three times the amount of soaking rainfall, respectively, from April to October in the span of one year. The CresDan function was used to interpolate data from over 700 sites nationwide onto a 0.1° × 0.1° horizontal grid. The northern boundaries were the latitude value that is closest to the northern boundary zone along 110°E in a given year. Therefore the northern boundary of East Asian summer monsoon has one latitude value in every year. Using the soaking rainfall as the criterion to demarcate the monsoon zone, the impact of the summer monsoon on plants, particularly crops, has underscored the monsoon boundary zone of China. [6] The studies by Wang and Li [2011] have indicated that considering 97.5°E as the boundary in the NW arid region of China, the SSHs in its eastern and western parts have different interannual variation trends in the four seasons. So this paper discusses the two distinct parts respectively. Correlation coefficients between the northern boundary of the EASM and the SSH flux in the eastern and western parts of the NW arid region in China, as well as the entire NW arid region, during various intervals between May and September are listed in Table 1. Table 1 demonstrates that the northern monsoon boundary has a strong and consistent negative correlation with the SSH in the eastern part of the NW arid region over these intervals. Specifically, the average coefficients from May to July, from May to August, and from May to September are all less than −0.70. Those average values in summer (June, July, and August (JJA)) and from May to June are around −0.65, and the coefficients in May and June are both close to −0.60. All of these values are valid at the 1% confidence level. As for the total NW arid region, only the coefficients in May and the average value from May to June exceed the 5% confidence level, whereas the rest of the periods display poor correlation. Although SSH transfer in the western part of the region is stronger than SSH transfer in the eastern part, it exhibits a weak correlation with the northern boundary of EASM. Together, the data indicate that the south-north migration of the northern boundary of the EASM is markedly influenced by SSH transfer in the eastern part of the NW arid region but not by that in the western part. Table 1. Correlation Coefficients Between the Northern Boundary of the EASM and the SSH for Different Time Intervals Average in the NW Arid Region NW Arid Region May–June May–July May–Aug. June-Aug. May–Sept. May June July Aug. Sep. Eastern −0.665a −0.724a −0.741a −0.627a −0.749a −0.598a −0.599a −0.294 −0.349 −0.271 Western −0.088 −0.071 −0.051 −0.048 −0.031 −0.055 −0.102 −0.031 0.020 0.089 Total −0.441b −0.196 −0.084 0.057 −0.036 −0.500b −0.365 0.319 0.303 0.253 a 0.01 confidence by t test, α0.01 = 0.505. b 0.05 confidence by t test, α0.05 = 0.396. [7] Figure 1 clearly illustrates that when the summer average SSH flux in the eastern part of the NW arid region is strong, the northern boundary of the EASM shifts southward, and vice versa. Data from other time intervals also display a similar pattern (figures not shown). Rainfall is one of the significant characteristics of the monsoon; as such, precipitation can be used to characterize the monsoon. Tang et al. [2006] indicated that a 100 mm isohyet in summer, similar to the monsoon in its annual migration (northward or southward), can be used to approximate the northernmost boundary of the summer monsoon. On the other hand, Shi [1996] defined the monsoon boundary zone of China as the areas in which there is annual precipitation of 200–450 mm (or 500 mm). Our analysis of monthly precipitation data from 743 sites nationwide showed that the May-September precipitation on average accounts for 75.1% of the annual precipitation nationwide and over 80% of the annual precipitation in northern China. Hence, we use the 200–400 mm isohyet from May to September to approximate the northern boundary of the summer monsoon in this paper; specifically, according to the standard that the average SSH abnormal flux from May to September in the eastern part of the NW arid region was over 2 W/m2 (one standard deviation) higher (lower) than during regular years; five years (1982, 1991, 1997, 2005 and 2006) with unusually strong SSH as well as five years (1985, 1988, 1992, 1994 and 2002) with unusually weak SSH were integrated and analyzed. The threshold 2 W/m2 was chosen because one standard deviation is an objective value for climatic anomaly analysis [Nagura and Konda, 2007]. Figure 1Open in figure viewerPowerPoint Evolution of the northern boundary of the EA summer monsoon (solid line) and the summer (JJA) average SSH in the eastern part of the NW arid region (dotted line) from 1982 to 2006. [8] Figure 2 shows the changes of the northern boundary zones and their locations of the EASM in different SSH transport conditions of the eastern part of the NW arid region. Figure 2a illustrates the average May-September precipitation distribution from 1982 to 2006 in China, the precipitation distribution when the SSH of the eastern part of the NW arid region was unusually strong (Figure 2b), and the precipitation distribution when the SSH was unusually weak (Figure 2c). By comparing Figures 2b and 2a, it can be seen that when there is strong SSH in the eastern part of the NW arid region, the 100 mm and 200 mm isohyets apparently migrate southward, the 400 mm isohyet shifts slightly southward, and the northern boundary zone of the summer monsoon slightly widens. Further, Figures 2c and 2a reveal that when there is weak SSH in this area, the 100 mm, 200 mm, and 400 mm isohyets all clearly shift northward, and the northern boundary zone of the summer monsoon narrows. Figure 2d clearly exhibits that when the summer average SSH flux in the eastern part of the NW arid region is unusually strong (weak), the northern boundary location of the EASM moves southerly (northerly). During years of aberrant SSH, the Hetao region and northern China display the most significant migrations of the northern boundary zone of the summer monsoon (Figure 2). These observations indicate that strong (weak) SSH results correspond to southward (northward) shift of isohyets that indicates the northern boundary zone of the summer monsoon in China. Table 2 lists the rain belt types and the anomalies when the average SSH from May to September in the eastern part of the NW arid region is unusually strong and unusually weak. These data appear to reveal a pattern that unusually strong SSH leads to a type II or III rain belts (i.e., rainfall concentrated in the Yangtze River basin or southern China) and that very weak SSH leads to a type I rain belt (i.e., rainfall concentrated in northern China). Nevertheless, a type III rain belt also appears in some years of weak SSH, which may stem from the northwestward shift of the subtropical high. This shift causes a double rain belt in both northern and southern China, which is consistent with the analysis of the rain belt type in China when the northern boundary of the summer monsoon shifts northward or southward [Huang et al., 2009]. Figure 2Open in figure viewerPowerPoint Changes of the northern boundary zones and their locations of the EASM. (a) Total precipitation from May to September of 1982–2006, average, (b) integrated data for years of unusually strong SSH, (c) integrated data for years of unusually weak SSH, (d) locations of the northern boundary of the EASM (dotted line is 100 mm summer isohyet of 1982–2006, average, and the continuous thin line (heavy solid line) is for years of unusually strong (weak) SSH). Table 2. Rain Belt Types and SSH Anomalies for Years of Unusually Strong (Weak) May–September SSH Years of Strong H H Anomaly Rain Belt Type Years of Weak H H Anomaly Rain Belt Type 1982 4.6 2 2002 −3.5 3 2005 3.8 2 1988 −2.9 1 1997 3.5 3 1992 −2.5 1 2006 2.9 3 1985 −2.4 1 1991 2.3 2 1994 −2.2 1 2000 2.0 2 1998 −2.1 3 2.2. Correlation Analysis of Summer Precipitation in China [9] Summer precipitation in China exhibits an apparent annual variation. There was a significant climate shift in 1976, and since 1977 there has been a drastic reduction of summer rainfall and continuous drought in northern China coupled with increased rainfall and frequent flooding in the Yangtz-Huaihe River basin [Huang et al., 1999b; Zhou and Huang, 2003]. Furthermore, these studies indicated that such a climatic evolution was heavily influenced by aberrant SSH in the arid regions of China. As discussed above, during the years of aberrant strong (weak) SSH, the northern boundary zone of the EASM usually shifts southward (northward), resulting in more frequent precipitation in the south (north). Hence, the correlation between the summer sensible heat flux and summer precipitation fields at over 700 sites is examined (Figure 3). As shown in Figure 3, the total summer precipitation and SSH variation exhibit negative correlations in the Hetao region (the Hetao region is located in the area that looks like "Л" in shape and its neighboring basin of the Yellow River), northern China, NE China, and the area south of the Yangtze, yet the two are positively correlated in the Yangtze-Huaihe River basin and in the plateau regions, which can be generalized into a "plus-minus-plus (− + −)" pattern from south to north. The correlation coefficients between the total summer precipitation and SSH in the entire Hetao region are valid at the 5% confidence level and at the 1% level in most areas there. Figure 3Open in figure viewerPowerPoint Correlation between summer SSH in the eastern part of the NW arid region and summer precipitation in China (shaded areas are statistically significant at the 0.05 confidence level; solid lines indicate positive correlations while dotted lines indicate negative correlations). [10] Table 3 presents the correlations between the May-September SSH (H5–H9) in the eastern part of the NW arid region and the May-September rainfall in the Hetao region and northern China (R5–R9). The rainfall data from May to September of 20 sites (Jingtai, Jingyuan, Yuzhong, Lintao, Narenbaolige, Darhanlianheqi, Hohhot, Otogqi, Dongsheng, Alashanzuoqi, Yinchuan, Zhongning, Yanchi, Wuqi, Hengshan, Haiyuan, Tongxin, Guyuan, Huanxian, and Lanzhou) that exhibit a high correlation (1% confidence level) with the SSH during the same period were selected in the Hetao region and in northern China between 1982 and 2006. Monthly average data were generated from the precipitation data before further analysis. As shown in Table 3, the SSH in the eastern part of the NW arid region exhibits the strongest negative correlation (all values are valid at the 1% confidence level) with precipitation in the Hetao region and in northern China during the corresponding period. The correlation coefficient is highest in June (−0.871). In addition, a sound negative correlation is found between the SSH in May and precipitation in June and between the SSH in August and precipitation in July (1% confidence level). These results suggest that, during the early summer (May), which corresponds to the onset of the monsoon, the SSH in the eastern part of the NW arid region inhibits the latter precipitation. On the other hand, during the peak of the monsoon (July), rainfall in the northern boundary zone of the monsoon suppresses increases in the SSH in the arid region. Thus, the two factors exhibit a mutual influence. Table 3. Correlation Between SSH in the Eastern Part of the NW Arid Region from May Through September (H5–H9) and Rainfall in Hetao and Northern China Regions from May to September (R5–R9) Correlation Coefficients H5 H6 H7 H8 H9 R5 −0.767 −0.235 −0.100 0.164 −0.020 R6 −0.593 −0.871 0.116 −0.166 0.000 R7 0.228 0.103 −0.757 −0.628 −0.203 R8 −0.022 −0.100 −0.377 −0.654 −0.341 R9 −0.117 0.092 0.122 0.201 −0.560 [11] The next question is, how does an unusually weak (strong) SSH affect atmospheric water vapor transport over the Chinese mainland? To address this question, according to the standard that the average summer SSH abnormal flux in the eastern part of NW arid region was over 2 W/m2 higher (lower) than during regular years, five years (1984, 1988, 1992, 1994 and 1996) with unusually weak SSH and six years (1982, 1991, 1997, 2001, 2005 and 2006) with unusually strong SSH are selected and analyzed. The alculation formula for moisture flux is [12] V is the meridional wind or zonal wind speed (m/s), q is specific humidity (g/Kg) and P is atmospheric pressure (hPa). All of the variable field data were derived from the NECP Reanalysis Data Set II. The anomaly distributions of the summer moisture flux vertically integrated from the ground surface to 300 hPa reveal that water vapor that originated from the western Pacific Ocean and the South China Sea can reach the Hetao region, northern China, and even NE China via the Yangtze-Huaihe River basin during years with unusually weak SSH fluxes in the eastern part of the NW arid region (Figure 4a). The accumulation of water vapor is conducive to summer rainfall in the Hetao region and northern China. There is insufficient water vapor in the Yangtze-Huaihe River basin, resulting in poor summer precipitation in this region. Therefore, during years of weak SSH flux, type I or III rain belts are generally observed. During years of strong sensible heat flux (Figure 4b), water vapor that originates from the Sea of Japan can reach the Yangtze-Huaihe River basin. On the other hand, water vapor that originated from the Bay of Bengal can reach the southern Qinghai-Tibet Plateau and the South China Sea. Therefore, during these years, water vapor that originated from the Bay of Bengal and the South China Sea cannot reach the areas north of the Yellow River, leading to poor summer precipitation in northern China and producing type II or III rain belts. Figure 4Open in figure viewerPowerPoint Distribution of the composite moisture flux anomaly vertically integrated from the ground surface to 300 hPa during years with (a)unusually weak and (b) unusually strong SSH fluxes in summer (unit: kg m−1 s−1). (Shaded areas are statistically significant at the 0.10 confidence level.) [13] The above analysis demonstrates that a relatively weak (strong) SSH flux in the summer in the eastern part of the NW arid region is favorable (unfavorable) for the northward transportation of water vapor and results in unusually high (low) precipitation in the Hetao region and in northern China but abnormally low (high) rainfall in the Yangtze-Huaihe River basin. Correspondingly, the northern boundary of the summer monsoon shifts unusually far southward (northward). Thus, the fluctuation of SSH in the NW arid region of China closely correlates with summer rainfall in China. The study of SSH in the arid region may provide an explanation for mechanisms of flood or drought development in northern China. 3. Analysis of Atmospheric Circulation Types During Years of Unusually Strong (Weak) SSH [14] Our above analyses reveal a sound correlation between the aberrant change in the SSH in the NW arid region of China and the northern edge of the EASM as well as the summer rainfall in China. Thus, it is necessary to analyze the cause of atmospheric circulation based on its properties during years when the summer sensible heat flux is unusually strong (weak). In this section, all of the variable field data were derived from the NECP Reanalysis Data Set II. 3.1. Changes of Geopotential Height Field at 500 hPa [15] Figure 5 illustrates the anomaly distribution of the 500 hPa geopotential height field in summer during years of weak (strong) sensible heat flux. During years with weak sensible heat flux, the midlatitude area at the anomalous 500 hPa displayed a "− + − +" wave train structure from west to east, in which negative anomaly centers of the geopotential height field appear in West Africa, the Arabian Peninsula, Lake Baikal, the western Pacific Ocean, and the east Siberian Sea and positive anomaly centers emerge in the western European continent, the Tian Shan mountains, the Central Siberian Plateau and the Japanese islands (Figure 5a). During these years, the eastern part (100°E–110°E) of the midlatitude to high-latitude region contains a long-wave anomaly trough. The subtropical high shifts northwestward and is relatively strong; its western boundary harbors water vapor migrating northward. There is an updraft in front of the long-wave trough, which results in frontal uplift after clashing with the strong cold air force behind the trough. This anomaly increases precipitation in the areas of the Hetao region and in northern China [Qian, 2004], and the northern boundary zone of the EASM therefore shifts northward. On the other hand, during the years of strong sensible heat, we can see from Figure 5b that the midlatitude area develops a wave train structure of "+ − + −" from west to east. Specifically, West Africa, the Arabian Peninsula, Lake Baikal, and northern China are the positive anomaly centers, and the Mediterranean Sea, the West Siberian Plain and the Japanese islands represent the negative anomaly centers. During these years, the subtropical high over the western Pacific is unusually weak and the geopotential height is unusually high in northern China, which are unfavorable to the northward migration of the summer monsoon and to subsequent precipitation; the northern boundary zone of the EASM shifts southward. Our analyses indicate that, in comparison with the years with weak sensible heat, the anomalous 500 hPa geopotential height field exhibits conspicuous changes in the Eurasian continent during years with strong sensible heat, and the northern China area transitions from a negative anomaly to a positive anomaly. Figure 5Open in figure viewerPowerPoint Same as Figure 4 but for an anomaly distribution of the geopotential altitude field at 500 hPa (unit: geopotential meters). 3.2. Changes at Low-Level and Upper-Level Atmospheric Circulation [16] Because the wind field at 850 hPa perfectly illustrates the characteristics of low-level monsoon circulation, we examine the anomaly pattern of the wind field at 850 hPa (Figure 6) during years in which the summer sensible heat is unusually weak and unusually strong. As shown in Figure 6a, during years with weak sensible heat, two monsoon circulation wave trains appear above the Eurasian continent and the western Pacific Ocean, respectively, and display aberrant teleconnection distributions. The midlatitude wave train exhibits an anticyclonic circulation anomaly above the Alps Mountains, a cyclonic circulation anomaly above the Caspian Sea, an anticyclonic circulation anomaly above Lake Balkash, a cyclonic circulation anomaly above the Mongolian Plateau, and an anticyclonic circulation anomaly above the area east of Japan. The low-latitude wave train displays an anticyclonic circulation anomaly above West Africa and the Arabian Peninsula, a cyclonic circulation anomaly above the Arabian Sea, an anticyclonic circulation anomaly above the South China Sea, and a cyclonic circulation anomaly above the western Pacific Ocean. At the same time, a southerly flow anomaly throughout NE China, northern China, and eastern China is favorable for the northward migration of the summer monsoon as well as the northward transportation of water vapor originating from the East China Sea and the Bay of Bengal. In the Hetao region and northern China, the water vapor meets with a northern dry and cold flow stemming from the cyclonic circulation anomaly above the Mongolian Plateau and results in rich summer rainfall. During years with strong sensible heat (Figure 6b), however, the two monsoon circulation wave trains that emerge above the Eurasian continent and the western Pacific Ocean display the opposite teleconnection distribution. Specifically, the midlatitude circulation wave train exhibits cyclonic circulation anomalies above the Alps Mountains, the West Siberian Plain and the area east of Japan, but it exhibits anticyclonic circulation anomalies above the Caspian Sea and the Mongolian Plateau. The low-latitude wave train exhibits cyclonic circulation anomalies above the Arabian Peninsula and the South China Sea and anticyclonic circulation anomalies above West Africa, the Arabian Sea, and the western Pacific Ocean. As such, a northerly flow disturbance appears above southern China, which severely affects the migration to the Hetao region and northern China of a warm and wet flow originating from the South China Sea and the Bay of Bengal, and thus reduces local rainfall and leads to continuous drought. Figure 6Open in figure viewerPowerPoint Same
Publication Year: 2011
Publication Date: 2011-08-05
Language: en
Type: article
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