ARTICLE: Lu and Huang

Interannual Variations of the Blocking Highs over the Northeastern Asia in Summer and Their Causes

LU Riyu and HUANG Ronghui
Institute of Atmospheric Physics
Chinese Academy of Sciences
Beijing 100029, China

Submitted to Scientia Atmospherica Sinica , 1997 - Edited by WANG Zifa


ABSTRACT

In this paper, by the ECWMF data during the period from 1980 to 1988, the interannual variations of the blocking highs over the northeastern Asia in summer and their relation to the precipitations over the Yangtze River and Huaihe River Basin in summer were analysed. The results showed that the blocking highs over the northeastern Asia in summer have obvious interannual variations. The results also showed that there is a close relation between blocking highs over the northeastern Asia and the precipitations over the Yangtze River and Huaihe River Basin: when blocking highs occur frequently over the northeastern Asia in summer, the precipitations over the Yangtze River and Huaihe River Basin are more than normal; when blocking highs occur seldom, the precipitations are less than normal.

To investigate the reason for the above noted results, we analysed the sea surface temperature(SST) anomalies, and simulated the influence of the SST anomalies in the tropical western Pacific on the blockinh highs over the northeastern Asia, using the composite SST anomalies. Result showed that the East Asia/Pacific teleconnection pattern caused by the SST anomalies in the tropical western Pacific is one of the important reasons for producing the interannual variations of the blocking highs over the northeastern Asia in summer and their relation to the summer precipitations over the Yangtze River and Huaihe River Basin.

Key Words: blocking highs over the northeastern Asia, precipitations over the Yangtze River and Huaihe River Basin, SST anomalies.

1. Introduction

Blocking highs are a typical kind of the persistent anomaly of the atmospheric circulation in the mid-high latitudes, their formation and collapse are accompanied with the acute changes of zonal and meridional circulations. Moreover, since the maintained periods of blocking highs are long, their spatial positions are stable and their changes are small, persistent anomalies of climate are frequently casued in the regions of the blocking highs and the surrouding areas. In addition, covering from one week to several weeks, the time scales of the blocking highs belong to the time scales of the medium-range weather processes, and this kind of anomalies have strong amplitudes, hence the studies on the blocking highs are a crucial problem in the extended forecasts. Therefore, the research on the blocking highs has been emphasized widely.

At present, the fields of the studies on the blocking highs are being extended from the studies on the individual evolution of blocking highs to the studies on the variations (such as interdecadal variations) of occurrences of blocking highs in the long periods, and to the studies on the simulation abilities of numerical models (Lejenas 1995; Ferranti et al. 1994; Kung et al. 1989; Kaas and Branstator 1993). The purposes of studies are to understand clearly the climatic behavior of blocking highs, and to improve the abilities of numerical models on simulating blocking highs and climate.

Generally emphasizing the blocking highs in winter, the previous studies payed less attention to the blocking highs over the northeastern Asia in summer. Moreover, the blocking highs over the northeastern Asia in summer have an obvious effect on the flood and drought in east China, for example, both of the heavy flood in 1991 and severe drought in 1994 in the Yangtze River and Huaihe River Basin have an close relation with the frequency of the blocking highs in Eurasia. Among the important factors that influence the climate in China, there are not only the influences from the low latitudes, but also the influences from the mid-high latitudes, and the typical one of the influences from the mid-high latitudes is the blocking highs in Eurasia. Recently, Wang (1992) investigated the impact of the blocking highs in Eurasia on the Meiyu in the Yangtze River and Huaihe River Basin and Baiu in Japan. According to the occurance regions of the blocking highs in Eurasia, he divided them into three types, i.e., the blocking highs over Europe, the blocking highs over Baikal Lake and the blocking highs over the northeastern Asia. He found that the blocking highs over the northeastern Asia have an obvious effect on the Meiyu in the Yangtze River and Huaihe River Basin. On the other hand, recent study (Sun 1995) showed that the blocking highs over the northeastern Asia have particular characteristics, the frequency of their occurrence in summer is much more than that in other seasons. Therefore, we will study the characteristics of variations of the blocking highs over the northeastern Asia in summer and their cause in the present paper.

In general, the previous studies emphasized the actual evolution precesses of the blocking highs, and many investigations on the possible physical mechanism of the formation and maintenance of blocking highs are made. Undoubtedly, these studies make us understand the blocking episodes in detail and can provide us a basis for forecasting the formation and collapse of blocking highs. However, with the deep investigation on blocking highs recently, the studies on the favourable circulation background for the frequent occurrence of blocking highs, i.e., under which kind of large-scale circulation condition the blocking highs will be easy to be formed and maintained, have begun to be made (Lu and Huang 1996a; Kaas and Branstator 1993).

Investigations showed that the variability of the tropical SST anomalies can influence the formation and maintenance of blocking highs in the mid-high latitutes, and it may provide the precondition of circulation for the frequent appearance of blocking highs (Lu and Huang 1996b; Ferranti et al. 1994). In fact, the influences of the tropical SST anomalies on the atmospheric circulation over the extratropics have been extensively studied. Especially, recent investigations showed that the thermal state of the western Pacific warm pool greatly influences the circulation over East Asia and the northern Pacific through the East Asia/Pacific teleconnection pattern (EAP pattern) (Huang and Li 1987; Huang 1992; Huang and Sun 1992). Through this kind of wave-train, the thermal state of the western Pacific warm pool can change the circulation over the northeastern Asia and East Asia. The changed circulation may influence the formation and maintenance of the blocking highs over the northeastern Asia. Thus, the tropical SST anomalies may be the reason for the interannual variations of the blocking highs over the northeastern Asia in summer.

In this paper, the above-mentioned possibility will be investigated. In Section 2, we will investigate the interannual variation of the blocking highs over the northeastern Asia in summer during the nine years from 1980 to 1988, and give out the anomaly background of circulation for the years when blocking highs occur frequently or seldom in summer. In Section 3, we will show briefly the relationship between the blocking highs over the northeastern Asia and the precipitations in the Yangtze River and Huaihe River Basin. The effects of the tropical SST anomalies will be studies in Section 4. Finally, the conclusions will be summarized in Section 5.

2. Interannual variations of the blocked days over the northeastern Asia in summer

There have been many kinds of definitions about blocking highs. These definitions can generally be classified into two categories: one depends on the wind, i.e., mainly depends on the splits of the westerlies or the longitudal differences between the front and behind of the highs during the maintenance of blocking highs (Rex 1950; Kaas and Branstator 1993; Noar 1983); another category depends on the anomalies of geopotential height (Hartmann and Ghan 1980; Lejenas and Okland 1983; Mullen 1986; Tibaldi and Molteni 1990; Tibaldi et al. 1993). The objective defintions can be derived from both of these categories, and can be used to identifiy blocking highs in a great deal of data through computers. Because the analysis of geopotential height is more reliable than wind speed, the second category of definition is used more widely than the first category, especially when the blocking highs in Northern Hemisphere are discussed.

In this study, we chose Sun Moguo's definition of blocking highs and the results identified by the definition. His definition is as follows.

(1) there must be a center of high;

(2) the center locates between 50 N and 70 N;

(3) the moving speed of the high in zonal direction is lower than 8 longitude per day;

(4) the center of high lasts at least five days.

He quantified these criterions with focus on the large-scale characteristics of blocking highs and their synoptic characteristics in the quantifying process. Thence, the effect of identification was satisfying. In the following, we will utilize these results of the identification to examine the interannual variations of the blocking highs over the northeastern Asia in summer.

The summer here represents a period from June 1 to August 31. The northeastern Asia represents a region from 110 E to 150 E in the mid-high latitues, i.e., a region including the east part of Russia and Okhotsk Sea. This definition was made according to Sun Moguo's statistical results which showed that the northeastern Asia is the place where blocking highs occur most frequently among whole Northern Hemisphere in summer. Therefore, the blocking highs over the northeastern Asia may have an important effect on the climatic anomaly in the east part of China in summer.

The blocked days in a period are defined here as the total days when blocking highs occur or maintain during the period. Figure 1 shows the interannual variations of the blocked days over the northeastern Asia in summer. It can be found that the range of the variations is quite large. The blocked days during 92 days of the summertime in 1980, 1982, 1983, 1986 and 1987 all exceed 30 days, while the blocked days during each summer of 1981, 1984 and 1985 are all less than 20 days, and among these three summers, there is no even one blocked day over the northeastern Asia during the whole summer in 1985. Thence, the interannual variations of the blocking highs over the northeastern Asia in summer are obvious. We define the years of 1980, 1982, 1983, 1986 and 1987 as more blocked day years (MBYs), and define the years of 1981, 1984 and 1985 as less blocked day years (LBYs). It is interesting to mention that the years of two El Nino events in 1980s', i.e., 1982-1983 and 1986-1987, are all MBYs.

Figure 4 shows the composite distributions of the global SST anomalies during the MBYs (1980, 1982, 1983, 1986 and 1987) and the LBYs (1981, 1984 and 1985) over the northeastern Asia. In order to harmonize the anomalies, we normalized the observed SST anomalies, i.e., the value at every grid is divided by the variance of the SST in nine years at the grid. It can be found from Fig. 4 that at first, in the MBYs over the northeastern Asia in summer (Fig. 4a), the most obvious characteristics among the SST anomalies are a wide region of positive anoamlies in the tropical eastern Pacific, and a region of obvious negative anomalies in the tropical western Pacific. They are the typical characteristics of El Nino. In fact, there are four years of El nino among the five years of MBYs over the northeastern Asia in summer, i.e., the El Nino of 1982-1983 and the El Nino of 1986-1987. In the summer of 1980, there is also a region of positive anomalies in the tropical eastern Pacific.

Fig. 1 The interannual variations of the blocked days over the northeastern Asia in the summers during the nine years from 1980 to 1988.

Five MBYs and three LBYs will be analysed by the composite method. Figure 2 shows the distribution of the composite anomalies of geopotential height at 500 hPa. It can be found obviously from the figure that in MBYs(see Fig. 2a), positive anomalies of geopotential height locate over the northeastern Asia, while negative anomalies locate over the north of the Yangtze River, Korean Peninsula, Japan and Bering Sea, and positive anomalies over the south of the Yangtze River. This kind of distribution is much silmilar to the wave-train of EAP teleconnection pattern which is caused by the negative SST anomalies in the tropical western Pacific. At the meantime, there are strong negative anomalies of geopotential height over Ural. It indicates that there may be less blocking episodes occurred and maintained over Ural. In the LBYs, however, the distribution of the anomalies of geopotential height over the above-mentioned areas is quite different.

Fig. 2 The composite distribution of geopotential height at 500 hPa in (a) MBYs and (b) LBYs of the blocking highs over the northeastern Asia in summer.

This kind of distribution of anomalies shows that the occurrance and maintenance of the blocking highs over the northeastern Asia may not be a local phenomenon, they may closely relate to other phenomena. The relationship will be examined further in the following.

3. Relation between the blocking highs over the northeastern Asia and precipitations over the Yangtze River and Huaihe River Basin

Chinese meteorologists early discovered that the blocking highs affect greatly the Meiyu in the Yangtze River and Huaihe River Basin. Chen (1957) analysed the circulation characteristics during the flood in the Yangtze River and Huaihe River Basin in 1954, and pointed out that due to the blocking highs over the northeastern Asia, the jet over the northeastern Asia splits, and the south split of the jet causes the persistent rainfall in the Yangetze River and Huaihe River Basin. Tang (1957) also pointed out that there are three rainbelts when a blocking high appears over the northeastern Asia. He found that among these three rainbelts, two ones appear at south of the blocking high and north of the subtropical high, respectively, and there is consistency in the variations of the locations of these two rainbelts. Recently, Bi and Ding (1993), and Wu et al. (1994) pointed out that the climate anomalies in east China during the summer of 1980 were related to the stable maintenance of the blocking high over the northeastern Asia during July and August.

In the following, we will examine further that relation between the blocking highs over the northeastern Asia in summer and the precipitations over the Yangtze River and Huaihe River Basin, and discuss the association between the blocking high over the northeastern Asia and the subtropical high. Figure 3 shows the interannual variations of the precipitations over the Yangtze River and Huaihe River Basin from 1980 to 1988. Here the Yangtze River and Huaihe River Basin represents a land region east from 110 E between 30 N and 34 N, including 14 stations with the data of precipitations. The definition depends on the results of Lu et al. (1995). It can be found from the Fig. 3 that except 1986, all of MBYs over the northeastern Asia in summer are the years when the precipitations over the Yangtze River and Huaihe River Basin are more than normal; while the LBYs are the years when the precipitations over the Yangtze River and Huaihe River Basin are less than normal, especially, the precipitations over the Yangtze River and Huaihe River Basin in 1985, when there is no one blocked day in the whole summer, are obviously less than those in other years.

Fig. 3 Interannual variations of the precipitations over the Yangtze River and Huaihe River Basin from 1980 to 1988.

4. Influences of the tropical SST anomalies on the blocking highs over the northeastern Asia in summer

It has been shown in the introdution that the variability of the tropical SST anomalies may provide the circulation precondition for the frequent appearance of blocking highs. In addition, Fig. 2 shows the wave-train of the EAP teleconnection. Some investigations (Huang and Li 1987; Huang 1992; Huang and Sun 1992) showed that the reason for the teleconnection is the anomalies of the surface thermal state of the warm pool in the tropical western Pacific. Moreover, the time-scale of the effect of SST on atmosphere covers the time-scale of short-term of climate. Thence, the variability of SST may provide the precondition of circulation for the establishment and maintenance of the blocking highs over the northeastern Asia in summer. We will examine the possible influences of SST in the following.

Fig. 4 shows the composite distributions of the global SST anomalies during the MBYs (1980, 1982, 1983, 1986 and 1987) and the LBYs (1981, 1984 and 1985) over the northeastern Asia. In order to harmonize the anomalies, we normalized the observed SST anomalies, i.e., the value at every grid is divided by the variance of the SST in nine years at the grid. In MBYs (Fig. 4a), the most obvious characteristics of the SST anomalies are a wide region of positive anomalies in the tropical eastern Pacific, and a region of obvious negative anomalies in the tropical western Pacific. These are the typical characteristics of El Nino. In fact, these are four years of El Nino among the five years of MBYs over the northeastern Asia in summer, i.e., the El Nino of 1982-1983 and the El Nino of 1986-1987. In the summer of 1980, there is also a region of positive anomalies in the tropical eastern Pacific, and a region of negative anomalies in the tripical western Pacific. Only the influences of the tropical SST anomalies are studied in the presented paper, the influences of the extratropical SST anonalies will be examined in another paper. Hence, besides the SST anomalies in tropical Pacific, there is another region of abvious positive anomalies in Arabic Sea and the Bay of Bengal. In the LBYs (Fig. 4b), the distribution of the SST anomalies is almost same as the distribution in the MBYs, with only the difference of the sign of anomalies and more strong anomalies in the tropical eastern Pacific, Arabic Sea and the Bay of Bengal.

Fig. 4. The composite distribution of the normalized SST anomalies in the (a) MBYs and (b) LBYs.

Ferranti et al. (1994) showed that the SST anomalies in the tropical eastern Pacific have no obvious influences on the blocking highs in the northern hemisphere, though the anomalies influence greatly the extratropical circulation. Thence, the influence of the SST anomalies in the tropical eastern Pacific on the blocking highs over the northeastern Asia will be not examined in this study. On the other hand, the simulated results by IAP (Institute of Atmospheric Physics) 2-L AGCM showed that the SST anomalies in Arabic Sea and the Bay of Bengal have also no obvious influences on the blocking highs over the northeastern Asia. Therefore, we will focus on the influences of the SST anomalies in the tropical western Pacific on the blocking highs in the following simulation study.

The influences of the SST anomalies in the tropical western Pacific on the blocking highs over the northeastern Asia will be studied simulatedly. Because the main objective of this paper is to examine the large-scale circulation background which is favourable for the formation and maintenance of the blocking highs, in the following investigation, we will focus on the distribution of the 500 hPa geopotential height anomaly and will not discuss directly on the blocking highs. In this way, it is possible to avoid the error resulting from the shortage of models in describing blocking highs. The model used here is IAP 2-L AGCM. The control experiment is obtained by the integration with climatological monthly mean SST field. The SST anomalies in the tropical western Pacific are added to the climatological SST field in the anomalous experiment. Figure 5 shows the SST anomalies in the tropical western Pacific added in the anomalous experiment, which are the composite SST anomalies in the tropical western Pacific in the MBYs over the northeastern Asia. Both of the control and anomalies experiments are obtained by the perpetual integrations. The date of these runs is July 15. Among the simulated results of 70 days, only the results of later 30 days are analysed.

Fig. 5 The composite SST anomalies in the tropical western Pacific added in the anomalous experiment. Unit in C

Fig. 6 shows the 500 hPa geopotential height anomalies obtained by adding the composite SST anoamlies in the tropical western Pacific. It can be found that positive anomalies of geopotential height locate over the northeastern Asia, and negative anomalies locate over the north China and Bering Sea. This kind of anomaly distribution provides the precondition for the formation and maintenance of the blocking highs over the northeastern Asia, and is similar to the distribution of the observed geopotential height anomalies in the MBYs over the northeastern Asia, which has been shown in Fig. 2a. The similarity between the simulated and observed results shows that the negative SST anomalies in the tropical western Pacific are favourable for the formation and maintenance of the blocking highs over the northeastern Asia in summer.

Fig. 6 The simulated geopotential height anomalies due to the SST anomalies in the tropical western Pacific. Unit in GPM.

According to the above results, it can be inferred that there may not be direct association between the MBYs over the northeastern Asia in summer and the SST anomalies in the tropical eastern Pacific. That the SST anomalies in tropical eastern Pacific are positive in the MBYs, and negative in the LBYs may be due to the influences of the SST anomalies in the tropical western Pacific on the blocking high over the northeastern Asia, and the negative correlation between the SST anomalies in the tropical western Pacific and those in the tropical eastern Pacific.

5. Conclusions and discussion

In this paper, by the ECWMF data during the period from 1980 to 1988, the interannual variations of the blocking highs over the northeastern Asia in summer and their relation to the precipitations over the Yangtze River and Huaihe River Basin in summer were analysed. The SST anomalies in the tropical western Pacific were used to explain the interannual variations. The main results are as follows.

(a) The blocking high over the northeastern Asia in summer has obvious interannual variations, the blocked days can be almost half of all days in the summer of MBYs, on the other hand, there may be no even one blocked day in the summer of LBYs. There is a close relation between blocking highs over the northeastern Asia and the precipitations over the Yangtze River and Huaihe River Basin: when blocking highs occur frequently over the northeastern Asia in summer, the precipitations over the Yangtze River and Huaihe River Basin are more than normal; when blocking highs occur seldom, the precipitations are less than normal.

The reason for the variations is found to be the variability of the SST anomalies in the tropical western Pacific. The reason for the variations is found to be the variability of the SST anomalies in the tropical western Pacific. The reason for the variations is found to be the variability of the SST anomalies in the tropical western Pacific. The reason for the variations is found to be the variability of the SST anomalies in the tropical western Pacific.

(b) It was found that the reason for the above results is the SST anomalies in the tropical western Pacific. Analyses of observed data showed that the SST anomalies in the tropical western Pacific are negative in the MBYs over the northeastern Asia in summer, and positive in the LBYs. The simulated results showed that the negative composite SST anomalies in the tropical western Pacific can cause the wave-train which is similar to the East Asia/Pacific teleconnection pattern, i.e., positive anomalies of geopotential height over the northeastern Asia, and negative anomalies of geopotential height over south of the northeastern Asia. This kind of anomaly distribution is very helpful to the formation and maintenance of the blocking high over the northeastern Asia.

These results show that the formation and maintenance of the blocking highs over the northeastern Asia are not a local phenomenon, they relate to the very large-scale circulation over East Asia, i.e., positive anomalies of geopotential height over the northeastern Asia, and negative anomalies of geopotential height over south of the northeastern Asia. positive anomalies of geopotential height over the northeastern Asia, and negative anomalies of geopotential height over south of the northeastern Asia. positive anomalies of geopotential height over the northeastern Asia and negative anomalies of geopotential height over south of the northeastern Asia will be benefial for the formation and maintenance of the blocking high over the northeastern Asia. In addition, the blocking high over the northeastern Asia in summer relate to the subtropical high through the wave train of EAP pattern, which is shown in Fig. 2. The location of the subtropical high moves southward in the MBYs over the northeastern Asia; while in the LBYs the location moves northward. Through the realtionship of the location, the blocking high over the northeastern Asia and the subtropical high can influence the summer precipitations over the Yangtze River and Huaihe River Basin. On the one hand, in the MBYs, the more blocked days over the northeastern Asia mean the stable circulation in East Asia, and the stable circulation can lead to frequent appearance of the low troughs over Northeast China and Baikal Lake, providing the persistent cold air to the Meiyu front over the Yangtze River and Huaihe River Basin. On the other hand, at the meantime, the warm and wet air moves along the subtropical high, which shifts southward, to the Yangtze River and Huaihe River Basin, so that the summer monsoon rainbelt is maintained persistently over the Yangtze River and Huaihe River Basin. This relationship between the blocking high over the northeastern Asia and the subtropical high can also explain the location consistency between the rainbelt at south of the blocking high over the northeastern Asia and the rainbelt at north of the subtropical high: because both of the blocking high over the northeastern Asia and the subtropical high are all influenced by the East Asia/Pacific teleconnection pattern, and there is consistency between the variations of locations of these two highs.

6. Reference

Bi Muying and Ding Yihui, 1993, A study of budget of potential vorticity of blocking high during the drought period in summer of 1980, Quarterly J. of Applied Meteorology, 3, 145-156.

Chen Hanyao, 1957: The characteristics of circulation during the severe flood in the Yangtze River and Huaihe River valley in 1954, Acta Meteorologica Sinica, 28, 1-12(in Chinese).

Ferranti,L.,F.Molteni and T.N. Palmer, 1994: Impact of localized tropical and extratropical SST anomalies in emsembles of seasonal GCM integrations. Q. J. R. Meteorol. Soc., 120, 1613-1645

Hartmann, D. H. and S. J. Ghan, 1980: A statistical study of the dynamics of blocking. Mon. Wea. Rev., 108, 1144-1159

Huang, R.H. and W.J. Li, 1987: Influence of the heat source anomaly over the western tropical Pacific on the subtropical high over East Asia. Proc. International Conference on the General Circulation of East Asia, April 10-15, 1987, Chengdu, 40-51

Huang, R.H., 1992: The East Asia/Pacific pattern teleconnection of summer circulation and climate anomaly in East Asia, Acta Meteorological Sinica, 6, 25-37

Huang, R.H. and Sun Fengying, 1992: Impacts of the tropical western Pacific on the East Asia summer monsoon. J. of Meteor. Soc. of Japan, 70, 243-256

Kaas, E. and G. Branstator, 1993: The relationship between a zonal index and blocking activity. J. Atoms. Sci., 50,3061 -3077

Kung, E. C., H. L. Tanaka and W. E. Baker, 1989: Energetics examination of winter blocking simulations in the Northern Hemisphere. Mon. Wea. Rev., 117, 2019-2040

Lejenas, H., 1995: Long term variations of atmospheric blocking in the Northern Hemisphere. J. Meteor. Soc. Japan, 73, 79-89

Lejenas, H. and H. Okland, 1983: Characteristics of Northern Hemisphere blocking as determined from a long time series of observational data. Tellus, 35A, 350-362

Lu, R.Y. and R.H. Huang, 1996a: Energetics examination of the blocking episodes in the Northern Hemisphere. Chinese J. of Atmos. Sci., 20, 118-130.

Lu, R.Y. and R.H. Huang, 1996b: Numerical simulation of the effect of the SST anomalies in the tropical western Pacific on the blocking highs over the northeastern Asia. Adv. in Atmos. Sci., 13, 411-424.

Lu Riyu, Huang Ronghui, and Yin Baoyu, 1995: A comparative study on the variations of precipitations in East Asia. Collected Papers on Atmospheric Sciences(1), Meteorological Press, 6-13(in Chinese).

Mullen, S. L., 1986: The local balances of vorticity and heat for blocking anticyclones in a spectral general circulation model. J. Atmos. Sci., 43, 1406-1441

Noar, P.F., 1983: Numerical modeling of blocking, with reference to June 1982. Aust. Met. May., 31, 37-49

Rex, D.F., 1950: Blocking action in the middle troposphere and its effect upon regional climate, I, Tellus, 2, 196-211

Sun, M.G., 1995: Statistical characteristics of the blocking highs in the northern hemisphere and analyses of potential vorticity on the blocking highs over the northeastern Asia. Master Degree Thesis, Institute of Atmospheric Physics, Chinese Academy of Sciences.

Tang Moutsang, 1957: On the blocking situation of the eastern Asia and its climate effects. Acta Meteorologica Sinica, 28, 282-293(in Chinese).

Tibaldi, S. and F. Molteni, 1990: On the operational predictability of blocking. Tellus, 42A, 343-365

Tibaldi, S., P. E. Ruti and M. Maruca, 1993: Operational predictability of winter blocking: an ECMWF update. Preceedings of the ECMWF Seminars on Validation of Forecasts and Large-Scale simulations over Europe. Reading, UK, 7-11 September 1992, 91-105

Wang, Y., 1992: Effects of blocking anticyclones in Eurasia in the rainy season (Meiyu/Baiu season). J. Meteor. Soc. Japan, 70, 929-951

Wu Guoxiong, Liu Hui, Chen Fei, Zhao Yucheng and Lu Ying, 1994: Transient eddy transfer and formation of blocking high¡ª On the persistently abnormal weather in the summer of 1980. Acta Meteorologica Sinica, 52, 308-320(in Chinese).


Dr. Lu Riyu, Associate Professor, lr@sgi50s.iap.ac.cn
Prof. Huang Ronghui, Academician, hrh@sgi50s.iap.ac.cn
Institute of Atmospheric Physics Chinese Academy of Sciences Beijing 100029, China