Some Characteristics of the Summer Circulation Over the Qinghai-Xizang (Tibet) Plateau and Its Neighborhood

Transcription

1 Some Characteristics of the Summer Circulation Over the Qinghai-Xizang (Tibet) Plateau and Its Neighborhood Abstract Horizontal and vertical circulation patterns over the QinghaiXizang (Tibet) plateau during summer, derived from meteorological observations, are compared with results from rotating annulus experiments. There are several striking features during the season when the plateau acts as a huge elevated heat source: 1) a heat low dominates the planetary boundary layer over the plateau; 2) this heat low is broken up into several cells, giving rise to shear-line development; 3) surrounding the heat low is an anticyclonic belt; 4) the northern and southern portions of this belt approach each other as one proceeds into the upper troposphere and finally merge into a large anticyclone over the plateau; and 5) significant circulation cells appear in meridional and zonal cross sections, attesting to the strong influence of the plateau on the general circulation of the atmosphere. 1. Introduction Besides having o b v i o u s d y n a m i c effects on circulation patterns, the Q i n g h a i - X i z a n g (Tibet) Plateau d u r i n g s u m m e r constitutes a huge heat source that greatly affects the a t m o s pheric circulation. Because of-its large size and its complex t o p o g r a p h y, the plateau has a special influence on the weather systems c o m i n g f r o m the outside and passing over it, but also p r o d u c e s its own systems with certain properties peculiar to the p l a t e a u. A l m o s t the entire t r o p o s p h e r e over it is potentially unstable in s u m m e r. In contrast to its neighborh o o d it is a region of high t e m p e r a t u r e and high humidity, with a huge anticyclone in the u p p e r t r o p o s p h e r e a n d lower stratosphere and a large heat low in the planetary b o u n d a r y layer over the p l a t e a u. U n d e r these general c o n d i t i o n s of circulation, the highly b r o k e n t o p o g r a p h y results in various specific weather systems situated in relatively fixed locations. Quite a few of these weather systems are p h e n o m e n a of the planetary b o u n d a r y layer only. They are m o r e or less indep e n d e n t of the w e a t h e r systems a b o v e them in the middle and high t r o p o s p h e r e. H o w e v e r, when the u p p e r and lower systems are c o o r d i n a t e d properly, the lower ones may develop a n d sometimes move out of the plateau. They may even result in severe w e a t h e r d o w n s t r e a m (see p a p e r by T a o a n d 'Prof. Ye Duzheng (Tu-cheng Yeh) studied at the University of Chicago after World War II and received a Ph.D. degree from that university. He is now Director of the Institute of Atmospheric Physics, Academia Sinica; President of the Chinese Meteorological Society; Deputy to the National People's Congress; and Vice- 14 D u z h e n g Ye 1 Institute of Atmospheric Physics The Chinese Academy of Sciences D i n g, pp ). Also the characteristics of weather systems m o v i n g over the p l a t e a u f r o m the o u t s i d e are usually m o d i fied by t h e r m a l a n d d y n a m i c effects. These outside systems a n d the ones locally p r o d u c e d may interact with each other. All these processes m a k e the s u m m e r circulation quite c o m plicated over the p l a t e a u. This short report will discuss only s o m e characteristics of the s u m m e r circulation related to t h e r m a l effects of the plateau. 2. Atmospheric heat and cold sources over the plateau Since the 1950s Chinese meteorologists have been involved in the study of this p r o b l e m, a n d various calculations of different c o m p o n e n t s of the heat budget of the plateau have been done. Table 1 gives the results of one of these recent calculations of the intensity (E) of the a t m o s p h e r i c heat sources over the p l a t e a u. Values were derived a c c o r d i n g to the e q u a t i o n (Yeh, 1979) E = S H + LR + SR + L P - LR where SH is the t u r b u l e n t sensible heat transfer f r o m the e a r t h ' s surface, LR the effective long-wave radiation f r o m the e a r t h ' s surface, SR the a b s o r p t i o n of solar r a d i a t i o n, L P the latent heat of p r e c i p i t a t i o n, a n d LR the o u t g o i n g longwave radiation f r o m the t r o p o p a u s e. It can be seen f r o m T a b l e 1 that in the winter half-year the t r o p o s p h e r e over the p l a t e a u is, on the average, a cold source, achieving m a x i m u m intensity in D e c e m b e r ( 160 c a l / (cm 2 day, or 670 X j o u l e / ( m 2 d a y ) ). In the s u m m e r halfyear it is a heat source, with m a x i m u m intensity in J u n e a n d J u l y, a r o u n d 220 c a l / ( c m 2 day) (or 920 X 104 j o u l e / ( m 2 day)). Because of the height of the plateau the heat is added directly t o the middle a n d higher t r o p o s p h e r e a n d used only by half of the total mass of the a t m o s p h e r e. So the same a m o u n t of heat will be used m o r e effectively over the plateau than over the a d j a c e n t low-level terrain. Chairman of the Working Group on Atmospheric Science under the Committee on Science and Technology (the Chairman of that committee is Vice-Premier Feng Yi). In spite of all these official duties Prof. Yeh maintains a very active involvement in many research projects, ranging from numerical and geophysical modeling to objective long-range forecasting. (Comments by E. R. Reiter.) Vol. 62, No. 1, January 1981

2 Bulletin American Meteorological Society 15 TABLE 1. The heat source intensity, of the troposphere over the plateau 1 (unit: cal/(cm 2 day) or 4.19 X 10 4 joule/(m 2 day)). Month t: Since the meteorological data of the plateau are still insufficient, the values in this table should only be considered as order of magnitude. 3. Low-level circulation over the plateau and its surroundings In response to the seasonal variation of the atmospheric heat source over the plateau, the circulation over it reveals remarkable seasonal changes, especially in the lower layers. In winter the monthly mean 600 mb map shows a shallow cold high over the plateau (not shown here). It changes into a heat low in summer(fig. l)(yeh and Gao, 1980). Accompanying this seasonal change in pressure systems is a change of wind systems over the plateau. Gao 2 and Tang (1980) called this seasonal change of wind systems the ''plateau monsoon." Referring to Fig. 1, we would like to emphasize the following points. The summer heat low of the plateau is not an integral entity. It is broken into several systems. It has two main centers, one in the southwest and the other one in the southeast of the plateau. In addition there are minor ones. (Some of them are not shown in the mean chart.) Along with the small lows there occur quite a few small highs (not shown in the mean chart). These small lows and small highs render the features of the circulation in the planetary boundary layer quite complicated. It is believed that these complications are related to the complex features of the broken topography of the plateau (Tang, 1980). It is also seen from Fig. 1 that to the south of the chain of heat lows is a narrow belt of relatively high pressure that runs almost parallel to the southern periphery of the plateau. The importance of this narrow ridge is emphasized by Tang (1980). To the north of the heat low region is also a belt of high pressure consisting of several small highs. Both belts of high pressure incline towards the plateau with altitude. As these two ridges approach each other, a long mean shear line, which is also an important weatherproducing system over the plateau, forms between them. Summarizing the above, it may be visualized that in a timeaveraged configuration the plateau is covered in the lower layers by a large heat low, elongated in the zonal direction and narrow in the meridional direction. The top of this mean heat low is reached a little above the 500 mb surface in the western part of the plateau and a little bit below that surface in the eastern part. This large low is not a single weather system. It consists of two main centers (and three minor ones), separated by shear lines, and containing low vortices and small convective weather systems. On two sides (north and south) of this large low are narrow high-pressure belts, which incline toward the plateau's interior with height and finally merge above the 500 mb surface into one large anticyclone, which increases in intensity and size with height and reaches 2 In an informally published paper by Y. X. Gao. FIG. 1. Mean July 600 mb contours (decameters for 1200 GMT). Dotted line provides outline of Qinghai-Xizang (Tibet) Plateau. its highest intensity near 150 mb. The systems just described are, of course, a monthly-mean summer feature. The daily situations are much more complex. 4. Low vortices and convective activity The atmosphere over the plateau in summer is constantly in a convectively unstable state. There are also many mountains on the plateau whose peaks act as heat islands in the atmospheric ocean. These mountains are the sources of convective activity. In addition, shear lines and vortices will also produce systematic convection in a convectively unstable atmosphere. All these factors make the plateau a region of very high convective activity. Taking the station Tuotuohe (34 13' N, 92 26' E) as an example 3, on the average more than 82% of the observed clouds are cumulonimbi that reach their top level of development (to almost 100%) at 20:00 Beijing time. During July the average number of thunderstorm days is 15; the maximum number is 23. From 1966 to 1975 there were 195 rainy days in July, of which showers accounted for 98%. The convective clouds, under certain favorable conditions, may be grouped and developed into cloud clusters and even vortices and, in turn, the vortices are also potential sources of convective activity. The low vortices are important small and mesoscale weather systems over the plateau in summer. 3 See the manuscript by the staff of the weather station at Tuotuohe, 1974: Some characteristics of precipitation and high wind at Tuotuohe under the thermal and dynamic influence of the plateau.

3 16 Vol. 62, No. 1, January 1981 There are two types of vortices. One type is produced by cold air advection. This type derives its energy from baroclinicity. The other type of vortex has a warm-core structure. The energy for the development of this type does not depend on cold air activity, but comes from the latent heat of precipitation 4. However, some of the low vortices are not of a uniform warm-core type throughout their whole depth. They may have a double structure, with a warm core in the upper part and a cold core in the lower layers 5. Some typical warm-core vortices possess spiral bands of clouds converging toward the center and diverging cirrus clouds in front of the vortices. This structure is quite similar to that of tropical cyclones. 5. Summer vertical circulation over the plateau and its surroundings FIG. 2. The mean July meridional and vertical circulation of the sector 75 E-110 E. Because of the height (over 4 km on the average) of the plateau, the heated air over it can easily be uplifted to the high troposphere and even to the stratosphere. From there it will be carried over great distances by the prevailing westerlies or easterlies. Since the plateau is situated in the belt of the subtropics, the heat source over it will greatly affect the structure of the Hadley circulation. Again, the dynamical effects of the plateau will further complicate the structure of the vertical circulation. Figure 2 (Yeh et al., 1979) shows the mean July meridional and vertical circulation in the longitude sector 75 E-110 E. In this figure we can see a huge monsoonal circulation system with an ascending branch over the plateau and a descending branch somewhere in the Southern Hemisphere. Koteswaram (1958) first mentioned this monsoonal circulation and Chen and Li (1964) proved its existence. (But according to them the descending branch of the monsoonal circulation is located in the Northern Hemisphere.) Figure 2 also shows air currents ascending to the plateau from the north. These ascending currents from the north are not like those from the south, which come from the lowest layers of the troposphere. The northerly flow comes from the midtroposphere, somewhere in the layer mb. Below this ascending current from the north there is a descending current, gliding down along the northern slopes of the plateau. This descending current is in accord with the desert climate in that region. To show this situation in more detail, we give the mean July meridional and vertical circulation along 90 E (Fig. 3) (Yeh et al., 1979). In this figure the huge monsoonal circulation is also clearly evident. However, within this large cell there are two small vertical cells, one in the northern and the other in the southern part of the plateau. Of these two small cells, the southern one, which reaches as high as 150 mb, is more dominant. The northern one only reaches to 300 mb. The bottom of both cells is situated near 500 mb. Recently Li and collaborators 6 also found a southern small cell, but it is a 4 Research Group of the Low Pressure Systems over Qinghai- Xizang Plateau, 1976: Studies of the midsummer low pressure system of Qinghai-Xizang Plateau. institute of Atmospheric Physics, 1976: Case studies of the structure of vortices of southwest China. 6 W. L. Li: unfinished work. FIG. 3. The mean July meridional and vertical circulation along 90 E. FIG. 4. The mean July zonal and vertical circulation along 35 N. few degrees longitude to the west of 90 E. Now let us consider the mean July zonal and vertical circulation along 35 N (Fig. 4) (Yeh et al., 1979). The important feature of this figure is the huge west-east circulation system, with an ascending branch over the plateau and its neighborhood, and descending motion that reaches as far east as

4 Bulletin American Meteorological Society Annulus simulation of the summer circulation over the plateau and its surroundings only s o m e results of the e x p e r i m e n t s relevant to the foregoing discussions, d u e to the shortness of this article. F i g u r e 5a (Research G r o u p, 1977) is a p h o t o g r a p h s h o w ing the h o r i z o n t a l circulation at the level n e a r the t o p of a heated model p l a t e a u in a fluid initially motionless relative t o the r o t a t i n g a n n u l u s. (The experimental c o n d i t i o n s are described in the figure c a p t i o n. ) Figure 5b is a r o u g h sketch of Fig. 5a. F r o m these figures it can clearly be seen that near the t o p of the heated model p l a t e a u there is a low which is confined within the b o r d e r s of the p l a t e a u. H o w e v e r, s u r r o u n d ing this low is a large anticyclonic circulation. T h e r e f o r e, between this low a n d the current circling it are n a r r o w high p r e s s u r e belts. C o m p a r i n g Fig. 1 a n d Fig. 5b one can easily f i n d a striking similarity. H i g h e r u p, a b o v e the t o p of the model p l a t e a u, the circulation gradually changes into an anticyclone that reaches its highest intensity a n d largest size at the highest level a b o v e the model plateau (not s h o w n here) (Yeh a n d C h a n g, 1974). This transition is quite similar to the o b s e r v a t i o n s described in Section 2. N o w let us t u r n o u r a t t e n t i o n to the a n n u l u s s i m u l a t i o n of the s u m m e r vertical circulation. Figure 6a shows the vertical circulation in a west-east vertical plane across the center of the model plateau a n d Fig. 6b gives a sketch of the circulation characteristics. T h e f e a t u r e of p a r t i c u l a r interest in this figure is the existence of t w o regions of u p w a r d m o t i o n, with a region of d o w n w a r d m o t i o n (or sometimes relatively weak u p w a r d m o t i o n ) in between. In each of these t w o regions of u p w a r d m o t i o n the t e m p e r a t u r e m e a s u r e m e n t s show a series of intense pulses (not s h o w n here). This m e a n s t h a t the t w o regions of u p w a r d m o t i o n are actually regions of s t r o n g convection. T h e h o r i z o n t a l scale of the regions is 1-2 cm. This p h e n o m e n o n was particularly discussed in a p a p e r by the Research G r o u p (1978). It is interesting to note t h a t the surface t e m p e r a t u r e field of the heated model p l a t e a u possessed only one m a x i m u m, which was situated only slightly to the southwest of the center of the model (Research G r o u p, 1977). F u r t h e r m o r e, the t w o regions of strong u p w a r d m o t i o n did not coincide with the center of m a x i m u m surface t e m p e r a tures. T h u s the existence of t w o centers of strong convection needs theoretical e x p l a n a t i o n. T h e Research G r o u p (1977) p r o v i d e d an e x p l a n a t i o n using C h a n d r e s e k h a r ' s (1961) t h e o r y of convection in a r o t a t i n g fluid. O u r interest here is to relate this p h e n o m e n o n to the a p p e a r a n c e of two main low centers over the Q i n g h a i - X i z a n g Plateau in s u m m e r (Fig. 1). The results of this a n n u l u s experiment may provide a partial explanation f o r the meteorological observations. In recent years a series of a n n u l u s experiments on the simulation of the d y n a m i c a n d t h e r m a l effects of the QinghaiXizang (Tibet) Plateau on the general circulation has been carried o u t at the Institute of A t m o s p h e r i c Physics, A c a d e mia Sinica (see, f o r example, Yeh a n d C h a n g, 1974; Research G r o u p on E x p e r i m e n t a l S i m u l a t i o n, 1977, 1978; C h a n g et al., 1977; Li et al., 1976; etc.). In these experiments the plateau was simulated simply by an idealized half-ellipsoidal b o d y placed at the p r o p e r latitude on the b o t t o m of an a n n u lus. ( S o m e t i m e s an even m o r e realistic model was used.) This m o d e l p l a t e a u m a y be heated or cooled to simulate its thermal influence. Three types of experiments have been carried o u t, namely: heated p l a t e a u, cooled p l a t e a u, a n d p l a t e a u w i t h o u t heating or cooling. In the following we shall give F i g u r e 7a shows the experimental meridional circulation in a n o r t h - s o u t h vertical p l a n e across the center of a heated m o d e l p l a t e a u. T h e s c h e m a t i c sketch is given in Fig. 7b. A n o t e w o r t h y f e a t u r e in this figure is the two-cell structure over the m o d e l p l a t e a u, one in its n o r t h e r n a n d one in its s o u t h e r n p a r t. This f e a t u r e can be c o m p a r e d with the t w o small meridional cells observed in the real a t m o s p h e r e in July over the Q i n g h a i - X i z a n g (Tibet) Plateau (Fig. 3). T h e t w o vertical m e r i d i o n a l cells in the a n n u l u s experiment are confined to the region over the m o d e l p l a t e a u, whereas the t w o cells in the real a t m o s p h e r e are not. F u r t h e r m o r e, there are discrepancies between the meridional circulation outside the plateau in the a n n u l u s experiment a n d that in real a t m o s p h e r e. Since the experimental setup of the a n n u l u s experiment is so different f r o m the c o n f i g u r a t i o n of the N o r t h e r n H e m i s p h e r e, one FIG. 5. (a) Photograph of the horizontal circulation on a level near the top of a heated model plateau in a fluid initially motionless relative to the rotating annulus. Experimental conditions: Radius of inner cylinder, 9.2 cm; radius of outer cylinder, 38.2 cm; depth of the working substance (mixture of water and glycerine, specific weight 1.043), 6 cm; major axis of the model plateau, 7.0 cm, minor axis, 4.0 cm, height, 3.0 cm; rate of rotation of the annulus, s 1 ; intensity of heating of the model plateau, watt/cm 2, (b) Sketch of the circulation shown in (a). 180 E. This large west-east vertical circulation system extends 150 in longitude a n d occupies the whole t r o p o s p h e r e. In the early 1970s K r i s h n a m u r t i (1971) h a d already s h o w n t h a t, based on the velocity potential field on the 200 m b s u r f a c e in s u m m e r, there s h o u l d exist such a zonal circulation, a n d n a m e d it west-east circulation.

5 18 Vol. 62, No. 1, January 1981 FIG. 6. (a) Photograph of the vertical circulation in a west-east vertical plane across the center of a heated model plateau. Experimental conditions: same as in Fig. 5a. (b) Sketch of the circulation shown in (a). should not expect to obtain full agreement between experiment and observations. However, the fairly good agreement between the circulation over the plateau observed in the real atmosphere and that in the experiment promises some insight into the formation mechanisms of the mean circulation over the plateau and its surroundings from the annulus experiment. To illustrate further the validity of the last statement one may add the following: It has already been pointed out that over the heated model plateau in the rotating annulus there appears a huge anticyclone at the top layer. We also observed that the occurrences of this high and of the vertical motion in the two convective regions (mentioned previously) almost coincide, the time difference between their appearance being less than one annulus day. This suggests that there is mutual interaction between the small-scale convective weather systems and the very large-scale circulation. It may be that under favorable large-scale conditions the small convective systems are produced, and, in turn, the convergence in the lower layer of the aggregated convective systems maintains the large-scale low-pressure configuration in the planetary boundary layer. The divergence in the upper layer of the aggregated convective systems maintains the huge anticyclone in the upper troposphere over the plateau. Along this line of thought, the author and his collaborators 7 obtained a rough estimate of the vorticity budget, heat budget, and water vapor budget of the mean summer troposphere over the Qinghai-Xizang (Tibet) Plateau and found it very likely that the small-scale convective weather systems could be the primary ones maintaining the large-scale circulation over the plateau. Chen (1979) summarized these discussions in Chapter 15 of a recently published book, Meteorology of Qinghai- Xizang Plateau (Yeh et al., 1979). 7 Yeh, T.C., et al., 1974: The maintenance of large-scale mean summer circulation over Qinghai-Xizang Plateau by convective activities. (An informally published paper.) FIG.7. (a) Photograph of the vertical circulation in the northsouth vertical plane across the center of a heated model plateau. Experimental conditions: same as in Fig. 5a. (b) Sketch of the circulation shown in (a). References Stabil- Chandresekhar, S., 1961 : Hydrodynamic andhydromagnetic ity. Oxford at Clarendon Press, Oxford, England. Chang, K., Z. T. Chen, M. Y. Zhou, K. Q. Li, Z. S. Song, G. F. Wang, K. J. Wang, T. C. Yeh, and C. C. Chang, 1977: The annulus simulation of the movement of Qinghai-Tibetan high and its application to the forecast of summer flow patterns of high troposphere. Sci. Sinica, 20, Chen, C. S., and L. Wei-Lian, 1964: A comparison of mean wind field and mean meridional circulation between southwest monsoon area in southeast Asia and Pacific trade wind area in July, Acta Meteorol. Sinica, 34, Chen, C. T., 1979: The maintenance of large-scale mean summer circulation over Qinghai-Xizang (Tibet) plateau by convective activities. In Meteorology of Qinghai-Xizang Plateau, edited by T. C. Yeh, Y. X. Gao, M. C. Tang, S. W. Lo, C. B. Shen, D. Y. Gao, Z. S. Song, Y. F. Qian, F. M. Yuan, G. Q. Li, Y. H. Ding, Z. T. Chen, M. Y. Zhou, K. J. Yang, and Q. Q. Wang, Science Press, Beijing (in Chinese). Koteswaram, P., 1958: The easterly jet stream in the tropics. Tellus, 10, Krishnamurti, T. N., 1971: Tropical east-west circulation duringthe northern summer. J. Atmos. Sci., 28, Li, K., R. Y. Chen, K. J. Yang, Z. S. Song, Z. T. Chen, K. S. Chang, M. Y. Zhou, Y. F. Xu, T. C. Yeh, and C. C. Chang, 1976: An annulus experimental simulation of the low vortex to the southeast of Tsinghai-Tibetan plateau. Sci. Sinica, 19, Research Group on Experimental Simulation, 1977: An experimental simulation on three-dimensional structures of airflow field over the Tsinghai-Tibetan plateau in summer. Sci. Atmos. Sinica, 1,

6 Bulletin American Meteorological Society 16, 1978: The annulus simulation of the summer large-scale convective systems over Tsinghai-Tibetan plateau. Sci. Sinica, 21, Tang, M. C., 1980: Basic characteristics of climate of Qinghai- Xizang (Tibet) plateau. To appear in Proceedings of the Symposium on Qinghai-Xizang Plateau, Beijing, China, 25 May-1 June, Yeh, T., 1979: Introduction, in Meteorology of Qinghai-Xizang {Tibet) Plateau, edited by T. C. Yeh and Y. X. Gao et al., chap. 1, Science Press, Beijing (in Chinese)., and C. C. Chang, 1974: A preliminary experimental simulation on the heating effect of the Tibetan plateau on the general circulation over eastern Asia in the summer. Sci. Sinica, 12, , and Y. X. Gao, 1980: The seasonal variation of heat sources and sinks over Qinghai-Xizang (Tibet) plateau and its role in the general circulation. To appear in Proceedings of the Symposium on Qinghai-Xizang {Tibet) Plateau. Science Press, Beijing (in Chinese)., Y. X. Gao, M. C. Tang, S. W. Lo, C. B. Shen, D. Y. Gao, Z. S. Song, Y. F. Qian, F. M. Yuan, G. Q. Li, Y. H. Ding, Z. T. Chen, M. Y. Zhou, K. J. Yang, and Q. Q. Wang, 1979: Meteorology of Qinghai-Xizang (Tibet) Plateau. Science Press, Beijing (in Chinese)., G. J. Yang, and X. D. Wang, 1979: The average vertical circulations over East Asia and the Pacific area, (I) in summer. Sci. Atmos. Sinica, 3, announcements 1 AAAS Award for Scientific Freedom and Responsibility The American Association for the Advancement of Science (AAAS) has established a new award for Scientific Freedom and Responsibility. The award, which will be presented for the first time at the 1982 AAAS Annual Meeting in Washington, D.C., will consist of a plaque and a cash prize of $1000. The award was established by action of the AAAS Board of Directors in June Under the criteria approved by the AAAS Board, the purpose of the award is to honor scientists and engineers whose actions, often at significant personal cost, have exemplified outstandingly principles of scientific freedom and responsibility. The new prize will recognize scientists and engineers who have: acted to protect the public's health, safety, or welfare; focused public attention on important potential impacts of science and technology on society by their responsible participation in public policy debates; or established important new precedents in carrying out the social responsibilities or in defending the personal freedoms of scientists and engineers. Members of AAAS or its affiliated professional societies are invited to nominate candidates for the award by providing the following information: the name and address of their nominee; a brief statement (about 100 words) describing the action(s) of their nominee that they believe merit(s) recogni- 1 Notice of registration deadlines for meetings, workshops, and seminars, deadlines for submittal of abstracts or papers to be presented at meetings, and deadlines for grants, must be received at least three months prior to deadline dates. News Ed. tion; general background information about their candidate (no longer than three pages); and names and addresses of one or two other persons (one of whom must be a scientist) who support(s) the nomination. Nominations will be reviewed by the Scientific Freedom and Responsibility Award Committee, who may recommend a nominee or nominees to the Chairman of the AAAS Board for final approval. Nominations should be sent to: Scientific Freedom and Responsibility Award, American Association for the Advancement of Science, 1515 Massachusetts Ave., N.W., Washington, D.C Deadline for receipt of nominations is 30 June Conference on Time Series Methods in Hydrosciences Call for papers An International Conference on Time Series Methods in Hydrosciences will be held at the Canada Centre for Inland Waters in Burlington, Ontario, Canada, during 6-8 October Scientists, statisticians, and users of time series methods in limnology, hydrology, water quality control, and forecasting and modeling of marine environments are invited to participate in this conference. Abstracts of proposed papers should be forwarded before I June 1981 to: A. El-Shaarawi, Aquatic Physics and Systems Division, NWRI, Canada Centre for Inland Waters, P.O. Box 5050, Burlington L7R 4A6, Ontario, Canada (tel: ). Any conference inquiries also may be addressed to El-Shaarawi. {continued on page 22)