THE NUMERICAL SIMULATION OF THE THREE-DIMEN-SIONAL TELECONNECTIONS IN THE SUMMER CIRCULATION OVER THE NORTHERN HEMISPHERE

In this paper, a quasi-geostrophic, 34-level spherical coordinate model with Rayleigh friction, Newtonian cooling and the horizontal eddy thermal diffusivity is used to simulate the three-dimensional telecon nection in the summer circulation over the Northern Hemisphere.The computed results show that the change of the heat source over the Tibetan Plateau may cause the change of the atmospheric circulation over the middle and high latitudes in the Northern Hemisphere. When the heal source over the Tibetan Plateau is enhanced, it may cause the Tibetan high to enhance over South Asia and cause the change of the atmospheric circulation over East Asia and North America, i. e., Northeast China and North Japan will be controlled by a trough, which brings about a cold summer in this area. In the same way, an anticyclone will be enhanced over the Okhotsk sea. Moreover, another trough will be formed over Alaska, while another ridge will develop to the northeast of North America. Besides, the Pacific subtropical high will be weakened. These results are in good agreement with those obtained from the observed data.     

THE INTERFACE EFFECT AND THE FORMATION OF A LOW-LEVEL JET ALONG THE EAST SIDE OF THE ROCKY MOUNTAINS

Based upon the analysis of several different causes for the low-level jet along the east side of the Rocky Mountains, the concept of "Interface Effect" is established. The basic mechanism for the formation of the low-level jet in North America has been found to be the compression and divergence, under the driving of ageostrophic winds, of the air columns between two surfaces-the ground and the bottom of inversion-which slope with different patterns in a cross-section normal to the jet stream. As a result, the air parcel is accelerated along the streamline and the anticyclonic shear of the current increased. Also, the diurnal variation of the jet is determined by the interface effect.     

THE ROLE OF THE QINGHAI-XIZANG PLATEAU IN FEEDBACK MECHANISMS AFFECTING THE PLANETARY CIRCULATION

3. Observational Evidence. Figure 7 shows the Line Island precipitation index from 1910 to 1975. This indexwas computed and combined for the precipitation stations of Fanning Island, Washing-ton Island and Christmas Island. It is defined by assigning the value of 100 to thewattest in a long series of months, say January, and the value 0 to the driest month inthe same series. The interval between the wettest and driest month of January is thus     

THE LARGE-SCALE TOPOGRAPHY AND THE STABILITY OF ROSSBY WAVE IN THE BAROTROPIC ATMOSPHERE

The effects of the large-scale topography on the stability of Rossby wave are discussed by usingthe method of the multiple scale analysis. The results show that the influences of the topographywith north-south or west-east slopes on Rossby wave and energy propagation are different.     

IMPACTS OF THE ONSET OF THE SOUTHEAST ASIAN SUMMER MONSOON ON THE BEGINNING OF THE RAINY SEASON IN YUNNAN

1 INTRODUCTIONSummer monsoon in Southeast Asia can causelarge-scale precipitation in the region in early summer,which is featured by prevailing low-level southwesterlyfrom the Bay of Bengal to South China Sea (SCS). Ithas characteristics of its own as well as those of Asianmonsoons in general. As found in studies over recentyears on East Asian monsoons[1],the earliest onset ofthe Southeast Asian summer monsoon occurs in earlysummer over the SCS, among all members of themonsoon syst…     

THE RELATIONSHIP BETWEEN THE MOVEMENT OF THE MEIYU/BAIU RAIN BELT AND THE PERIODIC NORTHWESTWARD PROPAGATION OF THE CONVECTIVE ACTIVITY FROM TROPICAL WEST PACIFIC

In order to investigate the effect of the factors in tower latitudes on Meiyu/Baiu front,adiagnostic analysis for the two cases during June to July of 1985 and 1986 was examined.We foundthat (1)when the tropical convective activity moves westward to 10.5-15.5′N/140°E from eastside of 10.5-15.5°N/160°E,the northward shifts of the Meiyu/Baiu rain belt occurs;(2)themain factor which results in the northward and southward shifts of Meiyu/Baiu rain belt is thoughtas the 8,18 and 30 day oscillations of the tropical convective activity around West Pacific.Meanwhile,the wave train propagating from Lake Baikal via Okhotsk Sea to the tropics couldsometimes shift Baiu rain belt southward;(3)the onsets of Meiyu in China of both cases tend totake place just when the convective activity around lower latitudes moves westward through about140°E with the 8,18 and 30 day oscillation periods firstly coming to June.     

ON THE RELATIONSHIPS BETWEEN THE SUMMER RAINFALL IN CHINA AND THE ATMOSPHERIC HEAT SOURCES OVER THE EASTERN TIBETAN PLATEAU AND THE WESTERN PACIFIC WARM POOL

The relationships between the summer rainfall in China and the atmospheric heat sources over the eastern Tibetan Plateau and the western Pacific warm pool were analyzed comparatively, using the NCEP/NCAR reanalysis daily data. The strong (weak) heat sou…     

ON THE PARAMETERIZATION OF THE VERTICAL VELOCITY AT THE TOP OF PLANETARY BOUNDARY LAYER

In this paper, an equation of the vertical velocity at the top of PBL is derived by use of a PBL model which is based on an analytic and actual form of K. Results show that the vertical velocity is a function of geostrophic vorticity, geostrophic wind speed, Coriolis parameter and the roughness of the ground, thus improving Charney-Eliassen's formula. The order of magnitude of the vertical velocity computed from our equation is in agreement with that from the latter, but more factors affecting the vertical velocity are included.     

THE MONSOON PRECIPITATION VARIATION IN THE CLIMATE CHANGE

First,studies on the East Asian monsoon simulation were reviewed.Then the monsoon precipitation change in thepaleoclimate was simulated and analyzed.This paper also analyzed and simulated the interannual changes of monsoonprecipitation and their relations with the sea surface temperature (SST) changes.Finally,the simulated monsoon precipi-tation change in the CO_2-induced climate change was discussed.     

THE EFFECTS OF THE QINGHAI-XIZANG PLATEAU ON THE MEAN SUMMER CIRCULATION OVER EAST ASIA

Four numerical experiments of simulation have been conducted in this paper by the use of a five-layer primitive equation numerical model with incorporated pressure-sigma vertical coordinate system. The initial fields are taken from the July zonal mean data of many years, while the heat sources and sinks are ideally specified according to the mean heating field over the East Asia calculated from the real data of July, 1979. On the basis of simulated results of temperature and geopctential height patterns we emphatically discuss the effects of the topography and the heating of the Qinghai-Xizang Plateau. From the analyses in this paper, it appears that the heating over the Bengal region makes a larger contribution to the middle and the south branches of the monsoon cell and is also the main cause for the existence of the southerly channel to the east of the Plateau, for the break of the subtropical anticyclcne belt below the 500 hPa level and for the formation of the summer Asian anticyclone at the 300 hP     

EFFECT OF THE INDIAN PENINSULA ON THE COURSE OF THE ASIAN TROPICAL SUMMER MONSOON

In terms of the NCAR Community Climate Model (CCM3),the effect of the Indian Peninsulaon the course of the Asian tropical summer monsoon is simulated in this paper,and numericalexperimental results show that the Indian Peninsula plays a critical role in the establishmentprocess of the Asian tropical summer monsoon.When the CCM3 includes the Indian Peninsula,the model successfully simulates out the course of the Asian tropical summer monsoon,i.e.theSouth China Sea (SCS) summer monsoon at first bursts in middle May,while the Indian monsoonjust establishes until middle June.However when the Indian Peninsula topography is deleted in themodel,the Indian and SCS summer monsoons almost simultaneously establish in late May.Numerical results further indicate that in the former experiment the sensible heating of the IndianPeninsula warms the air above and produces evident temperature contrast between the peninsulaand its adjacent SCS and Bay of Bengal (BOB).which results in the strengthening and maintenanceof the BOB trough in the low-middle layer of the troposphere in the end of spring and early summerand thus the earliest establishment of the Asian tropical summer monsoon in the SCS in middleMay.However,the Indian summer monsoon just establishes until middle June when the strongwest wind over the Arabian Sea shifts northwards and cancels out the influence of the northwestflow behind the BOB trough.In the latter experiment the effect of Tibetan Plateau only produces avery weak BOB trough,and thus the SCS and Indian summer monsoons almost simultaneouslyestablish.     

A STATISTICAL PREDICTING SCHEME OF THE INTENSITY OF THE STH OVER THE WESTERN NORTH PACIFIC

By performing error analysis of the information from the 48-hr forecasting charts of the 500-hPa fields by the B model over eastern Asia in the period of July to September 1982 and expansions of the height fields of westerlies and the subtropical zone by use of the Chebyshev polynomial and EOF, respectively, a scheme is developed for predicting the synchronous STH coefficient (i. e. time coefficient) in terms of the Chebyshev one, thus making possible statistical forecasting of the 500-hPa subtropical field within 48 hr. Tests with independent samples indicate that, to a certain extent, this scheme can be used in operational prediction as a reference.     

NUMERICAL SIMULATIONS OF THE EFFECTS OF AEROSOLS IN THE ATMOSPHERIC BOUNDARY LAYER ON THE CLIMATE

The climatic effects of the atmospheric boundary aerosols are studied by the use of a three-dimensional climatemodel.Simulated results show that the climate states both at the surface and in the atmosphere change remarkably whenthe aerosols with different optical thicknesses and properties are introduced into the atmospheric boundary layer of themodel.The aerosols absorb and scatter the solar shortwave radiation,therefore,they reduce the solar energy reachingthe ground surface and decrease the surface and the soil temperatures.The temperature in the boundary layer increasesbecause of the supplementary absorption of radiation by the boundary aerosols.In the atmosphere,the temperatures atall isobaric surfaces rise up except for the 100 hPa level.The atmospheric temperatures below the 500 hPa level aredirectly influenced by the boundary aerosols,while the atmospheric temperatures above the 500 hPa level are influencedby the heating due to convective condensation and the changes in the vertical motion field.Cyclonic differential circula-tions appear over the desert areas at the low levels,and anticyclonic differential circulations exist at the upper levels inthe horizontal flow fields.The vertical motions change in correspondence with the differential circulations.The changesin precipitation are directly related to that of vertical motions.The mechanisms of climate effects of the boundaryaerosols are also discussed in this paper.     

THE IMPACT OF INITIAL FORCED WIND ON THE PREDICTABILITY OF THE ZEBIAK-CANE COUPLED OCEAN-ATMOSPHERE MODEL

With simultaneous observed sea surface temperature anomaly (SSTA), the difference between NCEP/NCAR 925hPa reanalysis wind stress anomaly (NCEPWSA) and FSU wind stress anomaly (FSUWSA) is analyzed, and the prediction abilities of Zebiak-Cane coupled ocean-atmosphere model (ZC coupled model) with NCEPWSA and FSUWSA serving respectively as initialization wind are compared. The results are as follows. The distribution feature of NCEPWSA matches better with that of the observed SSTA than counterpart of FSUWSA both in 1980s and in 1990s; The ZC ocean model has a better skill under the forcing of NCEPWSA than that of FSUWSA, especially in 1990s. Meanwhile, the forecast abilities of the ZC coupled model in 1990s as well as in 1980s have been improved employing NCEPWSA as initialization wind instead of FSUWSA. Particularly, it succeeded in predicting 1997/1998 El Ni?o 6 to 8 months ahead; further analysis shows that on the antecedent and onset stages of the 1997/1998 El Ni?o event, the horizontal cold and warm distribution characteristics of the simulated SSTA from ZC ocean model, with NCEPWSA forcing compared to FSUWSA forcing, match better with counterparts of the corresponding observed SSTA, whereby providing better predication initialization conditions for ZC coupled model, which, in turn, is favorable to improve the forecast ability of the coupled model.     

STUDY ON THE AIR-SEA INTERACTION ON THE INTERANNUAL TIME SCALE IN THE SOUTH CHINA SEA

In this paper we document the correlationship between sea surface temperature (SST) and lowlevel-winds such as sea level wind and 850 hPa wind in the South China Sea (SCS) based onCOADS (1958—1987) and ECMWF objective analysis data (1973—1986).Further statisticalanalyses tell us that there is a fixed SCS basin mode for variations both of SST and low-level windsin the region on the interannual time scale due to air-sea interactions.A simplified,coupled model that is designed following the McCreary and Anderson's (1985)model and includes the feedback between the upper ocean and the circulation of East Asianmonsoon demonstrates an interannual oscillation in the coupled air-sea system,which is similar tothe observations in the SCS.     

THE WIND IN THE BAROCLINIC BOUNDARY LAYER WITH THREE SUBLAYERS INCORPORATING THE WEAK NONLINEAR EFFECT

In considering the weak non-linear effect, and using the small parameter expansion method, the analytical expressions of the wind distribution within PBL (planetary boundary layer) and the vertical velocity at the top of the PBL are obtained when the PBL is divided into three layers and different eddy transfer coefficients K are adopted for the three layers. The conditions of barotropy and neutrality for the PBL are extended to that of baroclinity and non-neutral stratification. An example of a steady circular vortex is used to display the characteristics of the horizontal wind within the PBL and the vertical velocity at the top of the PBL. Some new results have been obtained, indicating that the magnitude of the speed in the lower height calculated by the present model is larger than that by the model in which k is a constant within the whole boundary layer, for example, in the classical Ekman boundary layer model and the model by Wu (1984). The angle between the wind at the top of the PBL and the wind     

A COMPARATIVE STUDY OF THE HEATING EFFECTS OF THE TIBETAN PLATEAU AND THE WESTERN PACIFIC

A zonal domain primitive equation modeling system(ZDMS)is used to study the effects of theinitial heating anomalies over the Tibetan Plateau and the western Pacific on the East Asian and theChinese summer climate,the relative importance and the mechanisms are discussed.Results showthat in spite of the different locations of the heating anomalies the influences of the two anomalyareas are much similar to each other when the scaling of the two areas is the same.The two areasof heating anomalies have their own affecting domains in which one is more important than the oth-er.In the western Pacific the heating anomaly over the western Pacific is more evident and in theTibetan Plateau area the heating anomaly over the Tibetan Plateau is more obvious.For the eastpart of China the effects of the two heating anomalies both exist and almost have the equal impor-tance.The initial anomaly of the sea surface temperature(SST)over the western Pacific can bekept during the entire time integration while in the Tibetan Plateau it can not be maintained.     

THE INTERANNUAL VARIATION OF MEDIUM-RANGE OSCILLATION CHARACTERISTICS IN THE UPPER TROPOSPHERE OVER THE SUBTROPICAL REGION

By using the power spectrum analysis, the interannual variation of medium-range oscillation characteristics in the upper troposphere over the subtropical region in China during June-August, 1966-1981 is studied. The quasi-two and quasi-one week oscillations are the two major oscillations generally existing in the subtropical region, and their intensities have obvious quasi-triennial variation period. These medium range oscillation characteristics are closely related to the South Asian high, and in some degree to the summer precipitation in China. The quasi-two week oscillation is probably a display of the inherent oscillation of the south Asian high itself, and the quasi-one week oscillation is probably that of the forced oscillation from westerly disturbances.     

ON THE INTERACTIONS BETWEEN ENSO AND THE ASIAN MONSOON ON THE SCALE OF QUASI-BIENNIAL OSCILLATION

A diagnostic analysis is performed of the quasi-biennial oscillations during the ENSO cycle and the results are based to study the interactions between ENSO and the Asian monsoons. It shows that the Asian monsoons have significant influence on the ENSO cycle on the quasi-biennial scale. Materialized through the onset and southward progression of the winter monsoon, the influence appears in the tropical western Pacific to excite severe convection and to further affect the ENSO cycle. The phenomenon is not only reflected in the quasi-biennial mode but the annual variation of the Asian winter monsoon in reality.     

THE ROLE PLAYED BY THE STRATOSPHERE IN GREENHOUSE EFFECT

Two one-dimensional radiative-convective models with the same scheme and the different ranges that one is fromsurface to stratopause and the other is from surface to tropopause,have been developed to study the role played by thestratosphere in greenhouse effect.It is shown that the addition of stratospheric response may lead to an increase of 7—50percent in radiative forcing at the tropopause,and an increase of 20—60 percent in surface temperature when the con-centration of the same gas in the two models increases at the same time;and when the same change in radiative forcing atthe tropopause due to the same agent in the two models occurs,the addition of stratospheric response may lead to an in-crease of 5—20 percent in surface temperature;and allowing for the stratospheric adjustment means that the tempera-ture responses to the same flux change due to different causes are in far disagreement.