GLIMMER Antarctic Ice Sheet Model,an experimental research of moving boundary condition

A 3-D coupled ice sheet model, GLIMMER model is introduced, and an idealized ice sheet experiment under the EISMINT-1 criterion of moving boundary condition is presented. The results of the experiment reveal that for a steady-state ice sheet profile the characteristic curves describe the process of evolution which are accordant with theoretical estimates. By solving the coupled thermodynamics equations of ice sheet, one may find the characteristic curves which derived from the conservation of the mass, energy and momentum to the ice flow profile. At the same time, an agreement, approximate to the GLIMMER case and the confirmed theoretical results, is found. Present study is explorihg work to introduce and discuss the handicaps of EISMINT criterion and GLIMMER, and prospect a few directions of the GLIMMER model.

On a Simple Dynamics Model of Interaction between Oasis and Climate

This paper constructs a coupled system of oasis and atmosphere based on an oasis evolvement model by adding atmospheric motion to discuss the problem of oasis evolvement and its effects on regional climate. The results indicate that the range and scope of the negative temperature anomalies become larger when the oasis cover fraction increases. Correspondingly, the positive temperature anomalies becomes smaller in the desert no matter in summer or spring. And the variability is more obvious in summer than in spring. So it may be concluded that the oasis not only maintains and develops itself but also develops partial air over the desert into an oasis climate.

ENSO Indices and Analyses

New ENSO indices were developed and the spatial variability and temporal evolution of ENSO were analyzed based on the new indices and modeling experiments, as well as multiple data resources. The new indices, after being defined, were validated with their good diagnostic characteristics and correlation with wind and SST. In the analysis after the definition and validation of the new indices, ENSO feedbacks from wind, heat fluxes, and precipitation were spatially and temporally examined in order to understand ENSO variability and evolution with some emphasized points such as the interaction among the feedbacks, the role of westerly wind bursts and the transformation between zonal and meridional circulations in an ENSO cycle, and the typical pattern of modern ENSO.

Climatic Study on the Summer Tropical Easterly Jet at 200 hPa

The low latitude easterlies at 200 hPa in summer (May-October) is analysed climatically during the 13-year period from 1968 to 1980, with a special emphasis on the relationships between the anomalous tropical easterly jet Stream over South Asia and the low latitude atmospheric circulation, and also the summer monsoon precipitation in India. The compositing analysis shows that the tropical easterly jet stream over South Asia has five anomalous patterns at 200 hPa i.e. the western pattern, middle pattern, eastern pattern, two-branch pattern and multi-core pattern. Evidence has shown that the precipitaion in India anomalously increased during the anomalous period of the western pattern and the middle pattern, but reverse case is true in the eastern pattern. Some different anomalies of the precipitation in different area of India were found during the other two anomalous pattern.

Role of sea ice in air-sea exchange and its relation to sea fog

Synchronous or quasi-synchronous stereoscopic sea-ice-air comprehensive observation was conducted during the First China Arctic Expedition in summer of 1999. Based on these data, the role of sea ice in sea-air exchange was studied. The study shows that the kinds, distribution and thickness of sea ice and their variation significantly influence the air-sea heat exchange. In floating ice area, the heat momentum transferred from ocean to atmosphere is in form of latent heat; latent heat flux is closely related to floating ice concentration; if floating ice is less, the heat flux would be larger. Latent heat flux is about 21 23 6 W·m -2, which is greater than sensible heat flux. On ice field or giant floating ice, heat momentum transferred from atmosphere to sea ice or snow surface is in form of sensible heat. In the floating ice area or polynya, sea-air exchange is the most active, and also the most sensible for climate. Also this area is the most important condition for the creation of Arctic vapor fog. The heat exchange of a large-scale vapor fog process of about 500000 km 2 on Aug. 21 22,1999 was calculated; the heat momentum transferred from ocean to air was about 14 8×10 9 kW. There are various kinds of sea fog, radiation fog, vapor fog and advection fog, forming in the Arctic Ocean in summer. One important cause is the existence of sea ice and its resultant complexity of both underlying surface and sea-air exchange.

Critical Time Span and Nonlinear Action Structure of Climatic Atmosphere and Ocean

This paper studies the critical time span and the approximate nonlinear action structure of climatic atmosphere and ocean. The critical time span of the climatic atmosphere and ocean, which is related to the spatial resolution required, the strength of nonlinear action, and the calculation exactness, may represent the relative temporal scale of predictability. As far as the same characteristic spatial scale is concerned, the minimum critical time span of the ocean is about 9 times of that of atmosphere, several days or more. Usually, the stronger the nonlinear action, the shorter the critical time span with smooth changes of external forces. The approximate structure of nonlinear action of climatic atmosphere and ocean is: the nonlinear action decreases usually with increasing latitude, which is related to the role of the Coriolis force in fluid motion (forming geostrophic current); the nonlinear action changes with the anomalous cyclonic or anticyclonic circulation shear, for instance, when the strength of anomalous eastward zonal circulation is comparable to that of anomalous meridional circulation, the nonlinear action is the strongest; wind stress plus gradient forces enhance the nonlinear action, etc.

Predictability of the 500 hPa Height Field

The dimensions of attractors and predictability are estimated from phase space trajectories of observed 500 hPa height over the Northern Hemisphere. As a first estimate the dimensions of attractors are about 11.5 and the doubling time of the initial error is 6 to 7 days for original data. But the former is shorter and the latter is longer for low frequency data set.To verify if the predictability estimated by this method and by general circulation model is identical, the doubling time of the initial error of a model data set by both methods is estimated. It is shown that the predictability obtained from phase space trajectories is overestimated to sufficient small initial error. But it is underestimated to the time being equal to the climatological RMS error.

Medium-Range Oscillations in the Summer Tropical Easterlies at 200 hPa

By the use of space-time spectral analysis and band-pass filter, some of the features of the medium-range oscillations in the summer tropical easterlies (10 S-20 N) at 200 hPa are investigated based on a two-year (1980 and 1982) wind (u, v) data set for the period from May to September. Space-time power spectral analysis shows that the total energy of the westward moving waves was the largest and that of the standing waves and eastward mov ing waves was relatively small in the 200 hPa easterlies: the total energy of the eastward moving waves was m minimum at 10° N. Three kinds of the medium-range oscillations with about 50 day, 25 day and quasi-biweekly periods were found in the easterlies, which all show a remarkable interannual variations and latitudinal differences in these two years. The wave energy of zonal wind is mainly associated with the planetary waves (1-3). which all may make important contributions to the 50 day and 25 day oscillations in different years or different latitudes, The quasi-biweekly oscillation is mainly related to the synoptic waves (4-6). In equatorial region, the 50 day oscillation was dominant with a eastward phase propagation in 1982 while the dominant oscillation in 1980 was of 25 day period with a westward phase propagations in 1980. Both of them are of the mode of zonal wavenumber 1. Strong westward 50 day oscillation was found in 10° N-20° N in these two years. Regular propagations of the meridional wind 50 cay oscillation were also found in the easterlies.The 50 day and 25 day oscillation of zonal wind all demonstrate southward phase propagation over the region of the South Asia monsoon and northward phase propagation near international date line, where are the climatic mean position of the tropical upper-tropospheric easterly jet and the tropical upper tropospheric trough (TUTT). respectively.

STUDY OF PHYSICAL PROCESSES AFFECTING THE TRANSFORMATION OF COLD AIR OVER LAND AFTER OUTBREAK OF COLD WAVES IN EAST ASIA

Authors have studied the transformation processes of cold air over land in East Asia for eight cases which occurred in different months of 1981.First,the surface eddy sensible and latent heat fluxes,and drag coefficient were estimated according to the approach of similarity theory.Then,the apparent heat source,the apparent moisture sink,and solar and long-wave radiative heating(or cooling)were further calculated through the budget method and physical parameterization algorithm.It has been found that the cold air immediately starts the transformation process over land once it moves away from its region of origin.In winter,the degree of transformation of cold air mass gradually intensi- fied as it travelled southeastward;while arriving in the ocean,the cold air mass underwent the most significant transfor- mation process.In summer,the most vigorous transformation of thermal and moisture fields was observed in North China and Mongolian region,with much greater intensity than that in winter.

INERTIAL THEORY FOR OCEANIC CROSS-EQUATORIAL JET

In this paper, a theory for inertial boundary layer is developed to study the northward forced and the southward induced cross-equatorial jets by easterlies in the Southern Hemisphere in west and east boundaries respectively. The solutions of the nonlinear potential vorticity equation and the Bernoulli equation show that subtle changes of the physical parameters can produce different equi- librium states and the velocity of these jets all can reach 10°m/s which are comparable to observa- tions. Simulations show that the induced current in the east boundary is very important to the for- mation of the local eastward equatorial current in the east boundary. This can be used to study the characteristics of the local surface eastward equatorial current during E1 Nino periods,

NUMERICAL SIMULATION OF FRONTOGENESIS FORCED BY DUST RADIATIVE HEATING

In this paper,the frontogenesis forced by dust radiative heating and the radiative effects of an isolated duststorrn on a frontal circulation system are examined by means of two-and three-dimensional numerical models.Results indicate that as a duststorm breaks out, frontogenesis is caused in by dust radiative heating in the lower atmosphere.A marked isentropic potential temperature layer is formed in the middle troposphere.The low-level convergence occurs along the direction of the front movement.Atnight,dust radiative cooling results in frontolysis in the lower atmosphere. An obvious vertical circulation is forced by radiative heating of an isolated duststorm along the direction of the pre- vailing wind.It is stronger at day,weaker and reverse at night.The response of the horizontal wind field to dust radiative forcing is different at different levels.

THE FOUNDATION AND MOVEMENT OF TROPICAL SEMI-GEOSTROPHIC ADAPTATION

The breakdown and foundation of geostrophic balance is one of the important movements in the mid-and high-latitude atmosphere and oceans.In the tropical area,the value of Coriolis pa- rameter is so small that it is difficult to satisfy the bi-geostrophic equilibrium between the pressure and velocity fields.However,in the tropical area,the zonal velocity of some motions in the atmo- sphere and oceans is large,so the Coriolis force is not small,geostrophic balance can exist in zonal direction,i.e.semi-geostrophic balance.Furthermore,in the dominant area of Hadley circulation in the atmosphere or the area near the ocean meridional boundary,the meridional velocity is large, so geostrophic balance can also exist in meridional direction.In this paper,the process of the dis- persion of inertial gravity wave and the foundation of semi-geostrophic balance are first discussed. Second,the adjustment process between the velocity and pressure fields after adaptation is also viewed,and the scale criterion of the semi-geostrophic adaptation is discussed,i.e.for the motion with meridional scale greater than the equatorial Rossby radius of deformation,the velocity and pressure fields after adaptation change to fit the initial pressure field;on the contrary,the fields change to fit the initial zonal velocity field,and the strength of the fields after adaptation depends on the zonal scale.

THE CLIMATIC CHARACTERISTICS OF THE SUBTROPICAL HIGH IN WEST PACIFIC FROM SATELLITE OBSERVATIONS

The activities of Subtropical High (SH)in West Pacific (WP)during summer are much related to the rainfall of eastern China, to which attention has been paid by many weather forecasters. In the early 1960s, Tao et al. studied the climatic activities of SH by using the height field of observation data set and showed that there was close relation between the seasonal northward shifts of SH and the seasonal northward displacement

NUMERICAL EXPERIMENT OF THE INFLUENCES OF HEAT AND WIND STRESS ON THE EQUATORIAL OCEAN CIRCULATION

A time-dependent linear model on the equatorial beta plane is developed in this paper.Its vertical structure consists of two active layers with equal density and temperature above the thermocline and a quasi-stationary layer with constant density below the thermocline. The results of numerical experiments show that the direct influence of heat on the equatorial ocean is much smaller than that of wind stress.Nevertheless,through the tropical ocean-atmosphere interaction, the change of wind stress resulting from the thermal forcing may set a determinant effect on the equilibrium and anomalous development of the ocean-atmosphere circulation.

INSTABILITY OF THE OCEANIC WAVES IN THE TROPICAL REGION

In this paper, the effects of the large-scale mean sea temperature fields of the tropical ocean and the zonal current field (southern equatorial current) have been comprehensively entered in consideration on the basis of Chao and Ji (1985), and Ji and Chao (1986), the equatorial oceanic waves of the tropical ocean have been discussed by use of linearized primitive equations, then, the significant influence of the climatic back- ground fields of the tropical ocean upon the oceanic waves of this region has been further testified. When very cold water appears in the tropical region, and the southern equatorial current is also relatively strong, the effect of the Rossby wave weakens, as a consequence, there are substitutive slow waves (i.e. thermal waves) which travel in opposite direction (eastward) to the Rossby wave. The characteristics of the slow wave are similar to those of Rossby waves, only the travelling direction is opposite. Under a certain environ- mental background field, the slow wave and the modified Rossby wave may be instable. With this conclu- sion, the mechanism of the occurrence, development and propagation of El Nino events has been studied. It is pointed out that the opposite travelling direction of the thermal wave and Rossby wave will bring re- pectively into action under different marine environmental background fields. The physical causes for that the abnormal warm water inclines to occur along the South American coast have also been explored in this paper.

NUMERICAL EXPERIMENTS ON THE TROPICAL AIR-SEA INTERACTION WAVES

By means of the numerical method,the tropical air-sea interaction waves are studied.The results show that when the Kelvin waves are filtered out and only the equatorial Rossby waves are reserved both in the atmosphere and in the ocean,the disturbances can also propagate eastward because of the air-sea interaction.The critical wavelength of the eastward propagating waves is related to the intensity of the air-sea interaction.The stronger the air-sea interaction,the larger the eastward propagating components of the air-sea interaction waves.The results of the numerical experiments are in good agreement with those of the theoretical analysis(Chao and Zhang,1988).

THE OBSERVATIONAL COMPARISON OF TEMPERATURE STRATIFICATION BY SODAR OVER THE MOUNTAIN, URBAN AND SUBURBAN AREAS OF BEIJING IN AUTUMN

I.INTRODUCTION The temperature stratification is an important factor which strongly influences the transportation and diffusion processes of pollutants in atmospheric boundary lay-

PHYSICOCHEMICAL PROPERTIES OF SEA SURFACE LAYER AEROSOL OVER THE WESTERN PACIFIC

This report uses information obtained from the first cruise operated by the Sino-American cooperative sea-air interaction program in December 12, 1985—February 21, 1986 to discuss the physicochemical properties of marine aerosol over the western Pacific.

A NEW CUMULUS PARAMETERIZATION SCHEME AND ITS APPLICATION TO PRECIPITATION NUMERICAL PREDICTION

According to the characteristics of cumulus and stratiform clouds during the meiyu period (plum rains) over Jianghuai valleys (the Changjiang (Yangtze) River and the Huaihe River), a modified Kuo-type cumulus parameterization scheme applicable to midlatitude con-vective systems is suggested in this paper. It is often observed that cumulus and stratiform clouds coexist in a rain-bearing synoptic systems and the precipitation amount associated with this system may be amplified by their interaction. With some important processes of cloud physics taken into account, we use a simple seeder-feeder model (including colloidal instability, collision effect and entrainment) to describe this process of interaction within framework of Kuo-type cumulus parameterization. It is found that the rainfall amount caused by ice crystal effect accounts for 30-40% of total rainfall, but the collision effect is not so great generally. We introduced this scheme to the regional numerical model used by Wuhan Observatory of Hubei Meteorological Service to make tests of its performance. With six experiments of prediction of precipitation during the meiyu period, the results are very encouraging, especially good in the cases of coexistence of cumulus and stratiform clouds.

Interaction between sea ice of the Antarctic and Arctic

Sea ice of the Antarctic and Arctic are two huge heat sinks of global atmosphere-ocean thermal machine, and give a significant effect on global atmospheric circulation and climate. Up to now, most of the studies on sea ice on the two polars and their relationship with atmospheric circulation are limited to sea ice variation of the Antarctic and the Arctic and their separate relationship with climatete. This note will do a comprehensive research with a principal foothold on global scale. In addition to their separate impact on