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Warren M. Washington
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Warren M. Washington

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This paper shows that a general circulation model at the National Center for Atmospheric Research is capable of simulating many aspects of the Asian-African winter monsoon. We concentrate on a climatological descriptive comparison of wind patterns, particularly the reversed flow of the low-level Somalian jet near the east coast of Africa, sea-level pressure, and cloudiness and precipitation over the monsoon region.

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Warren M. Washington

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We describe in this paper a set of general circulation model experiments on possible climate changes caused by man's generation of thermal energy or pollution. Three experiments were carried out: one in which we introduced only a small initial error, one in which we added the expected ultimate levels of thermal energy generation, and one in which we added a negative amount of thermal energy. In an three experiments, we obtained the same results, indicating that the thermal pollution effect is probably small compared to the natural fluctuations of the model. We also discuss some limitations of the present model for inferring the proper climatic-change response.

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William Blumen and Warren M. Washington

The scope of activities and accomplishments in areas of atmospheric dynamics and numerical weather prediction under investigation in the People's Republic of China during the period 1949–1966 is surveyed. The principal topics considered include cumulus and turbulent boundary layer dynamics and the dynamics of meso-, synoptic-, and planetary-scale motions. Attention is focused on the complementary research paths followed in theoretical and numerical dynamics, particularly in relation to the development of operational forecasting models. These latter accomplishments are traced from the late 1950s until mid-1966, at which time overseas distribution of Chinese scientific journals was discontinued. Significant investigations of both regional and global circulation regimes have also been noted. However, a more exhaustive overview of the contributions made by Chinese meteorologists to the theory of the general circulation appears warranted.

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WARREN M. WASHINGTON and AKIRA KASAHARA

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Results of a January simulation experiment with the two-layer version of the NCAR global circulation model are discussed. The model includes a hydrological cycle, horizontal and vertical turbulent transports of momentum, heat, and water vapor from the lower boundary and within the atmosphere, and calculations of solar and terrestrial radiation. Although the water vapor field interacts with the radiation calculations, the cloud distribution is a function of latitude and season. In this version of the model, the earth's orography is omitted as well as an explicit calculation of the surface temperature.

This version of the model has a spherical horizontal mesh spacing of 5° in both longitude and latitude and two vertical layers at 6-km height, increments. The details of the finite-difference scheme for the model are presented.

The initial conditions for this experiment are based on an isothermal atmosphere at rest. The zonal mean cloudiness, the mean sea level temperature distribution, and the sun's declination are specified for January. The early stage of the numerical integration is characterized by a Hadley-type direct circulation due to the thermal contrasts between the continents and oceans. Within 2 weeks, the Hadley circulation breaks down due to baroclinic instability. This results in the typical three-cell meridional circulation. The comparison between computed and observed January climatology is discussed together with the presentation of momentum, moisture, and energy budgets. The main result from these budget calculations is that the Hadley cell is of dominant importance in the transport of various quantities within the Tropics and that baroclinic eddies are important in midlatitudes.

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Akira Kasahara and Warren M. Washington

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This paper describes the method of incorporating into the NCAR global circulation model the dynamic effect of mountains, the prediction of cloudiness for radiation calculations, and the calculation of ground surface temperature using a heat balance equation. Other aspects of the physics of the model and the finite-difference schemes are very similar to those discussed by the authors in 1967 and 1970. For the simulation of seasonal climate we specify two parameters: the sun's declination and the distribution of ocean surface temperatures. Since the prediction of cloudiness is parameterized in terms of the relative humidity and the vertical motion fields, solar and atmospheric radiation processes interact closely with the dynamics of the atmosphere through variations in the fields of cloudiness, temperature and water vapor. Coupling between radiation and dynamics helps to maintain stronger baroclinic activity in middle latitudes. Although a hydrologic cycle is included in the model atmosphere and the ground surface temperature is computed, a hydrologic cycle in the ground is not taken into account. Instead, it is assumed that the latent heat transport from the ground to the atmosphere and the soil heat transport below the surface are both functions of the sensible heat transport between the ground and the atmosphere.

Experiments are conducted to simulate January climate with and without the earth's orography. In both experiments the domain of continents, the January mean ocean surface temperatures, and the sun's declination for mid-January are unchanged during the time integrations. The model has a spherical horizontal mesh spacing of 5° in both longitude and latitude and six vertical layers at 3-km height increments. The time step is 6 min and both cares are integrated up to 80 days starting from an isothermal atmosphere at rest. The results of the 41–70 days of the time integration are analyzed for various diagnostic studies. Synoptic comparisons of the two experiments are made for selective meteorological variables to discuss the relative importance of the thermal and orographic influences upon the large-scale motions of the atmosphere. Detailed studies are made on the balance of momentum, water vapor, heat and energy. The present experiments indicate that the six-layer and 5° mesh model can simulate successfully a January climate and that the earth's orography plays a minor role over the thermal effect of continentality in determining the major features in the transport mechanism of momentum, water vapor, heat and energy in terms of the zonal mean state. However, for the regional aspects of general circulation the effects of orography are significant.

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AKIRA KASAHARA and WARREN M. WASHINGTON

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This paper describes a model of the general circulation of the earth's atmosphere which has been developed and experimented with, since 1964, at the National Center for Atmospheric Research (NCAR), Boulder, Colo. A distinguishing feature of the NCAR model is that the vertical coordinate is height rather than pressure, though hydrostatic equilibrium is maintained in the system. In fact, the dynamical framework of the model is very similar to the one proposed by L. F. Richardson in 1922.

Various physical processes in the atmosphere, such as energy transfer due to solar and terrestrial radiation, small-scale turbulence and convection, etc., are incorporated in the model. An explicit prediction of the moisture field is avoided. Instead, it is assumed that the atmosphere is completely saturated by water vapor. Thus, the release of latent heat of condensation can be computed. In addition to a description of the model, the equations for the zonal mean and eddy energy are presented. Finally, a baroclinic stability analysis of the model is made in order to gain an insight into the finite-difference formulation of the present model. Long term (over 100 days) numerical integrations are being performed successfully with a two-layer version of the present model. Details of finite-difference schemes and the results of numerical calculations will be described in a separate article.

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Warren M. Washington and Robert M. Chervin

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January and July experiments were performed with the NCAR general circulation model (GCM) to assess the potential climatic impact of the thermal energy released from a projected United States cast coast megalopolis circa 2000 A.D. The model has six layers in the vertical and a 5° latitude-longitude horizontal resolution. The ocean surface temperatures were held fixed with respect to time in both experiments at the appropriate observed climatological values for each month. To determine the statistical significance of the model response, sets of random perturbation experiments were performed for each month to obtain a measure of the model noise level (i.e., the estimated standard deviation of monthly means). Larger surface temperature changes are found in the January thermal pollution experiment. with a maximum of 12°C in the vicinity of the beat input. Smaller but still significant changes with a maximum of 3°C are found in the July experiment. Significant changes in precipitation and soil moisture also result in the prescribed change region. However, neither experiment produces any evidence of a coherent statistically significant downstream response or “teleconnection” over the Atlantic Ocean or Europe.

Although these experiments are not complete climate change experiments, in that the ocean surface temperatures and sea ice distributions are not permitted to respond to the inputed waste heat, they do demonstrate the sensitivity of a current “state of the art” GCM to such surface forcing. Furthermore, the necessity of considering different seasons in performing climatic impact studies is made apparent by the vastly different model response in the January and July experiments with the identical prescribed change in surface forcing.

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David L. Williamson and Warren M. Washington

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Yongqiang Liu, Filippo Giorgi, and Warren M. Washington

Abstract

A summertime season climate over east Asia is simulated with a regional climate model (RegCM) developed at the National Center for Atmospheric Research (NCAR) to validate the model's capability to produce the basic characteristics of monsoon climate over the region. The RegCM used here is a modified version of the NCAR-Pennsylvania State University Mesoscale Model (MM4), in which the Biosphere-Atmosphere Transfer Scheme and a detailed radiative transfer package have been implemented for climate application. The model horizontal resolution is 50 km, and the domain covers a 5200 km × 4700 km area encompassing eastern Asia and adjacent ocean regions. The simulation period is June–August 1990, and the model-driving initial and lateral boundary conditions are from European Centre for Medium-Range Weather Forecasts analyses of observations. The simulated patterns of the monsoon circulation, precipitation, and land-surface temperature are in general agreement with observations, although the model is somewhat too dry and cool. Furthermore, the RegCM captures terrain-induced local rain maxima and temperature centers. Three special aspects of the model results are examined for assessment of model performance: 1) the RegCM reproduces the entire progress of a summer monsoon and the accompanying rain belt, including different steady phases and sudden transitions between two adjacent phases; 2) the paths of tropical storms occurring during the simulated period are closely traced by the model; and 3) realistic patterns of soil moisture are simulated.

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