Search Results

You are looking at 1 - 10 of 40 items for

  • Author or Editor: Warren M. Washington x
  • Refine by Access: All Content x
Clear All Modify Search
Warren M. Washington

Abstract

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.

Full access
Warren M. Washington
Full access
Warren M. Washington

Abstract

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.

Full access
Warren M. Washington
and
Robert M. Chervin

Abstract

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.

Full access
Warren M. Washington
and
David P. Baumhefner

Abstract

A simple method of reducing the amplitude of Lamb waves in primitive equation model forecasts has been proposed and tested. This method makes use of a Boussinesq-type approximation in which the vertical mean mass divergence is set equal to zero. It effectively reduces the Lamb waves by a factor of 3 in the example shown here and does not degrade the forecast accuracy. The largest reduction in Lamb wave amplitude is found in the tropical regions.

Full access
David L. Williamson
and
Warren M. Washington

Abstract

Full access
David L. Williamson
and
Warren M. Washington

Abstract

This paper presents results of experiments designed to test the importance of arithmetic precision in short-term forecasts and long-term climate simulations with the NCAR global circulation model. It is expected that the next-generation computers will have a sizable speed gain when using lower-precision arithmetic. To determine how precision affects the model results, we compare several short- and long-term experiments using 48-bit mantissa arithmetic (normal for the CDC 6600 and 7600 computers) with corresponding experiments using 24- and 21-bit mantissa arithmetic. The errors due to the lower precision are much smaller than typical observational errors. In addition, it appears that in the short-term experiments the rapid error growth of the model dominates the round-off error accumulation resulting from the lower-precision arithmetic. Therefore, the lower precision used by the next-generation computers should not have a detrimental effect on short-term forecast accuracy. The long-term climate simulation experiments indicated a very similar conclusion. Even though there were some differences in the results of the experiments, climate indicators such as zonal wind, zonal temperature or eddy transport are quite similar.

Full access
Akira Kasahara
and
Warren M. Washington

Abstract

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.

Full access
Gerald A. Meehl
and
Warren M. Washington

Abstract

Area-averaged surface hydrological processes from two global spectral general circulation climate models coupled to simple slab-ocean mixed layers are compared for the climates simulated with present-day (control) and increased atmospheric carbon dioxide (CO2). The models were developed at the National Center for Atmospheric Research (NCAR) and the Geophysical Fluid Dynamics Laboratory (GFDL). Both models use highly parameterized surface processes and the so-called “bucket” (15-cm field capacity) soil-moisture method. For increased CO2 compared to the control, both models simulate more snowmelt in winter and early spring and less in late spring. more runoff in early spring and less in late spring, and increased precipitation, evaporation, and latent-heat flux, particularly in sprint However, the models differ in several key respects for the increased CO2 compared to the control. In spite of a qualitatively similar annual cycle of soil moisture, the NCAR model simulates soil-moisture amounts much less than saturation, while the GFDL model shows soil moisture near saturation in winter and spring. Therefore, the runoff is significantly less in the NCAR model than in the GFDL model. Accordingly, the increased winter and spring precipitation with increased CO2, (similar in both models) mostly runs off in the GFDL model, but is retained in the soil-moisture “byckets” at most gridpoints in the NCAR model. The increased springtime evaporation rate (also similar in both models) results in a soil-moisture deficit in the GFDL model almost as soon as the warm season begins, while in the NCAR model the excess soil moisture retained in the “buckets” during winter and spring must first be evaported before a soil-moisture deficit can occur. This delays or even prohibits a “summer drying” which is noted in the GFDL model. In addition, a soil-moisture-cloud-precipitation feedback occurs which either prolongs the soil-moisture surplus well into the warm season (NCAR) or further accentuates the summer dryness (GFDL). The critical factor determining the magnitude of the summer drying is the soil-moisture amount in the control case, particularly during spring. The highly parameterized hydrology in the models, lack of appropriate observed data, and complexity of hydrological processes in the real world prohibit accurate verification and/or Calibration of the parameterizations in the models. Observed estimates of surface runoff based on streamflow suggest that the NCAR model is simulating too little soil moisture and the GFDL model too much. This would imply that, when both models use the highly parameterized bucket method, the NCAR model is underestimating and the GFDL overestimating summer dryness due to of an increase of CO2.

Full access
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.

Full access