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W. S. Harley

Abstract

Thirty years of daily 1000–500 mb thickness data from 25–90°N latitude at 383 grid points are used to obtain charts of mean temperature change in the lower troposphere between successive 5-year periods from 1949–53 to 1974–78 [1000–500 mb thickness is proportional to the mean (virtual) temperature of the layer]. These charts are then intersected in succession to determine areas of negative or positive trends lasting 25 years or more. A negative trend lasting 25 years is found in four areas and a positive trend in one, while an unbroken negative trend is found in two of the four areas.

The layer mean temperature changes between 5-year periods are averaged over all grid points within four latitude belts. Warming is found between the 1954–58 and 1959–63 periods and a stronger cooling between the 1959–63 and 1964–68 periods in all four belts. The analysis also shows that cooling is accompanied by a significant increase in the number of negative layer mean temperature changes at individual grid points (indicating an increase in the total area experiencing temperature decrease).

Time series of 5-year, annual and seasonal mean 1000–500 mb thickness values for the areas of cooling or warming are analyzed to determine the characteristics of the trends within each area. Areas containing only one grid point are increased in size to at least 106 km2 by the inclusion of surrounding grid points to reflect regional rather than merely local influences. A negative trend extending over the 30-year period is found in the east Asia area in summer. A positive trend of 25 years is found in north Iran in the fall.

Five-year mean 1000–500 mb thickness values over the 30-year period in each area are examined for evidence of climatic change using criteria proposed by Rosini. Evidence of a change to a cooler regime in the lower troposphere is found in East Asia in summer, and in eastern North America in winter. Thirty years of data are found of insufficient length to determine whether the cooling constitutes a climatic change under the given criteria. No evidence of climatic warming is found.

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W. S. Harley

Abstract

A complete operational method for quantitative precipitation forecasting (Q.P.F.), is developed by combining the technique for determining large scale vertical velocities by Penner with one for determining precipitable water content using 1000–500-mb thickness lines and the Godson precipitation rate formula. Methods are included for taking into account the effects of initial unsaturation, topography, release of latent heat during condensation, friction, release of potential instability and height of cloud base. A case study is presented to illustrate the results of the method and an example is given of a complete Q.P.F. computation.

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W. S. Harley

Abstract

Deviations of the 1000–500 mb thickness from the 1949–76 mean (the period of record) and from the 1965–76 mean (a period of apparent warning in the lower troposphere) are presented for the Northern Hemisphere (25–85°N), the arctic (70–85°N), and the low-latitude belt (25–40°N). Results are compared with those obtained by other investigators from surface and upper air data.

A dramatic drop in the mean temperature of the lower troposphere to the lowest point of the record occurred between January 1975 and August 1976. This cooling followed a slow warming trend between 1965 and 1975 which was greater at low latitudes than in the arctic.

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C. P. Weaver, X.-Z. Liang, J. Zhu, P. J. Adams, P. Amar, J. Avise, M. Caughey, J. Chen, R. C. Cohen, E. Cooter, J. P. Dawson, R. Gilliam, A. Gilliland, A. H. Goldstein, A. Grambsch, D. Grano, A. Guenther, W. I. Gustafson, R. A. Harley, S. He, B. Hemming, C. Hogrefe, H.-C. Huang, S. W. Hunt, D.J. Jacob, P. L. Kinney, K. Kunkel, J.-F. Lamarque, B. Lamb, N. K. Larkin, L. R. Leung, K.-J. Liao, J.-T. Lin, B. H. Lynn, K. Manomaiphiboon, C. Mass, D. McKenzie, L. J. Mickley, S. M. O'neill, C. Nolte, S. N. Pandis, P. N. Racherla, C. Rosenzweig, A. G. Russell, E. Salathé, A. L. Steiner, E. Tagaris, Z. Tao, S. Tonse, C. Wiedinmyer, A. Williams, D. A. Winner, J.-H. Woo, S. WU, and D. J. Wuebbles

This paper provides a synthesis of results that have emerged from recent modeling studies of the potential sensitivity of U.S. regional ozone (O3) concentrations to global climate change (ca. 2050). This research has been carried out under the auspices of an ongoing U.S. Environmental Protection Agency (EPA) assessment effort to increase scientific understanding of the multiple complex interactions among climate, emissions, atmospheric chemistry, and air quality. The ultimate goal is to enhance the ability of air quality managers to consider global change in their decisions through improved characterization of the potential effects of global change on air quality, including O3 The results discussed here are interim, representing the first phase of the EPA assessment. The aim in this first phase was to consider the effects of climate change alone on air quality, without accompanying changes in anthropogenic emissions of precursor pollutants. Across all of the modeling experiments carried out by the different groups, simulated global climate change causes increases of a few to several parts per billion (ppb) in summertime mean maximum daily 8-h average O3 concentrations over substantial regions of the country. The different modeling experiments in general do not, however, simulate the same regional patterns of change. These differences seem to result largely from variations in the simulated patterns of changes in key meteorological drivers, such as temperature and surface insolation. How isoprene nitrate chemistry is represented in the different modeling systems is an additional critical factor in the simulated O3 response to climate change.

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