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T. M. L. Wigley

Abstract

The one-dimensional theory for the condensation of buoyant plumes is extended to include supersaturation as an extra variable. An additional equation describing the dynamics of droplet growth is used to make the system tractable. Some simple mathematical results are obtained which allow one to relate the theory to, and so extend, a commonly used graphical representation of the condensation process. The theory is then simplified to a single nonlinear first-order differential equation for the condensed water content. This is solved numerically for a typical jet, scrubbed industrial plume and natural-draft cooling tower plume to obtain down-plume profiles of condensed water content, supersaturation and mean droplet size. High supersaturation is predicted in all three cases, corresponding to mean relative humidities of up to 170% (jet), 150% (scrubbed plume) and 105% (cooling tower). These results may be important in predicting the growth of “foreign” carry-over droplets in plumes from industrial sources or cooling towers. Predictions of plume length in these cases is found to be insensitive to supersaturation, but plume length is noticeably affected by supersaturation in the case of a jet. In the examples considered maximum mean droplet radii never exceed 10 μm which supports the belief that rain-out is caused primarily by carry-over from imperfect mist eliminators.

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T. M. L. Wigley

Abstract

The application of the maximum plume rise formula for bent-over industrial plumes to visible cooling tower plumes depends on the validity of two assumptions: the neglect of finite source size and the neglect of condensation effects. These produce errors which, in many cases, tend to compensate. The effect of finite source size is examined analytically and an alternative formula for maximum plume rise is derived.

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T. M. L. Wigley

Abstract

This paper presents the results of a numerical solution of the equations of moist plume rise and compares the trajectories of wet and dry cooling tower and scrubbed industrial plumes under a wide range of atmospheric stability conditions. Similar comparisons have been made previously by Wigley and Slawson, Hanna, and Weil, and the results of these authors are discussed. It is found that their results are all qualitatively correct, but that there are important quantitative differences between their results and the numerical solution. Previous approximate analytic results have shown that the critical lapse rate for the transition to unstable plume behavior for wet plumes is close to the saturated adiabatic lapse rate. The more-complete numerical solution confirms this result when one allows for the variation of the saturated adiabatic lapse rate with height. The approximate analytic formula for the maximum height of rise of dry plumes is also examined and found to overestimate plume rise by 6–20% when compared with the numerical solution.

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T. M. L. Wigley and P. R. Slawson

Abstract

The theory of moist bent-over plume behavior given by Csanady and by Wigley and Slawson is expanded and clarified to illustrate the differences between moist and dry plume behavior under various atmospheric stability conditions associated with linear gradients of temperature and humidity. If plume types are defined according to the behavior of a dry plume in stable, neutral and unstable conditions, then it is found, for example, that a condensed (or ‘wet’) plume rising in an atmosphere with lapse rate equal to the saturated adiabatic lapse rate will behave as a ‘neutral’ plume, while a dry plume in the same atmosphere will behave as a ‘stable’ plume. Also, while the condensed portion of a given plume rises according to one stability criterion, the re-evaporated portion may rise according to another.

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P. D. Jones and T. M. L. Wigley

Abstract

The reliability of the Australian (June 1972–April 1985) and NOTOS (1957–62) gridded monthly-mean, mean sea level pressure datasets over Antarctica is examined by comparison with station data from 29 sites over the continent. After rejecting about 30% of the months in both sets of gridded data, the remaining “good” months are used in a principal component motion technique to reconstruct gridded data from the station data for 1957 to 1985. The regression technique uses the “good” Australian data for calibration and verifies the statistical relationships developed between station and grid point pressure data with the “good” NOTOS data. The reconstructions are shown to be reliable over all of Antarctica between 60° and 75°S except in the area to the east of the Ross Sea and adjacent areas of the southern Pacific Ocean.

The reconstructions are used to compare the NOTOS data with the more recent Australian gridded pressure data. Major differences between the two datasets are found over eastern Antarctica and the extreme southern Pacific and adjacent areas of western Antarctica. The first problem region was found to be related to extrapolation of the NOTOS data beyond their region of reliability as defined by the original published maps. The second problem region has a 10 mb difference between the two datasets, with the NOTOS data higher than the Australian. As this is the region of poorest data coverage anywhere in the world, the difference is difficult to resolve. In contrast, comparisons with the Taljaard et al. (1969) climatology show that this dataset contains fundamental spatial inconsistencies, and its further use cannot be recommended.

A composite dataset linking the Australian, NOTOS and the reconstructed data can be produced for the whole region except for the southern Pacific and wet Antarctic region. This extended dataset is used to examine changes in pressure patterns between the January 1957–May 1972 and June 1972–April 1985 periods. Some of the changes in temperature that have occurred over this period can be explained by changes in surface circulation patterns.

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T. M. L. Wigley and P. R. Slawson

Abstract

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T. M. L. Wigley and P. R. Slawson

Abstract

The theory of growth of dry plumes is extended to include the effects of moisture in both the vapor and liquid forms. A relation determining the point at which a moist plume first condenses is derived. Numerical solutions of this relation indicate that, under most atmospheric conditions, condensation either occurs very close to the stack or not at all. A method for predicting whether or not condensation will occur for arbitrary conditions of atmospheric relative humidity and initial temperature excess and relative humidity of the plume is given. The special case where the plume is initially saturated, corresponding to cooling tower effluents, is considered in more detail.

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T. M. L. Wigley and Tu Qipu

Abstract

A new technique in statistical crop-climate analysis, the direct linking of spatial patterns of crop yield and spatial patterns of climate, is explored. Yield and climate data from networks of crop reporting districts and meteorological stations are decomposed into orthogonal components using principal components analysis. Each yield component is then expressed as a function of the climate components using multiple regression. These regression equations are then combined to give an equation which relates interannual variations in the spatial patterns of yield to interannual variations in the spatial patterns of selected climate variables. The method is illustrated using wheat yield data from 59 crop reporting districts in southwestern Western Australia covering the period 1929–75. The regression models are calibrated using data for the period 1929–65 and the results are verified using data for the period 1966–75. The climate contribution is shown to be highly significant, with winter precipitation being the most important variable. A single equation relating yield and climate patterns correctly reproduces the differing results obtained for separate parts of the study area by earlier workers. The influence of winter and autumn precipitation is nonlinear and, as a consequence, the study area divides into three zones: a high rainfall area where rainfall is generally more than optimum so that lower rainfall gives higher yields; a low rainfall area where rainfall is, on average, less than optimum so that positive rainfall anomalies are associated with higher yields; and an intermediate zone where average rainfall is close to optimum so that anomalies in either direction tend to suppress yields. Our analysis shows no evidence for any significant change in the sensitivity of wheat yields to climate in spite of a complete change in the variety of wheat cultivated.

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J. M. Lough, T. M. L. Wigley, and J. P. Palutikof

Abstract

Scenarios for Europe in a warmer world, such as may result from increased atmospheric carbon dioxide levels, have been constructed using the early 20th century warming as an analogue. Mean temperature, Precipitation and pressure patterns for the period 1934–53 were compared with those for 1901–20. These are the warmest and cooler twenty-year periods this century based on Northern Hemisphere annual mean surface air temperature data, differing by 0.4°C. The climate scenarios show marked subregional scale differences from season to season, and individual season scenarios often show little similarity to the annual scenario. Temperature scenarios show warming for the annual mean and for spring, summer and autumn. The largest positive changes are found in higher latitudes. Winters over a large part of Europe are actually cooler and show greater interannual variability during the warmer period. These changes appear to be associated with a greater frequency of blocking activity. Precipitation changes occur in both directions in all seasons. There is, however, an overall tendency for spring and summer to be drier and autumn and winter to be wetter.

The climate scenarios are used to construct scenarios of the impact of a global warming on energy consumption and agriculture. Cooler winters alone would imply greater energy demand for space heating, but this is largely offset by warmer temperatures in spring and autumn which reduce the length of the heating season. Increased temperature variability combined with a general cooling during winter over north and northwestern Europe suggests a greater frequency of severe winters, and thus larger fluctuations in the demand for heating energy. The impact on agriculture is difficult to assess because of the complexity of crop-climate relationships and because of the importance of nonclimatic factors associated with technological change and, perhaps, with enhanced photosynthesis due to increased carbon dioxide concentrations. In northern latitudes, the increase in the length of the growing season would appear to be favorable for agriculture, but warmer summers drier springs and wetter autumns would be less favorable. A specific study was made of the effect of two different climate scenarios on crop yields in England and Wales with regression models constructed using a principal components regression technique. Most crops showed a decrease in yield for both warm-world scenarios, with largest decreases for hay yield and least effect on wheat yield. A similar regression analysis of French wine quality showed an improvement in the quality of Bordeaux and Champagne in a warmer world.

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T. M. L. Wigley, S. J. Smith, and M. J. Prather

Abstract

Reactive gas emissions (CO, NOx, VOC) have indirect radiative forcing effects through their influences on tropospheric ozone and on the lifetimes of methane and hydrogenated halocarbons. These effects are quantified here for the full set of emissions scenarios developed in the Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios. In most of these no-climate-policy scenarios, anthropogenic reactive gas emissions increase substantially over the twenty-first century. For the implied increases in tropospheric ozone, the maximum forcing exceeds 1 W m−2 by 2100 (range −0.14 to +1.03 W m−2). The changes are moderated somewhat through compensating influences from NOx versus CO and VOC. Reactive gas forcing influences through methane and halocarbons are much smaller; 2100 ranges are −0.20 to +0.23 W m−2 for methane and −0.04 to +0.07 W m−2 for the halocarbons. Future climate change might be reduced through policies limiting reactive gas emissions, but the potential for explicitly climate-motivated reductions depends critically on the extent of reductions that are likely to arise through air quality considerations and on the assumed baseline scenario.

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