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A. B. Pittock

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A. B. Pittock

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Coincident observations of a layer of volcanic material and a sharp minimum in the vertical distribution of ozone over Boulder, Colo. (40N), are presented and discussed. The ozone minimum was observed at an altitude of 20–21 km for a month during the spring of 1964.

Quasi-horizontal advection of a thin stable layer of tropical air into which volcanic debris was injected when Mt. Agung (8S) erupted on 17 March 1963 is thought to be responsible. The layer is characterized by a “quasi-vertical” eddy diffusion coefficient Jess than or equal to 2.5 × 102 cm2 sec−1. Significant destruction of ozone by the volcanic debris is not indicated.

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A. B. Pittock

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In order to gain an understanding of the spatial connections and representativeness of instrumental and proxy climatic data from particular sites, a 30-year data set for a network of 87 stations in Argentina and Chile has been analyzed. In this paper the results for precipitation are presented. These show three dominant patterns of year-to-year variability which together account for more than 40% of the total variance. Two methods have been used to show how these patterns are linked to variations in the general circulation. Significant correlations are found between precipitation variations and fluctuations in each of four indices of the general circulation: an index of the Southern Oscillation; an index of the pressure difference across the Antarctic between Tasmania and the Falkland Islands region., the latitude of the high-pressure belt off the coast of Chile; and an index of the pressure difference across the tropical Atlantic Ocean. An unexpected link is found between the pressure fluctuations in the tropical Atlantic and the midlatitude circulation.

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A. B. Pittock

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Topographic effects on climate, and particularly on precipitation, are well known in the literature. Nevertheless their separation on the mesoscale from possible anthropogenic effects has proved difficult. A method based on patterns of correlation between local climate elements and indices of the general circulation, which was developed in a study of Australian rainfall, has been applied to precipitation in the State of Washington and surrounding areas where relief is much greater. Patterns are found which account for the major part of some climatic anomalies discussed in the literature and which have previously been ascribed to anthropogenic effects. The wider implications for the study of urban and other anthropogenic effects is discussed with reference to the La Porte anomaly and METROMEX.

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A. B. Pittock

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A 30-year data set of monthly means of the daily mean temperatures at a selected network of 50 stations in Argentina and Chile has been analyzed. Eigenvector analysis reveals that the first three patterns of year-to-year variability account for 42, 14 and 7% of the total variance, respectively. The most dominant pattern shows temperature anomalies of the same sign over practically the whole area, but these are highly seasonal, being correlated negatively with the east-west pressure difference across the tropical Atlantic in fall and winter, and positively in early summer. This seasonal reversal is found to be due to the seasonal reversal in land-sea temperature difference off the central Argentine coast. The second eigenvector of the temperature variations is most strongly correlated with the pressure difference between the Tasmanian and Falkland Islands regions, while the third eigenvector is associated with variations in the latitude of high pressure belt along the coast of Chile.

These results confirm those found for precipitation in Part I (Pittock, 1980) in that a few dominant circulation anomaly mechanisms appear to account for a major part of the climatic variations over Argentina and Chile. Clearly. these circulation mechanisms should be studied further, as should the relationship between Argentinean climate and sea surface temperature fluctuations in the south-west Atlantic.

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A. B. Pittock

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J. R. Garratt, A. B. Pittock, and K. Walsh

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The response of the atmospheric boundary layer to the appearance of a high-altitude smoke layer has been investigated in a mesoscale numerical model of the atmosphere. Emphasis is placed on the changes in mean boundary-layer structure and near-surface temperatures when smoke of absorption optical depth (AOD) in the, range 0 to 1 is introduced. Calculations have been made at 30°S, for different soil thermal properties and degrees of surface wetness, over a time period of several days during which major smoke-induced cooling occurs. The presence of smoke reduces the daytime mixed-layer depth and, for large enough values of AOD, results in a daytime surface inversion with large cooling confined to heights of less than a few hundred meters. Smoke-induced reductions in daytime soil and air temperatures of several degrees are typical, dependent critically upon soil wetness and smoke AOD. Locations near the coast experience reduced cooling whenever there is a significant onshore flow related to a sea breeze (this would also be the case with a large-scale onshore flow). The sea breeze itself disappears for large enough smoke AOD and, over sloping coastal terrain, a smoke-induced, offshore drainage flow may exist throughout the diurnal cycle.

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P. H. Whetton, A. B. Pittock, M. R. Haylock, and P. J. Rayner

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To assist in estimating likely future climate change in the Australian region, the authors examine the results of four different general circulation modeling experiments run to assess the equilibrium impact of doubling greenhouse gases. The results examined were the most recent available at the time of study from various research centers in North America and Europe, as well as those of the Commonwealth Scientific and Industrial Research Organisation (CSIRO). The approach used is, first, to assess the quality of the control ( 1 × C02) simulations from each of the models of mean sea level (MSL) pressure and precipitation in the Australian region by comparing these with the corresponding observed patterns; and, second, to then analyze the 2 × C02 results of only those model experiments with the best control simulations. Of the models examined two are chosen on the basis of their simulation of current climate in the region: the CSIRO four-level model (CSIR04) and the United Kingdom Meteorological Office (UKMO) model. For conditions of equivalent doubling of C02, both models show substantial increases in surface air temperature of around 4°–6° inland and 2°–4°C in coastal regions. Both models show decreased MSL pressure over the Australian continent and increases in rainfall over northern, central, and eastern Australia, particularly in the summer half of the year. The CSIR04 model, but not the UKMO model, also shows increased pressure to the south of the continent and decreased winter rainfall in southwest and southern Australia. Generally, field significance tests show the pattern and magnitude of the changes to be significant for CSIR04 (for which the necessary monthly simulated data were available).

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