R. E. (Ted) Munn — Founding editor; a mini-biography

Ted Munn founded Boundary-Layer Meteorology in 1970 and served as Editor for 75 volumes over a 25 year period. This short article briefly reviews Ted's scientific career with the Atmospheric Environment Service (of Canada), the International Institute for Applied Systems Analysis in Austria and with the Institute of Environmental Studies at the University of Toronto, and as editor of this journal.     

Boundary-layer flow over topography: Impacts of the Askervein study

One of the objectives of the Askervein Hill Project was to obtain a comprehensive and accurate dataset for verification of models of flow and turbulence over low hills. In the present paper, a retrospective of the 1982 and 1983 Askervein experiments is presented. The field study is described in brief and is related to similar studies conducted in the early 1980s. Data limitations are discussed and applications of numerical and wind-tunnel models to Askervein are outlined. Problems associated with model simulations are noted and model results are compared with the field measurements.     

Temporal trends in abundance of fish in the tidal Delaware River

Water quality in the tidal Delaware River has improved dramatically over the last several decades. Areas near Philadelphia that were once anoxic and formed a pollution block to migratory fish passage now rarely experience dissolved oxygen concentrations less than 3 ppm. To assess whether these improvements in water quality led to increased abundance of juvenile fishes, data from a beach seine survey conducted annually since 1980 were examined. The number of species captured increased throughout the tidal river, but the increase was greatest in the areas downstream of Philadelphia, wheare water quality has improved the most. Abundance of juvenile striped bass and American shad, two important game species in the river whose migratory patterns make them susceptible to water quality problems, both increased more than, 1,000-fold during the last decade. Correlatations between the temporal abundance patterns of these species in the tidal Delaware River and in other East Coast systems were poor, suggesting that increases in their numbers were related more closely to improving conditions within the Delaware than to factors affecting coastal stocks.     

Tropical soils could dominate the short-term carbon cycle feedbacks to increased global temperatures

Results of a simple model of the effects of temperature on net ecosystem production call into question the argument that the large stocks of soil carbon and greater projected warming in the boreal and tu ndra regions of the world willlead to rapid efflux of carbon from these biomes to the atmosphere. We show that low rates of carbon turnover in these regions and a relatively greater response of net primary production to changes in temperature may lead to carbon storage over some limited range of warming. In contrast, the high rates of soil respiration found in tropical ecosystems are highly sensitive to small changes in temperature, so that despite the less pronounced warming expected in equatorial regions, tropical soils are likely to release relatively large amounts of carbon to the atmosphere. Results for high-latitude biomes are highly sensitive to parameter values used, while the net efflux of carbon from the tropics appears robust.     

Climate spectra and detecting climate change

Part of the debate over possible climate changes centers on the possibility that the changes observed over the previous century are natural in origin. This raises the question of how large a change could be expected as a result of natural variability. If the climate measurement of interest is modelled as a stationary (or related) Gaussian time series, this question can be answered in terms of (a) the way in which change is estimated, and (b) the spectrum of the time series. These computations are illustrated for 128 years of global temperature data using some simple measures of change and for a variety of possible temperature spectra. The results highlight the time scales on which it is important to know the magnitude of natural variability. The uncertainties in estimates of trend are most sensitive to fluctuations in the temperature series with periods from approximately 50 to 500 years. For some of the temperature spectra, it was found that the standard error of the least squares trend estimate was 3 times the standard error derived under the naïve assumption that the temperature series was uncorrelated. The observed trend differs from zero by more than 3 times the largest of the calculated standard errors, however, and is therefore highly significant.     

The structure of low frequency phenomena in the tropics and its interaction with the extratropics

The structure of planetary scale low frequency phenomena in the tropics is studied, and an attempt is made to de-termine its influence and interactions with phenomena at higher latitudes.In the tropics, it is found that the majority of the variance in the zonal wind structure is made up in wave num-bers 1 and 2. During warm events in the Pacific Ocean, when the Southern Oscillation Index is negative, almost all of the variance resides in the gravest mode which undergoes a 40o eastward phase shift. Meanwhile, the second logitudinal mode almost disappears. On the other hand, the meridional wind field possesses maximum amplitude at higher wave numbers. However, near the equator, the amplitude is small with extreme values occurring in the subtropics. The difference in scale and the location of extrema of the meridional and zonal wind components indicate that the tropical atmosphere is responding to two different driving mechanisms,Correlation analyses between variations of the zonal wind at reference points along the equator with variations of component elsewhere show that there are strong logitudinal connections. The strongest correlations between the tropics and higher latitudes exist in the region of the equatorial westerlies. In fact, stronger correlations occur between variations in U anywhere along the equator and the middle latitudes to the north and south of the equatorial wester-lies than to the latitudes immediately to the north and south of the reference points. We interpret this “remote” corre-lation pattern as indicating a two-stage teleconnection process which emphasizes the importance of the equatorial tropical westerlies of the Pacific Ocean as a “corridor” of communication between the low and high latitudes. The regionality of the correlations confirms, to some extent, recent theoretical development regarding trapped equatorial modes. Finally, time lagged correlations from plus and minus six months between variations of U and OLR indicate that the interactions between the extratropics and low latitudes possess an organized sequence. The extratropical in-fluence appears to propagate into the tropics followed by an eastward propagation along the equator. Finally, a propagation from the tropics to the extratropics in the upper troposphere occurs in the eastern Pacific Ocean. The time-lagged correlation sequence does not appear to be symmetric about the equator.     

Evolution of late pleistocene and holocene climates in the circum-south pacific land areas

Paleovegetation maps were reconstructed based on a network of pollen records from Australia, New Zealand, and southern South America for 18 000, 12000, 9000, 6000, and 3000 BP and interpreted in terms of paleoclimatic patterns. These patterns permitted us to speculate on past atmospheric circulation in the South Pacific and the underlying forcing missing line mechanisms. During full glacial times, with vastly extended Australasian land area and circum-Antarctic ice-shelves, arid and cold conditions characterized all circum-South Pacific land areas, except for a narrow band in southern South America (43° to 45°S) that might have been even wetter and moister than today. This implies that ridging at subtropical and mid-latitudes must have been greatly increased and that the storm tracks were located farther south than today. At 12000 BP when precipitation had increased in southern Australia, New Zealand, and the mid-latitudes of South America, ridging was probably still as strong as before but had shifted into the eastern Pacific, leading to weaker westerlies in the western Pacific and more southerly located westerlies in the eastern Pacific. At 9000 BP when, except for northernmost Australia, precipitation reached near modern levels, the south Pacific ridges and the westerlies must have weakened. Because of the continuing land connection between New Guinea and Australia, and reduced seasonality, the monsoon pattern had still not developed. By 6000 BP, moisture levels in Australia and New Zealand reached their maximum, indicating that the monsoon pattern had become established. Ridging in the South Pacific was probably weaker than today, and the seasonal shift of the westerlies was stronger than before. By 3000 BP essentially modern conditions had been achieved, characterized by patterns of high seasonal variability.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program     

Longitudinal heating gradient: Another possible factor influencing the intensity of the Asian summer monsoon circulation

The Largest longitudinal heating gradients in the tropics exist between the African desert and Asian convective regions during summer once the South Asian monsoon is established. The heating gradients are anchored by the la-tent heat release and net radiative flux convergence over the monsoon region, and by the dominant net radiative flux divergence over the desert.An apparent relationship is found between the intensity of the Asian summer monsoon circulation and the longitudinal healing gradients mentioned, in addition to the latitudinal heating gradients cross the monsoon region. The monsoon circulation measured in terms of the zonal wind component is stronger when the longitudinal heating gradients are large, and vice versa. Thus, we claim that the longitudinal heating gradient may be another important factor which influences the intensity of the Asian summer monsoon circulation. There is little evidence that the interannual variability of the longitudinal heating gradients between Africa and Asia and, thus, the intensity of the Asian summer monsoon circulation, is a strong function of the El Nino / Southern Oscillation cycle.