Lightning flash climatology in the southern great lakes region

Abstract

We have made a preliminary study of cloud‐to‐ground lightning over southern Ontario and the adjoining Great Lakes region. The lightning data set, using magnetic direction finding, is sufficiently accurate to study lightning climatology. Cloud‐to‐ground flash totals have been found for the three warm seasons 1989–91. A large variation in flash total, lightning‐day frequency and number of high flash density storms occurs over the area, with the maximum in southwestern Ontario. The area of the maximum also has a strong diurnal cycle and relatively few positive flashes. Several physical causes may contribute to this. Lake areas usually have slightly fewer flashes than nearby land areas and warm water usually has more flashes than cold water. The Great Lakes do produce more lightning than ocean areas. Convergence lines of lake breezes and other lake circulations can, however, be sites for storms with intense lightning. High surface temperature and moisture leads to an increase in lightning generation. Over land, upslope flow increases lightning‐producing storms and downslope flow decreases them. High flash density storms may be favoured by smooth rather than rough ground, and by open farmland rather than forest. On the other hand, there does not seem to be a clear urban effect increasing lightning in the Great Lakes     

Maintaining a sustainable economic base in rural towns: a case study of Leeton

Leeton, a town of 6000 in the Murrumbidgee Irrigation Area, has in recent times suffered major economic upheaval. In 1993 the Letona Co‐operative stone fruit cannery, Leeton's masthead industry since 1921, was placed in receivership and closed after extensive search for a new investor in stone fruit processing failed. The removal of a substantial income stream from the local community has placed great stress on Leeton's economic and social fabric. However, the town in recent years has developed an economy that is no longer completely reliant on a narrow range of agricultural processing and service activities. Utilising factors of location, irrigation‐supported production flexibility and security, cheap land and utilities, and a stable and productive workforce, the combined efforts of the Leeton Shire Council, local community groups, the Riverina Development Board, and State Government departments have attracted a range of new industries to the town and shire over the past decade. It is these industries that will allow Leeton to survive the loss of Letona, sustain its economy and look to the future with confidence.     

Cation segregation and the O-H stretching vibration of the olivenite-adamite series

The behaviour of the O-H stretching infrared spectra of the synthetic olivenite-adamite series described by Brathwaite (1983) is accounted for in terms of the crystal structure and cation distribution. There are three absorption bands: Two at 3,540 and 3,510 cm^?1 correspond to OH groups bonded to Zn₃ and CuZn₂ respectively. The third band corresponds to OH groups bonded to both combinations Cu₂Zn and Cu₃ and its frequency varies with the proportions of those two combinations. Preferential occupation of the five-fold site by Zn is confirmed from its effect on the infrared spectra, the ratio Zn^V/Zn^VI being roughly 4:1. There is evidence for clustering of Zn into Zn₃ groups around OH. Differences in the degree of segregation and clustering of Zn will affect the infrared spectra of natural olivenites and adamites and this may limit the usefulness of infrared spectroscopy as a determinative method.     

Particle trapping in stratified estuaries: Application to observations

Estuarine turbidity maxima (ETM) retain suspended particulate matter (SPM) through advection, settling, aggregation, and nonlinearities in bed processes, but the relative importance of these processes varies strongly between systems. Observations from two strongly advective systems (the Columbia and Fraser Rivers) are used to investigate seasonal cycles of SPM retention and the effects of very high flows. Results for the Fraser and Columbia plus literature values for 13 other estuaries illustrate the applicability of scaling parameters and the response of ETM phenomena to a range of river flow (U _r ) levels and tidal forcing. The most efficient trapping (represented by Trapping EfficiencyE, the ratio of maximum ETM concentration to the source SPM concentration) occurs for low ratios of river flow to tidal current amplitude (U_T), represented by low values of the Supply number S_r.E in the Columbia is found to be maximal in a null zone where advection or tidal asymmetry (represented by Advection numberA) is weak(A ∼ 0). The ratio of aggregation to disaggregation (the Floc number Θ) is maximal on neap tides, while the ratio of erosion to deposition (the Erosion number P) is maximal on spring tides. The ratio of settling velocity to vertical mixing (Rouse numberP) is relatively constant in the Columbia ETM(P ∼ 0.7), because particle settling velocity and turbulence levels adjust together. Assuming that this result applies broadly, scaling variables and data are combined to express ETM properties in terms of the friction velocity (U_*),U _r , andU _T , allowing a considerable simplification of the parameters used to describe ETM.     

A newly-discovered coal measures marine band in billinge beacon quarry,lancashire, and its stratigraphical significance

A thin band yielding conodonts and Foraminifera and therefore demonstrably marine, has been found in mudstone lying immediately above the uppermost coal horizon in Billinge Beacon Quarry. The existence of this newly recognized horizon, which is very likely to be the Langley Marine Band at the top of the Lenisulcata Chronozone, much strengthens the correlation of the Billinge Beacon sandstones with the regionally developed Crutchman Sandstone. An alternative correlation of the Billinge Beacon sandstones with the Dyneley Knoll Flags of Burnley, which was recently proposed by F. M. Broadhurst, is not supported by the new evidence, nor by the evidence of boreholes, since it appears that the Dyneley Knoll Flags die out some distance to the north of Billinge.     

GEOMORPHOLOGICAL PHOTOGRAMMETRY

The broad requirements of the geomorphologist for original mapping are reviewed. The extent to which aerial photogrammetry can meet these requirements is exemplified through typical approaches and mapping products in fluvial, coastal and glacial specialisms.     

COASTAL AIR SURVEY: CHANGING TIDES OF FORTUNE?

This study of coastal air survey draws together the main characteristics of the coastal zone, scientific sites of interest, statutory spheres of responsibility, existing coastal photography and survey, and evidence of survey practices by many with responsibilities in these environments. In contrast to the surveyor/photogrammetrist steeped in survey techniques and map use, the majority of people who commission and use air photographs and photogrammetric mapping have very different backgrounds and interests and have widely differing objectives. They come largely from the disciplines of economics, planning, engineering, geography, biological sciences and accountancy. They, too, have their own view of the value of air survey and the analysis here of the trends in demand and use for such material suggests that these sources of information play only a minor and occasional part in their everyday work.