OUR DISCIPLINE'S DEMOGRAPHIC FUTURES: RETIREMENTS,VACANCIES, AND APPOINTMENT PRIORITIES

Age profiles of geographers having varying topical and areal subfields are compiled using the Guide to Graduate Departments of Geography in the United States and Canada, 1983–1984 and the 1982 AAG Directory. Major retirement trends for the next 10 to 20 years suggest that replacement of faculty may raise key appointment issues and priorities that may significantly change the nature of academic geography.     

An Overview of the Disposition of Solar Radiation in the Lower Atmosphere: Connections to the SORCE Mission and Climate Change

Solar radiation is the primary energy source for many processes in Earth's environment and is responsible for driving the atmospheric and oceanic circulation. The integrated strength and spectral distribution of solar radiation is modified from the space-based {Solar {Radiation and {Climate (SORCE) measurements through scattering and absorption processes in the atmosphere and at the surface. Understanding how these processes perturb the distribution of radiative flux density is essential in determining the climate response to changes in concentration of various gases and aerosol particles from natural and anthropogenic sources, as is discerning their associated feedback mechanisms. The past decade has been witness to a tremendous effort to quantify the absorption of solar radiation by clouds and aerosol particles via airborne and space-based observations. Vastly improved measurement and modeling capabilities have enhanced our ability to quantify the radiative energy budget, yet gaps persist in our knowledge of some fundamental variables. This paper reviews some of the many advances in atmospheric solar radiative transfer as well as those areas where large uncertainties remain. The SORCE mission's primary contribution to the energy budget studies is the specification of the solar total and spectral irradiance at the top of the atmosphere.     

Martian channels and valleys: Their characteristics,distribution, and age

All Martian channels and valleys visible at a resolution of 125 to 300 meters between 65°N and 65°S were mapped at a scale of 1:5,000,000 and the maps then digitized. Correlations of valley presence with other surface features show that almost all valleys are in the old cratered terrain. preferentially in areas of low albedo, low violet/red ratios, and high elevation. The networks are open, the individual drainage basins are small relative to Earth, and large distances separate the basins, features which all suggest an immature drainage system. The simplest explanation of the correlations and the restriction of valley networks to old terrain is that the channels themselves are old, and that the climatic conditions necessary for their formation did not prevail for long after the decline in the cratering rate around 3.9 billion years ago. Two types of outflow channel are distinguished: unconfined, in which broad swaths of terrain are scoured, and confined, in which flow is restricted to discrete channels. The outflow channels have a wide range of ages and may form under present climatic conditions. Fretted channels are largely restrited to two latitude belts centered on 40°N and 45°S, where relatively rapid erosion along escarpments results from mass wasting. They probably form by enlargement of preexisting channels by escarpment retreat.     

Re-inventing government: Emerging geographies in the aftermath of the 1984 reforms in New Zealand

Introduction

Re-inventing government: Emerging geographies in the aftermath of the 1984 reforms in New Zealand     

A tracer dilution method for fracture characterization in bedrock wells

This investigation was undertaken to develop an integrated method of downhole fracture characterization using a tracer. The method presented can be used to locate water-bearing fractures that intersect the well, to determine the ambient fracture flow rate and hydraulic head, and to calculate fracture transmissivity. The method was tested in two fractured crystalline bedrock wells located at the University of Connecticut in Storrs. The method entails injecting a tracer (uranine dye) into the well, while at the same time water is pumped out of the well. After steady-state conditions are reached, a borehole tracer concentration profile is developed. The dilution of the tracer is used to locate the inflowing fractures and to determine their flow rate. The fracture flow rate, plus the drawdown in the well, is then used to determine the fracture hydraulic head, transmissivity, and ambient flow rate.     

On the mean particle size and water content of polar mesospheric clouds

The ultraviolet spectrometer on board the Solar Mesosphere Explorer (SME) satellite has been measuring the scattering of ultraviolet sunlight from optically thin cloud layers in the upper boundary of the mesosphere (85 km) since the launch of the spacecraft in October 1981. These layers are present only at high latitudes during the summer season. During Summer 1983 an observing sequence was undertaken to measure the cloud radiance at two different scattering angles—one in the forward hemisphere at 50°, the other in the backward hemisphere at 130°. The data show a pronounced tendency for the brighter clouds to exhibit greater forward-scattering behavior, indicating that particle size may be the most important factor in determining the cloud brightness. We conclude that if the particles are monodisperse water ice aggregates, their radii do not exceed 70 nm. Estimates are provided for the water content and column particle number of the clouds, depending upon the unknown shape of the particle size distribution. Characterizing the distribution by two parameters, the spherical equivalent particle radius and the width of the distribution, the bulk cloud properties are shown to be dependent upon the limb radiance and the width parameter. For narrow widths the water ice content is less than that expected for the water vapor content at mesopause heights of a few parts per million. This confirms our earlier analysis using a smaller data set and assuming the cloud particles are monodisperse. However if the size dispersion is broad, the implied water ice exceeds the static atmospheric water supply. The calculated column number for the brightest clouds exceeds our estimates for the total supply of condensation nuclei. The alternative is that the brighter clouds are limited to a fairly narrow range of particle sizes from 40 to 60 nm. This conclusion is supported by theoretical time dependent calculations by Turco et al. (1982).