Relationship of Caspian tern foraging ecology to nesting success in the Columbia River estuary, Oregon, USA

The prevalence of juvenile salmonids (Oncorhynchus spp.) and marine forage fishes in the diet of Caspian terns (Hydroprogne caspia) nesting in the Columbia River estuary has been established, but the relationship between diet composition, foraging distribution, and productivity of these birds has received little attention. We used radio-telemetry and on-colony observations to relate changes in off-colony distribution to patterns of colony attendance, diet composition, and productivity of adult terns nesting on East Sand Island during two years of different river and prey conditions. Average distance from the East Sand Island colony (located in the marine zone of the estuary) was 38% (6.6 km) greater in 2000 compared to 2001, associated with lower availability of marine forage fish near East Sand Island and lower prevalence of marine prey in tern diets. Colony attendance was much lower (37.0% vs. 62.5% of daylight hours), average trip duration was 40% longer (38.9 min), and nesting success was much lower (0.57 young fledged pair⁻¹ vs. 1.40 young fledged pair⁻¹) in 2000 compared to 2001. Higher proportions of juvenile salmonids in the diet were associated with relatively high use of the freshwater zone of the estuary by radio-tagged terns, which occurred prior to chick-rearing and when out-migrating salmonid smolts were relatively abundant. Lower availability of marine prey in 2000 apparently limited Caspian tern nesting success by markedly reducing colony attendance and lengthening foraging trips by nesting terns, thereby increasing chick mortality rates from predation, exposure, and starvation.     

Signal contribution sections and their use in resistivity studies

Summary. The electrostatic analogue to direct current resistivity prospecting is employed to construct vertical sections through lines of four electrodes. These show the relative contributions made by individual volume elements of earth to the total potential difference measured between the two potential electrodes. Signal contribution sections enable a comparison of the response of various electrode configurations to subsurface conditions and help to explain, for example, why the dipole—dipole configuration is so suited to horizontal profiling and the Wenner and Schlumberger configurations to vertical sounding.
The spurious response of apparent resistivity curves to near surface lateral resistivity variations is also explained with particular attention being given to the Wenner tripotential configurations.     

Evidence for a poleward meridional flow on the sun

We define for observational study two subsets of all polar zone filaments, which we call polemost filaments and polar filament bands. The behavior of the mean latitude of both the polemost filaments and the polar filament bands is examined and compared with the evolution of the polar magnetic field over an activity cycle as recently distilled by Howard and LaBonte (1981) from the past 13 years of Mt. Wilson full-disk magnetograms. The magnetic data reveal that the polar magnetic fields are built up and maintained by the episodic arrival of discrete f-polarity regions that originate in active region latitudes and subsequently drift to the poles. After leaving the active-region latitudes, these unipolar f-polarity regions do not spread equatorward even though there is less net flux equatorward; this indicates that the f-polarity regions are carried poleward by a meridional flow, rather than by diffusion. The polar zone filaments are an independent tracer which confirms both the episodic polar field formation and the meridional flow. We find:

1. The mean latitude of the polemost filaments tracks the boundary of the polar field cap and undergoes an equatorward dip during each arrival of additional polar field.
2. Polar filament bands track the boundary latitudes of the unipolar regions, drifting poleward with the regions at about 10 m s^-1.
3. The Mt. Wilson magnetic data, combined with a simple model calculation, show that the filament drift expected from diffusion alone would be slower than observed, and in some cases would be equatorward rather than poleward.
4. The observation that filaments drift poleward along with the magnetic regions shows that fields of both polarities are carried by the meridional flow, as would be expected, rather than only the f-polarity flux which dominates the strength. This leads to the prediction that in the mid-latitudes during intervals between the passage of f-polarity regions, both polarities are present in nearly equal amounts. This prediction is confirmed by the magnetic data.

     

Comparison of ground-based and Viking Orbiter measurements of Martian water vapor: Variability of the seasonal cycle

Earth-based observations of Mars atmospheric water vapor, made from McDonald Observatory, are presented for the 1975–1976, 1977–1978, and 1983 apparitions. Comparisons are made with near-simultaneous spacecraft measurements made from the Viking Orbiter MarsAtmospheric Water Detection experiment during 1976–1978 and with previous Earth-based measurements (made since 1964). Differences occur between the behavior in the different years, and may be related to the Mars climate. Measurements during the southern summer in 1969 indicate a factor of three times as much water as is present at this same season in other years.This difference may have resulted from the sublimation of water from the south polar residual cap upon removal of most or all of the CO₂ ice present; sublimation of all the CO₂ ice during some years could be a result of a greater thermal load being placed on the cap due to the presence of differing amounts of atmospheric dust. If substantiated, the water vapor variability will turn out to be a very sensitive indicator of yearly variability in the Martian climate.     

The characteristics of Pc 3 and Pc 4 geomagnetic micropulsations recorded at Sanae,Antarctica

Digital dynamic spectra of micropulsations recorded at SANAE (L ～ 4) show that Pc 3 pulsations have frequencies which decrease throughout the day. Both the onset frequency and the rate of decrease of frequency depend on the level of magnetic activity during the previous night. The variation of Pc 3 amplitudes and frequencies is explained in terms of the position of the plasmapause and the associated Pc 3 resonance region in the plasmatrough.For Pc 4 pulsations a constant frequency is observed on most days and it is not possible to infer the presence of a Pc 4 resonance region.