Mid-latitude Locations Research Articles

Atmospheric deposition of 7Be and 10Be

Measurements of {sup 10}Be in precipitation taken in Hawaii, Illinois and New Jersey over a period of five years are reported. The problem of contamination by the isotope being resuspended on wind blown soil that is also collected is addressed. Rain collected at Mauna Loa, Hawaii has such low values of dust contamination that it has been taken as clean, and the data from Illinois and New Jersey are evaluated on that assumption. The conclusion is that the deposition in a given amount of rain for the non-resuspended component is the same for all three stations, and the authors propose that the annual rate for mid-latitude locations have moderate rainfall is proportional to the local rainfall. {sup 7}Be, which is probably negligibly contributed to the measurements by soil contamination was measured for individual rains in Illinois and found to have a deposition of 1.4 {times} 10{sup 4} atom/cm{sup 3}. The authors have found that concentration variations between precipitation events greater than a factor of 20 exist for both isotopes and that relatively rare, high concentration events dominate deposition, thereby requiring long periods of observation to avoid significant error. Based on their own and other data they conclude that the bestmore » value for {sup 10}Be deposition is 1.5 {times} 10{sup 4} atom/cm{sup 3}, uncertain by 20%, and for {sup 7}Be is 1.2 {times} 10{sup 4} atom/cm{sup 3}, uncertain by 25%. A global average deposition rate cannot be inferred directly for either isotope from these kinds of data; however, the theoretical global deposition rate for {sup 10}Be is shown to be consistent with the deposition reported here, if the concentration in equatorial rain is about 3300 atom/g.« less

The shape of ionospheric irregularities in the auroral zone

The evidence that ionospheric irregularities are elongated along the magnetic field is overwhelming. The actual extent of the elongation may, at least for mid-latitude locations, be considerably more than is usually quoted. Several years ago it was suggested that ionospheric irregularities, particularly at night in the auroral zone, are also elongated in the horizontal direction along the L shells. Since that time, there have been a number of investigations of this phenomenon, but there still seems to be some doubt about the actual degree of the anisotropy. This paper uses a limited number of navy navigation satellite system data from a high-latitude station (Sach's Harbour, N.W.T.) and a much more extensive HILAT satellite data set collected at Churchill, Man., to explore the question in a somewhat more direct, though statistically less definitive, way. The results give no clear support for the postulated L-shell extension.

Injection of dust into the martian atmosphere: Evidence from the viking gas exchange experiment

It is proposed that dust storms on Mars that develop during predawn hours may be triggered by a freeze/thaw dust injection process. The model is based on a phenomenon that was observed during the Viking Gas Exchange experiments on Mars, in which adsorbed gas was catastrophically desorbed from soil samples when exposed to humidification at ∼5°C. Similar conditions may develop at midlatitude locations on Mars near perihelion, and a similar humidification-driven desorption process might occur in the soil column. If soils are dampened during humikification, desorbed gases in confined pore spaces could possibly reach 8.6 bar. Diurnal freezing may possibly cause H 2O to crystallize within the pores, possibly producing cohesive soil failure, release of the trapped gas, and explosive injection of freeze-dried powdery overburden dust into the atmospheric column. The process could potentially occur at 5–20 cm depth, and the freeze/thaw dust injection event may initiate after 10:00 PM local time (20°S lat). Dust would be injected at velocities approaching 450 m sec −1 and it would remain in the atmosphere for several hours before settling out. The plumes could potentially regenerate diurnally until the growing atmospheric dust load produced sufficient dampening of the diurnal thermal wave to prevent freeze/thaw. Seasonal replenishment of H 2O could potentially occur by upward migration from depth during the period between 150 and 475 sols after perihelion. The model was experimentally tested and the results were in good agreement with predictions, although a factor of 14 times more gas evolved from the laboratory samples than from the Viking samples. Most of the characteristics of the predawn storms could possibly be adequately explained by the freeze/thaw injection model, including (1) predawn onsets, (2) postperihelion seasonal occurence, (3) daily recurrence during the initial phases of the storms, and (4) generation of blue clouds (H 2O ice) at the storm sites. The process may possibly occur over widespread locations at midlatitudes during seasonal retreat of “tempofrost” from these latitude belts. Permanent low albedo features in these latitude belts may possibly be regions of preferential humidification-induced dust entrainment and net dust removal. The H 2O injected into the atmosphere may potentially be a major source of H 2SO 4 and HCl aerosols, which may possibly chemically react with the regolith to form soluble sulfate and chloride salts. Mg 2+ may be preferentially depleted from the dust.

An interpretation of induced electric currents in long pipelines caused by natural geomagnetic sources of the upper atmosphere

Electric currents in long pipelines can contribute to corrosion effects that limit the pipe's lifetime. One cause of such electric currents is the geomagnetic field variations that have sources in the Earth's upper atmosphere. Knowledge of the general behavior of the sources allows a prediction of the occurrence times, favorable locations for the pipeline effects, and long-term projections of corrosion contributions. The source spectral characteristics, the Earth's conductivity profile, and a corrosion-frequency dependence limit the period range of the natural field changes that affect the pipe. The corrosion contribution by induced currents from geomagnetic sources should be evaluated for pipelines that are located at high and at equatorial latitudes. At midlatitude locations, the times of these natural current maxima should be avoided for the necessary accurate monitoring of the pipe-to-soil potential.

Distribution of fallout cesium-137 in Hawaii.

The concentration of 137Cs was determined by gamma spectrometry in soils and surface-deposited volcanic sublimates from various climatic locations on the islands of Hawaii, Oahu and Maui. A distinct pattern of higher concentrations on the wetter windward sides of the islands and a correlation between 137Cs concentration and amount of rainfall were observed, which confirm the source of the 137Cs as atmospheric fallout. In the soils, the concentrations measured (to 1.93 pCi/g) are within the range reported for the continental United States and other mid-latitude locations in the northern hemisphere. In the basaltic lavas, the concentration of 137Cs was found to be variable but was overall very low, and is apparently controlled by the porosity and permeability of the lavas in addition to rainfall.

Influence of northern and southern hemisphere Sq current systems on equatorial magnetic variations

The H and D daily variations at Huancayo (75°W) and Ribeirão (49°W), both located at the dip equator in the South American region, were compared with those at nearby midlatitude locations Tatuoca in the north and Vassouras in the south, for the six day interval 17–22 September 1970 for which simultaneous data were available. It was noticed that whereas Huancayo was under the influence of the Sq current system of the southern hemisphere, Ribeirão was under the influence of the Sq current system of the northern hemisphere, indicating a very twisted equatorial boundary between the two Sq current systems in this region.

Comparison of storm-time changes of ionospheric total electron content at nearby locations in mid-latitudes.

The changes in the total electron content (TEC) at some mid-latitude locations in the American zone are compared during nine geomagnetc storms which are comparatively clean (clear-cut single main phase). It is found that TEC changes are sometimes related to sudden storm commencement (SSC) and sometimes to main phase onset (MPO) and the changes are sometimes positive and sometimes negative with no obvious relationship either with season or with any particular phase of the geomagnetic storm. It is concluded that there is no direct cause-effect relationship between ionospheric changes and changes of geomagnetic field as such and the only thing common between these is their common source viz, impact of interplanetary plasma blobs while subsequent evolutions are independent and unrelated.

Some Features of the Heat Island in an Equatorial City

In April-May, 1971 and 1972, temperatures measured in Quito, Ecuador, at a height of 1.4 m were characterised by horizontal differences which contrasted strongly with the generally accepted patterns for mid-latitude cities. The separated heat islands over the old and modern sections of the city achieved their greatest magnitudes between 1200 and 1300 hours solar time, and these were frequently 5-10 times greater than the mid-day values reported from mid-latitude locations. On the other hand, in the three-hour period preceeding midnight, when heat islands in mid-latitude cities generally achieve their greatest magnitudes, those in Quito were obliterated by the drainage of cooler air from the very steep slopes to the west. By day, the horizontal temperature gradients between Quito's parks and open spaces on the one hand and its modern section on the other were much steeper than any which have been previously reported from other locations. A previous analysis of those critical wind velocities which, in seven mid-latitude cities, caused the destruction of heat islands, indicated that, if no additional factor was involved, such features in Quito should have been obliterated when the wind speed reached 7.9 m/sec. However, there were several occasions on which winds of 9-11 m/sec. permitted well-developed heat islands to remain as dominant features of the daytime temperature pattern. An examination of the possible reasons for the differences in magnitude between the two separated parts of Quito's heat island indicated that albedo was the dominant factor. Finally, it is suggested that the results of an urban climatic study should only be extrapolated within the same macroclimatic region and to areas where the local topography is essentially similar.