Vertical electrical sounding as an exploration technique to improve on the certainty of groundwater yield in the fractured crystalline basement aquifers of eastern Uganda

Groundwater in eastern Uganda mostly occurs in fractures in the crystalline basement rocks and at the interface between the overburden and bedrock. The study was aimed at improving the success rate of boreholes through the use of complimentary geophysical siting procedures in 16 locations in Kamuli District, eastern Uganda. Boreholes that were sited after applying appropriate geophysical techniques yielded adequate quantities of water, whereas those sited where such procedures were not applied were out of service sooner than expected. Techniques to determine the precise location of resistivity anomaly and vertical electrical sounding (VES) models were used to locate water-bearing zones. VESs were undertaken to provide an overview of the geology. The apparent resistivities of the water-bearing zones both from VES and resistivity profiling data, had a relationship with the success rates of the boreholes. Electrical resistivities were correlated with hydrogeological parameters. The majority of successful boreholes had, within water-bearing zones, minimum apparent resistivity values less than 200 and 100 Ohmm, from the resistivity profiling anomalies and VES, respectively. The depth to bedrock was generally greater than 20 m below ground level, which indicates potential for medium yielding boreholes.     

Ein selbstkompensierender Elektrometerröhrenverstärker zur Registrierung des luftelektrischen Potentialgefälles

Zusammenfassung Es wird ein selbstkompensierender Elektrometerröhrenverstärker zur Registrierung des luftelektrischen Potentialgefälles beschrieben. Das Gerät hat einen hohen, über den ganzen Meßbereich konstanten Eingangswiderstand von 10¹⁴ Ohm und eine lineare Anzeige über einen beliebig wählbaren Meßbereich, z. B. von –200 bis + 300 Volt.

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Summary A self-compensating electrometer-tube amplifier for recording the electric field of the atmosphere is described. The instrument has a high input resistance of 10¹⁴ ohms constant over the whole range and a linear indication covering any range desired, as e. g. from –200 to +300 volts.

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Résumé On décrit un amplificateur autocompensateur à lampe électromètre pour l'enregistrement du champ électrique de l'atmosphère. L'apparen possède une forte résistance d'entrée de 10¹⁴ ohms, constante pour toute l'échelle de mesure, et une indication linéaire valable pour n'importe quelle échelle, par exemple de –200 à +300 volts.

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Temporal Evolution of the Solar Wind Bulk Velocity at Solar Minimum by Correlating the STEREO A and B PLASTIC Measurements

The two STEREO spacecraft with nearly identical instrumentation were launched near solar activity minimum and they separate by about 45° per year, providing a unique tool to study the temporal evolution of the solar wind. We analyze the solar wind bulk velocity measured by the two PLASTIC plasma instruments onboard the two STEREO spacecraft. During the first half year of our measurements (March?–?August 2007) we find the typical alternating slow and fast solar wind stream pattern expected at solar minimum. To evaluate the temporal evolution of the solar wind bulk velocity we exclude the spatial variations and calculate the correlation between the solar wind bulk velocity measured by the two spacecraft. We account for the different spacecraft positions in radial distance and longitude by calculating the corresponding time lag. After adjusting for this time lag we compare the solar wind bulk velocity measurements at the two spacecraft and calculate the correlation between the two time-shifted datasets. We show how this correlation decreases as the time difference between two corresponding measurements increases. As a result, the characteristic temporal changes in the solar wind bulk velocity can be inferred. The obtained correlation is 0.95 for a time lag of 0.5 days and 0.85 for 2 days.

     

Harvest dates in ancient mesopotamia as possible indicators of climatic variations

Butzer (1958; also, Lamb, 1968) puts forward observations to the effect that about 2500 B.C. a period of increased aridity set in in the general area of the Near East, including Mesopotamia, and that rainier conditions returned after about 850 B.C. Because in the Mediterranean type of climate (winter rains) of the Near East winter temperatures and seasonal rainfall are highly correlated in a negative sense, we expect that the above mentioned period of aridity was also a period of relative warmth, whereas the period after 850 B.C. up to Roman times, was a period of cool winters. This negative correlation is thought to be due to the fact that in the Near East rainfall is usually produced in the migratory cyclones, especially close and behind the associated cold fronts which bring in cold air as well. A failure of these cyclones to reach the region in numbers, manifests itself both in reduced rainfall and comparatively high winter temperatures. In order to check on these ideas on temperature conditions, a search was undertaken of references to barley harvest dates in the literature (clay tablets) of ancient Babylonia comprising two periods: 1800-1650 B.C. (Late Old Babylonian Period = L.O.B.P.) and 600-400 B.C. (Neo-Babylonian Period = N.B.P.). It turns out that in the former, the harvest began late in March or early in April, while in the latter, it began late in April or in May, amounting to a difference of about a month or slightly more. In our own era, in what was once central and northern Babylonia, harvest begins in the second half of April or so. Thus in the L.O.B.P., harvest opened 10–20 days earlier and in the N.B.P. 10–20 days later than at present. The differences between the harvest dates of the two periods seem to be too large to be explained by changes in the barley varieties cultivated. On the other hand, the above mentioned inverse relationship between rainfall and winter temperatures supports the interpretation that the L.O.B.P. was warmer, and the N.B.P. cooler than the present era, and goes some way toward explaining the inferred differences in harvest dates.     

Tages- und Jahresgänge der luftelektrischen Elemente in Arosa

Zusammenfassung Die Verfasser berichten über die Ergebnisse luftelektrischer Registrierungen in drei Höhenlagen von 1840, 2050 und 2650 m ü. M. während der Jahre 1957 bis 1959 in und bei Arosa. Die Tages- und Jahresgänge von Potentialgradienten, polarer Leitfähigkeit und Vertikalstromdichte werden diskutiert. Es zeigt sich ein deutlicher Zusammenhang zwischen dem Jahresgang des Potentialgradienten und dem mit dem Dobson-Spektrometer gemessenen Ozongehalt; auf eine mögliche Erklärung wird hingewiesen.

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Summary The authors report on the results of records of atmospheric electricity in the levels of 1840, 2050, 2650 m above sea level during the years 1957 to 1959 at Arosa and nearby (Switzerland). The diurnal and annual variation of potential gradient, polar conductivity and air-earth-current density are discussed. It is demonstrated that there is a clear relation between the annual variation of the potential gradient and ozone content measured by a Dobson spectrometer; a plausible explanation is discussed.

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Résumé On discute des enregistrements de l'électricité atmosphérique pour les années 1957, 1958, 1959 éffectuées aux altitudes de 1840 m, 2050 m et 2650 m à et au-dessus d'Arosa. Les variations diurnes et annuelles du gradient du potentiel, de la conductibilité polaire et de la densité du courant électrique vertical sont analysées. Les auteurs mettent en évidence une relation entre les variations annuelles du gradient du potentiel et de la concentration en ozone mesurée avec un spectromètre Dobson; une interprétation possible de cette constatation est envisagée.

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