Amplitude Response of a LCR Gravimeter with Feedback at Periods of Microseisms and Earthquake Waves

The amplitude response of a LCR gravimeter with the SRW-E feedback was determined on a vertical vibrating platform. The ink-pen recorder was connected parallel with the digital voltmeter input to obtain an analog response of the gravimeter to the harmonic motion of the base with a peak-to-peak amplitude of 10 m and periods excited in an interval of 4 - 10 s as by the ground motion of meteorological microseisms, and in the interval 10 -100 s as by surface waves of distant strong earthquakes. In the first interval, an unexpected maximum of the amplitude response was observed with the double amplitude of apparent 6,5 Gal (6.5 × 10 _–8 m/s ² ) at a period of 4.8 s, and a baseline shift with the amplitude of–64Gal was observed at the same period. The value of this direct component cannot be separated from the effect of the Earth's gravity field. In the second interval, the amplitude response of the gravimeter displayed one expected maximum at a period of 40 s with the double amplitude of 8.1Gal. At the usual level of microseisms with a peak-to-peak amplitude of up to 2 m the fluctuation of the gravimeter on the direct baseline shifted by –4.9 Gal was estimated at 1 Gal. With typical Rayleigh surface waves with periods of 20 s and double amplitudes of up to 100 m, the fluctuation reached 67 Gal.     

Magnetic particles in atmospheric particulate matter collected at sites with different level of air pollution

Magnetic measurements of deposited atmospehric dust can serve as an additional parameter in assessing environmental pollution. This method is based on the assumption that atmospherically deposited particles contain significant portion of ferrimagnetic iron oxides of anthropogenic origin, which can be easily detected. Aim of this paper is to identify clearly magnetic fraction of daily samples of particulate matter less than 10 μm (PM10), routinely used for air quality assessment and monitoring. We used combination of thermomagnetic analyses and other physical and chemical methods, including scanning electron microscopy (SEM) and Mössbauer spectroscopy. Our results show that daily samples of PM10, collected at sites with different degree of atmospheric pollution, contain magnetite of spherical shape, which is presumably of industrial origin. Thus, magnetic methods can be applied directly to the same substances, which are used routinely in air quality assessment and monitoring.     

The basic characteristics of the scintillation of radio waves after passing through the ionosphere

Резюме Анализируются величины, пригодные для характеристики сцинтилляций плоской волны после прохождения через ионосферу, которые одновременно позволяют провести сравнение сцинтилляций с геофизическими параметрами ионосферы и геометрией распространения волн. Предположим, что источником сцинтилляций являются изотропные области повыпенной электронной концентрации в тонком слое, где происходит слабое рассеяние. Для распределения амплитуды сцинтилляций предлагаетсят-распределение Накагами, показательт которого одновременно пригоден в качестве основного параметра сцинтилляции из корреляционной теории сцинтилляций были выведены выражения для рассеяния амплитуды и фазы и взаимные корреляции амплитуды или фазы на различных частотах. Для расчетов таких рассеяний было выбрано две модели функции корреляции флуктуаций показателя преломления (Гаусса и Бесселя), а для вывода были использованы спектральные функции по методу Татарского. В заключение для упомянутых моделей были выведены выражения для среднего числа превышений данного уровня и среднего числа максимумов амплитуды сцинтилляций; такие средние числа могут с успехом служить в качестве приближенных характеристик сцинтилляций. Полученные результаты сравниваются с опубликованными результатами измерений и указывается на некоторые недостатки в теоретических моделях сцинтилляции, применяем. в качестве основния для интерпретации результатов измерений.

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Address: Boční II, Praha 4-Spořilov.     

Analysis of soil moisture trends in the Salt River watershed of central Arizona

In this investigation, we generate estimates of soil moisture for the Salt River basin on which the expanding city of Phoenix, Arizona relies upon for nearly half of its water supply. While previous empirical studies have produced mixed results concerning recent drought trends in the southwestern USA, our results support the many numerical climate models which predict that this region will become drier in response to the buildup of greenhouse gases. Over the period 1895–2007, we found that soil moisture levels revealed no significant change. However, if we restrict the study to the period 1980–2007, soil moisture levels have decreased at a highly statistically significant rate. We could find little evidence that the trend is associated with variations in El Niño–Southern Oscillation and the Pacific Decadal Oscillation. Increasing surface pressure over our study area during the latter half of the twentieth century may be a catalyst for the drier conditions.     

Explanation of the internal air pressure effect on the worden gravity meter dial constant

Summary A model, explaining the effect of air pressure changes in the space of the measuring system on the fine dial counter constant of the Worden and similar gravity meters, is presented. It is based on the changes of the bellows volume with compensating the gravity changes. It is shown that the resetting the gravity meter in the whole range has practically no influence on the fine dial counter constant.

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Expansion of the northern hemisphere subtropical high pressure belt: trends and linkages to precipitation and drought

A critical issue in research concerning long-term climate change is the relationship between circulation features and global temperature variations. We establish that the annual areal size of the northern hemisphere subtropical high pressure belt (SHPB), as defined by seven 500-hPa height isohypses, shares over 70% of the variability with global annual near-surface air temperature since 1948. The area enclosed by the 5850-m isohypse of the 500-hPa surface in the northern hemisphere has more than doubled since the 1950s, with greatest increases over northern Africa, the Middle East and India. A long-term historical run of a coupled global climate model shows rapidly increasing SHPB annual sizes, since the mid-1970s. Since the SHPB’s descending air produces increased aridity, SHPB expansion may transition humid regions to more arid lands. To examine this aspect, first, variations in recorded precipitation using a gridded database for the region experiencing expansion of the SHPB show a decrease in precipitation (though significant only at the 88% confidence level) over the last 60?years. Second, variations in a 0.5° spatial resolution monthly drought index, the Standardized Precipitation Evapotranspiration Index, are highly correlated (+0.78) with annual variations in the area enclosed by the 500-hPa height isohypses. These results support those of previous investigations that suggest further northward expansion of the northern hemisphere subtropical dry zones with continued global climate change.