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  • Springer Science + Business Media  (1,731)
  • 1995-1999  (1,731)
  • 1999  (1,731)
  • 1
    Publication Date: 1999-10-01
    Description: The distribution of controlling pressure formations, occurring in the Northern Hemisphere during the winters (January and February) of the years 1952 – 1996, has been analysed. It was found that the deepening of the Icelandic and Aleutian pressure lows is connected not only with a particular QBO phase and level of geomagnetic activity (Bochníček et al., 1999) but also with a particular level of solar activity. ©1999 StudiaGeo s.r.o.
    Print ISSN: 0039-3169
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  • 2
    Publication Date: 1999-01-01
    Description: The low frequency (LF) nighttime radio-wave absorption in the lower ionosphere has been measured at Průhonice (50°N, 15°E) in central Europe for over 35 years. Digital measurements, performed since summer 1988, allow absorption oscillations in the period range 10 – 180 mins, which are believed to reflect gravity wave activity, to be derived. Unfortunately, problems with the transmitter in recent years terminated the evaluation of gravity wave activity. The analysis of the available information (∼6 years of data) allows two conclusions to be drawn as to the effects of the solar activity on gravity wave activity: (1) there is no detectable effect of the solar ∼27-day variation on gravity wave activity; (2) there is an indication that the positive effect of the 11-year solar cycle on gravity wave activity in the winter half of the year is remarkable (lack of data in summer). The result concerning the solar cycle effect is, to a certain extent, preliminary, because the available data do not cover a complete solar cycle. A comparison with results from other stations and an interpretation of results are presented. ©1999 StudiaGeo s.r.o.
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  • 3
    Publication Date: 1999-07-01
    Description: The equatorial ring current is the symmetrical plasmaspheric drift current of energetic plasma trapped by the geomagnetic field. Assuming that, during a geomagnetic storm, the ring can exchange energy with other regions of the magnetosphere, a second-order differential equation must be considered as its dynamical expression, and contributions other than the solely solar-wind-induced electric field must express the forced input. The decay parameters of the recovery phase of the storm must be determined considering periods with Bz(IMF) ≍ Bz′(IMF) ≍ 0. ©1999 StudiaGeo s.r.o.
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  • 4
    Publication Date: 1999-05-01
    Description: The natural variations of the Earth's magnetic field of periods spanning from milliseconds to decades can be used to infer the conductivity-depth profile of the Earth's interior. Satellites provide a good spatial coverage of magnetic measurements, and forthcoming missions will probably allow for observations lasting several years, which helps to reduce the statistical error of the estimated response functions. Two methods are used to study the electrical conductivity of the Earth's mantle in the period range from hours to months. In the first, known as the potential method, a spherical harmonic analysis of the geomagnetic field is performed, and the Q-response, which is the transfer function between the internal (induced) and the external (inducing) expansion coefficients is determined for a specific frequency. In the second approach, known as the geomagnetic depth sounding method, the C-response, which is the transfer function between the magnetic vertical component and the horizontal derivative of the horizontal components, is determined. If one of these transfer functions is known for several frequencies, models of the electrical conductivity in the Earth's interior can be constructed. This paper reviews and discusses the possibilities for induction studies using high-precision magnetic measurements from low-altitude satellites. The different methods and various transfer functions are presented, with special emphasis on the differences in analysing data from ground stations and from satellites. The results of several induction studies with scalar satellite data (from the POGO satellites) and with vector data (from the Magsat mission) demonstrate the ability to probe the Earth's conductivity from space. However, compared to the results obtained with ground data the satellite results are much noisier, which presumably is due to the shorter time series of the satellite studies. The results of a new analysis of data from the Magsat satellite indicate higher resistivity in oceanic areas than in continental areas. However, since this holds for the whole range of periods between 2 and 20 days, this difference probably is not caused purely by differences in mantle conductivity (for which one would expect less difference for the longer periods). Further studies with data from recently launched and future satellites are needed. ©1999 Kluwer Academic Publishers
    Print ISSN: 0169-3298
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  • 5
    Publication Date: 1999-03-01
    Description: Liquid and solid particles in the plumes of jet aircraft cruising in the upper troposphere and lower stratosphere lead to the formation of ice clouds (contrails), modify the microphysical properties of existing cirrus clouds, and provide sites for heterogeneous chemical reactions. Characterization of aviation-produced particles in terms of physico-chemical properties is an important step in assessing the global impact of aircraft emissions upon atmospheric chemistry and climate parameters. Chemistry and microphysics of the gas-aerosol system in aircraft plumes and its evolution in the atmosphere is a field of intense research. This paper reviews the current knowledge (mid-1998) and outlines possible atmospheric implications. ©1999 Kluwer Academic Publishers
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  • 6
    Publication Date: 1999-01-01
    Description: Measurements on thermal conductivity and diffusivity as functions of temperature (up to 1150 K) and pressure (up to 1000 MPa) are presented for Archaean and Proterozoic mafic high-grade rocks metamorphosed in middle and lower crustal pressures, and situated in eastern Finland, central Fennoscandian Shield. Decrease of 12–20% in conductivity and 40–55% in diffusivity was recorded between room temperature and 1150 K, which can be considered as typical of phonon conductivity. Radiative heat transfer effects were not detected in these samples. Pressure dependencies of the samples are weak if compared to crystalline rocks in general, but relatively typical for mafic rocks. The temperature and pressure dependencies of thermal transport properties (data from literature and the present study) were applied in an uncertainty analysis of lithospheric conductive thermal modellings with random (Monte Carlo) simulations using a 4-layer model representative of shield lithosphere. Model parameters were varied according to predetermined probability functions and standard deviations were calculated for lithospheric temperature and heat flow density after 1500 independent simulations. The results suggest that the variations (uncertainties) in calculated temperature and heat flow density values due to variations in the temperature and pressure dependencies of conductivity are minor in comparison to the effects produced by typical variations in the room temperature value of conductivity, heat production rate or lower boundary condition values. ©1999 Kluwer Academic Publishers
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  • 7
    Publication Date: 1999-01-01
    Description: Planetary magnetospheres are natural laboratories for many interesting plasma physical processes which are difficult to study under normal laboratory conditions. Among the major processes occurring in space plasmas are the reconnection phenomenon and field line resonances. This paper deals with the second of these processes. A field line resonance is the resonant coupling between an isotropic mode and an anisotropic mode in a magnetized plasma. Field line resonances allow us to understand many features of ultra-low frequency oscillations in the terrestrial magnetosphere, that is resonant mode coupling is the current paradigm to explain geomagnetic pulsations. A brief historical introduction as well as a physical description of the field line resonance is given. Resonant mode coupling is discussed for the terrestrial, Hermean (Mercury), and Kronian (Saturn) magnetospheres, which represent natural laboratories with different conditions such as size of the laboratory, the background plasma density and composition, and the strength of the magnetic field. This comparative approach allows a deeper insight into the critical coupling problem than an isolated study of the terrestrial field line resonance phenomenon. Finally, resonant mode coupling between elastic wave modes in the solid Earth is briefly tackled and compared with the magnetospheric situation. ©1999 Kluwer Academic Publishers
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  • 8
    Publication Date: 1999-12-15
    Description:  The relationship between European surface temperature and winds over the eastern North Atlantic are investigated for the years 1988 to 1997. Daily Special Sensor Microwave Imager SSM/I observations are used to evaluate a monthly surface wind index that quantifies the influence of southwesterly flow. Our wind index and the monthly-mean surface-air temperatures in late winter and early spring over France and northern-latitude Europe are highly correlated. In February, the year-to-year increases/decreases match every year for France (correlation of 0.82 with the Index); and every year with just one exception for Europe (correlation with the Index of 0.76 for a longitudinal strip through Europe 45–50° N, and 0.73 for the 50–60° N strip). In March, the increases/decreases of the wind Index and of the temperatures for France also match, but the correlation with the Index is lower, 0.65. The high correlation between our Index and the large interannual fluctuations in the monthly temperature in late winter and early spring indicate that the onset of the spring conditions in Europe is significantly influenced by the wind patterns over the eastern North Atlantic. Coinciding with the fluctuations from warm-Europe/high-Index winter to the opposite conditions, we observe “seesaw” effects, fluctuations over the North Atlantic, in opposite directions in the east (25–5° W), and the west (65–45° W). In the low-Index years we find that: (a) the surface-air temperatures in the west are appreciably higher than in the east (but slightly lower in the high-Index year), and (b) the difference between the 500 mb meridional wind in the west and that in the east is positive and large, exceeding 10 m s−1 (but it becomes negative and small in the high-Index years). The “seesaw” effects suggest that a positive feedback exits between these cross-Atlantic temperature differences and the surface winds. ©1999 Springer-Verlag/Wien
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  • 9
    Publication Date: 1999-12-15
    Description:  The summer monsoon circulation shows various spatial and temporal oscillations and often a combination of systems produces an integrated effect. In this study phases of the southwest (SW) monsoon have been identified in an objective manner with the help of T-mode principal component analysis (PCA) of weekly rainfall anomalies. Mean composite charts have been prepared utilising all available upper air data (1977–1986) for each category of the SW monsoon epochs identified by the PCA. These sets of charts have been constructed for both the strong and weak phases associated with the first four significant principal components (PCs). A well defined east-west oriented trough system, extending from about 28° N Latitude/65° E Longitude to 20° N Latitude/90° E Longitude, in the lower levels, has been the main feature associated with the strong phase of the monsoon corresponding to PC I. The trough in the lower levels is more marked in the eastern half compared to the western half in both the sets of charts associated with strong phases of the monsoon related to the PC II and PC III. With PC II, the position of the troughs in the lower levels is further north of its location in PC III. The east-west trough system associated with the strong phase of PC IV has a large southward tilt with height. The charts corresponding to the weak phases of these PCs have synoptic features, such as the position of the trough close to the foothills of the Himalayas, and the shifting of middle and upper tropospheric anticyclones to the south. The study suggests an objective method of interpretation of principal components by utilising synoptic data. In addition, synoptic models and data sets corresponding to different phases of the monsoon can also be prepared in an objective manner by such PCA. ©1999 Springer-Verlag/Wien
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  • 10
    Publication Date: 1999-12-15
    Description:  The variations and trends of hourly sunshine duration at Ankara for the period 1955–1996 were examined. A tangible change of 7 percent was determined relative to the annual baseline. Decreases were detected in each hour of the day and appear to be highest at sunrise and sunset. Changes in relative humidity that may lead to changes in the threshold of the sunshine recorders were evaluated in order to explain the decreases of sunshine duration. Correlations with other meteorological parameters were also analysed. The results indicate that the variations and trends in sunshine duration can be explained by changes in the other meteorological parameters. ©1999 Springer-Verlag/Wien
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  • 11
    Publication Date: 1999-12-15
    Description:  Degree-days as a measure of accumulated temperature deviations from a base temperature have many practical applications in various human related activities such as home cooling, heating, plant growth in agriculture and power generation in addition to energy requirement. Long temperature records are necessary for their reliable estimations at given stations. In this paper, degree-day measure has been applied to monthly temperature records for systematically changed base temperature values from − 25 °C to + 35 °C with 5 °C increments at 255 meteorology stations in Turkey. The results are represented in the form of spatial degree-day distribution maps, which are then related to various climatic, meteorological and topographic features of Turkey. For instance, free surface water bodies in forms of surrounding seas, lakes and rivers insert retardation in the expansion of heating degree-days over large regions. On the other hand, cold air penetration from polar regions in the northeastern Turkey originating from Siberia appears at moderate base temperature heating degree-days. ©1999 Springer-Verlag/Wien
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  • 12
    Publication Date: 1999-12-15
    Description:  The Mediterranean basin experiences considerable cyclone activity mostly during fall, winter and spring and diminished activity during summer. In this study we present results of synoptic disturbance track analysis for two contrasting winter months and two, near average, summer months over the eastern Mediterranean. The surface and 500 hPa disturbance tracks were subjectively analyzed from two points of view. First, looking at tracks of conventionally defined cyclone centers (eddies) based on actual pressure and height distribution and second, looking at tracks of transient cyclonic disturbances (TRADs), defined as centers of negative deviations from the time mean. The second type of analysis demonstrated a considerable increase in the number of detectable tracks. Over the Mediterranean and vicinity the ratio between the number of surface TRAD tracks to cyclone tracks is, about 2, whereas at 500 hPa the ratio is much higher, about 5. However, the average life span of transient disturbances was only slightly longer than that of conventional cyclones (mainly at 500 hPa). At the surface and at 500 hPa about 50% of the cyclone tracks coincided to a certain extent with TRAD tracks. In summer, when conventional analysis over the eastern Mediterranean yields mostly quasi‐stationary low pressure centers associated with the Persian Gulf Trough, we detected clear signs of transient disturbances. Some interpretations of the differences between cyclones and TRADs in terms of weather in the eastern Mediterranean are also made. ©1999 Springer-Verlag/Wien
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  • 13
    Publication Date: 1999-12-15
    Description:  Numerical models are often the only means available to generate solar irradiance (SR) information, for historical or future SR specifications as well as due to inadequacies of contemporary SR measurements. This paper evaluates five such models that have been proposed as generic and applied as such. Special emphasis is given to Solar123, an integrative model rooted in Lambert’s Cosine Law and Bouguer’s Law with globally-parameterized atmospheric property functions and with input limited to precipitation, air temperature, geographic location, topography and rudimentary land cover information. The selected SR models in general perform well in reproducing the SR data for the USA, with a root mean square error-to-data mean ratio (RMSE/SRmean ratio) of 9.8–11.4%. A possible exception is the Bristow-Campbell logic as implemented by the Vegetation/Ecosystem Modeling and Analysis Project. Beyond the USA, Solar123 yields an RMSE/SRmean ratio of 8–17% by region (196 stations in total), generally outperforming the other SR models. Compared to time-sequential monthly SR data, projections by Solar123 have an RMSE/SRmean ratio of 8.6–14.1% for six weather stations representative of major climate regimes in Canada, or an RMSE/SRmean ratio of 13–24% for three forest sites in the USA, Germany and Japan. Solar123 projections also compare favorably against the output from the General Circulation Models in terms of ratio change in SR with the doubling of the atmospheric carbon-dioxide concentration: the two fall within ±10% of each other for 85% of a total 264 cases, and within ±20% for all but 3 of the cases. The above statistics suggest that Solar123 represents an improvement over other SR models not only in configuration but also in projection accuracy, and that Solar123 is useful for projecting spatial variation in SR across weather stations around the world and over different land covers, and for projecting temporal variation in SR under the present climate regimes and likely for regimes changed beyond the present fluctuation range. The work further calls into question the common practice of applying SR data irrespective of local land cover. ©1999 Springer-Verlag/Wien
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  • 14
    Publication Date: 1999-12-15
    Description:  The question discussed in this study is how to calculate linear trends in data that are not distributed evenly in time. This is examined with time series of ten climate elements at a single station, stratified according to a classification based on daily circulation patterns. Trends are calculated in three different ways: (i) from seasonal means, which is a common approach, (ii) from means of individual events, the event being defined as a sequence of days classified as one particular type, preceded and succeeded by another type, and (iii) from individual daily values. The most common method of estimating trend significance, i.e. the t -test of the Pearson correlation coefficient, has been shown to be applicable to seasonal and event-mean trends for all variables. For daily trends, the Monte Carlo test should be used instead. The daily, event-mean and seasonal trends differ from each other considerably for many combinations of climate variable and circulation type. The reason for this difference is identified. ©1999 Springer-Verlag/Wien
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  • 15
    Publication Date: 1999-10-28
    Description:  The surface air temperature time series of both hemispheres and the North Atlantic European area as well as the Southern Oscillation (SO) index time series were analysed using a wavelet transform technique. The values of the so-called singularity exponents of these series were estimated and compared with such estimations for some surrogate time series artificially created from the observed temperature series. It was concluded that the climate dynamics on interannual and interdecadal scales may be considered as a kind of classical Brownian motion although its consideration as a flicker-noise is also possible. The extracted temperature variations were shown to be closely coupled with the SO process. The wavelet-transformed SO series reveals itself as a whole self-similar “tree” the main branches of which are the appearances of the strongest El-Ninos of 1898 – 1899, 1941 – 1942, and 1982 – 1983. Similar “trees” can be seen in the wavelet-transformed temperature series. Thus, the extracted temperature variations were shown to be closely coupled with the SO process, and a decomposition of the current global climate dynamics into three climatic epochs (of about 40-year long) seems to be appropriate. ©1999 Springer-Verlag/Wien
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  • 16
    Publication Date: 1999-12-15
    Description:  Daily maximum and minimum temperatures from 40 stations in Israel were analyzed to detect long-term trends and changes in temporal and spatial distribution patterns during the second half of the 20th Century. The trend analysis, reveals a rather complex changing pattern, with a significant decreasing trend of both the daily maximum and minimum temperature, during the cool season, and an increasing trend during the warm season. On an annual basis, there seems to be almost no temporal trends in minimum and maximum temperatures since the changes in winter and summer show an opposite tendencey. ©1999 Springer-Verlag/Wien
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  • 17
    Publication Date: 1999-10-28
    Description:  We investigate in the present paper the relationship between satellite count, global irradiance and other solar and illumination resource components, bringing a particular attention to low solar elevation situations (below 20 °) which are very important in northern latitudes. Our investigation is based on data from two geostationary satellites, METEOSAT and GOES, backed by ground measurements in Switzerland and the northeastern USA. The study of different clear sky normalizations lead to the conclusion that a linear correlation between the global clearness index and the irradiance (like the heliosat method) would be inaccurate for low solar elevations, and therefore for high latitude regions. We developed a model that directly relates an elevation dependent clearness index to the could index. This methodology presents a definite advantage because it can be generalized to address the clearness index of other solar radiation components, besides global irradiance, such as direct irradiance, diffuse illuminance, etc. The correlations described in this paper were developed on the data from Geneva (in the frame of the EC program “Satellight”) and evaluated on two other independent data sets (Albany, USA and Lausanne, Switzerland). Their precisions, on a hourly basis, are respectively 30%, 40% and 60% for the global, diffuse and beam components) (90,55 and 95 W/m2). The use of independent data for thederivation and the validation of the models shows thatthose can be used in a wide range of locations, even if the applicability has to be assessed for very different climates. ©1999 Springer-Verlag/Wien
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  • 18
    Publication Date: 1999-12-15
    Description:  Anomalously wet and dry months in the Mediterranean basin were identified during the period 1860–1990 from observations at five stations located along the west-east axis of the Mediterranean basin (Barcelona, Florence, Malta, Athens and Jerusalem), supplemented by data from Madrid and Lisbon. Wet and dry months were characterized by hydric indices (HI) based on values of the standardized precipitation anomalies. Different patterns of anomalously wet and dry months were qualitatively identified on the basis of the spatial distributions of the hydric indices. The standardized sea level pressure values at 56 grid points in the domain 35° N–65° N, 30° W–40° E, for each of the anomalously wet and dry months, were subjected to T-mode Principal Component Analysis. The mean hydric indices associated with each principal component in each season are arranged in four distinct different spatial distributions for wet months and in three for dry months as following: (a) Mediterranean wide distribution of positive/negative anomalies; (b1) Strong positive anomalies to the west, but weaker to eastern Mediterranean; (b2) Strong negative anomalies to the west, but weaker or normal to the east; (c1) Strong positive anomalies to the west and to the east and weaker ones to the central Mediterranean; (c2) Negative anomalies to the west and east, but weaker, or normal, or positive to the central Mediterranean; (d) Relatively strong positive anomalies to the east and weaker ones to the western Mediterranean. Finally, monthly mean charts of standardized anomaly and mean sea level pressure are presented for each principalcomponent in each season. These charts are used to interpret the spatial distribution of the positive and negative precipitation anomalies in terms of mean circulation over the domain. ©1999 Springer-Verlag/Wien
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  • 19
    Publication Date: 1999-12-15
    Description:  The moisture flux and water balance over the South China Sea (SCS) during late boreal spring and summer are studied using the reanalysis data of the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP/NCAR). It is shown that the SCS is a water vapor sink during that period of time. Climatologically, the SCS works like a “reservoir of water vapor” for its special geographical location. In early May, water vapor is brought into the SCS area through its eastern, southern, and western boundaries, and is transported out of that area through its northern boundary. From June to August, the western and southern boundaries of the SCS are inflow passes of moisture flux to that region, while the northern and eastern boundaries are outflow passes. It is the intense convergence of moisture to the SCS area that maintains the local heavy precipitation. The northward branch of moisture flux feeds the precipitation over eastern China. ©1999 Springer-Verlag/Wien
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  • 20
    Publication Date: 1999-12-15
    Description:  Extended non-hierarchical cluster analysis is improved by deriving the initial cluster number and estimating the outliers in the final cluster set. These improvements are tested and compared with an established cluster algorithm using a toy example. Applying the improved cluster analysis to a classification of the European climates shows that the proposed techniques can be of great practical relevance. ©1999 Springer-Verlag/Wien
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  • 21
    Publication Date: 1999-10-28
    Description:  Since 1990 the Laboratory for Atmospheric Physics at the University of León has made use of a network of 250 hailpads spread over an area of 1000 km2 in the province of León (north-western Spain). By the end of 1995, the network had detected 25 hailfalls of more than 15 km2 in area, registered on 13 different days during the summer months. The 25 hailfalls were precipitated over more than 300 separate hailpads, leaving nearly 40 000 measurable prints. The size of each hailstone, whose mass and kinetic energy were taken simply as a function of the diameter of the stone was calculated using the hailpad network. In this way, an estimate has been made of the total quantity of ice which fell in each hailfall (circa 19 000 metric tons on average, although a figure ten times this was calculated for one particular hailstorm). The spatial evolution of the physical variables of the hail, determined from each pad, has also been graphically represented. In addition, the distribution of hailstone sizes has been analysed, and the characteristic distribution parameters calculated. Although exponential distribution is often used, the Kolmogorov-Smirnov test of goodness-of-fit shows a better fit for gamma distribution. The information provided by these parameters has been analysed for both distributions, in relation to some specific variables associated with hail. There is a good correlation between total energy and mass precipitated, but the quantity of hail per unit area correlates with the total energy or mass of the precipitation only through the area affected. The size distribution parameters only show good correlations with the maximum hailstone size recorded. ©1999 Springer-Verlag/Wien
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  • 22
    Publication Date: 1999-10-28
    Description: The qualitative agreement of two climate models, HADCM2 and ECHAM3, on the response of surface climate to anthropogenic climate forcing in the period 2020 – 2049 is studied. Special attention is paid to the role of internal climate variability as a source of intermodel disagreement. After illustrating the methods in an intermodel comparison of simulated changes in June–August mean precipitation, some global statistics are presented. Excluding surface air temperature, the four-season mean proportion of areas in which the two models agree on the sign of the climatic response is only 53 – 60% both for increases in CO2 alone and for increases in CO2 together with direct radiative forcing by sulphate aerosols, but somewhat larger, 59 – 70% for the separate aerosol effect. In areas where the response is strong (at least twice the standard error associated with internal variability) in both models, the agreement is better and the contrast between the different forcings becomes more marked. The proportion of agreement in such areas is 57 – 75% for the response to increases in CO2 alone, 64 – 84% for the response to combined CO2 and aerosol forcing, and as high as 88 – 94% for the separate aerosol effect. The relatively good intermodel agreement for aerosol-induced climate changes is suggested to be associated with the uneven horizontal distribution of aerosol forcing. ©1999 Springer-Verlag/Wien
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  • 23
    Publication Date: 1999-10-28
    Description:  Bright sunshine duration (BSD) is of singular importance for estimating solar irradiance, and its data base is small in comparison. This paper reports a generic algorithm that captures global variation in monthly BSD data in relation to temperature, precipitation and geographic location. The algorithm depicts BSD in terms of reduction from daylength as a negative exponential function of standard station pressure, with the exponential reduction rate as proportional to the product of a series of multiplicative functions reflective of global generalities and regional idiosyncrasies. The algorithm is parameterized by regression fitting to monthly climate normal data for 729 stations worldwide. It accounts statistically for 85% of the variance in the BSD data, with a root mean square error of 1.0 hr, or 15% of the data mean. The data fitting tends to be least robust for tropical humid climates or for tropical and subtropical monsoonal Asia. The spatially-based algorithm projects with a reasonable accuracy 5-yr sequential monthly BSD data for five stations representative of the climate regimes in the conterminous United States: the absolute error is within ±1.5 hr for 70% to 93% of the 60 monthly mean BSD values for each of the stations. ©1999 Springer-Verlag/Wien
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  • 24
    Publication Date: 1999-10-28
    Description:  Vertical profiles of drainage winds were monitored continuously by a Doppler-Mini-Sodar during case studies in two valleys, on both sides of the U. S. Continental Divide. A tethered balloon provided additional information on the vertical temperature and wind structure up to the Divide level. Ambient wind data were collected by a radar wind profiler on the west side, and a tower on the crest of the Divide. The onset, evolution and breakup of the drainage flow were studied on two nights, when the ridge-top winds were westerly and skies were clear. To study the influence of the ambient flow on drainage winds, changes in drainage wind speed, direction and depth, along with the volume flux were examined. It was found that, on the leeward side, the drainage was strongly influenced by the ambient winds (King, 1995b), which led to interruption and erosion of the locally generated valley flow. The drainage on the windward side of the Divide was almost undisturbed. A comparison of balloon and sodar wind profiles showed very good agreement during steady drainage conditions. ©1999 Springer-Verlag/Wien
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  • 25
    Publication Date: 1999-10-28
    Description: Rainfall amounts and the distribution across the landscape are critical to decision-making and evaluation of hydrological models. Spatial variation in rainfall has been observed through anecdotal evidence and limited studies; however, there is little quantitative evidence that can be used to assess rainfall variation within a watershed on a daily, monthly, or yearly temporal scale. This study was conducted to quantify the spatial variation within a watershed in central Iowa and to determine if there were consistent differences among rain gages for the period from 1991 through 1998. The study was conducted within Walnut Creek watershed located south of Ames, Iowa on the Des Moines Lobe Landform region. The topography of this 5130 ha watershed is characterized by gently rolling fields with a narrow area of steeper land along the stream in the lower part of the watershed. Twenty-two tipping bucket rain gages were placed throughout the watershed and rainfall was recorded as 5 minute totals and then aggregated into daily totals. Accumulation of errors of the 5 minute values into the daily totals were considered to be random. There was a large coefficient of variation in the average daily totals; however, there was no consistent pattern of variation among rain gages, and coefficient of variation decreased with amount of rain. Each rain gage had an equal chance of receiving the lowest or highest rainfall total for any given storm event. When the daily average was computed over the year, there were no differences among rain gages. Monthly and yearly totals showed a decreased coefficient of variation compared to daily totals. There was no consistent pattern of spottiness within the watershed and if daily rainfall amounts are required for a decision, then direct measurements may be required. ©1999 Springer-Verlag/Wien
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  • 26
    Publication Date: 1999-10-28
    Description:  Using climatic data from Fairbanks and rurally situated Eielson Air Force Base in Interior Alaska, the growth of the Fairbanks heat island was studied for the time period 1949 – 1997. The climate records were examined to distinguish between a general warming trend and the changes due to an increasing heat island effect. Over the 49-year period, the population of Fairbanks grew by more than 500%, while the population of Eielson remained relatively constant. The mean annual heat island observed at the Fairbanks International Airport grew by 0.4 °C, with the winter months experiencing a more significant increase of 1.0 °C. Primary focus was directed toward long-term heat island characterization based on season, wind speed, cloud cover, and time of day. In all cases, the minima temperatures were affected more than maxima and periods of calm or low wind speeds, clear winter sky conditions, and nighttime exhibited the largest heat island effects. ©1999 Springer-Verlag/Wien
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  • 27
    Publication Date: 1999-10-28
    Description:  Six methods were used to interpolate the monthly mean climatological data from German climate stations to three Bavarian forest climate stations. The observed forest climatological data at the Bavarian forest climate stations were used as the reference data to which the interpolated data were compared. The results show that, for monthly mean daily maximum temperature at valley and plain forest climate stations, each of the six interpolation methods can give accurate estimates. For monthly mean daily maximum temperature, minimum temperature, air temperature and water vapor pressure at mountain forest climate stations, topographically aided interpolation can give the most accurate estimates. Barnes interpolation combined with empirical transfer functions can give accurate estimates forall climate variables at the plain and valley forest climate stations, and it can also give accurate estimates for monthly mean wind speed and monthly precipitation at the mountain forest climate station. The empirical transfer functions are very important for estimating the forest climatological data. These transfer functions will be used for reconstruction of long-term forest climatological data in Bavaria. ©1999 Springer-Verlag/Wien
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  • 28
    Publication Date: 1999-10-28
    Description:  A K-type diffusion model coupled with a massconsistent wind model is applied for one of the rural biological waste disposal sites in Austrian Alps. The site is situated in the Pöls valley in the eastern Alps, 250 km south-west of Vienna in Austria Aim of the study is to demonstrate dispersion of H2S from the site to near by village. Model simulations are carried out each for an evening and a morning transition case characterized by flow reversals. The role of locally generated wind in changing the pollutant distribution over nearby residential area is investigated. Surface observations at two stations toward the open boundaries of the main valley are used to derive the turbulence parameters and then to obtain initial inputs of wind profiles. The turbulence parameters behave analogous to that over a plane terrain after the establishment of the valley wind. The model simulations are done for eight hours during the evening transition and eighteen hours for the morning transition by incorporating the wind field from a mass consistent wind model. The results are compared with SF6 tracer experiments conducted during those periods. The model outputs and the observations at various points inside the valley are in good correlation except for NW part of the valley after the reversal of valley wind. The results also reveal the potential of a simple approach with minimized inputs. ©1999 Springer-Verlag/Wien
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  • 29
    Publication Date: 1999-08-24
    Description: A lack of information for surface water vapor pressure (WVP) represents a major impediment to model-assisted ecosystem analysis for understanding plant-environment interactions or for projecting biospheric responses to global climate change. This paper reports on a generic algorithm that captures global variation in monthly WVP. The algorithm solves WVP in terms of reduction from saturation WVP as a negative exponential function of potential evapotranspiration; the reduction rate per unit potential evapotranspiration in turn varies with monthly precipitation and a series of variables that distinguish local climate regimes. Data input to the algorithm is limited to monthly air temperature and precipitation, plus latitude, longitude and elevation. The algorithm is specified through regression fitting to monthly climate normal data from 852 stations around the world. It accounts for 96% of the variance in the WVP data, with a root mean square error of 0.17 kPa, or 12% of the data mean. The algorithm closely reproduces five-year sequential monthly WVP data for each of five selected United States locations representitative of diverse climate regimes: the average error generally falls within ±12% of the data mean, and the absolute error within ±0.2 kPa. Its projections also compare favorably against the WVP output from the General Circulation Models for temperature and precipitation conditions under the scenario of a doubled atmospheric carbon-dioxide concentration: the two fall within ±10% of each other for 75% of a total 264 data cases, or within ±20% for 94% of the cases. These statistics suggest that the spatially-based algorithm is useful for projecting temporal variation in WVP, and for extrapolative applications beyond the fluctuation range of present climate. ©1999 Springer-Verlag/Wien
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  • 30
    Publication Date: 1999-08-24
    Description: This paper describes an attempt to define mesoscale daily precipitation and temperature regimes over Sardinia and their relation to different synoptic patterns. In order to address this task an extensive Cluster Analysis was performed on the whole data set using a number of methods, each including several distance measures. Thirty years of daily data, for the period ranging from 1951 to 1980 for the 114 stations with precipitation and 20 with temperature, were used in the study. In order to retrieve homogeneous clusters, non-hierarchical methods were found to be more effective and the use of a correlation-like distance was more effective for precipitation. To discriminate between the different clusters, the corresponding mean mass fields for the 500 hPa height and sea level pressure were used and an analysis of synoptic situations linked to mesoscale regimes was performed. The results show that at least two mean surface patterns exist corresponding to clearly different synoptic situations. Nevertheless, physical considerations led us to consider three distinct clusters, two of which correspond to specific synoptic circulations with slight, but meteorologically significant, differences. ©1999 Springer-Verlag/Wien
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  • 31
    Publication Date: 1999-08-24
    Description: A statistical-dynamical downscaling procedure is applied to investigate the climatological wind field over a complex terrain area in central Germany. The model domain, 80×87 km, is dominated by flat terrain in the westerly and northerly part and encompasses the Teuteburger Wald and the Wiehengebirge areas with hills up to 330 m a.m.s.l. in the southeasterly region. The downscaling procedure combines a large-scale regionally representative wind statistic and a high-resolution numerical atmospheric mesoscale model. A cluster analysis of a 12-years time series of radiosonde data provides 143 clusters each being a combination of the geostrophic wind components and the vertical temperature gradient. These parameter sets constitute the reference state for highly-resolved steady-state wind field simulations with a non-hydrostatic model. Weighting the resulting wind fields with the corresponding cluster frequency gives climatologically representative frequency distributions of the wind speed and -direction. By combining the wind speed frequency distribution with the power curve of wind turbines the yearly energy output of 46 wind turbines inside the simulation domain was calculated and compared to the actual production. No bias or systematic trend in the deviation was found. The relative differences for the smallest turbines reach 100 percent with a decreasing tendency to larger units. ©1999 Springer-Verlag/Wien
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  • 32
    Publication Date: 1999-08-24
    Description: Annual cyclone and anticyclone numbers in addition to the temperature data for the northern hemisphere are processed through simple models leading to meaningful interpretations. Historical climatological characteristics of the cyclone and anticyclone numbers are modeled by a first order Markov process. Statistically indistinguishable synthetic cyclone and anticyclone numbers are generated. Polygon diagrams which show the mutual relationships between average cyclone (anticyclone) numbers and the temperature are employed for finding possible relevant climatological changes during the record period. A polygon diagram concept is proposed and applied in order to identify sub-period warming and cooling spells of any desired short or long term durations and their relationship to the annual number of cyclone (anticyclone) occurrence numbers. The results indicate a decrease (increase) in the cyclone and anticyclone numbers during cooling (warming) periods. The methodologies proposed in this paper can be easily adopted for cyclone and anticyclone numbers modeling in any part of the world. ©1999 Springer-Verlag/Wien
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  • 33
    Publication Date: 1999-10-28
    Description:  The winter wind regime of Göteborg, located on the West coast of Sweden, is composed of three different wind systems besides the ambient wind; a nocturnal low level jet (NLLJ), a winter land breeze (WLB) and an urban heat island circulation (UHIC). An inversion divides the air column into two layers, one between 10 – 50 m and one between 50 – 100 m. The UHIC is located in the lower layer, the WLB in the top layer and the NLLJ above the top layer. The intensity of the interacting processes depends on the stability of each layer as calculated from the bulk Richardson number (BRilow and BRihigh) using continuous data collected during four years (1991 – 94) from two sites (one within and one outside the urban area) and sampled at three levels. In the evening the WLB develops from the ground level and increases in height until after midnight. At about the same time an UHIC develops in the urban area, below the WLB and causing an uplift of the latter. However, at both sites the WLB does not exceed the 100 m level. At this time BRi in both layers are below one resulting in continuous coupling between the WLB, the UHIC layers and the regional wind. Consequently, the exchange of momentum is still effective between all layers and this is highlighted by a change in the wind direction and a regulation of wind-speed to more constant levels. When BRihigh≥1, the layers become frictionally decoupled, as indicated by a return in the wind direction in the top level to the regional wind, and an acceleration of the top wind. The top level then becomes incorporated in to a nocturnal low-level jet (NLLJ) system. The normally acknowledged development of the NLLJ, with a start around sunset, is in this case delayed for several hours at the top level. The reason for this is that there are meso-scale/local wind systems present in layers beneath the jet causing an interaction between the layers. In the morning, when the layers are again coupled the top layer wind is once more influenced by the WLB and therefore changes direction and speed. The local and meso-scale wind systems thus delay the current nocturnal wind development. ©1999 Springer-Verlag/Wien
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  • 34
    Publication Date: 1999-08-24
    Description: Groundnut production strongly contributes to Senegal’s economy. Interannual variations of groundnut yield for the country as a whole, and their relationship with rainfall amounts, are examined for the 31-yr period 1960–1990. It is shown that on that scale, and after removing decadal trends, almost half of the variance is explained by rainfall variability, especially that of the early part of the rainy season (July–August). Given the high spatial coherence of seasonal rainfall in the region, teleconnections with global- and regional-scale climate dynamics, including sea-surface temperatures, are assessed. Though some features are similar to the rest of the Sahel, others are more specific, such as the higher sensitivity to ENSO (El-Niño Southern Oscillation) and to coupled ocean-atmosphere climate anomalies over the nearby Tropical North Atlantic Ocean, which are associated to the latitudinal location of the ITCZ over the ocean. Lag-correlations with pre-season SST are also discussed. Some of these teleconnections are used to define preliminary empirical models for rainfall and groundnut yield prediction for Senegal. ©1999 Springer-Verlag/Wien
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  • 35
    Publication Date: 1999-06-23
    Description:  Reports of changes in the seasonal and annual rainfall in Nigeria suggests that a more detailed analyses of the geographic extent of these changes and of their impact on agriculture could be of value. Variation in the growing season (April to September) rainfall from stations across Nigeria was analysed over the 30-yr period, 1960–90. Regression analyses were used to examine long-term trends. Principal component and cluster analyses were used to group stations with similar trends in standardised seasonal rainfall. Mean accumulated standardised seasonal rainfall were used to examine short- and medium-term trends for each of the groups identified. Significant ( P  ≤ 0.05) decreases in rainy season rainfall were found at 8 stations mostly in the Guinea and arid/semi-arid savannas of northern Nigeria, whereas no station showed significant increases. Examination of the monthly (April through September) rainfall showed that only three – Kano, Sokoto and Potiskum in the arid/semi-arid savanna – of the twenty-three stations used in the analysis had declining rainfall trends for each of the months April to September and subsequently declining seasonal rainfall trends. However, 12 to 15 stations had consistently declining rainfall trends in atleast some but not all the growing season months. However, a similar pattern was not the case in terms of increasing rainfall trends, where only one to three stations had consistently increasing rainfall trends in some but not all of the months from April to September. Stations that showed increasing rainfall trends were in the southern parts of Nigeria. Six groups with similar patterns in standardised seasonal rainfall were identified by Principal Component and Cluster analyses. For most of the groups, the period from 1967 to 1973 was that of consistently below average seasonal rainfall. However, the timing and extent of the decline varied with location. Common to stations in four of the six groups was a negative trend in seasonal rainfall for the period considered. The geographic variation in seasonal rainfall trends has tremendous agricultural significance since there are indications that the reliability of the season is decreasing from the humid forest zone with positive seasonal trends to the arid/semi-arid savanna with significant negative seasonal trends. ©1999 Springer-Verlag/Wien
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  • 36
    Publication Date: 1999-06-23
    Description:  An attempt has been made to relate a large-scale airflow classification to the local weather at two stations in Estonia. To describe the features of the general circulation over Europe, the large-scale circulation patterns ( Grosswetterlagen ) of the German Weather Service have been chosen. Daily precipitation and temperature deviations from the monthly mean in Pärnu and Tartu for 1961–1993 have been used. It can be said that the weather in Estonia shows a good relationship with the general circulation types ( Zirkulationsformen ) that are defined by means of the Grosswetterlagen . Zonal circulation brings to Estonia wet weather that in winter is warmer than average and in summer cooler than average. Mixed circulation is associated with warmer winters and average summers. Meridional circulation brings cold winters and variable weather in summer. To explain the large dispersion of values of meteorological elements within any one circulation type, a more detailed analysis of the relationships between circulation patterns and meteorological situation in Estonia is needed. ©1999 Springer-Verlag/Wien
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  • 37
    Publication Date: 1999-06-23
    Description:  The global distribution of the contrail coverage is computed for several scenarios of aviation in the years 2015 and 2050 and compared to 1992 using meteorological analysis data representative of present temperature and humidity conditions and assuming 0.5% cover in a reference region 30° W–30° E, 35° N–75° N covering parts of western Europe and the North Atlantic. The mean contrail coverage of the Earth is computed to increase by a factor of about three compared to 1992 and to reach 0.25% in 2015. For three different scenarios of aviation and for constant climatic conditions, the global mean contrail coverage reaches values between 0.26% and 0.75% for 2050. Contrail coverage increases more strongly than total fuel burn mainly because of more traffic in the upper troposphere and because of more efficient engines with cooler exhaust. The overall efficiency of propulsion is expected to grow from about 0.3 in the fleet average of 1992, to 0.4 in 2015, and to 0.5 in 2050. The expansion of air traffic makes Canada, Alaska, the North Pacific route from North America to Japan and most of the Asian continent new regions where contrails are expected to cover more than 0.5% on average. ©1999 Springer-Verlag/Wien
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  • 38
    Publication Date: 1999-08-24
    Description: Having in mind the high complexity of the sky radiance distribution, the Commission of the European Communities, in the frame of the Solar Energy R&D in the European Community Programme, developed among other related fields of research a clear sky radiance model. This model, the so-called EC-Model, was intended for the estimation of the diffuse irradiance falling on an inclined surface by integration of the sky radiance field. It represents a progress development over its predecessor, the Berlin model, and takes into account all the scientific knowledge about this topic, lying heavily on the principles of the Liebelt formulation and the work of Steven and Unsworth on the observed relative radiance distribution. The European Solar Radiation Atlas was in part prepared by the adoption of the EC-Model and could not take into account Valko’s new results about sky radiance distributions, because of time coincidence and that only previous results were ready at the time it was published. In this work, we focus on the EC-Model behaviour, against experimental sky radiance data from Toronto, Canada. The SKYSCAN’834 Data Set is a well-known database, which we have used in order to investigate the EC-Model behaviour both under its original formulation (the one that has been used in the development of the Atlas) and under the modified version suggested by Valko’s results. Even though we are considering data from outside Europe, the results of this test let us establish the model limitations and the modifications that should be done to it. ©1999 Springer-Verlag/Wien
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  • 39
    Publication Date: 1999-06-23
    Description:  A study of the variability of Australian surface maximum and minimum temperature on seasonal and longer time scales for the period 1950 to 1994 is described. Using principal component analysis in the S-mode, it is shown that the variability of Australian temperature is dominated by the large scale, with approximately 80 percent of the temporal variance being explained by five independent modes. The application of orthogonal rotation techniques to these modes, has revealed that this variability displays much simple structure and is physically interpretable in terms of five largely non-overlapping spatial patterns. These five patterns, centred over the east, north, southwest, northwest and southeast of Australia are found when the analysis is performed on maximum and minimum temperature, using monthly, seasonal and annual data and appear to be a natural and optimal subdivision of the Australian region for the description of land surface temperature variability. The highly compressed description of the temperature data provided by the rotated principal component modes is then used to investigate the characteristics and some mechanisms of Australian temperature variability. This analysis confirms the presence of a secular warming trends across much of Australia, but also reveals that some 80 to 90 percent of the temporal variance is unrelated to this trend. The role of rainfall and the El Niño-Southern Oscillation (ENSO) in modulating temperature is also investigated. ©1999 Springer-Verlag/Wien
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  • 40
    Publication Date: 1999-06-23
    Description:  Historical daily rainfall events, measured at different Italian stations, are found to follow fractal relationships within specific time ranges. It is found that the fractal dimension D describes the strength of the clustering of daily rainfall events in a more realistic way than the commonly used number of daily rainfall events: the more isolated the clusters, the smaller the value of D. The large dependence of D and of the specific scaling region on the threshold intensity is an indication of a more complex property of the rainfall called multifractality: a large-scale rain-field is successively broken into smaller and smaller eddies, each receiving an amount of the total field specified by a multiplicative parameter. Circumstantial evidence indicates, moreover, that the significant secular decreases of D over the Mediterranean area can be reasonably related to the simultaneous coherent decrease of zonal atmospheric circulation. ©1999 Springer-Verlag/Wien
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  • 41
    Publication Date: 1999-06-23
    Description:  The effects of urbanization on the Athens National Observatory (NOA) long records are investigated, in the present study, examining the mean monthly maximum and minimum air temperature for the period 1925–1996, for NOA and the corresponding time series for Aliartos (ALI), a rural station located 70 km NW of Athens. The existing small urbanization effect in NOA before the second world war period increased after the war and up to about 1990, when the effect became stationary. The urbanization effect in NOA referred mainly to maximum temperature and to the warmer seasons of the year. It is attributed to the extensive building of Athens after the war around NOA site and up to the sea which increases the temperature of the sea breeze. The effect is also attributed to the rapid increase of the population and the number of motor vehicles mainly after 1970. Moreover the decreasing trend of precipitation during the period 1970–1990 may have contributed to the increase of maximum air temperature. The urbanization effect on maximum temperatures of NOA amounts about 2 °C in spring, summer and less in fall, while no urbanization effect is clear in winter. ©1999 Springer-Verlag/Wien
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  • 42
    Publication Date: 1999-06-23
    Description:  We investigate whether the rainfall distribution of a drought prone region is characterized by different scaling properties in comparison to those in temperate regions of the world. We present a Rescaled Range (R/S) analysis of precipitation time series for 21 stations in northeast Brazil. In order to avoid the inclusion of short term variability, the data were smoothed by a moving average procedure. Three different algorithms were applied to the data: the empirical procedure proposed by Hurst; the evaluation of the standard mean deviation around the average profile; the evaluation ofthe mean deviation around the best fit line. The latter two methods have also been used for the evaluation of the nature of surface irregularities (rugosity) in surface profiles. The results obtained by the R/S method point to an average value H =0.709 〉 0.5. This value indicates that the records show a degree of persistence quite close to that found for 10 stations in Spain. It also shows that drought occurrence does not alter the persistence of the rainfall distribution. ©1999 Springer-Verlag/Wien
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  • 43
    Publication Date: 1999-06-23
    Description:  One of the major forcings for the interannual variability of the Asian Summer Monsoon is the Sea Surface Temperature (SST) distribution in the tropical Pacific Ocean. El Niño years are characterized by a negative Southern Oscillation Index (SOI) and decreased monsoon rainfall over India leading to drought conditions. On the other hand, La Nina years are characterized by a positive SOI and generally good monsoon conditions over India. The monsoon ENSO relation is not a consistent one. The monsoons of 1991 and 1994 are good examples. The spring SOI was the same (−1.3) during both years. However, the All India Summer Monsoon Rainfall (AISMR) was 91.4% of normal in 1991 and 110% in 1994. Though the SOI was same during the spring of both years, the spatial distribution of SSTs was different. In the present study, the impacts of different SST distributions in the tropical Pacific Ocean, on the monsoons of 1991 and 1994 have been examined, to assess the UKMO-unified model’s sensitivity of SST. It is observed that the simulated monsoon was much stronger in 1994 than in 1991, in terms of precipitation and circulation. The wind and the Outgoing Long-wave Radiation (OLR) simulated by the model are compared with NCEP/NCAR reanalyses data, while precipitation is compared with Xie-Arkin merged rainfall data. ©1999 Springer-Verlag/Wien
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  • 44
    Publication Date: 1999-06-23
    Description:  An S -mode principal component analysis was applied to the correlation and covariance matrices of a 700 hPa height window centered over eastern North America. The first five components were retained and rotated. K-means clustering algorithm was applied to the four solutions to generate 22 circulation types for each. Regression models were built, relating monthly mean temperature anomalies to monthly circulation type frequencies. The results were compared to those obtained in an earlier study using a correlation-based approach to classify the same data set. It was found that i) the amount of within-type variability is comparable for the two and that ii) the difference between cold and warm days of a circulation type is for both classification approaches an anomaly located to the east of the lake. A detailed analysis of this difference indicated that some information is contained in the scores for the first five principal components (and could therefore be used to improve the regression results) but that some is contained in the higher order components and was thus lost. Differences in the PC scores between warm and cold days were used to divide the circulation types into warm and cold subtypes. This improved the regression results but the best results were still inferior to those that had been obtained with the correlation-based classification. ©1999 Springer-Verlag/Wien
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  • 45
    Publication Date: 1999-06-23
    Description:  There is evidence that the area burned by wildland fire has increased in certain regions of Canada in recent decades. One cause for this increase is changes in the mid-tropospheric circulation at 500 hPa over northern North America. This study examines the physical links between anomalous mid-tropospheric circulation over various regions of Canada and wildland fire severity. Analysis of monthly and seasonal burned areas for the period 1953 to 1995 reveals a bimodal distribution with distinct low and extreme high burned area years. The high/low burned area years coincide with positive/negative 500 hPa height anomalies over north-western, western, west-central and east-central Canada. Total area burned and the 500 hPa height anomaly data are analyzed for statistical relationships using the Spearman rank correlation non-parametric measure. Results for the May to August fire season indicate statistically significant correlations between regional total area burned and clusters of anomalous 500 hPa geopotential height values immediately over, and immediately upstream of the affected region. For the north-western and west-central regions, significantly correlated clusters are found in the central Pacific as well, providing evidence of the influence of a teleconnection structure on the summer climate of western and north-western North America. Two sample comparison tests show statistically significant differences in both the means and variances of the fire data populations during negative and positive phases of mid-tropospheric flow, and the means of the height anomaly populations during extremely high and extremely low area burned seasons. Increases in regional total area burned are related to increases in mean 500 hPa heights, taken from the significantly correlated clusters of height values, between two successive periods 1953–74 and 1975–95. For Canada as a whole, the five lowest area burned seasons all occurred during the early period, while the five highest seasons occurred during the later period. The difference in the geopotential height fields between the two periods identifies an increase in 500 hPa heights over most of Canada with an amplification of the western Canada ridge and an eastward shifted Canadian Polar Trough (CPT). ©1999 Springer-Verlag/Wien
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  • 46
    Publication Date: 1999-08-24
    Description: Two UV-Biometer 501A instruments were used to estimate global erythemal irradiance at two locations in southwest Sweden; the Earth Sciences Centre, University of Göteborg (57.69° N; 11.92° E) and the island of Nordkoster, 200 km to the north (58.83° N; 10.72° E). A semi-empirical radiative transfer model was used to calculate the global erythemally effective irradiance under clear skies. A ratio of the hourly measured to clear-sky modelled irradiance was then derived for zenith angles 35–70°. Subsequent comparisons were then made with routine measurements of sunshine duration at Göteborg and sunshine duration, cloud cover, type and height at Nordkoster. Cloud transmission of UV-B irradiance decreases with increasing solar zenith angle, with cloud attenuation being 8% stronger at Nordkoster Island for zenith angles 〉〉;60°. Transmission also decreases with increasing cloud cover such that overcast cloud conditions reduce transmissions by an average of 75%. In addition, cloud type affects the amount of ground incident irradiant flux. Fractus cloud afforded the least UV-B transmission (0.16), while cirrus filaments afforded the most (0.95). The spatial and temporal distribution of clouds appears tobe non-random. Under conditions of 1 to 3 octas, sky cover, clouds appear to be concentrated in line with the sensor and Sun on more occasions than that expected given a random cloud distribution. The same cloud cover condition also resulted in many instances of ground incident irradiance above clear-sky values. The presence of cumuliform clouds appears to increase the likelihood of the latter phenomena. ©1999 Springer-Verlag/Wien
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  • 47
    Publication Date: 1999-08-24
    Description: Among the peculiarities of the urban climatology, a relevant one concerns the interactions with monuments, which include stone weathering, deposition and removal of airborne pollutants. In order to know more about the case of the Pisa Leaning Tower, Italy, a field survey has been made for one year, measuring the microclimate interacting with the structure, the vertical temperature and humidity profiles, the Tower surface temperature at different locations and the concentration of particles in air. Also more general information was collected studying the meteorological parameters in the area of Pisa. The correlation between rainfalls and wind evidenced that the windborne droplets arrive from preferential directions, determined on the regional scale by the sea shore on the west (sea breeze) and the channelling operated by the valley of the Arno river on the west. The tilting of the Tower gives a natural shield to the southern part, which is hardly washed by rainfall. The complex balance between airborne particulate matter deposition, tower tilting, rainfall washout and surface runoff determines the pattern of the black crusts which disfigure the elegance of this historical building. The land and sea breezes transport air with different moisture content, and the urban heat island accentuates the mid day drop on relative humidity, determining condensation-evaporation cycles in the stone micropores. The urban climatology of Pisa and the interactions with the Leaning Tower are discussed in view of the conservation of this monument. ©1999 Springer-Verlag/Wien
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  • 48
    Publication Date: 1999-04-29
    Description:  Intra-seasonal fluctuations of summer convection over southern Africa are studied through principal components (PC) analysis. Pentad (5 day) satellite outgoing long-wave radiation (OLR) departures are used to characterise the space and time scales of terrestrial cloudiness in the domain 10–35° S, 10–40° E. Areas of intra-seasonal convective influence are analysed according to spatial pattern and corresponding temporal character. Eight distinct geographic domains are identified, four tropical and four sub-tropical. The three most significant modes occur over southern Tanzania, Namibia, and Zambia, and refer to pulsing of: the Indian NE monsoon, surface heating in the western desert, and the zonal ITCZ, respectively. Temporal characteristics vary widely but an underlying near-monthly rhythm is detected. The variety of modes suggests that convective weather systems respond to external forcing (wave trains) and internal dynamics, to produce intra-seasonal fluctuations over southern Africa. ©1999 Springer-Verlag/Wien
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  • 49
    Publication Date: 1999-06-23
    Description:  Series of annual and seasonal precipitation from 32 stations, distributed over all Italian territory and divided in two groups climatically homogeneous, were studied for the period 1833–1996. The series were checked for homogeneity and the time series analysis was performed with the Mann Kendall test and its progressive application according to Sneyers (1990). The results show considerably different trends for different seasons and zones. On a yearly basis a decreasing trend is present over all Italy, but it is statistically significant only in the Central-South. On a seasonal basis a decreasing trend is significant only for spring in Central-South, and for autumn in the North. ©1999 Springer-Verlag/Wien
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  • 50
    Publication Date: 1999-04-29
    Description:  This paper summarizes results from a mesoscale modeling study to quantify the possible meteorological and energy-use impacts of large-scale increases in surface albedo and vegetative fraction. Ten regions in the U.S. were characterized and simulated in base- and modified-surface conditions. Time- and space-dependent meteorological variables were simulated for each region in four 3-day episodes to represent a range of seasonal variations. Using a simple interpolative procedure, a complete year of hourly weather data was created for each region (based on episodic meteorological simulation results) and input into energy-use models. The modified weather input was used to assess the effects of large-scale albedo and vegetative fraction changes on annual energy consumption in each of the ten areas targeted in this study. The simulations suggest annual electricity savings of between 1and 6.7 kWh m−2 (of roof area) in residential neighborhoods and between 2 and 6.1 kWh m−2 in office areas, depending on region. Annual gas penalties amount to up to 34.8 MJ m−2 (of roof area) in residential neighborhoods and up to 21.1 MJ m−2 in office areas. ©1999 Springer-Verlag/Wien
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  • 51
    Publication Date: 1999-04-29
    Description:  We consider the wind climatology of the Adriatic Sea derived from three different sources: an operational meteorological model, a simplified wind model, and traditional ship reports. The simplified wind model is found to provide reliable results in storm conditions, but it partly smoothes the fields when the meteorological pattern is not well defined and fairly uniform at the basin scale. The ship reports show a strong evident bias towards low values. This is partly interpreted as a tendency for ships to avoid rough weather and not to report in these types of conditions. A second reason is a bias present in the transfer from the Beaufort to the metric scale. The best results are provided by the operational meteorological model, after its results have been corrected for a bias in wind speed, associated with the resolution of the model with respect to the dimensions of the basin under study. ©1999 Springer-Verlag/Wien
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  • 52
    Publication Date: 1999-04-29
    Description:  Investigations of the temporal change of the probability of defined sequences and dynamical entropy (Nicolis et al., 1997) are presented using the daily maximum and minimum of the air temperature of the Potsdam time series, which spans the 102 years from 1893–1994. To reduce the number of parameters a nonhierarchical cluster analysis algorithm (Steinhausen and Langer, 1977) was used. This algorithm assigns one of five clusters each day, classified as very cold, cold, temperate, warm or hot. According to the algorithm, each day is described by only one of the symbols vc , c , t , w or h . Subsequently a time series analysis on this series of symbols was performed. The basic analysis length was defined by a 30 year window, which was shifted over the entire time series thus yielding 73 analysis sections. The quantities vary from window to window. Their variations were used for the detection of climate change. One of the major findings was the increased persistence of typical temperature characteristics. Within the windows we investigate relatively long-term correlations which extend over many days. The results show the time series to be markedly non-Markov. ©1999 Springer-Verlag/Wien
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  • 53
    Publication Date: 1999-04-29
    Description:  The work reported on was part of a more comprehensive study dealing with threatening sand movement towards the northwestern part of the Gezira irrigation scheme, Sudan. An irrigated sand blocking shelterbelt Eucalyptus microtheca is used to prevent canals and gravity irrigated crop land to be further affected. The objective of this paper is to report on the wind data that were obtained, mainly windward of this belt, and to deal with their implications and those of the belt characteristics and deposited sand in interaction with the wind for combating local sand movements and further desertification. Outside the influence of the belt, wind speed over eroded land was increasingly higher than that over irrigated land with the growth of cotton. Both these values were considerably higher than those reported from the nearest meteorological stations. The two prevailing winds, of which the summer SW wind was perpendicular to the belt, had consistent annual patterns during three years of observation. Also the diurnal patterns were very reproducible. Wind speed within the belt, at 1 m height, showed fast reduction inwards above the deposited sand. Efforts to control moving sand in the source area should be joined with those made at the borders of agricultural land. ©1999 Springer-Verlag/Wien
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  • 54
    Publication Date: 1999-04-29
    Description:  Statistical aspects of intense snowstorms over Austria are discussed based on the daily fresh snow depth-recordings from a sample of 81 stations over a 19-year period from the 1970/71 to the 1988/89-winter seasons. The study focuses on heavy snowfall events (HSEs) defined as at least a 20 cm-intensity threshold for a 24-hour accumulation of new snow. Calculation of the geometric center of the area experiencing heavy snowfall allows for the estimation of storm spatial characteristics (e.g., its expansion, eccentricity, and the number of stations involved) and the objective assignment of storms to one of four distinct regions, located to the north and south of the Alpine main crest. Temporal characteristics investigated include the annual and seasonal frequencies of HSEs, whereas considerations of intensity put an emphasis on the average and maximum new snow-depth from intense storms. The biggest 24-hour snow accumulation within the period of study was 170 cm, measured at Sillian (Eastern Tyrol) in 1986. ©1999 Springer-Verlag/Wien
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  • 55
    Publication Date: 1999-03-24
    Description: Melting snow is often patchy, and advection of heat from warm patches of snow-free ground can accelerate the melting. For large-scale atmospheric modelling applications, snowmelt rates and fluxes of heat and moisture over surfaces with snow cover distributed on scales too small to be resolved by the model grid have to be parametrized. In this paper, a boundary-layer model is used to model advection over surfaces with short vegetation and varying fractions of snow cover. Boundary-layer model results are used to assess the performance of a tile model, which calculates separate fluxes for snow-covered and snow-free fractions of the surface given area-average temperatures, humidities and windspeeds at a reference height in the atmosphere. It is found that the tile model can give good results, but its performance depends strongly on the choice of reference height. ©1999 Springer-Verlag/Wien
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  • 56
    Publication Date: 1999-10-01
    Description: The anisotropy of Pg-wave velocity in the area of the central External Dinarides is measured by using arrival time data as reported by local and regional seismological stations. The observed velocity varies between 5.73 km/s (in the ESE-WNWdirection) and 6.20 km/s (in the SSW-NNE direction), indicating azimuthal anisotropy with symmetry axis azimuths of 23°±n 90°. These closely match the orientation of the principal stress axes in the region, as revealed by analyses of available fault-plane solutions. The observed anisotropy may be modelled by assuming a system of vertical/subvertical cracks in the upper crust, aligned under the influence of the regional tectonic stress field. ©1999 StudiaGeo s.r.o.
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  • 57
    Publication Date: 1999-10-01
    Description: Low-temperature oxidation under atmospheric conditions affects the magnetic properties of magnetite in natural rocks: the coercivities of magnetite grains increase and other parameters change accordingly. It was recently shown that heating to 150°C largely removes the effects of low-temperature oxidation (van Velzen and Zijderveld, 1995). Heating may therefore serve as a detection tool for the presence of the effect of low-temperature oxidation. In the present study, a collection of loess and paleosol samples from various loess regions of the world is examined for the influence of low-temperature oxidation. In all samples of the collection a decrease of coercivities was found after heating to 150°C. Generally loess samples were affected to a larger extent than paleosol samples. The original range of remanent coercivities ( B cr) of 21-58 mT changed to 20-42 mT after heating. The IRM capacity of the samples decreased from 0 up to 25%. ARM showed changes between a decrease of 10% and an increase of 15%. The grain-size indicative parameter IRM/ARM is considerably influenced by the heating and therefore by low-temperature oxidation. The changes in susceptibility are limited and will not influence the interpretation of large-scale features of the susceptibility record as a paleoclimate proxy. Small variations, however, may be obscured by the varying influence of oxidation in the outcrop, which can significantly modify the rock-magnetic record. Rock-magnetic parameters used to determine magnetic mineral content and grain sizes should be corrected for the effect of low-temperature oxidation. To this end heating to 150°C is recommended. The occurrence of the changes is in itself already an indication for the presence of magnetite. Low-temperature oxidation will not only be due to recent weathering in the outcrop, but also to earlier oxidation processes in the source area, during transport and deposition of the loess and during pedogenesis. Truly fresh sediment samples are only influenced by this earlier oxidation. In that case heating will reveal the degree of ancient low-temperature oxidation, which may be related to climate at the time of deposition and pedogenesis. ©1999 StudiaGeo s.r.o.
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  • 58
    Publication Date: 1999-07-01
    Description: A 3D kinematic geodynamo model in a sphere with the conductive solid inner core is considered. The 3D magnetic field and velocity field are resolved in the physical space for r- and θ-coordinates, whereas the sin- and cos-decomposition is applied to the Φ-coordinate. The additional boundary conditions for the case of non-zero velocity field on the boundaries of the liquid spherical shell and for different magnetic diffusivities of the inner and outer core are applied. The computer code was tested by free decay mode solutions and comparisons were made also with results reported by other authors. This work is a part of a project to study 3D inviscid geodynamo models. ©1999 StudiaGeo s.r.o.
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  • 59
    Publication Date: 1999-04-01
    Description: Three-dimensional general circulation models (GCMs) are 'state-of-the-art' tools for projecting possible changes in climate. Scenarios constructed for the Czech Republic are based on daily outputs of the ECHAM-GCM in the central European region. Essential findings, derived from validating, procedures are summarized and changes in variables between the control and perturbed experiments are examined. The resulting findings have been used in selecting the most proper methods of generating climate change projections for assessing possible hydrological and agricultural impacts of climate change in selected exposure units. The following weather variables have been studied: Daily extreme temperatures, daily mean temperature, daily sum of global solar radiation, and daily precipitation amounts. Due to some discrepancies revealed, the temperature series for changed climate conditions (2×CO 2 ) have been created with the help of temperature differences between the control and perturbed runs, and the precipitation series have been derived from an incremental scenario based on an intercomparison of the GCMs' precipitation performance in the region. Solar radiation simulated by the ECHAM was not available and, therefore, it was generated using regression techniques relating monthly means of daily extreme temperatures and global radiation sums. The scenarios published in the paper consist of monthly means of all temperatures, their standard deviations, and monthly means of solar radiation and precipitation amounts. Daily weather series, the necessary input to impact models, are created (i) by the additive or multiplicative modification of observed weather daily series or (ii) by generating synthetic time series with the help of a weather generator whose parameters have been modified in accord with the suggested climate change scenarios. ©1999 StudiaGeo s.r.o.
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  • 60
    Publication Date: 1999-04-01
    Description: The relation between the number of seismic events N and their magnitude and/or energetic magnitude is one of the basic relations in the statistics of earthquakes and mining-induced events. A detailed analysis of the b-values in the relation log N =a−b logE for the induced seismic events occurring in the Ostrava-Karviná Coal Basin is given in this paper. The least-squares method, as well as the maximum likelihood method were applied in solving this problem mathematically. Based on the results of frequency-energy distribution analysis, it was proved that the variations of b-values in space and time do exist, and that these values are inversely proportional to the level of induced seismicity influenced by the various mining activities being carried out in-situ. This statement could, in general, be supported by the fact that lower b-values correspond to higher seismic activity, while higher b-values correspond to low and moderate seismic activity. ©1999 StudiaGeo s.r.o.
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  • 61
    Publication Date: 1999-01-01
    Description: In this contribution we explore the analogy between GPS ambiguity resolution on the one hand, and the problem of statistical classification, on the other hand. As classification rules we discuss the Bayes-, the MAP-, the ML- and the Minmax-rule. It is shown to what extent ambiguity resolution may be considered a classification problem. It turns out that both problems show many similarities, although some marked differences exist as well. These similarities and differences are discussed. ©1999 StudiaGeo s.r.o.
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  • 62
    Publication Date: 1999-01-01
    Description: Geopotential values ―W of the mean equipotential surfaces representing the mean ocean topography were computed on the basis of four years (1993 - 1996) TOPEX/POSEIDON altimeter data: ―W = 62 636 854.10m 2 s −2 for the Pacific (P), ―W = 62 636 858.20m 2 s −2 for the Atlantic (A), ―W = 62 636 856.28m 2s−2 for the Indian (I) Oceans. The corresponding mean separations between the ocean levels were obtained as follows: A − P = − 42 cm, I− P = − 22 cm, I − A = 20 cm, the rms errors came out at about 0.3 cm. No sea surface topography model was used in the solution. ©1999 StudiaGeo s.r.o.
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  • 63
    Publication Date: 1999-10-01
    Description: A mathematical model of the disturbance of the stationary geothermal field due to a three-dimensional perturbing body embedded near the surface of a two layered earth. The theoretical analysis is based on the generalized theory of the double-layer potential, similar to the boundary integral method likely to direct current geoelectricity problems. Special attention is paid to cases in which a pan of the body's surface is tangential to the planar boundaries of the substratum or of the surface of the earth The numerical calculations are performed for a three-dimensional prism using methods similar to the boundary element method (BEM). Numerous graphs are shown for the disturbance of the temperature field and of the heat flow on the surface of the earth and along vertical profiles (boreholes). ©1999 StudiaGeo s.r.o.
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  • 64
    Publication Date: 1999-07-01
    Description: The purpose of this research is to demonstrate the possibility of applying one geophysical method to studying untraditional systems as is the case with Portland-cement-based materials. The research demonstrates how conventional paleomagnetic methodology can be employed in studying the mode of magnetic recording in present-day industrial materials. Portland-cement admixtures such as fly ashes and furnace slags should be discriminated, because those particles interact in soils and sediments in nature. Moreover, a better undertanding of magnetic remanent acquisition in model materials can serve to improve the interpretation of magnetic remanent acquisition in natural rocks formed a long time ago. The magnetic constituents of Portland-cement paste and mortar acquire a magnetic remanence due to their alignment with the earth's magnetic field at the casting place. This magnetization can be measured using ordinary paleomagnetic techniques. The alignment of the individual magnetic particles accounts for the intensity of the magnetic remanence, which can be increased by adding water and by vibration before setting and hardening. Blast furnace slag admixtures also add to the enhancement of the intensity of remanence. The magnetization of Portland-cement-based materials shows a near linear relationship with the water /cement (w/c) ratios employed in the experimental work; the w/c ratios range between 0.2 – 0.6 in pastes and 0.3 – 0.6 in mortar. Stable remanent magnetization was obtained during the first seven days of setting and hardening, a period necessary for magnetic particles to become locked parallel to the earth's magnetic field. The stability of magnetic remanence predicts the usefulness of the methodology in studying the properties of Portland cement and particularly in the control of iron-bearing admixtures. ©1999 StudiaGeo s.r.o.
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  • 65
    Publication Date: 1999-01-01
    Description: Temporal variations in the nine elements of the Earth's inertia ellipsoid due to sea surface topography dynamics were derived from TOPEX/POSEIDON altimeter data 1993 - 1996. The variations amount to about 10 mm in the position of the center of the Earth's inertia ellipsoid (E i ), 0.15'' in the polar axis direction of E i and to about 0.0003 in the denominator of its polar flattening. The approach used is based on the temporal variations of distortions computed by means of the geopotential model EGM96 which is used as reference. ©1999 StudiaGeo s.r.o.
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  • 66
    Publication Date: 1999-01-01
    Description: As is known, the secular deceleration of the Earth's diurnal rotation is explained mainly by the tidal friction in the ocean. Below we consider this mechanism in some detail, taking into account also elastic deformations of the mantle under the action of ocean loading and the interaction between the tide-generating body, ocean tidal wave, liquid outer core, and solid inner core. It is shown that elastic displacements of the core-mantle boundary under the action of ocean loading are of about the same amplitude and phase as the elastic loading displacements of the Earth's outer surface. As a result, side by side with the mechanism of secular deceleration of diurnal rotation of the mantle, there are also (1) the opposite mechanism of secular acceleration of diurnal rotation of the outer liquid core and of the solid inner core and (2) the mechanism of excitation of differential rotation in the liquid core. Taking these effects into account, we compare theoretical and modern observed data on the eastward drift of the solid inner core. It is shown that the best agreement may be obtained if the turbulent viscosity of the liquid core is about 2 × 10 3 Poise ©1999 StudiaGeo s.r.o.
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  • 67
    Publication Date: 1999-01-01
    Description: The dispersion relation for Love waves in a layer on a half-space is modified by introducing the wave number and its square instead of the phase velocity. The implicit function theorem is then used to derive the analytical formulae for the group velocity and for the phase- and group-velocity partial derivatives with respect to the parameters of the medium. The formulae are compared with those obtained by Novotný (1971) where the traditional formulation of the dispersion relation was used. ©1999 StudiaGeo s.r.o.
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  • 68
    Publication Date: 1999-05-01
    Description: Electromagnetic (EM) techniques are the most commonly used geophysical methods in mineral exploration. However, the use of EM measurements for environmental and engineering applications like the detection of contaminant plumes or the exploration of waste sites is relatively new. The reason for the success of the application of EM methods to environmental problems lies in the variation of conductivity caused by different geometry of pore fluids and clay contents in rocks, and by the presence of organic and inorganic contaminants. Many EM methods/instruments used for mapping near surface geology exist and nowadays they play a central role in environmental geophysics. In general, these methods can be classified in two blocks: EM methods using a plane wave source of excitation and EM methods using a controlled source like a magnetic dipole or a loop source. The Very Low Frequency (VLF, VLF-R) and Radiomagnetotelluric (RMT) methods are chosen as representative methods for plane wave techniques, while horizontal loop EM methods operating in low induction numbers (EM31, EM34) and Transient Electromagnetic methods (TEM) are chosen as representatives of magnetic dipole or loop source techniques. Basic principles, advantages and disadvantages of each technique as well as their connection to specific environmental problems will be discussed. Different successful applications of these methods are reported in the literature. However, this review will focus on three major subjects: waste site exploration, detection of contaminated earth layers, and groundwater exploration. Case histories are presented illustrating the suitability of EM methods for solving such problems. ©1999 Kluwer Academic Publishers
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  • 69
    Publication Date: 1999-05-01
    Description: Joint use of electrical and electromagnetic techniques is found to be useful for better understanding of the subsurface electrical resistivity structure. Detection of thin buried layers (conductive or resistive), which may be difficult to identify by a single method alone, could possibly be identified by a combination of methods. Further, distortion or error in the observed data could be corrected, as both methods depend on the same physical parameter, namely electrical conductivity. Although these methods have been known for the last several decades, joint interpretation of data sets is increasingly being used in recent years, especially for complex geological problems. This review covers the main results of the combination of these methods, giving more emphasis to case histories. ©1999 Kluwer Academic Publishers
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  • 70
    Publication Date: 1999-01-01
    Description: For detailed modeling of atmospheric chemistry it is necessary to consider aqueous-phase reactions in cloud droplets and deliquesced aerosol particles. Often, the gas-phase concentration is in equilibrium with the aqueous phase. Then Henry′s law can be used to describe the distribution between the phases provided that the Henry′s law coefficient is known. In some cases, thermodynamic equilibrium will not be reached and it is necessary to use kinetic expressions of the rates involved. These rates depend on diffusion constants, accommodation coefficients, Henry′s law coefficients, particle size distributions, and several other parameters. This review describes how these processes can be treated in computer modeling and how the necessary data can be obtained. Even though it is written primarily for use in modeling atmospheric chemistry, some parts will also be useful for waste water and pesticide control and in other areas where the distribution of chemicals between the aqueous and the gas phase is important. ©1999 Kluwer Academic Publishers
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  • 71
    Publication Date: 1999-05-01
    Description: The lower crust is generally considered to be an aseismic, weak zone where fluid distribution might be governed by textural equilibrium geometries. Saline fluids below the transition from brittle to ductile rheology have been advanced as a joint explanation for deep crustal conductivity and seismic reflectivity, the depth of onset of both phenomena being apparently bounded by isotherms in the 300–450 °C temperature range. Some petrologists, meanwhile, contest that the deep crust should be devoid of extensive fluid networks. This review exposes some geophysical exceptions to the statistical norm suggested by global geophysical data compilations and presents counter-arguments that the lower crust in places may be both dry and strong, that fluids if at all present at such depths may not necessarily be connected and that fluid mobility in the lower crust may be more limited and heterogeneous than commonly assumed. Laboratory data on crustal rocks implies that the transition from brittle to ductile rheology actually occurs over a much broader range of temperatures than 300–450 °C, and the apparent association of deep crustal conductive horizons with a temperature field of 300–450 °C may be interpretable in terms of formation temperatures of graphite, rather than fluids and brittle-ductile transition rheology. High vP/vS ratios from a 6 km thick, seismically layered zone below the Weardale granite, NE England can be explained by underplated mafic material. They are unlikely to be explained by fluids in an area where deep crustal conductance has been shown to be relatively low, unless conventional assumptions regarding deep crustal fluid distribution are inadequate or false. Perusal of the literature reveals that lower crustal seismicity is less seldom than generally appreciated. Interpretation of earthquakes nucleating at lower crustal depths is ambiguous, but in some tectonic regimes may indicate preservation of brittle rheology to the Moho and a lower crust that is predominantly mafic and dry. A better understanding of lower crustal deformation mechanisms and history may provide better insight into deep crustal conductivity mechanisms. Recent rock mechanical experiments suggest that permeability (and thus fluid connectivity) may be decreased by ductile shearing, whereas ductile shearing may aid graphitisation at lower crustal temperatures. If the lower crust in some regions is strong, this may explain the apparent preservation of both extant- and palaeostress orientations in interpretations involving electrical anisotropy. ©1999 Kluwer Academic Publishers
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  • 72
    Publication Date: 1999-10-28
    Description:  Long time series of daily meteorological data that are needed in various applications are not always available or appropriate for use at many locations. The Weather Generation Model (WGEN) developed by Richardson and Wright (1984) was evaluated as a substitute for daily observed data at 17 sites located in the main climatic zones of Nigeria. The Wilcoxon-Mann-Whitney U-test has shown that the number of months per year, for which the differences between the long-term monthly mean observed meteorological and WGEN simulated data, were significant, was less than 4 at most of the study sites. ©1999 Springer-Verlag/Wien
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