Observation of Precipitating Systems over Complex Orography with Meteorological Doppler Radars: A Feasibility Study

Summary  This paper concerns the use of airborne or ground-based Doppler radars to observe precipitating systems over complex orography. As nearly all of the previous experiments involving Doppler radars were conducted over flat surfaces over the continents or the oceans, new techniques are needed firstly to separate ground clutter from meteorological signal and, in the case of airborne Doppler observations, to deduce navigational errors. Secondly, it is necessary to take the atmospheric circulation induced by orography into account in the three-dimensional wind field analysis. Variational techniques are presented to solve these problems. The proposed methods are tested with simulated ground-based and airborne Doppler radar observations for analytic flows over analytic terrains and for numerically simulated wind and reflectivity fields for the Brig event (22 September 1993) of heavy precipitation over the southern flank of the Alps (Cosma and Richard, 1998), and with actual airborne Doppler data relative to weak snow showers over the Rocky Mountains on 12 March 1995. Received March 22, 1999/Revised June 1, 1999     

Refinement of the modified time-to-failure method for intermediate-term earthquake prediction

The modified time-to-failure method for intermediate-term earthquake prediction utilizes empirical relationships to reduce the number of unknown parameters providing a stable and unique solution set. The only unknown parameters in the modified time-to-failure method are the time and size of the impending main shock. The modified time-to-failure equation is used to model the precursory events and a prediction contour diagram is constructed with the magnitude and time-of-failure as the axes of the diagram. The root-mean-square (rms) is calculated for each set of time and magnitude on the prediction diagram representing the difference between the model (calculated) acceleration and the actual accelerated energy release of the precursory events. A small region, corresponding to the low rms region on the diagram, defines the prediction. The prediction has been shown to consistently under-estimate the magnitude and over-estimate the time-of-failure. These shortcomings are caused by an underestimation in energy release of the modified time-to-failure equation at the very end of the sequence. An empirical correction can be applied to the predicted results to minimize this problem. A main shock location search technique has been developed for use with the modified time-to-failure method. The location technique is used to systematically search an earthquake catalog and identify locations corresponding to precursory sequences that display accelerated energy releases. It has shown good results when applied in retrospective predictions, and is essential for the practical application of the modified time-to-failure method. In addition, an observed linear characteristic in long-term energy release can be used to minimize false predictions. The refined empirical relationships that eliminate or constrain unknown constants used in the modified time-to-failure method and the main shock location search technique are used in a practical application in the New Madrid Seismic Zone (NMSZ). The NMSZ, which is over due for a magnitude 6 event according to recurrence rates (Johnston and Nava, 1985), makes this region ideal for testing the method. One location was identified in the NMSZ as a high risk area for an event in the magnitude 4.5 range. The prediction, if accurate, is of scientific interest only because of the relatively small size of the main shock.     

Faunas from the upper silurian (upper ludlovian) in the ludlow-much wenlock district,England

Faunal lists for 17 sections in the Overton Formation are presented. Faunal diversity appears to increase towards the formations base while faunal dominance appears to increase towards its top.     

Brachiopods from China seas

A collection of brachiopods by the Institute of Oceanology, Academia Sinica (Qingdao), contains eight species from seven genera. Six of the species have been recorded previously from China seas—Lingula adamsi, L. anatina, Discinisca stella, Pelagodiscus atlanticus, Campages mariae, Terebratalia coreanica. Two species (Terebratulina hataiana andFrenulina sanguinolenta) have been described from other parts of the Pacific area. The apparent absence of any endemic species is a noteworthy feature of Chinese in comparison with Japanese faunas.     

Assessment of atmosphere-ocean general circulation model simulations of winter northern hemisphere atmospheric blocking

An assessment of six coupled Atmosphere-Ocean General Circulation Models (AOGCMs) is undertaken in order to evaluate their ability in simulating winter atmospheric blocking highs in the northern hemisphere. The poor representation of atmospheric blocking in climate models is a long-standing problem (e.g. D’Andrea et?al. in Clim Dyn 4:385–407, 1998), and despite considerable effort in model development, there is only a moderate improvement in blocking simulation. A modified version of the Tibaldi and Molteni (in Tellus A 42:343–365, 1990) blocking index is applied to daily averaged 500?hPa geopotential fields, from the ERA-40 reanalysis and as simulated by the climate models, during the winter periods from 1957 to 1999. The two preferred regions of blocking development, in the Euro-Atlantic and North Pacific, are relatively well captured by most of the models. However, the prominent error in blocking simulations consists of an underestimation of the total frequency of blocking episodes over both regions. A more detailed analysis revealed that this error was due to an insufficient number of medium spells and long-lasting episodes, and a shift in blocking lifetime distributions towards shorter blocks in the Euro-Atlantic sector. In the Pacific, results are more diverse; the models are equally likely to overestimate or underestimate the frequency at different spell lengths. Blocking spatial signatures are relatively well simulated in the Euro-Atlantic sector, while errors in the intensity and geographical location of the blocks emerge in the Pacific. The impact of models’ systematic errors on blocking simulation has also been analysed. The time-mean atmospheric circulation biases affect the frequency of blocking episodes, and the maximum event duration in the Euro-Atlantic region, while they sometimes cause geographical mislocations in the Pacific sector. The analysis of the systematic error in time-variability has revealed a negative relationship between the high-frequency variability of the transient eddies in the areas affected by blocking and blocking frequency. The blocking responses to errors in the low-frequency variability are different according to the region considered; the amplitude of the low-frequency variability is positively related to the blocking frequency and persistence in the Euro-Atlantic sector, while no such consistency is observed in the Pacific.     

Observations of the structure and evolution of solar flares with a soft X-ray telescope

132 soft X-ray flare events have been observed with The Aerospace Corporation/Marshall Space Flight Center S-056 X-ray telescope that was part of the ATM complement of instruments aboard Skylab. Analyses of these data are reported in this paper. The observations are summarized and a detailed discussion of the X-ray flare structures is presented. The data indicated that soft X-rays emitted by a flare come primarily from an intense well-defined core surrounded by a region of fainter, more diffuse emission. Loop structures are found to constitute a fundamental characteristic of flare cores and arcades of loops are found to play a more important role in the flare phenomena than previously thought. Size distributions of these core features are presented and a classification scheme describing the brightest flare X-ray features is proposed. The data show no correlations between the size of core features and: (1) the peak X-ray intensity, as indicated by detectors on the SOLRAD satellite; (2) the rise time of the X-ray flare event, or (3) the presence of a nonthermal X-ray component. An analysis of flare evolution indicates evidence for preliminary heating and energy release prior to the main phase of the flare. Core features are found to be remarkably stable and retain their shape throughout a flare. Most changes in the overall configuration seem to be the result of the appearance, disappearance or change in brightness of individual features, rather than the restructuring or re-orientation of these features. Brief comparisons with several theories are presented.     

An assessment of geologic sequestration potential in the panhandle of Florida USA

One alternative to reduce global greenhouse gas emissions is to store the emissions in underground geologic sequestration repositories. The efficacy of this approach has been favorably evaluated by numerous authors over the last 15 years. This paper discusses an assessment of the overall feasibility of storing emissions in three different repositories in the Florida panhandle located in the Southeastern United States. The feasibility assessment evaluates both saline aquifers and oil reservoirs located in the panhandle region. The overall feasibility is driven by the available geologic sequestration capacity, the transportation cost to deliver emissions to a respective repository, and other engineering and regulatory issues. The geologic sequestration capacity is generally controlled by the so-called storage efficiency, a variable dependent on the site-specific geology, reservoir conditions, and the injected fluid characteristics. For this paper, storage efficiency for saline repositories was assessed in more detail using numerical modeling. Based on the work completed, the 3 repositories studied have at least 4.55 gigatonnes of capacity to sequester CO₂.     

Correlation of T-log with E-log in coal-bearing formations

The profile of temperature gradient versus depth (T-log) has been found to be very useful for correlation with electrical resistivity log (E-log) in coal-bearing formations. A positive correlation between electrical resistivity and thermal resistivity is observed in coal sections whereas a negative correlation is found in sandstone/shale beds, thus helping in coal prospect evaluation. T logs have been used to correct the location of coal bed which had apparently been misinterpreted by the E-log. Hole to hole correlation of T-log and E-log is found to be excellent and it is observed that thermal resistivity characteristics of given formations remain fairly uniform. A rough estimation of coal grade is possible from the detailed study of the T-logs. Abrupt changes of temperature gradient as also its reversals have been observed in burnt coal sections.     

Simulating the moderating effect of a lake on downwind temperatures

A steady-state, two-dimensional numerical model is used to simulate air temperatures and humidity downwind of a lake at night. Thermal effects of the lake were modelled for the case of moderate and low surface winds under the cold-air advective conditions that occur following the passage of a cold front. Surface temperatures were found to be in good agreement with observations. A comparison of model results with thermal imagery indicated the model successfully predicts the downwind distance for which thermal effects due to the lake are significant.