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  • 1990-1994  (238)
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  • 1
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary This paper examines the performance of several atmospheric instability indices for operational hail forecasting in the Greek National Hail Suppression Program (GNHSP). These indices are part of the adopted forecasting procedure in the GNHSP, which also involves a synoptic index of convection and a synoptic scale typing scheme. The assessment of the indices is accomplished objectively through a multivariate statistical technique, namely factor analysis. The analysis resulted in grouping of the indices into three factors. The indices with high loading and scores are considered to best detect convection for hail forecasting in the GNHSP.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary Hailpads are used to provide quantitative hailfall measurements in several hail experiments and hail suppression operations around the world. The dented hailpads record the time-integrated size distribution and concentration of hailfall. In the five-year Greek National Hail Suppression Program (GNHSP) hailpad data have been used to estimate the global (impact) energy of hailswaths for the evaluation of the GNHSP. In this paper a systematic hailpad calibration procedure is developed applicable to operational programs. To meet this objective a calibration experiment has been conducted consisting of several tests to: consider differences between pad types; to examine the effects of ultra violet-light on hailpads for varying periods of time; to investigate the effect of painting and inking of the hailpad surfaces; to consider the effect of analyst's variability, loose hailpad stands, and bouneing; and to develop calibration eqqations. The concluded results seem to justify the design and performance of the hailpad calibration procedure.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Meteorology and atmospheric physics 45 (1991), S. 113-123 
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary The equivalent potential energy of the moist atmosphere is defined as the sum of its total potential energy and latent heat. The available equivalent potential energy is the amount of equivalent potential energy available for conversion into kinetic energy. For the isolated moist atmospheres, we may find the equivalent lowest state which is the limit of the states attained through all the actual processes involving water condensation and possesses the least equivalent potential energy. Thus, the maximum available equivalent potential energy with respect to the equivalent lowest state can be estimated for any provided initial state. This study may extend the understanding for the development of precipitation systems in the moist atmosphere.
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  • 4
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary The role of stationary (monthly mean) and transient (departure from monthly mean) waves within the atmospheric energy cycle is examined using global analyses from the European Centre for Medium Range Weather Forecasts (ECMWF) for the period 1980–1987. Only January and July averages are considered. It is confirmed that planetary stationary waves are basically baroclinic. Their contribution to the globally averaged energy cycle of the atmosphere is comparable to that of the transient waves. In January they contribute about 40% to the baroclinic conversion (CA) from zonal mean to eddy available potential energy. Local values for the northern hemisphere even show a predominant role of the stationary wave conversions over those originating from transient waves. Part of the available potential energy of stationary waves (A SE) is converted to kinetic energy by warm air rising and cold air sinking. Nonlinear energy conversion, which can be interpreted as destruction of stationary temperature waves by transients, is the second sink forA SE. The order of magnitude of these two processes is similar. Barotropic nonlinear conversions, though negligible in the global average, reveal large conversion rates between the mean positions of the polar and the subtropical jets. Their orientation is suggestive of a tendency to increase stationary wave kinetic energyK SE at its local minimum between the jets at the expense of the synoptic scale transients. While all terms of the energy cycle related to stationary waves reveal a predominance of the planetary scale (zonal wave numbers 1–3) transient waves are governed by synoptic scale waves (zonal wave numbers 4–9) only with respect to the baroclinic and barotropic conversions: a significant amount of transient wave energy (50% for the global average ofA TE) is due to planetary scale waves.
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  • 5
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary The FSU Global Spectral Model including comprehensive physical parameterization and high resolution (T 106) is used to make predictions to 48 hours for two cases of African easterly wave disturbances which occurred during FGGE. Model output is compared with FGGE III-b analyses to qualitatively assess the model's performance. The results of energetics calculations for the two case studies are included in this study. These calculations are based on model output to 24 hours. The energetics results confirm that combined barotropic/baroclinic instability provides the primary energy source for the African waves. Such energetics results, based on individual case studies, also provide an interesting and valuable comparison with compositing studies on African waves. An aspect of this study deals with the definition of a double jet stream structure at 700 mb for the two cases under consideration. The energetics patierns in zones to the north and south of each of these jets are separately portrayed.
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  • 6
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary In this paper an attempt for predicting smoke concentration levels in Athens for spring and autumn is presented. The regression models are based on equations relating wind speed and smoke values. It is found that both of them become more effective if corrections related to wind speed categories are applied to the equations. In this way good prediction is achieved for the next 24 hours.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Meteorology and atmospheric physics 45 (1991), S. 187-187 
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
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  • 8
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary The implications of the hydrostatic assumption for an anelastic two-dimensional numerical model of a gravity current intruding into a neutrally stratified environment are studied. Particular interest is focused on situations where the gravity current encounters an orographic barrier. Considerable discrepancies between hydrostatic and nonhydrostatic calculations are found in the head region for high Froude numbers, when the resolution is high enough to resolve the head of the current. However, the propagation speed and the depth of the feeder flow are well represented in the hydrostatic model.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary The effects of surface temperature anomalies (STAs) upon frontal cyclones are investigated with a nonlinear model. The model used is a modified version of the NCAR Community Climate Model (CCM 1). The experiments are run with hemispheric domain and R 30 (rhomboidal) truncation. The present study isolates the effects of sensible heating. Topography and latent heating are excluded from this model. The initial data are created from a solution (normal mode) to the linear eigenvalue problem. Six experiments use various locations and intensities for dipole-shaped STA; one control case is run without STA. The intensity is either ±5 or ±10°K and the anomalies ae located at 40°N, 50°N, or 35°N. The jet is centered at 40°N. All cases are run for 20 days. Nonlinear, time-dependent, growth rate and phase frequency are derived and compared to the linear (eigenvalue) amounts. The resulting waves grow primarily by baroclinic instability. Perturbation fields at higher levels grow faster before they mature (“occlude”) and decay faster afterward, than do lower level fields. The baroclinic conversion of energy lessens as the perturbations mature. The principal hypothesis tested is that: the STA alters the static stability which in turn modulates the baroclinic instability. Over warm anomalies the static stability should be reduced, enhancing baroclinic instability. Over cold anomalies the opposite may happen. The nonlinear simulations confirm this hypothesis in part. In the present study, the intensity of the warm anomaly produces greater growth rate during and after the storm's mature state. Larger STA intensity increases the maximum amplitude of the perturbation in a roughly linear fashion. However, the STA effects are nonlinear after maximum amplitude is reached: during decay, the difference in amplitude between the control case and the 10°K STA case is more than twice the difference between the control and 5°K case. In contrast, little deviation from the control case is found for perturbations over the cold anomaly, indicating a nonlinear link between STA and wave growth. The latitudinal variation used of the surface temperature anomaly centers had no significant influence on the baroclinic growth. Secondary growths of storms after 10 days are more commonly seen in cases with STA.
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  • 10
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary The linearized atmospheric equations system is solved analytically in a two layer model. The solutions show that the thermal disturbance located at the interface can induce internal gravity wave, which propagates downstream in the stable layer and brings about flow disturbances in the lower unstable layer. Motion of roll vortices with flow pattern similar to that found in the convective cloud street forms in the lower part of the upper layer and the upper part of the lower layer. If proper content of water vapor exists the cloud lines presenting small angle with the mean wind appear at the top of the lower layer. The effects of the wind speed and the temperature structures of the atmosphere in the lower convective layer and the overlying stable layer on the characteristics of the roll vortices are also discussed in this study.
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