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1
Majda, Andrew J. "New Multiscale Models and Self-Similarity in Tropical Convection". Journal of the Atmospheric Sciences 64, n. 4 (1 aprile 2007): 1393–404. http://dx.doi.org/10.1175/jas3880.1.
Testo completoAbstract (sommario):
Abstract One of the unexplained striking features of tropical convection is the observed statistical self-similarity in clusters, superclusters, and intraseasonal oscillations through complex multiscale processes ranging from the mesoscales to the equatorial synoptic scales to the intraseasonal/planetary scales. Here new multispatial-scale, multitime-scale, simplified asymptotic models are derived systematically from the equatorial primitive equations on the range of scales from mesoscale to equatorial synoptic to planetary/intraseasonal, which provide a useful analytic framework for addressing these issues. New mesoscale equatorial synoptic dynamical (MESD) models and balanced MESD (BMESD) models are developed for the multitime, multispace interaction from mesoscales to equatorial synoptic scales; new multitime versions of the intraseasonal planetary equatorial synoptic dynamics (IPESD) models are developed for multiple spatiotemporal interactions on equatorial synoptic scales and planetary scales. The mathematical character derived below for all these simplified models explicitly demonstrates that the main nonlinear interactions across scales are quasi-linear where eddy flux divergences of momentum and temperature from nonlinear advection from the smaller-scale spatiotemporal flows as well as mean source effects accumulate in time and drive the waves on the successively larger spatiotemporal scales. Furthermore, these processes that transfer energy to the next larger, longer, spatiotemporal scales are self-similar in a suitable sense established here. On the other hand, the larger scales set the environment for this transport through processes such as mean advection of the smaller scales.
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Biello, Joseph A., Andrew J. Majda e Mitchell W. Moncrieff. "Meridional Momentum Flux and Superrotation in the Multiscale IPESD MJO Model". Journal of the Atmospheric Sciences 64, n. 5 (1 maggio 2007): 1636–51. http://dx.doi.org/10.1175/jas3908.1.
Testo completoAbstract (sommario):
Abstract The derivation of the meridional momentum flux arising from a multiscale horizontal velocity field in the intraseasonal, planetary, equatorial synoptic-scale dynamics (IPESD) multiscale models of the equatorial troposphere is presented. It is shown that, because of the balance dynamics on the synoptic scales, the synoptic-scale component of the meridional momentum flux convergence must always vanish at the equator. Plausible Madden–Julian oscillation (MJO) models are presented along with their planetary-scale meridional momentum fluxes. These models are driven by synoptic-scale heating fluctuations that have vertical and meridional tilts. Irrespective of the sign of the synoptic-scale meridional momentum flux (direction of the tilts) in each of the four MJO examples, the zonal and vertical mean meridional momentum flux convergence from the planetary scales always drives westerly winds near the equator: this is the superrotation characteristic of actual MJOs. The concluding discussion demonstrates that equatorial superrotation occurs when the planetary flow due to the vertical upscale momentum flux from synoptic scales reinforces the horizontally convergent flow due to planetary-scale mean heating.
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Brewer, Matthew C., e Clifford F. Mass. "Projected Changes in Western U.S. Large-Scale Summer Synoptic Circulations and Variability in CMIP5 Models". Journal of Climate 29, n. 16 (4 agosto 2016): 5965–78. http://dx.doi.org/10.1175/jcli-d-15-0598.1.
Testo completoAbstract (sommario):
Abstract Large-scale synoptic circulations have a profound effect on western U.S. summer weather and climate. Heat waves, water availability, the distribution of monsoonal moisture, fire-weather conditions, and other phenomena are impacted by the position and amplitude of large-scale synoptic circulations. Furthermore, regional weather is modulated by the interactions of the large-scale flow with terrain and land–water contrasts. It is therefore crucial to understand projected changes in large-scale circulations and their variability under anthropogenic global warming. Although recent research has examined changes in the jet stream, storm tracks, and synoptic disturbances over the Northern Hemisphere under global warming, most papers have focused on the cold season. In contrast, this work analyzes the projected trends in the spatial distribution and amplitude of large-scale synoptic disturbances over the western United States and eastern Pacific during July and August. It is shown that CMIP5 models project weaker mean midtropospheric gradients in geopotential height as well as attenuated temporal variability in geopotential height, temperature, vorticity, vertical motion, and sea level pressure over this region. Most models suggest reduced frequency of troughs and increased frequency of ridges over the western United States. These changes in the variability of synoptic disturbances have substantial implications for future regional weather and climate.
4
Keyser, Daniel, e Louis W. Uccellini. "Regional Models: Emerging Research Tools for Synoptic Meteorologists". Bulletin of the American Meteorological Society 68, n. 4 (aprile 1987): 306–20. http://dx.doi.org/10.1175/1520-0477(1987)068<0306:rmertf>2.0.co;2.
Testo completo
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Lindborg, E., K. K. Tung, G. D. Nastrom, J. Y. N. Cho e K. S. Gage. "Comment on "Reinterpreting aircraft measurements in anisotropic scaling turbulence" by Lovejoy et al. (2009)". Atmospheric Chemistry and Physics Discussions 9, n. 5 (22 ottobre 2009): 22331–36. http://dx.doi.org/10.5194/acpd-9-22331-2009.
Testo completoAbstract (sommario):
Abstract. Recently, Lovejoy et al. (2009) argued that the steep ~k−3 atmospheric kinetic energy spectrum at synoptic scales (≳1000 km) observed by aircraft is a spurious artefact of aircraft following isobars instead of isoheights. Without taking into account the earth's rotation they hypothesise that the horizontal atmospheric energy spectrum should scale as k−5/3 at all scales. We point out that the approximate k−3-spectrum at synoptic scales has been observed by a number of non-aircraft means since the 1960s and that general circulation models and other current models have successfully produced this spectrum. We also argue that the vertical movements of the aircraft are far too small to cause any strong effect on the measured spectrum at synoptic scales.
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Lindborg, E., K. K. Tung, G. D. Nastrom, J. Y. N. Cho e K. S. Gage. "Comment on "Reinterpreting aircraft measurement in anisotropic scaling turbulence" by Lovejoy et al. (2009)". Atmospheric Chemistry and Physics 10, n. 3 (8 febbraio 2010): 1401–2. http://dx.doi.org/10.5194/acp-10-1401-2010.
Testo completoAbstract (sommario):
Abstract. Recently, Lovejoy et al. (2009) argued that the steep ~k−3 atmospheric kinetic energy spectrum at synoptic scales (≥1000 km) observed by aircraft is a spurious artefact of aircraft following isobars instead of isoheights. Without taking into account the earth's rotation they hypothesise that the horizontal atmospheric energy spectrum should scale as k−5/3 at all scales. We point out that the approximate k−3-spectrum at synoptic scales has been observed by a number of non-aircraft means since the 1960s and that general circulation models and other current models have successfully produced this spectrum. We also argue that the vertical movements of the aircraft are far too small to cause any strong effect on the measured spectrum at synoptic scales.
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Grooms, Ian, K. Shafer Smith e Andrew J. Majda. "Multiscale models for synoptic–mesoscale interactions in the ocean". Dynamics of Atmospheres and Oceans 58 (novembre 2012): 95–107. http://dx.doi.org/10.1016/j.dynatmoce.2012.09.003.
Testo completo
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Laîné, Alexandre, Masa Kageyama, David Salas-Mélia, Gilles Ramstein, Serge Planton, Sébastien Denvil e Sophie Tyteca. "An Energetics Study of Wintertime Northern Hemisphere Storm Tracks under 4 × CO2 Conditions in Two Ocean–Atmosphere Coupled Models". Journal of Climate 22, n. 3 (1 febbraio 2009): 819–39. http://dx.doi.org/10.1175/2008jcli2217.1.
Testo completoAbstract (sommario):
Abstract Different possible behaviors of winter Northern Hemisphere storm tracks under 4 × CO2 forcing are considered by analyzing the response of two of the ocean–atmosphere coupled models that were run for the fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC-AR4), namely the Institut Pierre Simon Laplace’s global coupled model (IPSL-CM4) and the Centre National de Recherches Meteorologiques’s coupled ocean–atmosphere model (CNRM-CM3). It is interesting to compare these models due to their very different responses, especially concerning the North Atlantic storm track. A local energetics study of the synoptic variability in both models is performed, derived from the eddy energy equations, including diabatic terms. The ability of both models to simulate the present-day eddy energetics is considered, indicating no major discrepancies. Both models indicate that the primary cause for synoptic activity changes at the western end of the storm tracks is related to the baroclinic conversion process, due to mean temperature gradient changes in some localized regions of the western oceanic basins, but also resulting from changes in the eddy efficiency to convert energy from the mean flow. Farther downstream, latent heat release during the developing and mature stages of eddies becomes an important eddy energy source especially in terms of changes between 4 × CO2 and preindustrial conditions. This diabatic process amplifies the upstream synoptic (hence usually baroclinic) changes, with more and/or stronger storms implying more latent heat being released (and the converse being true for weaker synoptic activity). This amplification is asymmetrical for the models considered under the simulated 4 × CO2 conditions, due to a greater amount of water vapor contained in warmer air and hence the potential for more condensation for a given synoptic activity. The magnitude of the reduced latent heating is attenuated, whereas increased latent heating is strengthened. Ageostrophic geopotential fluxes are also important in relocating eddy kinetic energy, especially in the vertical.
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Yang, Qiu, e Andrew J. Majda. "Upscale Impact of Mesoscale Disturbances of Tropical Convection on Synoptic-Scale Equatorial Waves in Two-Dimensional Flows". Journal of the Atmospheric Sciences 74, n. 9 (1 settembre 2017): 3099–120. http://dx.doi.org/10.1175/jas-d-17-0068.1.
Testo completoAbstract (sommario):
Abstract Superclusters on the synoptic scale containing mesoscale systems are frequently organized by convectively coupled equatorial waves (CCEWs). Present-day global models struggle to simulate multiscale tropical convection, and the upscale effects of mesoscale systems are not well understood. A simple two-dimensional multiscale model with prescribed two-scale heating and eddy transfer of momentum and temperature drives the synoptic-scale circulation, successfully reproduces key features of flow fields with a front-to-rear tilt, and compares well with results from a cloud-resolving model (CRM). In the scenario with an elevated upright mean heating, the tilted vertical structure of synoptic-scale circulation is still induced by the upscale impact of mesoscale disturbances. In a faster propagation scenario, the upscale impact becomes less important as a result of competing effects of eddy transfer of momentum and temperature, while the synoptic-scale circulation response to mean heating dominates, in agreement with cloud-resolving models. In the unrealistic scenario with upward–westward-tilted mesoscale heating, positive potential temperature anomalies are induced in the leading edge, which will suppress shallow convection in a moist environment.
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Majda, Andrew J., e Samuel N. Stechmann. "Models for Multiscale Interactions. Part II: Madden–Julian Oscillation, Moisture, and Convective Momentum Transport". Meteorological Monographs 56 (1 maggio 2016): 10.1–10.5. http://dx.doi.org/10.1175/amsmonographs-d-15-0005.1.
Testo completoAbstract (sommario):
Abstract It is well known that the envelope of the Madden–Julian oscillation (MJO) consists of smaller-scale convective systems, including mesoscale convective systems (MCS), tropical cyclones, and synoptic-scale waves called “convectively coupled equatorial waves” (CCW). In fact, recent results suggest that the fundamental mechanisms of the MJO involve interactions between the synoptic-scale CCW and their larger-scale environment (Majda and Stechmann). In light of this, this chapter reviews recent and past work on two-way interactions between convective systems—both MCSs and CCW—and their larger-scale environment, with a particular focus given to recent work on MJO–CCW interactions.
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Liu, Zheng, e Axel Schweiger. "Synoptic Conditions, Clouds, and Sea Ice Melt Onset in the Beaufort and Chukchi Seasonal Ice Zone". Journal of Climate 30, n. 17 (settembre 2017): 6999–7016. http://dx.doi.org/10.1175/jcli-d-16-0887.1.
Testo completoAbstract (sommario):
Cloud response to synoptic conditions over the Beaufort and Chukchi seasonal ice zone is examined. Four synoptic states with distinct thermodynamic and dynamic signatures are identified using ERA-Interim reanalysis data from 2000 to 2014. CloudSat and CALIPSO observations suggest control of clouds by synoptic states. Warm continental air advection is associated with the fewest low-level clouds, while cold air advection generates the most low-level clouds. Low-level clouds are related to lower-tropospheric stability and both are regulated by synoptic conditions. High-level clouds are associated with humidity and vertical motions in the upper atmosphere. Observed cloud vertical and spatial variability is reproduced well in ERA-Interim, but winter low-level cloud fraction is overestimated. This suggests that synoptic conditions constrain the spatial extent of clouds through the atmospheric structure, while the parameterizations for cloud microphysics and boundary layer physics are critical for the life cycle of clouds in numerical models. Sea ice melt onset is related to synoptic conditions. Melt onsets occur more frequently and earlier with warm air advection. Synoptic conditions with the highest temperatures and precipitable water are most favorable for melt onsets even though fewer low-level clouds are associated with these conditions.
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James, Kenneth A., David J. Stensrud e Nusrat Yussouf. "Value of Real-Time Vegetation Fraction to Forecasts of Severe Convection in High-Resolution Models". Weather and Forecasting 24, n. 1 (1 febbraio 2009): 187–210. http://dx.doi.org/10.1175/2008waf2007097.1.
Testo completoAbstract (sommario):
Abstract Near-real-time values of vegetation fraction are incorporated into a 2-km nested version of the Advanced Research Weather Research and Forecasting (ARW) model and compared to forecasts from a control run that uses climatological values of vegetation fraction for eight severe weather events during 2004. It is hypothesized that an improved partitioning of surface sensible and latent heat fluxes occurs when incorporating near-real-time values of the vegetation fraction into models, which may result in improved forecasts of the low-level environmental conditions that support convection and perhaps even lead to improved explicit convective forecasts. Five of the severe weather events occur in association with weak synoptic-scale forcing, while three of the events occur in association with moderate or strong synoptic-scale forcing. Results show that using the near-real-time values of the vegetation fraction alters the values and structure of low-level temperature and dewpoint temperature fields compared to the forecasts using climatological vegetation fractions. The environmental forecasts that result from using the real-time vegetation fraction are more thermodynamically supportive of convection, including stronger and deeper frontogenetic circulations, and statistically significant improvements of most unstable CAPE forecasts compared to the control run. However, despite the improved environmental forecasts, the explicit convective forecasts using real-time vegetation fractions show little to no improvement over the control forecasts. The convective forecasts are generally poor under weak synoptic-scale forcing and generally good under strong synoptic-scale forcing. These results suggest that operational forecasters can best use high-resolution forecasts to help diagnose environmental conditions within an ingredients-based forecasting approach.
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Purich, Ariaan, Tim Cowan, Wenju Cai, Peter van Rensch, Petteri Uotila, Alexandre Pezza, Ghyslaine Boschat e Sarah Perkins. "Atmospheric and Oceanic Conditions Associated with Southern Australian Heat Waves: A CMIP5 Analysis". Journal of Climate 27, n. 20 (7 ottobre 2014): 7807–29. http://dx.doi.org/10.1175/jcli-d-14-00098.1.
Testo completoAbstract (sommario):
Abstract Atmospheric and oceanic conditions associated with southern Australian heat waves are examined using phase 5 of the Coupled Model Intercomparison Project (CMIP5) models. Accompanying work analyzing modeled heat wave statistics for Australia finds substantial increases in the frequency, duration, and temperature of heat waves by the end of the twenty-first century. This study assesses the ability of CMIP5 models to simulate the synoptic and oceanic conditions associated with southern Australian heat waves, and examines how the classical atmospheric setup associated with heat waves is projected to change in response to mean-state warming. To achieve this, near-surface temperature, mean sea level pressure, and sea surface temperature (SST) from the historical and high-emission simulations are analyzed. CMIP5 models are found to represent the synoptic setup associated with heat waves well, despite showing greater variation in simulating SST anomalies. The models project a weakening of the pressure couplet associated with future southern Australian heat waves, suggesting that even a non-classical synoptic setup is able to generate more frequent heat waves in a warmer world. A future poleward shift and strengthening of heat wave–inducing anticyclones is confirmed using a tracking scheme applied to model projections. Model consensus implies that while anticyclones associated with the hottest future southern Australian heat waves will be more intense and originate farther poleward, a greater proportion of heat waves occur in association with a weaker synoptic setup that, when combined with warmer mean-state temperatures, gives rise to more future heat waves.
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Verdon-Kidd, D., e A. S. Kiem. "On the relationship between large-scale climate modes and regional synoptic patterns that drive Victorian rainfall". Hydrology and Earth System Sciences Discussions 5, n. 5 (10 ottobre 2008): 2791–815. http://dx.doi.org/10.5194/hessd-5-2791-2008.
Testo completoAbstract (sommario):
Abstract. In this paper regional (synoptic) and large-scale climate drivers of rainfall are investigated for Victoria, Australia. A non-linear classification methodology known as self-organizing maps (SOM) is used to identify 20 key regional synoptic patterns, which are shown to capture a range of significant synoptic features known to influence the climate of the region. Rainfall distributions are assigned to each of the 20 patterns for nine rainfall stations located across Victoria, resulting in a clear distinction between wet and dry synoptic types at each station. The influence of large-scale climate modes on the frequency and timing of the regional synoptic patterns is also investigated. This analysis revealed that phase changes in the El Niño Southern Oscillation (ENSO), the Southern Annular Mode (SAM) and/or Indian Ocean Dipole (IOD) are associated with a shift in the relative frequency of wet and dry synoptic types. Importantly, these results highlight the potential to utilise the link between the regional synoptic patterns derived in this study and large-scale climate modes to improve rainfall forecasting for Victoria, both in the short- (i.e. seasonal) and long-term (i.e. decadal/multi-decadal scale). In addition, the regional and large-scale climate drivers identified in this study provide a benchmark by which the performance of Global Climate Models (GCMs) may be assessed.
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Verdon-Kidd, D. C., e A. S. Kiem. "On the relationship between large-scale climate modes and regional synoptic patterns that drive Victorian rainfall". Hydrology and Earth System Sciences 13, n. 4 (7 aprile 2009): 467–79. http://dx.doi.org/10.5194/hess-13-467-2009.
Testo completoAbstract (sommario):
Abstract. In this paper regional (synoptic) and large-scale climate drivers of rainfall are investigated for Victoria, Australia. A non-linear classification methodology known as self-organizing maps (SOM) is used to identify 20 key regional synoptic patterns, which are shown to capture a range of significant synoptic features known to influence the climate of the region. Rainfall distributions are assigned to each of the 20 patterns for nine rainfall stations located across Victoria, resulting in a clear distinction between wet and dry synoptic types at each station. The influence of large-scale climate modes on the frequency and timing of the regional synoptic patterns is also investigated. This analysis revealed that phase changes in the El Niño Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and/or the Southern Annular Mode (SAM) are associated with a shift in the relative frequency of wet and dry synoptic types on an annual to inter-annual timescale. In addition, the relative frequency of synoptic types is shown to vary on a multi-decadal timescale, associated with changes in the Inter-decadal Pacific Oscillation (IPO). Importantly, these results highlight the potential to utilise the link between the regional synoptic patterns derived in this study and large-scale climate modes to improve rainfall forecasting for Victoria, both in the short- (i.e. seasonal) and long-term (i.e. decadal/multi-decadal scale). In addition, the regional and large-scale climate drivers identified in this study provide a benchmark by which the performance of Global Climate Models (GCMs) may be assessed.
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Robinson, Dennis P., e Robert X. Black. "Baroclinic Development in Observations and NASA GSFC General Circulation Models". Monthly Weather Review 134, n. 4 (1 aprile 2006): 1161–73. http://dx.doi.org/10.1175/mwr3110.1.
Testo completoAbstract (sommario):
Abstract Comparative diagnostic analyses of developing synoptic-scale baroclinic disturbances in NCEP–NCAR reanalyses and the NASA–NCAR (NASCAR) and Aries [NASA’s Seasonal-to-Interannual Prediction Project (NSIPP)] general circulation model simulations are performed. In particular, lag composite analyses of wintertime cyclonic and anticyclonic events occurring in the North Pacific and North Atlantic storm tracks are constructed to pursue a synoptic and dynamic characterization of eddy development. The data are also seasonally stratified to study aspects of the North Pacific midwinter suppression phenomenon. Winter-averaged results indicate that the model-simulated events are generally too weak in amplitude, particularly in the upper troposphere. For the North Pacific storm track, model-simulated events are also anomalously distended in the meridional direction. The existing model biases in eddy structure and magnitude lead to anomalously weak baroclinic energy conversions for both cyclonic and anticyclonic events over the North Pacific. For the North Atlantic storm track the NASCAR model provides a very good representation of the structure of developing cyclonic events. However, growing North Atlantic cyclones in the NSIPP model are anomalously weak and horizontally too isotropic (meridionally retracted). These latter two characteristics are also observed in both models for developing anticyclonic flow anomalies over the North Atlantic. The relative weakness of NSIPP synoptic events over the North Atlantic region is largely responsible for the 50% deficiency in areal-averaged baroclinic energy conversions. Conversely, the NASCAR model climatology features anomalously strong temperature gradients over the western North Atlantic that provide local enhancements to the baroclinic energy conversion field. A seasonally stratified diagnostic analysis reveals that the simulated climatological storm tracks over the North Pacific undergo larger spatial migrations during the cool season compared to observations. It is further determined that the suppression of synoptic eddy activity observed in the Pacific storm track is associated with a relative midwinter weakness in the magnitude of the growing cyclonic anomalies. Specifically, during midwinter the cyclonic perturbations entering the Pacific storm track are deficient in magnitude compared to their early and late winter counterparts. It is also discovered that the midwinter suppression pattern over the North Pacific region has a clear organized extension upstream into Siberia, the region from which incipient upper-tropospheric short-wave features emanate. This behavior is found in both observations and the model simulations. The results herein support the idea that the North Pacific midwinter suppression phenomenon is linked to a midwinter weakness in the upstream formation of upper-level short waves, leading to anomalously weak “seeding” of baroclinic disturbances in the Pacific storm track.
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Wang, G. Geoff, Shongming Huang, Robert A. Monserud e Ryan J. Klos. "Lodgepole pine site index in relation to synoptic measures of climate, soil moisture and soil nutrients". Forestry Chronicle 80, n. 6 (1 dicembre 2004): 678–86. http://dx.doi.org/10.5558/tfc80678-6.
Testo completoAbstract (sommario):
Lodgepole pine site index was examined in relation to synoptic measures of topography, soil moisture, and soil nutrients in Alberta. Data came from 214 lodgepole pine-dominated stands sampled as a part of the provincial permanent sample plot program. Spatial location (elevation, latitude, and longitude) and natural subregions (NSRs) were topographic variables that might be considered as synoptic measures of climate. Soil moisture regimes (SMRs) were used as synoptic measures of soil moisture supply. Soil nutrient regimes (SNRs) were used as synoptic measures of soil nutrient supply. Simple measures of geographic location (elevation, latitude, longitude) carried the most predictive power, explaining between 33% and 37% of the variation. Site index decreased with elevation, increased with latitude, and had a quadratic relationship with longitude. The Lower Foothills NSR had higher site index (16.1 m) than the Upper Foothills (14.0 m), Montane (11.8 m) and Subalpine (10.3 m) NSRs. Soil moisture regime variables were not significant. Soil nutrient regime variables were also not important, although one was significant in conjunction with elevation, latitude, and longitude (41% explained variation). Standard errors of estimate ranged between 2.64 and 2.94 m for the various synoptic models. Interaction terms between synoptic variables were examined but were found to be non-significant. Key words: site index, climate regime, soil moisture regime, soil nutrient regime, Pinus contorta
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Sang, Xiaozhuo, Xiu-Qun Yang, Lingfeng Tao, Jiabei Fang e Xuguang Sun. "Evaluation of synoptic eddy activities and their feedback onto the midlatitude jet in five atmospheric reanalyses with coarse versus fine model resolutions". Climate Dynamics 58, n. 5-6 (27 settembre 2021): 1363–81. http://dx.doi.org/10.1007/s00382-021-05965-9.
Testo completoAbstract (sommario):
AbstractInteraction between synoptic eddy and mean flow plays a crucial role in maintaining midlatitude westerly jet. In this study, climatologies of synoptic eddy activities and their feedback onto midlatitude jet for 1980–2016 are evaluated and compared through analyzing daily data from five atmospheric reanalyses with different resolutions including one coarse-resolution reanalysis (NCEP2) and four fine-resolution reanalyses (ERA-Interim, JRA-55, MERRA-2, and CFSR). Horizontal resolutions of the atmospheric models generating those reanalyses are approximately equivalent to 210, 79, 60, 50, and 38 km, respectively. Results show that the eddy activities and their feedback onto the midlatitude jet in those fine-resolution reanalyses are consistently and significantly stronger than those in the coarse-resolution reanalysis (NCEP2). The maximal relative increases that are found to occur primarily in the midlatitudes of the Southern Hemisphere are estimated to be up to 55% for the baroclinicity, 53% for the eddy energetics, 59% for the eddy forcing, and even 85% for the eddy feedback onto the mean flow. Those increases are reasonably conjectured to be related to increased model resolutions, since the synoptic eddy genesis is proportional to the low-level atmospheric meridional temperature gradient which is sensitive to the meridional resolution of atmospheric models. Although the coarse-resolution reanalysis resolves synoptic eddies insufficiently and thus underestimates their feedback onto the mean flow, the magnitudes of eddy-driven jets are almost the same among five reanalyses, implying a mismatch between the eddy feedback and the eddy-driven jet in the coarse-resolution reanalysis. Therefore, the results of this study imply the importance of using fine-resolution reanalyses in accurately understanding the midlatitude synoptic eddy–mean flow interaction.
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Samarasinghe, Savini M., Yi Deng e Imme Ebert-Uphoff. "A Causality-Based View of the Interaction between Synoptic- and Planetary-Scale Atmospheric Disturbances". Journal of the Atmospheric Sciences 77, n. 3 (25 febbraio 2020): 925–41. http://dx.doi.org/10.1175/jas-d-18-0163.1.
Testo completoAbstract (sommario):
Abstract This paper reports preliminary yet encouraging findings on the use of causal discovery methods to understand the interaction between atmospheric planetary- and synoptic-scale disturbances in the Northern Hemisphere. Specifically, constraint-based structure learning of probabilistic graphical models is applied to the spherical harmonics decomposition of the daily 500-hPa geopotential height field in boreal winter for the period 1948–2015. Active causal pathways among different spherical harmonics components are identified and documented in the form of a temporal probabilistic graphical model. Since, by definition, the structure learning algorithm used here only robustly identifies linear causal effects, we report only causal pathways between two groups of disturbances with sufficiently large differences in temporal and/or spatial scales, that is, planetary-scale (mainly zonal wavenumbers 1–3) and synoptic-scale disturbances (mainly zonal wavenumbers 6–8). Daily reconstruction of geopotential heights using only interacting scales suggest that the modulation of synoptic-scale disturbances by planetary-scale disturbances is best characterized by the flow of information from a zonal wavenumber-1 disturbance to a synoptic-scale circumglobal wave train whose amplitude peaks at the North Pacific and North Atlantic storm-track region. The feedback of synoptic-scale to planetary-scale disturbances manifests itself as a zonal wavenumber-2 structure driven by synoptic-eddy momentum fluxes. This wavenumber-2 structure locally enhances the East Asian trough and western Europe ridge of the wavenumber-1 planetary-scale disturbance that actively modulates the activity of synoptic-scale disturbances. The winter-mean amplitude of the actively interacting disturbances are characterized by pronounced fluctuations across interannual to decadal time scales.
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Kostarev, Sergey V., e Igor N. Rusin. "THE USE OF AUTOMATED SYNOPTIC TYPING FOR CONDITIONAL VERIFICATION OF NUMERICAL WEATHER PREDICTION IN THE PERM REGION". Географический вестник = Geographical bulletin, n. 1 (56) (2021): 68–80. http://dx.doi.org/10.17072/2079-7877-2021-1-68-80.
Testo completoAbstract (sommario):
The article discusses the possibility of verification of short-term 2-meter air temperature forecasts with the Global Forecast System and Global Environment Multiscale numerical weather prediction models depending on the observed synoptic type (a case study of the Perm region for the period 2018–2019). As part of the study, we have developed a system of automated determination of synoptic type based on a two-stage procedure, including decomposition of mean sea level pressure fields via principal component analysis and the subsequent clustering of decomposition coefficients using K-means. It has been established that GFS forecasts are more dependent on synoptic type in summer than in winter. The decline of forecast quality, expressed in systematic underestimation of forecast temperature by 0.6°–1.2°, is noted for synoptic types associated with warm air advection.: In contrast, GEM forecasts tend to lack accuracy in winter. A sharp decrease in forecast quality has been discovered in the central area of anticyclone at night, when the forecast accuracy drops to 44%. The obtained results could be useful in operational forecasting and model postprocessing.
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Dai, Jingru, Michael J. Manton, Steven T. Siems e Elizabeth E. Ebert. "Estimation of Daily Winter Precipitation in the Snowy Mountains of Southeastern Australia". Journal of Hydrometeorology 15, n. 3 (1 giugno 2014): 909–20. http://dx.doi.org/10.1175/jhm-d-13-081.1.
Testo completoAbstract (sommario):
Abstract Wintertime precipitation in the Snowy Mountains provides water for agriculture, industry, and domestic use in inland southeastern Australia. Unlike most of Australia, much of this precipitation falls as snow, and it is recorded by a private network of heated tipping-bucket gauges. These observations are used in the present study to assess the accuracy of a poor man’s ensemble (PME) prediction of precipitation in the Snowy Mountains based on seven numerical weather prediction models. While the PME performs quite well, there is significant underestimation of precipitation intensity. It is shown that indicators of the synoptic environment can be used to improve the PME estimates of precipitation. Four synoptic regimes associated with different precipitation classes are identified from upper-air data. The reliability of the PME forecasts can be sharpened by considering the precipitation in each of the four synoptic classes. A linear regression, based on the synoptic classification and the PME estimate, is used to reduce the forecast errors. The potential to extend the method for forecasting purposes is discussed.
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Niznik, Matthew J., Benjamin R. Lintner, Adrian J. Matthews e Matthew J. Widlansky. "The Role of Tropical–Extratropical Interaction and Synoptic Variability in Maintaining the South Pacific Convergence Zone in CMIP5 Models". Journal of Climate 28, n. 8 (7 aprile 2015): 3353–74. http://dx.doi.org/10.1175/jcli-d-14-00527.1.
Testo completoAbstract (sommario):
Abstract The South Pacific convergence zone (SPCZ) is simulated as too zonal a feature in the current generation of climate models, including those in phase 5 of the Coupled Model Intercomparison Project (CMIP5). This zonal bias induces errors in tropical convective heating, with subsequent effects on global circulation. The SPCZ structure, particularly in the subtropics, is governed by the tropical–extratropical interaction between transient synoptic systems and the mean background state. In this study, analysis of synoptic variability in the simulated subtropical SPCZ reveals that the basic mechanism of tropical–extratropical interaction is generally well simulated, with storms approaching the SPCZ along comparable trajectories to observations. However, there is a broad spread in mean precipitation and its variability across the CMIP5 ensemble. Intermodel spread appears to relate to a biased background state in which the synoptic waves propagate. In particular, the region of mean negative zonal stretching deformation or “storm graveyard” in the upper troposphere is displaced in CMIP5 models to the northeast of its position in reanalysis data, albeit with pronounced (≈25°) intermodel longitudinal spread. Precipitation along the eastern edge of the SPCZ shifts in accordance with a storm graveyard shift, and in general models with stronger storm graveyards show higher precipitation variability. Building on prior SPCZ research, it is suggested that SPCZs simulated by CMIP5 models are not simply too zonal; rather, in models the subtropical SPCZ manifests a diagonal tilt similar to observations while SST biases force an overly zonal tropical SPCZ, resulting in a more discontinuous SPCZ than observed.
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Juang, Hann-Ming Henry, Ching-Teng Lee, Yongxin Zhang, Yucheng Song, Ming-Chin Wu, Yi-Leng Chen, Kevin Kodama e Shyh-Chin Chen. "Applying Horizontal Diffusion on Pressure Surface to Mesoscale Models on Terrain-Following Coordinates". Monthly Weather Review 133, n. 5 (1 maggio 2005): 1384–402. http://dx.doi.org/10.1175/mwr2925.1.
Testo completoAbstract (sommario):
Abstract The National Centers for Environmental Prediction regional spectral model and mesoscale spectral model (NCEP RSM/MSM) use a spectral computation on perturbation. The perturbation is defined as a deviation between RSM/MSM forecast value and their outer model or analysis value on model sigma-coordinate surfaces. The horizontal diffusion used in the models applies perturbation diffusion in spectral space on model sigma-coordinate surfaces. However, because of the large difference between RSM/MSM and their outer model or analysis terrains, the perturbation on sigma surfaces could be large over steep mountain areas as horizontal resolution increases. This large perturbation could introduce systematical error due to artificial vertical mixing from horizontal diffusion on sigma surface for variables with strong vertical stratification, such as temperature and humidity. This nonnegligible error would eventually ruin the forecast and simulation results over mountain areas in high-resolution modeling. To avoid the erroneous vertical mixing on the systematic perturbation, a coordinate transformation is applied in deriving a horizontal diffusion on pressure surface from the variables provided on terrain-following sigma coordinates. Three cases are selected to illustrate the impact of the horizontal diffusion on pressure surfaces, which reduces or eliminates numerical errors of mesoscale modeling over mountain areas. These cases address concerns from all aspects, including unstable and stable synoptic conditions, moist and dry atmospheric settings, weather and climate integrations, hydrostatic and nonhydrostatic modeling, and island and continental orography. After implementing the horizontal diffusion on pressure surfaces for temperature and humidity, the results show better rainfall and flow pattern simulations when compared to observations. Horizontal diffusion corrects the warming, moistening, excessive rainfall, and convergent flow patterns around high mountains under unstable and moist synoptic conditions and corrects the cooling, drying, and divergent flow patterns under stable and dry synoptic settings.
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Ansari, Fazel, Madjid Fathi e Ulrich Seidenberg. "Problem-solving approaches in maintenance cost management: a literature review". Journal of Quality in Maintenance Engineering 22, n. 4 (10 ottobre 2016): 334–52. http://dx.doi.org/10.1108/jqme-04-2015-0012.
Testo completoAbstract (sommario):
Purpose The purpose of this paper is to investigate the use of problem-solving approaches in maintenance cost management (MCM). In particular, the paper aims to examine characteristics of MCM models and to identify patterns for classification of problem-solving approaches. Design/methodology/approach This paper reflects an extensive and detailed literature survey of 68 (quantitative or qualitative) cost models within the scope of MCM published in the period from 1969 to 2013. The reviewed papers have been critically examined and classified based on implementing a morphological analysis which employs eight criteria and associated expressions. In addition, the survey identified two main perspectives of problem solving: first, synoptic/incremental and second, heuristics/meta-heuristics. Findings The literature survey revealed the patterns for classification of the MCM models, especially the characteristics of the models for problem-solving in association with the type of modeling, focus of purpose, extent and scope of application, and reaction and dynamics of parameters. Majority of the surveyed approaches is mathematical, respectively, synoptic. Incremental approaches are much less and only few are combined (i.e. synoptic and incremental). A set of features is identified for proper classification, selection, and coexistence of the two approaches. Research limitations/implications This paper provides a basis for further study of heuristic and meta-heuristic approaches to problem-solving. Especially the coexistence of heuristic, synoptic, and incremental approaches needs to be further investigated. Practical implications The detected dominance of synoptic approaches in literature – especially in the case of specific application areas – contrasts to some extent to the needs of maintenance managers in practice. Hence the findings of this paper particularly address the need for further investigation on combining problem-solving approaches for improving planning, monitoring, and controlling phases of MCM. Continuous improvement of MCM, especially problem-solving and decision-making activities, is tailored to the use of maintenance knowledge assets. In particular, maintenance management systems and processes are knowledge driven. Thus, combining problem-solving approaches with knowledge management methods is of interest, especially for continuous learning from past experiences in MCM. Originality/value This paper provides a unique study of 68 problem-solving approaches in MCM, based on a morphological analysis. Hence suitable criteria and their expressions are provided. The paper reveals the opportunities for further interdisciplinary research in the maintenance cost life cycle.
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Cannon, Alex J. "Regression-Guided Clustering: A Semisupervised Method for Circulation-to-Environment Synoptic Classification". Journal of Applied Meteorology and Climatology 51, n. 2 (febbraio 2012): 185–90. http://dx.doi.org/10.1175/jamc-d-11-0155.1.
Testo completoAbstract (sommario):
AbstractRegression-guided clustering is introduced as a means of constructing circulation-to-environment synoptic climatological classifications. Rather than applying an unsupervised clustering algorithm to synoptic-scale atmospheric circulation data, one instead augments the atmospheric circulation dataset with predictions from a supervised regression model linking circulation to environment. The combined dataset is then entered into the clustering algorithm. The level of influence of the environmental dataset can be controlled by a simple weighting factor. The method is generic in that the choice of regression model and clustering algorithm is left to the user. Examples are given using standard multivariate linear regression models and the k-means clustering algorithm, both established methods in synoptic climatology. Results for southern British Columbia, Canada, indicate that model performance can be made to range between that of a fully unsupervised algorithm and a fully supervised algorithm.
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Prieto, L., R. Garcia, J. Diaz, E. Hernandez e T. del Teso. "NAO influence on extreme winter temperatures in Madrid (Spain)". Annales Geophysicae 20, n. 12 (31 dicembre 2002): 2077–85. http://dx.doi.org/10.5194/angeo-20-2077-2002.
Testo completoAbstract (sommario):
Abstract. Extremely cold days (ECDs), with minimum temperatures lower than -4.6°C, have been analysed for Madrid. This threshold corresponds to the 5th percentile of the period 1963–1999. Adopting a case analysis approach, five synoptic patterns have been identified that produce these extremely low temperatures. Three of them are associated with cold air flows over the Iberian Peninsula, and the other two with a lack of significant circulation over the region. A nonlinear association with the North Atlantic Oscillation (NAO) has been identified using log-linear models. The NAO positive phase leads to an increase in the winter frequency of those synoptic patterns associated with stagnant air flow over Iberia, while those characterised by cold, northern flows do not appear to be similarly influenced.Key words. Meteorology and atmospheric dynamics (climatology; synoptic-scale meteorology; general or miscellaneous)
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Sheridan, Scott C., e Cameron C. Lee. "Synoptic climatology and the general circulation model". Progress in Physical Geography: Earth and Environment 34, n. 1 (22 gennaio 2010): 101–9. http://dx.doi.org/10.1177/0309133309357012.
Testo completoAbstract (sommario):
One of the main research directions of synoptic climatology in recent years has been its application to the output of general circulation models. These applications have spanned the wide array of synoptic techniques, from traditional ones such as correlation-based maps to more recently developed ones such as self-organizing maps and fuzzy clusters. Here, we review the main themes of recent articles, including assessments of the ability of GCMs to replicate historical circulation pattern frequency, as well as the incorporation of synoptic methods to assess GCM capability in producing estimates of precipitation and the likelihood of extreme events. Results from these articles are quite heterogeneous, suggesting that the selection of the GCM, the variables that are used to drive the categorization, and the specific methodology chosen are all important in determining the efficacy of the research and application.
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Tozer, Carly R., James S. Risbey, Didier P. Monselesan, Dougal T. Squire, Matthew A. Chamberlain, Richard J. Matear e Tilo Ziehn. "Assessing the Representation of Australian Regional Climate Extremes and Their Associated Atmospheric Circulation in Climate Models". Journal of Climate 33, n. 4 (15 febbraio 2020): 1227–45. http://dx.doi.org/10.1175/jcli-d-19-0287.1.
Testo completoAbstract (sommario):
AbstractWe assess the representation of multiday temperature and rainfall extremes in southeast Australia in three coupled general circulation models (GCMs) of varying resolution. We evaluate the statistics of the modeled extremes in terms of their frequency, duration, and magnitude compared to observations, and the model representation of the midtropospheric circulation (synoptic and large scale) associated with the extremes. We find that the models capture the statistics of observed heatwaves reasonably well, though some models are “too wet” to adequately capture the observed duration of dry spells but not always wet enough to capture the magnitude of extreme wet events. Despite the inability of the models to simulate all extreme event statistics, the process evaluation indicates that the onset and decay of the observed synoptic structures are well simulated in the models, including for wet and dry extremes. We also show that the large-scale wave train structures associated with the observed extremes are reasonably well simulated by the models although their broader onset and decay is not always captured in the models. The results presented here provide some context for, and confidence in, the use of the coupled GCMs in climate prediction and projection studies for regional extremes.
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Howitt, George, Simon Stevenson, Alejandro Vigna-Gómez, Stephen Justham, Natasha Ivanova, Tyrone E. Woods, Coenraad J. Neijssel e Ilya Mandel. "Luminous Red Novae: population models and future prospects". Monthly Notices of the Royal Astronomical Society 492, n. 3 (7 gennaio 2020): 3229–40. http://dx.doi.org/10.1093/mnras/stz3542.
Testo completoAbstract (sommario):
ABSTRACT A class of optical transients known as Luminous Red Novae (LRNe) have recently been associated with mass ejections from binary stars undergoing common-envelope evolution. We use the population synthesis code COMPAS to explore the impact of a range of assumptions about the physics of common-envelope evolution on the properties of LRNe. In particular, we investigate the influence of various models for the energetics of LRNe on the expected event rate and light curve characteristics, and compare with the existing sample. We find that the Galactic rate of LRNe is ∼0.2 yr−1, in agreement with the observed rate. In our models, the luminosity function of Galactic LRNe covers multiple decades in luminosity and is dominated by signals from stellar mergers, consistent with observational constraints from iPTF and the Galactic sample of LRNe. We discuss how observations of the brightest LRNe may provide indirect evidence for the existence of massive (>40 M⊙) red supergiants. Such LRNe could be markers along the evolutionary pathway leading to the formation of double compact objects. We make predictions for the population of LRNe observable in future transient surveys with the Large Synoptic Survey Telescope and the Zwicky Transient Facility. In all plausible circumstances, we predict a selection-limited observable population dominated by bright, long-duration events caused by common envelope ejections. We show that the Large Synoptic Survey Telescope will observe 20–750 LRNe per year, quickly constraining the luminosity function of LRNe and probing the physics of common-envelope events.
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Pérez, Claudio F., Ana G. Ulke e María I. Gassmann. "Southern South American Long-Distance Pollen Dispersal and Its Relationship with Atmospheric Circulation". Aerobiology 2, n. 4 (12 ottobre 2024): 85–104. http://dx.doi.org/10.3390/aerobiology2040007.
Testo completoAbstract (sommario):
This paper addresses the study of synoptic-scale meteorological conditions that favor long-range pollen transport in southern South America combining airborne pollen counts, modeled three-dimensional backward trajectories, and synoptic and surface meteorological data. Alnus pollen transport trajectories indicate origins predominantly in montane forests of the Yungas between 1500 and 2800 m altitude. The South American Low-Level Jet is the main meteorological feature that explains 64% of the detected pollen arrival at the target site. Podocarpus and Nothofagus pollen instead are linked primarily to the widespread Subantartic forests in southern Patagonia. Their transport patterns are consistent with previous studies, which show an association with synoptic patterns related to cold front passages carrying pollen in the free atmosphere (27% for Nothofagus and 25% for Podocarpus). These results show the significance of understanding long-distance pollen transport for disciplines such as climate change reconstruction and agriculture, emphasizing the need for further research to refine atmospheric circulation models and refine interpretations of past vegetation and climate dynamics.
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KISLOV, A. V., U. I. ANTIPINA e I. A. KORNEVA. "EXTREME PRECIPITATION IN THE EUROPEAN ARCTIC IN SUMMER: STATISTICS AND SYNOPTIC MODELS". Meteorologiya i Gidrologiya, n. 7 (2021): 20–34. http://dx.doi.org/10.52002/0130-2906-2021-7-20-34.
Testo completoAbstract (sommario):
Extreme precipitation in summer is classified in terms of belonging to the certain baseline probability distribution. The Pareto distribution can be used as its approximation. Events deviating from the baseline distribution are represented by the largest daily total precipitation. For them, the compliance with the probability (or the average repetition time) is completely lost, that is, any anomalies can occur, but they do not exceed some limit values typical of the Arctic. Thus, for the entire set of extremes, a specific distribution law of random variables can be introduced, that describes anomalies not exceeding certain absolute values; the presence of the boundary is felt only when approaching it. For 50 analyzed years at each station in the European Arctic, approximately four such anomalies were recorded. Synoptic objects in which super-large precipitation anomalies occur are determined: these are cyclones or pressure troughs with high water vapor content in the air (exceeding ~25 kg/m2) and with mesoscale systems embedded into the fronts, which are characterized by the vertical wind shear.
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Kislov, A. V., U. I. Antipina e I. A. Korneva. "Extreme Precipitation in the European Arctic in Summer: Statistics and Synoptic Models". Russian Meteorology and Hydrology 46, n. 7 (luglio 2021): 434–43. http://dx.doi.org/10.3103/s1068373921070025.
Testo completo
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Yushkov, V. P. "Remote sounding and mesoscale synoptic models in studying the urban boundary layer". Atmospheric and Oceanic Optics 30, n. 5 (settembre 2017): 462–74. http://dx.doi.org/10.1134/s1024856017050165.
Testo completo
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Gibson, Peter B., Petteri Uotila, Sarah E. Perkins-Kirkpatrick, Lisa V. Alexander e Andrew J. Pitman. "Evaluating synoptic systems in the CMIP5 climate models over the Australian region". Climate Dynamics 47, n. 7-8 (9 gennaio 2016): 2235–51. http://dx.doi.org/10.1007/s00382-015-2961-y.
Testo completo
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Ren, Lei, Nanyang Chu, Zhan Hu e Michael Hartnett. "Investigations into Synoptic Spatiotemporal Characteristics of Coastal Upper Ocean Circulation Using High Frequency Radar Data and Model Output". Remote Sensing 12, n. 17 (1 settembre 2020): 2841. http://dx.doi.org/10.3390/rs12172841.
Testo completoAbstract (sommario):
Numerical models and remote sensing observation systems such as radars are useful for providing information on surface flows for coastal areas. Evaluation of their performance and extracting synoptic characteristics are challenging and important tasks. This research aims to investigate synoptic characteristics of surface flow fields through undertaking a detailed analysis of model results and high frequency radar (HFR) data using self-organizing map (SOM) and empirical orthogonal function (EOF) analysis. A dataset of surface flow fields over thirteen days from these two sources was used. A SOM topology map of size 4 × 3 was developed to explore spatial patterns of surface flows. Additionally, comparisons of surface flow patterns between SOM and EOF analysis were carried out. Results illustrate that both SOM and EOF analysis methods are valuable tools for extracting characteristic surface current patterns. Comparisons indicated that the SOM technique displays synoptic characteristics of surface flow fields in a more detailed way than EOF analysis. Extracted synoptic surface current patterns are useful in a variety of applications, such as oil spill treatment and search and rescue. This research provides an approach to using powerful tools to diagnose ocean processes from different aspects. Moreover, it is of great significance to assess SOM as a potential forecasting tool for coastal surface currents.
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Marchand, Roger, Nathaniel Beagley, Sandra E. Thompson, Thomas P. Ackerman e David M. Schultz. "A Bootstrap Technique for Testing the Relationship between Local-Scale Radar Observations of Cloud Occurrence and Large-Scale Atmospheric Fields". Journal of the Atmospheric Sciences 63, n. 11 (1 novembre 2006): 2813–30. http://dx.doi.org/10.1175/jas3772.1.
Testo completoAbstract (sommario):
Abstract A classification scheme is created to map the synoptic-scale (large scale) atmospheric state to distributions of local-scale cloud properties. This mapping is accomplished by a neural network that classifies 17 months of synoptic-scale initial conditions from the rapid update cycle forecast model into 25 different states. The corresponding data from a vertically pointing millimeter-wavelength cloud radar (from the Atmospheric Radiation Measurement Program Southern Great Plains site at Lamont, Oklahoma) are sorted into these 25 states, producing vertical profiles of cloud occurrence. The temporal stability and distinctiveness of these 25 profiles are analyzed using a bootstrap resampling technique. A stable-state-based mapping from synoptic-scale model fields to local-scale cloud properties could be useful in three ways. First, such a mapping may improve the understanding of differences in cloud properties between output from global climate models and observations by providing a physical context. Second, this mapping could be used to identify the cause of errors in the modeled distribution of clouds—whether the cause is a difference in state occurrence (the type of synoptic activity) or the misrepresentation of clouds for a particular state. Third, robust mappings could form the basis of a new statistical cloud parameterization.
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Yannuzzi, Victor T., Eugene E. Clothiaux, Jerry Y. Harrington e Johannes Verlinde. "Statistical Analysis of Forecasting Models across the North Slope of Alaska during the Mixed-Phase Arctic Clouds Experiment". Weather and Forecasting 24, n. 6 (1 dicembre 2009): 1644–63. http://dx.doi.org/10.1175/2009waf2222218.1.
Testo completoAbstract (sommario):
Abstract The National Centers for Environmental Prediction’s (NCEP) Eta Model, the models of the European Centre for Medium-Range Weather Forecasts (ECMWF) and the National Aeronautics and Space Administration’s (NASA) Global Modeling and Assimilation Office (GMAO) models, and the Regional Atmospheric Modeling System (RAMS) model are all examined during the Mixed-Phase Arctic Clouds Experiment (MPACE) that took place from 27 September through 22 October 2004. During two intensive observation periods, soundings were launched every 6 h from four sites across the North Slope of Alaska (NSA): Barrow, Atqasuk, Oliktok Point, and Toolik Lake. Measurements of temperature, moisture, and winds, along with surface measurements of radiation and cloud cover, were compared to model outputs from the Eta, ECMWF, GMAO, and RAMS models using the bootstrap statistical technique to ascertain if differences in model performance were statistically significant. Ultimately, three synoptic regimes controlled NSA weather during the MPACE period for varying amounts of time. Each posed a unique challenge to the forecasting models during the study period. Temperature forecasts for all models were good at the MPACE sites with mean bias errors generally under 2 K, and the models had the fewest significant errors predicting temperature. Forecasting moisture and wind proved to be more difficult for the models, especially aloft in the 500–300-hPa layer. The largest errors occurred in the GMAO model, with significant moist biases of 40% and wind errors of 10 m s−1 or more. The RAMS, Eta, and ECMWF models had smaller moist biases in this layer. Both the Eta and RAMS models overestimated the surface incident shortwave radiation, underestimated longwave radiation, and underestimated cloud cover fraction. Overall, the bootstrapping results coincided with findings from conventional statistical comparisons as model outputs with the largest errors were most likely to be captured and declared statistically significant in the bootstrapping process. The significant model errors during MPACE were predominantly traced to the inability of the models to simulate disturbances in synoptic regime I, warm or cold biases over higher inland terrain, a warm bias along the NSA coastal waters in the Beaufort Sea, and difficulty in forecasting the intensity of the explosive cyclone in synoptic regime III.
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Jones, Daniel M., e Alan F. Heavens. "Gaussian mixture models for blended photometric redshifts". Monthly Notices of the Royal Astronomical Society 490, n. 3 (27 settembre 2019): 3966–86. http://dx.doi.org/10.1093/mnras/stz2687.
Testo completoAbstract (sommario):
ABSTRACT Future cosmological galaxy surveys such as the Large Synoptic Survey Telescope (LSST) will photometrically observe very large numbers of galaxies. Without spectroscopy, the redshifts required for the analysis of these data will need to be inferred using photometric redshift techniques that are scalable to large sample sizes. The high number density of sources will also mean that around half are blended. We present a Bayesian photometric redshift method for blended sources that uses Gaussian mixture models to learn the joint flux–redshift distribution from a set of unblended training galaxies, and Bayesian model comparison to infer the number of galaxies comprising a blended source. The use of Gaussian mixture models renders both of these applications computationally efficient and therefore suitable for upcoming galaxy surveys.
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Peters, Karsten, Cathy Hohenegger e Daniel Klocke. "Different Representation of Mesoscale Convective Systems in Convection-Permitting and Convection-Parameterizing NWP Models and Its Implications for Large-Scale Forecast Evolution". Atmosphere 10, n. 9 (27 agosto 2019): 503. http://dx.doi.org/10.3390/atmos10090503.
Testo completoAbstract (sommario):
Representing mesoscale convective systems (MCSs) and their multi-scale interaction with the large-scale atmospheric dynamics is still a major challenge in state-of-the-art global numerical weather prediction (NWP) models. This results in potentially defective forecasts of synoptic-scale dynamics in regions of high MCS activity. Here, we quantify this error by comparing simulations performed with a very large-domain, convection-permitting NWP model to two operational global NWP models relying on parameterized convection. We use one month’s worth of daily forecasts over Western Africa and focus on land regions only. The convection-permitting model matches remarkably well the statistics of westward-propagating MCSs compared to observations, while the convection-parameterizing NWP models misrepresent them. The difference in the representation of MCSs in the different models leads to measurably different synoptic-scale forecast evolution as visible in the wind fields at both 850 and 650 hPa, resulting in forecast differences compared to the operational global NWP models. This is quantified by computing the correlation between the differences and the number of MCSs: the larger the number of MCSs, the larger the difference. This fits the expectation from theory on MCS–mean flow interaction. Here, we show that this effect is strong enough to affect daily limited-area forecasts on very large domains.
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Praveen, V., S. Sandeep e R. S. Ajayamohan. "On the Relationship between Mean Monsoon Precipitation and Low Pressure Systems in Climate Model Simulations". Journal of Climate 28, n. 13 (1 luglio 2015): 5305–24. http://dx.doi.org/10.1175/jcli-d-14-00415.1.
Testo completoAbstract (sommario):
Abstract The north-northwest-propagating low pressure systems (LPS) are an important component of the Indian summer monsoon (ISM). The objective detection and tracking of LPS in reanalysis products and climate model simulations are challenging because of the weak structure of the LPS compared to tropical cyclones. Therefore, the skill of reanalyses and climate models in simulating the monsoon LPS is unknown. A robust method is presented here to objectively identify and track LPS, which mimics the conventional identification and tracking algorithm based on detecting closed isobars on surface pressure charts. The new LPS tracking technique allows a fair comparison between the observed and simulated LPS. The analysis based on the new tracking algorithm shows that the reanalyses from ERA-Interim and MERRA were able to reproduce the observed climatology and interannual variability of the monsoon LPS with a fair degree of accuracy. Further, the newly developed LPS detection and tracking algorithm is also applied to the climate model simulations of phase 5 of the Coupled Model Intercomparison Project (CMIP5). The CMIP5 models show considerable spread in terms of their skill in LPS simulation. About 60% of the observed total summer monsoon precipitation over east-central India is found to be associated with LPS activities, while in model simulations this ratio varies between 5% and 60%. Those models that simulate synoptic activity realistically are found to have better skill in simulating seasonal mean monsoon precipitation. The model-to-model variability in the simulated synoptic activity is found to be linked to the intermodel spread in zonal wind shear over the Indian region, which is further linked to inadequate representation of the tropical easterly jet in climate models. These findings elucidate the mechanisms behind the model simulation of ISM precipitation, synoptic activity, and their interdependence.
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Kunze, Markus, Peter Braesicke, Ulrike Langematz, Gabriele Stiller, Slimane Bekki, Christoph Brühl, Martyn Chipperfield, Martin Dameris, Rolando Garcia e Marco Giorgetta. "Influences of the Indian Summer Monsoon on Water Vapor and Ozone Concentrations in the UTLS as Simulated by Chemistry–Climate Models". Journal of Climate 23, n. 13 (1 luglio 2010): 3525–44. http://dx.doi.org/10.1175/2010jcli3280.1.
Testo completoAbstract (sommario):
Abstract The representation of the Indian summer monsoon (ISM) circulation in some current chemistry–climate models (CCMs) is assessed. The main assessment focuses on the anticyclone that forms in the upper troposphere and lower stratosphere and the related changes in water vapor and ozone during July and August for the recent past. The synoptic structures are described and CCMs and reanalysis models are compared. Multiannual means and weak versus strong monsoon cases as classified by the Monsoon–Hadley index (MHI) are discussed. The authors find that current CCMs capture the average synoptic structure of the ISM anticyclone well as compared to the 40-yr ECMWF Re-Analysis (ERA-40) and NCEP–NCAR reanalyses. The associated impact on water vapor and ozone in the upper troposphere and lower stratosphere as observed with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat is captured by most models to some degree. The similarities for the strong versus weak monsoon cases are limited, and even for present-day conditions the models do not agree well for extreme events. Nevertheless, some features are present in the reanalyses and more than one CCM, for example, ozone increases at 380 K eastward of the ISM. With the database available for this study, future changes of the ISM are hard to assess. The modeled monsoon activity index used here shows slight weakening of the ISM circulation in a future climate, and some of the modeled water vapor increase seems to be contained in the anticyclone at 360 K and sometimes above. The authors conclude that current CCMs capture the average large-scale synoptic structure of the ISM well during July and August, but large differences for the interannual variability make assessments of likely future changes of the ISM highly uncertain.
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Biello, Joseph A., e Andrew J. Majda. "A New Multiscale Model for the Madden–Julian Oscillation". Journal of the Atmospheric Sciences 62, n. 6 (1 giugno 2005): 1694–721. http://dx.doi.org/10.1175/jas3455.1.
Testo completoAbstract (sommario):
Abstract A multiscale model of the MJO is developed here that accounts, in a simplified fashion, for both the upscale transfer from synoptic to planetary scales of momentum and temperature from wave trains of thermally driven equatorial synoptic-scale circulations in a moving convective envelope as well as direct mean heating on planetary scales. This model involves idealized thermally driven congestus synoptic-scale fluctuations in the eastern part of the moving wave envelope and convective superclusters in the western part of the envelope. The model self-consistently reproduces qualitatively many of the detailed structural features of the planetary circulation in the observations of the MJO, including the vertical structure in both the westerly onset region and the strong westerly wind burst region, as well as the horizontal quadrupole planetary vortex structure. The westerly midlevel inflow in the strong westerly region and the quadrupole vortex are largely produced in the model by the upscale transport of momentum to the planetary scales, while the midlevel easterly jet in the westerly onset region is substantially strengthened by this process. The role of wave trains of tilted organized synoptic-scale circulations is crucial for this fidelity with observations. The appeal of the multiscale models developed below is their firm mathematical underpinnings, simplicity, and analytic tractability while remaining self-consistent with many of the features of the observational record.
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BĂRBĂRIE, MANUELA, ANCA ALBU, DARIA BRATU e SILVIU COSTACHIE. "Freezing rain phenomena. Case study: Bucharest metropolitan area, January 24-29, 2019." Risks and Catastrophes Journal 29, n. 2 (1 dicembre 2021): 43–56. http://dx.doi.org/10.24193/rcj2021_13.
Testo completoAbstract (sommario):
The paper has a structure with four parts and presents the climatic risk aspects that happened in Romania during the winter of the year 2019, concentrating on Bucharest, where a very rare and dangerous phenomenon occurred, `freezing rain`. The first part contains the theoretical analysis of the subject under discussion (the notion of risk and freezing rain), in the second part we analyzed the synoptic context (the causes that led to the phenomena) and the datacollected, the third part presents the results of the research (the duration of phenomena and the case study in the city), and the last part deals with proposed measures in order to reduce the risk of freezing rain, measures that can apply to any dangerous weather phenomena with freezing deposits. Therefore, the study aims to analyze this risk starting from the theoretical explanation of the synoptic context that generated its production to the quantitative analysis of the phenomena. To achieve this objective, the periods ECMWF models and the synoptic databases were accessed, with the help of which the representation and evolution of the phenomena was managed.
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Rubel, Franz, e Michael Hantel. "Correction of Daily Rain Gauge Measurements in the Baltic Sea Drainage Basin". Hydrology Research 30, n. 3 (1 giugno 1999): 191–208. http://dx.doi.org/10.2166/nh.1999.0011.
Testo completoAbstract (sommario):
Within the framework of BALTEX regular measurements made at about 4,200 rain gauge sites have been collected by the BALTEX Meteorological Data Centre. This network of rain gauges is about 10 times denser than the synoptic network; here it is used for the objective analysis of daily precipitation fields on the grids of the mesoscale models developed in the research project NEWBALTIC during the pilot period PIDCAP (August to October 1995). The observations were corrected for systematic measuring errors with the Dynamic Correction Model. Its main purpose is to correct for the wind-induced losses which is the largest error. The correction formulae use the synoptic observations of wind speed, temperature and rain intensity at the rain gauge station considered. For non-synoptic stations the values of the closest synoptic station are used as estimates; the mean distance of the synoptic stations within the drainage basin is 30 km. For evaporation and wetting losses, which represent the second largest error of the precipitation measurements, climatological corrections are applied. The formulae in the Dynamic Correction Model take instrument-specific properties into account; these comprise HELLMANN UNSHIELDED, SMHI SHIELDED, H&H-90 SHIELDED and TRETJAKOV SHIELDED. The spatial distribution of corrected precipitation values were objectively analysed according to Rubel (1998). They yield daily gridded precipitation fields over the drainage basin which are systematically higher than the uncorrected fields. The corresponding increase of the freshwater input into the Baltic Sea drainage basin is 4.7% in August, 5.8% in September and 9.1% in October 1995. Finally, the perspective for further developments and the generation of a ten-year data base of the BALTEX main intensive observational and modelling period BRIDGE is introduced.
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Archer, Cristina L., Joseph F. Brodie e Sara A. Rauscher. "Global Warming Will Aggravate Ozone Pollution in the U.S. Mid-Atlantic". Journal of Applied Meteorology and Climatology 58, n. 6 (giugno 2019): 1267–78. http://dx.doi.org/10.1175/jamc-d-18-0263.1.
Testo completoAbstract (sommario):
AbstractThe goal of this study is to evaluate the effects of anthropogenic climate change on air quality, in particular on ozone, during the summer in the U.S. mid-Atlantic region. First, we establish a connection between high-ozone (HO) days, defined as those with observed 8-h average ozone concentration greater than 70 parts per billion (ppb), and certain weather patterns, called synoptic types. We identify four summer synoptic types that most often are associated with HO days based on a 30-yr historical period (1986–2015) using NCEP–NCAR reanalysis. Second, we define thresholds for mean near-surface temperature and precipitation that characterize HO days during the four HO synoptic types. Next, we look at climate projections from five models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) for the early and late midcentury (2025–34 and 2045–54) and analyze the frequency of HO days. We find a general increasing trend, weaker in the early midcentury and stronger in the late midcentury, with 2 and 5 extra HO days per year, respectively, from 16 in 2015. These 5 extra days are the result of two processes. On one hand, the four HO synoptic types will increase in frequency, which explains about 1.5–2 extra HO days. The remaining 3–3.5 extra days are explained by the increase in near-surface temperatures during the HO synoptic types. Future air quality regulations, which have been successful in the historical period at reducing ozone concentrations in the mid-Atlantic, may need to become stricter to compensate for the underlying increasing trends from global warming.
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Odoulami, Romaric C., Piotr Wolski e Mark New. "Attributing the driving mechanisms of the 2015–2017 drought in the Western Cape (South Africa) using self-organising maps". Environmental Research Letters 18, n. 7 (1 luglio 2023): 074043. http://dx.doi.org/10.1088/1748-9326/ace26f.
Testo completoAbstract (sommario):
Abstract The Southwestern Cape (SWC) region in South Africa experienced a severe rainfall deficit between 2015–2017. The resulting drought caused the City of Cape Town to almost run out of water during the summer of 2017–2018. Using the self-organising maps approach, we identify and classify the synoptic circulation states over Southern Africa known to influence the local climate in the SWC into three groups (dry, intermediate, and wet circulation types) using large ensembles of climate model simulations with anthropogenic forcing and natural forcing. We then assessed the influence of anthropogenic climate change on the likelihood of these circulation types and associated rainfall amounts over the SWC during the drought. Our findings suggest that during the drought, the frequency of dry (wet) circulation types increases (decreases) across all models under anthropogenic forcing relative to the natural forcing. While there was no clear direction in the associated rainfall change in the dry circulation types, rainfall decreased across most models in wet nodes. All models agree that anthropogenic climate change has increased the likelihood of dry circulation types (median probability ratio (PR): 0.93–0.96) and decreased that of wet circulation types (median PR: 1.01 and 1.12), indicating a shift towards lesser (more) wet (dry) synoptic circulation states and associated rainfall during the drought. The long-term climatology also depicts similar patterns indicating the drought may result from long-term changes in the frequency of wet circulations and their associated rainfall. This study further explains the anthropogenic influence on the dynamic (synoptic circulation states) and thermodynamic (rainfall) factors that influenced the SWC 2015–2017 drought.
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Khouider, Boualem, e Andrew J. Majda. "Multicloud Models for Organized Tropical Convection: Enhanced Congestus Heating". Journal of the Atmospheric Sciences 65, n. 3 (1 marzo 2008): 895–914. http://dx.doi.org/10.1175/2007jas2408.1.
Testo completoAbstract (sommario):
Abstract Despite the recent advances in supercomputing, the current general circulation models (GCMs) poorly represent the large-scale variability associated with tropical convection. Multicloud model convective parameterizations based on three cloud types (congestus, deep, and stratiform), introduced recently by the authors, have been revealed to be very useful in representing key features of organized convection and convectively coupled waves. Here a new systematic version of the multicloud models is developed with separate upper- and lower-troposphere basis functions for the congestus and stratiform clouds. It naturally leads to a new convective closure for the multicloud models enhancing the congestus heating in order to better pinpoint the congestus preconditioning and moistening mechanisms. The models are studied here for flows above the equator without rotation effects. First, the new model results consist of the usual synoptic-scale convectively coupled moist gravity wave packets moving at 15–20 m s−1 but, in addition, these packets have planetary-scale envelopes moving in the opposite direction at about 6 m s−1 and have many of the self-similar features of convectively coupled waves, reminiscent of the Madden–Julian oscillation. Second, when a warm pool forcing is imposed, dry regions of roughly 250 km in extent form “convective barriers” surrounding the warm pool region where only congestus heating survives. Deep convection and moist gravity waves are thus confined within the warm pool region. Finally, linear analysis reveals that, for sufficiently dry mean states, in addition to the inherent synoptic-scale moist gravity waves, the new model supports a planetary (wavenumber 1) standing congestus mode that provides, within its congestus active phase, a region where moist gravity waves evolve and propagate, which results in a Walker-like circulation over a uniform SST background.
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Cao, Liying, Bao Zhang, Junyu Li, Yibin Yao, Lilong Liu, Qishun Ran e Zhaohui Xiong. "A Regional Model for Predicting Tropospheric Delay and Weighted Mean Temperature in China Based on GRAPES_MESO Forecasting Products". Remote Sensing 13, n. 13 (5 luglio 2021): 2644. http://dx.doi.org/10.3390/rs13132644.
Testo completoAbstract (sommario):
Accurate tropospheric delay (TD) and weighted mean temperature (Tm) are important for Global Navigation Satellite System (GNSS) positioning and GNSS meteorology. For this purpose, plenty of empirical models have been built to provide estimates of TD and Tm. However, these models cannot resolve TD and Tm variations at synoptic timescales since they only model the average annual, semi-annual, and/or daily variations. As a result, the existed empirical models cannot perform well under extreme weather conditions. To address this limitation, we propose to estimate Zenith Hydrostatic Delay (ZHD), Zenith Wet Delay (ZWD), and Tm directly from the stratified numerical weather forecasting products of the mesoscale version of the Global/Regional Assimilation and PrEdiction System (GRAPES_MESO) of China. The GRAPES_MESO forecasting data has a temporal resolution of 3 h, which provides the opportunity to resolve the synoptic variation. However, it is found that the estimated ZWD and Tm exhibit apparent systematic deviation from in situ observation-based estimates, which is due to the inherent biases in the GRAPES_MESO data. To solve this problem, we propose to correct these biases using a linear model and a spherical cap harmonic model. The estimates after correction are termed as the “CTropGrid” products. When validated by the radiosonde data, the CTropGrid product has biases of 1.5 mm, −0.7 mm, and −0.1 K, and Root Mean Square (RMS) error of 8.9 mm, 20.2 mm, and 1.5 K for ZHD, ZWD, and Tm. Compared to the widely used GPT2w model, the CTropGrid products have improved the accuracies of ZHD, ZWD, and Tm by 11.9%, 55.6%, and 60.5% in terms of RMS. When validating the Zenith Tropospheric Delay (ZTD) products (the sum of ZHD and ZWD) using the IGS ZTD data, the CTropGrid ZTD has a bias of −0.7 mm and an RMS of 35.8 mm, which is 22.7% better than the GPT2w model in terms of RMS. Besides the accuracy improvements, the CTropGrid products well model the synoptic-scale variations of ZHD, ZWD, and Tm. Compared to the existing empirical models that only capture the tidal (seasonal and/or diurnal) variations, the CTropGrid products capture well the non-tidal variations of ZHD, ZWD, and Tm, which enhances the tropospheric delay corrections and GNSS water vapor monitoring at synoptic timescales. Therefore, the CTropGrid product is an important progress in GNSS positioning and GNSS meteorology.
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Walker, J. K., V. Yu Semenov e T. L. Hansen. "Synoptic models of high latitude magnetic activity and equivalent ionospheric and induced currents". Journal of Atmospheric and Solar-Terrestrial Physics 59, n. 12 (agosto 1997): 1435–52. http://dx.doi.org/10.1016/s1364-6826(96)00168-x.
Testo completo
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Soriano, C., A. Fernández e J. Martin-Vide. "Objective synoptic classification combined with high resolution meteorological models for wind mesoscale studies". Meteorology and Atmospheric Physics 91, n. 1-4 (15 settembre 2005): 165–81. http://dx.doi.org/10.1007/s00703-005-0133-z.
Testo completo