Bora Wind Research Articles

Kilometer-scale trends, variability, and extremes of the Adriatic far-future climate (RCP 8.5, 2070−2100)

Due to orography-driven dynamics at a (sub-)kilometer scale (e.g., the bora wind) and a complex ocean bathymetry that includes numerous channels, depressions and ridges, the atmosphere-ocean dynamics within the semi-enclosed Adriatic region is not well reproduced by the available regional climate models. The Adriatic Sea and Coast (AdriSC) kilometer-scale atmosphere-ocean model was thus specifically developed to accurately assess the Adriatic climate hazards under both historical (1987-2017) and far-future (2070-2100) conditions. In this study, we analyze the impact of climate change on the projected Adriatic trends, variability and extreme events. In the atmosphere, our results mostly follow the already published literature: strong land-sea contrasts, increased droughts and extreme rainfall events, and decreased wind speeds in the coastal areas. In the ocean, strong and constant rise in surface and intermediate temperatures is associated with salinity decrease, except in surface during summer when salinity rises in the coastal areas. At the bottom and for the ocean circulation, our results exhibit strong contrasts. In the coastal areas, bottom temperature rises, and bottom salinity decreases at the same rate than in surface while changes in current speed are negligible. In the deepest part of the Adriatic, negative bottom temperature trends result in a rise 2.5°C slower than in surface while bottom salinity increases. Further, ocean currents accelerate in the surface and intermediate layers but decelerate at the bottom. These ocean results suggest a reduction of the dense water formation in the northern Adriatic, an intensification and shrinking of the southern Adriatic cyclonic gyre, and a strengthening of the vertical stratification in the deepest part of the Adriatic probably linked to changes in the Adriatic-Ionian water mass exchanges. Given the potential impact of these changes on the Adriatic coastal communities and marine life, this study highlights the need to increase the ongoing kilometer-scale modelling efforts in the Adriatic region with the aim to implement policies and adaptation plans better tailored to the local climate changes projected in this specific region.

Misalignment between the propagation direction of the bora wind and its pulsations

AbstractThe bora is a well‐known downslope windstorm that blows at the eastern coast of the Adriatic Sea from inland towards the sea, mainly from the northeasterly direction. One of the notable bora characteristics is the quasi‐periodic gust pulsations. We address their characteristics during strong to severe bora events by applying rotational spectral analysis on 9 months of continuous high‐frequency sonic anemometer measurements in the town of Senj, Croatia. The analysis shows that the orientation of the pulsations' plane of oscillation does not correspond to the measured near‐ground wind direction. In particular, these two directions seem to be negatively correlated. Although the structure of the pulsations is mostly rectilinear, the positive rotational component was larger than the negative one in all except one bora event. The coincidence of the wind shear direction within the lee‐side jet with the orientation of the plane of oscillation leads to a tentative conclusion that its orientation was governed by the Kelvin–Helmholtz instability, at least in the cases presented.

SAR Based Sea Surface Complex Wind Fields Estimation: An Analysis over the Northern Adriatic Sea

Nowadays, sea surface analysis and monitoring increasingly use remote sensing, with particular interest in Synthetic Aperture Radar (SAR). Several SAR techniques exist in literature to understand the marine phenomena affecting the sea surface. In this work, we focus on the Doppler Centroid Anomaly (DCA), which accounts for the Doppler shift induced by sea surface movements. Starting from SAR raw data, we develop a processing chain to elaborate them and output the surface velocity map using DCA. The DCA technique has often been presented in the marine literature for estimating sea surface velocity, but more recently it has also been used to detect near-surface wind fields. This paper deals with estimating the sea surface wind field using Doppler information and SAR backscatter, combined with wind information provided by ECMWF and geophysical wind and Doppler model functions. We investigate the application of the approach in the coastal area of the northern Adriatic Sea (Northeast Italy). The test site is interesting, both for its particular orography, as it is a semi-enclosed basin largely surrounded by mountains, and for its complex meteorological phenomena, such as the Bora wind. Results obtained combining SAR backscatter and DCA information show an improvement in wind field estimation.

A high‐impact meso‐beta vortex in the Adriatic Sea

AbstractOn the evening of November 12, 2019, an exceptional high tide – the second‐highest in the ranking since sea‐level data have been recorded – hit the city of Venice in northern Italy and its entire lagoon, damaging a large part of its historical center. A small warm‐core mesoscale cyclone, which formed in the central Adriatic Sea and intensified during its northwestward movement toward the Venice lagoon, was responsible for the event. The cyclone was preceded by intense northeasterlies (Bora) in the northern Adriatic, which turned to southeasterlies (Sirocco) and then southwesterlies after its passage. Simulations with different initialization times were carried out with the Weather Research and Forecasting (WRF) model. Simulation results show a strong sensitivity to the initial conditions, since the track (and strength) of the cyclone was determined by the exact position of an upper‐level potential vorticity (PV) streamer. The factors responsible for the cyclone development and its characteristics are also investigated. The pre‐existence of positive low‐level cyclonic vorticity, associated with the convergence of the Sirocco and Bora winds in the central Adriatic, made the environment favorable for cyclone development. Also, the interaction between the upper‐level PV anomaly and the low‐level baroclinicity, created by the advection of warm, humid air associated with the Sirocco, was responsible for the cyclone's intensification, in a manner similar to a transitory (stable) baroclinic interaction at small horizontal scales. Sensitivity experiments reveal that convection, latent heat release and sea‐surface fluxes did not play a significant role, indicating that this cyclone did not show tropical‐like characteristics, notwithstanding its low‐level warm core. Thus, the warm‐core feature appears mainly as a characteristic of the environment in which the cyclone developed rather than a consequence of diabatic processes. Lastly, the cyclone does not fall into any of the existing categories for Adriatic cyclones.

The Effect of Orography on Bora Wind Turbulence

The Effect of Orography on Bora Wind Turbulence

Multi-platform study of the extreme bloom of the barrel jellyfish Rhizostoma pulmo (Cnidaria: Scyphozoa) in the northernmost gulf of the Mediterranean Sea (Gulf of Trieste) in April 2021

Abstract. On 7 April 2021, an exceptional bloom of the scyphomedusa Rhizostoma pulmo was observed in the Gulf of Trieste (Italy). Blooms of this species in the northern Adriatic Sea have been reported since the late 1800s: the density of jellyfish observed in 2021 reached more than 10 specimens per square metre. We analyse the bloom from a multi-platform approach using observations and model data at different timescales. We attempt to explain the intensity of the bloom as a consequence of thermohaline and hydrodynamical conditions in the gulf. Meteo-oceanographic conditions that may have contributed to the exceptional aggregation of jellyfish observed along the northernmost coast of the Adriatic Sea are discussed in detail. Specifically, our results indicate that this bloom was enabled by (1) the presence of a high number of jellyfish in the gulf, probably linked to the anomalously warm sea conditions in spring 2020 and winter 2021, which may have favoured a longer reproductive period and enhanced survival of adult R. pulmo, respectively; and (2) strong wind events, such as the bora wind for the Gulf of Trieste, which enhanced upwelling and mixing processes in the gulf, bringing the jellyfish from the deeper waters to the surface and clustering them along the coast.

Experimental modeling of Bora wind loads on vehicles

Experimental modeling of Bora wind loads on vehicles

Spatio-temporal variations of cave-air CO2 concentrations in two Croatian show caves: Natural vs. anthropogenic controls

Carbon dioxide (CO2) concentration (CDC) plays an important role in karst processes, governing both carbonate deposition and dissolution, affecting not only natural processes, but also human activities in caves adapted for tourism. Its variations due to various controlling parameters was observed from 2017 to 2021 in two Croatian show caves (Manita peć and Modrič) where we examined inter- and within-cave correlation of internal aerology regarding the sources, sinks and transport mechanism of CDC in a karst conduit setting. In both caves, the main sources of CO2 are: i) plant and microbial activity i.e. root respiration and organic matter decay within soil horizons and fractured epikarst, and ii) degassing from CO2-rich percolation water. The main sink of CO2 is dilution with outside air due to cave ventilation. Chimney-effect driven ventilation controlled by seasonal differences between surface and cave air temperatures shows winter (Tout<Tcave) and summer (Tout>Tcave ) ventilation regime, which are modulated by the geometry of cave passages, the transmissivity of the overlying epikarst, and occasionally by the external winds, especially the gusty north-eastern bora wind. In these terms, the Modrič Cave appears to be more confined and less ventilated, with a substantial CDC difference between the left (550-7200 ppm) and right (1475- >10,000 ppm) passages. The Manita peć Cave is, in contrast, ventilated almost year-round, having 7 months of CDC equilibrated with the outside atmosphere and the highest summer CDC values of ~1410 ppm. In both caves, at the current level of tourist use, anthropogenic CO2 flux is not a matter of concern for cave conservation. In turn, in the innermost part of the right Modrič Cave passage visitors’ health might be compromised, but the tourists are allowed only in the left passage. Speleothem growth rate, recognized as a useful palaeoenvironmental proxy for speleothem-based palaeoclimate studies, strongly depends on CDC variations, so the high CDCs recorded in the Modrič Cave indicate the potential periods with no speleothem deposition due to the hampered degassing of CO2 from the dripping groundwater. The opposite effect i.e. enhanced ventilation (that supports calcite precipitation) during the windy glacials/stadials, as well as substantial vegetational changes must also be taken into consideration when interpreting environmental records from spelean calcite.

Perfomance-based wind engineering assessment of critical telecommunication infrastructure subjected to bora wind

Wind phenomena present significant societal risks in many regions of the world due to, among others, economic losses resulting from damages to the built environment, discomfort to people, and disturbances in marine, air, and road traffic. These risks have motivated the development of performance-based design methodologies to support the decision makers in making rational and optimal measures to mitigate those risks. This paper investigates the application of the Performance-Based Wind Engineering (PBWE) methodology to the risk assessment to the critical telecommunication infrastructure subjected to wind hazard. Motivated by failures of telecommunication infrastructure due to wind load, the focus of the study is on the implementation of the PBWE methodology to estimate the expected annual losses to typical lattice frame steel telecommunication towers subjected to the Bora wind along the Croatian coastline. The statistical description of the wind hazards is based on long-term meteorological measurements available at several locations to capture the local variations characteristic for the Bora wind. The uncertainties in the wind hazard and the structural parameters were propagated to the structural response (e.g., displacements, internal forces) through a set of Monte Carlo analyses. The analyses provided a basis to estimate the probabilities of exceeding the serviceability and ultimate limit states. The resulting probabilities were used as an input to the loss function that evaluates risks from the wind hazard. The risk estimates provide valuable information to the stakeholders and decision makers that enable improved strategies for managing risks from wind hazard.

Simulated regional dust cycle in the Carpathian Basin and the Adriatic Sea region during the Last Glacial Maximum

The climate and environmental conditions in the Carpathian Basin and the adjacent northern Italy/Adriatic region during the Last Glacial Maximum (LGM) exhibit some major differences, as compared to present-day conditions. For instance, high accumulation rates recorded in loess deposits point to an active dust cycle during the LGM. Here, we investigate the climate conditions and provide new insights into the regional dust cycle based on regional climate simulations for both LGM and present-day boundary conditions. The high-resolution model output (grid spacing of ~8.5 km) is in good agreement with available proxy data, showing much colder (particularly during winter) and drier conditions during the LGM over the model domain. Further, the simulated aeolian dust cycle of small grain size particles (<20 μm) is investigated in more detail for LGM conditions. Highest dust emissions are simulated to the east of the Alpine ice sheet and in the Kvarner Bay region. In the northern Carpathian Basin, dust deposition plumes indicate prevailing northerly (NW, N and NE) winds. Strong Bora winds flowing down the slopes of the Dinaric Alps appear to play a major role in the local to regional dust cycle in the northern Adriatic region. From a seasonal perspective, the dust cycle is most active during winter and spring. A closer look at climate and environmental conditions at key areas reveals that high mean wind speeds and low precipitation rates correlate well with the high dust emissions during winter and spring. In contrast, lower wind speeds, increasing precipitation and the greening of vegetation prevent high dust emissions during summer and autumn. An additional analysis of the occurrence frequency of cyclonic circulation patterns in the Adriatic shelf region reveals that individual passing cyclones played an important role in the transport of dust particles from the alluvial Po plain towards the eastern Adriatic loess stacks.

Far future climate (2060–2100) of the northern Adriatic air–sea heat transfers associated with extreme bora events

The northernmost part of the Mediterranean Sea, the northern Adriatic shelf, is a complex area where the intensity of dense water formation and the consequent Adriatic-Ionian thermohaline circulation are shaped by a combination of extreme wintertime bora winds and substantial freshwater loads. To better understand the impact of global warming on extreme bora dynamics and the associated sea surface cooling, this study applies the Adriatic Sea and Coast (AdriSC) kilometer-scale modelling suite to the far future climate (2060–2100) period. Under both Representative Concentration Pathway (RCP) 4.5 and RCP 8.5 greenhouse emission scenarios, the AdriSC simulations are carried out via the combination of a statistical approach—consisting of an ensemble of 3-day simulations for 22 extreme bora events, and a pseudo-global warning (PGW) methodology—imposing a climatological change to the forcing used to produce the evaluation (present climate) runs. Despite a noteworthy decrease in intensity of the bora winds (by up to 3 m/s), the latent heat losses are simulated to increase (by up to 150 W/m2) due to the reduction in relative humidity in the northern Adriatic (by up to 3%). Consequently, the sea surface cooling associated with severe bora events and preconditioning the dense shelf water formation in the northern Adriatic is projected to not significantly change compared to present climate. Although these results need to be further confirmed, this study thus provides a new view on the future of processes driven by sea surface cooling, such as the dense shelf water formation or the Adriatic-Ionian thermohaline circulation, that were projected to decrease in the future climate by regional climate models an order of magnitude coarser than the AdriSC simulations.

Simulation of pollutants spreading from a sewage outfall in the Rijeka Bay

Results from a 3D numerical simulation of wind-induced currents and pollution spreading from a sewage outfall are described.The goal was to predict seawater sanitary quality in the Rijeka Bay, Adriatic Sea. A sea motion model was coupled with a modelof transport and chemical reactions of fecal coliforms (FC), fecal streptococci (FS) and dissolved oxygen. The selected simulationperiod of 36 hours following wastewater discharge was found to be sufficient for a significant extinction of bacteria. The simulationwas carried out for eight wind directions and two intensities (moderate and high). Mesh convergence was obtained. Twomesh sizes were coupled: coarse, for the whole Bay, and fine, for the northern part of the Bay, close to the sewage discharge ofthe Rijeka city.For all considered wind directions, the pollution plume with a concentration higher than 100 FC and 100 FS per 100 ml of seawateris conveyed mostly parallel to the coast in either north-west or south-east directions. The plume does not rise to the surfacebut stays at the depth of 10 to 20 meters. This is a consequence of the hydrodynamics of the Rijeka Bay: the bora wind carriesthe surface water layer out of the Bay through the Middle and Great Gates, while cold water enters the Bay from the layer belowthe thermocline. During the southern wind (jugo), the situation is reversed: warmer surface water enters the Bay through eitherthe Middle Gate or the Great Gate, while cold seawater exits through the bottom layer, accumulating warmer seawater in the Bay.The conclusion is that the Rijeka city sewage discharge Delta is well-designed, and the microorganism concentration is wellwithin the suggested regulatory range. The discharge site is far enough from the coast, where local streamlines are mostly parallelto the coast, hence the elevated pollution concentration does not come close to swimming and recreational areas. Even if thedischarge increases by 50%, which is unlikely in the near future, the pollution at beaches will stay within regulatory boundaries.

Using multi-platform 4D-Var data assimilation to improve modeling of Adriatic Sea dynamics

A year-long Four-Dimensional Variational (4D-Var) data assimilation experiment, formulated on the physical-space statistical analysis system (PSAS) algorithm, has been applied to the Adriatic Sea for the very first time. High-resolution multi-platform observations were assimilated into the Regional Ocean Modeling System (ROMS) forced by mesoscale atmospheric model ALADIN/HR (Aire Limitée Adaptation dynamique Développement InterNational), including important freshwater river inflows and realistic open boundary conditions for the period between October 2014 and September 2015. The observations included sea surface temperature (SST) measured by satellites, in situ temperature and salinity data measured by various moving (Argo profiling floats, shipborne CTDs, sea glider, towed CTD profiler) and moored platforms, ocean current profiles measured by moored Acoustic Doppler Current Profilers (ADCPs), and 30-minute de-tided surface currents from high-frequency (HF) radars. Three model simulations were integrated: (1) a non-assimilative simulation over a year-long period — baseline simulation; (2) a non-assimilative simulation initiated by the previous assimilation 4-day cycle — background simulation, and (3) a fully assimilative simulation that used all available observations during the 4-day assimilation cycle — analysis simulation. The assimilation significantly improved the modeling system performance, especially in SST, with time average rmse equaling 0.9, 0.7 and 0.5 °C and bias equaling 0.39, 0.15, 0.01 °C for the baseline, background and analysis simulations, respectively. These reductions were mostly achieved during the wintertime outbreaks of a cold and dry bora wind, caused by an underestimation of heat and momentum fluxes by the atmospheric model. Such fine adjustments in the northern and middle Adriatic may be responsible for improved reproduction of dense water generation and the associated Adriatic thermohaline circulation.

Near-Ground Profile of Bora Wind Speed at Razdrto, Slovenia

Southwest Slovenia is a region well-known for frequent episodes of strong and gusty Bora wind, which may damage structures, affect traffic, and poses threats to human safety in general. With the increased availability of computational power, the interest in high resolution modeling of Bora on local scales is growing. To model it adequately, the flow characteristics of Bora should be experimentally investigated and parameterized. This study presents the analysis of wind speed vertical profiles at Razdrto, Slovenia, a location strongly exposed to Bora during six Bora episodes of different duration, appearing between April 2010 and May 2011. The empirical power law and the logarithmic law for Bora wind, commonly used for the description of neutrally stratified atmosphere, were evaluated for 10-min averaged wind speed data measured at four different heights. Power law and logarithmic law wind speed profiles, which are commonly used in high resolution computational models, were found to approximate well the measured data. The obtained power law coefficient and logarithmic law parameters, which are for modeling purposes commonly taken to be constant for a specific site, were found to vary significantly between different Bora episodes, most notably due to different wind direction over complex terrain. To increase modeling precision, the effects of local topography on wind profile parameters needs to be experimentally assessed and implemented.

Seawater Icicles of the Adriatic Sea

AbstractThe marine icicles that form on coastal constructions (e.g., piers and railings) are very common in polar and subpolar areas. The occasional formation of icicles in the coastal zones of the Mediterranean Sea occurs in relation to cold-air outbreaks from the polar region, such as the one presented in this paper in February 2018. The air temperatures over the northern Adriatic Sea, the northernmost part of the Mediterranean, dropped below –2.1°C, a necessary condition for seawater to freeze, with salinity between 38.0 and 38.5 PSU. The formation of icicles on the coastal structures was further enabled by the bora wind and related high seas along the coast. Measurements presented in this paper confirm that the icicles in the Bay of Piran in the Gulf of Trieste (45.55°N) were formed from the seawater. The measured salinity level of the melted icicles, around 9 PSU, is a typical value reported for marine icicles in polar regions.

How environment selects: Resilience and survival of microbial mat community within intermittent karst spring Krčić (Croatia)

AbstractWe conducted an on‐site monitoring study involving seasonal collection of microbial mats samples from the Krčić spring located in the Dinaric karst in Croatia. This intermittent karst spring is characterized by oligotrophic conditions and extreme water regime fluctuations. Extreme conditions at the Krčić included summer drought followed by strong rains in the autumn as well as freezing ambient temperature during winter. By using two phylogenetic markers, 16S rRNA (total Bacteria) and internal transcribed spacer (ITS) region (Cyanobacteria), we aimed to detect the impact of intense seasonal fluctuations of environmental parameters in shaping (and/or selecting) the microbial mat community of the Krčić spring. Microbial mat community was found to harbour bacteria belonging to 11 different phyla with Cyanobacteria making the community core (&gt;50%), followed by Alphaproteobacteria. The most abundant cyanobacterial genera included Microcoleus, Phormidium, and uncultured Antarctic cyanobacterium. In two mat samples, collected during conditions of low temperatures and strong bora wind (winter 2014) and during drought period (summer 2015), Cyanobacteria were diminished within the community. Under the extreme cold populations found to proliferate included Planctomycetes and candidate phylum TM6, found specifically in this sample. Members of the phyla Firmicutes were strictly found during the drought summer period followed by Cytophagia‐Fibrella, Polymorphobacter, Polaromonas, and Massilia. During the event of high water inflow following the drought, Cyanobacteria represented 90% of the community in which specific desiccant‐tolerant Chroococcidiopsis, Calothrix, and Pleurocapsa species appeared having mechanisms for quick recolonization of environments.

Process‐based evaluation of the VALUE perfect predictor experiment of statistical downscaling methods

Statistical downscaling methods (SDMs) are techniques used to downscale and/or bias‐correct climate model results to regional or local scales. The European network VALUE developed a framework to evaluate and inter‐compare SDMs. One of VALUE's experiments is the perfect predictor experiment that uses reanalysis predictors to isolate downscaling skill. Most evaluation papers for SDMs employ simple statistical diagnostics and do not follow a process‐based rationale. Thus, in this paper, a process‐based evaluation has been conducted for the more than 40 participating model output statistics (MOS, mostly bias correction) and perfect prognosis (PP) methods, for temperature and precipitation at 86 weather stations across Europe.The SDMs are analysed following the so‐called “regime‐oriented” technique, focussing on relevant features of the atmospheric circulation at large to local scales. These features comprise the North Atlantic Oscillation, blocking and selected Lamb weather types and at local scales the bora wind and the western Iberian coastal‐low level jet.The representation of the local weather response to the selected features depends strongly on the method class. As expected, MOS is unable to generate process sensitivity when it is not simulated by the predictors (ERA‐Interim). Moreover, MOS often suffers from an inflation effect when a predictor is used for more than one station. The PP performance is very diverse and depends strongly on the implementation. Although conditioned on predictors that typically describe the large‐scale circulation, PP often fails in capturing the process sensitivity correctly. Stochastic generalized linear models supported by well‐chosen predictors show improved skill to represent the sensitivities.

Long-Term Trends, Variability and Extremes of In Situ Sea Surface Temperature Measured Along the Eastern Adriatic Coast and its Relationship to Hemispheric Processes

This paper examines long-term series of in situ sea surface temperature (SST) data measured at nine coastal and one open sea stations along the eastern Adriatic Sea for the period 1959–2015. Monthly and yearly averages were used to document SST trends and variability, while clustering and connections to hemispheric indices were achieved by applying the Principal Component Analysis (PCA) and Self-Organizing Maps (SOM) method. Both PCA and SOM revealed the dominance of temporal changes with respect to the effects of spatial differences in SST anomalies, indicating the prevalence of hemispheric processes over local dynamics, such as bora wind spatial inhomogeneity. SST extremes were connected with blocking atmospheric patterns. A substantial warming between 1979 and 2015, in total exceeding 1 °C, was preceded by a period with a negative SST trend, implying strong multidecadal variability in the Adriatic. The strongest connection was found between yearly SST and the East Atlantic (EA) pattern, while North Atlantic Oscillation (NAO) and East Atlantic/West Russia (EAWR) patterns were found to also affect February SST values. Quantification of the Adriatic SST and their connection to hemispheric indices allow for more precise projections of future SST, considered to be rather important for Adriatic thermohaline circulation, biogeochemistry and fisheries, and sensitive to ongoing climate change.

Bora wind and heavy persistent precipitation: atmospheric water balance and role of air–sea fluxes over the Adriatic Sea

The Adriatic basin is regularly affected by cold, strong and gusty bora winds blowing from the northeast, especially during winter. These events are characterized by intense air–sea interactions and produce important meteorological effects not only over the eastern Adriatic basin, where bora originates and attains its maximum intensity, but also downstream over the Italian peninsula where heavy rainfall and snowfall can occur.The present study aims at evaluating the impact of surface fluxes of sensible and latent heat, that characterize air–sea interaction during a bora episode, on wind strength and profiles over the Adriatic Sea, in relation to intense precipitation affecting the Apennines and the Italian coast. High‐resolution numerical simulations are used in order to assess the role of surface fluxes in modulating the atmospheric water balance, modifying the thermodynamic characteristic of the boundary layer and, in turn, the dynamics of the orographic flow regime.Results show that while surface evaporation is responsible for a relatively small contribution to the total atmospheric water budget over the Adriatic area, surface fluxes still have a remarkable impact on precipitation via dynamical processes. Both sensible and latent heat fluxes modify the speed, temperature and moisture profiles of the low‐level bora wind, sensibly changing the dynamical characteristics of interaction of the flow with the downstream orography. The orographic flow regime determines the intensity and location of orographically induced uplift and hence precipitation. Therefore, the picture that directly associates the precipitation amount upstream and over the Apennines with the degree of moistening of air during its passage over the sea and with orographic uplift is shown to be too simplistic. The variations of the wind speed and static stability due to surface fluxes involve complex and nonlinear effects, changing the flow regime in response to the orographic forcing and thus determining amount and location of heavy precipitation.

Mathematical simulation of gas dynamic flows accompanying the Bora winds

The local emergence of the Bora winds in the bay of Novorossiysk is researched. A mathematical model based on two-dimensional gas dynamic Euler equations taking gravity into account is presented. The motion of the air front through a coastal ridge with the subsequent emergence of a turbulent flow over the sea surface is simulated. The effects of the temperature, diagram and value of inflowing air velocity, as well as gravitation, are studied. It is shown that the Kelvin-Helmholtz instability that arises and develops in the shear flow leads to hurricane wind blasts over the sea surface and to possible catastrophic consequences on shore.