Meridional Velocity Component Research Articles

A wind farm consisting of two turbines - The combined influence of turbine spacing and rotational direction

Large-eddy simulations are conducted to investigate the impact of an actual decrease in turbine spacing on the wake structure for a small wind park consisting of two wind turbines in a row with a given rotor diameter D. A systematic variation of the inflow conditions (near-neutral and veering inflow) and the rotational direction of the rotors (clockwise and counterclockwise) provides an initial overview of the atmospheric flow fields in the wakes of both turbines. Whereas a smaller turbine spacing under near-neutral conditions results in a decrease of the streamwise flow component and an increase of turbulence, the situation is much more complicated under veering inflow. If a clockwise (counterclockwise) rotating turbine interacts with a Northern Hemispheric Ekman spiral, the combination of a rotor-induced v-component, which reduces (slightly amplifies) the meridional inflow velocity component, leads to a weakening (slight intensification) of this meridional wind in the vicinity of the downwind rotor.

Thermo‐electrohydrodynamic convection in the thermally driven spherical shell with differential rotation

AbstractThis study investigates thermo‐electrohydrodynamics (TEHD) convection in the thermally driven spherical shell with differential shell rotation. The TEHD convection is induced by an electric tension applied at the inner spherical shell whereas the outer shell is grounded. Hence, an electric central force field is present similar to terrestrial gravity in a planetary system. Spherical rotation mimics planetary rotation and is used to investigate the convective nature of the spherical gap. The results demonstrate four main convective regimes that depend on the strength of the electric tension and rotational forcing. The convective pattern formation is investigated by a Hammer‐Aitov projection, the radial and meridional velocity components to indicate convective or advective fluid motion related to the individual forcing. The heat transfer is characterised by the Nusselt number and showed a strong dependence on the forcing.

Flow deviation and critical choking in transonic turbine cascades operating with non-ideal compressible flows

In this work we examine the flow deviation and its relationship to critical choking, i.e., choking of the meridional component of velocity, in transonic turbine cascades operating with non-ideal compressible flows. To this purpose, a generalized expression of the corrected flow per unit area as a function of both the thermodynamic state and the molecular complexity of the working fluid, the Mach number, and the amount of swirl is derived. The trends of the corrected flow with respect to these quantities are used to infer physical insights on the flow deviation and on the operability of transonic turbine cascades in off-design conditions. Moreover, reduced-order models for the estimation of the flow deviation and the preliminary assessment of the losses have been developed and validated against the results of CFD simulations performed on a representative transonic turbine stator. Results suggest that flows of dense organic vapors exhibit larger deviations than those pertaining to compounds made of simple molecules, e.g., air. Furthermore, transonic turbines expanding dense vapors reach critical choking conditions at lower Mach numbers than the ones operating with simple molecules, and are affected by larger dissipation due to viscous mixing.

The sensitivity of the WRF-4DVar data assimilation system to the control variables: A study on heavy rainfall events over India

The impact of different formulations of background error covariances (BECs) is examined for three heavy rainfall episodes over north India with a regional 4-dimensional variational (4DVar) data assimilation (DA) system. Three BEC formulations are analyzed, in which two of them employ stream function and velocity potential (ψ and χ) and the third one uses zonal and meridional velocity components (v and v) as momentum control variables. The uv-based formulation is completely univariate whereas, the correlations among the control variables are taken into account in the ψχ-based formulations through linear regression relations. Among the two ψχ-based BECs, one uses univariate relation and the other one uses multivariate relations for the moisture field. The multivariate relationship allows for impacting the moisture analysis through the assimilation of temperature or wind observations. Three experiments are carried out for each case with cyclic 4DVar assimilation. The conventional surface and upper-air observations are assimilated in combination with atmospheric motion vectors (AMVs) and ocean surface winds. Free forecast for 48 h is performed from respective final analysis fields for all the experiments. The results indicate that the uv-based analysis fields are closer to the observations. A comparative analysis of the 4DVar experiments with the 3DVar DA system provided a critical insight on the role of the 4DVar DA system on implicitly accounting for the multivariate correlations. The precipitation forecasts confirm the improved performance of the ψχ-based experiment, when multivariate nature of the humidity is incorporated. The time evolution of the intense rainfall episodes over the location of maximum rainfall are relatively well reproduced in the uv-based experiment. The results indicate that the inclusion of multivariate humidity variable in the BEC formulation does have a significant impact on suppressing the excessive overestimation in rainfall intensity.

The Role of Freshwater Forcing on Surface Predictability in the Gulf of Mexico

AbstractThe potential predictability of fields at the ocean surface in the northern Gulf of Mexico (GoM) is investigated through five ensembles of regional ocean simulations between 2014 and 2016. The ensembles explore two horizontal resolutions and different representations of the riverine inflow, and focus on the interactions between the Loop Current system (LCS) and the riverine system. The potential predictability of the surface fields is high when simulated by an ocean‐only model forced by appropriate atmospheric forcing and boundary conditions, and the ensembles simulate similar LCS behavior up to 5 months. The ensemble spread provides a mean to quantify the potential predictability. The ensembles confirm that LCS‐riverine interactions are modulated by the LC mesoscale variability. The relationship is two‐ways, with the LCS being influenced by—And not only influencing—The freshwater plume. Whenever the freshwater flux is strong, the northward extension of the LCS is constrained by the intensified salinity fronts. This influence is slightly stronger if the riverine inflow is simulated in an active fashion with a meridional velocity component proportional to the flux. Sea surface temperature (SST) and salinity (SSS) predictability have opposite seasonality in their signal, with the SST (SSS) being more predictable in summer (winter). Partially resolving submesoscale instabilities and improving the realism of the riverine fluxes’ representation causes the spread to increase, especially in SST. When increasing resolution, the spread increases also for surface vorticity due to feedbacks between the mesoscale and submesoscale circulations. The intraseasonal and interannual signal in vorticity is however similar among ensembles.

Waves on the equatorial β-plane in the presence of a uniform zonal flow: Beyond the Doppler shift

Analytical and numerical solutions of the eigenvalue equation associated with zonally propagating waves of the linearized rotating shallow water equations are derived in a channel on the equatorial β-plane in the presence of a uniform mean zonal flow. The meridionally varying mean height field is in geostrophic balance with the prescribed mean zonal flow. In addition to the trivial Doppler shift of the free waves' phase speeds, the mean state causes the dispersion curves of each of the free Rossby and Poincaré waves to nearly coalesce in pairs of modes when the zonal wavenumber increases. For large zonal wavenumber or large mean flow, the latitudinal variation of the waves' amplitudes differs from that of free waves, i.e., Hermite functions (in wide channels) and harmonic functions (in narrow channels) do not describe the amplitude structure. For large mean speed and for large zonal wavenumber, the eigenvalue problem loses its Sturm–Liouville structure and the eigenfunctions have multiple extrema between successive zeros of the function itself. In contrast to free Kelvin waves, in the presence of a mean flow the meridional velocity component of these waves does not vanish identically. For zonal winds of order 20 m s−1 and for gravity wave speed of order 25 m s−1, conditions relevant to Earth's stratosphere, the phase speed with mean wind can be twice that of the classical theory with no mean zonal wind.

Modelling the residual mean meridional circulation at different stages of sudden stratospheric warming events

Abstract. Ensemble simulation of the atmospheric general circulation at altitudes up to the lower thermosphere is performed using the 3-D nonlinear mechanistic numerical model MUAM. The residual mean meridional circulation (RMC), which is the superposition of the mean Eulerian and wave-induced eddy components, is calculated for the boreal winter. Changes in the vertical and meridional RMC velocity components are analysed at different stages of a simulated composite sudden stratospheric warming (SSW) event averaged over 19 model runs. The simulation results show a general decrease in RMC velocity components up to 30 % during and after SSW in the mesosphere and lower thermosphere of the Northern Hemisphere. There are also increases in the downward and northward velocities at altitudes of 20–50 km at the northern polar latitudes during SSW. Associated vertical transport and adiabatic heating can contribute to warming the stratosphere and downward shifting of the stratopause during the composite SSW. The residual mean and eddy mass fluxes are calculated for different SSW stages. It is shown that before the SSW, planetary wave activity creates wave-induced eddy circulation cells in the northern upper stratosphere, which are directed upwards at middle latitudes, northward at high latitudes and downwards near the North Pole. These cells increase heat transport and adiabatic heating in the polar region. During SSW, the region of upward eddy vertical velocity is shifted to high latitudes, but the velocity is still downward near the North Pole. After SSW, upward eddy-induced fluxes span the entire polar region, producing upward transport and adiabatic cooling of the stratosphere and providing the return of the stratopause to higher altitudes. The obtained statistically significant results on the evolution of RMC and eddy circulation at different SSW stages at altitudes up to the lower thermosphere can be useful for a better understanding the mechanisms of planetary wave impacts on the mean flow and for the diagnostics of the transport of conservative tracers in the atmosphere.

50 ЛЕТ ТОМУ НАЗАД Ю.А. ИВАНОВ И ЕГО КОЛЛЕГИ ОТКРЫЛИ АНТИЛО-ГВИАНСКОЕ ТЕЧЕНИЕ

A brief history of the Antilles-Guiana Current discovery during cruise 5 of the scientific research vessel (R/V) “Akademik Kurchatov” in 1969 in the Atlantic Ocean is presented. This expedition of the Shirshov Institute of Oceanology of the USSR Academy of Sciences was targeted for experimental study of the Western Boundary Current System in the tropical Atlantic. The previous studies in this region revealed signs of the Southern flow within the system, which overall meridional velocity component was of the Northern direction. However, the traces of Southern currents in all such cases were usually interpreted as a manifestation of a large-scale eddy activity in the velocity field of the main North-Western water transport. In the expedition of 1969, for the first time in the Russian oceanography a non-trivial method for the direct measurements of a current velocity was applied. It is based on the results of an immediate preliminary hydrographic survey of the area, which proposed by Y.A. Ivanov. This method has made possible to determine in details the actual system of the Western boundary flows, in which the previously unknown to science the Antilles-Guiana Current was discovered. The other Russian expeditions, which have been carried out in 1970 and 1972 during 9 and 12 cruises of the R/V “Akademik Kurchatov”, revealed the interannual stability of this flow, including the mass transport, approximately equal to 30 Sv, i.e. almost half of the volume of water carried by the Gulf Stream.

Estimation of Coastal Currents Using a Soft Computing Method: A Case Study in Galway Bay, Ireland

In order to obtain forward states of coastal currents, numerical models are a commonly used approach. However, the accurate definition of initial conditions, boundary conditions and other model parameters are challenging. In this paper, a novel application of a soft computing approach, random forests (RF), was adopted to estimate surface currents for three analysis points in Galway Bay, Ireland. Outputs from a numerical model and observations from a high frequency radar system were used as inputs to develop soft computing models. The input variable structure of soft computing models was examined in detail through sensitivity experiments. High correlation of surface currents between predictions from RF models and radar data indicated that the RF algorithm is a most promising means of generating satisfactory surface currents over a long prediction period. Furthermore, training dataset lengths were examined to investigate influences on prediction accuracy. The largest improvement for zonal and meridional surface velocity components over a 59-h forecasting period was 14% and 37% of root mean square error (RMSE) values separately. Results indicate that the combination of RF models with a numerical model can significantly improve forecasting accuracy for surface currents, especially for the meridional surface velocity component.

Winds in the Middle Cloud Deck From the Near‐IR Imaging by the Venus Monitoring Camera Onboard Venus Express

AbstractFor more than 8 years the Venus Monitoring Camera (VMC) onboard the Venus Express orbiter performed continuous imaging of the Venus cloud layer in UV, visible and near‐IR filters. We applied the correlation approach to sequences of the near‐IR images at 965 nm to track cloud features and determine the wind field in the middle and lower cloud (49–57 km). From the VMC images that spanned from December of 2006 through August of 2013 we derived zonal and meridional components of the wind field. In low‐to‐middle latitudes (5–65°S) the velocity of the retrograde zonal wind was found to be 68–70 m/s. The meridional wind velocity slowly decreases from peak value of +5.8 ± 1.2 m/s at 15°S to 0 at 65–70°S. The mean meridional speed has a positive sign at 5–65°S suggesting equatorward flow. This result, together with the earlier measurements of the poleward flow at the cloud tops, indicates the presence of a closed Hadley cell in the altitude range 55–65 km. Long‐term variations of zonal and meridional velocity components were found during 1,200 Earth days of observation. At 20° ± 5°S the zonal wind speed increases from −67.18 ± 1.81 m/s to −77.30 ± 2.49 m/s. The meridional wind gradually increases from +1.30 ± 1.82 m/s to +8.53 ± 2.14 m/s. Following Bertaux et al. (2016) we attribute this long‐term trend to the influence from the surface topography on the dynamical process in the atmosphere via the upward propagation of gravity waves that became apparent in the VMC observations due to slow drift of the Venus Express orbit over Aphrodite Terra.

Three-dimensional structure of mesoscale eddies in the western tropical Pacific as revealed by a high-resolution ocean simulation

The three-dimensional structure of mesoscale eddies in the western tropical Pacific (6°S–20°N, 120°E–150°E) is investigated using a high-resolution ocean model simulation. Eddy detection and eddy tracking algorithms are applied to simulated horizontal velocity vectors, and the anticyclonic and cyclonic eddies identified are composited to obtain their three-dimensional structures. The mean lifetime of all long-lived eddies is about 52 days, and their mean diameter is 147 km. Two typical characteristics of mesoscale eddies are revealed and possible dynamic explanations are analyzed. One typical characteristic is that surface eddies are generally separated from subthermocline eddies along the bifurcation latitude (~13°N) of the North Equatorial Current in the western tropical Pacific, which may be associated with different eddy energy sources and vertical eddy energy fluxes in subtropical and tropical gyres. Surface eddies have maximum swirl velocities of 8–9 cm s−1 and can extend to about 1500 m depth. Subthermocline eddies occur below 200 m, with their cores at about 400–600 m depth, and their maximum swirl velocities can reach 10 cm s−1. The other typical characteristic is that the meridional velocity component of the eddy is much larger than the zonal component. This characteristic might be due to more zonal eddy pairs (two eddies at the same latitude), which is also supported by the zonal wavelength (about 200 km) in the high-frequency meridional velocity component of the horizontal velocity.

Principal velocity surfaces in stellar dynamics

Recent work by An and Evans has revived interest in the coordinate surfaces that lie along the principal axes of the stress tensor. Here we complete our list of non-axially symmetric systems with local integrals and prove that those principal velocity surfaces exist for all systems with three local integrals. We then demonstrate how systems in non-separable potentials evade the Eddington–An theorem by having distribution functions that lack perfect reflection symmetry in a meridional velocity component, and discuss other consequences of this remarkable theorem.

On the evolution of vortex rings with swirl

A laminar vortex ring with swirl, which has the meridional velocity component inside the vortex core, was experimentally generated by the brief fluid ejection from a rotating outlet. The evolution of the vortex ring was investigated with flow visualizations and particle image velocimetry measurements in order to find the influence of swirling flow in particular upon the transition to turbulence. Immediately after the formation of a vortex ring with swirl, a columnar strong vortex along the symmetric axis is observed in all cases of the present experiment. Then the characteristic fluid discharging from a vortex ring with swirl referred to as “peeling off” appears. The amount of discharging fluid due to the “peeling off” increases with the angular velocity of the rotating outlet. We conjectured that the mechanism generating the “peeling off” is related to the columnar strong vortex by close observations of the spatio-temporal development of the vorticity distribution and the cutting 3D images constructed from the successive cross sections of a vortex ring. While a laminar vortex ring without swirl may develop azimuthal waves around its circumference at some later time and the ring structure subsequently breaks, the swirling flow in a vortex ring core reduces the amplification rate of the azimuthal wavy deformation and preserved its ring structure. Then the traveling distance of a vortex ring can be extended using the swirl flow under certain conditions.

Multiobjective optimal design of runner blade using efficiency and draft tube pulsation criteria

In the present work new criteria of optimal design method for turbine runner [1] are proposed. Firstly, based on the efficient method which couples direct simulation of 3D turbulent flow and engineering semi empirical formulas, the combined method is built for hydraulic energy losses estimation in the whole turbine water passage and the efficiency criterion is formulated. Secondly, the criterion of dynamic loads minimization is developed for those caused by vortex rope precession downstream of the runner. This criterion is based on the finding that the monotonic increase of meridional velocity component in the direction to runner hub, downstream of its blades, provides for decreasing the intensity of vortex rope and thereafter, minimization of pressure pulsation amplitude. The developed algorithm was applied to optimal design of 640 MW Francis turbine runner. It can ensure high efficiency at best efficiency operating point as well as diminished pressure pulsations at full load regime.

Long-term changes in the nightly behaviour of the oxygen red 630.0 nm line nightglow intensity and trends in the thermospheric meridional wind velocity

Long-term changes in the nightly behaviour of the monthly/seasonal mean of the oxygen red 630.0 nm line intensity were observed at Abastumani (41.75° N, 42.82° E) from 1957 to 1993. The long-term increase in the red-line intensity after twilight and decrease at midnight is also mostly accompanied by an increase in the intensity before morning twilight. Using changes in mean seasonal nightly behaviour of the red-line intensity combined with the observed night-time negative trend in the ionosphere F2 layer peak height (hmF2) at Tbilisi (41.65° N, 44.75° E) from 1963 to 1986, the trend in the meridional component of thermospheric wind velocity is estimated. The obtained positive trend in the northward wind velocity (or decrease in the southward wind velocity) has a higher value in winter, where the hmF2 height decrease and the midnight/after midnight decrease in the red-line intensity are larger, and has lower values in spring and summer, where the decrease in hmF2 and midnight red-line intensity are comparatively smaller.

Dynamics of the combined extra-equatorial and equatorial deep jets in the Atlantic

The available meridional sections of zonal velocity with high vertical and meridional resolution reveal tall eastward jets at 2N and 2S, named the extra-equatorial jets (EEJ), straddling the stacked eastward and westward jets of smaller vertical scales right at the equator, the so-called equatorial deep jets (EDJ). In contrast to the semi-annual to interannual fluctuations in the zonal velocity component, the measured meridional velocity component is dominated by intraseasonal period. We argue here that the formation mechanism for both types of jets is linked to the intraseasonal variability in meridional velocity and the associated wave motions. A process study is complemented by high resolution primitive equation simulations based on a realistic background stratification and an oscillating forcing inside the western boundary layer. The forcing confined to the upper 2500 m excites a spectrum of waves, including a baroclinic short Mixed Rossby-Gravity (MRG), whose instability leads to the formation of the EDJ and short barotropic Rossby waves, whose instability gives rise to the EEJ. The modeled EEJ and EDJ response is confined to the same depth range as the forcing. Potential vorticity is homogenized within specific depth ranges of westward EDJ and is found to be latitudinally confined between 2N and 2S by the EEJ. The combined EDJ and EEJ increase lateral mixing at the equator but also act as barriers at ±2 degrees of latitude.

Role of variations in galactic cosmic rays in tropical cyclogenesis: Evidence of Hurricane Katrina

Based on the analysis of experimental data on vertical temperature profiles in the propagation region of Hurricane Katrina and variations in fluxes of galactic cosmic rays (hereafter, cosmic rays), we established an interrelation between temperature variations at the tropopause level and variations in the level of atmosphere ionization by cosmic rays. We found that variations in temperature and its spatial gradient related to the Forbush depression of cosmic ray flux induced by a magnetic storm could lead to variation in the direction of the meridional component of velocity and the intensification of Hurricane Katrina.

Destabilization of mixed Rossby gravity waves and the formation of equatorial zonal jets

The stability of mixed Rossby gravity (MRG) waves has been investigated numerically using three-dimensionally consistent high-resolution simulations of the continuously stratified primitive equations. For short enough zonal wavelength, the westward phase propagating MRG wave is strongly destabilized by barotropic shear instability leading to the formation of zonal jets. The large-scale instability of the zonally short wave generates zonal jets because it consists primarily of sheared meridional motions, as shown recently for the short barotropic Rossby wave problem.Simulations were done in a variety of domain geometries: a periodic re-entrant channel, a basin with a short MRG wave forced in its western part and a very long channel initialized with a zonally localized MRG wave. The characteristics of the zonal jets vary with the geometry. In the periodic re-entrant channel, barotropic zonal jets dominate the total flow response at the equator and its immediate vicinity. In the other cases, the destabilization leads to zonal jets with quite different characteristics, especially in the eastward group propagating part of the signal. The most striking result concerns the formation of zonal jets at the equator, alternating in sign in the vertical, with vertical scale short compared to the scale of the forcing or initial conditions.A stability analysis of a simplified perturbation vorticity equation is formulated to explain the spatial scale selection and growth rate of the zonal jets as functions of the characteristics of the basic state MRG wave. For both types of zonal jets, the model predicts that their meridional scales are comparable to the zonal scale of the MRG wave basic state, while their growth rates scale as μ ∝ Fr |k|, where Fr is the Froude number of the meridional velocity component of the basic state and k its non-dimensional zonal wavenumber. The vertical scale of the baroclinic zonal jets corresponds to the dominant harmonic ppeak of the basic state in the fastest growing mode, given by ppeak≈0.55k2. Thus, the shorter the zonal wavelength of the basic state MRG wave, the narrower the meridional scale of the zonal jets, both barotropic and baroclinic, with the vertical scale of the baroclinic jets being tied to their meridional scale through the equatorial radius of deformation, which decreases as the square root of the vertical wavenumber. The predictions of the spatial scales are in both qualitative and quantitative agreement with the numerical simulations, where shorter vertical scale baroclinic zonal jets are favoured by shorter-wavelength longer-period MRG wave basic states, with the vertical mode number increasing as the square of the MRG wave period.An Appendix deals with the case of zonally long and intermediate wavelength MRG waves, where a weak instability regime causes a moderate adjustment involving resonant triad interactions without leading to jet formation. For eastward phase propagating waves, adjustment does not lead to significant angular momentum redistribution.

Variability at Intermediate Depths at the Equator in the Atlantic Ocean in 2000–06: Annual Cycle, Equatorial Deep Jets, and Intraseasonal Meridional Velocity Fluctuations

Abstract Time series of high vertical resolution current meter measurements between 600-m and 1800-m depths on the equator in the Atlantic were obtained at two locations, 10° and 23°W. The measurements have a time span of almost 7 years (2000–06) and provide insights into the temporal scales and vertical structure of variability at intermediate depths. Variability in the zonal velocity component records is dominated by semiannual, annual, and interannual fluctuations. At semiannual and annual periodicities, vertical scales are large, on the order of 2000 stretched meters (sm), and show upward phase propagation. In contrast, interannual variability is associated with small vertical scale flows, called equatorial deep jets (EDJs), presenting downward phase propagation most of the time. Fitting a plane wave to these small vertical-scale flows leads to velocity amplitude, vertical scale, and temporal scale estimates of 8 (normalized) cm s−1, 440 sm, and 4.4 yr. However, this plane wave cannot explain all the variability presenting small vertical scales. Indeed, the data suggest that, along with a seasonal cycle of much larger vertical scale, different features with EDJ vertical scale coexist, with the possibility of a semipermanent eastward jet at around 1500 sm. Variability in the meridional velocity component is dominated by intraseasonal fluctuations. In addition, at 23°W, the meridional component shows low-frequency flows that may be due to the interaction of zonal fluctuations with the Mid-Atlantic Ridge.

European rain rate modulation enhanced by changes in the NAO and atmospheric circulation regimes

The aim of this study is to classify the circulation patterns in the Atlantic-European sector and to reveal linkages between anomalies in the pressure field over the North Atlantic (e.g. North Atlantic Oscillation (NAO)) and its respective circulation pattern occurrence over continents on the one hand and rain fields on the other hand. Changes in atmospheric circulation over Europe during the past 50 years were examined using both objective (modes of low-frequency variability inferred by regression analysis and objective cluster classification of circulation types—fuzzy logic) and subjective (Hess–Brezowsky classification of weather types) methods. The grid monthly geopotential (H700), wind zonal and meridional velocity components (U850 and V850) as well as the surface atmosphere pressure (SAP) and precipitation fields acquired from the NCEP/NCAR reanalysis dataset (for 1948–1998) were employed in this study. Joint regression analysis and fuzzy logic classification of these fields was a basic tool for finding major circulation regimes. The fuzzy set analysis of these fields revealed that the major circulation regimes over eastern North Atlantic and Europe were determined in summer by three vorticity poles: (1) North-western (Scandinavia), (2) Western Mediterranean and (3) Caucasian. It is worth noting that an anticyclone occurred in the western part of the North Atlantic for both seasons. The Scandinavia cyclone area explains rain rate maximums located in the 50–60° latitude European area and the lower rain rate in Southern Europe because of hot and dry African air inflow. In late fall and winter the vorticity system consists of three other poles: (1) North-western, (2) Northern Africa and (3) Northern Russia (Kara Sea). A zonal circulation type dominates in this case and more precipitation is delivered from the Atlantic. Rain rate is more uniformly distributed in the winter in various latitude belts across Europe than in summer, but more intensive precipitation occurred in Southern Europe because of strong moisture transport into this area from Atlantic NAO as well as the substantially larger their magnitude of Arctic Oscillation (AO) indexes in the late 1980s and 1990s during global warming. The atmospheric circulation patterns, which transported very wet Atlantic air, moved northward during last two decades. As a consequence, the climate in Southern Europe became drier and respective rain amounts reduced primarily in the warmer part of year. In contrast, the rain rate increased here in the colder part of the year. This leads to more frequent floods and a wetter climate in autumn/winter.