Meridional Wind Components Research Articles

Objective Definition of Climatologically Homogeneous Areas in the Southern Balkans Based on the ERA5 Data Set

An objective definition of climatologically homogeneous areas in the southern Balkans is attempted with the use of daily 0.25° × 0.25° ERA5 meteorological data of air temperature, dew point, zonal and meridional wind components, Convective Available Potential Energy, Convective Inhibition, and total cloud cover. The classification of the various grid points into climatologically homogeneous areas is carried out by applying Principal Component Analysis and K-means Cluster Analysis on the mean spatial anomaly patterns of the above parameters for the 10-year period of 2008 to 2017. According to the results, 12 climatologically homogenous areas are found. From these areas, eight are mainly over the sea and four are mainly over the land. The mean intra-annual variations of the spatial anomalies of the above parameters reveal the main climatic characteristics of these areas for the above period. These characteristics refer, for example, to how much warmer or cloudy the climate of a specific area is in a specific season relatively to the rest of the geographical domain. The continentality, the latitude, the altitude, the orientation, and the seasonal variability of the thermal and dynamic factors affecting the Mediterranean region are responsible for the climate characteristics of the 12 areas and the differences among them.

Daytime Ionospheric TEC Weather Study Over Latin America

AbstractThe present work is the first of a two‐part weather study of the ionospheric Total Electron Content (TEC), based on data collected by four ground‐based Global Navigation Satellite System networks that cover the whole Latin America from the Patagonia to the north of Mexico. From the best of our knowledge, the maps presented here are the first TEC maps obtained using ground‐based data that covers the entire Latin America region, which represent an advance to the space weather monitoring and forecasting of the ionosphere. This work provides a qualitative and quantitative daytime analysis of the ionospheric TEC variation, which encompasses: (a) the response of TEC to the solar flux at midday; (b) the seasonal variation of TEC in different latitudinal ranges; and (c) the North‐South asymmetry of TEC over Latin America. The response to the solar flux is based on day‐to‐day TEC variations during two periods of different solar activity conditions: 2011 (ascending phase) and 2014 (maximum). The approximations of meridional wind component derived from Horizontal Wind Model‐14 model and hmF2 obtained from International Reference Ionosphere model were used. Equinoctial asymmetries with an opposite configuration in high and moderate solar activity were identified in the TEC variation. For 2011, it was related to the solar flux change. However, in 2014, according to the hmF2 variation, the influence of neutral wind becomes dominant. Among the results, we highlight an absence of winter anomaly in the Northern Hemisphere in 2014 and a stronger annual anomaly for latitudes under −20∘.

Heavy Rainfall Associated with Double Low-Level Jets over Southern China. Part I: Ensemble-Based Analysis

AbstractHeavy rainfall occurred at both the inland frontal zone and coastal warm sector in southern China during 10–11 May 2014, which is a typical pattern in the early-summer rainy season. To clarify the key factors controlling the rainfall, we conduct an ensemble-based analysis using the operational global ensemble forecasts from ECMWF. The forecasts of frontal (warm sector) rainfall have a relatively small (large) spread and a small (large) bias of ensemble-mean amount, suggesting an obvious difference in the predictability. It is shown that double low-level jets (LLJs) in the southwesterly moist flow play a significant role in the heavy rainfall over southern China. The inland frontal rainband is closely related to the synoptic-system-related low-level jet (SLLJ) with maximum wind speed at 850–700 hPa, especially for its meridional wind component. The more intense cold front is accompanied by the stronger southwesterly SLLJ on the adjacent south side, favoring more precipitation near the front. The warm-sector heavy rainfall, a few hundred kilometers away from the front, is associated with the boundary layer jet (BLJ) at 925 hPa. The southerly BLJ occurs over the northern region of the South China Sea and reaches its maximum wind speed in the early morning. The variations of the BLJ are mainly induced by the surface low and related upper-level short-wave trough upstream. The large pressure gradient to the southeast of the surface low can accelerate the BLJ by increasing the geostrophic winds. The diurnal cycle of the low-level winds, seen in the climatology, also contributes in part to the development of the BLJ at night.

Assessment of the changes in the Etesians in the EURO‐CORDEX regional model projections

The northerly Etesian winds blow persistently over the Aegean Sea and eastern Mediterranean (EM) during summer months (June, July and August). This study investigates the July–August (JA) characteristics of the Etesians for a present time period (1981–2000) from both ECMWF ERA‐Interim Reanalysis data set (observations) and 11 EURO‐CORDEX regional climate model (RCM) simulations and assesses future changes using the associated RCP8.5 simulations. An EOF analysis applied to observations near surface meridional wind component (v10) over eastern Mediterranean demonstrates its strength as the leading mode, which explains 43.6% of the total variance, as the principal component (PC) time series of EOF1 has a very high correlation (r = 0.98) with an index showing the intensity of the Etesians. A composite analysis involving the opposite phases in the PC time series reveals that the strong Etesians develop when high pressure takes place towards Balkans and the Black Sea, which increases the meridional pressure gradient over the Aegean Sea. Some of the RCMs reproduce quite realistically pressure system and its associated Etesian winds. However, the intensity of the Etesians in these simulations is usually not as high as that in observations despite their higher horizontal resolutions. In general, the Etesians are projected to be stronger in the future periods as a result of the increasing pressure gradient over the Aegean Sea. This result suggests that the wind energy potential of the region that already attracts investment from the energy sector will increase in the future.

Assimilation of horizontal line‐of‐sight winds with a mesoscale EnKF data assimilation system

This paper compares the horizontal line‐of‐sight (HLOS) wind observations with a single wind component and full wind information in a limited‐area domain over Europe and the North Atlantic. The motivation for the study is the forthcoming Aeolus mission of the European Space Agency which will provide vertical profiles of HLOS winds.A new observing system simulation experiment framework was developed using the Data Assimilation Research Testbed (DART) ensemble adjustment Kalman filter (EAKF) data assimilation with the Weather Research and Forecasting (WRF) model at a horizontal resolution of 15 km. The 50‐member EAKF/WRF is nested in the operational 50‐member ensemble prediction system of ECMWF (ENS) using model‐level data available twice per day. The ensemble spread at lateral boundaries provided by ENS, especially in the North Atlantic, is shown to be sufficient to carry out experiments without covariance inflation.Results show that the information content of HLOS winds is on average divided linearly between the zonal and meridional wind components depending on the observation azimuth. In areas of significant covariances such as fronts in the Atlantic, multivariate covariance information provides significant useful analysis increments from the HLOS wind observations, especially if observations are aligned along the front. The application of the spatially and temporally adaptive prior inflation improved all scores compared with the case without inflation.

A dynamical model for diagnosing orographic rainfall across Assam–Burma hills in India

An attempt has been made to diagnose the orographic rainfall associated with internal gravity waves excited by the Assam–Burma hills (ABH) in India, during south west monsoon season (SWMS). To develop this model ABH has been synthesised by two 3-D elliptical barriers, separated by a valley of some finite distance. In this paper, a three dimensional frictionless, laminar, adiabatic, boussinesq, non-rotating and inviscid moist airflow with realistic vertical variation of wind and temperature, has been considered. Here also the basic flow consists of two components such as zonal wind component U(z) and meridional wind component V(z). The perturbation technique is used to linearise the governing equations of the airflow and to obtain perturbation vertical velocity ( $$w^{\prime}$$ ) the quasi-numerical approach have been used. The perturbation vertical velocity ( $$w^{\prime}$$ ) is used to compute the rainfall intensity (RFI) over ABH during SWMS. Also, we examine the sensitivity of the computed RFI on the length (d) of the valley. Finally, the computed results have compared with Gridded Rainfall Data set, generated by India meteorological Department (IMD), India.

Evaluation of RapidScat Ocean Vector Winds for Data Assimilation and Reanalysis.

The RapidScat scatterometer was built as a low cost follow-on to the QuikSCAT mission. It flew on the International Space Station (ISS) and provided data from 3 October 2014 to 20 August 2016 and provided surface wind vectors retrieved from surface roughness estimates taken at multiple azimuth angles. These measurements were unique to the historical scatterometer record in that the ISS flies in a low inclination, non-sun-synchronous orbit. Scatterometry-derived wind vectors have been routinely assimilated in both forward processing and reanalysis systems run at the Global Modeling and Assimilation Office (GMAO). As the RapidScat retrievals were made available in near-real-time, they were assimilated in the forward processing system, and the methods to assimilate and evaluate these retrievals are described. Time series of data statistics are presented first for the near-real-time data assimilated in GMAO forward processing. Second, the full data products provided by the RapidScat team are compared passively to the MERRA-2 reanalysis. Both sets of results show that the root mean squared (RMS) difference of the observations and the GMAO model background fields increased over the course of the data record. Furthermore, the observations and the backgrounds are shown to be biased for both the zonal and meridional wind components. The retrievals are shown to have had a net forecast error reduction via the forecast sensitivity observation impact (FSOI) metric, which is a quantification of 24 hour forecast error reduction, though the impact became neutral as the signal to noise ratio of the instrument decreased over its lifespan.

Evaluation of the impact of observations on blended sea surface winds in a two-dimensional variational scheme using degrees of freedom

This paper presents an evaluation of the observational impacts on blended sea surface winds from a two-dimensional variational data assimilation (2D-Var) scheme. We begin by briefly introducing the analysis sensitivity with respect to observations in variational data assimilation systems and its relationship with the degrees of freedom for signal (DFS), and then the DFS concept is applied to the 2D-Var sea surface wind blending scheme. Two methods, a priori and a posteriori, are used to estimate the DFS of the zonal (u) and meridional (v) components of winds in the 2D-Var blending scheme. The a posteriori method can obtain almost the same results as the a priori method. Because only by-products of the blending scheme are used for the a posteriori method, the computation time is reduced significantly. The magnitude of the DFS is critically related to the observational and background error statistics. Changing the observational and background error variances can affect the DFS value. Because the observation error variances are assumed to be uniform, the observational influence at each observational location is related to the background error variance, and the observations located at the place where there are larger background error variances have larger influences. The average observational influence of u and v with respect to the analysis is about 40%, implying that the background influence with respect to the analysis is about 60%.

Anomalias de Circulação Atmosférica em Baixos Níveis do Verão (2013-2014) Anomalamente Quente nas Regiões Sul e Sudeste do Brasil

In this study the anomalous behavior of air temperature on South and Southeast Brazilian regions during summer (2013-2014), as well as the low-levels atmospheric circulation anomalies, were analyzed employing MERRA reanalysis dataset. Such anomalies were obtained from 1979-2008 climatology for two quarters: DJF (December 2013, January and February 2014) and JFM (January, February and March 2014). It was verified that for the designation of “abnormally warm”, JFM was the most representative quarter. By streamline anomaly field in 850 hPa an intensification of northern meridional wind component, that advected moist and warm air mass from Amazonian region (causing a positively anomalous behavior of specific humidity in this level, as well as temperature in surface), was observed. Moreover, a probably greater frequency and/or intensity of extratropical cyclones in Southeast of South America was verified. However, the cold fronts associated with them did not reach the study area.

Effects of the midnight temperature maximum observed in the thermosphere–ionosphere over the northeast of Brazil

Abstract. The midnight temperature maximum (MTM) has been observed in the lower thermosphere by two Fabry–Pérot interferometers (FPIs) at São João do Cariri (7.4° S, 36.5° W) and Cajazeiras (6.9° S, 38.6° W) during 2011, when the solar activity was moderate and the solar flux was between 90 and 155 SFU (1 SFU = 10−22 W m−2 Hz−1). The MTM is studied in detail using measurements of neutral temperature, wind and airglow relative intensity of OI630.0 nm (referred to as OI6300), and ionospheric parameters, such as virtual height (h′F), the peak height of the F2 region (hmF2), and critical frequency of the F region (foF2), which were measured by a Digisonde instrument (DPS) at Eusébio (3.9° S, 38.4° W; geomagnetic coordinates 7.31° S, 32.40° E for 2011). The MTM peak was observed mostly along the year, except in May, June, and August. The amplitudes of the MTM varied from 64 ± 46 K in April up to 144 ± 48 K in October. The monthly temperature average showed a phase shift in the MTM peak around 0.25 h in September to 2.5 h in December before midnight. On the other hand, in February, March, and April the MTM peak occurred around midnight. International Reference Ionosphere 2012 (IRI-2012) model was compared to the neutral temperature observations and the IRI-2012 model failed in reproducing the MTM peaks. The zonal component of neutral wind flowed eastward the whole night; regardless of the month and the magnitude of the zonal wind, it was typically within the range of 50 to 150 m s−1 during the early evening. The meridional component of the neutral wind changed its direction over the months: from November to February, the meridional wind in the early evening flowed equatorward with a magnitude between 25 and 100 m s−1; in contrast, during the winter months, the meridional wind flowed to the pole within the range of 0 to −50 m s−1. Our results indicate that the reversal (changes in equator to poleward flow) or abatement of the meridional winds is an important factor in the MTM generation. From February to April and from September to December, the h′F and the hmF2 showed an increase around 18:00–20:00 LT within a range between 300 and 550 km and reached a minimal height of about 200–300 km close to midnight; then the layer rose again by about 40 km or, sometimes, remained at constant height. Furthermore, during the winter months, the h′F and hmF2 showed a different behavior; the signature of the pre-reversal enhancement did not appear as in other months and the heights did not exceed 260 and 350 km. Our observation indicated that the midnight collapse of the F region was a consequence of the MTM in the meridional wind that was reflected in the height of the F region. Lastly, the behavior of the OI6300 showed, from February to April and from September to December, an increase in intensity around midnight or 1 h before, which was associated with the MTM, whereas, from May to August, the relative intensity was more intense in the early evening and decayed during the night.

A comparison of 11-year mesospheric and lower thermospheric winds determined by meteor and MF radar at 69 ° N

Abstract. The Andenes Meteor Radar (MR) and the Saura Medium Frequency (MF) Radar are located in northern Norway (69° N, 16° E) and operate continuously to provide wind measurements of the mesosphere and lower thermosphere (MLT) region. We compare the two systems to find potential biases between the radars and combine the data from both systems to enhance altitudinal coverage between 60 and 110 km. The systems have altitudinal overlap between 78 and 100 km at which we compare winds and tides on the basis of hourly winds with 2 km altitude bins. Our results indicate reasonable agreement for the zonal and meridional wind components between 78 and 92 km. An exception to this is the altitude range below 84 km during the summer, at which the correlation decreases. We also compare semidiurnal and diurnal tides according to their amplitudes and phases with good agreement below 90 km for the diurnal and below 96 km for the semidiurnal tides. Based on these findings we have taken the MR data as a reference. By comparing the MF and MR winds within the overlapping region, we have empirically estimated correction factors to be applied to the MF winds. Existing gaps in that data set will be filled with weighted MF data. This weighting is done due to underestimated wind values of the MF compared to the MR, and the resulting correction factors fit to a polynomial function of second degree within the overlapping area. We are therefore able to construct a consistent and homogenous wind from approximately 60 to 110 km.

Assessment of the ERA-Interim Winds Using High-Altitude Stratospheric Balloons

Abstract This study focuses on the ability of ERA-Interim to represent wind variability in the middle atmosphere. The originality of the proposed approach is that wind measurements are deduced from the trajectories of zero-pressure balloons that can reach high-stratospheric altitudes. These balloons are mainly used to carry large scientific payloads. The trajectories of balloons launched above Esrange, Sweden, and Teresina, Brazil, from 2000 to 2011 were used to deduce zonal and meridional wind components (by considering the balloon as a perfect tracer at high altitude). Collected data cover several dynamical conditions associated with the winter and summer polar seasons and west and east phases of the quasi-biennial oscillation at the equator. Systematic comparisons between measurements and ERA-Interim data were performed for the two horizontal wind components, as well as wind speed and wind direction in the [100, 2]-hPa pressure range to deduce biases between the model and balloon measurements as a function of altitude. Results show that whatever the location and the geophysical conditions considered, biases between ERA-Interim and balloon wind measurements increase as a function of altitude. The standard deviation of the model–observation wind differences can attain more than 5 m s−1 at high altitude (pressure P < 20 hPa). A systematic ERA-Interim underestimation of the wind speed is observed and large biases are highlighted, especially for equatorial flights.

Long term variabilities and tendencies of mesospheric lunar semidiurnal tide over Tirunelveli (8.7°N, 77.8°E)

The medium frequency radar deployed at Tirunelveli (8.7°N, 77.8°E), which is located near the southmost tip of peninsular India, have been providing continuous data from the year 1993 to the year 2012 that helped to study the long term tendencies in the lunar tidal variabilities over this geographic location. In the present paper we present the results of seasonal, interannual and long-term variabilities of lunar semi-diurnal tides in the upper mesosphere over Tirunelveli. The present study also includes comparison with model values. The study shows that the tidal amplitudes are larger in the meridional components of the mesospheric winds than the zonal winds. The seasonal variations of the tides are similar in both the components. The tides show maximum amplitudes of about ∼5 m/s in February/March, secondary maximum amplitudes of about ∼3 m/s in September and minimum amplitudes during summer months (May–August). The observed seasonal variation of the lunar tides do not compare well with Vial and Forbes (1994) model values, though it is consistent with earlier observations. The lunar tidal phase in meridional winds leads that in zonal winds from January to June and from September to November, while the latter leads the former during July/August. The lunar tides show large interannual variability. There are unusual amplitude enhancements in the lunar tide in meridional winds during the winters of 2006 and 2009, when major sudden stratospheric warmings (SSW) occurred at high latitude northern hemisphere, whereas zonal lunar tide does not show any clear association with the SSW. Vertical wavelengths of lunar tides in zonal and meridional wind are in the range of 20–90 km. The vertical wavelengths of lunar tides in both zonal and meridional component are smaller in June and larger in November and December. The monthly mean zonal and meridional winds are subjected to regression analysis to study the tidal response to long-period oscillations, namely, quasi-biennial oscillation (QBO), solar cycle variation and El-nino southern oscillation (ENSO). It is found the lunar tide in both zonal and meridional winds show significant QBO response, whereas zonal tide only shows significant negative response to solar cycle and positive response to ENSO. Besides, zonal tide only shows significant long-term increasing trend.

Investigação Climatológica na Península Antártica e no Arquipélago das Shetland do Sul

Based on 17 automatic weather stations distributed at different sub regions in South Shetland islands, and over the eastern and western Antarctic Peninsula (AP), this study aims to investigate potential changes of climatological features. Observed monthly data computed on three-month running means are applied to time series of temperature, and zonal and meridional wind components. It has been found that South Shetland islands, Bellingshausen and Jubany weather stations experienced a temperature increase by up to 0.8 °C and 1 °C over the period, but no significant change in wind speed. However, the other 15 weather stations present changes in temperature and winds. At the eastern part of the AP, positive temperatures are evident: 1.7 °C warming was observed at the Esperanza weather station over 56 years, with variations of zonal and meridional wind speed. At the western side of the AP, there is an increase in temperature in all stations, in particular at the Faraday station, where the mean temperature increased 3.2 °C in 63 years. Previous researches show the influence that Antarctica Oscillation exerts on temperature in Antarctica. Zonal and meridional wind components present variations of a few m/s at these stations.

Validation of gridded data set of global surface wind/wind-stress vector field

Gridded data of global surface wind/wind-stress vectors, called J-OFURO v2, were obtained from satellite scatterometer (QuikSCAT/SeaWinds) data for the decade from August 1999 to July 2009. The data were validated by comparing with (1) in situ measurements from moored buoy observations, (2) a data product from the same scatterometer using a different gridding procedure (IFREMER), and (3) data products based on numerical models (NCEP-1 and NCEP-2). The results on averaging all buoy data revealed lower mean differences, lower root-mean-square (RMS) differences, and higher correlations for the wind/wind-stress components for the J-OFURO v2 product than the other data products. The statistical values calculated for each buoy station showed tendencies of decreasing reliability with increasing latitude in the mid-latitude region, while the reliabilities in the equatorial areas were low. We performed intercomparisons between the J-OFURO v2 data and the other data sets to clarify discrepancies among different wind products in open ocean regions with few moored buoys. We determined that the meridional wind components from the NCEP products exhibited poleward deviations compared to data from the J-OFURO v2 product. Relatively high mean differences, high RMS differences, and low correlations were found in the equatorial ocean for the NCEP products. Striped features were spatially correlated with buoy locations in the equatorial Pacific, which suggested that the reliability of the NCEP products was governed by buoy locations in this region.

Two decades [1992–2012] of surface wind analyses based on satellite scatterometer observations

Surface winds (equivalent neutral wind velocities at 10m) from scatterometer missions since 1992 have been used to build up a 20-year climate series. Optimal interpolation and kriging methods have been applied to continuously provide surface wind speed and direction estimates over the global ocean on a regular grid in space and time. The use of other data sources such as radiometer data (SSM/I) and atmospheric wind reanalyses (ERA-Interim) has allowed building a blended product available at 1/4° spatial resolution and every 6h from 1992 to 2012. Sampling issues throughout the different missions (ERS-1, ERS-2, QuikSCAT, and ASCAT) and their possible impact on the homogeneity of the gridded product are discussed. In addition, we assess carefully the quality of the blended product in the absence of scatterometer data (1992 to 1999). Data selection experiments show that the description of the surface wind is significantly improved by including the scatterometer winds. The blended winds compare well with buoy winds (1992–2012) and they resolve finer spatial scales than atmospheric reanalyses, which make them suitable for studying air-sea interactions at mesoscale. The seasonal cycle and interannual variability of the product compare well with other long-term wind analyses. The product is used to calculate 20-year trends in wind speed, as well as in zonal and meridional wind components. These trends show an important asymmetry between the southern and northern hemispheres, which may be an important issue for climate studies.

Современные изменения режимных характеристик ветра на станциях охотоморского побережья

Wind regime at the Okhotsk Sea coast is considered on the base of anemometer data obtained by the Hydrometeorological Centre of Russia since early 1970s (vanes were used for the wind rate measurements before). Climatic-scale trends in wind direction and wind rate are revealed for the 43 years period. The wind rate has a tendency to decreasing in all seasons, in spite of seasonal change of the dominant direction, with the regime shift in the late 1980s. However, the main patterns of the atmospheric circulation over the Okhotsk Sea have changed slightly, so the direction of the prevailing winds is rather stable: weakening of the zonal wind component in winter was observed for several stations in the late 1990s - early 2000s only and insignificant weakening of the meridional (south) wind component occurred in summer.

EVENTOS DE INTENSIFICACIÓN Y RELAJACIÓN DEL VIENTO EN LA BAHÍA DE SANTA MARTA (CARIBE COLOMBIANO): IMPLICACIONES OCEANOGRÁFICAS

Events of wind intensification and relaxation bring changes in their components that can be favorable or not to the coastal upwelling because there is a change in the alignment of these with respect to the coast line. In order to assess the oceanographic dynamics in the bay of Santa Marta during 2014 and 2015 in response to changes in the zonal and meridional wind component, wind data were analyzed in an adjacent marine point at Santa Marta’s bay and measurements of temperature, salinity and dissolved oxygen were conducted in the water column during the months of March, May, July, and October 2014 and 2015 at a fixed station in the bay up to 18 m deep. Interannual oceanographic differences were found in March and June, which were explained by intra-seasonal variations in the wind field during 2015; in March alternating events of wind intensification and relaxation occurred with changes in both magnitude and direction, which explain the increases in temperature and water advection from La Guajira with lower oxygen values. In June 2015, an event of wind intensification, associated with changes in magnitude but no direction, was recorded, which explained the decrease in temperature, which was lower than the one in 2014. That month was characterized by strong winds and waves, but the directions were not favorable to the coastal upwelling, which explained that no low values of dissolved oxygen as expected in this type of events were found.

A Validation of the Antarctic Mesoscale Prediction System Using Self-Organizing Maps and High-Density Observations from SNOWWEB

This study compares high-resolution output (1.1-km horizontal grid length) from twice-daily forecasts produced by the Antarctic Mesoscale Prediction System (AMPS) with a dense observational network east of Ross Island. Covering 10 000 km2, 15 SNOWWEB stations significantly increased the number of observation stations in the area to 19 during the 2014–15 austral summer. Collocated “virtual stations” created from AMPS output are combined with observations, producing a single dataset of zonal and meridional wind components used to train a self-organizing map (SOM). The resulting SOM is used to individually classify the observational and AMPS datasets, producing a time series of classifications for each dataset directly comparable to the other. Analysis of class composites shows two dominant weather patterns: low but directionally variable winds and high but directionally constant winds linked to the Ross Ice Shelf airstream (RAS). During RAS events the AMPS and SNOWWEB data displayed good temporal class alignment with good surface wind correlation. SOM analysis shows that AMPS did not accurately forecast surface-level wind speed or direction during light wind conditions where synoptic forcing was weak; however, it was able to forecast the low wind period occurrence accurately. Coggins’s regimes provide synoptic-scale context and show a reduced synoptic pressure gradient during these classes, increasing reliance on the ability of Polar WRF to resolve mesoscale dynamics. Available initialization data have insufficient resolution for the region’s complex topography, which likely impacts performance. The SOM analysis methods used are shown to be effective for model validation and are widely applicable.

Wind influence on surface current variability in the Ibiza Channel from HF Radar

Surface current variability is investigated using 2.5 years of continuous velocity measurements from an high frequency radar (HFR) located in the Ibiza Channel (Western Mediterranean Sea). The Ibiza Channel is identified as a key geographical feature for the exchange of water masses but still poorly documented. Operational, quality controlled, HFR derived velocities are provided by the Balearic Islands Coastal Observing and Forecasting System (SOCIB). They are assessed by performing statistical comparisons with current-meter, ADCP, and surface lagrangian drifters. HFR system does not show significant bias, and its accuracy is in accordance with previous studies performed in other areas. The main surface circulation patterns are deduced from an EOF analysis. The first three modes represent almost 70 % of the total variability. A cross-correlation analysis between zonal and meridional wind components and the temporal amplitudes of the first three modes reveal that the first two modes are mainly driven by local winds, with immediate effects of wind forcing and veering following Ekman effect. The first mode (37 % of total variability) is the response of meridional wind while the second mode (24 % of total variability) is linked primarily with zonal winds. The third and higher order modes are related to mesoscale circulation features. HFR derived surface transport presents a markedly seasonal variability being mostly southwards. Its comparison with Ekman-induced transport shows that wind contribution to the total surface transport is on average around 65 %.