Mean Sea Level Pressure Fields Research Articles

CyTRACK: An open-source and user-friendly python toolbox for detecting and tracking cyclones

This work introduces CyTRACK (Cyclone TRACKing framework), a new open-source, comprehensive and user-friendly Python toolbox for detecting and tracking cyclones in model and reanalysis datasets. The kernel of CyTRACK is based on detecting critical cyclone centres in the mean sea level pressure field at a single time slice, which are then filtered following several threshold parameters. This paper also compares ten years of CyTRACK outputs forced with the ERA5 reanalysis against best-track archives and available cyclones track datasets. The results reveal that CyTRACK can capture the inter-annual (year to year) and intra annual (seasonal cycle) variability of cyclone frequency, life cycle characteristics and spatial distribution of track densities. Largest differences were observed in the annual and seasonal frequency. In summary, CyTRACK provides a user-friendly framework for sensitivity analysis of several free parameters used to perform the tracking, and it is useful for case or climatological studies of cyclone features.

European Summer Synoptic Circulations and Their Observed 2022 and Projected Influence on Hot Extremes and Dry Spells

AbstractIn 2022, western Europe experienced its hottest summer on record and widespread dry conditions, with substantial impacts on health, water and vegetation. We use a reanalysis to classify daily mean sea level pressure fields and to investigate the influence of synoptic circulations on the occurrence of temperature extremes and dry days. Summer 2022 featured an above‐normal occurrence of anticyclones extending from the British Isles to the Baltic countries, as well as enhanced easterly, southerly and low‐flow conditions which contributed to the observed extremes over southern and western Europe. While the hot summer of 2022 is only partially explained by circulation anomalies, such anomalies played a key role in the exceptional occurrence of dry days. The comparison with summer circulation anomalies projected by twenty global climate models moreover suggests that future circulation changes will further exacerbate hot and dry extremes over Europe.

Mean sea-level pressure and related fields from control and tropical relaxation summer seasonal hindcasts using the Met Office GloSea5 system.

Mean sea-level pressure and related fields from control and tropical relaxation summer seasonal hindcasts using the Met Office GloSea5 system.

Caspian Sea Level Change Observed by Satellite Altimetry

We analyze satellite altimeter observed Caspian Sea level (CSL) changes over the period January 1993 to December 2021 using the lake level series from the Hydroweb project and global sea level anomalies (SLA) grids provided by the Copernicus Marine Environment Monitoring Service (CMEMS). The two altimeter-based CSL series agree well at interannual and longer time scales, but show significantly large discrepancies at seasonal and shorter time scales. The large discrepancies are found to be introduced by the approximately inverted barometer (IB) correction applied to the CMEMS SLA over the Caspian Sea. The IB correction over the Caspian Sea or any enclosed lakes needs to be treated separately from the ocean by using the correct reference mean pressure. The actual IB effects over the Caspian Sea are significantly smaller than those applied in the CMEMS SLA grids. After applying an improved IB correction using the global mean sea level pressure fields from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis atmospheric model, the two CSL series agree remarkably well. Altimeter observed CSL series show a significant decreasing trend on top of strong seasonal variations. The estimated linear trends for the Hydroweb and CMEMS CSL series are −5.37 ± 0.11 and −5.40 ± 0.11 cm/yr, respectively. Annual amplitudes are 17.03 ± 1.33 vs. 15.79 ± 1.30 cm, with nearly the same phases. The CSL change shows notable acceleration in the decreasing trend since around 2005, and the estimated trends have increased to −8.86 ± 0.10 and −8.81 ± 0.10 cm/yr, respectively for the two-altimeter CSL series.

Global Climatology of Extratropical Cyclones From a New Tracking Approach and Associated Wave Heights From Satellite Radar Altimeter

AbstractExtratropical cyclones (ECs) produce comparable wave heights and hazardous sea states to those under hurricanes. With strong wind speeds and considerably larger diameters, the impact of ECs on the global wave climate is substantial. Because ECs occur more frequently, move more quickly, and exist in a large variety of sizes and shapes, these storms are not as well documented. Here, we present findings from a global EC tracking algorithm aimed at creating an EC database of wave producing storms. We focus on the major ocean basins of extratropical cyclone activity: The North Atlantic, North Pacific, and Southern Oceans. Our tracking algorithm uses mean sea level pressure fields from the European Centre for Medium‐Range Weather Forecasts (ECMWF) high resolution, advanced data assimilating, ERA5 reanalysis over the years 1979–2020. The 42 year‐long data set of thousands of cyclone tracks allows seasonal patterns and longer‐term trends of EC activity to be analyzed in these ocean regions. In addition, we employ 36 years of satellite radar altimeter‐derived significant wave height (Hs) data from 14 inter‐calibrated satellite missions to study the wave climate induced by the identified ECs in each basin. The resulting wave climatology compares well with previous results in the mid to high latitudes. We then analyze average wave heights under different EC characteristics, including cyclone translational speed and maximum winds, which have strong effects on wave height variability. Finally, a brief analysis of EC and wave climate under positive and negative phases of the North Atlantic Oscillation is presented.

Algorithm for detecting cyclone and anticyclone centres from mean sea level pressure layer

ABSTRACT Automatic methods for identifying and tracking pressure systems have been traditionally focused on cyclones (and particularly on tropical cyclones), but the question of anticyclone centre detection remained unsolved since they are usually not a source of turbulent weather, precipitation, etc. An algorithm for automatic detection of both, cyclones and anticyclones based on the mean sea-level pressure field, is presented. The main advantages of our solution are easy implementation based on two-dimensional raster data, sufficient performance of the algorithm, and especially the possibility of high-pressure systems detection. Moreover, the presented solution does not need direct terrain filtering.

Comparison of Extreme Coastal Flooding Events between Tropical and Midlatitude Weather Systems in the Delaware and Chesapeake Bays for 1980–2019

Abstract Coastal flooding is one of the most costly and deadly natural hazards facing the U.S. mid-Atlantic region today. Impacts in this heavily populated and economically significant region are caused by a combination of the location’s exposure and natural forcing from storms and sea level rise. Tropical cyclones (TCs) and midlatitude (ML) weather systems each have caused extreme coastal flooding in the region. Skew surge was computed over each tidal cycle for the past 40 years (1980–2019) at several tide gauges in the Delaware and Chesapeake Bays to compare the meteorological component of surge for each weather type. Although TCs cause higher mean surges, ML weather systems can produce surges just as severe and occur much more frequently, peaking in the cold season (November–March). Of the top 10 largest surge events, TCs account for 30%–45% in the Delaware and upper Chesapeake Bays and 40%–45% in the lower Chesapeake Bay. This percentage drops to 10%–15% for larger numbers of events in all regions. Mean sea level pressure and 500-hPa geopotential height (GPH) fields of the top 10 surge events from ML weather systems show a low pressure center west-southwest of “Delmarva” and a semistationary high pressure center to the northeast prior to maximum surge, producing strong easterly winds. Low pressure centers intensify under upper-level divergence as they travel eastward, and the high pressure centers are near the GPH ridges. During lower-bay events, the low pressure centers develop farther south, intensifying over warmer coastal waters, with a south-shifted GPH pattern relative to upper-bay events. Significance Statement Severe coastal flooding is a year-round threat in the U.S. mid-Atlantic region, and impacts are projected to increase in magnitude and frequency. Research into the meteorological contribution to storm surge, separate from mean sea level and tidal phase, will increase the scientific understanding and monitoring of changing atmospheric conditions. Tropical cyclones and midlatitude weather systems both significantly impact the mid-Atlantic region during different times of year. However, climate change may alter the future behavior of these systems differently. Understanding the synoptic environment and quantifying the surge response and subbay geographic variability of each weather system in this region will aid in public awareness, near-term emergency preparation, and long-term planning for coastal storms.

Circulation pattern controls of wet days and dry days in Free State, South Africa

Atmospheric circulation is a vital process in the transport of heat, moisture, and pollutants around the globe. The variability of rainfall depends to some extent on the atmospheric circulation. This paper investigates synoptic situations in southern Africa that can be associated with wet days and dry days in Free State, South Africa, in addition to the underlying dynamics. Principal component analysis was applied to the T-mode matrix (variable is time series and observation is grid points at which the field was observed) of daily mean sea level pressure field from 1979 to 2018 in classifying the circulation patterns in southern Africa. 18 circulation types (CTs) were classified in the study region. From the linkage of the CTs to the observed rainfall data, from 11 stations in Free State, it was found that dominant austral winter and late austral autumn CTs have a higher probability of being associated with dry days in Free State. Dominant austral summer and late austral spring CTs were found to have a higher probability of being associated with wet days in Free State. Cyclonic/anti-cyclonic activity over the southwest Indian Ocean, explained to a good extent, the inter-seasonal variability of rainfall in Free State. The synoptic state associated with a stronger anti-cyclonic circulation at the western branch of the South Indian Ocean high-pressure, during austral summer, leading to enhanced low-level moisture transport by southeast winds was found to have the highest probability of being associated with above-average rainfall in most regions in Free State. On the other hand, the synoptic state associated with enhanced transport of cold dry air, by the extratropical westerlies, was found to have the highest probability of being associated with (winter) dryness in Free State.

ИСПОЛЬЗОВАНИЕ АВТОМАТИЧЕСКОЙ ТИПИЗАЦИИ СИНОПТИЧЕСКОЙ СИТУАЦИИ ДЛЯ УСЛОВНОЙ ВЕРИФИКАЦИИ ЧИСЛЕННЫХ ПРОГНОЗОВ ПОГОДЫ В ПЕРМСКОМ КРАЕ

The article discusses the possibility of verification of short-term 2-meter air temperature forecasts with the Global Forecast System and Global Environment Multiscale numerical weather prediction models depending on the observed synoptic type (a case study of the Perm region for the period 2018–2019). As part of the study, we have developed a system of automated determination of synoptic type based on a two-stage procedure, including decomposition of mean sea level pressure fields via principal component analysis and the subsequent clustering of decomposition coefficients using K-means. It has been established that GFS forecasts are more dependent on synoptic type in summer than in winter. The decline of forecast quality, expressed in systematic underestimation of forecast temperature by 0.6°–1.2°, is noted for synoptic types associated with warm air advection.: In contrast, GEM forecasts tend to lack accuracy in winter. A sharp decrease in forecast quality has been discovered in the central area of anticyclone at night, when the forecast accuracy drops to 44%. The obtained results could be useful in operational forecasting and model postprocessing.

Análise Climatológica das trajetórias de Ciclones Extratropicais formados na região da Península Antártica

Cyclones play an important role in the general circulation of the atmosphere, enabling the meridional transport of excess heat, humidity and momentum from low latitudes to high latitudes. In the Southern Hemisphere, the area between southern Brazil and the Peninsula Antarctica (AP) is described as one of the most favorable for the formation of cyclones (30°S to 70°S) due to the existence of strong temperature gradient between the ocean and the surface air layer above the ocean and also because of pre-existing baroclinic instabilities. This study is associated with the Project ATMOS (AnTarctic Modeling Observation System) and explored the role of extratropical cyclones in teleconnections between high and medium latitudes to track the trajectories of extratropical cyclones that are formed in the Antarctic Peninsula (AP) and move towards the central sector of the South Atlantic. The analysis of the tracked trajectories showed that the cyclones reached the central sector of the South Atlantic during the months of autumn (greater number) and winter (greater displacement), while the statistical analysis indicated that the intensity of the cyclones is more linearly linked to the mean sea level pressure field than to Superficial Sea Temperature Anomalies.

Long-term variability of the mean sea level pressure field over the Black Sea

This paper aims to evaluate spatiotemporal variability of the mean sea level pressure trends over the Black Sea using the gridded 40-year (1979-2018) reanalysis mean sea level pressure data from two different datasets. These datasets are the European Centre for Medium-Range Weather Forecasts ERA-Interim with a spatial resolution of 0.25° and temporal resolution of six hours, and the National Centers for Environmental Prediction/Climate Forecast System Reanalysis with a spatial resolution of 0.5° and temporal resolution of one hour. Data from both databases show that the mean sea level pressure tends to decrease towards the recent years over the entire Black Sea. The long-term averages of mean sea level pressure reflect the spatial variability over the Black Sea with much lower pressures in the eastern part of the Black Sea than that on the western side. The long-term variation is more intense in the eastern part of the Black Sea. Sea Level Anomaly over the Black Sea, spanning 26 years between 1993 and 2018, was analyzed using satellite altimetry data. It was found that there is a high Sea Level Anomaly where the mean sea level pressure is low, described by an inverted barometer response. The 39-year long Sea Surface Temperature Anomaly data (1981-2018) indicate the rising tendency in sea surface temperature towards recent years in the entire Black Sea. An inverse relationship is found between North Atlantic Oscillation index and sea surface temperature anomaly. On a seasonal scale, mean sea level pressure in winter (high-pressure system) is larger than that in summer (low-pressure system). Our analyses show that mean sea level pressure tends to decrease, sea surface temperature anomaly and sea surface temperature anomaly tends to increase in recent years over the Black Sea.

Ground-based and OMI-TROPOMI NO2 measurements at El Arenosillo observatory: Unexpected upward trends

Eleven years, January 2008 to June 2019, of hourly nitrogen dioxide (NO2) levels recorded at El Arenosillo observatory (Southwestern Europe) were analyzed. Annual averages ranged between 4 μg m−3 and 6 μg m−3 with peaks exceeding 40 μg m−3. A slight monthly variation was observed with maximum and minimum values in the cold (∼6 μg m−3) and warm (∼4 μg m−3) seasons respectively. A diurnal pattern was found with a weak amplitude (∼3 μg m−3). The monthly trends were investigated using surface observations and OMI (Ozone Monitoring instrument) satellite measurements. An unexpected upward trend was obtained in the last five years. The periods with elevated NO2 concentrations in the last years were analyzed, showing an increase in its frequency and concentrations, linked with the upward trend observed. The weather conditions in these NO2 peaks were studied using local surface meteorology, mean sea level pressure and wind fields from the data reanalysis of ERA5. The transport of NO2 was explored using TROPOMI (Tropospheric Monitoring Instrument) measurements. The events occurred under conditions governed by high-pressure systems, which induced weak synoptic airflows or the development of mesoscale processes. Four scenarios of NO2 transport were identified, associated with weak synoptic flows from inland or Southern Portugal and with mesoscale processes. The gulf of Cadiz plays an important role as a reservoir where the NO2 coming from the south of Portugal, the Western Mediterranean Basin and urban-industrial areas can be accumulated and later transported inland. A strong correlation was found between the increase of NO2 observed in the last years and positive anomalies of the temperature and geopotential height at 850 and 500 hPa levels. These findings could indicate that the causes of the changes in the NO2 would be attributed to alterations in the weather patterns associated with a warmer climate.

Isotropic High-Order Filter for a Local Domain on the Sphere

High-order filtering with isotropy of a local-domain data defined at an arbitrary location on the sphere, with an application to scale-decomposition of mean sea level pressure field, was investigated. The equation of high-order filter was based on the implicit hyper-diffusion of 8th-order, which was discretized by the Fourier-finite element method (FFEM). In order to apply the FFEM high-order filter to a local-domain data which is not represented with two-dimensional array, a rotation of coordinates was performed. The geometry of the rotated local domain was made to be either a polar cap (polar cap domain) or a symmetric window with respect to the Equator (Equatorial symmetric domain) to reduce the anisotropy of the local domains caused by the metric effect of spherical coordinates. The rotated local domains are extended by padding artificial data to match the boundary condition of vanishing gradient. The performance of the filters for the symmetric- or asymmetric- domain, was compared for both initial fields defined with an analytic function and the observed meteorological data. It turned out that the filters on the local domains with symmetry, i.e., the polar cap domain and the Equatorial symmetric domain, produced improved results over the local domains with asymmetry: Asymmetric error pattern between the northern and southern boundary, which is typical of the window domain defined on the middle latitude (or between the pole and the Equator), is reduced appreciably and the improvement is shown to become more significant for the window-domain closer to the pole. Through tests with wind fields, the performance of the filters on the polar cap domain and the Equatorial symmetric domain was found comparable to each other. The advantage of polar cap filter, being not available for the Equatorial symmetric domain filter, was illustrated by conducting a scale decomposition and composite analysis of the mean sea level pressure that requires the data manipulations such as a zonal averaging as well as azimuthal-phase shifting.

The Interannual Variability of Surface Winds in Antarctica and the Surrounding Oceans: A Climatological Analysis Using the ERA‐Interim Reanalysis Data

AbstractSeason‐dependent interannual variability of surface winds across Antarctica and the Southern Ocean is investigated using European Centre for Medium‐Range Weather Forecasts Interim (ERA‐Interim) reanalysis for 1979–2017 and the empirical orthogonal function (EOF) technique. The first three EOF modes, which account for 18–23%, 11–15%, and 8–10% of the total variances for the four austral seasons, are related to several known modes of Southern Hemisphere large‐scale circulation including the southern annular mode, Pacific South American (PSA), and Zonal Wave 3 (ZW3) and to sea surface temperature anomalies in eastern (Niño 3) and central (Niño 4) tropical Pacific Ocean. Specifically, EOF1 and EOF2 are significantly correlated with southern annular mode in all seasons except for autumn EOF2. Neither EOF1 nor EOF2 are significantly correlated to Niño 3, but Niño 4 is significantly correlated to winter EOF1 and to EOF2 in all seasons but winter. EOF1 is significantly related to ZW3 for all seasons but summer; however, no significant connection is found between EOF2 and ZW3. Significant correlations exist between spring and winter EOF2 and PSA1 and between spring EOF1 and PSA2. EOF3 is significantly correlated with Niño 3, Niño 4, and PSA2 in all seasons but summer. The spatial patterns of all three modes can be largely explained by the anomalous mean sea level pressure fields that strengthen or weaken climatological winds in different regions of the Antarctica and the Southern Ocean, although variations in katabatic forcing also plays a role in the variations of surface winds especially in East Antarctica and during winter season where and when katabatic forcing dominates.

Composite analysis of the tropopause inversion layer in extratropical baroclinic waves

Abstract. The evolution of the tropopause inversion layer (TIL) during cyclogenesis in the North Atlantic storm track is investigated using operational meteorological analysis data (Integrated Forecast System from the European Centre for Medium-Range Weather Forecasts). For this a total of 130 cyclones have been analysed during the months August through October between 2010 and 2014 over the North Atlantic. Their paths of migration along with associated flow features in the upper troposphere and lower stratosphere (UTLS) have been tracked based on the mean sea level pressure field. Subsets of the 130 cyclones have been used for composite analysis using minimum sea level pressure to filter the cyclones based on their strength. The composite structure of the TIL strength distribution in connection with the overall UTLS flow strongly resembles the structure of the individual cyclones. Key results are that a strong dipole in TIL strength forms in regions of cyclonic wrap-up of UTLS air masses of different origin and isentropic potential vorticity. These air masses are associated with the cyclonic rotation of the underlying cyclones. The maximum values of enhanced static stability above the tropopause occur north and northeast of the cyclone centre, vertically aligned with outflow regions of strong updraft and cloud formation up to the tropopause, which are situated in anticyclonic flow patterns in the upper troposphere. These regions are co-located with a maximum of vertical shear of the horizontal wind. The strong wind shear within the TIL results in a local minimum of Richardson numbers, representing the possibility for turbulent instability and potential mixing (or air mass exchange) within regions of enhanced static stability in the lowermost stratosphere.

UTJECAJ ZMORCA NA ONEČIŠĆENOST ZRAKA NA SPLITSKOM PODRUČJU

U radu se istražuje utjecaj zmorca na koncentraciju NO2, SO2, PM2.5 i PM10 na
 splitskom području prema mjernim postajama Split-centar i Kaštel Sućurac. Za
 proučavanje su izdvojeni dani u kojima je obalna cirkulacija bila neporemećena.
 U izdvojenim danima polje tlaka zraka bilo je bezgradijentno. Posebno su istraženi
 čestina i brzina vjetra u takvim danima. Zmorac u Splitu ima SW smjer, a u Kaštel
 Sućurcu WSW i W. Koncentracije onečišćujućih tvari uspoređene su s brzinama
 vjetra. Najprisutnija onečišćujuća tvar je NO2. Najviše ga ima u večernjim i jutarnjim
 satima dok zmorac još nije razvio veću brzinu ili mu se brzina smanjuje
 približavanjem večernjeg zatišja. Što je brzina zmorca veća, koncentracija NO2 je
 manja. Nastupom zmorca povećava se koncentracija lebdećih čestica zbog turbulencije
 vjetra unutar grada te mogućeg donosa morskog aerosola i nusprodukata
 pomorskog prometa. NO2 dostiže veće vrijednosti u Splitu nego u Kaštel Sućurcu.
 Lebdeće čestice imaju veće koncentracije u Kaštel Sućurcu nego u Splitu. Vrijednosti
 svih onečišćujućih tvari ispod su graničnih vrijednosti za zdravlje ljudi.

Utjecaj zmorca na onečišćenost zraka na splitskom području

U radu se istražuje utjecaj zmorca na koncentraciju NO2, SO2, PM2.5 i PM10 na splitskom području prema mjernim postajama Split-centar i Kaštel Sućurac. Za proučavanje su izdvojeni dani u kojima je obalna cirkulacija bila neporemećena. U izdvojenim danima polje tlaka zraka bilo je bezgradijentno. Posebno su istraženi čestina i brzina vjetra u takvim danima. Zmorac u Splitu ima SW smjer, a u Kaštel Sućurcu WSW i W. Koncentracije onečišćujućih tvari uspoređene su s brzinama vjetra. Najprisutnija onečišćujuća tvar je NO2. Najviše ga ima u večernjim i jutarnjim satima dok zmorac još nije razvio veću brzinu ili mu se brzina smanjuje približavanjem večernjeg zatišja. Što je brzina zmorca veća, koncentracija NO2 je manja. Nastupom zmorca povećava se koncentracija lebdećih čestica zbog turbulencije vjetra unutar grada te mogućeg donosa morskog aerosola i nusprodukata pomorskog prometa. NO2 dostiže veće vrijednosti u Splitu nego u Kaštel Sućurcu. Lebdeće čestice imaju veće koncentracije u Kaštel Sućurcu nego u Splitu. Vrijednosti svih onečišćujućih tvari ispod su graničnih vrijednosti za zdravlje ljudi.

Possible teleconnections between East and South Asian summer monsoon precipitation in projected future climate change

The present paper examined the teleconnections between two huge Asian summer monsoon components (South and East Asia) during three time slices in future: near-(2010–2039), mid-(2040–2069) and far-(2070–2100) futures under the RCP4.5 and RCP8.5 scenarios. For this purpose, a high-resolution atmospheric general circulation model is used and integrated at 40 km horizontal resolution. To get more insight into the relationships between the two Asian monsoon components, we have studied the spatial displaying correlation coefficients (CCs) pattern of precipitation over the entire Asian monsoon region with that of South Asia and three regions of East Asia (North China, Korea–Japan and Southern China) separately during the same three time slices. The possible factors responsible for these teleconnections are explored by using mean sea level pressure (MSLP) and wind fields at 850 hPa. The CC pattern of precipitation over South Asia shows an in-phase relationship with North China and an out-of-phase relationship with Korea–Japan, while precipitation variations over Korea–Japan and Southern China exhibit an out-of-phase relationship with South Asia. The CCs analysis between the two Asian blocks during different time slices shows the strongest CCs during the near and far future with the RCP8.5 scenario. The CC pattern of precipitation over Korea–Japan and Southern China with the wind (at 850 hPa) and MSLP fields indicate that the major parts of the moisture over Korea–Japan gets transported from the west Pacific along the western limb of NPSH, while the moisture over Southern China comes from the Bay of Bengal and South China Seas for good monsoon activity.

Seasonal and inter-annual variations of Arctic cyclones and their linkage with Arctic sea ice and atmospheric teleconnections

The seasonal and inter-annual variations of Arctic cyclone are investigated. An automatic cyclone tracking algorithm developed by University of Reading was applied on the basis of European Center for Medium-range Weather Forecasts (ECMWF) ERA-interim mean sea level pressure field with 6 h interval for 34 a period. The maximum number of the Arctic cyclones is counted in winter, and the minimum is in spring not in summer. About 50% of Arctic cyclones in summer generated from south of 70°N, moving into the Arctic. The number of Arctic cyclones has large inter-annual and seasonal variabilities, but no significant linear trend is detected for the period 1979–2012. The spatial distribution and linear trends of the Arctic cyclones track density show that the cyclone activity extent is the widest in summer with significant increasing trend in CRU (central Russia) subregion, and the largest track density is in winter with decreasing trend in the same subregion. The linear regressions between the cyclone track density and large-scale indices for the same period and pre-period sea ice area indices show that Arctic cyclone activities are closely linked to large-scale atmospheric circulations, such as Arctic Oscillation (AO), North Atlantic Oscillation (NAO) and Pacific-North American Pattern (PNA). Moreover, the pre-period sea ice area is significantly associated with the cyclone activities in some regions.

Spatio-temporal modelling of extreme wave heights in the Mediterranean Sea

This study reveals characteristics of the Mediterranean Seas wave climate by illustrating the results of a spatial assessment of extreme significant wave heights. The assessment was based on a 37-year wind and wave hindcast database covering the entire area at 10-km resolution. A point-wise GEV (Generalized Extreme Values) model was employed to generate the assessments results. Overall, the spatial model proved capable of providing an accurate description of extreme return levels of significant wave heights and their spatial variability, especially on a basin-wide scale and with greatest precision on the mesoscale. However, return level estimates are found less reliable in certain coastal areas because the traditional point-wise approach is not refined enough to address the entire wave spectrum of an area as complex as the Mediterranean Sea. Therefore, MSLP (Mean Sea Level Pressure) fields were incorporated as covariates to improve localized assessment. These covariates represent meteorological forcing and allow analysis of the role of different cyclonic regimes in defining wave features and their spatial variability. Finally, the broad temporal span and high spatial resolution of the hindcast database allow for EOF (Empirical Orthogonal Function) and CCA (Canonical Correlation Analysis) analysis of wind and waves fields. This analysis validates spatial wave distribution assessment, revealing that the main processes governing the Mediterranean Seas wave climate can be attributed to four main modes.