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This work aims to assess the performance of state-of-the-art global climate models in representing the upper-tropospheric Rossby wave pattern in the Northern Hemisphere and over the European–Atlantic sector. A diagnostic based on finite-amplitude local wave activity is used as an objective metric to quantify the amplitude of Rossby waves in terms of Rossby wave activity. This diagnostic framework is applied to a set of coupled historical climate simulations at different horizontal resolutions, performed in the framework of the PRIMAVERA project and compared with observations (ERA5 reanalysis). At first, the spatio-temporal characteristics of Rossby wave activity in the Northern Hemisphere are examined in the multimodel mean of the whole PRIMAVERA set. When examining the spatial distribution of transient wave activity, only a minimal improvement is found in the high-resolution ensemble. On the other hand, when examining the temporal variability of wave activity, a higher resolution is beneficial in all models apart from one. In addition, when examining the Rossby wave activity time series, no evident trends are found in the historical simulations (at both standard and high resolutions) and in the observations. Finally, the spatial distribution of Rossby wave activity is investigated in more detail focusing on the European–Atlantic sector, examining the wave activity pattern associated with weather regimes for each model. Results show a marked inter-model variability in representing the correct spatial distribution of Rossby wave activity associated with each regime pattern, and an increased horizontal resolution improves the models' performance only for some of the models and for some of the regimes. A positive impact of an increased horizontal resolution is found only for the models in which both the atmospheric and oceanic resolution is changed, whereas in the models in which only the atmospheric resolution is increased, a worsening model performance is detected.

Nares Strait is a major pathway along which multi-year sea ice leaves the Arctic, an ice class that has seen a recent dramatic reduction in extent. The winds that blow along the strait play an important role in modulating this ice export as well as in establishing the Arctic’s largest and most productive polynya, the North Water, that forms at its southern terminus. However, its remote location has limited our knowledge of the winds along the strait. Here we use automatic weather station data from Hans Island, in the middle of the strait, to assess the ability of a set of atmospheric renalyses and analyses with a common lineage but with varying horizontal resolution to represent the variability in the wind field. We find that the flow is highly bidirectional, consistent with topographic channeling, with the highest wind speeds from the north and that a model resolution of ~ 9 km is required to capture the observed variability. The wind field at Hans Island is also found to be representative of variability in the flow along much of Nares Strait.

We study the impact of horizontal resolution in setting the North Atlantic gyre circulation and representing the ocean–atmosphere interactions that modulate the low-frequency variability in the region. Simulations from five state-of-the-art climate models performed at standard and high-resolution as part of the High-Resolution Model Inter-comparison Project (HighResMIP) were analysed. In some models, the resolution is enhanced in the atmospheric and oceanic components whereas, in some other models, the resolution is increased only in the atmosphere. Enhancing the horizontal resolution from non-eddy to eddy-permitting ocean produces stronger barotropic mass transports inside the subpolar and subtropical gyres. The first mode of inter-annual variability is associated with the North Atlantic Oscillation (NAO) in all the cases. The rapid ocean response to it consists of a shift in the position of the inter-gyre zone and it is better captured by the non-eddy models. The delayed ocean response consists of an intensification of the subpolar gyre (SPG) after around 3 years of a positive phase of NAO and it is better represented by the eddy-permitting oceans. A lagged relationship between the intensity of the SPG and the Atlantic Meridional Overturning Circulation (AMOC) is stronger in the cases of the non-eddy ocean. Then, the SPG is more tightly coupled to the AMOC in low-resolution models.

A new monthly global sea level reconstruction for 1900–2015 was analyzed and compared with various observations to examine regional variability and trends in the ocean dynamics of the western North Atlantic Ocean and the US East Coast. Proxies of the Gulf Stream (GS) strength in the Mid-Atlantic Bight (GS-MAB) and in the South Atlantic Bight (GS-SAB) were derived from sea level differences across the GS. While decadal oscillations dominate the 116-year record, the analysis showed an unprecedented long period of weakening in the GS flow since the late 1990s. The only other period of long weakening in the record was during the 1960s–1970s, and red noise experiments showed that is very unlikely that those just occurred by chance. Ensemble empirical mode decomposition (EEMD) was used to separate oscillations at different timescales, showing that the low-frequency variability of the GS is connected to the Atlantic Multi-decadal Oscillation (AMO) and the Atlantic Meridional Overturning Circulation (AMOC). The recent weakening of the reconstructed GS-MAB was mostly influenced by weakening of the upper mid-ocean transport component of AMOC as observed by the RAPID measurements for 2005–2015. Comparison between the reconstructed sea level near the coast and tide gauge data for 1927–2015 showed that the reconstruction underestimated observed coastal sea level variability for timescales less than ∼5 years, but lower-frequency variability of coastal sea level was captured very well in both amplitude and phase by the reconstruction. Comparison between the GS-SAB proxy and the observed Florida Current transport for 1982–2015 also showed significant correlations for oscillations with periods longer than ∼5 years. The study demonstrated that despite the coarse horizontal resolution of the global reconstruction (1∘ × 1∘), long-term variations in regional dynamics can be captured quite well, thus making the data useful for studies of long-term variability in other regions as well.

This study investigates the spatial structure and the seasonal occurrence of foehn wind to the east of the Andes using a flow blocking analysis in a 20-year climate simulation. The latter was performed by the Eta-CPTEC regional model at 50-km horizontal resolution. This version of the model includes a cut-cell scheme to represent topography and a finite-volume vertical advection scheme for dynamic variables. The results indicate that foehn wind more frequently blows during winter and spring on the eastern slopes of the Andes, except to the south of 37° S where it blows at all seasons. Higher mountains of the Central Andes (27° S–35° S) and the High Plateau (15° S–27° S) result in blocked foehn events, with a weak adjustment to the geostrophic balance. On the Central Andes, rain and snow on mountain tops may also contribute to generate foehn wind on the eastern slopes. The results show that a low pressure develops to the east of the Central Andes, and also to the east of the High Plateau when foehn blows. Lower mountains in Patagonia (to the south of 37° S) result in more frequent non-blocked foehn event, with better adjustment to the geostrophic balance., Facultad de Ciencias Astronómicas y Geofísicas

A rapid retreat Are the rates at which we observe ice shelves shrinking today representative of how fast they shrank in the past? Dowdeswell et al. report observations of the Antarctic seafloor that reveal the presence of submarine grounding-zone wedges on the Larsen continental shelf (see the Perspective by Jakobsson). The authors interpret these ridges as being caused by the tidal rise and fall of the ice shelf at the grounding line, which squeezes the underlying sediments when it rests on the seafloor. From this, they calculated that ice shelf retreat at this location about 14,000 years ago was at times as much as 100 times as fast as the average over the past 10,000 years. Science , this issue p. 1020 ; see also p. 939

In our previous works, we presented a fundamentally new method for detecting underground rectilinear objects by means of georadars. To improve the lateral resolution of the proposed method, a variant of this method using two transmitting antennas fed in antiphase was proposed. In this letter, we extend the previous work and present a deeper analysis of this method. It is shown that using the proposed method, a significant increase in both the relative area reflectivity (RAR) of rectilinear objects and the lateral resolution in the detection of underground narrow objects can be achieved. Our calculations show that using this method, it is possible to achieve a high horizontal resolution of the order of 0.2 m at depths of 20–30 m. The dependencies of RAR on the object’s depth and width are calculated and presented. This method is applicable for both orthogonal and any other scanning scheme.

We compile and analyze all available geothermal heat flow measurements collected in and around Greenland into a new database of 419 sites and generate an accompanying spatial map. This database includes 290 sites previously reported by the International Heat Flow Commission (IHFC), for which we now standardize measurement and metadata quality. This database also includes 129 new sites, which have not been previously reported by the IHFC. These new sites consist of 88 offshore measurements and 41 onshore measurements, of which 24 are subglacial. We employ machine learning to synthesize these in situ measurements into a gridded geothermal heat flow model that is consistent across both continental and marine areas in and around Greenland. This model has a native horizontal resolution of 55 km. In comparison to five existing Greenland geothermal heat flow models, our model has the lowest mean geothermal heat flow for Greenland onshore areas. Our modeled heat flow in central North Greenland is highly sensitive to whether the NGRIP (North GReenland Ice core Project) elevated heat flow anomaly is included in the training dataset. Our model's most distinctive spatial feature is pronounced low geothermal heat flow (

A regional ocean model for Fram Strait provides a framework for interpretation of the variability and structure of acoustic tomography arrivals. The eddy-permitting model (52 vertical levels and 4.5 km horizontal resolution) was evaluated using long-term moored hydrography data and time series of depth-range averaged temperature obtained from the inversion of acoustic tomography measurements. Geometric ray modeling using the ocean model fields reproduces the measured arrival structure of the acoustic tomography experiment. The combination of ocean and acoustic models gives insights into acoustic propagation during winter and spring. Moreover, overlapping arrivals coming from different vertical angles can be resolved and explained. The overlapping arrival of purely refracted rays and surface-reflected/bottom-reflected (SRBR) rays has implications for the inversion of tomography data in Fram Strait. The increased knowledge about the ray-length variations of SRBR rays is valuable for choosing appropriate observation kernels for the data assimilation of acoustic tomography data in Fram Strait.

This work examines the effect of horizontal resolution and topography on the North American monsoon (NAM) in experiments with an atmospheric general circulation model. Observations are used to evaluate the fidelity of the representation of the monsoon in simulations from the Community Atmosphere Model version 5 (CAM5) with a standard 1.0° grid spacing and a high-resolution 0.25° grid spacing. The simulated monsoon has some realistic features, but both configurations also show precipitation biases. The default 1.0° grid spacing configuration simulates a monsoon with an annual cycle and intensity of precipitation within the observational range, but the monsoon begins and ends too gradually and does not reach far enough north. This study shows that the improved representation of topography in the high-resolution (0.25° grid spacing) configuration improves the regional circulation and therefore some aspects of the simulated monsoon compared to the 1.0° counterpart. At higher resolution, CAM5 simulates a stronger low pressure center over the American Southwest, with more realistic low-level wind flow than in the 1.0° configuration. As a result, the monsoon precipitation increases as does the amplitude of the annual cycle of precipitation. A moisture analysis sheds light on the monsoon dynamics, indicating that changes in the advection of enthalpy and moist static energy drive the differences between monsoon precipitation in CAM5 1.0° compared to the 0.25° configuration. Additional simulations confirm that these improvements are mainly due to the topographic influence on the low-level flow through the Gulf of California, and not only the increase in horizontal resolution.

There is growing evidence that the atmospheric dynamics of the Euro‐Atlantic sector during winter is driven in part by the presence of quasi‐persistent regimes. However, general circulation models typically struggle to simulate these with, for example, an overly weakly persistent blocking regime. Previous studies have showed that increased horizontal resolution can improve the regime structure of a model but have so far only considered a single model with only one ensemble member at each resolution, leaving open the possibility that this may be either coincidental or model dependent. We show that the improvement in regime structure due to increased resolution is robust across multiple models with multiple ensemble members. However, while the high‐resolution models have notably more tightly clustered data, other aspects of the regimes may not necessarily improve and are also subject to a large amount of sampling variability that typically requires at least three ensemble members to surmount., Key Points Climate models have difficulty representing Euro‐Atlantic regime structure correctlyIncreasing horizontal resolution improves the significance of regime clustering across multiple modelsSpatial patterns and persistence levels of regimes do not necessarily improve with increased resolution

Ground-penetrating radar (GPR) and the seismic surface wave method are two geophysical techniques commonly used in near-surface surveys up to a depth of tens of meters. GPR can be utilized to clearly distinguish lithologic interfaces, while the seismic surface wave method (hereby referred to as the Rayleigh wave) is employed for its high sensitivity to the shear (S) wave velocity. However, the propagation velocity of the electromagnetic (EM) wave which is both initiated and tracked by GPR is difficult to determine within the stratum. Unfortunately, this can affect the time–depth conversion and interpretation of the radargram. Moreover, both the horizontal resolution and the detectability of the properties of the shallow stratum are limited by the seismic geometry of the Rayleigh wave data. It is important to note that the non-uniqueness of geophysical inversion problem also generates additional biases. To overcome the problems mentioned above, we put forward an interactive integrated geophysical system that utilizes the thickness as a bridge to connect GPR and the Rayleigh wave data in the data processing and inversion. In this study, we employed the velocity of a radagram and the Rayleigh wave dispersion curve inversion based on a genetic algorithm to reconstruct the near-surface distribution. Then, we set the thickness derived from the GPR data as limit of the Rayleigh wave dispersion curve inversion. Hence, we applied the constrained inversion result to determine the most accurate EM wave velocity. As expected, both the constrained inversion of the Rayleigh wave dispersion curve and the velocity correction of the radargram performed better than did the geophysical method alone, both in the numerical models and in the field. Finally, we found the interactive integrated geophysical system to be more conducive for geological interpretation in near-surface surveys.

The influence of a high horizontal resolution (5–15 km) on the general circulation and hydrography in the North Atlantic is investigated using the Finite Element Sea Ice–Ocean Model (FESOM). We find a stronger shift of the upper-ocean circulation and water mass properties during the model spinup in the high-resolution model version compared to the low-resolution (~1°) control run. In quasi equilibrium, the high-resolution model is able to reduce typical low-resolution model biases. Especially, it exhibits a weaker salinification of the North Atlantic subpolar gyre and a reduced mixed layer depth in the Labrador Sea. However, during the spinup adjustment, we see that initially improved high-resolution features partially reduce over time: the strength of the Atlantic overturning and the path of the North Atlantic Current are not maintained, and hence hydrographic biases known from low-resolution ocean models return in the high-resolution quasi-equilibrium state. We identify long baroclinic Rossby waves as a potential cause for the strong upper-ocean adjustment of the high-resolution model and conclude that a high horizontal resolution improves the state of the modeled ocean but the model integration length should be chosen carefully.

Satellite observations of the last two decades have led to a major breakthrough emphasizing the existence of a strongly energetic mesoscale turbulent eddy field in all the oceans. This ocean mesoscale turbulence (OMT) is characterized by cyclonic and anticyclonic eddies (with a 100‐‐300 km size and depth scales of ~500‐‐1000 m) that capture approximatively 80% of the total kinetic energy and is now known to significantly impact the large‐scale ocean circulation, the ocean's carbon storage, the air‐sea interactions and therefore the Earth climate as a whole. However, OMT revealed by satellite observations has properties that differ from those related to classical geostrophic turbulence theories. In the last decade, a large number of theoretical and numerical studies has pointed to submesoscale surface fronts (1‐‐50 km, not resolved by satellite altimeters and not fully taken into account by geostrophic turbulence theories) as the key suspect explaining these discrepancies. Submesoscale surface fronts have been shown to impact mesoscale eddies and the large‐scale ocean circulation in counter‐intuitive ways, leading in particular to up‐gradient fluxes. The ocean engine is now known to involve energetic scale interactions, over a much broader range of scales than expected one decade ago, from 1 km to 5000 km. New space observations with higher spatial resolution are however needed to validate and improve these recent theoretical and numerical results.

This study attempted to demonstrate the skill of the regional ocean model system (ROMS) is simulating the hydrographic property of the Arabian Sea (AS). Additionally, the impact of horizontal resolution is investigated. In this regard, ROMS is integrated over AS covering [30˚E-80˚E; 5˚N-30N˚] at two different horizontal resolutions 1/6˚(~ 17km) and 1/4˚(~ 25km) for ten years. The comparison of model results with available observation and reanalysis indicates reasonable resemblances in reproducing the spatial-temporal distribution of surface and subsurface hydrographic property i.e. sea surface temperature (SST), sea surface salinity (SSS), sea surface currents, and subsurface temperature and salinity at both resolutions. The increasing resolution shows minimal improvement, indicating the fact that its not always guaranty to enhance the performance towards increasing resolution for every aspect.

Western boundary currents transport a large amount of heat from the Tropics toward higher latitudes; furthermore they are characterized by a strong sea surface temperature (SST) gradient. For such reasons they have been shown to be fundamental in influencing the climate of the Northern Hemisphere and its variability, and a potentially relevant source of atmospheric predictability. General circulation models show deficiencies in simulating the observed atmospheric response to SST front variability. The atmospheric horizontal resolution has been recently proposed as a key element in understanding such differences. However, a multi-model analysis to systematically investigate differences between low-resolution and high-resolution atmospheric response to oceanic forcing is still lacking. The present work has the objective to fill this gap, analysing the atmospheric response to Gulf Stream SST front (GSF) shifting using data from recent High Resolution Model Intercomparison Project (HighResMIP). Ensembles of historical simulations performed with three atmospheric general circulation models (AGCMs) have been analysed, each conducted with a low-resolution (LR, about 1°) and a high-resolution (HR, about 0.25°) configuration. AGCMs have been forced with observed SSTs (HadISST2 dataset), available at daily frequency on a 0.25° grid, during 1950–2014. Results show atmospheric responses to the SST-induced diabatic heating anomalies that are strongly resolution dependent. In LR simulations a low-pressure anomaly is present downstream of the SST anomaly, while the diabatic heating anomaly is mainly balanced by meridional advection of air coming from higher latitudes, as expected for an extra-tropical shallow heat source. In contrast, HR simulations generate a high-pressure anomaly downstream of the SST anomaly, thus driving positive temperature advection from lower latitudes (not balancing diabatic heating). Along the vertical direction, both in LR and HR simulation, the diabatic heating in the interior of the atmosphere is balanced by upward motion south of GS SST front and downward motion north and further south of the Gulf Stream. Finally, LR simulations show a reduction in storm-track activity over the North Atlantic, whereas HR simulations show a meridional displacement of the storm-track considerably larger (yet in the same direction) than that of the SST front. HR simulations reproduce the atmospheric response obtained from observations, albeit weaker. This is a hint for the existence of a positive feedback between ocean and atmosphere, as proposed in previous studies. These findings are qualitatively consistent with previous results in literature and, leveraging on recent coordinated modelling efforts, shed light on the effective role of atmospheric horizontal resolution in modelling the atmospheric response to extra-tropical oceanic forcing.

A high-resolution coupled ocean–sea ice model is set up within the Labrador Sea. With a horizontal resolution of 1∕60∘, this simulation is capable of resolving the multitude of eddies that transport heat and freshwater into the interior of the Labrador Sea. These fluxes strongly govern the overall stratification, deep convection, restratification, and production of Labrador Sea Water. Our regional configuration spans the full North Atlantic and Arctic; however, high resolution is only applied in smaller nested domains within the North Atlantic and Labrador Sea. Using nesting reduces computational costs and allows for a long simulation from 2002 to the near present. Three passive tracers are also included: Greenland runoff, Labrador Sea Water produced during convection, and Irminger Water that enters the Labrador Sea along Greenland. We describe the configuration setup and compare it against similarly forced lower-resolution simulations to better describe how horizontal resolution impacts the representation of the Labrador Sea in the model.

The results of numerical experiments on setting the NEMO model during its preparation for the assimilation of oceanographic data are presented. The modeling of ocean circulation and sea ice characteristics is performed with two different configurations of NEMO with a 1° horizontal resolution and with two versions of the sea ice model LIM2 and LIM3. The sensitivity of simulation results to the variations in the vertical resolution of the model grid and to the selection of the methods for describing ice processes is studied. It is shown that the increased vertical resolution and the calculations with several ice thickness gradations lead to a better agreement between model simulations and observations. The model configuration used for simulations with the corresponding setting parameters is suitable for its inclusion to the ocean data assimilation system.

Three-dimensional (3-D) resistivity surveys usually use a rectangular grid of electrodes to accurately resolve the subsurface structures in areas with very complex geology. However, in some survey areas such as heavily urbanized areas, it is not possible to use a normal grid of electrodes due to physical obstructions such as constructions, buildings, or other types of obstacle. The only practical arrangement is to use electrodes confined to the perimeter of the survey area. Many approaches have been proposed to investigate subsurface features for confined areas, such as the “Baker” and “L and Corner” arrays. These techniques normally use heuristic rules and are designed for perimeters with sharp corners such as rectangles, but might not be applicable for perimeters with smooth shapes such as a circle. New techniques that automatically select arrays that maximize the model resolution can be adapted to select optimum arrays for perimeters of any shape. We study the effectiveness of two sets of optimized perimeter arrays generated based on a modified “Compare R” (CR) method. The performance of these optimized perimeter arrays is compared with the standard “L and Corner” arrays. This is demonstrated by using two synthetic examples and one field survey dataset. In the synthetic models, the results show that, when using both the optimized and standard arrays, the vertical resolution is poorer than the horizontal resolution. However, the optimized perimeter arrays produce better resolution and structure detectability than “L and Corner” arrays. In addition, there is a slight improvement with the noise-weighted optimized dataset, which shows slightly higher resistivity contrasts and the lowest data misfits.

Spatial and seasonal variabilities of submesoscale currents in the northeastern South China Sea are investigated by employing a numerical simulation with a horizontal resolution of 1 km. The results suggest that submesoscale currents are widespread in the surface mixed layer mainly due to the mixed layer instabilities and frontogenesis. In horizontal, submesoscale currents are generally more active in the north than those in the south, since that active eddies, especially cyclonic eddies, mainly occur in the northern area. Specifically, submesoscale currents are highly intensified in the east of Dongsha Island and south of Taiwan Island. In temporal sense, submesoscale currents are more active in winter than those in summer, since the mixed layer is thicker and more unstable in the winter. The parameterization developed by Fox-Kemper et al. is examined in terms of vertical velocity, and the results suggest that it could reproduce the vertical velocity if mixed layer instability dominates there. This study improves our understanding of the submesoscale dynamics in the South China Sea.

International audience; The West Spitsbergen Current (WSC) cools and freshens as it flows northward along the western Svalbard shelf. The cooling takes place at the ocean surface through interaction with the atmosphere and also in subsurface. We present observations with high horizontal resolution (around 2 km)from a SeaExplorer glider deployed in July 2017 for 14 days in the WSC offshore Kongsfjorden around 79°N.They document small lenses (less than 10-km diameter) of cold (less than 3.8 °C) and fresh (less than35.2 g/kg) waters in the core of the WSC, coming from the shelf and contributing to its cooling and freshening. Data show that water from the shelf cascades to the bottom of the slope and then detaches on the offshore side of the WSC core where it is baroclinically unstable. The presence of these lenses from the shelf can be related to the wind regime. Strong southerly winds cause upwelling of the warm Atlantic Water onto the shelf in winter. Weak and/or northerly winds allow modified Atlantic Water formed by mixing with cold waters on the shelf to cascade down the slope, leading to lenses of colder and fresher water protruding into the WSC. If lenses are common in the WSC, they could be contributing significantly to its cooling and freshening especially in summer when the influence of the atmosphere on the cooling of the WSC is less important.

A three dimensional, regional coupled ice-ocean model based on the open-source Community Earth System Model has been developed and implemented for the Baltic Sea. The model consists of 66 vertical levels and has a horizontal resolution of approx. 2.3 km. The paper focuses on sea ice component results but the main changes have been introduced in the ocean part of the coupled model. The hydrodynamic part, being one of the most important components, has been also presented and validated. The ice model results were validated against the radar and satellite data, and the method of validation based on probability was introduced. In the last two decades satellite and model results show an increase in the ice extent over the whole Baltic Sea, which is an evidence of a negative trend in air temperature in recent decades and increasing of winter discharge from the catchment area.

Using a regional circulation model of the Baltic Sea with the horizontal resolution of 0.5 nautical miles and with an open western boundary, time series of bottom friction velocity and bottom salinity were simulated for the period of April 2010–July 2016 and analysed at specific points of interest along the inflow water pathway. The model reproduces reasonably well observations of the bottom currents and salinity at monitoring stations in the Bornholm and Gotland deeps. The bottom friction velocity at chemical warfare dumpsites in the Bornholm and Gotland basins was found to be permanently below the resuspension thresholds for the suspended particulate matter and fine sand, and even the Major inflows could not violate the balance. Occasionally the bottom friction velocity may exceed the resuspension threshold for the fine biogenic material (fluffy layer and cysts) almost everywhere in the deep Baltic basins, though additional studies are necessary to assess the likelihood of potential transport and dispersion of the chemical warfare by-products due to high sorption ability of the fine biogenic material.

Using the third generation WAVEWATCH III wave model in an unstructured formulation, and driven by HARMONIE-AROME mesoscale model hourly winds with a 2.5 km horizontal resolution, we reproduce the winter storms of 2013/2014 and analyse their effect on the western coastline of Ireland. WAVEWATCH III was forced at its ocean boundaries by directional wave spectra obtained from the ECMWF ERA-Interim re-analysis dataset. The wave model has a high resolution grid (up to 225 m resolution in the nearshore) with around 20 000 nodes, producing an abundance of important wave parameters outputted hourly, enabling a high quality, high-resolution analysis of the winter storms of 2013/2014.

Atmospheric circulation types, blockings, and cyclones are central features of the extratropical flow and key to understanding the climate system. This study intercompares the representation of these features in 10 reanalyses and in an ensemble of 30 climate model simulations between 1980 and 2005. Both modern, full-input reanalyses and century-long, surface-input reanalyses are examined. Modern full-input reanalyses agree well on key statistics of blockings, cyclones, and circulation types. However, the intensity and depth of cyclones vary among them. Reanalyses with higher horizontal resolution show higher cyclone center densities and more intense cyclones. For blockings, no strict relationship is found between frequency or intensity and horizontal resolution. Full-input reanalyses contain more intense blocking, compared to surface-input reanalyses. Circulation-type classifications over central Europe show that both versions of the Twentieth Century Reanalysis dataset contain more easterlies and fewer westerlies than any other reanalysis, owing to their high pressure bias over northeast Europe. The temporal correlation of annual circulation types over central Europe and blocking frequencies over the North Atlantic–European domain between reanalyses is high (around 0.8). The ensemble simulations capture the main characteristics of midlatitudinal atmospheric circulation. Circulation types of westerlies to northerlies over central Europe are overrepresented. There are too few blockings in the higher latitudes and an excess of cyclones in the midlatitudes. Other characteristics, such as blocking amplitude and cyclone intensity, are realistically represented, making the ensemble simulations a rich dataset to assess changes in climate variability.

A set of idealized experiments are developed using the Community Atmosphere Model (CAM) to understand the vertical velocity response to reductions in forcing scale that is known to occur when the horizontal resolution of the model is increased. The test consists of a set of rising bubble experiments, in which the horizontal radius of the bubble and the model grid spacing are simultaneously reduced. The test is performed with moisture, through incorporating moist physics routines of varying complexity, although convection schemes are not considered. Results confirm that the vertical velocity in CAM is to first‐order, proportional to the inverse of the horizontal forcing scale, which is consistent with a scale analysis of the dry equations of motion. In contrast, experiments in which the coupling time step between the moist physics routines and the dynamical core (i.e., the “physics” time step) are relaxed back to more conventional values results in severely damped vertical motion at high resolution, degrading the scaling. A set of aqua‐planet simulations using different physics time steps are found to be consistent with the results of the idealized experiments.

Karimata Strait located between Kalimantan and Bangka Islands, while Gaspar Strait located between Bangka and Belitung Islands. Volume transport variations through Karimata and Gaspar Straits during 2010-2014 were studied using three-dimensional numerical model of HAMburg Shelf Ocean Model (HAMSOM). Simulated area is located in 1°0′0′′N - 4°30′0′′N and 104°0′15′′E - 110°30′0′′E with a horizontal resolution of 0.5′ (about 0.94 km). The correlations value of current velocity from model with observation is quite high i.e. 0.85 for zonal component (u) and 0.89 for meridional (v) with 95% of significance level. The results of signal analysis showed that the volume transport is strongly influenced by the seasonal period. In addition to seasonal wind, there was also weak and medium phase of El Niño and La Niña during 2010 - 2014 that affected volume transport. The average volume transport from 2010-2014 through Karimata and Gaspar Straits are -2.75 Sv and -1.98 Sv, respectively (1 Sv = 106 m3/s). The negative value shows the southward volume transport, while positive to north. Total transport to south indicates that there are may be due to parts of Indonesia Through Flow (ITF) flow through South China Sea, Karimata Strait, and Gaspar Strait to the Java Sea.Keywords: volume transport, Karimata Strait, Gaspar Strait

Mixed Layer Depths (MLDs) diagnosed by conventional numerical models are generally based on a density difference with the surface (e.g., 0.01 kg.m − 3 ). However, the temperature-salinity compensation and the lack of vertical resolution contribute to over-estimated MLD, especially in regions of deep convection. In the present work, we examined the diagnostic MLD, associated with the deep convection of the Labrador Sea Water (LSW), calculated with a simple density difference criterion. The over-estimated MLD led us to develop a new tool, based on an observational approach, to recalculate MLD from model output. We used an eddy-permitting, 1/12° regional configuration of the Nucleus for European Modelling of the Ocean (NEMO) to test and discuss our newly defined MLD. We compared our new MLD with that from observations, and we showed a major improvement with our new algorithm. To show the new MLD is not dependent on a single model and its horizontal resolution, we extended our analysis to include 1/4° eddy-permitting simulations, and simulations using the Modular Ocean Model (MOM) model.

Synoptic monthly gridded (SMG) world ocean temperature (T) and salinity (S) fields with (1° × 1°) horizontal resolution and 28 standard vertical levels from the ocean surface to 3000 m deep have been established from the observational (T, S) profiles from the NOAA National Centers for Environmental Information (NCEI) World Ocean Database (WOD) from January 1945 to December 2014 and the Global Temperature and Salinity Profile Programme (GTSPP) from January 1990 to December 2009 using the optimal spectral decomposition (OSD) method. The world ocean abstract geostrophic currents (u, v) are calculated from the 4D SMG-WOD and SMG-GTSPP (T, S) data using the P-vector inverse method. The SMG-WOD (T, S, u, v) and SMG-GTSPP (T, S, u, v) fields with a higher horizontal resolution (0.25° × 0.25°) have also been produced for the Mediterranean Sea, the Japan/East Sea, and the Gulf of Mexico.

The multichannel analysis of surface wave (MASW) method has been effectively and widely used to determine near-surface shear-wave velocity. Horizontal resolution of the MASW method represents the minimum horizontal length of recognizable geologic anomalous bodies on a pseudo-2D S-wave velocity [Formula: see text] section. Accurately assessing the achievable lateral resolution is one of the main issues in lateral variation reconstruction using the MASW method. It is difficult to quantitatively estimate the horizontal resolution of the MASW method because of the many influencing factors, such as parameters of the observation system, the depth of an anomalous body, and the velocity contrast between the anomalous body and the surrounding rocks. We first analyzed the horizontal resolution of the MASW method based on numerical simulation experiments. According to different influencing factors of the horizontal resolution, we established different laterally heterogeneous models and observation systems and then simulated several synthetic multichannel records with a finite-difference method along a linear survey line using the roll-along acquisition mode. After the extraction of dispersion curves of Rayleigh waves and inversion for S-wave velocity profiles for each synthetic shot gather, a pseudo-2D S-wave velocity section can be generated by aligning the 1D S-wave velocity models. Ultimately, we evaluated the horizontal resolution capability of the MASW method on pseudo-2D [Formula: see text] maps. Our numerical investigation results and field data analysis indicate that [Formula: see text] values on the maps are not the same as the true [Formula: see text] values for structures whose lateral dimension is shorter than a receiver spread length and that anomalous bodies, which are larger and have high velocity contrast, are easier to distinguish on [Formula: see text] maps with a shorter receiver spread length. The horizontal resolution decreases with the increasing depth and is approximately one-half of the shortest Rayleigh wavelength that can penetrate to the depth.

This study evaluated tropical cyclone (TC) activity simulated by two regional climate models (RCMs) incorporated in the Coordinated Regional Climate Downscaling Experiment (CORDEX) framework with two different horizontal resolutions. Evaluation experiments with two RCMs (RegCM4 and MM5) forced by reanalysis data were conducted over the CORDEX-East Asia domain with 25 km and 50 km horizontal resolutions. The 20-year (1989–2008) mean performances of the experiments were investigated in terms of TC genesis, track, intensity, and TC-induced precipitation. In general, the simulated TC activities over the western North Pacific (WNP) varied depending on the model type and horizontal resolution. The MM5 tended to simulate more reasonable TC activity compared with the RegCM4. For both models, higher horizontal resolution improved the simulation of TC tracks near the coastal regions of East Asia, whereas the coarse horizontal resolution led to underestimated TC genesis compared with the best track data because of greater convective precipitation and enhanced atmospheric stabilization. In addition, the increased horizontal resolution prominently improved the simulation of TCs landfalling in East Asia and associated precipitation around coastal regions. This finding implies that high-resolution RCMs can produce added value in improving the simulation of TCs over the WNP; thus, they have an advantage in climate change assessment studies.

In this study, we produced grid climate data sets of 1km×1km and 5km×5km horizontal resolutions based on MK (Modified Korean)-PRISM (Parameter-elevation Regressions on Independent Slopes Model), a statistical method that can estimate grid data of horizontal high-resolution using observational station data in Korea. To compare the MK-PRISM performance according to resolution, RMSEs of 1km resolution data and 5km resolution data were calculated and analyzed. The RMSEs of the two data sets were similar, but the results classified according to the elevation were different. The 1km high resolution estimated data was shown to better reflect the impact of the terrain for the daily mean temperature and daily maximum temperature, whereas the difference between the two data sets for daily minimum temperature was not statistically significant at each elevation. Furthermore, we also divided the temperature data into 9-classes based on the observed temperatures, and then compared the estimated performance of the two data sets according to elevation. For the low temperature group, performance of the 1 km resolution data at high elevations outperformed that of the 5 km resolution data, regardless of the season. In addition, we have verified the improved PRIDE (PRism based Dynamic downscaling Error correction) model, which can produce future high-resolution scenarios data using the results of RCM and MK-PRISM.

The authors implemented the Regional Ocean Modelling System (ROMS) to coastal waters on the west coast of Ireland. The Connemara model has c.200 m horizontal resolution and has 20 vertical sigma le...

Purpose. The study addresses rotational motion of geophysical fluids in the horizontal and vertical planes. It is aimed mainly at tracing the development of high-resolution numerical modeling of the ocean, as well as at demonstrating new physical processes due to more correct consideration both of the tides in the eddy-resolving numerical models and sub-mesoscale dynamics in the models of the sea straits. Methods and Results. The ocean eddies and their interaction with tides are studied using numerical simulations by four NEMO models for the European North-West shelf with the resolutions ranging from 7 to 1.5 km. The vertical characteristics of motion in the Bosporus Strait were studied using numerical simulations with SCHISM , the unstructured grid model with the ultra-fine model resolution (less than 100 m). The barotropic tidal forcing resulted in substantial flattening of the slopes of the spectral curves. The most important difference between the spectral featurws of four models occurs in the motion rotational component. In the model with the 1.5 km resolution, the magnitude of the vorticity power spectral density at the scales ~70 km is by an order of magnitude higher than in the other three models. Although most of the tidal flattening is associated with the internal tides, beyond a certain horizontal resolution, the eddy dynamics become affected by the barotropic tides. The shelf of the Biscay Bay and the shallows around the Faroe Islands are the most sensitive areas to adding of the barotropic tides to the model forcing. Due to the grid ultra-fine resolution, new elements of physical motion emerged in the Bosporus region. The lateral circulation is dominated by the systems of multiple circulation cells with the scales ~ 1 km. In some areas, the lateral flow magnitude exceeds 0.5 m/s, which is comparable with the magnitude of the axial flow. This reveals importance of the helical elements of the strait circulation for overturning of water masses in the Bosporus. Conclusions. Without proper resolution, the models of tidal oceanic dynamics simulate the ocean general circulation, but do not describe correctly the energy cascades at the eddy scales including interaction between the tides and the mesoscale eddies. Absence of this sub-mesoscale dynamics in the models can largely affect their capability to simulate the two-layer inter-basin exchange.

Inevitable drawbacks occur when the Asian monsoon is simulated at a horizontal resolution that is too low to resolve topographic effects and sub-grid processes. By comparing the Coupled Model Intercomparison Project (CMIP) phase 5 simulations conducted at higher (∼1°) and lower (∼3°) horizontal resolutions, this study attempted to extend understanding of potential resolution limits in simulating the East Asian presummer climate. April–May is found to have considerable resolution-dependent contrasts in position and strength of precipitation (spring rains and pre–Meiyu) among the simulations. The low-resolution models cannot simulate ascending vertical motion over the mountainous regions in the southern Tibetan Plateau and subtropical East Asia, which coincides with the overestimation of the strength of the lower-tropospheric westerly in 90°–105°E and of the downstream southerly in 110°–130°E. Because of the southerly wind bias, the East Asian presummer precipitation simulated in the low-resolution models is lower in amount and located farther north compared with the observed and high-resolution models. Despite distinct large-scale climatology between April and late May, the East Asian precipitation contrasts in these two periods are similar between the high- and low-resolution models, which could be possibly explained as a systematic response to resolution. Systematically less precipitation in the high-resolution model compared with the low-resolution model is also observable over the Maritime Continent, whereas a further connection to the East Asian precipitation simulation remains unclear. Regarding projected changes, the resolution-dependent contrasts are also considerable; the contrasts further suggest potential regional interactions such as between the subtropical South and East Asia (10°–20°N).

Analyses of 1-min data from automatic weather stations (AWSs) in the Gulf of Carpentaria region are used to study southerly nocturnal bores over northeastern Australia. The data cover the time period 1 August to 31 December in the three years 2012-2014. A total of 12 days on which a bore passed over the region of interest were found. Ten of the disturbances occurred between August and mid-October in the presence of synoptic-scale ridging across the continent behind a frontal trough. The other two occurred in early November in the presence of localized ridging behind an inland trough separate from a frontal trough. Six of the bores were followed some hours later by a clear air mass change. Four of the 12 cases are examined in detail wherein interpretations of the AWS data are aided by analysis fields from the European Centre for Medium-range Weather Forecasts (ECMWF). The results indicate that the longevity of the bore is related to the time of day that the cold front interacts with the stable maritime layer to the north of it. The ECMWF analyses are able to capture the frontal troughs as well as the timing of their passage through the AWS network. In the analyses, the troughs are seen as narrow strips of elevated cyclonic vorticity at 950 mb. Vertical cross-sections intersecting the troughs showed structural characteristics of a shallow cold front, but the horizontal resolution of the analyses is inadequate to capture the generation of bores ahead of the fronts.

A recently published method of automatically finding magnetic depths to magnetic layers is demonstrated, finding depths to significant details in the magnetic basement under Melville Island, Northern Territory.By using a method that simulates a magnetic basement as a series of layers of random dipoles, the depths to basement are satisfactorily obtained. Multiple layers appear in the results. However the inversion method used has coarse horizontal resolution, and the layers may be separated horizontally within the sample.To resolve the ambiguity a forward model, also composed of layers of dipoles, is built on the information obtained from the inversions. Forward modelling requires Fourier convolution for speed. The cycle of analysis is logically completed by comparing the synthetic depth profile with the depth profile obtained by inverting the survey data.

Rainfall-triggered landslides have posed significant threats to human lives and property each year in China. This paper proposed a meteorological-geotechnical early warning system GRAPES-LFM (GRAPES: Global and Regional Assimilation and PrEdiction System; LFM: Landslide Forecast Model), basing on the GRAPES model and the landslide predicting model TRIGRS (Transient Rainfall Infiltration and Grid-based Regional Slope-Stability Model) for predicting rainfall-triggered landslides. This integrated system is evaluated in Dehua County, Fujian Province, where typhoon Bilis triggered widespread landslides in July 2006. The GRAPES model runs in 5 km×5 km horizontal resolution, and the initial fields and lateral boundaries are provided by NCEP (National Centers for Environmental Prediction) FNL (Final) Operational Global Analysis data. Quantitative precipitation forecasting products of the GRAPES model are downscaled to 25 m×25 m horizontal resolution by bilinear interpolation to drive the TRIGRS model. Results show that the observed areas locate in the high risk areas, and the GRAPES-LFM model could capture about 74% of the historical landslides with the rainfall intense 30mm/h. Meanwhile, this paper illustrates the relationship between the factor of safety (FS) and different rainfall patterns. GRAPES-LFM model enables us to further develop a regional, early warning dynamic prediction tool of rainfall-induced landslides.

A new version of the ocean data assimilation system (ODAS) developed at the Hydrometcentre of Russia is presented. The assimilation is performed following the sequential scheme analysis–forecast–analysis. The main components of the ODAS are procedures for operational observation data processing, a variational analysis scheme, and an ocean general circulation model used to estimate the first guess fields involved in the analysis. In situ observations of temperature and salinity in the upper 1400-m ocean layer obtained from various observational platforms are used as input data. In the new ODAS version, the horizontal resolution of the assimilating model and of the output products is increased, the previous 2D-Var analysis scheme is replaced by a more general 3D-Var scheme, and a more flexible incremental analysis updating procedure is introduced to correct the model calculations. A reanalysis of the main World Ocean hydrophysical fields over the 2005–2015 period has been performed using the updated ODAS. The reanalysis results are compared with data from independent sources.

Operational statistics for the Spray underwater glider are presented to demonstrate capabilities for sustained observations. An underwater glider is an autonomous device that profiles vertically by changing buoyancy and flies horizontally on wings. The focus has been on sustained observations of boundary currents to take advantage of the glider’s small size, which allows it to be deployed and recovered from small vessels close to land, and the fine horizontal resolution delivered by the glider, which is scientifically desirable in boundary regions. Since 2004, Spray underwater gliders have been deployed for over 28 000 days, traveling over 560 000 km, and delivering over 190 000 profiles. More than 10 gliders, on average, have been in the water since 2012. Statistics are given in the form of histograms for 297 completed glider missions of longer than 5 days. The statistics include mission duration, number of dives, distance over ground, and horizontal and vertical distance through water. A discussion of problems, losses, and short missions includes a survival analysis. The most extensive work was conducted in the California Current system, where observations on three across-shorelines have been sustained, with 97% coverage since 2009. While the authors have certain advantages as developers and builders of the Spray underwater glider and Spray may have design and construction advantages, they believe these statistics are a sound basis for optimism about the widespread future of gliders in oceanographic observing.

Present work elucidates the impact of 3DVAR data assimilation technique for the simulation of one of the heavy rainfall events reported over Kotdwara region in the North-West Himalayan (NWH) region on 4th August 2017. We have examined the impact of conventional and satellite-based radiance datasets on the simulated results with and without assimilating the observations into the Weather Research and Forecasting (WRF) model. Three experiments have been designed with 3 nested domains of variable resolutions, one without assimilation (referred as control experiment) and other two experiments after assimilating conventional and satellite radiances observations (refer as DA-OBS and DA-SAT respectively). In the present study, assimilation of surface, upper air and the satellite-based radiance observations has been carried out for the outermost domain with horizontal resolution of 9 km. Statistical analysis suggests that the correlation coefficient is high (0.55) and root mean square error (RMSE) is low (17.12) for DA-SAT experiment as compared to other two experiments. Substantial improvement in the location, pattern and intensity of extreme rainfall event is noted after assimilation of both conventional and satellite observations with respect to the observed rainfall data. However, it is noted that the assimilation of satellite radiances has greater impact in simulating better intensity of the heavy rainfall event as compared to the assimilation of conventional observations. Plausible reason behind this could be the non-availability of the conventional observations close to the extreme rainfall event affected region.

This study analyses the distribution of ocean wind waves in response to extratropical cyclones over the western Mediterranean Sea. To this end we use an ERA40-based database of atmospheric cyclones and a 3-hourly wind wave hindcast with high horizontal resolution (1/6°) based on an ERA40 downscaled forcing for the region of study. The imprint of winds on surface waves is evaluated through composites of modelled significant wave height, surface wind and wave peak period collocated under the storms. Results highlight an asymmetric pattern that depends on the translational speed and size of the cyclonic perturbations. Uncertainties of the composites are at most 10% at 95% confidence interval, with an average maximum perturbation of significant wave height near 2 m for those cyclones moving faster than 10 m/s., This work was partially supported by the Research Project CLIMPACT (CGL201454246‐C21‐R, AEI/FEDER, UE) funded by the Spanish Ministry of Economy. T.T. is grateful to the Région Bretagne JALI supporting grant. J.M.S. is hired under the The Netherlands Organization for Scientific Research (NWO) VIDI Grant No. 397 864.13.011. G.J. acknowledges a Ramón y Cajal contract (RYC‐2013‐14714) funded by the Spanish Ministry of Economy and the Regional Government of the Balearic Islands.

The currents of the northern shelf of the Yellow Sea are investigated using observations of current and hydrography and numerical current model results. The Regional Ocean Model System (ROMS) with a horizontal resolution about 1km is implemented for the Yellow Sea and the Bohai Sea, and the results are produced for the year 2014 and 2015. Observations from bottom moored ADCP profilers and CTD on the northern shelf of the Yellow Sea are used for validation of the model. The comparison of current time series and bottom temperature evolution show good agreement between model and observation. Barotropic tides are the dominant current component throughout the year on the shelf and consistently mixing the water column in the shallower parts. A thermal front and associated jet exists during the summer creating a robust current structure on the western part of the shelf. The winds in the region are changing constantly creating episodic currents in the upper part of the sea lasting from hours to a couple of days. publishedVersion

To date, seasonal forecasts are often performed by applying horizontal resolutions of 75–150 km due to lack of computational resources and associated operational constraints. As this resolution is too coarse to represent fine scale structures impacting the large scale circulation, a convection permitting (CP) resolution of less than 4 km horizontal resolution is required. Most of the simulations are carried out as limited area model (LAMs) and thus require boundary conditions at all four domain boundaries. In this study, the Weather Research and Forecasting (WRF) model is applied in a latitude belt set-up in order to avoid the application of zonal boundaries. The horizontal resolution is 0.03\(^{\circ }\) and 0.45\(^{\circ }\) spanning a belt between 65\(^{\circ }\)N and 57\(^{\circ }\)S encompassing 12000 * 4060 * 57 grid boxes for the high-resolution domain. The simulations are driven by ECMWF analysis and high resolution SST data from multiple sources. The simulation period was February 1st–July 1st, 2015 which was a strong El Nino period.

We created a new, 100 m horizontal resolution bathymetry raster and used it to define 29 canyons of the eastern Bering Sea (EBS) slope area off of Alaska, USA. To create this bathymetry surface we proofed, edited, and digitized 18 million soundings from over 200 individual sources. Despite the vast size (~1250 km long by ~3000 m high) and ecological significance of the EBS slope, there have been few hydrographic-quality charting cruises conducted in this area, so we relied mostly on uncalibrated underway files from cruises of convenience. The lack of hydrographic quality surveys, anecdotal reports of features such as pinnacles, and reliance on satellite altimetry data has created confusion in previous bathymetric compilations about the details along the slope, such as the shape and location of canyons along the edge of the slope, and hills and valleys on the adjacent shelf area. A better model of the EBS slope will be useful for geologists, oceanographers, and biologists studying the seafloor geomorphology and the unusually high productivity along this poorly understood seafloor feature.