Explore the vast range of titles available.

A new eddy-permitting ocean reanalysis has been recently completed at ECMWF. It is called Ocean ReAnalysis Pilot 5 (ORAP5), and it spans the period 1979–2012. This work describes the new system, evaluates its performance, and investigates how the estimation of climate indices are affected by the assimilation system settings. ORAP5 introduces several upgrades with respect to its predecessor ORAS4, including increased horizontal and vertical resolution, an prognostic sea-ice component, new versions of the ocean and data assimilation system, revised surface fluxes, new version and treatment of satellite sea surface height data, and assimilation of sea-ice concentration, among others. ORAP5 shows similar performance to ORAS4, with improvements in the northern extratropics (especially in salinity), and slight degradation in the Southern Ocean, probably because the observations are insufficient to constrain the increased level of variability in ORAP5. The sensitivity experiments show that superobbing of altimeter data and correlation length-scales of the background errors have a visible impact on the time evolution of global steric height and its partition into thermo/halo-steric contributions. The sensitivities are especially large in the pre-Argo period, when there is the risk of producing unrealistic steric height variations by overfitting the altimeter data. Compared with a control run without data assimilation, all the assimilation experiments also show stronger variability in the halosteric component in the pre-Argo period. The results highlight the importance of sub-surface observations to assist the assimilation of altimeter data, and the need of using a variety of metrics for evaluating ocean reanalysis systems.

Understanding historical and projected coastal sea-level change is limited because the impact of large-scale ocean dynamics is not well constrained. Here, we use a global set of tide-gauge records over nine regions to analyse the relationship between coastal sea-level variability and open-ocean steric height, related to density fluctuations. Interannual-to-decadal sea-level variability follows open-ocean steric height variations along many coastlines. We extract their common modes of variability and reconstruct coastal sterodynamic sea level, which is due to ocean density and circulation changes, based on steric height observations. Our reconstruction, tested in Earth system models, explains up to 91% of coastal sea-level variability. Combined with barystatic components related to ocean mass change and vertical land motion, the reconstruction also permits closure of the coastal sea-level budget since 1960. We find ocean circulation has dominated coastal sea-level budgets over the past six decades, reinforcing its importance in near-term predictions and coastal planning.Coastal sea levels are impacted by local vertical land motion plus local and remote changes to ocean circulation, density and mass changes. Tide-gauge records are used to reconstruct the coastal sea-level budget over nine regions, showing its variability has been dominated by ocean circulation since 1960.

Observations from Coastal Data Information Program (CDIP) moored buoys off the coast of Florida reveal tidally driven wave–current interactions that modify significant wave heights by up to 25% and shift peak periods by up to a second. A case study at Fernandina Beach, Florida, shows surface waves steepening on following tidal currents and becoming less steep on opposing tidal currents, with the largest modulations occurring in the long-period swell band. To better understand tidal modulations as a function of the phase of the tide, we use simplified analytical and numerical solutions to the equations of geometrical optics and conservation of wave action under the assumption of a one-dimensional tide acting as a progressive shallow-water wave. The theoretical frameworks allow us to identify parameters that characterize the magnitude of variation in surface waves due to tidally induced currents and changes in water depth. We compute modulations to the omnidirectional and directional wave spectrum (between 0.05 and 0.15 Hz), as well as characteristic bulk parameters such as significant wave height and peak period. The theory is corroborated using directional wave and surface current observations from the Fernandina Beach CDIP station (located in water of average depth of 16 m). We find that the numerical results reproduce the observed wave modulations due to tidal currents and changes in water depth. Specifically, surface waves traveling in the direction of the tide are strongly modulated, and the relative speeds between the tide and surface waves set the sign and magnitude of these modulations. Given knowledge of tidal currents, water-depth variations, and wave climatology, theoretical and numerical predictions may be used to provide both statistical and instantaneous estimates of wave-height variations due to tides. Because operational forecasts and nowcasts do not routinely include tides or currents, these findings can help to accurately represent nearshore surface wave variability.

We used the tropospheric and lower stratospheric 3D winds for four consecutive years (2017–2020) to study the momentum flux (MF) and vertical wind power spectra (VWP) over Andøya, Norway (69.30°N, 16.04°E) using the Middle Atmosphere Alomar Radar System. The spectra range from 3.5 days−1 > f > 30 min−1, which are categorized in terms of observed/ground‐based frequency (as the local inertial period is 13 h over Andøya), height ranges, and seasons. Our results indicate for the first time that (a) both the zonal and meridional MF display peaks around the inertial period (13 h) in the troposphere (1.80–12.00 km) during all seasons (with some exceptions), while VWP exhibits such features in the whole height range (1.80–18.00 km), (b) the minimum variability in MF, VWP, and kinetic energy is observed during summer, and (c) both the MF and VWP demonstrate height variation with maximum deviations below the tropopause. Plain Language Summary The wind measurements are used to study the height and seasonal variation of momentum flux and vertical wind power spectra during 2017–2020. We report for the first time that both the momentum flux and vertical wind power spectra depict more variations in the tropospheric heights (around 1.80–7.20 km), below the tropopause, with the minimum amplitudes in the summer months (June–July–August). Moreover, long‐period oscillations have more energy than short‐period oscillations, and therefore, contribute more to the energy or flux transfer from the lower to the higher atmosphere. The month versus height profile of kinetic energy also portrays a similar feature with considerably more magnitude for the long‐period oscillations than the short‐period ones. The kinetic energy displays an enhancement of magnitude near the tropopause (∼5.00–10.00 km). Key Points The zonal and meridional momentum flux spectra exhibit a peak around the inertial period of 13 h in the troposphere (1.80–12.00 km) Height profiles of momentum flux, vertical wind power spectra, and kinetic energy display seasonal variation with a minimum during summer The maximum variability of momentum flux and vertical wind power spectra is noticed below tropopause and decreases with increasing height

We revisit the classical problem of the behaviour of the wind in the steady atmospheric Ekman layer. We show, for general variable eddy viscosities, that in the Northern Hemisphere the time-averaged ageostrophic wind profile always decays in magnitude and turns clockwise with increasing height. This general result is new; all previous work is based on a few explicit, special examples. As part of the development, we present two ways of formulating the problem, one of which is a novel approach (making use of a transformation to polar coordinates) that helps to explain the complex nature of these flows. The two formulations are supported by several examples that show, for instance, how the deflection angle can be other than the familiar \\[45^\\circ \\]. These results can be used as the basis for testing, and developing, various models for the height variation of eddy viscosity.

The evolution of the atmospheric boundary layer (ABL) varies greatly with terrain, so that the spatial and temporal variabilities of the ABL height remain poorly understood over complex terrain. Using radar wind-profiler measurements obtained from rural mountainous (Yanqing) and adjoining urban-plain (Haidian) landscapes of Beijing, China in 2019, ABL heights are calculated based on a normalized signal-to-noise-ratio threshold. The seasonally contrasting features of ABL height variation and growth rate over the two sites are revealed for clear-sky conditions. Interestingly, the ABL in spring remains suppressed during the morning and evolves rapidly in the afternoon over Haidian; however, a usual diurnal ABL evolution is observed over Yanqing. During the winter, more rapid evolution of the ABL is observed over Haidian, although on average the daytime ABL height remains less than 800 m above ground level. The growth rate of ABL height is found to undergo a more pronounced seasonal variation over Haidian while being relatively less variable over Yanqing. As expected, the lowest (highest) growth rate of 90 m h−1 (188 m h−1) occurs in winter (summer) over Haidian. The analysis of the seasonal variations in wind profiles reveals deeper insights into the development of the local plain-to-mountain flow circulation over the region and possible implications on the contrasting seasonal ABL variations, particularly during the spring and summer. Additionally, the slower ABL evolution over Haidian in autumn and winter could be associated with an aerosol-induced stable ABL as well as stronger urban heat accumulation. The findings have implications for the better understanding of air pollution meteorology in regions with mountainous terrain.

Understanding the thermal comfort and safety of diverse populations within indoor settings requires a quantitative understanding of the primary heat exchange pathways between occupants and their surroundings: radiation and free convection. Thus far, however, free convective heat transfer coefficients have only been determined for the average Western adult. To this end, we investigated how variation in body shape impacts free convection heat transfer using an experimentally validated numerical model. The multiphysics model was compared against experiments conducted using the thermal manikin ANDI (\"Advanced Newton Dynamic Instrument\") in a climate-controlled enclosure across five air-to-skin temperature differences ranging from 4.9 to 13.9°C. The difference between measured and simulated heat fluxes for the whole body, and per anatomical region, was typically <5%, occasionally reaching 15–20%, for some body regions due to physical features not modeled in the virtual ANDI model. Using the validated model, we simulated free convection around a family, or diverse group, of virtual manikins representing the 1 st to 99 th percentile body mass index (BMI) and height variation in the United States adult population. Our results show that the free convection heat transfer coefficient is independent of human sex and height but decreases slightly with increased BMI. However, the variation from the average manikin in the whole body and regional free convection coefficients with BMI was small, not exceeding 8% and 16%, respectively. Furthermore, our regression coefficients and exponents can be derived from the theorical correlation for free turbulent convection from a vertical plate, which also explains the observed independence of the heat transfer coefficient from the manikins’ height. Overall, these findings demonstrate the general applicability of using an average body shape in indoor thermal audits and/or overheating risk assessments to understand thermal comfort and heat stress. The results and valid application of the model support critical insights for human health, productivity, and well-being connected to heat and cooling in buildings.

In recent years, with daily progress in technology, application of wind turbines for energy generation has become common all around the world. Installation of these turbines at sea encountered a great deal of challenge. One of the most important challenges is scouring around the piles of these turbines due to sea waves and current interaction. Many studies have been conducted in this respect; however, the results are insufficient, and the phenomenon remains poorly understood in tripod wind turbines. In this work, an attempt is made by combining the waves and currents, and changing the substructure of the turbine and the type of the bed materials, to extend the investigation of this phenomenon. The current research is focused on presenting the trend of changes in the amount of scouring. By changing the conditions (including variation in the wave height, variation of the current velocity, variation of the pile diameter, and variation in the size of bed particles), one can arrive at an appropriate estimate and prediction of the shape and the depth of the scour pit.

Estimates of trends in planetary boundary layer height over Europe are presented, based on daily radiosonde observations at 25 stations during 1973–2010 and using a bulk Richardson number approach to determine heights. Most stations show statistically significant increases in daytime heights in all four seasons, but fewer show statistically significant trends in nighttime heights. Daytime height variations show an expected strong negative correlation with surface relative humidity and strong positive correlation with surface temperature at most stations studied, on both year-to-year and day-to-day time scales. Similar relations hold for long-term trends: increasing daytime boundary layer height is associated with decreasing surface relative humidity and increasing surface temperature atmost stations. The extent towhich these changes are regionally representative or local reflections of environmental changes near the observing stations is difficult to ascertain.

Geophysical sensing in the open ocean is both costly and technically challenging. Here we developed a novel distributed fiber optic sensing technique that employs microwave modulation for phase measurement in signals returned from submarine repeaters. We transformed a trans‐Atlantic telecom cable into an 81‐sensor array and measured sub‐millihertz strains. The strains correlate with ocean tide height variations in phase, suggesting a dominant factor of the cable's Poisson's effect. Large strains observed at fiber spans located in the shallow water match the strong variations of simulated seafloor temperature. This study presents the first experimental confirmation of detecting sub‐millihertz signals using trans‐oceanic distributed sensing with submarine cables at span‐wise spatial resolution (∼80 km), opening the potential for cost‐efficient tsunami early warning and long‐term ocean temperature monitoring compatible with active data‐carrying fibers.