Unified Wind Wave Growth and Spectrum Functions for All Water Depths: Field Observations and Model Results

Wind wave development is governed by the fetch- or duration-limited growth principle that is expressed as a pair of similarity functions relating the dimensionless elevation variance (wave energy) and spectral peak frequency to fetch or duration. Combining the pair of similarity funtions the fetch or duration variable can be removed to form a dimensionless function of elevation variance and spectral peak frequency, which is interepreated as the wave enegry evolution with wave age. The relationship is initially developed for quasi-neural stability and quasi-steady wind forcing conditions. Further analyses show that the same fetch, duration, and wave age similarity functions are applicable to unsteady wind forcing conditions, including rapidly accelerating and decelerating mountain gap wind episodes and tropical cyclone (TC) wind fields. Here it is shown that with the dimensionless frequency converted to dimensionless wavenumber using the surface wave dispersion relationship, the same similarity function is applicable in all water depths. Field data collected in shallow to deep waters and mild to TC wind conditions, and synthetic data generated by spectrum model computations are assembled to illustrate the applicability. For the simulation work, the finite-depth wind wave spectrum model and its shoaling function are formulated for variable spectral slopes. Given wind speed, wave age, and water depth, the measrued and spectrum-computed significant wave heights and the associated growth parameters are in good agreement in forcing conditions from mild to TC winds and in all depths from deep ocean to shallow lake.

Mortality among people hospitalised with covid-19 in Switzerland: a nationwide population-based analysis

Objectives: To investigate mortality among people hospitalised with covid-19 in Switzerland according to epidemic wave, age, sex, comorbid conditions and intensive care unit (ICU) occupancy. Design: Population-based, national study.Setting: Mandatory surveillance reports from all hospitals in Switzerland. Participants: All 22,648 people who tested positive for SARS-CoV-2 infection and were hospitalised between February 24, 2020 and March 01, 2021 in Switzerland with complete information about age, sex, and comorbidities. Main outcome measures: Survival after positive SARS-CoV-2 test among people hospitalised with covid-19 by epidemic wave, age, sex, comorbid conditions and ICU occupancy, expressed as adjusted hazard ratios (aHR) of death and probability of survival over time and at 40 days, all with 95% credible intervals (CrI). Results: Of 22,648 people hospitalised with covid-19, 4,785 (21.1%) died. Bayesian survival models adjusted for age, sex, and the presence of comorbidity showed that survival was lower during the first epidemic wave than the second (standardised predicted survival probability at 40 days 76.1% versus 80.5%; aHR of death 1.38, 95% CrI 1.28 to 1.48). During the second epidemic wave, occupancy among all available ICU beds (certified beds and add-on beds) in Switzerland varied between 51.7% and 78.8%. Modelling the association between survival and ICU occupancy with restricted cubic splines indicated stable survival when ICU occupancy was below 70%, but worse survival when ICU occupancy exceeded 70%. This threshold of 70% occupancy among total available ICU beds corresponded to around 85% occupancy among certified beds. Survival was decreased for men, older people, and patients with comorbid conditions. Comorbid conditions reduced survival more in younger people than in older people. As single comorbid condition, hypertension was not associated with poorer survival, but appeared to increase the risk of death in combination with a cardiovascular disease. Conclusion: Survival after hospitalisation with covid-19 has improved over time, consistent with improved management of severe covid-19. The decreased survival starting at approximately 70% ICU occupancy in Switzerland supports the need to introduce measures for prevention and control of SARS-CoV-2 transmission in the population far before ICUs are full.

Relationship between Sea Surface Drag Coefficient and Wave State

The sea surface drag coefficient plays an important role in momentum transmission between the atmosphere and the ocean, which is affected by ocean waves. The total air–sea momentum flux consists of effective momentum flux and sea spray momentum flux. Sea spray momentum flux involves sea surface drag, which is largely affected by the ocean wave state. Under strong winds, the sea surface drag coefficient (CD) does not increase linearly with the increasing wind speed, namely, the increase of CD is inhibited by strong winds. In this study, a sea surface drag coefficient is constructed that can be applied to the calculation of the air–sea momentum flux under high wind speed. The sea surface drag coefficient also considers the influence of wave state and sea spray droplets generated by wave breaking. Specially, the wave-dependent sea spray generation function is employed to calculate sea spray momentum flux. This facilitates the analysis not only on the sensitivity of the sea spray momentum flux to wave age, but also on the effect of wave state on the effective CD (CD, eff) under strong winds. Our results indicate that wave age plays an important role in determining CD. When the wave age is >0.4, CD decreases with the wave age. However, when the wave age is ≤0.4, CD increases with the wave age at low and moderate wind speeds but tends to decrease with the wave age at high wind speeds.

Epidemiological, clinical Characteristics and mortality of patients Infected with SARS-CoV-2 Admitted of Kinshasa University Hospital, Democratic Republic of the Congo from March 24, 2020 to January 30, 2021: Two waves, two faces?

BackgroundThe objective of our retrospective study was to establish a comparison between the first and the second waves of demographic and clinical characteristics as well as mortality and its determinants.MethodsA total of 411 COVID-19 patients were enrolled in Kinshasa University Hospital and categorized into two groups according to the pandemic pattern, demographics, and disease severity. The clinical characteristics were compared according to the two waves. To describe survival from the first day of hospitalization until death, we used Kaplan Meier’s method. We used the Log Rank test to compare the survival curves between the two waves. The Cox regression was used to identify independent predictors of mortality.ResultsDuring the study period, 411 patients with confirmed COVID-19 were admitted to the hospital. The average age of patients in the 2nd wave was higher than in the first wave (52.4 ±17.5 vs 58.1 ±15.7, p=0.026). The mean saturation was lower in the first wave than in the second. The death rate of patients in the first wave was higher than in the second wave (p=0.009). Survival was reduced in the first wave compared to the second wave. In the first wave, age over 60 years, respiratory distress, law oxygen saturation (≤89%) and severe stage of COVID-19 emerged as factors associated with death, while in the second wave it was mainly respiratory distress, law oxygen saturation (≤ 89%) and severe stage. The predictors of mortality present in both the first and second waves were respiratory distress and severe COVID-19 stage.ConclusionMortality decreased in the second wave. Age no longer emerged as a factor in mortality in the second wave. Health system strengthening and outreach to those at high risk of mortality should continue to maintain and improve gains.

Skewness and Kurtosis of the Surface Wave in the Coastal Zone of the Black Sea

Purpose. The aim of the study is to analyze variability of the statistical moments characterizing deviations of the sea surface elevation distributions from the Gaussian. Methods and Results. Field studies of the sea waves’ characteristics were carried out from the stationary oceanographic platform located in the Black Sea near the Southern coast of Crimea. The data obtained both in summer and winter, were used. The statistical moments were calculated separately for wind waves and swell. The measurements were performed in a wide range of meteorological conditions and wave parameters (wind speed varied from 0 to 26 m/s, wave age – from 0 to 5.2 and steepness – from 0.005 to 0.095). For wind waves, the coefficients of skewness correlation with the waves’ steepness and age were equal to 0.46 and 0.38. The kurtosis correlation coefficients with these parameters were small (0.09 and 0.07), but with the confidence level 99.8% – significant. For swell, the correlation coefficients were 1.5 – 2.0 times lower. Conclusions. The statistical moments of the sea surface elevations of the third and higher orders are the indicators of the wave field nonlinearity, which should be taken into account when solving a wide range of the applied and fundamental problems. The deviations of the surface elevation distributions from the Gaussian one are not described unambiguously by the steepness and wave age. At the fixed values of these parameters, a large scatter in the skewness and kurtosis of the surface elevations is observed. This imposes significant limitations on the possibility of applying the nonlinear wave models based on the wave profile expansion by small parameter (steepness) degrees, in engineering calculations.

The Changed Sign of Swell Coherent Stress During Swell Conditions

<p>Data measured by ultrasonic anemometer moored at a fixed platform located in South China Sea has been used to analyze turbulence within wave boundary layer. Compared to wind seas, it can be found a dominant area in power spectra, cospectra and Ogive curves under swell conditions from the measurements at 8 m height above sea surface, which is consistent with earlier studies. Our result also shows that the cospectra have both negative and positive regions, which represent the upward and downward momentum induced by swell waves. The wave coherent stress derived from the cospectra shows that it is more larger than the traditional method, implying earlier studies have greatly underestimated the stress of swell. Our study also found that the change of sign of swell coherent stress was related to the wave age,<em> i.e</em>. for <em>c</em><sub>p</sub>/<em>u</em><sub>*</sub> ≥ 60, swell induced the upward momentum, for <em>c</em><sub>p</sub>/<em>u</em><sub>*</sub> < 60, vice versa.  </p>

Global Trends of Sea Surface Gravity Wave, Wind, and Coastal Wave Setup

Assessing trends of sea surface wave, wind, and coastal wave setup is of considerable scientific and practical importance in view of recent and projected long-term sea level rise due to global warming. Here we analyze global significant wave height (SWH) and wind data from 1993 to 2015 and a wave model to (i) calculate wave age and explain the causal, or the lack thereof, relationship between wave and wind trends; and (ii) estimate trends of coastal wave setup and its contributions to secular trends of relative sea level at coastal locations around the world. We show in-phase, increasing SWH and wind trends in regions dominated by younger waves, and decreasing SWH trends where older waves dominate and are unrelated to the local wind trends. In the central North Pacific where wave age is transitional, in-phase decreasing wave and wind trends are found over the west-northwestern region, but wave and wind trends are insignificantly correlated in the south-southeastern region; here, a reversed, upward momentum flux from wave to wind is postulated. We show that coastal wave setup depends primarily on open-ocean SWH but only weakly on wind, varying approximately like SWH/(wind speed)1/5. The wave-setup trends are shown to be increasing along many coastlines where the local relative sea level trends are also increasing: the North and Irish Seas, Mediterranean Sea, East and South Asian seas, and eastern United States, exacerbating the potential for increased floods along these populated coastlines.

Air–sea gas exchange at wind speeds up to 85 m s⁻¹

Gas transfer velocities were measured in two high-speed wind-wave tanks (Kyoto University and the SUSTAIN facility, RSMAS, University of Miami) using fresh water, simulated seawater and seawater for wind speeds between 7 and 85 m s−1. Using a mass balance technique, transfer velocities of a total of 12 trace gases were measured, with dimensionless solubilities ranging from 0.005 to 150 and Schmidt numbers between 149 and 1360. This choice of tracers enabled the separation of gas transfer across the free interface from gas transfer at closed bubble surfaces. The major effect found was a very steep increase of the gas transfer across the free water surface at wind speeds beyond 33 m s−1. The increase is the same for fresh water, simulated seawater and seawater. Bubble-induced gas transfer played no significant role for all tracers in fresh water and for tracers with moderate solubility such as carbon dioxide and dimethyl sulfide (DMS) in seawater, while for low-solubility tracers bubble-induced gas transfer in seawater was found to be about 1.7 times larger than the transfer at the free water surface at the highest wind speed of 85 m s−1. There are indications that the low contributions of bubbles are due to the low wave age/fetch of the wind-wave tank experiments, but further studies on the wave age dependency of gas exchange are required to resolve this issue.

STABILITY AND CHANGE IN DEPRESSIVE SYMPTOMS AND COGNITION FOR CENTENARIAN COHORTS

The purpose of the study was to examine the stability and change of cognition and depression levels and how they predict each other over time. Participants of the Health and Retirement Study who survived to centenarian status (N = 331) were included in this study. The total cognition summary score and the CES-D summary score of depressive symptoms were used to conduct four cross-lagged regression analyses from wave 2 to wave 6. Age was used as a covariate. Results indicated that the stability coefficients for depressive symptoms and cognition from wave 2 to wave 6 were high. Depressive symptoms at wave 2 significantly predicted change in cognition at wave 3, whereas depressive symptoms at all other waves did not predict change in cognition in the next wave. Cognition did not predict changes in depressive symptoms for any wave. Age as a covariate predicted change in cognition in each following wave, particularly from wave 2 to wave 5. The coefficients without stability for depressive symptoms and cognition from wave 2 to wave 5 predicted each other significantly over time, except for the last wave. In conclusion, cognition and depressive symptoms predict each other over time, but they do not predict each other if stabilities are included in the analyses. Further research needs to examine the stability and change in depressive symptoms and cognition including more waves in order to examine whether cross-lagged effects fade or continue in very late life.

The impact of ocean waves on spray stress and surface drag coefficient

Purpose The behaviors of sea surface drag coefficient should be well understood for an accurate hurricane prediction. The speed of wind has been applied to characterize the spray production; however, this could result in inaccurate spray productions compared to the experimental or field data if the influence of wave state is not considered. This paper aims to integrate a new sea spray generation function, described by windsea Reynolds number, into the spray momentum flux formula to calculate the spray momentum. Design/methodology/approach On the basis of this spray momentum, this study proposes the new formulas of spray stress and drag coefficient when the wind speed is high. Findings Results of the revised formulas show that wave status had significant effects on the spray stress and sea surface drag coefficient. Also, wave age was found to be an important parameter that affects the drag coefficient. The drag coefficient decreased with the increasing wave age. Comparison between this study’s theoretical and observation values of drag coefficient shows that the study results are close to the measured values. Research limitations/implications The research findings can enhance the understanding of the behaviors of sea surface drag for an accurate hurricane prediction. Originality/value A new sea spray generation function, described by windsea Reynolds number, is integrated into the spray momentum flux formula to calculate the spray momentum. On the basis of this spray momentum, this study proposes the new formulas of spray stress and drag coefficient when the wind speed is high.