Measurement of tsunamis in the open ocean

Abstract

The spectrum of long waves, which are a background to tsunamis, is analyzed on the basis of records of near‐bottom pressure sensors obtained in the Northwest Pacific during the first and second USA‐USSR expeditions on the investigation of tsunamis in the open ocean (1975 and 1978). Instrumental trends, tidal oscillations, and quasistationary longwave noise were contained in the records. Special filters were used to pick out small waves generated by the seismicity of the ocean bottom. A decrease of noise level from 10² cm (including tides) to 10°¹ cm could be reached. The level of long‐wave noise is found to depend on the instrument's location. Minimal disturbances in the records were observed at stations situated on the edge of the continental slope. The influence of cyclones passing over the instrument's site is deduced. It shows an increase in noise level on Nyquist frequency (0.5 min°¹), which possibly is caused by the action of swell generated by the cyclone. Seismicity of the region under investigation for the second expedition (August‐October 1978) is described, and the recurrence of tsunamis is estimated, including microtsunamis. Taking into account this analysis, records were filtered and sections corresponding to probable arrivals of tsunamis from most strong earthquakes were selected. The anomalous disturbance of ocean level with a height of about 0.5 cm was found. Presumably, it was generated by an earthquake with magnitude M = 6.     

Measurement of ocean surface winds using synthetic aperture radars

A methodology for retrieving high-resolution ocean surface wind fields from satellite-borne synthetic aperture radar (SAR) data is introduced and validated. The algorithms developed are suited for ocean SAR data, which were acquired at the C band of either vertical (VV) or horizontal (HH) polarization in transmission and reception. Wind directions are extracted from wind-induced streaks that are visible in SAR images of the ocean at horizontal scales greater than 200 m. These wind streaks are very well aligned with the mean surface wind direction. To extract the orientation of these streaks, two algorithms are introduced, which are applied either in the spatial or spectral domain. Ocean surface wind speeds are derived from the normalized radar cross section (NRCS) and image geometry of the calibrated SAR images, together with the local SAR-retrieved wind direction. Therefore, several C-band models (CMOD IFR2, CMOD4, and CMODS) are available, which were developed for VV polarization, and have to be extended for HH polarization. To compare the different algorithms and C-band models as well as demonstrate their applicability, SAR-retrieved wind fields are compared to numerical-model results considering advanced SAR (ASAR) data from Environmental Satellite (ENVISAT), a European satellite.     

Measurement of ocean wave spectra using narrow-beam HE radar

A data interpretation algorithm is developed to extract ocean wave information from HF radar backscatter observed by a narrow-beam antenna system. The basis of this measurement is the inversion of the integral equation representing the second-order radar cross section of the ocean surface. This equation is numerically inverted by approximating it as a matrix equation and pseudoinverting the kernel matrix using a singular value decomposition. As a test of this algorithm, comparisons are made between wave spectrum estimates obtained from a WAVEC buoy and a pair of 25.4-MHz ground wave radars, using data collected during the 1986 Canadian Atlantic Storms Program (CASP). Overall, the results of this experiment have been positive and have demonstrated both the basic feasibility of the inversion algorithm and the wave sensing capability of HF radar. For example, significant wave height estimates deduced by two radars differed from the buoy, in an absolute value sense, by only 0.12 m on average. When using only one radar, the mean difference of this important parameter from the buoy was a reasonable 0.33 m     

Measurement of ocean wave spectra using a ship-mounted HF radar

The work describes an inversion algorithm for HF radar measurement of nondirectional wave spectra using an omnidirectional receive/transmit antenna. Such a radar would be suitable for deployment on a stationary ship or drill rig. In this approach, wave information is extracted from the radar observations by numerically inverting the integral equation representing the backscatter return from the ocean. Test results of this technique applied to data collected using a 25.4-MHz radar installed on a ship have been very positive. For the two measurements collected, there is a high degree of correlation between the radar wave estimates and those of a WAVE-TRACK buoy     

Measurement of ocean surface currents using a long-range,high-frequency ground wave radar

High-frequency (HF) ground wave radar (GWR) is emerging as a significant tool for monitoring ocean surface conditions at ranges well beyond the line-of-sight horizon that limits conventional systems. An experimental GWR system at Cape Race, Newfoundland, Canada that has been operational since 1991, has the ability to performing routine surveillance of oceanic surface parameters and surface target detection. Operating in the frequency range between 5 and 8 MHz, the frequency modulated interrupted continuous wave (FMICW) radar has a nominal range capability of 200 km. An experiment was performed during the period of October 20-November 21, 1992 to test the surface current measuring capability of the Cape Race system. Here, near real-time radial surface current information is extracted from the Doppler spectra of the radar time series data and a comparison is performed to the Lagrangian velocities derived from the position-time tracks of Accurate Surface Tracker (AST) drifters. A wide range of oceanic conditions were experienced during the experimental period, and favorable results were obtained from the comparison regardless of the sea state conditions. The analysis shows the standard deviation in the radar radial velocity component to be approximately 5 cm/s     

GPM和TRMM卫星与海洋定点浮标观测降水日变化的比较

基于热带大洋地区共23个海洋定点浮标雨量器数据比较了GPM和TRMM两种卫星降水数据(IMERG和TMPA)对热带海洋降水日变化的观测能力,选取时间为2014年4月1日—2018年4月30日。相较于浮标观测结果,2种卫星数据都低估了降水日变化范围。在太平洋和印度洋,IMERG和TMPA都能捕捉到降水极大值出现在早上、极小值出现在傍晚的特征,与浮标观测结果基本吻合。在大西洋,两种卫星数据与浮标观测的降水日变化特征有较大差异,主要是由于大西洋降水较少,而卫星对小降水的观测存在较大偏差,同时浮标观测在小降水区域更容易存在误差。     

Regeneration of silicate in the ocean

Regeneration of silicate in the Japan Sea, an example of semi-closed sea, was studied. In the Japan Sea Proper Water the apparent regenerative ratio of the nutrients was determined to be:O C N P Si=–289 (116)14.3181.It was assumed that the dissolved silicate present in sea water is grouped into three fractions; 1)preformed silicate of conservative nature, 2)oxidative silicate which dissolves in oxidation process of organisms with consumption of oxygen, and 3)non-oxidative silicate which dissolves without oxygen consumption. The dissolution rate ofnon-oxidative silicate in the Japan Sea Proper Water was estimated to be 0.07g-at. Si/l/yr from the data ofAOU values and assumed rates of oxygen consumption. This dissolution rate ofnon-oxidative silicate agreed with that obtained in the deep Pacific by the vertical advection diffusion model byKido andNishimura (1972).     

Lagrangian fronts in the ocean

We introduce the concept of Lagrangian fronts (LFs) in the ocean and describe their importance for analyzing water mixing and transport and the specific features and differences from hydrological fronts. A method of calculating LFs in a given velocity field is proposed. Based on altimeter velocity fields from AVISO data in the northwestern Pacific, we calculate the Lagrangian synoptic maps and identify LFs of different spatial and temporal scales. Using statistical analysis of saury catches in different years according to the Goskomrybolovstvo (State Fisheries Committee of the Russian Federation), we show that LFs can serve as good indicators of places that are favorable for fishing.     

Turbulent dispersion in the ocean

The mathematical framework for turbulent transport in the ocean is reasonably well established. It may be applied to large-scale fields of scalars in the ocean and to the instantaneous or continuous discharge from a point. The theory and its physical basis can also provide an interpretation of passive scalar spectra. Spatial variations in the rate of turbulent transfer can be related to the movement of the center of mass of a scalar and to a formulation in terms of entrainment. The relative dispersion of a scalar with respect to its center of mass and the streakiness of the concentration field within the relative dispersion domain need to be considered. In many of these problems it is valuable to think in terms of simple models for individual streaks, as well as overall statistical properties.     

Geodetic measurements in the ocean

This paper covers the topic of marine geodesy, its goals, and applications. Specifically discussed are position determination and establishment of geodetic control on the ocean bottom, ocean surface, and subsurface, and the determination of the geoid, a vertical reference surface. The various techniques used in position determination (including satellite, airborne, radio, inertial and acoustic techniques) are assessed in terms of accuracy, coverage, and contribution to the solution of specific problems associated with position and control. The results of several marine geodetic control experiments are presented. Classical techniques for the determination of the geoid are discussed and assessed, as are new techniques such as satellite altimetry. The outlook for marine geodetic measurements in the ocean is outlined in terms of what is being planned or considered for the next decade, and several recommendations are made.     

CABARET in the ocean gyres

A new high-resolution Eulerian numerical method is proposed for modelling quasigeostrophic ocean dynamics in eddying regimes. The method is based on a novel, second-order non-dissipative and low-dispersive conservative advection scheme called CABARET. The properties of the new method are compared with those of several high-resolution Eulerian methods for linear advection and gas dynamics. Then, the CABARET method is applied to the classical model of the double-gyre ocean circulation and its performance is contrasted against that of the common vorticity-preserving Arakawa method. In turbulent regimes, the new method permits credible numerical simulations on much coarser computational grids.     

Vertical exchange in the ocean

We analyze the expressions for vertical turbulent flows and the coefficients of turbulent exchange in the ocean and their dependences on the stratification of density. It is shown that, in the case of high density gradients, turbulent mixing is localized in separate bounded relatively small zones (turbulized spots or layers). Formulas for typical vertical sizes of turbulent spots and local coefficients of vertical turbulent exchange depending on the Väisälä-Brunt frequency are presented. We consider a model of vertical turbulent exchange for the case of spot-like intermittent turbulence (a similar model was independently developed at the Marine Hydrophysical Institute of the Ukrainian Academy of Sciences with certain differences in the statement the problem and methodology). We emphasize the priority of A. G. Kolesnikov in the investigations of vertical turbulent exchange in the ocean by the direct method, in the development and construction of quick-response measuring devices with detectors of pulsations of the components of velocity and temperature, and in the first determination of the characteristics of turbulence in lakes, seas, and oceans performed by using this equipment.     

Mercury concentration in the ocean

Seventy percent of 342 seawater samples collected in the Bering Sea, North and South Pacific, Japan Sea, East and South China Seas, and Indian Ocean had concentrations of “total” mercury ranging from 3 to 6 ng Hg l^?1 with an arithmetic mean of 5.3 ng l^?1 and a geometric mean of 5.0 ng l^?1. In some cases, a higher concentration was observed at the surface, at the halocline or thermocline, or in the bottom water. But in general, there was no consistent correlation between mercury concentration and depth, except for a statistical tendency for mercury concentration to be slightly higher in the surface water. This tendency suggests that mercury in the ocean is supplied from the atmosphere by rain washout. The latitudinal variation of surface mercury concentrations showed that the maximum concentration at each latitude decreased from 40°N to 30°S. This variation provides evidence that atmospheric mercury is emitted mainly from continental areas naturally or anthropogenically.     

Solubility of calcite in the ocean

The apparent solubility product K′_sp of calcite in seawater was measured as a function of temperature, salinity, and pressure using potentiometric saturometry techniques. The temperature effect was hardly discernible experimentally. The value of K′_sp at 25°C was 4.59·10⁻⁷ mole²/(kg seawater)² at 35‰S, 5.34·10⁻⁷ at 43‰S, and 3.24·10⁻⁷ at 27‰S. The apparent partial molal volume was found to be −34.4 cm³ at 25°C and −42.3 cm³ at 2°C from a linear fit of log(K′_sp ^P/K′_sp ¹). These results were used in conjunction with field data to calculate the degree of saturation in the oceans and showed undersaturation at shallower depths than previously reported.     

Effects of the deep ocean circulation on the reservoir characteristics of the ocean

To examine the effects of the deep ocean circulation on the characteristics of the ocean as a reservoir, age distributions of the material whose source and sink are at the ocean surface are calculated using an idealized vertical two-dimensional model of the ocean. The results show that the large-scale vertical circulation of the deep water accelerates the renewal of deep water and reduces the average age of the material. It is also shown that the multi-layered structures of the deep circulation are more realistic than the one-layered structure and promote the renewal of the deep water.     

Particulate organic carbon in the global ocean derived from SeaWiFS ocean color

Satellite remote sensing offers new means of quantifying particulate organic carbon, POC, concentration over large oceanic areas. From SeaWiFS ocean color, we derived 10-year data of POC concentration in the surface waters of the global ocean. The 10-year time series of the global and basin scale average surface POC concentration do not display any significant long-term trends. The annual mean surface POC concentration and its seasonal amplitude are highest in the North Atlantic and lowest in the South Pacific, when compared to other ocean basins. POC anomalies in the North Atlantic, North Pacific, and global concentrations seem to be inversely correlated with El Niño index, but longer time series are needed to confirm this relationship. Quantitative estimates of POC reservoir in the oceanic surface layer depend on the choice of what should represent this layer. Global average POC biomass is 1.34 g m^?2 if integrated over one optical depth, 3.62 g m^?2 if integrated over mixed layer depth, and up to 6.41 g m^?2 if integrated over 200-m layer depth (when assumed POC concentration below MLD is 20 mg m^?3). The global estimate of total POC reservoir in the surface 200-m layer of the ocean is 228.61×10¹³ g. We expect that future estimates of POC reservoir may be even larger, when more precise calculations account for deep-water organic-matter maxima in oligotrophic regions, and POC biomass located just below the seasonal mixed layer in spring and summer in the temperate regions.     

海洋酸化研究进展

<正>海洋是巨大的碳库,不断地从大气吸收CO2,工业革命以来,海洋吸收了人类向大气排放CO2的30%~40%[1]。海洋吸收的CO2对于缓解全球变暖起着重要的作用,但是它破坏了海洋自身碳酸盐的化学平衡,导致海水酸度增加。这种由于海洋吸收了大气中人为CO2引起的海水酸度增加过程,被称为海洋酸化。目前全球海洋正处于5500万年以来海洋酸化速度最快的时期,工业革命以来,全球表层海水pH已     

Eddy-resolving ocean circulation in the Asian-Australian region inferred from an ocean reanalysis effort

The first global ocean reanalysis with focus on the Asian-Australian region was performed for the period October 1992 to June 2006. The 14-year experiment assimilated available observations of altimetric sea-level anomaly, satellite SST and quality-controlled in situ temperature and salinity profiles from a range of sources, including field surveys and the Argo float array. This study focuses on dominant circulation patterns in the South-East Asian/Australian region as simulated by an eddy-resolving and data-assimilating ocean general circulation model. New estimates of the ocean circulation are provided which are largely in agreement with the limited number of observations. Transports of key currents in the region are as follows: The total (top-to-bottom) annual mean Indonesian Throughflow transport and its standard deviation are 9.7 ± 4.4 Sv from the Pacific to the Indian Ocean with a minimum in January (6.6 Sv) and a maximum in April (12.3 Sv). The Leeuwin Current along the west coast of Australia is dominated by eddy structures with a mean southward transport of 4.1 ± 2.0 Sv at 34°S. Along the southern coast of Australia a narrow shelf edge current known as the South Australian Current advects 4.5 ± 2.6 Sv eastward at 130°E. The South Australian Current converges east of Tasmania with the eddy-rich extension of East Australian Current. At 32°S this current transports 36.8 ± 18.5 Sv southward. A dominating feature of the circulation between north-eastern Australia and Papua-New Guinea is the strong and quasi-permanent Coral Sea Gyre. This gyre is associated with the highly variable Hiri Current which runs along the south coast of Papua-New Guinea and advects 8.2 ± 19.1 Sv into the Western Pacific Ocean. All of these transport estimates are subject to strong eddy variability.     

Coupling winds to ocean surface currents over the global ocean

A Wind stress–Current Coupled System (WCCS) consisting of the HYbrid Coordinate Ocean Model (HYCOM) and an improved wind stress algorithm based on Donelan et al. [Donelan, W.M., Drennan, Katsaros, K.B., 1997. The air–sea momentum flux in mixed wind sea and swell conditions. J. Phys. Oceanogr. 27, 2087–2099] is developed by using the Earth System Modeling Framework (ESMF). The WCCS is applied to the global ocean to study the interactions between the wind stress and the ocean surface currents. In this study, the ocean surface current velocity is taken into consideration in the wind stress calculation and air–sea heat flux calculation. The wind stress that contains the effect of ocean surface current velocity will be used to force the HYCOM. The results indicate that the ocean surface velocity exerts an important influence on the wind stress, which, in turn, significantly affects the global ocean surface currents, air–sea heat fluxes, and the thickness of ocean surface boundary layer. Comparison with the TOGA TAO buoy data, the sea surface temperature from the wind–current coupled simulation showed noticeable improvement over the stand-alone HYCOM simulation.