Ocean Experiment Research Articles

Hazy clouds: Making black carbon visible in climate science

In 1995, a multimillion-dollar experiment – the Indian Ocean Experiment – discovered a dark mass of polluting air hovering above the Indian subcontinent. This mass of air was termed a cloud and found to be composed of a high amount of black carbon that was judged to be the second biggest threat to climate change after carbon-dioxide. In this article, an attempt is made to trace the life of black carbon by documenting its changing forms since the experiment. It emerges that the changing forms allow for the movement of air – smoke from traditional cookstoves and vehicular diesel emissions in India lead to the formation of the cloud – and reveal how an ethnography of air can be undertaken.

ОТ ЭКСПЕРИМЕНТА ПОЛИГОН-70 К ЭКСПЕРИМЕНТУ АБИССАЛЬ

The article discusses the issues of reconstructing the mesoscale fields of hydrophysical characteristics from measurement data, as well as the layout of moorings in the ocean experiments Polygon–70, SDE POLYMODE and Abyssal, in which the author of the article took part. A number of important results of the analysis of the vertical structure and variability of synoptic currents in the regions of these experiments are also presented.

Machine Learning Based Biomimetic Underwater Covert Acoustic Communication Method Using Dolphin Whistle Contours.

For underwater acoustic covert communications, biomimetic covert communications have been developed using dolphin whistles. The conventional biomimetic covert communication methods transmit slightly different signal patterns from real dolphin whistles, which results in a low degree of mimic (DoM). In this paper, we propose a novel biomimetic communication method that preserves the large DoM with a low bit error rate (BER). For the transmission, the proposed method utilizes the various contours of real dolphin whistles with the link information among consecutive whistles, and the proposed receiver uses machine learning based whistle detectors with the aid of the link information. Computer simulations and practical ocean experiments were executed to demonstrate the better BER performance of the proposed method. Ocean experiments demonstrate that the BER of the proposed method was 0.002, while the BER of the conventional Deep Neural Network (DNN) based detector showed 0.36.

The Southern Hemisphere Midlatitude Circulation Response to Rapid Adjustments and Sea Surface Temperature Driven Feedbacks

AbstractRapid adjustments—the response of meteorology to external forcing while sea surface temperatures (SST) and sea ice are held fixed—can affect the midlatitude circulation and contribute to long-term forced circulation responses in climate simulations. This study examines rapid adjustments in the Southern Hemisphere (SH) circulation using nine models from the Precipitation Driver and Response Model Intercomparison Project (PDRMIP), which perform fixed SST and coupled ocean experiments for five perturbations: a doubling of carbon dioxide (2xCO2), a tripling of methane (3xCH4), a fivefold increase in sulfate aerosol (5xSO4), a tenfold increase in black carbon aerosol (10xBC), and a 2% increase in solar constant (2%Sol). In the coupled experiments, the SH eddy-driven jet shifts poleward and strengthens for forcings that produce global warming (and vice versa for 5xSO4), with the strongest response found in austral summer. In austral winter, the responses project more strongly onto a change in jet strength. For 10xBC, which induces strong shortwave absorption, the multimodel mean (MMM) rapid adjustment in DJF jet latitude is ~75% of the change in the coupled simulations. For the other forcings, which induce larger SST changes, the effect of SST-mediated feedbacks on the SH circulation is larger than the rapid adjustment. Nevertheless, for these perturbations the magnitude of the MMM jet shift due to the rapid adjustment is still around 20%–30% of that in the coupled experiments. The results demonstrate the need to understand the mechanisms for rapid adjustments in the midlatitude circulation, in addition to the effect of changing SSTs.

Search and rescue at sea aided by hidden flow structures

Every year, hundreds of people die at sea because of vessel and airplane accidents. A key challenge in reducing the number of these fatalities is to make Search and Rescue (SAR) algorithms more efficient. Here, we address this challenge by uncovering hidden TRansient Attracting Profiles (TRAPs) in ocean-surface velocity data. Computable from a single velocity-field snapshot, TRAPs act as short-term attractors for all floating objects. In three different ocean field experiments, we show that TRAPs computed from measured as well as modeled velocities attract deployed drifters and manikins emulating people fallen in the water. TRAPs, which remain hidden to prior flow diagnostics, thus provide critical information for hazard responses, such as SAR and oil spill containment, and hence have the potential to save lives and limit environmental disasters.

Time-frequency modulation based mimicking dolphin whistle for covert underwater acoustic communication

For covert underwater communications, conventional bio-mimicking methods have been developed. Signal shapes of these methods are similar to real whistles, but not the same since they divide a dolphin whistle into symbols, which are modulated by conventional digital modulations. This paper proposes a dolphin whistle mimicking modulation method that transmits different consecutive whistles with the same frequency contour of the real dolphin whistles and different time-frequency locations. This paper also develops a demodulator for decoding the proposed mimicking whistles. The mimicking performance of the proposed time-frequency shift keying was compared with those of the conventional methods by using correlation coefficients, and the proposed scheme showed the better mimicking performance than the conventional chirp spread spectrum and continuously varying-carrier frequency modulation. Using computer simulations and practical ocean experiments, the bit error rate performance of the proposed demodulator was better than that of the cross-correlation method.

Surface Ocean Warming Around Australia Driven by Interannual Variability and Long‐Term Trends in Southern Hemisphere Westerlies

AbstractThe ocean surface temperature and sea level response around Australia to both interannual variability as well as observed and projected changes in surface winds is presented. A hindcast ocean experiment shows interannual southward shifts in the Southern Hemisphere westerly winds drive ocean surface warming events in the South Australian Basin. Twenty‐first century climate and ocean projections in an ensemble of the fifth Coupled Model Intercomparison Project (CMIP5) models show that wind trends could play a role comparable in magnitude to that of radiative warming in driving surface ocean temperature change in this region. To evaluate the wind's role in these projected changes, we use an ocean experiment perturbed by the projected end of 21st century wind anomalies to show that the wind trends alone can generate approximately half of the ocean surface warming and sea level rise predicted by the CMIP5 models in the Tasman Sea.

海洋激光雷达实验与仿真结果的对比

海洋激光雷达实验与仿真结果的对比

Snapping shrimp noise detection and mitigation for underwater acoustic orthogonal frequency division multiple communication using multilayer frequency

This paper proposes Snapping Shrimp Noise (SSN) detection and corrupted Orthogonal Frequency Division Multiplexing (OFDM) reconstruction methods to increase Bit Error Rate (BER) performance when OFDM transmitted signal is corrupted by impulsive SSNs in underwater acoustic communications. The proposed detection method utilizes multilayer wavelet packet decomposition for detecting impulsive and irregularly concentrated and SSN energy in specific frequency bands of SSN, and the proposed reconstruction scheme uses iterative decision directed-subcarrier reconstruction to recover corrupted OFDM signals using multiple carrier characteristics. Computer simulations were executed to show receiver operating characteristics curve for the detection performance and BER for the reconstruction. The practical ocean experiment of SAVEX 15 demonstrated that the proposed method exhibits a better detection performance compared with conventional detection method and improves BER by 250% and 1230% for uncoded and coded data, respectively, compared with the conventional reconstruction scheme.

Air‐Sea Heat and Momentum Fluxes in the Southern Ocean

AbstractThe Clouds, Aerosols, Precipitation, Radiation, and atmospherIc Composition Over the southeRn oceaN (CAPRICORN) experiment was carried out in March–April 2016 onboard R/V Investigator studying momentum (τ), sensible heat (Hs), and latent heat (Hl) fluxes over the Australian sector of the Southern Ocean including over one cyclonic cold‐core and one anticyclonic warm‐core mesoscale oceanic eddy. The turbulence‐based flux measurements obtained with the NOAA PSD flux system employing eddy covariance (EC) and inertial dissipation (ID) methods are compared with those obtained by the Coupled Ocean‐Atmosphere Response Experiment (COARE) 3.5 bulk model, and the neutral transfer coefficients are studied. The relative uncertainty between the turbulence‐based and COARE 3.5 estimates of τ, Hs, and Hl are 22%, 70%, and 26%, respectively, at 1‐hr time scale over the Southern Ocean. Further, the variability in bulk fluxes is investigated with respect to oceanic eddies, precipitation events, atmospheric stability, and extratropical cyclones encountered during the voyage. The main observed variability is an increase in significant wave height or γw (∼33%), τ (∼89%), Hs (∼187%), and Hl (∼79%) over the warm eddy as compared to average voyage values. During the passage of six extratropical cyclones, an increase in τ (∼62% average) and a decrease in Hs (∼235%) and Hl (∼79%) is noted in the warm sector, compared to prestorm conditions, but the pattern reverses behind the cold front.

Evaluating Himawari-8 Cloud Products Using Shipborne and CALIPSO Observations: Cloud-Top Height and Cloud-Top Temperature

AbstractCloud-top height (CTH) and cloud-top temperature (CTT) retrieved from the Himawari-8 observations are evaluated using the active shipborne radar–lidar observations derived from the 31-day Clouds, Aerosols, Precipitation Radiation and Atmospheric Composition over the Southern Ocean (CAPRICORN) experiment in 2016 and 1-yr observations from the spaceborne Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) cloud product over a large sector of the Southern Ocean. The results show that the Himawari-8 CTH (CTT) retrievals agree reasonably well with both the shipborne estimates, with a correlation coefficient of 0.837 (0.820), a mean bias error of 0.226 km (−2.526°C), and an RMSE of 1.684 km (10.069°C). In the comparison with CALIOP, the corresponding quantities are found to be 0.786 (0.480), −0.570 km (1.343°C), and 2.297 km (25.176°C). The Himawari-8 CTH (CTT) generally falls between the physical CTHs observed by CALIOP and the shipborne radar–lidar estimates. However, major systematic biases are also identified. These errors include (i) a low (warm) bias in CTH (CTT) for warm liquid cloud type, (ii) a cold bias in CTT for supercooled liquid water cloud type, (iii) a lack of CTH at ~3 km that does not have a corresponding gap in CTT, (iv) a tendency of misclassifying some low-/mid-top clouds as cirrus and overlap cloud types, and (v) a saturation of CTH (CTT) around 10 km (−40°C), particularly for cirrus and overlap cloud types. Various challenges that underpin these biases are also explored, including the potential of parallax bias, low-level inversion, and cloud heterogeneity.

Assessing Surface Heat Flux Products with In Situ Observations over the Australian Sector of the Southern Ocean

Given the large uncertainties in surface heat fluxes over the Southern Ocean, an assessment of fluxes obtained by European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim) product, the Australian Integrated Marine Observing System (IMOS) routine observations, and the Objectively Analyzed Air–Sea Heat Fluxes (OAFlux) project hybrid dataset is performed. The surface fluxes are calculated using the COARE 3.5 bulk algorithm with in situ data obtained from the NOAA Physical Sciences Division flux system during the Clouds, Aerosols, Precipitation, Radiation, and Atmospheric Composition over the Southern Ocean (CAPRICORN) experiment on board the R/V Investigator during a voyage (March–April 2016) in the Australian sector of the Southern Ocean (43°–53°S). ERA-Interim and OAFlux data are further compared with the Southern Ocean Flux Station (SOFS) air–sea flux moored surface float deployed for a year (March 2015–April 2016) at ~46.7°S, 142°E. The results indicate that ERA-Interim (3 hourly at 0.25°) and OAFlux (daily at 1°) estimate sensible heat flux H s accurately to within ±5 W m−2 and latent heat flux H l to within ±10 W m−2. ERA-Interim gives a positive bias in H s at low latitudes (<47°S) and in H l at high latitudes (>47°S), and OAFlux displays consistently positive bias in H l at all latitudes. No systematic bias with respect to wind or rain conditions was observed. Although some differences in the bulk flux algorithms are noted, these biases can be largely attributed to the uncertainties in the observations used to derive the flux products.

Constraining a nonminimally coupled curvature-matter gravity model with ocean experiments

We examine the constraints on the Yukawa regime from the non-minimally coupled curvature-matter gravity theory arising from deep underwater ocean experiments. We consider the geophysical experiment of Zumberge et al. of 1991 for searching deviations of Newton's inverse square law in ocean. In the context of non-minimally coupled curvature-matter theory of gravity the results of Zumberge et al. can be used to obtain an upper bound both on the strength $\alpha$ and range $\lambda$ of the Yukawa potential arising from the non-relativistic limit of the non-minimally coupled theory. The existence of an upper bound on $\lambda$ is related to the presence of an extra force, specific of the nonminimally coupled theory, which depends on $\lambda$ and on the gradient of mass density, and has an effect in the ocean because of compressibility of seawater. These results can be achieved after a suitable treatment of the conversion of pressure to depth in the ocean by resorting to the equation of state of seawater and taking into account the effect of the extra force on hydrostatic equilibrium. If the sole Yukawa interaction were present the experiment would yield only a bound on $\alpha$, while, in the presence of the extra force we find an upper bound on the range: $\lambda_{\rm max}= 57.4$ km. In the interval $1 \,{\rm m}<\lambda<\lambda_{\rm max}$ the upper bound on $\alpha$ is consistent with the constraint $\alpha<0.002$ found in Zumberge et al.

НАУЧНАЯ СТЕЗЯ Ю.А. ИВАНОВА – ВЫДАЮЩЕГОСЯ РОССИЙСКОГО ЭКСПЕРТА-ЭНЦИКЛОПЕДИСТА В ОБЛАСТИ ГИДРОФИЗИКИ ОКЕАНА В. Г. Нейман

The article contains a brief description of the main stages of scientific activity of the outstanding Russian scientist – oceanologist, versatile specialist in the field of marine hydrophysics – Yuri Alexandrovich Ivanov. This publication, as well as the entire issue of the journal «Oceanological research», dedicated to the memory of this wonderful man, who on October 10, 2019 would have turned 90 years old. Yu. A. Ivanov was born in 1929 in Jaroslavl, but most part of his life, after graduating in 1954 from the Leningrad Higher Marine College named after Admiral Stepan Osipovich Makarov, worked in Moscow, in the P.P. Shirshov Institute of Oceanology of the Russian Academy of Science. Here he went through all the stages of a scientist carrier from junior researcher to head of a large laboratory, defended his doctoral thesis, became a Professor, received the title of Honored Specialist of Science of Russia. His outstanding scientific achievements were awarded by the State prize of the USSR, also the most prestigious academic S.O. Makarov award in the field of Oceanology. Yu.A. Ivanov made a great contribution to the development of several major areas of the ocean Sciences. In this regard, he was a real encyclopaedist, one of the few in his scientific community, an outstanding expert scientist, who at the highest professional level was engaged in solving the problems of the General circulation of the World ocean, the Interaction of the ocean and atmosphere, Ocean climate, Physics of boundary layers and Wave processes in these two environments, General and particular problems of formation and evolution of the Hydrophysical regime of the ocean. Much attention, a lot of time and effort were dedicated by Yu.A. Ivanov to planning, organizing and conducting the field experiments in the real open ocean. He happened to be a participant of about 20 large sea expeditions, some of them were carried out under his direct supervision. Yuri Alexandrovich Ivanov was a brilliant scientist, kind, considerate, friendly person, cherishing the memory of him is with gratitude kept among his numerous students, colleagues, collaborators, friends and moons in distant sea voyages.

Mimicking dolphin whistles with continuously varying carrier frequency modulation for covert underwater acoustic communication

This paper proposes a covert underwater acoustic communication scheme to mimic dolphin whistles by continuously varying the carrier frequency and by using antipodal symbol modulation. The continuously varying carrier frequency precisely mimics dolphin whistles, while the conventional method utilizes discrete carrier-frequencies. The antipodal symbol modulation increases bit error rate (BER) performance by a larger Euclidean distance between symbols than conventional chirp spread spectrum (CSS). BER performance was tested by computer simulations and practical ocean experiments, and the degree of mimic (DoM) was evaluated by correlation coefficients and the mean opinion score (MOS) test. BER of the proposed method attains about a 3 dB SNR gain compared with that of conventional CSS, and the DoM of the proposed scheme demonstrates a larger correlation coefficient and a 39% greater MOS score than that of conventional CSS.

A new global ocean hydrographic climatology

ABSTRACTThis report describes the main features of the recently published World Ocean Experiment–Argo Global Hydrographic Climatology. This climatology is based on profile data from ships, Argo floats, and sensors attached to marine mammals. As an important deviation from the widely used climatologies produced previously by the National Oceanographic Data Center, the spatial interpolation was performed on local potential density surfaces, so that no ‘artificial water masses’ were created. In addition to monthly fields of temperature and salinity, gridded maps of the upper mixed layer depth are now provided.

Bayesian inference for water column and sediment inversion in ocean acoustics

Bayesian methods provide inference on unknown parameters given prior beliefs and a statistical model for the observations in a noisy environment. It was shown in “Sequential filtering and linearization for inversion in the Seabed Characterization Experiment,” J. Acoust. Soc. Am. 144, 1913 (2018) how geometry and sediment parameter estimation in an oceanic experiment can be achieved with a two-stage Bayesian approach. Here, we demonstrate the potential of the method for inversion with a different data set presenting challenges in identifying features of the acoustic field necessary for the second stage of the estimation process. The water column sound speed is complex in this experiment, necessitating a complex inverse model. The transmitted signals are lfm pulses and probability densities of multipath arrival times are calculated at the receivers. For the forward and inverse calculations, we compute the Jacobian matrix for sound speed estimation using EOF coefficients. The inversion, employing the direct and surface and bottom paths, leads to inference on the geometry and the water column sound speed profile. Using the computed probability densities and introducing one more arrival, sediment property densities are calculated. Results are in excellent agreement with expected values for the site. [Work supported by ONR.]

How Asymmetries Between Arctic and Antarctic Climate Sensitivity Are Modified by the Ocean

AbstractWe investigate how the ocean response to CO2 forcing affects hemispheric asymmetries in polar climate sensitivity. Intermodel comparison of Phase 5 of the Coupled Model Intercomparison Project CO2 quadrupling experiments shows that even in models where hemispheric ocean heat uptake differences are small, Arctic warming still exceeds Antarctic warming. The polar climate impact of this evolving ocean response to CO2 forcing is then isolated using slab ocean experiments in a state‐of‐the‐art climate model. Overall, feedbacks over the Southern Hemisphere more effectively dissipate top‐of‐atmosphere anomalies than those over the Northern Hemisphere. Furthermore, a poleward shift in ocean heat convergence in both hemispheres amplifies destabilizing ice albedo and lapse rate feedbacks over the Arctic much more so than over the Antarctic. These results suggest that the Arctic is intrinsically more sensitive to both CO2 and oceanic forcings than the Antarctic and that ocean‐driven climate sensitivity asymmetry arises from feedback destabilization over the Arctic rather than feedback stabilization over the Antarctic.

Simulated Responses of the West African Monsoon and Zonal‐Mean Tropical Precipitation to Early Holocene Orbital Forcing

AbstractThis study seeks to improve our mechanistic understanding of how the insolation changes associated with orbital forcing impact the West African monsoon and zonal‐mean tropical precipitation. We impose early Holocene orbital parameters in simulations with the Geophysical Fluid Dynamics Laboratory AM2.1 atmospheric general circulation model, either with fixed sea surface temperatures, a 50‐m thermodynamic slab ocean, or coupled to a dynamic ocean (CM2.1). In all cases, West African Monsoon rainfall expands northward, but the summer zonal‐mean Intertropical Convergence Zone does not—there is drying near 10°N, and in the slab ocean experiment a southward shift of rainfall. This contradicts expectations from the conventional energetic framework for the Intertropical Convergence Zone location, given anomalous southward energy fluxes in the deep tropics. These anomalous energy fluxes are not accomplished by a stronger Hadley circulation; instead, they arise from an increase in total gross moist stability in the northern tropics.

Determination of Intraseasonal Variation of Precipitation Microphysics in the Southern Indian Ocean from Joss–Waldvogel Disdrometer Observation during the CINDY Field Campaign

To date, the intraseasonal variation of raindrop size distribution (DSD) in response to the Madden–Julian Oscillation (MJO) has been examined only over the Indonesian Maritime Continent, particularly in Sumatra. This paper presents the intraseasonal variation of DSD over the Indian Ocean during the Cooperative Indian Ocean experiment on Intraseasonal Variability in the Year 2011 (CINDY 2011) field campaign. The DSDs determined using a Joss–Waldvogel disdrometer, which was installed on the roof of the anti-rolling system of the R/V Mirai during stationary observation (25 September to 30 November 2011) at (8°S, 80.5°E), were analyzed. The vertical structure of precipitation was revealed by Tropical Rainfall Measuring Mission Precipitation Radar (version 7) data. While the general features of vertical structures of precipitation observed during the CINDY and Sumatra observation are similar, the intraseasonal variation of the DSD in response to the MJO at each location is slightly different. The DSDs during the active phase of the MJO are slightly broader than those during the inactive phase, which is indicated by a larger mass-weighted mean diameter value. Furthermore, the radar reflectivity during the active MJO phase is greater than that during the inactive phase at the same rainfall rate. The microphysical processes that generate large-sized drops over the ocean appear to be more dominant during the active MJO phase, in contrast to the observations made on land (Sumatra). This finding is consistent with the characteristics of radar reflectivity below the freezing level, storm height, bright band height, cloud effective radius, and aerosol optical depth.