scholarly journals The internal seiche field in the changing South Aral Sea (2006–2013)

2016 ◽  
Author(s):  
Elena Roget ◽  
Elizaveta Khimchenko ◽  
Francesc Forcat ◽  
Peter Zavialov
Keyword(s):  
Nodal Line ◽  
Maximum Density ◽  
Sea Surface ◽  
Aral Sea ◽  
Main Body ◽  
Horizontal Structure ◽  
Easterly Wind ◽  
Northeasterly Wind ◽  
Sea Level Variations ◽  
First Time

Abstract. Internal standing waves (seiches) in the South Aral Sea are studied for the first time. The study, based on numerical simulations and field data and, focuses on two different campaigns: the first in autumn 2006, when the stratification was weak, and the second in autumn 2013, when it was strong. During this time, the sea surface level decreased 3.2 m but differences in stratification depend only on the time when the campaigns were carried out because the maximum density gradient decreases even though the sea continues to become saltier. In 2006 there was a mild prevailing northeasterly wind and in 2013 a mild easterly wind. The fundamental modes were identified as 36 h and 14 h, respectively. For both years we focused on the sub-inertial modes which were found to be either second or third vertical modes. In general, the vertical modes in 2013 are higher because of the strong stratification. For both years, it was found that the quasi homogeneous mixed deep upper layer could sustain internal waves under mild wind conditions. Regarding the horizontal structure, in 2006 they are first and second modes and in 2013 second and third horizontal modes. The results suggest that, due to sea level variations, the neck connecting the Chernyshev Bay to the main body of the lake can become critical for the development a nodal line in that neck.

scholarly journals The internal seiche field in the changing South Aral Sea (2006–2013)

2017 ◽  
Vol 21 (2) ◽  
pp. 1093-1105 ◽  
Author(s):  
Elena Roget ◽  
Elizaveta Khimchenko ◽  
Francesc Forcat ◽  
Peter Zavialov
Keyword(s):  
Nodal Line ◽  
Sea Surface ◽  
Aral Sea ◽  
Main Body ◽  
Easterly Wind ◽  
Oscillation Modes ◽  
Northeasterly Wind ◽  
Sea Level Variations ◽  
Critical Location ◽  
First Time

Abstract. Internal standing waves (seiches) in the South Aral Sea are studied for the first time. The study, based on numerical simulations and field data, focuses on two different campaigns: the first in autumn 2006, when the stratification was weak and there was a mild prevailing northeasterly wind, and the second in autumn 2013, when the stratification was strong and there was a mild easterly wind. Between these two campaigns, the sea surface level decreased by 3.2 m. The periods of the fundamental modes were identified as 36 and 14 h, respectively. In both years, either second or third vertical modes were found. In general, the vertical modes in 2013 were higher because of the broad and strong pycnocline. For both years, it was found that the deep quasi-homogeneous mixed upper layer could sustain internal waves under mild wind conditions. The observed first and second vertical modes in 2006 are the first and second horizontal modes and the second and third vertical modes in 2013 are the second and third horizontal modes. The results suggest that, due to sea level variations, the neck connecting the Chernyshev Bay to the main body of the lake can become a critical location for the development of a nodal line for all principal oscillation modes. Rotation effects on waves were not analyzed in this study.

Contributions of Wind Forcing and Surface Heating to Interannual Sea Level Variations in the Atlantic Ocean

2006 ◽  
Vol 36 (9) ◽  
pp. 1739-1750 ◽  
Author(s):  
Cécile Cabanes ◽  
Thierry Huck ◽  
Alain Colin de Verdière
Keyword(s):  
Atlantic Ocean ◽  
Sea Level ◽  
Wind Stress ◽  
Large Scale ◽  
Sea Surface Height ◽  
Sea Surface ◽  
Altimeter Data ◽  
Local Response ◽  
Sea Level Variability ◽  
Sea Level Variations

Abstract Interannual sea surface height variations in the Atlantic Ocean are examined from 10 years of high-precision altimeter data in light of simple mechanisms that describe the ocean response to atmospheric forcing: 1) local steric changes due to surface buoyancy forcing and a local response to wind stress via Ekman pumping and 2) baroclinic and barotropic oceanic adjustment via propagating Rossby waves and quasi-steady Sverdrup balance, respectively. The relevance of these simple mechanisms in explaining interannual sea level variability in the whole Atlantic Ocean is investigated. It is shown that, in various regions, a large part of the interannual sea level variability is related to local response to heat flux changes (more than 50% in the eastern North Atlantic). Except in a few places, a local response to wind stress forcing is less successful in explaining sea surface height observations. In this case, it is necessary to consider large-scale oceanic adjustments: the first baroclinic mode forced by wind stress explains about 70% of interannual sea level variations in the latitude band 18°–20°N. A quasi-steady barotropic Sverdrup response is observed between 40° and 50°N.

The equatorial wind structure in Jupiter's stratosphere from direct wind and temperature measurements with ALMA and IRTF/TEXES

2021 ◽  
Author(s):  
Bilal Benmahi ◽  
Thibault Cavalié ◽  
Thomas K. Greathouse ◽  
Vincent Hue
Keyword(s):  
Temperature Measurements ◽  
Tropical Region ◽  
Temperature Structure ◽  
Tropical Zone ◽  
Horizontal Structure ◽  
Thermal Wind ◽  
Wind Speeds ◽  
Wind Structure ◽  
Stratospheric Wind ◽  
First Time

<p>The stratosphere of Jupiter is subject to an equatorial oscillation of its temperature structure with a quasi-period of 4 years (Orton et al. 1991, Leovy et al. 1991) which could result in a complex vertical and horizontal structure of prograde and retrograde jets. Yet, the stratospheric wind structure in Jupiter’s equatorial zone has never been directly measured. It has only been inferred in the tropical region from the thermal wind balance using temperature measurements in the stratosphere and the cloud-top wind speeds as a boundary condition (Flasar et al. 2004). However, the temperatures are not well-constrained between the upper troposphere and the middle stratosphere from the observations.</p><p>In this paper, we obtain for the first time an auto-consistent determination of the tropical wind structure using wind and temperature measurements all performed in the stratosphere. The wind speeds have been measured by Cavalié et al. (submitted) at 1 mbar in the stratosphere of Jupiter in the equatorial and tropical zone in March 2017 with ALMA. The stratospheric thermal field was measured five days apart in the low-to-mid latitudes with the IRTF/TEXES instrument (Giles et al. 2020). For the wind derivation, we use the thermal wind equation (Pedlosky, 1979) and equatorial thermal wind equation (Marcus et al. 2019). We will present and discuss our results.</p><p>This paper is a follow-up to the EGU21-8726 paper.</p>

The equatorial wind structure in Jupiter’s stratosphere from direct wind and temperature measurements with ALMA and IRTF/TEXES

2021 ◽  
Author(s):  
Bilal Benmahi ◽  
Thibault Cavalié ◽  
Thomas K. Greathouse ◽  
Vincent Hue ◽  
Rohini Giles ◽  
...  
Keyword(s):  
Tropical Region ◽  
Temperature Structure ◽  
Horizontal Structure ◽  
Tropical Regions ◽  
Upper Troposphere ◽  
Thermal Wind ◽  
Wind Speeds ◽  
Wind Structure ◽  
First Time ◽  
Middle Stratosphere

<p>Since 30 years, an equatorial oscillation of the temperature structure with a quasi-period of 4 years has been discovered in the atmosphere of Jupiter (Orton et al. 1991, Leovy et al. 1991). This phenomenon results in a complex vertical and horizontal structure of prograde and retrograde jets. However, the wind structure of the stratosphere in the equatorial zone of Jupiter has not been measured directly. It has only been inferred in the tropical region from the thermal wind balance using temperatures measured in the jovian stratosphere and the cloud-top wind speeds measured as a initial condition (e.g. Flasar et al. 2004). But temperatures are not constrained between the upper troposphere and the middle stratosphere from observations, limiting thus the accuracy of the thermal wind balance.</p> <p>In this study, we derive self-consistently for the first time the structure of the tropical winds by utilizing wind and temperature observations all performed in the stratosphere. The wind speeds were obtained by Cavalié et al. (2021) at 1 mbar in Jupiter's stratosphere in both the equatorial and tropical regions in March 2017 with ALMA. The stratospheric thermal field was measured a few days before from the equator to the mid-latitudes with Gemini/TEXES (Giles et al. 2020). For the derivation of the wind, we use both the thermal wind equation (Pedlosky 1979) and the equatorial thermal wind equation (Marcus et al. 2019). In this paper, we will present and discuss our results.</p>

scholarly journals High Resolution 3-D Imaging of Mesospheric Sodium (Na) Layer Utilizing a Novel Multilayer ICCD Imager and a Na Lidar

2020 ◽  
Vol 12 (22) ◽  
pp. 3678
Author(s):  
Xuewu Cheng ◽  
Guotao Yang ◽  
Tao Yuan ◽  
Yuan Xia ◽  
Yong Yang ◽  
...  
Keyword(s):  
Focal Length ◽  
Horizontal Resolution ◽  
Density Profiles ◽  
Horizontal Structure ◽  
Charge Coupled Device ◽  
Observational Technique ◽  
Intensified Charge Coupled Device ◽  
Cassegrain Telescope ◽  
First Time ◽  
Different Altitudes

Equipped with a 1-meter Cassegrain telescope with 6.2 meter focal length and an electronically gated Intensified Charge-Coupled Device (ICCD), a multilayer Na imager is designed and developed at Wuhan in China. This novel instrument has successfully achieved the first preliminary 3-D image of the mesospheric Sodium (Na) layer when running alongside a Na lidar. The vertical Na layer profile is measured by the lidar, while the horizontal structure of the layer at different altitudes is measured by the ICCD imaging with a horizontal resolution of ~3.7 urad. In this experiment, controlled by the delay and width of the ICCD gating signal, the images of the layer are taken with three-second temporal resolution for every 5 km. The results show highly variable structures in both the vertical and horizontal directions within the Na layer. Horizontal images of the Na layer at different altitudes near both the permanent layer (80–100 km) and a sporadic Na layer at 117.5 km are obtained simultaneously for the first time. The Na number density profiles measured by the lidar and those derived from this imaging technique show excellent agreement, demonstrating the success of this observational technique and the first 3-D imaging of the mesospheric Na layer.

A New Approach to Kinematics Modelling of Snake-Robot Concertina Locomotion

2011 ◽  
Vol 110-116 ◽  
pp. 2786-2793
Author(s):  
Alireza Akbarzadeh ◽  
Jalil Safehian ◽  
Javad Safehian
Keyword(s):  
The Body ◽  
Function Parameter ◽  
Future Research ◽  
Main Body ◽  
New Approach ◽  
Snake Robot ◽  
Modelling Method ◽  
Dynamic Function ◽  
Basic Characteristics ◽  
First Time

In this paper, for the first time, kinematics modelling of snake robot travelling with concertina locomotion is presented. Next a novel kinematics modelling method is presented which has an advantage of allowing natural snake like locomotion. During concertina motion, certain parts of the body contract, expand or do not change their shape. This results into having different body curves for different parts of a snake. To simulate this, first we introduce a mathematical equation, called dynamic function, in which by varying a certain function parameter, body curve during motion is realized. To obtain concertina gait, the snake body is divided into three different modules, head module, tail module and main body module that connects the head to the tail module. Each module forms a specific curve which can be modelled using the proposed dynamic function. At each moment during snake locomotion, the kinematics of different links can be derived by fitting links to the body curve. Finally concertina locomotion is simulated using Webots software. Results indicate concertina locomotion can be obtained. Furthermore, the proposed dynamic function requires relatively lower computation requirement. Therefore, adaption of body curve to other real snake like gaits as well as mixed type locomotion is made possible. This works represents a first approach to a simulation of a snake-like mechanism in order to get basic characteristics of such locomotion and to enable our future research.

Ambivalent Alliance: Chinese Policy towards Indonesia, 1960–1965

2015 ◽  
Vol 221 ◽  
pp. 208-228 ◽  
Author(s):  
Taomo Zhou
Keyword(s):  
Chinese Foreign Policy ◽  
Diplomatic History ◽  
Main Body ◽  
Chinese History ◽  
Republic Of China ◽  
Ethnic Chinese ◽  
Chinese Policy ◽  
The Republic ◽  
Foreign Ministry ◽  
First Time

AbstractFrom 1960 until 1965, the People's Republic of China (PRC) built a remarkably cordial quasi alliance with the Republic of Indonesia. At the same time, however, the years between 1960 and 1965 were marked by two large waves of anti-Chinese movements in Indonesia. Although more than half a century has passed since these events, our understanding of Chinese foreign policy towards Indonesia during these turbulent years remains incomplete. In 2008, the Chinese Foreign Ministry Archives declassified for the first time documents produced during the years between 1961 and 1965. However, very recently in summer 2013, the Chinese Foreign Ministry Archives re-classified the main body of its collection. Through examining this body of fresh but currently inaccessible official records, this article aims to bridge the gap between scholarly works on the PRC's diplomatic history and overseas Chinese history. By tracing the processes by which Chinese diplomats dealt with Sukarno, the ethnic Chinese in Indonesia, and the Communist Party of Indonesia (Partai Komunis Indonesia, or the PKI), this article argues that the ambivalent Chinese alliance with Indonesia was shaped by three disparate pressures which interacted and competed with one another: the strategic need to befriend Third World countries, ethnic ties to the Chinese in Indonesia and ideological commitment to the international communist movement.

scholarly journals Distribution Patterns of Microplastics in Seawater Surface at a Portuguese Estuary and Marine Park

2020 ◽  
Vol 8 ◽  
Author(s):  
Diana Rodrigues ◽  
Joana Antunes ◽  
Vanessa Otero ◽  
Paula Sobral ◽  
Maria Helena Costa
Keyword(s):  
Marine Protected Area ◽  
Marine Pollution ◽  
Temporal Distribution ◽  
Distribution Patterns ◽  
Sea Surface ◽  
Trophic Chain ◽  
Anthropogenic Pressures ◽  
Marine Park ◽  
Baseline Evaluation ◽  
First Time

Measuring local levels of marine pollution by microplastics (MP) and identifying potential sources in coastal areas is essential to evaluate the associated impacts to environment and biota. The accumulation of floating MP at the sea surface is of great concern as the neustonic habitat consists of a feeding ground for primary consumers (including filter-feeders) and active predators, which makes these organisms a relevant via of MP input into the marine trophic chain. Here, a baseline evaluation of MP accumulation at the sea surface was conducted with a neuston net (335 μm mesh) at the Arrábida coastal area, in Portugal. The study site encompasses a marine protected area and an estuary, both under strong anthropogenic pressures due to multiple activities taking place. A short-term investigation on local spatiotemporal distribution, concentration and composition of MP was performed for the first time, through the monthly collection (summer 2018 to winter 2019) of samples at 6 stations. All the neuston samples contained MP and their mean concentration was 0.45 ± 0.52 items m−3 (mean ± SD). Both the averaged MP:neuston and MP:ichthyoplankton ratios were higher in December, when concentrations of organisms decreased. Temporal distribution patterns followed expected trends, as MP concentration was clearly higher in winter months due to precipitation and runoff. Although mean MP concentrations did not vary significantly between sampling stations, there was a spatial distribution of MP in relation to particle shape and size. Fragments were the most abundant shape and MP belonging to 1–2 mm size class were dominant. Amongst a diversity of 10 polymers identified by FTIR analysis, polyethylene (PE), polypropylene (PP) and copolymer PP/PE were the most abundant. Potential links between local sources/activities and the different polymers were suggested. Altogether, the information provided in this study aims to raise awareness among the identified sectors and consequently to act toward the prevention of MP inputs in the region.

scholarly journals Description of the first Lessepsian squid migrant, Sepioteuthis lessoniana (CEPHALOPODA: Loliginidae), in the Aegean Sea (Eastern Mediterranean)

2009 ◽  
Vol 10 (2) ◽  
pp. 87 ◽  
Author(s):  
E. LEFKADITOU ◽  
M. CORSINI-FOKA ◽  
G. KONDILATOS
Keyword(s):  
Pacific Ocean ◽  
Species Distribution ◽  
Eastern Mediterranean ◽  
Aegean Sea ◽  
Main Body ◽  
Morphometric Measurements ◽  
Important Resource ◽  
Commercially Important ◽  
Sepioteuthis Lessoniana ◽  
First Time

Loliginid squids of the Sepioteuthis lessoniana complex are widely spread in the Indo-Pacific Ocean, where they constitute a commercially important resource for neritic fisheries. Sepioteuthis lessoniana is the only Lessepsian squid migrant till now, recorded for the first time in the Mediterranean in 2002 along the Turkish Levantine coasts. Two maturing males, with mantle lengths 193 mm and 244 mm, have been recently caught near the coasts of Rhodes Island (SE Aegean), extending the species distribution northward, into Hellenic waters. Their identity was confirmed by comparison of the main body, beak characteristics and morphometric measurements with those available in the literature for this species. Suspected expansion of the Lessepsian loliginid into the Aegean Sea, due to the gradual warming of the sea, is discussed.

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