Ocean Trajectories Research Articles

A New Trajectory Clustering Method for Mining Multiple Periodic Patterns from Complex Oceanic Trajectories

Oceanic trajectories frequently exhibit multiple periodic patterns across various time intervals, e.g., tidal variations, mesoscale eddies, and El Niño events correspond to diurnal, seasonal, and interannual fluctuations in environmental factors. To explore hidden spatiotemporal multiple periodic behaviors in noisy ocean data, we propose a novel trajectory clustering method, namely DTID-STFC. It first identifies dense time intervals (DTIs) in which trajectories occur frequently. Subsequently, within each DTI, it utilizes spectral embedding to project trajectories onto a latent subspace and proposes three-way fuzzy clustering to obtain results. We evaluate the proposed method on simulated datasets and compare it with traditional and state-of-the-art trajectory clustering approaches. Experimental results indicate that it outperforms other methods across all five metrics. Moreover, when applying the DTID-STFC method to the analysis of mesoscale cyclonic eddies in the South China Sea and vessel data, it demonstrates more discernible results than traditional methods, and it aligns well with physical oceanographic processes. This proposed method offers valuable insights into identifying periodic behaviors from complex and noisy spatiotemporal oceanic trajectory data.

Fog and rain water chemistry in a tea plantation of northern Taiwan.

Tea plantations are expanding globally and many are in mountainous areas with frequent fog but few studies have examined fog chemistry in these areas. We examined chemical composition of fog and rain water at a tea plantation in northern Taiwan. Fog water was collected using a Kroneis passive cylindrical fog-water collector and rain water was collected using a 20-cm-diameter funnel. The most abundant ions were Cl- and Na+ in both fog and rain waters due to the proximity of the site to the coast. The order of abundance of other ions was NO3- > Mg2+ > SO42- > Ca2+ > NH4+ > K+ > H+ in fog water and SO42- > K+ > NO3- > NH4+ > Ca2+ > Mg2+ > H+ in rain water. The concentration enrichment ratio (fog to rain) ranged between 2.2 (K+) and 22 (Mg2+) lying between sites near major emission sources and sites in remote areas, possibly because the immediate surrounding landscape is covered with secondary forests although it is near large cities. Factor analysis highlights the influences of sea-salt aerosols on the variation of fog and rain water chemistry. Sea-salt corrections using Na+ as the sea salt tracer led to negative concentrations of Cl- and Mg2+ suggesting that assumptions involved in sea-salt corrections were not satisfied. Agriculture influence is identified as a unique factor for explaining variance of K+, NH4+, and dissolved organic nitrogen (DON) concentrations in fog water but not rain water. Ion concentrations in fog and rain water were generally higher in the weekly samples associated with air trajectories passing through the continental East Asia than those associated with oceanic trajectories pointing to the role of regional pollution sources in affecting local fog and rain water chemistry. Our study highlights greater effects of tea agriculture on fog than rain water chemistry.

The Beginning/End of Diaspora: A Kernel of Time in a Mystical Mode of Existence


 
 
 This article considers the potential payoffs of the diasporic as an analytical category developed from Indian Ocean histories that are related to and distinct from various castings of the global. Historically tracing the Indian Ocean trajectories of a Sufi Muslim family from Hadhramawt in relation to changing terms of sovereignty from the late-eighteenth century through the interwar period, the contours and crises of a normative framework for collective and individual life are recuperated and reexamined. The history of these individuals and the theory of life they presuppose and at times explicitly predicate or oppose afford the historian a view of the diasporic as capable of materializing the simultaneity of this- and other-worldly modes of existence. The article concludes that mystical interruptions of historical time that a critical diasporic lens again makes legible as an enduring global form of life represent rarely appreciated sites of emancipation.
 
 

Coral Stone Architecture, Chinese Porcelain, and Indian Ocean Artifacts along the Swahili Coast: Cross-Cultural Dynamics in Medieval East Africa

While the use of Chinese porcelain dishes in the stone towns along the Swahili coast has recently found much attention in art historical scholarship regarding the eighteenth to early twentieth centuries, the pre-history of these dynamics in the medieval period has up to now only been fully considered in other fields such as archaeology and anthropology. This paper sheds new light on the interrelations between the built environment and material culture in coastal East Africa from an art historical perspective, focusing on premodern Indian Ocean trajectories, the role of Chinese porcelain bowls that were immured into Swahili coral stone buildings, and on architecture across boundaries in a medieval world characterized by far-reaching transcultural entanglements and connectivity. It will show how Chinese porcelain bowls in premodern Swahili architecture linked the stone towns along the coast with other sites both inland and across the Indian Ocean and beyond, and how these dynamics were shaped by complex intersections between short-distance and long-distance-relationships and negotiations between the local and the global along the Swahili coast and beyond.

The Ocean Version of the Lagrangian Analysis Tool LAGRANTO

AbstractThe Lagrangian Analysis Tool (LAGRANTO) is adopted and applied to ECMWF’s latest ocean reanalysis. The primary motivation behind this study is to introduce and document LAGRANTO Ocean (LAGRANTO.ocean) and explore its capabilities in combination with an eddy-permitting ocean reanalysis. The tool allows for flexibly defining starting points, within circles, cylinders, or any user-defined region or volume. LAGRANTO.ocean also offers a sophisticated way to refine a set of computed trajectories according to a wide range of mathematical operations that can be combined into a single refinement criterion. Tools for calculating—for example, along-trajectory cross sections or trajectory densities—are further provided. After introducing the tool, three case studies are presented, which were chosen to reflect a selection of phenomena on different spatial and temporal scales. The case studies also serve as hands-on examples. For the first case study, at the mesoscale, ocean trajectories are computed during the formation of a Gulf Stream cold-core ring to study vertical motion in the developing eddy. In the second example, source waters are traced to the East Greenland Spill Jet. This example highlights the usefulness of a Lagrangian method for identifying sources or sinks of buoyancy. The third example, on annual time scales, focuses on the temporal evolution of extreme potential temperature anomalies in the South Pacific and the memory of the involved water parcels. Near-surface trajectories reveal that it takes approximately 5 months after the highest temperature anomaly before the involved water parcels cool to their climatological mean values at their new positions. LAGRANTO.ocean will be made publicly available.

Migration and diving behavior of Centrophorus squamosus in the NE Atlantic. Combining electronic tagging and Argo hydrography to infer deep ocean trajectories

A total of nine leafscale gulper sharks Centrophorus squamosus (Bonnaterre, 1788), were tagged with pop-up, satellite, archival, transmitting tags (PSAT) in the Marine Protected Area (MPA) of El Cachucho (Le Danois Bank) located in waters to the north of Spain, (NE Atlantic). Tags provided data on time, pressure and temperature that were used to examine movement patterns and diving behavior. Data collected from Argo floats in the study area have been used to devise a simple geolocation algorithm to infer the probable routes followed by this species. Tag release points revealed that C. squamosus moved both to the west (Galician waters) and to the north (Porcupine Bank) from the tagging area, suggesting well defined preferred pathways. The inferred trajectories indicated that sharks alternate periods constrained to specific geographical regions with quick and prompt movements covering large distances. Two sharks made conspicuous diurnal vertical migrations being at shallower depths around midnight and at maximum depths at midday, while other sharks did not make vertical migrations. Vertical movements were done smoothly and independently of the fish swimming long-distances or resting in the area. Overall results confirm that this species is highly migratory, supporting speeds of 20 nautical miles.day−1 and well capable to swim and make vertical migrations well above the abyssal plain.

A surface ocean trajectories visualization tool and its initial application to the Galician coast

Alavai is a free tool built with Processing to visualize forecasts of drift trajectories in the sea in a very fast and user-friendly graphic environment. It plots trajectories of both passive particles trapped near the ocean surface and oil slicks. Input data come from an operational configuration of the ROMS ocean model focused on the Euroregion Galicia (Spain) – North Portugal, however, this tool is easily adaptable to run with outputs coming from any operational high resolution ocean model configuration. The Prestige accident is used here in hindcast mode to demonstrate the main characteristics of Alavai.

Comparisons of mercury sources and atmospheric mercury processes between a coastal and inland site

Comparisons of mercury sources and atmospheric mercury processes were conducted between a coastal and inland site in northeastern North America. Identifying sources of atmospheric Hg is essential for understanding what is potentially contributing to Hg bioaccumulation at these two sites. A data set consisting of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), particle‐bound mercury, ozone, trace gases, particulate ions, and meteorological data were analyzed using principal components analysis (PCA), absolute principal component scores (APCS), and back trajectories. The PCA factors representing gaseous Hg condensation on particles during winter and combustion and industrial sources were found at both sites. However, the PCA factor for combustion/industrial sources was not found in 2010 at either site, likely because of SO2 emissions reductions from coal utilities from 2008 to 2010. Using APCS and back trajectories, the combustion/industrial factor at the coastal site was narrowed down to shipping ports along the Atlantic coast. Hg sources affecting coastal sites are different from those affecting inland sites because of the influence of marine airflows. GEM evasion from the ocean was evident from a PCA factor containing GEM, relative humidity, wind speed, and precipitation along with significantly higher contributions of this source (APCS) from oceanic trajectories compared to land/coastal trajectories. Analysis of the effects of ozone and water vapor mixing ratio on %GOM/total gaseous mercury suggest that Hg‐Br photochemistry occurred at lower ozone concentrations (<40 ppb) at the coastal site and the absence of free troposphere transport of GOM.

Pollution‐enhanced reactive chlorine chemistry in the eastern tropical Atlantic boundary layer

This study examines atmospheric reactive chlorine chemistry at the Cape Verde Atmospheric Observatory in the eastern tropical Atlantic. During May–June, 2007, Cl2 levels ranged from below detection (∼2 ppt) to 30 ppt. Elevated Cl2 was associated with high HNO3 (40 to 120 ppt) in polluted continental outflow transported in the marine boundary layer (MBL) to the site. Lower Cl2 was observed in recently subsided air masses with multiday free tropospheric oceanic trajectories and in air containing Saharan dust. Model simulations show that the observations of elevated Cl2 in polluted marine air are consistent with initiation of Cl chemistry by OH + HCl and subsequent heterogeneous, autocatalytic Cl cycling involving marine aerosols. Model estimates suggest that Cl atom reactions significantly impact the fates of methane and dimethylsulfide at Cape Verde and are moderately important for ozone cycling.

Verification of the geographical origin of modeled air-mass trajectories by means of the isotope composition of rainwater during the SALLJEX experiment

The SALLJEX experiment was held during the summer 2002–2003. It consisted of three-dimensional observation of the atmosphere to study the structure of the low level jet along the eastern slopes of the Andes. Daily precipitation water samples were collected at two stations (Resistencia and Salta) in northern Argentina and isotope content was analyzed. The isotope data were used in conjunction with air parcel trajectories obtained from a 3-D kinematic model (3D-MTC) developed by the University of Sao Paulo, Brazil. Values of deuterium excess were related with air masses of continental origin, whilst low values were associated with air masses with longer oceanic trajectories. Furthermore, although data are scarce, results show that oxygen-18 and deuterium excess in rainwater are related with the occurrence of the low level jet.

Elemental concentrations in aerosols at the Belgian coast versus seasons and air mass trajectories

Marine aerosols have extensively been monitored in the framework of a research project to investigate the inorganic and organic nutrient fluxes of the atmospheric nitrogen input into the North Sea. As a part of this project bulk analysis was also performed by energy dispersive X-ray fluorescence (EDXRF) on a total of 366 samples in order to provide detailed elemental composition. Samples have been clustered per campaign and differences were related to backward trajectories. Elements as Cl, Si, and S appeared to be the best tracers for coastal aerosols. Therefore they have been chosen to represent each campaign and to map the seasonal variations. It is clear that Cl is an excellent tracer for oceanic trajectories, while a less clear correlation between the soil dust components and the air mass trajectories is found.

Ionic and trace element composition of cloud water collected on the Olympic Peninsula of Washington State

Field measurements of the chemical composition of boundary-layer clouds that formed in clean, marine air are presented as a background reference point for comparison to cloud water composition in more polluted regions. An impaction-based sampler was used to simultaneously collect cloud water on two stages, where the ratio of droplet diameter was ∼1.1 for the two droplet size fractions. Analysis revealed that large droplets were more concentrated than smaller cloud droplets by a factor of 1.5 for sea-salt-derived species. Cloud water concentrations of ionic species were generally five times greater the concentrations of the same ions in rain water. Aqueous-phase solute concentrations in cloud varied over two orders of magnitude but generally were quite low, correlated to each other and to aerosol (CN) concentration, but negatively correlated to LWC. Air-equivalent solute concentrations were calculated, allowing the detection of the influence of air-mass trajectory on cloud-water composition. A multivariate statistical analysis of the cloud water data suggested sea salt, biogenic, crustal, and anthropogenic emission source contributions; the last two sources existed only for continental air-mass trajectories. Coastal and oceanic trajectories were selected for the purpose of estimating a northern hemisphere, mid-latitude, marine, background cloud water composition of 8 neq m −3 non-sea salt SO 4 2− and 4 neq m −3 NO 3 −.

Drifting derelicts in the North Atlantic 1883–1902

In December 1883 the U.S. Navy Hydrographic Office began to publish monthly Pilot Charts. These showed the positions and drifts of abandoned derelict sailing vessels and other danger to navigation in the North Atlantic. During the years 1887–1893 a total of 1,628 derelict sightings were made. The repeated sightings of 200 derelicts identified by name gave the first large-scale and long-term measurement of ocean trajectories. A new chart of these trajectories between 1883 and 1902 is presented showing features of the general ocean circulation and early evidence of the variability of ocean currents.

Drifting derelict trajectories in the North Atlantic

In December 1883 the U.S. Navy Hydrographic Office, a branch of the Bureau of Navigation of the Navy Department, began to publish monthly Pilot Charts. Earlier, oceanographer M.F. Maury had produced some summary survey charts showing ocean currents, winds, sailing routes, and the locations of whales. The new charts were unique in that they showed updated positions of derelict vessels and other drifting debris. From this series of positions of identified derelicts the first ocean trajectories were obtained. Much of this information has been forgotten during the last 100 years, and good collections of the Pilot Charts are rare. (The only complete collection that I could find is held by the Defense Mapping Agency.) This article is a recompilation and description of these early trajectories and a reminder of the usefulness of the Pilot Charts. It also provides a glimpse of a little known part of maritime history, the last days of wooden sailing vessels.

Properties of spectra of atmospheric turbulence at 100 metres

AbstractThe properties of spectra of vertical and horizontal turbulence and of their cross‐spectra, at elevations near 100m, are summarized; a few spectra from lower levels are considered. The following tentative conclusions are drawn: At frequencies of the order of 100c/hr and above, the spectral intensity is proportional to the square of the mean wind speed and essentially independent of the radiation intensity. At lower frequencies, the ratio of spectral intensity to the square of the wind speed increases with increasing incoming radiation. The intensity‐ratio of the co‐spectrum of vertical and horizontal velocity to the spectrum of vertical velocity increases with increasing wind shear. It also decreases with increasing frequency, n, approximately as n−1. At low frequencies, the spectral intensity of the horizontal velocity components is generally much large than that of the vertical velocity. At high frequencies, the spectral intensities of all velocity components are of the same order of magnitude. At low frequencies, the ratio of vertical to horizontal spectral density increases with increasing radiation. The quadrature spectra at a given frequency tend to be negative with large radiation, positive with little radiation. This indicates that edies are low and wide with little radiation, and tall with much radiation. The frequency at the maximum of the vertical velocity spectrum decreases with increasing height and increasing radiation intensity. The ratio of tubulent to mean energy is somewhat larger for air with over‐land trajectories than for air with oceanic trajectories.

The pilot chart of the North Atlantic Ocean, issued monthly by the United States Hydrographic Office

In December 1883 the U.S. Navy Hydrographic Office began to publish monthly Pilot Charts. These showed the positions and drifts of abandoned derelict sailing vessels and other danger to navigation in the North Atlantic. During the years 1887–1893 a total of 1,628 derelict sightings were made. The repeated sightings of 200 derelicts identified by name gave the first large-scale and long-term measurement of ocean trajectories. A new chart of these trajectories between 1883 and 1902 is presented showing features of the general ocean circulation and early evidence of the variability of ocean currents.