Ocean surface conditions associated to tropical cyclones intensification over American Tropical Seas
Following the different cases of Tropical Cyclone (TC) intensification that has been associated to TC-warm ocean feature encounters, it is analyzed here a statistical correlation among both of the satellite surface parameters, SST and SLA, and the triggering of maximum hurricane intensity. Using satellite data of altimetry and SST (Reynolds) and UNYSIS best-track data base of hurricane parameters, Ocean Surface Conditions (OSC) are investigated in relation to intensification of Tropical Cyclone (TC) during the last 15-yr period. The study region of apply is the American tropical seas, which includes Gulf of Mexico, Caribbean Sea and Eastern Tropical Pacific (ETP). In both of the basins, it is systematically identifying the OSC for each hurricane event, which were previously prevailing on the closest presence of the hurricane track at the time registered of their peak intensity. Results indicate a major thermal favorable OSC for the TC intensify on the eastern Gulf of Mexico and northwestern Caribbean Sea than the ETP. Moreover, SLA seems to be a significant role on boosting the TC intensification, nevertheless about half of the major hurricanes that developed in each of both of the regions appear to have encountered negative anomalies of their prevail OSC. These precedents represent a high complex degree for TC intensification monitoring and forecasting challenge by the only use of OSC tracking by satellite sensoring, but also to deal operatively with TC intensity maintenance.
Design of an integrated flow sensor device with application for monitoring in-situ pH and redox of hydrothermal diffuse flow fluids at mid-ocean ridges
In-situ measurement of fluid chemistry with chemical sensors at deep sea conditions is always affected by drifting phenomena, which can be especially serious for long-term monitoring studies. Although fundamental changes in sensor design can be used to lessen the effect of this, in-situ calibration is still an unusually effective means to ensure measurement accuracy. With recent development of more reliable valves and pumps applicable for deep sea operation, together with results of laboratory studies showing the viability of solid state chemical sensors, it now possible to achieve in-situ calibration for sensor measurements under challenging chemical and physical conditions. Thus, a new flow device has been designed to facilitate chemical sensor measurements (e.g., pH and redox) in diffuse flow hydrothermal systems at mid-ocean ridges. The integrated calibration and measurement system was developed with a notion of promoting in-situ data acquisition at deep-sea vents for extended periods of time. Accordingly, it enables integration of multiple thermal and chemical sensors, while allowing automated in-situ calibration during deployment. Laboratory tests have successfully demonstrated the effectiveness of this in-situ calibration. For instance in the case of pH measurement with Ir/IrOx pH sensor in NaCl-bearing fluid at 220 bars, the device not only insured reliable measurement in seawater-type fluids, but also revealed effectiveness during measurement of fluids having dissolved CO2 up to 0.52 mol/kg, which is relevant to conditions likely in volcanically active back- arc settings, fluids issuing from cold seeps, as well as monitoring studies in connection with different carbon sequestration scenarios. The sea-going device consists of a sensor cell with limited internal volume of ~ 1 ml for more effectively enhancing interaction between incoming sample fluid and integrated temperature/chemical sensors. The instrument also contains a computer-controlled process control valve, which permits automatic selection of source fluid (sample, standards). Importantly, the control valve limits exposure of the chemical and temperature sensors to the local environment, limiting potential problems associated with bio fouling. The devise can be connected to a fluid delivery and data logging system with flexible flow line and undersea cables for conducting in-situ measurement and calibration tasks on moderately long time scales (Tan et al., 2009). The instrument is designed in such a way that it can be easily operated by a manipulator on HOV and ROV submersibles. During recent studies at seafloor diffuse flow vent sites at 9°N EPR and also at Mid- Atlantic Ridge, solid state iridium pH electrode and Pt (redox) electrode, together with a Ag/AgCl reference electrode, and thermistor, provided effective, high-resolution, time series data. During these deployments, several in-situ calibrations for pH measurement were successfully performed. Although the in-situ measurement and calibration device was largely developed for seafloor hydrothermal diffuse vent fluid applications, a wide range of other applications are possible, especially if power limitations can be overcome, as possible with the advance of cabled observatories. Reference Tan C., Ding K., Jin B., Seyfried W. E., Jr., and Chen Y. (2009) In-situ pH calibration and measurement in deep sea environments.IEEE Journal of Oceanic Engineering (submitted).
High Precision 13C/12C Measurement of Dissolved Carbon Using a Transportable Cavity Ring-Down Spectrophotometer System
We report here on the measurement of high precision δ13C from total inorganic carbon (TIC) and dissolved organic carbon (DOC) using a sample preparation system coupled to a small footprint Wavelength- Scanned Cavity Ring-Down Spectrometer (WS-CRDS). This system is capable of applying a 5% H3PO4 solution or a sodium persulfate oxidation process to a water sample in an exetainer vial, thereby liberating gaseous CO2 and permitting stable carbon isotope measurement in TIC and DOC, respectively. The isotopic carbon signature determination can then be used to trace the origin of carbonates or organic carbon compounds. In a first phase, a manual process was employed in which TIC containing samples were acidified and the evolved CO2 was collected inside gas pillows. The gas pillows were then connected to the inlet of the isotopic WS-CRDS instrument for carbon ratio measurement. In a second phase, the CO2 liberation processes were automated in an integrated analyzer enabling software control of a sample preparation system directly connected to the gas inlet of the isotopic WS-CRDS instrument. A measurement precision of the isotopic ratio in the range of 0.2 to 0.4 permil was achieved in minutes of measurement time. Such precision readily distinguishes the isotopic TIC and DOC signatures from a set of three different stream water samples collected from various sites in Northern California. The current TIC/DOC- CRDS setup will enable shipboard measurement and presents a rugged, portable and inexpensive analytical instrumentation alternative to the traditional use of methods based on the more complex and lab-confined isotope ratio mass spectrometry technique.
Passive Acoustic Techniques for Monitoring Ocean Dynamics
Ambient noise in the ocean carries vast information about physical properties of the propagation medium, including sound speed and current velocity fields in the water column and geoacoustic parameters of the sea floor. Passive acoustic techniques utilize the ambient noise and sound sources of opportunity, such as shipping, to retrieve environmental information from measurements of acoustic pressure on hydrophone arrays without need for any controlled sound sources. Non-invasive nature of passive acoustic techniques and the types of the environmental characteristics these provide, combined with their low power requirements and the intrinsic needs for long observation times, near real-time access to data, and rather large data flows, make the passive acoustics ideally suited for incorporation into cabled ocean observatories. In this paper, we focus on retrieval of environmental parameters from the cross-correlation function of ambient noise. It is shown theoretically that, with the averaging time being sufficiently long, the two-point correlation function of diffuse ambient noise in an arbitrary inhomogeneous, moving medium contains as much information about the environment as can be obtained acoustically by placing transceivers in the two points. Thus, measurements of the noise cross-correlation allow one to quantify flow-induced acoustic non-reciprocity and evaluate both spatially averaged flow velocity and sound speed between the two points. Limitations are discussed which arise from the fact that ambient noise in the ocean is neither perfectly diffuse nor stationary. As an example of opportunities offered by coherent processing of ambient noise, we introduce the concept of a passive inverted echo sounder which would provide measurements of the heat content of the ocean and characterize the local internal gravity wave processes, much like conventional, active inverted echo sounders. Instead of radiating sound, the passive inverted echo sounder employs high-frequency acoustic noise generated by interaction and breaking of waves on the ocean surface as well as low-frequency noise from distant shipping to measure two-way acoustic travel times between near-bottom acoustic sensors and reflective ocean surface as well as scattering layers in the water column. The use of linear hydrophone arrays to decrease the necessary averaging times and improve accuracy of the correlation measurements of acoustic travel times will be discussed.
Can Ionospheric Sounding Help Oceanic Monitoring ?
A series of ionospheric anomalies following the Sumatra tsunami has been reported in the scientific literature (e.g., Liu et al. 2006; DasGupta et al. 2006; Occhipinti et al. 2006). Similar anomalies were also observed after the tsunamigenic earthquake in Peru in 2001 (Artru et al., 2005). All these anomalies show the signature in the ionosphere of tsunami-generated internal gravity waves (IGW) propagating in the neutral atmosphere over oceanic regions. The strong amplification mechanism of atmospheric IGW allows to detect these anomalies when the tsunami is offshore where the see level displacement is still small. In addition, the dense coverage of ionospheric sounding instruments over the oceans increases over time and more instruments will be able to provide ionospheric measurements: i.d., Doppler sounding, over-the-horizon radar (OTH) and space-based GPS data (e.g., COSMIC). Most of the ionospheric anomalies are also deterministic and reproducible by numerical modeling (Occhipinti et al., 2006, 2008) via the ocean/neutral atmosphere/ionosphere coupling mechanism. In addition, the numerical modeling supplies useful helps in the estimation of expected anomalies The sensitivity of altimeters, OTH radar, ground-based and space-based GPS measurements is analyzed in this work by the way of the modeling and data. The results are used to discuss the role of ionospheric sounding in the future oceanic monitoring and tsunami warning system. [Artru et al., 2005] Geophys. J. Int., 160, 2005 [DasGupta et al., 2006] Earth Planet. Space, 35, 929-959. [Liu et al., 2006] J. Geophys. Res., 111, A05303. [Occhipinti et al., 2006] Geophys. Res. Lett., 33, L20104, 2006 [Occhipinti et al., 2008] Geophys. J. Int., 173, 3, 753-1135, 2008.