Assessing year to year variability of inertial oscillation in the Chukchi Sea using the wavelet transform

Master's Project (M.S.) University of Alaska Fairbanks, 2016Three years of ocean drifter data from the Chukchi Sea were examined using the wavelet transform to investigate inertial oscillation. There was an increasing trend in number, duration, and hence total proportion of time spent in inertial oscillation events. Additionally, the Chukchi Sea seems to facilitate inertial oscillation that is easier to discern using north-south velocity records rather than east-west velocity records. The data used in this analysis was transformed using wavelets, which are generally used as a qualitative statistical method. Because of this, in addition to measurement error and random ocean noise, there is an additional source of variability and correlation which makes concrete statistical results challenging to obtain. However, wavelets were an effective tool for isolating the specific period of inertial oscillation and examining how it changed over time

Frequency-Domain Stochastic Modeling of Stationary Bivariate or Complex-Valued Signals

There are three equivalent ways of representing two jointly observed real-valued signals: as a bivariate vector signal, as a single complex-valued signal, or as two analytic signals known as the rotary components. Each representation has unique advantages depending on the system of interest and the application goals. In this paper we provide a joint framework for all three representations in the context of frequency-domain stochastic modeling. This framework allows us to extend many established statistical procedures for bivariate vector time series to complex-valued and rotary representations. These include procedures for parametrically modeling signal coherence, estimating model parameters using the Whittle likelihood, performing semi-parametric modeling, and choosing between classes of nested models using model choice. We also provide a new method of testing for impropriety in complex-valued signals, which tests for noncircular or anisotropic second-order statistical structure when the signal is represented in the complex plane. Finally, we demonstrate the usefulness of our methodology in capturing the anisotropic structure of signals observed from fluid dynamic simulations of turbulence.Comment: To appear in IEEE Transactions on Signal Processin

Circular components in center of pressure signals

Static posturography provides an objective assessment of postural control by characterizing the body sway during upright standing. The Center-of-Pressure (CoP) signal is recorded by a force platform and it is analyzed by means of many different models and techniques. Most of the parameters calculated according to these different approaches are affected by relevant intra- and inter-subject variability and/or do not have a clear physiological interpretation. Traditional approaches decompose the CoP signal into antero-posterior and medio-lateral time series, corresponding to ankle plantar/dorsiflexion and hip adduction/abduction, respectively. In this study we hypothesized that CoP signals show inherent rotational characteristics. To verify our hypothesis we applied the rotary spectra analysis to the 2-dimensional CoP signal to decompose it into clockwise and counter-clockwise rotational components. We demonstrated the presence of rotational components in the CoP signal of healthy subjects, providing a reference data set of the spectral characteristics of these component

Inertial oscillations in the Gulf of Mexico during 2005 hurricane season

Near Inertial Oscillations (NIOs) are widely observed in ocean current data after severe weather. In this work, we analyzed the NIOs in the Central Gulf of Mexico (GoM) associated with 6 hurricanes/tropical storms in 2005, including Katrina and Rita, based on the deep ocean mooring from Coastal Studies Institute (CSI), LSU. The basic characteristics of the NIOs, such as phase speed, group speed, frequency, energy were discussed. The phase speed ranged from 0.56 cm/s to 2 cm/s above the thermocline for the NIOs during Hurricane Katrina and Rita, while the group velocity varied from 0.047 cm/s above the thermocline to 0.25cm/s below it for the NIOs during Hurricane Karina. The theory of NIO frequency: feff=f+ζ/2 were examined with Sea Surface Height (SSH) data, and a correlation between the real and theoretical frequencies was established (R2=0.32). A comparison between the strength of Loop Current (LC) and NIOs induced by severe hurricanes was also made. The result shows that the LC could have comparable instant high energy as severe hurricane induced NIOs, while the impact of a strong LC could last longer

The Variability of High-Frequency Motions and Their Interactions with the Mesoscale on the Mississippi Shelf

In this study, we examine the spatial and temporal variability of high-frequency and low-frequency motions across the Mississippi Shelf and how the high-frequency motions are modulated by low-frequency mesoscale motions. For this purpose, we use Acoustic Doppler Current Profiler (ADCP) measurements collected at nearshore (23 m), mid-shelf (60 m), and shelf break (88 m) stations. High-frequency motions are defined as motions with periods less than 36 hours, whereas mesoscale motions have larger periods. The collected datasets are analyzed through bandpass filtering, least square harmonic analysis, spectral analysis, and empirical orthogonal functions (EOF). We find that along-shelf barotropic mesoscale motions contain the most energy. While weak barotropic tidal motions are present, near-inertial motions with diurnal frequencies constitute a significant fraction of the high-frequency motions. In shallow water, the wind-induced near-inertial motions are found to be suppressed by low-frequency downwelling that destroys or subdues the water column stratification. However, the correlation between mesoscale processes and high-frequency motions is not found at the mid-shelf and shelf break stations

FIRST MEASUREMENTS OF BURA WIND AT SENJ WITH A THREE-AXIS ANEMOMETER

Measurements of the bora wind at Senj (east Adriatic) with a three-axis anemometer showed that at the periods smaller than 1 min turbulent eddies propagating downstream prevail, in accordance with conventional wisdom. At the periods of 5-10 min bora pulsations were observed, with rotary spectral analysis pointing to hithertho unsuspected dynamics of these pulsations

Inertia gravity waves in the upper troposphere during the MaCWAVE winter campaign – Part I: Observations with collocated radars

During the {MaCWAVE} campaign, combined rocket, radiosonde and ground-based measurements have been performed at the Norwegian Andøya Rocket Range (ARR) near Andenes and the Swedish Rocket Range (ESRANGE) near Kiruna in January 2003 to study gravity waves in the vicinity of the Scandinavian mountain ridge. The investigations presented here are mainly based on the evaluation of continuous radar measurements with the ALWIN VHF radar in the upper troposphere/ lower stratosphere at Andenes (69.3° N, 16.0° E) and the ESRAD VHF radar near Kiruna (67.9° N, 21.9° E). Both radars are separated by about 260 km. Based on wavelet transformations of both data sets, the strongest activity of inertia gravity waves in the upper troposphere has been detected during the first period from 24–26 January 2003 with dominant vertical wavelengths of about 4–5 km as well as with dominant observed periods of about 13–14 h for the altitude range between 5 and 8 km under the additional influence of mountain waves. The results show the appearance of dominating inertia gravity waves with characteristic horizontal wavelengths of ~200 km moving in the opposite direction than the mean background wind. The results show the appearance of dominating inertia gravity waves with intrinsic periods in the order of ~5 h and with horizontal wavelengths of 200 km, moving in the opposite direction than the mean background wind. From the derived downward energy propagation it is supposed, that these waves are likely generated by a jet streak in the upper troposphere. The parameters of the jet-induced gravity waves have been estimated at both sites separately. The identified gravity waves are coherent at both locations and show higher amplitudes on the east-side of the Scandinavian mountain ridge, as expected by the influence of mountains

Inertia gravity waves in the upper troposphere during the MaCWAVE winter campaign - Part I: Observations with collocated radars

During the {MaCWAVE} campaign, combined rocket, radiosonde and ground-based measurements have been performed at the Norwegian Andøya Rocket Range (ARR) near Andenes and the Swedish Rocket Range (ESRANGE) near Kiruna in January 2003 to study gravity waves in the vicinity of the Scandinavian mountain ridge. The investigations presented here are mainly based on the evaluation of continuous radar measurements with the ALWIN VHF radar in the upper troposphere/ lower stratosphere at Andenes (69.3° N, 16.0° E) and the ESRAD VHF radar near Kiruna (67.9° N, 21.9° E). Both radars are separated by about 260 km. Based on wavelet transformations of both data sets, the strongest activity of inertia gravity waves in the upper troposphere has been detected during the first period from 24–26 January 2003 with dominant vertical wavelengths of about 4–5 km as well as with dominant observed periods of about 13–14 h for the altitude range between 5 and 8 km under the additional influence of mountain waves. The results show the appearance of dominating inertia gravity waves with characteristic horizontal wavelengths of ~200 km moving in the opposite direction than the mean background wind. The results show the appearance of dominating inertia gravity waves with intrinsic periods in the order of ~5 h and with horizontal wavelengths of 200 km, moving in the opposite direction than the mean background wind. From the derived downward energy propagation it is supposed, that these waves are likely generated by a jet streak in the upper troposphere. The parameters of the jet-induced gravity waves have been estimated at both sites separately. The identified gravity waves are coherent at both locations and show higher amplitudes on the east-side of the Scandinavian mountain ridge, as expected by the influence of mountains

Northwest Tropical Atlantic Station (NTAS) : velocity data report for deployments 1 to 5

This report presents velocity data from the Northwest Tropical Atlantic Station (NTAS) deployments 1 through 5, from March 30, 2001, to February 28, 2006. The NTAS project has maintained a series of moorings near 14°50'N, 51°00'W in the northwest tropical Atlantic for air-sea flux measurement. The moorings include a surface buoy outfitted with Air- Sea Interaction Meteorology (ASIMET) systems for determination of bulk air-sea fluxes and oceanographic sensors along the upper 120 m of the mooring line. This report describes and presents the velocity data recovered from current meters and Acoustic Doppler Current Profilers (ADCPs) during the first five years of the NTAS project.Funding was provided by the National Oceanic and Atmospheric Administration under Grant No. NA09OAR432012