There are a number of people who have contributed to my success in graduate school. First, I'd li... more There are a number of people who have contributed to my success in graduate school. First, I'd like to thank my PhD advisor, Prof. Thomas Orlando, for support, valuable critiques on ideas and manuscripts, and for always amazingly coming through just in the nick of time when it really mattered. Maria Rusert, my partner, for her understanding and encouragement and for generally being awesome. Drs. Alexandr
Interactions and Transformation in the Chemical Sciences Division. His research interests include... more Interactions and Transformation in the Chemical Sciences Division. His research interests include theories of chemical reactions, with focus on the effects of molecular environment (liquids, solids, and interfaces) on chemical reaction rates, molecular theories of gas-to-particle nucleation, and molecular simulations of molecular processes at aqueous interfaces. He is an American Physical Society Fellow.
Arctic coastal waters are characterized by seasonal retreat and advance of sea ice. The timing of... more Arctic coastal waters are characterized by seasonal retreat and advance of sea ice. The timing of advance and retreat varies substantially from year to year. Various activities, ranging from marine transport to the use of sea ice as a platform for industrial activity or winter travel, are affected by variations in the timing of break-up and freeze-up, resulting in a need for indicators to document the regional and temporal variations in coastal areas. Here we develop indicators based on daily sea ice concentrations derived from satellite passive microwave measurements. The "day of year" indicators are designed to optimize value for users while building on past studies characterizing break-up and freeze-up dates in the open pack ice. Relative to indicators for broader adjacent seas, the coastal indicators show later break-up at sites known to have extensive landfast ice, for which break-up typically lags retreat of the adjacent, thinner drifting ice. The coastal indicators also show an earlier freeze-up at some sites in comparison with freeze-up for broader offshore regions, likely tied to earlier freezing of shallow water regions and areas affected by freshwater input from nearby streams and rivers. A factor analysis performed to synthesize the local indicator variations shows that the local break-up and freeze-up indicators have greater spatial variability than corresponding metrics based on regional ice coverage. However, the trends towards earlier break-up and later freeze-up are unmistakable over the post-1979 period in the synthesized metrics of the coastal break-up/freeze-up and their corresponding regional ice coverage. The findings imply that locally defined indicators can serve as key links between pan-Arctic or global indicators such as sea-ice extent or volume and local uses of sea ice, with the potential to inform community-scale adaptation and response.
The timing of sea ice retreat and advance in Arctic coastal waters varies substantially from year... more The timing of sea ice retreat and advance in Arctic coastal waters varies substantially from year to year. Various activities, ranging from marine transport to the use of sea ice as a platform for industrial activity or winter travel, are affected by variations in the timing of breakup and freeze-up, resulting in a need for indicators to document the regional and temporal variations in coastal areas. The primary objective of this study is to use locally based metrics to construct indicators of breakup and freeze-up in the Arctic and subarctic coastal environment. The indicators developed here are based on daily sea ice concentrations derived from satellite passive-microwave measurements. The "day of year" indicators are designed to optimize value for users while building on past studies characterizing breakup and freeze-up dates in the open pack ice. Relative to indicators for broader adjacent seas, the coastal indicators generally show later breakup at sites known to have landfast ice. The coastal indicators also show earlier freeze-up at some sites in comparison with freeze-up for broader offshore regions, likely tied to earlier freezing of shallow-water regions and areas affected by freshwater input from nearby streams and rivers. A factor analysis performed to synthesize the local indicator variations shows that the local breakup and freeze-up indicators have greater spatial variability than corresponding metrics based on regional ice coverage. However, the trends towards earlier breakup and later freeze-up are unmistakable over the post-1979 period in the synthesized metrics of coastal breakup and freeze-up and the corresponding regional ice coverage. The findings imply that locally defined indicators can serve as key links between pan-Arctic or global indicators such as sea ice extent or volume and local uses of sea ice, with the potential to inform community-scale adaptation and response.
The primary goal of this paper is to demonstrate the dependence of Arctic Ocean sea-ice transport... more The primary goal of this paper is to demonstrate the dependence of Arctic Ocean sea-ice transport pathways on climate variations. We build our analysis on the results of Proshutinsky and Johnson (1997), Johnson and others (1999), Polyakov and others (1999) and Proshutinsky and others (1999), where we have shown that wind-driven ice motion and upper ocean circulation alternate between anticyclonic and cyclonic states. Shifts between regimes occur at 5−7 year intervals, resulting in a 10−15 year period. The anticyclonic circulation regime has been observed in our model results for 1946−52,1958−62,1972−79,1984−88 and 1998−present. The cyclonic circulation regime prevailed during 1953−57,1963−71,1980−83 and 1989−97. The regime shifts are fundamentally important to understanding the Arctic’s general circulation and particularly useful for estimating pollution transport by sea ice and surface waters. It is important to pollution studies to understand which circulation regime prevails. Ini...
Variability in sea ice conditions, combined with strong couplings to the atmosphere and the ocean... more Variability in sea ice conditions, combined with strong couplings to the atmosphere and the ocean, lead to a broad range of complex sea ice dynamics. More in-situ measurements are needed to better identify the phenomena and mechanisms that govern sea ice growth, drift, and breakup. To this end, we have gathered a dataset of in-situ observations of sea ice drift and waves in ice. A total of 15 deployments were performed over a period of 5 years in both the Arctic and Antarctic, involving 72 instruments. These provide both GPS drift tracks, and measurements of waves in ice. The data can, in turn, be used for tuning sea ice drift models, investigating waves damping by sea ice, and helping calibrate other sea ice measurement techniques, such as satellite based observations.
This study was motivated by a strong warming signal seen in mooring-based and oceanographic surve... more This study was motivated by a strong warming signal seen in mooring-based and oceanographic survey data collected in 2004 in the Eurasian Basin of the Arctic Ocean. The source of this and earlier Arctic Ocean changes lies in interactions between polar and sub-polar basins. Evidence suggests such changes are abrupt, or pulse-like, taking the form of propagating anomalies that can be traced to higher-latitudes. For example, an anomaly found in 2004 in the eastern Eurasian Basin took $1.5 years to propagate from the Norwegian Sea to the Fram Strait region, and additional $4.5-5 years to reach the Laptev Sea slope. While the causes of the observed changes will require further investigation, our conclusions are consistent with prevailing ideas suggesting the Arctic Ocean is in transition towards a new, warmer state.
Kelvin waves excited by the wind in the western equatorial Pacific Ocean propagate eastward to th... more Kelvin waves excited by the wind in the western equatorial Pacific Ocean propagate eastward to the boundary and then poleward along the coast. Poleward propagating coastal Kelvin waves produce a signal that propagates away from the coast as westward propagating Rossby waves with amplitude proportional to the amplitude of the passing Kelvin wave. The frequency of the Kelvin wave signal sets the frequency of the Rossby response and the possible wavelengths through the Rossby dispersion relation. This paper examines the role of coastal Kelvin waves in the mid-latitude response of the ocean in general, and the mid-latitude 1982-1983 FJ Nino response in particular, using two primitive equation numerical models of the equatorial and northeast Pacific Oceans. The equatorial model, in agreement with observations, shows a large amplitude Kelvin wave propagating eastward along the equator as a prelude to the 1982-1983 FJ Nino and then poleward along the coast. A time series of the model coastal signal from 1975 through 1984, extracted from the equatorial model, forces a northeast PacifIC Ocean model near the coast at 18°N, allowing signals to propagate from the equator through low-latitudes to mid-latitudes. Model results show, (1) that the coastal Kelvin wave initializes and defmes the frequency of the offshore propagating Rossby wave (2) that the Keivin-Rossby response is fundamental to the development of the mid-latitude 1982-1983 FJ Nino and, (3) that Rossby waves at 30 ° N extend the signal seaward from the coast several thousand kilometers, although the Rossby wave signal loses its identity in the region of the California Current several hundred kilometers from the coast.
F airballks J~ J. O'BRIEN Mut)$Cale Air-Sea InteractWft GrOllp, Florida S1QU Uniwrsil)'. Tallahas... more F airballks J~ J. O'BRIEN Mut)$Cale Air-Sea InteractWft GrOllp, Florida S1QU Uniwrsil)'. Tallahas.ree A wind-driven,l1OII1inear, reduced gravity, primitive equatim model is used to simulate the circulation cI: the northeast Pacific Ocean includmg the northeast Gulf of AJaska. 11IC mOOel includes the affects of bottoo1 tOIX>graPlY. Model geometry m~ses the entire Gulf of AJaska regim frc:m V an~ver Island to west of K<XIiak Island. This region is traditimally beyond the latiwde limiu of the reduced gravity model imposed by a weakening thermocline away ~ the equator. The model resolutioo, 0.025" in latitude and lmgitude, is very fine. This is die first time that a model of this type and resolutioo has been successfully run at these latitudes. Ahhough we expected that such resolutim would allow the mesoscale eddy field to devdop, it did not. One reason may be the coarse spatial and temporal winds. Twenty year of Comprehensive Ocean-AtmosPlere Data Set pseudo wind stress data used to drive the model are statistically analyzed to obtain a wind stress climatology. After model lPn-up, the mmthly stresses for 1986-1989 are used to drive the model. The model reproduces many of the regional oceanographic features such as the Alaskan Gyre, the Alaska Current, the Alaska Coastal Current, the Sitka eddy, and an intense, cyclonic eddy (that has not yet been reponed in the literature) northwest of the Queen OIarlotte Island in the spring. In additim, the model displays seasonal and interannual variability. Model results are validated through comparisons with National Ocean Service coastal sea level records and a multilayer, oceanic basin scale model being run at the Institute for Naval Oceanography.
The ocean's response to atmospheric forcing and to forcing along the coast by Kelvin waves is exa... more The ocean's response to atmospheric forcing and to forcing along the coast by Kelvin waves is examined in light of nearshore seasonal variability and the major 1982-1983 El Nino. In addition to driving the northeast Pacific gyre and local currents, the wind modifies the depth to the main thermocline, changing the apparent westward phase speed of Rossby waves excited by passing Kelvin waves. The amplitude of the passing Kelvin wave determines whether the Rossby wave depresses or raises the thermocline while propagating westward. Along the northeast Pacific coast from Oregon to Washington, model results suggest that the wind raises the main thermocline during the 1982-1983 El Nino. Generally, the coastal response off Oregon and Washington appears to be strongly driven by the large-scale atmosphere, while along the California coast and south to the equator, the doniinant El Nino signal has an oceanic origin. That signal, with periods between 2 and 5 years, originates in the western equatorial Pacific Ocean and is tracked eastward through the equatorial waveguide and then poleward along the coast to SOON using data from two reduced gravity, primitive equation models coupled at 18"N. At shorter, seasonal time scales, the acceleration of the wind appears to be an important mechanism in driving coastal currents.
Journal of the Acoustical Society of America, May 1, 1995
Travel times of acoustic signals were measured between the bottom-mounted Kaneohe source near Oah... more Travel times of acoustic signals were measured between the bottom-mounted Kaneohe source near Oahu and seven SOSUS stations at 3000–4000-km distance during 1983–1989. The Naval Research Laboratory hydrodynamic eddy resolving model yields changes in travel time whose standard deviations are consistent with the data. The model predicts that between 1981–1993, Rossby waves modify travel times by one second. Mesoscale eddies modify travel times little compared to Rossby waves. The largest Rossby waves are descendants of El Nino. Travel times changes are sensitive indicators of predictable features in the Naval Research Laboratory model. [Work supported by the Strategic Environmental Research and Development Program, managed by the Advanced Research Projects Agency.]
Variadons in dJe theImocline depth of the northeast Pacific Ocean during 1970-1989 are investigat... more Variadons in dJe theImocline depth of the northeast Pacific Ocean during 1970-1989 are investigated using a reduced-gravity numerical model forced by dJe local surface wind stress and at the southern land-ocean boundary by a coastal Kelvin wave signal. Three experiments are presented with forcings by wind only, Kelvin wave only, and a combination of both. The wind forcing generates an anticyclonic gyre cin;u1ation with mostly annual variatiOns. The Kelvin waves along the coast excite Rossby waves that propagate into the basin interior, producing changes in upper-layer thickness (related to changes in thermocline depth) that last for years after the Kelvin signal has passed. Two sequential upwelling Kelvin waves in 1973 and 1975 produce upwelling Rossby waves that reduce the mean upper-layer thickness by approximately 10-20 m during 1976. This shift is reinforced by later upwelling events lasting until the early 19808. The authors present a new hypothesis that the previously known climate shift observed in winter sea surface temperature is influenced by changes in the depth of the pennanent thermocline induced by remotely forced Rossby waves. Acoustic thermometry might be a sensitive means to detect Rossby waves, motivating a thermometric approach to studying interannual variatiOns in the ocean. The role of the Rossby waves in the travel time variations of acoustic signals on geodesic paths from Hawaii to the North American coast are calculated using the scheme of Roed. Wind forcing produces mainly annual variations in the acoustic travel time anomalies, except for the high latitude paths above 4/J"N that exhibit sudden shifts in travel times due to changes in the magnitude of the wind stress. The Rossby waves are primarily responsible for interannual variations.
3. The changes in travel time were shown to be due to variations in the spatially averaged temper... more 3. The changes in travel time were shown to be due to variations in the spatially averaged temperature along the sections. Fluctuations in currents, salinity, hydrostatic pressure, and acoustic path were shown to have small contributions to the changes ill travel time. Temperature variations as little as 0.02 °C were detected. Ab6troCt-The Kaneohe source experiment in the 1980's demonstrated the feasibility of \lSing sound to monitor global warming trends in the ocean with sound. This experiment used a source cabled to shore and the Navy's SOSUS stations for receivers. The GAMOT group is developing new instruments to obtain similar data in near-real time but at about one-eighth the cost of instruments cabled to shore. This approach has the potential for obtaining global oceall measurements of temperature at 500 km resolution less oxpensively than that routinely expended for measuring atmospheric temperatures. GAMOT is using state-of-the art models of the ocean to luterpret temperature changes.
The Journal of the Acoustical Society of America, 1999
The difficulties in detecting anthropogenic changes in ocean temperature due to the industrial re... more The difficulties in detecting anthropogenic changes in ocean temperature due to the industrial revolution are discussed using acoustic thermometry data taken between Oahu and seven SOSUS receivers at distances of 3000–4000 km. Measurements were made in late 1983, and over two 5-month intervals between 1987 and 1989. The travel times are dominated by interannual fluctuations. Two hydrodynamic ocean models are used to identify plausible oceanic features that could cause these variations. Modeled El Niños and La Niñas exhibit oceanic teleconnections between the Equator and mid-latitudes that lead to Rossby waves that propagate westward at mid−latitudes. Rossby waves are the dominant model features which affect the modeled acoustic travel times, and hence section-averaged temperatures in the eastern North Pacific. Modeled predictions of the travel times are significantly different than some of the data. The magnitude and rates of changes of the data are the same as those which result fr...
Complex empirical orthQIOnal function (CEOP) analysis is used to investigate the coastal Kelvin w... more Complex empirical orthQIOnal function (CEOP) analysis is used to investigate the coastal Kelvin wave driven Rossby wave response in the northeast Pacific. Using CEOF analysis, a spatial stmcture function is obtained from model upper layer thickness data. The model is a nonlinear, reduced gravity model of the northeast Pacific forced by coastal Kelvin waves originatinl in the equatorial Pacific. The spatial stmcture function is used to extract the interannual Rossby wave response from observed 300-m-depth temperature anomalies. The observed Rossby wave signal is termed the projection mode. Rossby wavelike feanues observed in the projection mode are onIer 1(MX) km long with most periods ranging between 2 and 4 years. The wave numbeR and frequencies found are consistent with Rossby d~cs. The mean phase speed of the Rossby wavelike features within the projection mode is 1.3 cm s-1, in agreement with the theoretical Rossby wave phase speed at 400N. Large amplitude nearshore and decreasing amplitude away from shore suggests nearshore generation of these waves. An important source of sea level variability along the east coast of North America at periods of 2-4 years was identified by Pares-Sierra and O'Brien (1989) as poleward propaga~n~ Kelvin waves. Since the Rossby wavelike features observed in the projection mode have a ~ty of their periods raDging between 2 and 4 yean, their forcing can be attributed to long-period Kelvin waves. Spectral comparisons between the nearshore values in the projection mode and coastal sea level show greater than 90% coherence in the period band 3-4.4 years. The high coherence between coastal sea level variations and the projection mode shows that there is a strong correlation between the Rossby wavelike features within the projection mode and coastal Kelvin wave propaption. It is concluded that the Rossby waves within the projection mode are forced by coastal Kelvin wave propagation. The projection mode accounts for 47.5% of the variance in the 300-m-depth temperature anomalies. The implication of this result is that the physical mechanism of the numerical model, i.e., Rossby waves excited by coastal Kelvin wave propagation, accounts for 47.5% of the variance in the observed 300-m depth temperature anomalies.
The International Journal of Supercomputing Applications, 1990
Two numerical models utilizing primitive equations (two momentum equations and a mass continuity ... more Two numerical models utilizing primitive equations (two momentum equations and a mass continuity equation) simulate the oceanography of the Pacific Ocean from 20°S to 50°N. Results show Kelvin waves thousands of kilometers long propagating from the equator to the northeast Pacific Ocean. Kelvin waves are very long waves that propagate along the equator and along solid boundaries with the boundary to their right. They are important to simulations of ocean circulation along the North American coast because they carry information at seasonal and longer periods from the equator poleward. Modeling an extensive region such as the Pacific Ocean with adequate two-dimensional resolution places heavy demands on computer memory and storage. We have found that the best way to examine the abundant model data is through visualization, by animating the appro priate model fields and viewing the time history of each model simulation as a color movie. The animations are used as research products to a...
In the regions of flat immobile landfast ice (shallow Siberian Seas with depths less than 25-30 m... more In the regions of flat immobile landfast ice (shallow Siberian Seas with depths less than 25-30 m), the models generally overestimate both the total observed sea ice thickness and rates of September and October ice growth from observations by more than 4 times and more than one standard deviation, respectively. The models do not reproduce conditions of fast ice formation and growth. Instead, the modeled fast ice is replaced with pack ice which drifts, generating ridges of increasing ice thickness, in addition to thermodynamic ice growth. Considering all observational data sets, the better correlations and smaller differences from observations are from the Estimating the Circulation and Climate of the Ocean, Phase II and Pan-Arctic Ice Ocean Modeling and Assimilation System models.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
There are a number of people who have contributed to my success in graduate school. First, I'd li... more There are a number of people who have contributed to my success in graduate school. First, I'd like to thank my PhD advisor, Prof. Thomas Orlando, for support, valuable critiques on ideas and manuscripts, and for always amazingly coming through just in the nick of time when it really mattered. Maria Rusert, my partner, for her understanding and encouragement and for generally being awesome. Drs. Alexandr
Interactions and Transformation in the Chemical Sciences Division. His research interests include... more Interactions and Transformation in the Chemical Sciences Division. His research interests include theories of chemical reactions, with focus on the effects of molecular environment (liquids, solids, and interfaces) on chemical reaction rates, molecular theories of gas-to-particle nucleation, and molecular simulations of molecular processes at aqueous interfaces. He is an American Physical Society Fellow.
Arctic coastal waters are characterized by seasonal retreat and advance of sea ice. The timing of... more Arctic coastal waters are characterized by seasonal retreat and advance of sea ice. The timing of advance and retreat varies substantially from year to year. Various activities, ranging from marine transport to the use of sea ice as a platform for industrial activity or winter travel, are affected by variations in the timing of break-up and freeze-up, resulting in a need for indicators to document the regional and temporal variations in coastal areas. Here we develop indicators based on daily sea ice concentrations derived from satellite passive microwave measurements. The "day of year" indicators are designed to optimize value for users while building on past studies characterizing break-up and freeze-up dates in the open pack ice. Relative to indicators for broader adjacent seas, the coastal indicators show later break-up at sites known to have extensive landfast ice, for which break-up typically lags retreat of the adjacent, thinner drifting ice. The coastal indicators also show an earlier freeze-up at some sites in comparison with freeze-up for broader offshore regions, likely tied to earlier freezing of shallow water regions and areas affected by freshwater input from nearby streams and rivers. A factor analysis performed to synthesize the local indicator variations shows that the local break-up and freeze-up indicators have greater spatial variability than corresponding metrics based on regional ice coverage. However, the trends towards earlier break-up and later freeze-up are unmistakable over the post-1979 period in the synthesized metrics of the coastal break-up/freeze-up and their corresponding regional ice coverage. The findings imply that locally defined indicators can serve as key links between pan-Arctic or global indicators such as sea-ice extent or volume and local uses of sea ice, with the potential to inform community-scale adaptation and response.
The timing of sea ice retreat and advance in Arctic coastal waters varies substantially from year... more The timing of sea ice retreat and advance in Arctic coastal waters varies substantially from year to year. Various activities, ranging from marine transport to the use of sea ice as a platform for industrial activity or winter travel, are affected by variations in the timing of breakup and freeze-up, resulting in a need for indicators to document the regional and temporal variations in coastal areas. The primary objective of this study is to use locally based metrics to construct indicators of breakup and freeze-up in the Arctic and subarctic coastal environment. The indicators developed here are based on daily sea ice concentrations derived from satellite passive-microwave measurements. The "day of year" indicators are designed to optimize value for users while building on past studies characterizing breakup and freeze-up dates in the open pack ice. Relative to indicators for broader adjacent seas, the coastal indicators generally show later breakup at sites known to have landfast ice. The coastal indicators also show earlier freeze-up at some sites in comparison with freeze-up for broader offshore regions, likely tied to earlier freezing of shallow-water regions and areas affected by freshwater input from nearby streams and rivers. A factor analysis performed to synthesize the local indicator variations shows that the local breakup and freeze-up indicators have greater spatial variability than corresponding metrics based on regional ice coverage. However, the trends towards earlier breakup and later freeze-up are unmistakable over the post-1979 period in the synthesized metrics of coastal breakup and freeze-up and the corresponding regional ice coverage. The findings imply that locally defined indicators can serve as key links between pan-Arctic or global indicators such as sea ice extent or volume and local uses of sea ice, with the potential to inform community-scale adaptation and response.
The primary goal of this paper is to demonstrate the dependence of Arctic Ocean sea-ice transport... more The primary goal of this paper is to demonstrate the dependence of Arctic Ocean sea-ice transport pathways on climate variations. We build our analysis on the results of Proshutinsky and Johnson (1997), Johnson and others (1999), Polyakov and others (1999) and Proshutinsky and others (1999), where we have shown that wind-driven ice motion and upper ocean circulation alternate between anticyclonic and cyclonic states. Shifts between regimes occur at 5−7 year intervals, resulting in a 10−15 year period. The anticyclonic circulation regime has been observed in our model results for 1946−52,1958−62,1972−79,1984−88 and 1998−present. The cyclonic circulation regime prevailed during 1953−57,1963−71,1980−83 and 1989−97. The regime shifts are fundamentally important to understanding the Arctic’s general circulation and particularly useful for estimating pollution transport by sea ice and surface waters. It is important to pollution studies to understand which circulation regime prevails. Ini...
Variability in sea ice conditions, combined with strong couplings to the atmosphere and the ocean... more Variability in sea ice conditions, combined with strong couplings to the atmosphere and the ocean, lead to a broad range of complex sea ice dynamics. More in-situ measurements are needed to better identify the phenomena and mechanisms that govern sea ice growth, drift, and breakup. To this end, we have gathered a dataset of in-situ observations of sea ice drift and waves in ice. A total of 15 deployments were performed over a period of 5 years in both the Arctic and Antarctic, involving 72 instruments. These provide both GPS drift tracks, and measurements of waves in ice. The data can, in turn, be used for tuning sea ice drift models, investigating waves damping by sea ice, and helping calibrate other sea ice measurement techniques, such as satellite based observations.
This study was motivated by a strong warming signal seen in mooring-based and oceanographic surve... more This study was motivated by a strong warming signal seen in mooring-based and oceanographic survey data collected in 2004 in the Eurasian Basin of the Arctic Ocean. The source of this and earlier Arctic Ocean changes lies in interactions between polar and sub-polar basins. Evidence suggests such changes are abrupt, or pulse-like, taking the form of propagating anomalies that can be traced to higher-latitudes. For example, an anomaly found in 2004 in the eastern Eurasian Basin took $1.5 years to propagate from the Norwegian Sea to the Fram Strait region, and additional $4.5-5 years to reach the Laptev Sea slope. While the causes of the observed changes will require further investigation, our conclusions are consistent with prevailing ideas suggesting the Arctic Ocean is in transition towards a new, warmer state.
Kelvin waves excited by the wind in the western equatorial Pacific Ocean propagate eastward to th... more Kelvin waves excited by the wind in the western equatorial Pacific Ocean propagate eastward to the boundary and then poleward along the coast. Poleward propagating coastal Kelvin waves produce a signal that propagates away from the coast as westward propagating Rossby waves with amplitude proportional to the amplitude of the passing Kelvin wave. The frequency of the Kelvin wave signal sets the frequency of the Rossby response and the possible wavelengths through the Rossby dispersion relation. This paper examines the role of coastal Kelvin waves in the mid-latitude response of the ocean in general, and the mid-latitude 1982-1983 FJ Nino response in particular, using two primitive equation numerical models of the equatorial and northeast Pacific Oceans. The equatorial model, in agreement with observations, shows a large amplitude Kelvin wave propagating eastward along the equator as a prelude to the 1982-1983 FJ Nino and then poleward along the coast. A time series of the model coastal signal from 1975 through 1984, extracted from the equatorial model, forces a northeast PacifIC Ocean model near the coast at 18°N, allowing signals to propagate from the equator through low-latitudes to mid-latitudes. Model results show, (1) that the coastal Kelvin wave initializes and defmes the frequency of the offshore propagating Rossby wave (2) that the Keivin-Rossby response is fundamental to the development of the mid-latitude 1982-1983 FJ Nino and, (3) that Rossby waves at 30 ° N extend the signal seaward from the coast several thousand kilometers, although the Rossby wave signal loses its identity in the region of the California Current several hundred kilometers from the coast.
F airballks J~ J. O'BRIEN Mut)$Cale Air-Sea InteractWft GrOllp, Florida S1QU Uniwrsil)'. Tallahas... more F airballks J~ J. O'BRIEN Mut)$Cale Air-Sea InteractWft GrOllp, Florida S1QU Uniwrsil)'. Tallahas.ree A wind-driven,l1OII1inear, reduced gravity, primitive equatim model is used to simulate the circulation cI: the northeast Pacific Ocean includmg the northeast Gulf of AJaska. 11IC mOOel includes the affects of bottoo1 tOIX>graPlY. Model geometry m~ses the entire Gulf of AJaska regim frc:m V an~ver Island to west of K<XIiak Island. This region is traditimally beyond the latiwde limiu of the reduced gravity model imposed by a weakening thermocline away ~ the equator. The model resolutioo, 0.025" in latitude and lmgitude, is very fine. This is die first time that a model of this type and resolutioo has been successfully run at these latitudes. Ahhough we expected that such resolutim would allow the mesoscale eddy field to devdop, it did not. One reason may be the coarse spatial and temporal winds. Twenty year of Comprehensive Ocean-AtmosPlere Data Set pseudo wind stress data used to drive the model are statistically analyzed to obtain a wind stress climatology. After model lPn-up, the mmthly stresses for 1986-1989 are used to drive the model. The model reproduces many of the regional oceanographic features such as the Alaskan Gyre, the Alaska Current, the Alaska Coastal Current, the Sitka eddy, and an intense, cyclonic eddy (that has not yet been reponed in the literature) northwest of the Queen OIarlotte Island in the spring. In additim, the model displays seasonal and interannual variability. Model results are validated through comparisons with National Ocean Service coastal sea level records and a multilayer, oceanic basin scale model being run at the Institute for Naval Oceanography.
The ocean's response to atmospheric forcing and to forcing along the coast by Kelvin waves is exa... more The ocean's response to atmospheric forcing and to forcing along the coast by Kelvin waves is examined in light of nearshore seasonal variability and the major 1982-1983 El Nino. In addition to driving the northeast Pacific gyre and local currents, the wind modifies the depth to the main thermocline, changing the apparent westward phase speed of Rossby waves excited by passing Kelvin waves. The amplitude of the passing Kelvin wave determines whether the Rossby wave depresses or raises the thermocline while propagating westward. Along the northeast Pacific coast from Oregon to Washington, model results suggest that the wind raises the main thermocline during the 1982-1983 El Nino. Generally, the coastal response off Oregon and Washington appears to be strongly driven by the large-scale atmosphere, while along the California coast and south to the equator, the doniinant El Nino signal has an oceanic origin. That signal, with periods between 2 and 5 years, originates in the western equatorial Pacific Ocean and is tracked eastward through the equatorial waveguide and then poleward along the coast to SOON using data from two reduced gravity, primitive equation models coupled at 18"N. At shorter, seasonal time scales, the acceleration of the wind appears to be an important mechanism in driving coastal currents.
Journal of the Acoustical Society of America, May 1, 1995
Travel times of acoustic signals were measured between the bottom-mounted Kaneohe source near Oah... more Travel times of acoustic signals were measured between the bottom-mounted Kaneohe source near Oahu and seven SOSUS stations at 3000–4000-km distance during 1983–1989. The Naval Research Laboratory hydrodynamic eddy resolving model yields changes in travel time whose standard deviations are consistent with the data. The model predicts that between 1981–1993, Rossby waves modify travel times by one second. Mesoscale eddies modify travel times little compared to Rossby waves. The largest Rossby waves are descendants of El Nino. Travel times changes are sensitive indicators of predictable features in the Naval Research Laboratory model. [Work supported by the Strategic Environmental Research and Development Program, managed by the Advanced Research Projects Agency.]
Variadons in dJe theImocline depth of the northeast Pacific Ocean during 1970-1989 are investigat... more Variadons in dJe theImocline depth of the northeast Pacific Ocean during 1970-1989 are investigated using a reduced-gravity numerical model forced by dJe local surface wind stress and at the southern land-ocean boundary by a coastal Kelvin wave signal. Three experiments are presented with forcings by wind only, Kelvin wave only, and a combination of both. The wind forcing generates an anticyclonic gyre cin;u1ation with mostly annual variatiOns. The Kelvin waves along the coast excite Rossby waves that propagate into the basin interior, producing changes in upper-layer thickness (related to changes in thermocline depth) that last for years after the Kelvin signal has passed. Two sequential upwelling Kelvin waves in 1973 and 1975 produce upwelling Rossby waves that reduce the mean upper-layer thickness by approximately 10-20 m during 1976. This shift is reinforced by later upwelling events lasting until the early 19808. The authors present a new hypothesis that the previously known climate shift observed in winter sea surface temperature is influenced by changes in the depth of the pennanent thermocline induced by remotely forced Rossby waves. Acoustic thermometry might be a sensitive means to detect Rossby waves, motivating a thermometric approach to studying interannual variatiOns in the ocean. The role of the Rossby waves in the travel time variations of acoustic signals on geodesic paths from Hawaii to the North American coast are calculated using the scheme of Roed. Wind forcing produces mainly annual variations in the acoustic travel time anomalies, except for the high latitude paths above 4/J"N that exhibit sudden shifts in travel times due to changes in the magnitude of the wind stress. The Rossby waves are primarily responsible for interannual variations.
3. The changes in travel time were shown to be due to variations in the spatially averaged temper... more 3. The changes in travel time were shown to be due to variations in the spatially averaged temperature along the sections. Fluctuations in currents, salinity, hydrostatic pressure, and acoustic path were shown to have small contributions to the changes ill travel time. Temperature variations as little as 0.02 °C were detected. Ab6troCt-The Kaneohe source experiment in the 1980's demonstrated the feasibility of \lSing sound to monitor global warming trends in the ocean with sound. This experiment used a source cabled to shore and the Navy's SOSUS stations for receivers. The GAMOT group is developing new instruments to obtain similar data in near-real time but at about one-eighth the cost of instruments cabled to shore. This approach has the potential for obtaining global oceall measurements of temperature at 500 km resolution less oxpensively than that routinely expended for measuring atmospheric temperatures. GAMOT is using state-of-the art models of the ocean to luterpret temperature changes.
The Journal of the Acoustical Society of America, 1999
The difficulties in detecting anthropogenic changes in ocean temperature due to the industrial re... more The difficulties in detecting anthropogenic changes in ocean temperature due to the industrial revolution are discussed using acoustic thermometry data taken between Oahu and seven SOSUS receivers at distances of 3000–4000 km. Measurements were made in late 1983, and over two 5-month intervals between 1987 and 1989. The travel times are dominated by interannual fluctuations. Two hydrodynamic ocean models are used to identify plausible oceanic features that could cause these variations. Modeled El Niños and La Niñas exhibit oceanic teleconnections between the Equator and mid-latitudes that lead to Rossby waves that propagate westward at mid−latitudes. Rossby waves are the dominant model features which affect the modeled acoustic travel times, and hence section-averaged temperatures in the eastern North Pacific. Modeled predictions of the travel times are significantly different than some of the data. The magnitude and rates of changes of the data are the same as those which result fr...
Complex empirical orthQIOnal function (CEOP) analysis is used to investigate the coastal Kelvin w... more Complex empirical orthQIOnal function (CEOP) analysis is used to investigate the coastal Kelvin wave driven Rossby wave response in the northeast Pacific. Using CEOF analysis, a spatial stmcture function is obtained from model upper layer thickness data. The model is a nonlinear, reduced gravity model of the northeast Pacific forced by coastal Kelvin waves originatinl in the equatorial Pacific. The spatial stmcture function is used to extract the interannual Rossby wave response from observed 300-m-depth temperature anomalies. The observed Rossby wave signal is termed the projection mode. Rossby wavelike feanues observed in the projection mode are onIer 1(MX) km long with most periods ranging between 2 and 4 years. The wave numbeR and frequencies found are consistent with Rossby d~cs. The mean phase speed of the Rossby wavelike features within the projection mode is 1.3 cm s-1, in agreement with the theoretical Rossby wave phase speed at 400N. Large amplitude nearshore and decreasing amplitude away from shore suggests nearshore generation of these waves. An important source of sea level variability along the east coast of North America at periods of 2-4 years was identified by Pares-Sierra and O'Brien (1989) as poleward propaga~n~ Kelvin waves. Since the Rossby wavelike features observed in the projection mode have a ~ty of their periods raDging between 2 and 4 yean, their forcing can be attributed to long-period Kelvin waves. Spectral comparisons between the nearshore values in the projection mode and coastal sea level show greater than 90% coherence in the period band 3-4.4 years. The high coherence between coastal sea level variations and the projection mode shows that there is a strong correlation between the Rossby wavelike features within the projection mode and coastal Kelvin wave propaption. It is concluded that the Rossby waves within the projection mode are forced by coastal Kelvin wave propagation. The projection mode accounts for 47.5% of the variance in the 300-m-depth temperature anomalies. The implication of this result is that the physical mechanism of the numerical model, i.e., Rossby waves excited by coastal Kelvin wave propagation, accounts for 47.5% of the variance in the observed 300-m depth temperature anomalies.
The International Journal of Supercomputing Applications, 1990
Two numerical models utilizing primitive equations (two momentum equations and a mass continuity ... more Two numerical models utilizing primitive equations (two momentum equations and a mass continuity equation) simulate the oceanography of the Pacific Ocean from 20°S to 50°N. Results show Kelvin waves thousands of kilometers long propagating from the equator to the northeast Pacific Ocean. Kelvin waves are very long waves that propagate along the equator and along solid boundaries with the boundary to their right. They are important to simulations of ocean circulation along the North American coast because they carry information at seasonal and longer periods from the equator poleward. Modeling an extensive region such as the Pacific Ocean with adequate two-dimensional resolution places heavy demands on computer memory and storage. We have found that the best way to examine the abundant model data is through visualization, by animating the appro priate model fields and viewing the time history of each model simulation as a color movie. The animations are used as research products to a...
In the regions of flat immobile landfast ice (shallow Siberian Seas with depths less than 25-30 m... more In the regions of flat immobile landfast ice (shallow Siberian Seas with depths less than 25-30 m), the models generally overestimate both the total observed sea ice thickness and rates of September and October ice growth from observations by more than 4 times and more than one standard deviation, respectively. The models do not reproduce conditions of fast ice formation and growth. Instead, the modeled fast ice is replaced with pack ice which drifts, generating ridges of increasing ice thickness, in addition to thermodynamic ice growth. Considering all observational data sets, the better correlations and smaller differences from observations are from the Estimating the Circulation and Climate of the Ocean, Phase II and Pan-Arctic Ice Ocean Modeling and Assimilation System models.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
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