An Investigation of Surface Current Patterns Related to Upwelling in Monterey Bay, Using High Frequency Radar
An Investigation of Surface Current Patterns Related to Upwelling in Monterey Bay, Using High Frequency Radar

Author: Andres Enriquez

Publisher:

Published: 2004-06-01

Total Pages: 101

ISBN-13: 9781423518105

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High Frequency (HF) radar backscatter instruments are under development and testing in the marine science and defense science communities for their abilities to remotely sense surface parameters in the coastal ocean over large areas. In the Navy context, the systems provide real-time mapping of ocean surface currents and waves critical to characterization and forecasting of the battlespace environment. In this study, HF radar, aircraft and satellite information were used to investigate and describe surface current in Monterey Bay, California, for a period of ten months, from June 1, 2003 to March 31, 2004. A network of five CODAR-type HF radar instruments measured hourly surface currents over the bay. The measurements were averaged over one-hour intervals and total surface velocities were mapped on a grid in the Monterey Bay. Major upwelling events were observed during the period of June 14 to June 27, July 4 to July 19, August 8 to August 18 and other upwelling events were observed until late October. These periods of upwelling favorable winds are common during summer with durations of 10 to 20 days. Cyclonic circulation cells are developed on shore during upwelling conditions and an anticyclonic circulation in the middle of the bay is observed when the wind shifts to the southwest producing a strong flow out of the bay close to the coastline off Point Pi os. Downwelling conditions are much less common than upwelling, with occurrences during winter and early fall storms with events lasting between two to five days. When the wind blows to the northeast with an intensity of 4 m/s or more for more than 12 hours, a well developed anticyclonic gyre forms in the middle of the bay. This is associated with a strong current, 35 to 40 cm/s, which flushes out in the southern part of the bay close to the coast off Point Pi os. This flow reverses when the winds veer to the southwest and enter into the Bay with less intensity.

Evolution of Diurnal Surface Winds and Surface Currents for Monterey Bay
Evolution of Diurnal Surface Winds and Surface Currents for Monterey Bay

Author: Michael D. Foster

Publisher:

Published: 1993

Total Pages: 114

ISBN-13:

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The diurnal-period fluctuations of winds and surface currents are analyzed for September 1992 in and around Monterey Bay. Wind records are compared for three coastal stations and two mooring sites. Remotely-sensed surface current observations from two CODAR (HF radar) sites are used to explore the ocean's response to diurnal-period forcing. An average diurnal cycle is formed at each wind station and at all CODAR bins. The earliest sea breeze response is seen at the coastal wind stations where morning winds accelerate toward the coastal mountain ranges. A few hours later, the coastal winds accelerate to the southeast down the Salinas Valley. Offshore afternoon winds rotate from their normal alongshore orientation to also become aligned with the valley. The CODAR-derived surface currents respond in less than the two-hour sampling rate to the onset of the diurnal onshore winds. Currents accelerate in the direction of the Salinas Valley. As the day progresses, the more offshore currents rotate clockwise out from under the winds in a possible Ekman or inertial adjustment that continues throughout the night and spreads onshore. In the afternoon, a complicated eddy pattern develops near shore in a possible response to the coastal boundary.

Comparison of Trajectories Generated by the NOAA Oil Spill Model to Trajectories Produced Using HF Radar-Derived Curents in Monterey Bay
Comparison of Trajectories Generated by the NOAA Oil Spill Model to Trajectories Produced Using HF Radar-Derived Curents in Monterey Bay

Author: Margaret Smith

Publisher:

Published: 1997-09-01

Total Pages: 112

ISBN-13: 9781423565284

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HF radar-derived surface current data was examined for use in oil spill trajectory prediction in Monterey Bay. Trajectories produced by the NOAA/ HAZMAT On-Scene Spill Model, using different combinations of surface currents and winds, were compared to trajectories generated using HF radar-derived surface currents. Currents examined included Output from the NOAA circulation model and canonical-day averages of the HF radar-derived current maps, either as spatially constant but temporally varying currents (time file) or spatially varying two-hourly current patterns (grids). Results from OSSM using the NOAA circulation model currents did not compare favorably with HF radar-derived trajectories inside Monterey Bay. OSSM produced realistic overall trajectory patterns throughout the Bay using the canonical-day grid current files and, to a lesser degree, canonical-day time file currents. Both OSSM and HF radar-derived trajectories show sensitivity to release time. In the afternoon, trajectories display rapid southeastward flow. At night, currents are weaker. The week's worth of direct surface current data used in this study was found to be representative of the seasonal summertime pattern in Monterey Bay and provided realistic current patterns for use in OSSM for initial trajectory prediction in lieu of real time HF radar-derived surface currents.

Comparison of Trajectories Generated by the NOAA Oil Spill Model to Trajectories Produced Using HF Radar-derived Currents in Monterey Bay
Comparison of Trajectories Generated by the NOAA Oil Spill Model to Trajectories Produced Using HF Radar-derived Currents in Monterey Bay

Author: Margaret A. Smith

Publisher:

Published: 1997

Total Pages: 0

ISBN-13:

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HF radar-derived surface current data was examined for use in oil spill trajectory prediction in Monterey Bay. Trajectories produced by the NOAA/ HAZMAT On-Scene Spill Model, using different combinations of surface currents and winds, were compared to trajectories generated using HF radar-derived surface currents. Currents examined included Output from the NOAA circulation model and canonical-day averages of the HF radar-derived current maps, either as spatially constant but temporally varying currents (time file) or spatially varying two-hourly current patterns (grids). Results from OSSM using the NOAA circulation model currents did not compare favorably with HF radar-derived trajectories inside Monterey Bay. OSSM produced realistic overall trajectory patterns throughout the Bay using the canonical-day grid current files and, to a lesser degree, canonical-day time file currents. Both OSSM and HF radar-derived trajectories show sensitivity to release time. In the afternoon, trajectories display rapid southeastward flow. At night, currents are weaker. The week's worth of direct surface current data used in this study was found to be representative of the seasonal summertime pattern in Monterey Bay and provided realistic current patterns for use in OSSM for initial trajectory prediction in lieu of real time HF radar-derived surface currents.

Observations and Modeling of Currents Within the Monterey Bay During May 1988
Observations and Modeling of Currents Within the Monterey Bay During May 1988

Author: Kim A. Koehler

Publisher:

Published: 1990

Total Pages: 132

ISBN-13:

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April and May of 1988 along the central California coast were characterized as a period of strong coastal upwelling produced by moderate to strong northwesterly winds present throughout the period. A product of this upwelling event was the manifestation of southward geostrophic currents which extended to a distance of approximately 50 km from the coast. From 08 to 11 May 1988, hydrographic surveying was conducted within the Monterey Bay. Internal waves, with amplitudes of up to 30 m were present throughout the period and effectively masked the mean signal, implying that averaging is essential to avoid aliasing. The current -- temperature -- depth (CTD) data were averaged to estimate the mean field during this time frame. Acoustic Doppler Current Profiler (ADCP) data, were also averaged. The mean flow field and dynamic topography implied anticyclonic surface flow with cyclonic flow at 200 m depth. ADCP derived mean flows compared favorably with geostrophic mean flow rate in all areas except one, the deep outflow region along the northern wall of the Canyon. Application of ocean models of boundary layer flow of the geostrophic mean field yielded flows similar to those described above. Wind stress experiments indicated that strong wind field may influence surface circulation in the Bay. Interactions between the coastal upwelling geostrophic jet and the Monterey Submarine Canyon is believed to have been a major mechanism responsible for the mean flow.

Mapping Coastal Surface Winds in Monterey Bay Using High Frequency Radar
Mapping Coastal Surface Winds in Monterey Bay Using High Frequency Radar

Author: Raymond R. Delgado, III

Publisher:

Published: 1999-03-01

Total Pages: 134

ISBN-13: 9781423545019

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Over-water wind directions derived from high frequency (HF) radar - the new Multi-frequency Coastal Radar (MCR) - are compared to in-situ observations to determine the skill of the radar measurements. Conventional beam processing of data collected from two MCR sites located around Monterey Bay during summer 1997 is used to create wind directions based on the relative strength of the positive and negative Bragg-resonant peaks, which correspond to the wind-driven waves approaching and receding from the radar, respectively. Based on a selected functional relationship that converts the radar signal to wind direction, radar-derived wind directions are created using a new wind- retrieval algorithm and are compared to mooring observations under a variety of wind conditions. Analysis indicates that the signal not only follows wind direction, but also strongly correlates to the wind speed measured at the mooring. Results show that many of the Bragg peaks are close to the noise level, and consequently, low signal-to-noise ratios restrict the statistical confidence of the measurements. Nonetheless, maps of radar-derived wind directions show good agreement with in situ observations, especially when the wind speed is relatively strong and is sustained for long duration.

Characterization of Tidal Currents in Monterey Bay from Remote and In-situ Measurements
Characterization of Tidal Currents in Monterey Bay from Remote and In-situ Measurements

Author: Emil T. Petruncio

Publisher:

Published: 1993

Total Pages: 124

ISBN-13:

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A first order description of tidal heights and currents in Monterey Bay is provided. Analysis of sea level records indicate that a mixed, predominantly semidiurnal tide nearly co-oscillates within the bay. Analysis of month-long moored ADCP records obtained in the winter and summer of 1992 reveals that tidal-band currents account for approximately 50 percent of the total current variance in the upper ocean (20-200 m). A relatively strong (7 cm/s) fortnightly tide (MSf) is present in both seasons. Considerable rotation of the semidiurnal ellipse orientations occurs with depth during both seasons. A month- long record of surface current measurements obtained with CODAR, an HF radar system, during September 1992 reveals that the Monterey Submarine Canyon clearly influences the strength and direction of semidiurnal (M2) tidal currents. Good agreement exists between the strength and orientation of ADCP- and CODAR-derived tidal ellipses, with the exception of the constituent K1. Large, spatially uniform K1 surface currents (20-30 cm/s) appear to be the result of diurnal sea breeze forcing.

Mapping Coastal Surface Winds in Monterey Bay Using High Frequency Radar
Mapping Coastal Surface Winds in Monterey Bay Using High Frequency Radar

Author: Raymond R. Delgado

Publisher:

Published: 1999

Total Pages: 134

ISBN-13:

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Over-water wind directions derived from high frequency (HF) radar - the new Multi-frequency Coastal Radar (MCR) - are compared to in-situ observations to determine the skill of the radar measurements. Conventional beam processing of data collected from two MCR sites located around Monterey Bay during summer 1997 is used to create wind directions based on the relative strength of the positive and negative Bragg-resonant peaks, which correspond to the wind-driven waves approaching and receding from the radar, respectively. Based on a selected functional relationship that converts the radar signal to wind direction, radar-derived wind directions are created using a new wind-retrieval algorithm and are compared to mooring observations under a variety of wind conditions. Analysis indicates that the signal not only follows wind direction, but also strongly correlates to the wind speed measured at the mooring. Results show that many of the Bragg peaks are close to the noise level, and consequently, low signal-to-noise ratios restrict the statistical confidence of the measurements. Nonetheless, maps of radar-derived wind directions show good agreement with in situ observations, especially when the wind speed is relatively strong and is sustained for long duration.

Observations of Upwelling and Relaxation Events in the Northern Monterey Bay During August 2000
Observations of Upwelling and Relaxation Events in the Northern Monterey Bay During August 2000

Author:

Publisher:

Published: 2005

Total Pages: 22

ISBN-13:

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The interplay between the Point Ano Nuevo upwelling center, an offshore anticyclonic mesoscale eddy, and the waters of the Monterey Bay was studied during a series of up- and downwelling favorable wind events during August 2000. The upwelling events were characterized by the appearance of cold, salty water at Point Ano Nuevo at the north end of the bay that subsequently spread southward across the mouth of the bay as the winds continued. During the downwelling/relaxation events, the surface current and temperature response was dominated by the onshore translation of the offshore eddy and by local surface heating in the bay itself. The circulation within the bay was cyclonic during both wind regimes but slightly more barotropic under poleward forcing. The ICON model, a nested, data assimilating, sigma coordinate model, was used to simulate The upwelling and relaxation events and calculate the subsurface current and density fields. The model reproduced the dominant current and temperature patterns outside the bay, including the southward flowing upwelling filament, the movement of the offshore eddy, the poleward flow off Point Sur, and the circulation within the bay. The model salinity fields at the surface and 100 m levels show that during upwelling, the bay was filled with higher-salinity water stemming from the Point Ano Nuevo upwelling center to the north. During downwelling, the source water for both the surface and 100 m levels was the colder, fresher California Current water offshore, which had advected southward well past Point Pinos during the previous upwelling event.