Motions of a small spar buoy

The motions of a small spar buoy were measured in deep water. The measured variables were two buoy tilts, three accelerations, two wave slopes and the wave height. The variables were corrected for buoy motion and rotated to stationary coordinates, Fast Fourier Transformed, and analyzed spectrally. Analysis included power spectra, coherence, phase and transfer functions. It was found that the buoy was a surface follower at low frequencies up to the frequency of the peak of the wave spectrum. At higher sea wave frequencies, the buoy resists sea motion. The RMS tilts of the buoy are about 0.6 of the RMS sea slopes, and practically all of the buoy motion is concentrated in the frequency band from 0.1 to 0.3 Hertz

Analysis of meteorological and oceanographic data from Ocean Station Vessel N (30N 140W)

The thesis examines the principal air-sea properties at Ocean Station Vessel N (30N 140W). In a descriptive section, meteorological and oceanographic data for N are analyzed over 20 years (1951-1970) and 7 years (1964-1970), respectively. A rainfall estimate is constructed for the 20 year period. The yearly average rainfall is 22 centimeters, far less than current estimates. Daily and seasonal variations are presented. Heat budgets of the surface show that the two decades are distinctly different. Anomalies of the 20 years of all meteorological variables are calculated. The pressure anomaly appears to be loosely correlated with anomalous large scale events in the equatorial dry zone. Time series cross-sections are shown of the mixed layer depth, bottle temperature and salinity. The near surface density appears to be largely controlled by temperature. Surface wind speed, air pressure, sea temperature, air temperature and dew point spectra for a 10-year period (1961-1970) are shown in a spectral section. Spectra are computed separately for the 4 seasons. Rotary spectra for the wind are also calculated. In a discussion of mixed layer dynamics, theoretical calculations indicate that salinity is not a significant factor in the Eastern subtropics. In a final section, Denman's mixed layer model is applied to two cases of data from N. It is found that Denman's model describes the local mixed layer changes in the one case where advective effects could be resolved. It is suggested that mixed layer extinction lengths for sunlight are shorter than previously believed--about 5 meters. Denman's mixed layer model appears applicable to local changes in the Eastern subtropics

North Pacific Mesoscale Coupled Air-Ocean Simulations Compared with Observations

Executive summary The main objective of the study was to investigate atmospheric and ocean interaction processes in the western Pacific and, in particular, effects of significant ocean heat loss in the Kuroshio and Kuroshio Extension regions on the lower and upper atmosphere. It is yet to be determined how significant are these processes are on climate scales. The understanding of these processes led us also to development of the methodology of coupling the Weather and Research Forecasting model with the Parallel Ocean Program model for western Pacific regional weather and climate simulations. We tested NCAR-developed research software Coupler 7 for coupling of the WRF and POP models and assessed its usability for regional-scale applications. We completed test simulations using the Coupler 7 framework, but implemented a standard WRF model code with options for both one- and two-way mode coupling. This type of coupling will allow us to seamlessly incorporate new WRF updates and versions in the future. We also performed a long-term WRF simulation (15 years) covering the entire North Pacific as well as high-resolution simulations of a case study which included extreme ocean heat losses in the Kuroshio and Kuroshio Extension regions. Since the extreme ocean heat loss occurs during winter cold air outbreaks (CAO), we simulated and analyzed a case study of a severe CAO event in January 2000 in detail. We found that the ocean heat loss induced by CAOs is amplified by additional advection from mesocyclones forming on the southern part of the Japan Sea. Large scale synoptic patterns with anomalously strong anticyclone over Siberia and Mongolia, deep Aleutian Low, and the Pacific subtropical ridge are a crucial setup for the CAO. It was found that the onset of the CAO is related to the breaking of atmospheric Rossby waves and vertical transport of vorticity that facilitates meridional advection. The study also indicates that intrinsic parameterization of the surface fluxes within the WRF model needs more evaluation and analysis

The Dynamics of Northwest Summer Winds over the Santa Barbara Channel

A mesoscale model is used to examine the dynamics of northwest flow over the Santa Barbara Channel region. Three cases are considered, each characterized by typical summertime synoptic conditions, but with differences in pressure gradient strength and marine boundary layer depth (MBL). The first case examines a relatively deep MBL and strong pressure gradient. Case 2 is characterized by a more shallow MBL and weaker pressure gradient, and case 3 represents a transition from a deep MBL to shallow conditions. In all cases, simulated surface winds show reasonable agreement with observations over most of the model domain, with the exception of regions near abrupt terrain changes. Results from the model indicate that the flow with a deep MBL (~400 m) and strong pressure gradient (case 1) is supercritical, causing regions of acceleration and expansion in the lee of Point Conception. When the MBL is shallow (~150 m) (case 2), a transcritical flow scenario exists with subcritical flow upstream from Point Conception and a supercritical flow region over the Santa Barbara Channel and downstream from the Channel Islands. Flow over the channel is strongly affected by diurnal heating in shallow MBL cases, reversing direction in step with a land breeze circulation induced by nighttime cooling. The land breeze forces an internal wave disturbance that propagates westward across the channel, eliminating the supercritical flow region in the lee of Point Conception. Conditions with a deep MBL (~400 m) produce less variability in the surface winds, except for the region sheltered by the Santa Ynez Mountains. An expansion fan is still evident in this case, but it is produced by the interaction of the flow with higher terrain north and east of the channel. The low hills on Point Conception and the Channel Islands do not have a large blocking effect on the surface flow when the MBL is deep. Analysis of the momentum budget supports the conclusion that the boundary layer behaves like a transcritical hydraulic flow when the MBL is shallow. Except for the open ocean region, the Coriolis term is minor in comparison with the pressure and advection terms. Diurnal heating effects are evident in the nearshore pressure term, which varies from offshore during the late evening to onshore in the afternoon. These effects are most significant when the MBL is shallow and can augment the hydraulically forced pressure pattern, causing a stronger expansion fan in the late afternoon and a collapse of the expansion fan during the early morning

Coastal Perturbations of Marine-Layer Winds, Wind Stress, and Wind Stress Curl along California and Baja California in June 1999

Month-long simulations using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) with a horizontal resolution of 9 km have been used to investigate perturbations of topographically forced wind stress and wind stress curl during upwelling-favorable winds along the California and Baja California coasts during June 1999. The dominant spatial inhomogeneity of the wind stress and wind stress curl is near the coast. Wind and wind stress maxima are found in the lees of major capes near the coastline. Positive wind stress curl occurs in a narrow band near the coast, while the region farther offshore is characterized by a broad band of weak negative curl. Curvature of the coastline, such as along the Southern California Bight, forces the northerly flow toward the east and generates positive wind stress curl even if the magnitude of the stress is constant. The largest wind stress curl is simulated in the lees of Point Conception and the Santa Barbara Channel. The Baja California wind stress is upwelling favorable. Although the winds and wind stress exhibit great spatial variability in response to synoptic forcing, the wind stress curl has relatively small variation. The narrow band of positive wind stress curl along the coast adds about 5% to the coastal upwelling generated by adjustment to the coastal boundary condition. The larger area of positive wind stress curl in the lee of Point Conception may be of first-order importance to circulation in the Santa Barbara Channel and the Southern California Bight

North Pacific Mesoscale Coupled Air-Ocean Simulations Compared with Observations

Executive summary The main objective of the study was to investigate atmospheric and ocean interaction processes in the western Pacific and, in particular, effects of significant ocean heat loss in the Kuroshio and Kuroshio Extension regions on the lower and upper atmosphere. It is yet to be determined how significant are these processes are on climate scales. The understanding of these processes led us also to development of the methodology of coupling the Weather and Research Forecasting model with the Parallel Ocean Program model for western Pacific regional weather and climate simulations. We tested NCAR-developed research software Coupler 7 for coupling of the WRF and POP models and assessed its usability for regional-scale applications. We completed test simulations using the Coupler 7 framework, but implemented a standard WRF model code with options for both one- and two-way mode coupling. This type of coupling will allow us to seamlessly incorporate new WRF updates and versions in the future. We also performed a long-term WRF simulation (15 years) covering the entire North Pacific as well as high-resolution simulations of a case study which included extreme ocean heat losses in the Kuroshio and Kuroshio Extension regions. Since the extreme ocean heat loss occurs during winter cold air outbreaks (CAO), we simulated and analyzed a case study of a severe CAO event in January 2000 in detail. We found that the ocean heat loss induced by CAOs is amplified by additional advection from mesocyclones forming on the southern part of the Japan Sea. Large scale synoptic patterns with anomalously strong anticyclone over Siberia and Mongolia, deep Aleutian Low, and the Pacific subtropical ridge are a crucial setup for the CAO. It was found that the onset of the CAO is related to the breaking of atmospheric Rossby waves and vertical transport of vorticity that facilitates meridional advection. The study also indicates that intrinsic parameterization of the surface fluxes within the WRF model needs more evaluation and analysis

Bora event variability and the role of air-sea feedback

Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): C03S18, doi:10.1029/2006JC003726.A two-way interacting high resolution numerical simulation of the Adriatic Sea using the Navy Coastal Ocean Model (NCOM) and Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®) was conducted to improve forecast momentum and heat flux fields, and to evaluate surface flux field differences for two consecutive bora events during February 2003. (COAMPS® is a registered trademark of the Naval Research Laboratory.) The strength, mean positions and extensions of the bora jets, and the atmospheric conditions driving them varied considerably between the two events. Bora 1 had 62% stronger heat flux and 51% larger momentum flux than bora 2. The latter displayed much greater diurnal variability characterized by inertial oscillations and the early morning strengthening of a west Adriatic barrier jet, beneath which a stronger west Adriatic ocean current developed. Elsewhere, surface ocean current differences between the two events were directly related to differences in wind stress curl generated by the position and strength of the individual bora jets. The mean heat flux bias was reduced by 72%, and heat flux RMSE reduced by 30% on average at four instrumented over-water sites in the two-way coupled simulation relative to the uncoupled control. Largest reductions in wind stress were found in the bora jets, while the biggest reductions in heat flux were found along the north and west coasts of the Adriatic. In bora 2, SST gradients impacted the wind stress curl along the north and west coasts, and in bora 1 wind stress curl was sensitive to the Istrian front position and strength. The two-way coupled simulation produced diminished surface current speeds of ∼12% over the northern Adriatic during both bora compared with a one-way coupled simulation.The research support for J. Pullen, J. D. Doyle, and T. Haack was provided by the Office of Naval Research (ONR) program elements 0602435N and 0601153N

Coastally Trapped Wind Reversals: Progress toward Understanding

Coastally trapped wind reversals along the U.S. west coast, which are often accompanied by a northward surge of fog or stratus, are an important warm-season forecast problem due to their impact on coastal maritime activities and airport operations. Previous studies identified several possible dynamic mechanisms that could be responsible for producing these events, yet observational and modeling limitations at the time left these competing interpretations open for debate. In an effort to improve our physical understanding, and ultimately the prediction, of these events, the Office of Naval Research sponsored an Accelerated Research Initiative in Coastal Meteorology during the years 1993â 98 to study these and other related coastal meteorological phenomena. This effort included two field programs to study coastally trapped disturbances as well as numerous modeling studies to explore key dynamic mechanisms. This paper describes the various efforts that occurred under this program to provide an advancement in our understanding of these disturbances. While not all issues have been solved, the synoptic and mesoscale aspects of these events are considerably better understood.Most of the authors were supported through the Office of Naval Research Coastal Meteorology Accelerated Research Initiative, one of the authors (WTT) was supported by Program Element 0601153N, Naval Research Laboratory

What determines the spatial pattern in summer upwelling trends on the U.S. West Coast?

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): C08012, doi:10.1029/2012JC008016.Analysis of sea surface temperature (SST) from coastal buoys suggests that the summertime over-shelf water temperature off the U.S. West Coast has been declining during the past 30 years at an average rate of −0.19°C decade−1. This cooling trend manifests itself more strongly off south-central California than off Oregon and northern California. The variability and trend in the upwelling north of off San Francisco are positively correlated with those of the equatorward wind, indicating a role of offshore Ekman transport in the north. In contrast, Ekman pumping associated with wind stress curls better explains the stronger and statistically more significant cooling trend in the south. While the coast-wide variability and trend in SST are strongly correlated with those of large-scale modes of climate variability, they in general fail to explain the southward intensification of the trend in SST and wind stress curl. This result suggests that the local wind stress curl, often topographically forced, may have played a role in the upwelling trend pattern.H.S. acknowledges the WHOI supports from the Coastal Research Fund in Support of Scientific Staff, the Penzance Endowed Fund in Support of Assistant Scientists, and the Andrew W. Mellon Foundation Endowed Fund for Innovative Research. K.B. and C.E. acknowledge support by the National Science Foundation through grants OCE-1059632 and OCE 1061434.2013-03-0