Analysis of AVHRR, CZCS and historical in situ data off the Oregon Coast

The original scientific objectives of this grant were to: (1) characterize the seasonal cycles and interannual variability for phytoplankton concentrations and sea surface temperature (SST) in the California Current using satellite data; and (2) to explore the spatial and temporal relationship between these variables and surface wind forcing. An additional methodological objective was to develop statistical methods for forming mean fields, which minimize the effects of random data gaps and errors in the irregularly sampled CZCS (Coastal Zone Color Scanner) and AVHRR (Advanced Very High Resolution Radiometer) satellite data. A final task was to evaluate the level of uncertainty in the wind fields used for the statistical analysis. Funding in the first year included part of the cost of an image processing system to enable this and other projects to process and analyze satellite data. This report consists of summaries of the major projects carried out with all or partial support from this grant. The appendices include a list of papers and professional presentations supported by the grant, as well as reprints of the major papers and reports

The Impact of SST Specification on ECMWF Surface Wind Stress Fields in the Eastern Tropical Pacific

The impact of SST specification on low-level winds in the operational ECMWF numerical weather prediction model is investigated in the eastern tropical Pacific from comparisons of ECMWF wind stress fields with QuikSCAT satellite scatterometer observations of wind stress during the August–December cold seasons of 2000 and 2001. These two time periods bracket the 9 May 2001 change from the Reynolds SST analyses to the Real-Time Global SST (RTG_SST) analyses as the ocean boundary condition in the ECMWF model. The ocean–atmosphere interaction in the eastern tropical Pacific that is clearly evident in QuikSCAT wind stress divergence and curl fields is also evident in the ECMWF winds, but is more than twice as strong in the 2001 cold season as in the 2000 cold season, due primarily to the improved spatial and temporal resolution of the RTG_SST analyses compared with the Reynolds SST analyses. While a significant improvement compared with 2000, the response of the 2001 ECMWF wind stress field to SST is only about half as strong as the coupling inferred from QuikSCAT data and satellite observations of SST from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). It is concluded that the underrepresentation of the ocean–atmosphere coupling is attributable partly to underrepresentation of SST gradients in the RTG_SST fields and partly to inadequacies of the ECWMF model. The latter may be due to errors in the parameterization of boundary layer processes or to insufficient horizontal or vertical resolution in the model

Central California Coastal Circulation Study : drifter observations, February, July, October 1984 and January 1985

Surface drifters were depldyed and tracked over the continental shelf and upper continental slope off central California between Point Conception and Point Sur. The drifters were deployed and tracked from aircraft by Aero-Marine Surveys, Inc. under subcontract to Raytheon Service Company as part of the Central California Coastal Circulation Study sponsored by the Minerals Management Service. The objectives of this 18-month field program were to obtain a set of observations of the ocean water mass and velocity fields and develop a detailed description of these fields and their seasonal and shorter period variations. The ultimate goal is to assess the impact of exploitation of offshore oil and gas resources of the outer continental shelf region. This data report contains maps of drifter trajectories for a total of 78 drifters deployed and tracked during four separate months (February, July and October 1984, and January 1985). Also included are time series plots of winds during the times of deployment

Comment on "seasonal variation in wind speed and sea state from global satellite measurements"

In a recent paper, Sandwell and Agreen [1984; hereafter SA] presented figures of global seasonal wind speed and sea state as measured by the GEOS 3 satellite altimeter. Since that time, Chelton and McCabe [1985; hereafter CM] have found that problems exist in the algorithms used to retrieve wind speed from altimeter measurements of radar backscatter. These problems were discovered too late to be of use in the analysis of SA. However, because they have a significant impact on the accuracy of wind speed estimation from altimeters, it is important that they he pointed out now so that the results of SA are not misused. Although the results presented here do not alter many of the conclusions of SA in a qualitative sense, they do become important for any quantitative interpretation of the seasonal winds presented by SA. In addition, the data distribution maps presented here (Figures 3a-3i) are useful for pointing out limitations in other applications of GEOS 3 data (e.g., use of the altimeter sea level measurements to study surface geostrophic currents)

The effects of uncorrelated measurement noise on SWOT estimates of sea-surface height, velocity and vorticity

Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of the Atmospheric and Oceanic Technology 39(7), (2022): 1053–1083, https://doi.org/10.1175/jtech-d-21-0167.1.The Ka-band Radar Interferometer (KaRIn) on the Surface Water and Ocean Topography (SWOT) satellite will revolutionize satellite altimetry by measuring sea surface height (SSH) with unprecedented accuracy and resolution across two 50-km swaths separated by a 20-km gap. The original plan to provide an SSH product with a footprint diameter of 1 km has changed to providing two SSH data products with footprint diameters of 0.5 and 2 km. The swath-averaged standard deviations and wavenumber spectra of the uncorrelated measurement errors for these footprints are derived from the SWOT science requirements that are expressed in terms of the wavenumber spectrum of SSH after smoothing with a filter cutoff wavelength of 15 km. The availability of two-dimensional fields of SSH within the measurement swaths will provide the first spaceborne estimates of instantaneous surface velocity and vorticity through the geostrophic equations. The swath-averaged standard deviations of the noise in estimates of velocity and vorticity derived by propagation of the uncorrelated SSH measurement noise through the finite difference approximations of the derivatives are shown to be too large for the SWOT data products to be used directly in most applications, even for the coarsest footprint diameter of 2 km. It is shown from wavenumber spectra and maps constructed from simulated SWOT data that additional smoothing will be required for most applications of SWOT estimates of velocity and vorticity. Equations are presented for the swath-averaged standard deviations and wavenumber spectra of residual noise in SSH and geostrophically computed velocity and vorticity after isotropic two-dimensional smoothing for any user-defined smoother and filter cutoff wavelength of the smoothing.This research was supported by NASA Grant NNX16AH76G

Large-scale interannual physical and biological interaction in the California Current

Thirty years of temperature, salinity, steric height and zooplankton data are examined to explore the potential causes of large-scale biological variability in the California Current. The physical and biological properties are all found to be dominated by a pronounced interannual signal with very large spatial scale...

Satellite observations of chlorophyll, phytoplankton biomass, and Ekman pumping in nonlinear mesoscale eddies

Author Posting. © American Geophysical Union, 2013. 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: Oceans 118 (2013): 6349–6370, doi:10.1002/2013JC009027.Nonlinear mesoscale eddies can influence biogeochemical cycles in the upper ocean through vertical and horizontal advection of nutrients and marine organisms. The relative importance of these two processes depends on the polarity of an eddy (cyclones versus anticyclones) and the initial biological conditions of the fluid trapped in the core of the eddy at the time of formation. Eddies originating in the eastern South Indian Ocean are unique in that anticyclones, typically associated with downwelling, contain elevated levels of chlorophyll-a, enhanced primary production and phytoplankton communities generally associated with nutrient-replete environments. From analysis of 9 years of concurrent satellite measurements of sea surface height, chlorophyll, phytoplankton carbon, and surface stress, we present observations that suggest eddy-induced Ekman upwelling as a mechanism that is at least partly responsible for sustaining positive phytoplankton anomalies in anticyclones of the South Indian Ocean. The biological response to this eddy-induced Ekman upwelling is evident only during the Austral winter. During the Austral summer, the biological response to eddy-induced Ekman pumping occurs deep in the euphotic zone, beyond the reach of satellite observations of ocean color.This work was funded by NASA grants NNX08AI80G, NNX08AR37G, NNX10AO98G, and NNX13AD78G.2014-06-0

Spectral charactersitics of time-dependent orbit errors in altimeter height measurements

A mean reference surface and time-dependent orbit errors are estimated simultaneously for each exact-repeat ground track from the first two years of Geosat sea level estimates based on the Goddard Earth model (GEM)-T2 orbits. Motivated by orbit theory and empirical analysis of Geosat data, the time-dependent orbit errors are modeled as 1 cycle per revolution (cpr) sinusoids with slowly varying amplitude and phase. The method recovers the known "bow tie effect" introduced by the existence of force model errors within the precision orbit determination (POD) procedure used to generate the GEM-T2 orbits. The bow tie pattern of 1-cpr orbit errors is characterized by small amplitudes near the middle and larger amplitudes (up to 160 cm in the 2 years of data considered here) near the ends of each 5- to 6-day orbit arc over which the POD force model is integrated. A detailed examination of these bow tie patterns reveals the existence of daily modulations of the amplitudes of the 1-cpr sinusoid orbit errors with typical and maximum peak-to-peak ranges of about 14 cm and 30 cm, respectively. The method also identifies a daily variation in the mean orbit error with typical and maximum peak-to-peak ranges of about 6 cm and 30 cm, respectively, that is unrelated to the predominant 1-cpr orbit error. It is suggested that the two daily signals arise from daily adjustments of the drag coefficient in the GEM-T2 POD procedure. Application of the simultaneous solution method to the much less accurate Geosat height estimates based on the Naval Astronautics Group orbits concludes that the accuracy of POD is not important for collinear altimetric studies of time-dependent mesoscale variability (wavelengths shorter than 1000 km), as long as the time-dependent orbit errors are dominated by 1-cpr variability and a long-arc (several orbital periods) orbit error estimation scheme such as that presented here is used. The accuracy of POD becomes more important for studies of larger-scale variability

A geosat altimeter wind speed algorithm and a method for altimeter wind speed algorithm development

A Geosat altimeter wind speed algorithm is derived by cross-calibrating Geosat and Seasat altimeter estimates of the normalized radar cross section σ₀ and modifying an existing Seasat altimeter wind speed model function to obtain a model function appropriate for Geosat observations. It is argued that the σ₀ distribution measured by an altimeter is relatively stable over a sufficiently large geographical region and a long enough time period. Systematic differences between σ₀ estimates from two altimeters can therefore be identified based on comparisons of their σ₀ histograms. Any such systematic differences can then be corrected using independent σ₀ estimates. When this method is applied to the Geosat and Seasat altimeters, a systematic difference between the two σ₀ histograms is shown to be consistent with differences between Seasat altimeter and nadir Seasat scatterometer estimates of σ₀ deduced independently by a previous study. This supports the conclusions that (1) the σ₀ distribution is stable, and (2) the Seasat altimeter estimates of σ₀ were miscalibrated. After modifying the existing Seasat altimeter wind speed algorithm to account for this apparent σ₀ error, the resulting Geosat estimates of wind speed agree with high-quality buoy observations to within an rms difference of less than 2 m/s