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United States Department of Agriculture

Agricultural Research Service

Title: Evaluation of Doppler Lidar Measurements of Momentum Flux and Wind Variability Along An Upwelling Coast

Author
item Levinson, David

Submitted to: National Oceanic and Atmospheric Administration
Publication Type: Government Publication
Publication Acceptance Date: December 1, 1998
Publication Date: N/A

Interpretive Summary: A research study, based on a comprehensive ocean-atmosphere dataset obtained along the northern Oregon coast, was conducted to understand the effects of wind stress variability on coastal upwelling. The data for this study were collected during the Coastal Ocean Probing Experiment (COPE), which took place in September-October 1995. The objective of the research was two-fold, 1) to understand the complex interactions between the atmospheric boundary layer and the oceanic mixed-layer under a variety of wind conditions, and 2) to assess the applicability of using Doppler lidars to measure wind speed and wind stress in the coastal zone. The COPE field measurements along with a ten- year wind climatology were analyzed to diagnose the long- term wind variability along the coast. Wind rose frequently diagrams from the period 1987-96 showed that the coastal wind direction is oriented along-shore in the spring and summer, and more variable in direction and magnitude in fall and winter. Analysis of the wind and sea-surface temperature measurements showed that the relationship between wind stress variability and Ekman transport in the mixed-layer occurs on very short time-scales.

Technical Abstract: The data for this study were collected during the coastal Ocean Probing Experiment (COPE), which took place in September-October 1995. The objective of the research was two-fold, 1) to understand the complex interactions between the atmospheric boundary layer and the oceanic mixed-layer under a variety of wind conditions, and 2) to assess the applicability of using Doppler lidars to measure wind speed and wind stress in the coastal zone. A number of tests were performed to assess the performance of the 10.59 micro meter Doppler lidar system in measuring wind stress in a coastal environment. Uncertainty in the lidar derived momentum fluxes were plus or minus 0.05N/sq.m. in regions of good signal quality. Problems with water vapor attenuation and laser frequency stability necessitated the use of a velocity threshold technique. The standard deviations of the lidar derived wind stress were improved 20-25 percent after applying a signal threshold and a stability correction.

Last Modified: 10/1/2014
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