Available at: http://digitalcommons.calpoly.edu/theses/1566
Date of Award
MS in Electrical Engineering
The energy exchanged between the atmosphere and the ocean is an important parameter in understanding the Earth’s climate. One way of quantifying this energy exchange is through the use of “wind work,” or the work done on the ocean by the wind. Since wind work is calculated according to the interaction between ocean surface currents and surface wind stress, a number of surface current decompositions can be used to decompose wind work calculations. In this research, geostrophic, ageostrophic, Ekman, and total current decompositions are all used to calculate wind work. Geostrophic currents are formed by the balance of surface pressure gradients and the Coriolis effect. Ageostrophic currents, on the other hand, are difficult to calculate because they are made up of many types of currents, and are generally defined as any current not in geostrophic balance. The main component of ageostrophic currents, Ekman currents, are used in this work to approximate ageostrophic currents. Ekman currents are formed by the balance of surface wind stress and the Coriolis effect. Finally, total currents are the sum of all currents in the ocean.
Using high resolution, global NASA ocean models, the wind work on the global oceans is estimated via a number of decompositions, with results finding about 3.2 TW, .32 TW, and 3.05 TW for total, geostrophic, and Ekman wind work respectively, when taking a 7 day window average of surface currents and a 1 day average of surface stress. Averaging period for currents is found to significantly affect the resulting calculated wind work, with greater than 50 percent difference between 1 and 15 days of averaging. Looking at the same total, geostrophic, and Ekman wind work results for 1 day averages of wind stress and surface currents finds 5.5 TW, .03 TW, and 6.3 TW respectively. This result indicates that high frequency currents are very important to wind work. Seasonally, wind work is found to be at a maximum during the Northern Hemisphere (NH) summer, and at a minimum during the NH winter months.
To help motivate the funding of a Doppler Scatterometer, simulations are used to show the capabilities of such an instrument in measuring wind work. DopplerScat simulations find that a satellite capable of measuring coincident surface vector winds and surface vector currents, with 1.1 m/s wind speed error and .5 m/s current speed error, could estimate global wind work to within 2 percent accuracy on an 8 day average with daily global snapshots.