Abstract
Recently, Clarke and Lebedev showed that τ, the low-frequency eastward equatorial wind stress zonally averaged along the equator, can, in the case of the Pacific Ocean winds, be linearly estimated by Δp, the surface atmospheric pressure difference between the eastern and western ocean boundaries. The authors find that detrended interannual τ calculated from monthly winds is similarly linearly correlated with detrended Δp in the equatorial Atlantic and Indian Oceans since 1964 when enough wind data are available. The regression coefficient between τ and Δp enables the authors to estimate the turbulent stress atmospheric boundary layer height as being about 240 m for the equatorial Atlantic Ocean and 320 m for the equatorial Indian Ocean. Using a central Pacific pressure observation at 168°W, the authors similarly estimate the western and eastern Pacific turbulent stress atmospheric boundary layer heights as about 665 and 630 m, respectively.
Unlike the wind data, the pressure data do not contain systematic errors due to changing methods of measurement. Comparison of τ to Δp and τ from winds shows that there are strong false trends in Pacific and Atlantic τ estimated from winds. The τ from Δp records are not correlated on interannual timescales for any of the oceans, although the Indian and Pacific τ are negatively correlated if one restricts calculations to the period 1970–92. Decadal fluctuations are not visually correlated over the “short” records available. Most of the decadal Pacific variability comes from the western Pacific.
Theory and previous calculations for the Pacific indicate that interannual and decadal sea level on the eastern Pacific Ocean boundary is linearly related to τ. Calculations confirm this for the eastern Indian Ocean boundary and marginally support it for the Atlantic, where the low-frequency sea level records are short and of small amplitude. The Indian Ocean τ from Δp is much better correlated with sea level than τ from the winds. Large decadal sea level fluctuations occur on the eastern Indian Ocean boundary. On this timescale, anomalous westerly equatorial Indian Ocean winds have raised the Indian Ocean eastern boundary sea level since about 1970 and during most of the 1950s, while anomalous easterly equatorial Indian Ocean winds lowered the eastern Indian Ocean boundary sea level in the 1960s.
* Additional affiliation: Geophysical Fluid Dynamics Institute, Tallahassee, Florida.
Corresponding author address: Dr. Allan J. Clarke, Dept. of Oceanography, 3048, The Florida State University, Tallahassee, FL 32306-3048.
Email: clarke@ocean.fsu.edu
