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Richard Legeckis
and
Tong Zhu

The introduction of the 10-bit, five-band, multispectral visible and thermal infrared scanner on the National Oceanic and Atmospheric Administration's GOES-8 satellite in 1994 offers an opportunity to estimate sea surface temperatures from a geostationary satellite. The advantage of the Geostationary Operational Environmental Satellite (GOES) over the traditional Advanced Very High Resolution Radiometer is the 30-min interval between images, which can increase the daily quantity of cloud-free ocean observations. Linear regression coefficients are estimated for GOES-8 by using the sea surface temperatures derived from the NOAA-14 polar-orbiting satellite as the dependent variable and the GOES infrared split window channels and the satellite zenith angle as independent variables. The standard error between the polar and geostationary sea surface temperature is 0.35°C. Since the polar satellite sea surface temperature is estimated within 0.5°C relative to drifting buoy near-surface measurements, this implies that the GOES-8 infrared scanner can be used to estimate sea surface temperatures to better than 1.0°C relative to buoys. Daily composites of hourly GOES-8 sea surface temperatures are used to illustrate the capability of the GOES to produce improved cloud-free images of the ocean. Hourly time series reveal a 2°C diurnal surface temperature cycle in the eastern subtropical Pacific with a peak near 1200 LT. The rapid onset of coastal up welling along the southern coast of Mexico during December of 1996 was resolved at hourly intervals.

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Richard V. Legeckis

Abstract

High-resolution thermal infrared data from the NOAA polar orbiting satellites are studied for the Gulf Stream between Florida and Cape Hatteras from the fall of 1974 to the spring of 1977. The sea surface temperature boundaries of the current are detectable in infrared images from fall to spring of each year. Seasonal changes in air-sea temperatures appear to limit the detection of the surface temperature gradients during the warmer months. A persistent seaward deflection of the western boundary is found southeastward of Charleston, South Carolina, in the vicinity of a bulge in the continental slope. The maximum deflection angle is time dependent and varies from 60° to 120° from true north. Downstream from the initial deflection, the western boundary is often wave-like. Several distinct and repeatable wave patterns are described. The separation between adjacent wave crests (wavelength) averages 150 km and the waves appear to move northward at an average phase speed of 40 km day−1. Monthly frequency distributions of wavelength show that values range from 90 to 260 km downstream from the deflection and wavelengths increase between February and April of 1977. The phase of the low-frequency wave motion is illustrated in space-time diagrams during February 1976 and April 1977. The small-scale cyclonic spin-off eddies previously described by Lee and Mayer (1977) as forming off Florida appear to increase in amplitude downstream from the deflection. On a seasonal time scale, the variability of the position of the western boundary of the Gulf Stream increases by a factor of 3 downstream from the deflection. This suggests that the current is forced by the change in the depth at the bulge in the continental slope off Charleston.

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Harry G. Stumpf
and
Richard V. Legeckis

Abstract

Active mesoscale (300 km diameter) eddy formation off the Pacific coast of Central America was observed during February 1976 by a thermal infrared sensor aboard the NOAA 4 satellite. These anticyclonic eddies, closely associated with wind-induced upwellings, propagate westward at an average speed of 13 km day−1, which is approximately the speed of nondispersive baroclinic Rossby waves at latitude 12°N.

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Richard Legeckis
,
William Pichel
, and
George Nesterczuk

Geostationary satellite observations of a zonally oriented sea surface temperature front in the eastern equatorial Pacific were made between 1975 and 1981. Long waves appeared along the front mainly during the summer and fall, except during 1976, the year of an El Niño. The waves have averaged periods of 25 days and wavelengths of 1000 km. At the end of 1981, the long waves also were detected in a new sea surface temperature analysis based on multichannel infrared measurements from a polar-orbiting satellite. This quantitative analysis may improve the ability to resolve low-frequency equatorial wave motions from satellite observations.

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