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Satellite Observations of the Wind Jets off the Pacific Coast of Central America. Part II: Regional Relationships and Dynamical Considerations

Dudley B. CheltonCollege of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon

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Michael H. FreilichCollege of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon

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Steven K. EsbensenCollege of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon

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Abstract

Satellite estimates of winds at 10 m above the sea surface by the NASA scatterometer (NSCAT) during the 9-month period October 1996–June 1997 are analyzed to investigate the correlations between the three major wind jets along the Pacific coast of Central America and their relationships to the wind and pressure fields in the Inter-American Seas and eastern tropical Pacific. Comparisons with sea level pressure confirm the conventional view that Tehuantepec wind variations are driven by pressure variations in the Gulf of Mexico associated with North American cold-air outbreaks. The three jets sometimes developed sequentially from north to south. Statistically, however, the Papagayo and Panama jets were poorly correlated with variations of the Tehuantepec jet over the NSCAT observational period. The Papagayo and Panama jets were significantly correlated with each other and were coupled to coherent variations of the trade winds extending from the Caribbean Sea to the eastern tropical Pacific.

The detailed structures of the wind fields within the three jets are examined to infer dynamical balances within the jets. After leaving the coast, the northerly Tehuantepec and Panama jets turn anticyclonically toward the west in manners that are consistent with jets that are inertially balanced at the coast and become progressively more geostrophically balanced with increasing distance from the coast. There is no evidence of anticyclonic turning of the easterly Papagayo jet, suggesting that the winds may remain in approximate geostrophic balance through the gap over the Nicaraguan lake district.

NSCAT observations are compared with operational analyses by ECMWF to investigate the detailed structures of the wind fields over the Gulfs of Tehuantepec, Papagayo, and Panama. Systematic differences between the NSCAT observations and the ECMWF analyses of the divergent off-axis fanning of all three jets suggest that there may be systematic errors in parameterizations of boundary layer processes in the ECMWF “first-guess” fields in these data-sparse regions.

Corresponding author address: Dudley B. Chelton, College of Oceanic and Atmospheric Sciences, Oregon State University, 104 Ocean Admin Building, Corvallis, OR 97331-5503.

Email: chelton@oce.orst.edu

Abstract

Satellite estimates of winds at 10 m above the sea surface by the NASA scatterometer (NSCAT) during the 9-month period October 1996–June 1997 are analyzed to investigate the correlations between the three major wind jets along the Pacific coast of Central America and their relationships to the wind and pressure fields in the Inter-American Seas and eastern tropical Pacific. Comparisons with sea level pressure confirm the conventional view that Tehuantepec wind variations are driven by pressure variations in the Gulf of Mexico associated with North American cold-air outbreaks. The three jets sometimes developed sequentially from north to south. Statistically, however, the Papagayo and Panama jets were poorly correlated with variations of the Tehuantepec jet over the NSCAT observational period. The Papagayo and Panama jets were significantly correlated with each other and were coupled to coherent variations of the trade winds extending from the Caribbean Sea to the eastern tropical Pacific.

The detailed structures of the wind fields within the three jets are examined to infer dynamical balances within the jets. After leaving the coast, the northerly Tehuantepec and Panama jets turn anticyclonically toward the west in manners that are consistent with jets that are inertially balanced at the coast and become progressively more geostrophically balanced with increasing distance from the coast. There is no evidence of anticyclonic turning of the easterly Papagayo jet, suggesting that the winds may remain in approximate geostrophic balance through the gap over the Nicaraguan lake district.

NSCAT observations are compared with operational analyses by ECMWF to investigate the detailed structures of the wind fields over the Gulfs of Tehuantepec, Papagayo, and Panama. Systematic differences between the NSCAT observations and the ECMWF analyses of the divergent off-axis fanning of all three jets suggest that there may be systematic errors in parameterizations of boundary layer processes in the ECMWF “first-guess” fields in these data-sparse regions.

Corresponding author address: Dudley B. Chelton, College of Oceanic and Atmospheric Sciences, Oregon State University, 104 Ocean Admin Building, Corvallis, OR 97331-5503.

Email: chelton@oce.orst.edu

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