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Numerical simulations of the remotely forced ocean response to westerly wind bursts prior to and during the 1991–1992 El Niño are examined; the models are forced by wind stress from the U.S. Navy's atmospheric global operational analysis/forecast system. The study focuses on (1) the relative response of the first and second internal modes to a single episode of westerly bursts; (2) the role of westerly bursts in producing the eastern Pacific sea level variations from October 1990 to February 1992; and (3) the relative importance of the remotely forced sea level responses generated by central and western Pacific wind anomalies. The simulations use the Naval Research Laboratory global multilayer formulation; the suite of experiments includes hydrodynamic simulations that use both one‐ and three‐active‐layer reduced gravity models as well as an experiment that also includes thermodynamic effects. The models are executed from January 1, 1990, to March 1, 1992, a period that includes 10 significant westerly wind bursts or burst clusters and the 1991–1992 El Niño event. The numerical experiments reveal an ability to accurately simulate the eastern Pacific sea level variations during this period. In response to a single burst the three‐layer hydrodynamic simulation reveals that the second internal mode Kelvin wave yields a sea level change at the eastern boundary that is approximately one third that of the first mode and a surface velocity signature that is equivalent to the first mode. During the onset of the El Niño event the inclusion of higher modes also produces a more realistic representation of the observed eastern boundary sea level signal. Furthermore, by comparing the model response to particular wind bursts with the observed sea level at Baltra, Galapagos, a value of 2.5–2.6 m/s is suggested as the most appropriate mean speed for the first internal mode Kelvin wave during the onset phase. The models reveal the following scenario for the onset of the 1991–1992 El Niño. The eastern boundary sea level exhibited three, distinct pulselike events superimposed on a general rise; the observed sea level pulses occurred in October–November, December–January, and February. The numerical simulations indicate that the pulses in December–January and February were the result of three powerful, westerly wind bursts in the western Pacific preceded by westerly anomalies in the central Pacific. The Kelvin wave pulse generated in the western Pacific by the wind burst in late December to early January was reinforced by a strong central Pacific westerly wind anomaly in mid‐January. These westerly wind events were associated with the development of western Pacific tropical cyclones near the equator in one or both hemispheres.

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NASA, NOAA, and the Department of Defense use common infrastructure and directed research to address the research-to-operations problem for satellite data assimilation. The Joint Center for Satellite Data Assimilation (JCSDA) was established by the National Aeronautics and Space Administration (NASA) and National Oceanic and Atmospheric Administration (NOAA) in 2001, with the Department of Defense (DoD) agencies becoming partners in 2002. The goal of JCSDA is to accelerate the use of observations from Earth-orbiting satellites in operational environmental analysis and prediction models for the purpose of improving weather forecasts, improving seasonalto-interannual climate forecasts, and increasing the accuracy of climate datasets. Advanced instruments of the current and planned satellite missions do and will increasingly provide large volumes of data related to the atmospheric, oceanic, and land surface states. During this decade, the plan will result in a five order

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Atmospheric water vapor data derived from the special sensor microwave/imager (SSM/I) are used to make time-coincident, wet tropospheric range corrections to Geosat altimeter data in the northeast Pacific. The original and corrected sea surface height residuals along numerous tracks are examined to determine the impact of water vapor on the altimeter signal. Mesoscale feature analyses of corrected and uncorrected altimeter data are used to assess the impact of water vapor path lengthening in areas of low sea surface height variability. Results indicate that the horizontal spatial variations in the water vapor height corrections are frequently similar to true oceanographic gradients. interpretation of altimeter data is affected in several ways. The unaccounted-for presence of atmospheric water vapor may mimic or mask the true ocean features, and even small changes in the water vapor over short spatial scales can enhance a partially obscured feature. Analyses of all Geosat tracks crossing the area of interest in September 1987 clearly illustrate that water vapor frequently contaminates the ocean topography measurements, making the water vapor adjustment critical before the altimeter data can be successfully used to locate and identify mesoscale ocean features. Furthermore, the SSM/I and Geosat data must be closely matched in both space and time, a difficult task since it takes 3.5 days to obtain global SSM/I coverage with one operational sensor. To optimize the mesoscale oceanographic application of altimeter data, a bore-sighted radiometer should be included on all altimeter spaceborne platforms.

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The long-term goal of this and companion projects is to improve our ability to analyze and predict the upper ocean/lower atmosphere environment, using sophisticated techniques that can exploit data from all available sources. This ability is fundamental to meeting DOD's needs for real-time analysis and improved air/sea simulation and prediction on a variety of scales, including mesoscale to tactical scale support in littoral environments and on the battlefield. To meet these needs, the Naval Research Laboratory is developing the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) 1 , and has already transitioned the atmospheric prediction system and ocean analysis components to operations. Same as Report (SAR) 18. NUMBER OF PAGES 6 19a. NAME OF RESPONSIBLE PERSON