Simulation of the 2001–02 Anomalous Intrusion in the Northeast Pacific

Abstract

A numerical model, the Parallel Ocean Program (POP) was used to run a 46-year simulation of the North Pacific Ocean beginning in January 1960. The model had a horizontal resolution of 0.25°, 28 vertical levels, and employed spectral nudging that, unlike standard nudging, nudges only specific frequency and wavenumber bands. This simulation was nudged to the mean and monthly Levitus climatology of potential temperature and absolute salinity (S A). The model was forced with the mean monthly winds, sea level pressure, net heat flux, and precipitation from the National Centers for Environmental Prediction (NCEP). The simulation was used to examine the anomalous intrusions, previously observed from 2001 to 2002, of cooler and fresher (less spicy) water flowing southward along the coast of western North America. The simulated anomaly began in 1999 in the North Pacific, progressed southeastward towards the coast and then southward, at least as far south as southern California. The southward velocity signal, modulated by a strong annual cycle, reached Point Conception in 2000 while the temperature and S A anomalies arrived later, in 2002-03. The simulated velocity anomalies were eastward at about 3 cm s −1 in the northeast Pacific near 47°N in agreement with observations. Simulated coastal southward flow speeds reached 10-20 cm s −1 during the summer from 2000 to 2002. This intrusion was by far the largest to occur over the entire length of the simulation. It was also the only time during the simulation when the Victoria mode was positive (associated with enhanced flow to the east via the North Pacific Gyre Oscillation (NPGO)) and the Multivariate El Niño-Southern Oscillation (ENSO) Index (MEI) was negative (La Niña conditions), tending to cause a southward flow anomaly along the coast. RÉSUMÉ [Traduit par la rédaction] Nous avons utilisé un modèle numérique, le Parallel Ocean Program (POP), pour exécuter une simulation sur 46 ans de l'océan Pacifique Nord à partir de janvier 1960. Le modèle avait une résolution horizontale de 0,25°, 28 niveaux verticaux et employait la technique du « poussage spectral » qui, contrairement au poussage ordinaire, ne pousse que certaines bandes de fréquence ou de nombre d'ondes. Cette simulation a été poussée vers la climatologie moyenne et mensuelle de Levitus de la température potentielle et de la salinité absolue (S A). Le modèle a été forcé avec les vents mensuels moyens, la pression au niveau de la mer, le flux de chaleur net et les précipitations des NCEP (National Centers for Environmental Prediction). La simulation a servi à examiner les intrusions anormales, précédemment observées de 2001 à 2002, d'eau plus froide et plus douce (moins épicée) circulant vers le sud le long de la côte ouest de l'Amérique du Nord. L'anomalie simulée a commencé en 1999 dans le Pacifique Nord et a progressé vers le sud-est en direction de la côte puis vers le sud, au moins jusque vis-à-vis le sud de la Californie. Le signal de vitesse vers le sud, modulé par un fort cycle annuel, a atteint Point Concept...

Decadal Trends in Oxygen Concentration in Subsurface Waters of the Northeast Pacific Ocean

“…We cannot assess the extent to which Haida 1998 might have influenced O 2 and Θ at these neighbouring locations. The coincidence of both O 2 and Θ anomalies suggests the eddy may have affected these outer stations, but the weather systems shifted significantly between spring 1998 and summer 1999 and also changed subsurface currents and water properties (Donohue & Stacey, 2013), which could have changed O 2 and Θ along WOCE line P1.…”