Typhoon-Induced Variability of the Oceanic Surface Mixed Layer Observed by Argo Floats in the Western North Pacific Ocean

Abstract

This study takes advantage of the newly established observational network of Argo floats to investigate the variability of the oceanic surface mixed layer (ML) in response to typhoons occurring over the period 2000-08 in the western North Pacific Ocean. After removing the background variability due to the seasonal cycle, the regionally averaged ML response is statistically analyzed as a function of the distance from the typhoon centre, the time after typhoon passage, the geographic location, the translation speed of the typhoon and the pre-existing patterns of oceanic circulation. Based on an unprecedented amount of new observational data, our analysis reveals some notable differences between ML temperature and ML depth changes induced by a typhoon, including the delayed response of ML temperature relative to ML depth, the longer restoring time of ML temperature, and the tendency of pre-existing cold-core features to favour ML cooling while warm-core features favour ML deepening.RÉSUMÉ [Traduit par la rédaction] La présente étude tire profit du nouveau réseau de balises d'observation Argo qui étudie la variabilité de la couche de mélange de la surface océanique en réponse aux typhons survenus durant la période 2000-2008 dans l'ouest du Pacifique Nord. Après avoir éliminé la variabilité de fond due au cycle saisonnier, nous faisons une analyse statistique de la réponse de la couche de mélange, moyennée dans une région, en fonction de la distance du centre du typhon, du temps écoulé depuis le passage du typhon, du lieu géographique, de la vitesse de déplacement du typhon et des configurations de circulation océanique préexistantes. En se basant sur une quantité sans précédent de nouvelles données d'observation, notre analyse révèle des différences notables entre les changements de température et de profondeur de la couche de mélange produits par le typhon, y compris la réponse retardée de la température de la couche de mélange par rapport à la profondeur de la couche de mélange, le temps de rétablissement plus long de la température de la couche de mélange et la tendance des caractéristiques de noyaux froids préexistantes à favoriser le refroidissement de la couche de mélange pendant que les caractéristiques de noyaux chauds favorisent l'approfondissement de la couche de mélange.

Understanding surface and subsurface temperature changes induced by tropical cyclones in the Kuroshio

“…Argo program automatically collected nearly in situ temperature profiles in the upper 2000-m global ocean with an interval of a few days and provided a unique opportunity to study ocean subsurface responses to translating TCs (Park et al 2011;Sun et al 2012;Vissa et al 2012;Wu and Chen 2012). Unlike these studies which were all focused on the open ocean, the present study will be focused on understanding the subsurface temperature changes of the Kuroshio by means of 10-year satellite SST images and Argo data during the periods of TCs' passage.…”

Tropical cyclone footprint in the ocean mixed layer observed by Argo in the Northwest Pacific

“…Figure 4 gives the statistical characteristic of changes for the ILD, MLD, BLT, and ILT under the different types of TCs. The uncertainty is estimated by the standard deviation divided by the root mean square of the number of profile pairs in each bin [Wu and Chen, 2012]. The uncertainties in the inner core of all TCs except for the fast TCs are small.…”

“…The Array for Real-time Geostrophic Oceanography (Argo) floats measure the global ocean (0-2000 m) temperature and salinity even under extreme atmospheric and oceanic conditions such as TC passage, and thus provide a complete picture of the upper ocean structure and variability in response to TCs [Roemmich and Owens, 2000] [Liu et al, 2007] shows a weakly positive correlation between the ILD change and the wind speed, and implies that the high wind speeds not only induce strong vertical mixing (increasing ILD) but also cause upwelling (decreasing ILD). The response of the upper ocean to typhoons is reexamined in the northwest Pacific Ocean using the Argo profile data (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008) with the seasonal variability removed [Wu and Chen, 2012]. The result reveals a delayed response of ILT relative to ILD and the longer restoring time of ILT.…”

“…(2) The selected Argo profile is paired with another profile taken before the passage of the TC to represent the variation induced by the TC. The maximum distance between the paired is restricted within 50 km [Wu and Chen, 2012]. This scale selection is based on a trade-off between the data availability and the closeness of data points to estimate the local response.…”

“…Under storms, energy transferred from atmosphere to ocean generates upwelling, near-inertial waves, and currents [Price et al, 1994;Wang and Huang, 2004;Liu et al, 2008;Jaimes and Shay, 2010;Chang et al, 2012Chang et al, , 2013. As TC's translation speed is less than phase speed of the first baroclinic mode, oceanic response tends to be barotropic, geostrophic, and cyclonic gyre with upwelling in the storm's center [Chang and Anthes, 1978;Chang, 1985;Ginis and Sutyrin, 1995], which weakens the IL deepening near the storm's centers [Wu and Chen, 2012]. If the TC's translation speed is faster than the phase speed of the first baroclinic mode, the currents in the wake become more near-inertial after the first half inertial period.…”