Study On Multi-timescale Variations Of The Global Ocean Temperature Inferred From Argo

Based on wavelet analysis of weekly mean sea temperature data from Argo(Array for Real-time Geostrophic Oceanography) during2003to2008, the spatialcharacters of the annual (327-389days) and semiannual (164-195days) variations oftemperature in the upper2000m and the intra-seasonal oscillation (ISO;14-97dayperiods) of temperature in the upper2000m in the global upper ocean are given.Analysis and discussion are also given for the mechanism of these three periods oftemperature. These results can provide useful information for the design of fieldobservation in the global ocean.As to annual and semiannual variations of temperature, it is shown that seasurface temperature in middle and high latitudes of the northern and southernhemispheres are dominated by variations of the annual period. In the tropical ocean,surface temperature mainly shows semiannual period, while temperature near thethermocline shows both annual and semiannual periods (annual period is obvious inthe equatorial Pacific Ocean, the southeast Indian Ocean and the western equatorialAtlantic Ocean, while in the eastern and western equatorial Indian Ocean thesemiannual oscillation can be clearly seen). Temperature of the annual period inmiddle and high latitudes of the northern and southern hemispheres and that of thesemiannual period in the low latitude and the middle latitude of the north hemispherehave both the maximum extension, the highest significance, the strongest intensityand the leading phase in the surface. As depth increases, the extension reduces,significance decreases, intensity weakens and phase lags, with evident signals mainlyconcentrating in the upper50m and can reach up to150m. In contrast, the largestextension, significance, intensity and the leading phase occur at about100m in theequatorial Pacific Ocean, the southeast Indian Ocean and the western equatorial Atlantic for temperature of the annual period, and in the eastern and westernequatorial Indian Ocean for that of the semiannual period; these oscillation signalsmainly concentrate in the vicinity of the thermocline, and can reach up to500m.The results about ISO of temperature are shown as follow. Near surface the ISOexist mainly in the band east of60oE between10oS and10oN, and the region aroundthe Antarctic Circumpolar Current (ACC); at other levels we analyzed, including50m,100m,1000m, the ISO also exists in the regions of the Kuroshio, the Gulf Stream, theIndonesian through flow, the Somalia current, and the subtropical countercurrent(STCC) of the north Pacific. The intra-seasonal signals can be seen even at depth ofabout2000m in some regions of the global ocean. Largest amplitude of ISO appearsat the thermocline of the equatorial Pacific, Atlantic and Indian Ocean, with maximumstandard deviation (STD) exceeding1.2oC. The ACC, the Kuroshio and the GulfStream are all regions exhibiting large STD for all levels we analyzed; especially at1000m, largest STD appears at the south and southeast of the South Africa-a part ofthe ACC, with maximum value reaching0.5oC. Small amplitude of ISO appears nearthe10oN of the western Pacific near surface, the northeast Pacific and Atlantic at100m, with minimum STD being between0.05oC and0.1oC. At1000m, minimumSTD is between0.02oC and0.05oC in most of the Pacific and the tropical Atlantic.The ratios of the intra-seasonal temperature variance to the total variance at1000mand at the equator indicate that in considerable part of the global deep ocean, the ISOis dominant in the variations of temperature since such ratio exceeds even50%there.A case study also confirms the existence of the ISO at deep ocean.