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    Kuroshio/Oyashio Watch 2014/10/20


    1. Sea surface temperature and typhoons

    Figure 1.1 shows the sea surface temperature (SST) anomaly of the JCOPE2 from September 21 to 30 (Fig. 1.1a) and from October 1 to 10, 2014 (Fig. 1.1b). The negative SST anomaly east of Japan spread during early October (indicated by the red arrow in Fig. 1.1b).  The NOAA OISST on October 18, 2014 (Fig. 1.2) shows that the negative SST anomaly of the North Pacific Ocean is mainly in the western mid-latitude.  All over the North Pacific except it, the temperature anomaly is overall positive. According to the NOAA Climate Prediction Center, the positive Pacific Decadal Oscillation Index increased in September.

    Fig1.1
    Anomaly of SST of the JCOPE2 analysis relative to the 1993-2012 climatology averaged (a) between September 21 and 30, 2014, (b) between October 1 and 10, 2014.

    Fig. 1.1


    Fig1.2
    Preliminary estimate of SST anomaly on October 18 in the NOAA Optimum Interpolation 1/4 Degree Daily Sea Surface Temperature Analysis (OISST) dataset.

    Fig. 1.2


    South of Japan (indicated by the blue arrows), Fig 1.1b shows the negative anomalies which correspond to the traces of the strong typhoons Phanfone and Vongfong. Figure 1.3 and Figure 1.4 shows the SST sequences in the JCOPE-T as the Phanfone and the Vongfong passed, respectively. Note that the estimates by the JCOPE-T underestimate some strength of the typhoons since the atmospheric forcing used in the JCOPE-T is from a global model (NCEP). For example, the sea level pressure of the typhoon Vongfong became as low as 900 h Pa in reality.

    Recent studies have suggested the importance of not only SST but also subsurface temperature for intensification of typhoons (for example, Lin et al. 2008). Figure 1.5a shows the 26ºC isotherm depth of the JCOPE2 estimate averaged between October 1 to 5 before the two typhoons passed. The tracks of the typhoons Phanfone and Vongfong (the blue and red lines in Fig. 1.5a, respectively) were on the relatively thick warm temperature, which is likely to have affected the intensification of these two strong typhoons. The 26ºC isotherm depth below the typhoon paths in 2014 (Fig. 1.5a) was deeper than that in 2013 (Fig. 1.5b)  or in the climatology (Fig 1.5c).

    Fig1.3
    SST (shade, deg. C) and sea level pressure (contour, interval 5 h Pa) of the JCOPE-T (the extended EAS run) analysis from 9 JST October 1 to 8 JST October 7.

    Fig 1.3


    Fig1.3
    SST (shade, deg. C) and sea level pressure (contour, interval 5 h Pa) of the JCOPE-T (the extended EAS run) analysis from 9 JST October 7 to 23 JST October 14.

    Fig 1.4


    Fig1.5
    Shades are the 26ºC isotherm depth (m) calculated from the JCOPE2 during October 1-5 (a) in 2014, (b) in 2013, and (c) in the 1993-2012 climatology. The thick blue and red lines in (a) are the tracks of the typhoon Phanfone and Vongfong, respectively. The track data are obtained from the Digital Typhoon web site (for Phanfone and Vongfong). 

    Fig. 1.5


    Other information:


    2. Kuroshio path south of Japan

    Figure 2.1 shows the analysis and predictions starting from October 11 of JCOPE2. The last Kuroshio/Oyashio Watch predicted a temporal return to a nearshore path in mid-October from the path near Hachijo Island (Fig 2. 3 in the last issue). In fact, the latest JCOPE2 analysis (Fig. 2.1b) and the Quick Bulletin by Kanagawa Fishery Technology Center on October 14 confirm that the Kuroshio path indeed shifted northward. 

    Fig2.1
    Analyses and predictions starting October 11 of temperature and velocity at 200m depth from JCOPE2.

    Fig. 2.1


    Figure 2.2 shows the three recent analysis and prediction of the sea level height (SSH) near Hachijyo island, which is an index of the Kuroshio nearshore/offshore path around the Izu islands. The recent three prediction from September 27 (the black line), from October 4 (the blue line) and from October 11 (the red line) show similar behavior until November: The Kuroshio path would fluctuate, but gradually shift to the offshore path (decrease of SSH near Hachijyo island). At the end of October, the Kuroshio path would approach Hachijo Island again (Fig. 2.1c).

    Figure 2.2 also shows that the predictions significantly diverge in December. This divergence suggests that the uncertainty of the predictions in December (Fig. 2.1d) is large.  Figure 2.3 compares the sequences of SSH in the prediction from October 4 (Fig 2.3a) and in the prediction from October 11 (Fig. 2.3b). Figure 2.3 shows that the eddy detachment from the Kuroshio near the Izu Islands in November in the prediction from October 11 (Fig. 2.3b) makes the difference of the prediction seen in Fig. 2.2.

    Fig2.2
    Sea level height (m) near Hachijo island (33.1ºN, 139.7ºE) form the JCOPE2 analysis and prediction from September 27 (black curve), from October 4 (blue curve), and from October 11 (red curve).

    Fig 2.2


    Fig2.3
    Sequence of SSH from October 12 to December 11, 2014 in the JCOPE2 predictions (a) from October 4 and (b) the prediction from October 11.

    Fig. 2.3



    Other information


    3. Oyashio

    Temperature less than 5ºC at 100 m depth is often used as an index of the area influenced by the Oyashio Current (for example, the monitoring by the Japan Meteorological Agency, in Japanese). Figure 3.1 shows the time series of the Oyashio area defined as an area less than 5ºC in 141-148ºE, 35-43ºN at 100 m depth (104 km2) using JCOPE2. The Oyashio area during spring in 2014 (thick black line in Fig. 3.1)  was larger than that in the climatology (the thin black line in Fig. 3.1). See the section 1 in the 2014/04/25 issue and section 1 in the 2014/06/02 issue for the topics during spring.

    In August, the Oyashio area (thick black line in Fig. 3.1) dropped to a value less than that in the climatology (thin black line in Fig. 3.1). This drop synchronized with occurrence of the "warm water tongue", mentioned in the section 1 of 2014/8/11 issue.

    The current Oyashio area is near the value of the climatology. The prediction by the JCOPE2 (the thick red line in Fig. 3.1) suggests that the Oyashio area in the next two months would stay near the value of the current one, which was larger than that of the climatology in the coming months (the thin black line in Fig. 3.1). See the JCOPE web page for the analysis and the prediction of temperature distribution at 100 m depth by the JCOPE2.  

    Fig3.1

    Time series of the Oyashio area defined as an area less than 5ºC in 141-148ºE, 35-43ºN at 100 m depth (104 km2) using JCOPE2. Thick black line: the reanalysis in 2014. Thin black line: the 1993-2012 climatology. Red thick line: the prediction by the JCOPE from October 11, 2014.

    Fig. 3.1

    4. Upcoming events

    5. Recent papers

    Papers using JCOPE2 data

    Papers, part of JCOPE study
    Papers by authors/coauthors of JAMSTEC

    Others

    Contact: jcope at_mark jamstec.go.jp