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  • JAMSTEC

    Kuroshio/Oyashio Watch 2016/09/05

    Contents

    1. Sea surface temperature and sea surface height anomalies
    2. Kuroshio path south of Japan
    3. Oyashio
    4. Typhoons in August 2016 and sea surface temperature
    5. Upcoming events
    6. Recent papers

    1. Sea surface temperature and sea surface height anomalies

    Figure 1.1 shows the sea surface temperature (SST) anomalies of the JCOPE2 from August 1 to 10 (Fig. 1.1a), from August 11 to 20 (Fig. 1.1b), and August 21 to 31, 2016 (Fig. 1.1c).

    Fig1.1
    Anomalies of SST (K) of the JCOPE2 analysis relative to the 1993-2012 climatology of each period. The thick lines are the best tracks of the typhoons. The data of the best track were obtained fromDigital Typhoon.

    Fig. 1.1



    Following the figure for June 2016 (Fig. 1.2 in the 2016/07/11 issue),;Fig. 1.2a;and;b;show the sea surface height (SSH) and anomalies in July and August, respectively. Fig 1.3d shows the SSH anomaly averaged in the region 31-36ºN, 140-165ºE (the box in;Fig. 1.2), which was defined by;Qiu et al. (2014);as a good indicator of the dynamics state of the Kuroshio Extension, remained higher than the climatology (See also the positive anomaly in Fig. 1.2ab). Thus, the southern recirculation of the Kuroshio Extension remained strong.;

    The thick black curve in;Fig 1.3a;is the time series of the path length of the upstream Kuroshio-Extension path integrated from 141E to 153E, which is an index of the stability of the Kuroshio Extension.; In July and August, the length showed increases, indicating the upstream Kuroshio Extension was unstable.

    The time series of the path length of the downstream Kuroshio-Extension path integrated from 153 to 165ºE in;Fig. 1.3b showed increases in August. The long path means that the downstream Kuroshio Extension was also unstable.;;

    The mean latitudes of the Kuroshio Extensios was higher than the climatological position (Fig. 1.3c).

    The positive SSH anomaly in the Oyashio area (C) was consistent with the warm Oyashio area. See;Section 3.

    The negative SSH anomaly south of Japan (D) disappeard in August (Fig. 1.2b) because of the shift to a Kuroshio nearshore path (See;Section 2).

    Fig1.2
    (a) The sea-surface-height contour lines of 5 cm in the JCOPE2 are regarded as the Kuroshio axes. The thin green lines are daily Kuroshio paths from July 1 to July 31, 2016. The red line is the Kuroshio path averaged in July. The black line is the climatological (1993-2012) Kuroshio path in July. Color shade shows the sea surface height anomaly in July 2016 relative to the 1993-2012 climatology (m). The dashed box is used for the calculation of;Fig. 1.3d. (b) The same as (a) except for August (Data until August 28 were used).

    Fig. 1.2

    Fig1.2
    (a) Time series of the upstream Kuroshio-Extension path length integrated from 141 to 153E using JCOPE2 reanalysis.
    (b) Time series of the downstream Kuroshio-Extension path length integrated from 153 to 165E using JCOPE2 reanalysis.
    (c) Time series of the mean latitude of the Kuroshio-Extension path between 141 and 153E using JCOPE2 reanalysis.
    (d) Time series of the SSH anomalies averaged over the region 31N-36N, 140E-165E (the box in Fig. 1.2) using JCOPE2 reanalysis. Thick black line: the reanalysis in 2015 and 2016. Thin black line: the daily 1993-2012 climatology with the range of the daily standard deviation (gray shade).

    Fig. 1.3



    Link to other information:


    2. Kuroshio path south of Japan

    Figure 2.1 shows the analysis and predictions of JCOPE2 starting from August 27, 2016.;The Kuroshio path has become a nearshore one (Fig. 2.1a,b)

    Figure 2.2 shows the recent analysis and prediction of the sea level height (SSH) near Hachijo Island, which is an index of the Kuroshio nearshore/offshore path around the Izu Islands. The increase of the SSH in August (the black stars in Fig. 2.2) indicates the shift to the nearshore path.

    The prediction in the last issue (the black curve) predicted a temporal decrease of SSH (a temporal return to an offshore path). However, it did not happen.

    The latest predictions (the green, blue, red lines in Fig. 2.2) suggest that the nearshore path (the high SSH) will continue. See also Fig. 2.1c. However, Fig. 2.2 also shows fluctuation of the path (SSH) will become large from late September. See also Fig. 2.1d.

    The left panels in Fig. 2.3 show the sequence of SSH in the latest prediction. To highlight short-term fluctuations, the right panels of Fig 2.3 show the sequence of the SSH anomaly relative to the 41-day running mean. The continuation of the nearshore path in the prediction mentioned above depends on the development of the negative anomaly A in Fig. 2.3.; In the current prediction, the development of the negative anomaly A will not be large enough to cause an offshore path.

    The right panels of Fig. 2.3 show that the propagation and development of positive and negative anomalies especially after late September. These anomalies will cause the fluctuation of the Kuroshio path mentioned above.

    Figure 2.3 also shows that a small meander east of Kyushu will develop after the propagation and development of the negative anomaly B. See also the small meander in Fig. 2.1d (pointed by the blue arrow).

    Please note that the Japanese version of the Kuroshio/Oyashio Watch is updated every week.

    Fig2.1
    The latest analyses and predictions of temperature and velocity at 200m depth from JCOPE2. Red star marks are the location of Hachijo Island.

    Fig. 2.1

    Fig2.2
    Sea level height (m) near Hachijo Island (33.1N, 139.7E) from the JCOPE2 analysis (black stars) and recent predictions (black, green, blue, and red curves).

    Fig 2.2


    Fig2.3

    Development of the SSH in the latest prediction. (Left) Sequence of SSH (m, c.i.=0.1 m). (Right) Sequence of the SSH anomaly (m, c.i.=0.05 m) relative to the 41-day running mean (the mean of available data if all 41-day data are not available).

    Fig. 2.3


    Link to other information


    3. Oyashio

    As an index of the area influenced by the Oyashio Current, Figure 3.1 shows the time series of the Oyashio area defined as an area less than 5 ºC in 141-148ºE, 35-43ºN (the box enclosed by the dashed line in Fig. 3.4) at 100 m depth (104 km2) using JCOPE2. The Oyashio area calculated by the JCOPE2 reanalysis (the thick black curve) was less than the prediction in the last issue (the yellow curve). The Oyashio area was far below the climatological value (the thin black curve).

    Fig. 3.1 shows that the recent predictions of the Oyashio area (the green, blue, red curves). The latest one (the red curve) predicts that the Oyashio area will continue to be far below the climatological value (the thin black line).

    Following the figure for June (Fig. 3.2 of the 2016/07/11 issue), Figure 3.2 andFigure 3.3 compare the Oyashio area each year in July and August, respectively. The value in July 2016 was the second smallest since 1993.The value in August 2016 so far (until August 28) was the smallest since 1993.

    Figure 3.4 compares temperature and velocity at 100m depth on August 27, 2016 and the climatological (the 1993-2012 average) values. The southward intrusion of the first branch of the Oyashio Current this year (A in Fig. 3.2) was weaker than that of the climatology because of the existence of a warm anticyclonic eddy.

    Figure 3.4 also shows that the region north of the Kuroshio Extension (B) was warmer than the climatology because of the meandering Kuroshio Extension discussed in Section 1.

    See more in the JCOPE web page for the analysis and the prediction of the temperature distribution at 100 m depth.


    Fig3.1

    Time series of the Oyashio area defined as an area less than 5 ºC in 141-148ºE, 35-43ºN at 100 m depth (104km2) using JCOPE2. Thick black line: the reanalysis in 2015-2016. Thin black line: the 1993-2012 climatology with the range of the daily standard deviation (gray shade). Yellow, green, blue, and red thick lines: the predictions by the JCOPE from July 23, August 13, 20 and 27. respectively.

    Fig. 3.1

    Fig3.2
    Comparison of the Oyashio Area in July each year since 1993

    Fig. 3.2

    Fig3.2
    Comparison of the Oyashio Area in August each year since 1993

    Fig. 3.3

    Fig3.2
    (Left) Temperature (ºC) and velocity (m/s) at 100m depth on August 27, 2016. (Right) Climatological values (1993-2012 average) for comparisons. The box enclosed by the dashed line is used for the calculation of the Oyashio area in Figs. 3.1. The 5ºC temperature contour is used to define the Oyashio area.

    Fig. 3.4

    Link to other information:

    4. Typhoons in August 2016 and sea surface temperature

    In mid-July, The typhoons OMAIS (5th typhoon in 2016), CONSON (6th), CHANTHU (7th), MINDULLE (9th), LIONROCK (10th), and KOMPASU approached Japan. They cooled SST. Figure 4.1 (movie) shows the SST sequences in the JCOPE-T (Varlamov et al., 2015).

    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 August 5 to 8 JST September 1, 2016. Note that the estimates by the JCOPE-T might underestimate some strength of the typhoon since the atmospheric forcing used in the JCOPE-T is from a global model (NCEP).

    Fig. 4.1


    5. Upcoming events

    Events


    6. Recent papers

    Paper by the author/coauthor of the Application Laboratory, JAMSTEC

    Paper using the JCOPE data

    Paper using the OFES data

    Paper by author/coauthor of JAMSTEC

    Others

    Contact: jcope at_mark jamstec.go.jp