The released data mainly cover the data sparse era and area in the present available data set such as the Comprehensive Ocean-Atmosphere Data Set(COADS;Woodruff et al.,1984):the period from 1901 to 1931,especially in 1910s around World War I and the North Pacific(more than 80% of the released data).See Figs.4(a)and(b)of Manabe(1999)on the details of temporal and spatial distributions of the released Kobe Collection data.Therefore,it is expected that the Kobe Collection data can considerably contribute the clarification of more robust climate variation in the North Pacific before World War II.Especially,these may be useful for the clarification of El Nino/ Southern Oscillation(ENSO)phenomena and the decadal to interdecadal variations found in the Pacific sector(e.g.,Nitta and Yamada,1989;Trenberth.1990;Tanimoto et al.,1993;1997;Minobe,1997;Zhang et al.,1997).
However,as mentioned above,we have to pay careful attention on the treatment of SST data taken in the period of the bucket method.If some instrumental or methodological biases exist,they have to be properly corrected.The purpose of this article is to examine the validity of correction to historical SST data proposed by Folland and Parker(1995),using the independent data set of the long-term coastal SST(CSST)data taken around Japan,whose measurements have been conducted by JMA and Japan Fisheries Agency(JFA).
This report is the essence of the paper by Hanawa et al.(2000)to be published in the Journal of Meteorological Society of Japan.
2. The data used and Folland and Parker's correction
(a) Coastal sea surface temperature(CSST)
JMA and JFA have conducted CSST measurements at several tens stations around Japan Islands as well as the coasts of Korean Peninsula since early this century,and several stations of them are continued to the present(Tokai Regional Fisheries Research Laboratory,1982;Yoshida,1997).In the present study,we use the data at 9 CSST stations whose time series are relatively longer and are spanning before and after the period of World War II.Among them,3 stations of Suttsu(henceforth Station a),Miyako(e)and Ishigakijima(i)are belonging to JMA,and 6 stations of Shiokubi(b),Sirakamisaki(c),Inahozaki(d),Enoshima(f),Nojimazaki(g)and Hachiojyojima(h)are belonging to JFA.Positions of 9 stations are shown in Fig.1.
From the beginning of measurements to mid 1970s,JMA CSST data had been taken by the bucket and the stem thermometer once(10:00 am at local time)every day.After mid 1970s,it is replaced by the electric measurement using platinum-wire resistor.So,in the present study,we use only the data taken before 1971.On the other hand,JFA CSST data had been taken only every 5 days using the bucket and the stem thermometer.So,although we use monthly mean data,the JFA data may be insufficient ones in quality compared with the JMA data.
(b) Sea surface temperature(SST)
In the present study,we use the raw(individually ship-reported)SST data archived in COADS and the Kobe Collection.
