Fig Operational climatological regions and locations of stations

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1 1. Explanatory notes 1.1 About the Annual Report on Climate System The Japan Meteorological Agency (JMA) has published the Annual Report on Climate System (CD-ROM version) since From 2008, a new Annual Report on Climate System (printed version) is issued. This report contains monthly and annual summaries of the climate system as well as related topics such as extreme climate events in Japan, characteristics of the La Niña event and Asian summer monsoons in It is provided mainly to national meteorological services, research institutes, universities and other users interested in the climate system, and aims to share knowledge on the climate system including the causes of extreme climate events. Here, the climate system consists of the atmosphere, oceans and land including snow, sea ice and vegetation. This report deals mainly with the atmosphere, oceanographic conditions, sea ice and snow, which influence the climate in Japan and all over the world. A summary of monthly climate system highlights and other detailed climate information are also available under Monthly Highlights on Climate System and Climate System Monitoring on the Tokyo Climate Center website at The data sources and analysis methods used in this report are described in principle in each section. 1.2 Climate in Japan The descriptions in this section mainly relate to Sections 3.1 and Japanese average temperature Annual mean surface temperature anomalies since 1898 for Japan are illustrated in Fig (p. 35) shown in Section Anomalies for each year are derived relative to the average from temperatures recorded at 17 meteorological observatory stations (Abashiri, Nemuro, Suttsu, Yamagata, Ishinomaki, Fushiki, Nagano, Mito, Iida, Choshi, Sakai, Hamada, Hikone, Miyazaki, Tadotsu, Naze, Ishigakijima), which are deemed to avoid a strong influence from urbanization Climatorological normal and rank in Japan In this section, climate characteristics are summarized for each month and each region of Japan for monthly mean temperature anomalies, monthly precipitation ratios and monthly sunshine duration ratios in distribution map and climate table format. The monthly mean data used in this section come from operational daily observations at 151 surface meteorological stations. The climatological normals are averages over the 30-year period from 1971 to Anomalies of temperature from the normal, as well as ratios of precipitation and sunshine duration to its normal, are calculated for each station. Regional averages are calculated for the four divisions of Northern Japan, Eastern Japan, Western Japan and Okinawa/Amami as well as for the eleven subdivisions of Hokkaido, Tohoku, Kanto-koshin, Hokuriku, Tokai, Kinki, Chugoku, Shikoku, Kyushu-hokubu, Kyushu-nambu and Okinawa. For precipitation and sunshine duration ratios, the divisions are further divided into the Pacific side and the Sea of Japan side as shown in Fig (p. 2). The climate table ( e.g. Table (p. 36) and Table (p. 56)) contains regional averages of temperature anomalies, precipitation and sunshine duration ratios along with their ranks. The three ranks of below normal, near normal and above normal are created based on regional mean anomalies or ratios from the normals for each element, so that each rank has an equal relative frequency (33%) for the period from 1971 to An additional two ranks, significantly below normal and significantly above normal, are defined to cover a relative frequency of 10% at each end. 1.3 World climate The descriptions in this section relate to Sections 3.2 and Global average temperature Annual mean global surface temperature anomalies over the period since 1891 are illustrated in the figure (Fig (p. 40)) shown in Section Anomalies for each year are derived relative to the average from land surface temperatures (derived from monthly CLIMAT reports received via the Global Telecommunication System (GTS) from WMO members from 2000 onward, and from Global Historical Climate Network (GHCN) datasets by the National Climatic Data Center (NCDC) of the National Oceanographic and Atmospheric Administration (NOAA) prior to that) combined with sea surface temperatures (1 x 1 grid temperatures from COBE-SST datasets; JMA, 2006). Land surface temperature anomalies at each observatory station, along with sea surface temperature anomalies in each grid, are incorporated into 5 x 5 grid anomalies, which are weighed in proportion to the area of the grid and averaged all over the globe. The anomalies are 1

2 Fig Operational climatological regions and locations of stations Fig Region names in the world 2

3 accompanied with 90% confidence intervals that are derived from estimated errors due to the inhomogeneity of data availability (Ishihara, 2007) Data and climatological world normals Figures are produced using CLIMAT reports. Climatological normals for monthly mean temperature and monthly precipitation amount are calculated from historical observational data for the period These data are derived from the GHCN for the period until May 1982 and from CLIMAT reports thereafter. The following subsections describe the calculation methods according to the averaged periods for the figures contained in this report. World region names are described in Fig (p. 2) Monthly figures For extreme climate event figures by station (e.g. Fig (p. 56)), monthly mean temperature anomalies are marked as extremely high (or low) temperature when they are 1.83 times larger than their standard deviations. Monthly precipitation amounts are marked as extremely heavy (or light) precipitation when their quintile category is 6 (above the maximum in ) or 0 (below the minimum in ). The station with the most extreme temperature or precipitation in each 5 5 grid box is marked Annual figures For annual mean temperature anomaly figures (normalized) (Fig (p. 41)), values normalized by their standard deviations averaged in 5 5 grid boxes are indicated in categories. For annual precipitation ratio figures (Fig (p. 41)), ratio values to the normal of averaged in 5 5 grid boxes are indicated in categories. For figures on the frequency of extreme events (Fig and Fig (p. 42)), values of extremely high/low temperature and heavy/light precipitation based on monthly observational data for the year are calculated by dividing the total number of extreme events by the total number of all available observational data in each 5 5 grid box. The frequency is indicated by the semicircle size. If less than eight observations are available in each grid box, semicircles are not shown. Since the expected frequency value is about 3%, grid boxes with a frequency of 10-20% or more are considered above normal. 1.4 Atmospheric circulation The descriptions in this section mainly relate to Sections 3.3, 3.4, and Atmospheric circulation data are based on six-hourly global objective analyses at 00, 06, 12 and 18 UTC produced by JMA s Climate Data Assimilation System (JCDAS), which is consistent in quality with the Japanese 25-year reanalysis (JRA-25) (Onogi et al., 2007). Normals are also calculated from six-hourly analyses by JRA-25 for the period The details of the normals are referred to in Monthly Report on Climate System Separated Volume No.13 (JMA, 2007). The following subsections describe the calculation method for other figures in the report Extratropical circulation Wave activity flux indicates a propagating packet of Rossby waves, and is calculated as described by Takaya and Nakamura (2001) Tropical circulation and convection Tropical convective activities (e.g. Fig (p. 50) and Fig (p. 57)) are inferred from Outgoing Longwave Radiation (OLR). Lower values of OLR correspond to more enhanced convective activity, except for the middle latitudes in the winter season and for high altitudes. OLR is derived from observations by NOAA s polar orbital satellite, and provided by the Climate Prediction Center (CPC) in the National Centers for Environmental Prediction (NCEP) of the National Oceanic and Atmospheric Administration (NOAA) for the current. The OLR normal data are based on interpolated OLR data provided by NOAA s Earth System Research Laboratory (ESRL) as averaged over the period The stream function (e.g. Fig (p. 51) and Fig (p. 52)) is calculated from rotational wind, and its anomaly indicates the intensity of anticyclonic or cyclonic circulation compared to its normal. Velocity potential, indicating large-scale divergence or convergence, is defined as follows: divv χ = 2 χ (χ: velocity potential, V χ : divergent wind) The intra-seasonal oscillation associated with the Madden-Julian Oscillation (MJO) is analyzed from the time-longitude cross section of five-day mean 200 hpa velocity potential and OLR. 3

4 1.4.3 Atmospheric and oceanic monitoring indices in the tropics In Section 3.4, atmospheric and oceanographic monitoring indices and their characteristics are described. The Southern Oscillation Index (SOI) is defined as the difference in monthly mean sea-level pressure anomalies between Tahiti and Darwin normalized by their standard deviations. The difference is normalized again by its standard deviation. The sea-level pressure anomalies are based on CLIMAT reports, and the normal is the average over the period OLR indices are defined as the regional mean OLR anomalies with reversed sign, normalized by their standard deviations. Positive and negative values therefore indicate convective activities above and below the normal respectively, as averaged over the period Equatorial zonal wind indices are defined as regional mean zonal wind anomalies normalized by their standard deviations for the five regions shown in Table (p. 53)). The normal is calculated for the period Asian summer monsoon OLR indices (SAMOI) are derived from OLR from May to October. SAMOI are suffixed with (A), (N) and (W), indicating the overall activity of the Asian summer monsoon, the northward and the westward shift of the active convection respectively. SAMOI definitions are as follows: SAMOI (A) = (-1)x(W+E), SAMOI (N) = S-N, SAMOI (W) = E-W W, E, N and S indicate regional mean OLR anomalies for the respective regions shown in Fig normalized by their standard deviations. The details are referred to in JMA (1997). The El Niño monitoring indices are regional mean values of 1 1 SST analyses for the four El Niño monitoring regions shown in Table The normal is calculated as the average over the period Information Service (NESDIS). The normal is calculated as the average over the period Oceanographic conditions The descriptions in this section relate to Sections 3.5 and Sea Surface Temperature (SST) (e.g. Fig (p. 54) and Fig (p. 57)) is analyzed in 1 1 grid boxes. It is named COBE-SST. Anomalies are derived relative to the average. The details of the SST analysis and its normal are described by JMA (2006). References Ishihara, K., 2007: Estimation of standard errors in global average surface temperatures (in Japanese), Weather Service Bulletin, Vol. 74, JMA, 1997: Monthly Report on Climate System, June JMA, 2006: Characteristics of the Global Sea Surface Temperature Data (COBE-SST), Monthly Report on Climate System, Separated Volume No.12. JMA, 2007: New Climatological Normals based on the JRA-25, Monthly Report on Climate System, Separated Volume No.13. Onogi, K., J. Tsutsui, H. Koide, M. Sakamoto, S. Kobayashi, H. Hatsushika, T. Matsumoto, N. Yamazaki, H. Kamahori, K. Takahashi, S. Kadokura, K. Wada, K. Kato, R. Oyama, T. Ose, N. Mannoji and R. Taira, 2007: The JRA-25 Reanalysis. J. Meteorol. Soc. Japan, 85, Takaya, K., and H. Nakamura, 2001: A formulation of a phase-independent wave-activity flux for stationary and migratory quasigeostrophic eddies on a zonally varying basic flow. J. Atom. Sci., 58, Sea ice The number of days covered with sea-ice condensation in the Northern Hemisphere (Fig (p. 47)) is based on observations by the Special Sensor Microwave/Imager (SSM/I) on board the Defense Meteorological Satellite Program (DMSP) s polar-orbiting satellites. Sea ice data are provided courtesy of the National Climatic Data Center (NCDC) of NOAA s National Environmental Satellite, Data, and 4

5 Fig The areas of Asian Summer Monsoon OLR Indices (SAMOI) 5