DESCRIPTION OF THE DATA SET - Daily Temperature and Precipitation Data for 223 Former-USSR Stations The dataset documented here contains daily temperature and precipitation measurements collected at 223 USSR stations over the period 1881-2000. It was compiled from digital and manuscript records archived at RIHMI in Obninsk, Russia. This section describes: - the meteorological, geographical, and historical variables contained in the dataset; - the methods and instruments used in collecting the meteorological observations; and - the temporal and spatial coverage of the station network. Variables Daily mean, minimum, and maximum temperatures are available (to the nearest tenth of a degree Celsius) for each station. Temperature observations were taken eight times a day from 1966-89, four times a day from 1936-65, and three times a day from 1881-1935. Daily mean temperature is defined as the average of all observations for each calendar day. Daily maximum/minimum temperatures are derived from maximum/minimum thermometer measurements. Daily precipitation totals are also available (to the nearest tenth of a millimeter) for each station. Throughout the record, daily precipitation is defined as the total amount of precipitation recorded during a 24-h period, snowfall being converted to a liquid total by melting the snow in the gauge. From 1936 on, rain gauges were checked several times each day; the cumulative total of all observations during a calendar day was presumably used as the daily total. Wetting corrections <=0.2 mm were applied beginning in 1966, depending upon the type and amount of precipitation. Extensive geographical and historical information supplements each time series (this info. can be found the in the files named "station_inventory.txt"and "station_history.txt"). Geographical parameters include station name, coordinates, and elevation. Historical parameters include station relocation date(s), the distance and direction of any such move(s), and the date on which the station switched to the Tretyakov-type rain gauge. Only 32 stations remained at their initial locations through 1989, and all stations switched to the Tretyakov-type gauge during the period 1946-60. Recording Methods and Instrumentation Recording methods and instrumentation varied considerably over the period of record. The following describes the types of instruments used throughout the network, the apparatus employed to shelter these instruments, and the times at which observations were taken. Temperature and precipitation are addressed separately. Additional information regarding the history of the network is contained in publications and instruction manuals prepared by the Academy of Sciences of the Russian Empire (1892, 1893, 1894, 1896, 1897, 1898, 1900, 1902, 1908, 1912), The Nicholas Main Physical Observatory (1915), The Voyeikov Main Geophysical Observatory (1928, 1931, 1963), the Central Administration of the Unified Hydrometeorological Service of the USSR (1935, 1936, 1939, 1940), the Council of Ministers of the USSR (1946, 1954, 1958, 1962, 1969, 1985), and Gidrometeoizdat (1972). Temperature The types of thermometers in use at each station remained the same throughout the period of record (Table 1). Minimum temperature was consistently measured with an alcohol thermometer, whereas hourly and maximum temperatures were each collected with separate mercury thermometers. When the air temperature approached the freezing point of mercury (-38.9 C), either an alcohol thermometer, or in some cases a minimum thermometer alcohol column, was used in place of the mercury thermometer. Whether or not (much less when) the thermometers themselves were replaced at each station is not currently known. The type of shelter or screen surrounding the thermometers varied considerably before 1930. In 1912, official instructions recommended sheltering thermometers with the Stevenson-type screen (before 1912, no such guidelines existed). However, it is likely that this change was not implemented at many stations. From 1920-30, Stevenson screens were replaced with the current screens (name unknown) at all operating stations. In 1928, additional guidelines regarding the exact dimensions of the shelters and their mounting heights were issued (before 1928, no such specifications had been defined). Therefore, from 1930 on, most stations had their thermometers sheltered in roughly the same fashion. Major changes in the time of observation occurred in 1936 and 1966. Prior to 1936, "hourly" measurements for computing daily mean temperature were taken at 0700, 1300, and 2100 Local Mean Time (LMT) (minimum and maximum thermometers were checked at one of these hours or at 0900 LMT, depending upon the year). Because of the lack of nighttime observations, daily mean temperature was probably overestimated by some location-dependent amount during this period. Beginning in 1936, all thermometers (hourly, minimum, and maximum) were checked at 0100, 0700, 1300, and 1900 LMT at most stations. As a result, the bias in daily mean temperature dropped to ~0.2 C. From 1966 present, all thermometers were checked at 3-h intervals beginning at midnight Moscow winter Legal Time (MLT) (MLT being three hours later than Greenwich Mean Time). This rendered the bias in daily mean temperature insignificant. Table 1. Temperature recording methods and instrumentation Year Recording method/instrumentation implemented ---- -------------------------------------------- 1881 Measurements for computing daily mean temperature taken at 0700, 1300, and 2100 LMT; mercury thermometer used; because of lack of nighttime observations, daily mean temperature probably overstated. 1881 Daily minimum temperature thermometer checked at 0900 LMT; alcohol thermometer used. 1881 Daily maximum temperature thermometer checked at 0900 LMT; mercury thermometer used. 1881 No regulations regarding type of shelter surrounding thermometers. 1883 Daily minimum temperature thermometer checked at 0700 and 2100 LMT (lower value chosen); multiple measurements taken only to determine approximate time of occurrence of minimum. 1891 Daily maximum temperature thermometer checked at 1300 and 2100 LMT (higher value chosen); multiple measurements taken only to determine approximate time of occurrence of maximum. 1912 Official meteorological instructions recommended use of Stevenson screen to shelter thermometers; practice not implemented at all stations. 1920 Official meteorological instructions recommended use of current screen to shelter thermometers; practice implemented over next ten years. 1928 Official meteorological instructions specified exact size/height of screens. 1936 Measurements for computing daily mean temperature taken at 0100, 0700, 1300, and 1900 LMT (or at 0700, 1300, 1900, and 2100 LMT); bias in daily mean temperature dropped to ~0.2 C; daily maximum and minimum thermometers may or may not have been checked each hour. 1966 Measurements for all temperature variables collected at 3-h intervals beginning at midnight MLT; bias in daily mean temperature eliminated. Precipitation The type of rain gauge used at each station changed at least once during the period of record (Table 2). In particular, the old-style gauge (type unknown) was replaced with the Tretyakov-type gauge over the period 1946-60 (see the file named "station.history" for the date of implementation at each site). Whether or not other gauge replacements occurred at each station is not currently known. The type of shielding surrounding the rain gauges varied considerably over time. For example, in 1883, official instructions recommended that cross- shaped zinc strips be inserted into the gauge to prevent snow from drifting. Other shielding guidelines were issued at various times over the next half- century, up until the Tretyakov-type gauge was introduced. However, whether or not (much less when) any of the shields were installed at each station is not currently known. Changes in the time of observation occurred in 1936, 1966, and 1986. Before 1936, rainfall was measured only at 0700 LMT. From 1936-65, gauges were checked at 0700 and 1900 LMT. Beginning in 1966, the time of observation became time-zone dependent (the USSR being comprised of 11 time zones). In particular, from 1966-85, readings were taken at 0300, 0900, 1500, and 2100 MLT in zone 2 (i.e., Moscow); at 0300, 0600, 1500, and 1800 MLT in zones 3-5; at 0300 and 1500 MLT in zones 6-8; at midnight, 0300, 1200, and 1500 MLT in zones 9-11; and at 2100, 0300, 0900, and 1500 MLT in zone 12 (the easternmost part of the USSR). In 1986, the 0300 and 1500 MLT observations were discontinued in all but the second time zone. Table 2. Precipitation recording methods and instrumentation Year Recording method/instrumentation implemented ---- -------------------------------------------- 1881 Rain gauge measurements taken at 0700 LMT; snowfall converted to a liquid total by melting snow in gauge; type of gauge and shielding not standardized. 1883 Official meteorological instructions recommended that cross- shaped zinc strips be inserted into the gauge to prevent snow from drifting; change probably not implemented at all stations. 1887 Official meteorological instructions recommended surrounding the gauge with the funnel-shaped Nifer's shield; change probably not implemented at all stations. 1892 Official meteorological instructions recommended erecting a fence around the gauge; change probably not implemented at all stations. 1902 Official meteorological instructions recommended erecting a double fence around the gauge; change probably not implemented at all stations. 1936 Rain gauge measurements taken at 0700 and 1900 LMT; daily total rainfall obtained by summing all measurements for the calendar day. 1946-60 Old-style gauge (exact type unknown) replaced with the Tretyakov-type gauge (see the file named "station.history" for the exact date of implementation at each site). 1966 Rain gauge measurements taken at 0300, 0900, 1500, and 2100 MLT in time zone 2; at 0300, 0600, 1500, and 1800 MLT in zones 3-5; at 0300 and 1500 MLT in zones 6-8; at midnight, 0300, 1200, and 1500 MLT in zones 9-11; and at 2100, 0300, 0900, and 1500 MLT in zone 12; wetting corrections <=0.2 mm applied to each hourly measurement (Because four observations per day were collected at stations in time zones 2-5 and 9-12, four corrections were counted in the daily total; therefore, total daily corrections are higher for stations in these areas.) 1986 Rain gauge measurements at 0300 and 1500 MLT discontinued at all stations except those in time zone 2. Temporal and Spatial Coverage The size of the observing network has increased with time. Twenty-three sites contain daily measurements dating to 1881 (though for 76 stations, maximum and/or minimum temperature observations began several years after mean temperature and precipitation). Aside from the period 1914-21 (i.e., during World War I, the Russian Revolution, and the Civil War), the number of stations rose at a relatively constant rate over the next half-century. The largest change in the network occurred in 1936, when an additional 65 observing posts were opened. Thereafter, only modest additions are evident, all stations collecting data by 1966 and only five (Adamovka, Vereb'e, Oktiabr'skaya, Rostov-na-Donu, and Surgut) closing before 1989. As the number of operational stations increased, spatial coverage improved. The distribution of posts early in the record, for example, is biased. In fact, most stations were located in population centers west of the Ural mountains and at ports along the Black and Caspian seas, whereas vast tracts of Siberia were entirely unsampled. Spatial coverage was much more representative of the country for the mid-1930s, with the exception of certain areas east of the Urals and north of the Arctic Circle. From a practical standpoint, the dataset can probably be used to study long-term climate variations over the entire USSR for the period 1936-2001. The density of stations, as well as their spatial distribution, was even better by 1985. Except for areas along the coast of the Arctic Ocean, most of the country was extremely well-sampled. In general, however, Arctic regions in the eastern part of the country are somewhat underrepresented throughout the record. The amount of missing data varies from element to element and station to station. Typically, the records of minimum/mean temperature are more complete than those of maximum temperature and rainfall. Most stations (90%) have at least 50 years of data for each parameter. REFERENCES Academy of sciences of the Russian Empire. 1892, 1893, 1894, 1896, 1897, 1898, 1900, 1902, 1908, 1912. Guide to second grade meteorological stations. St. Petersburg. Alexandersson, H. 1986. A homogeneity test applied to precipitation data. Journal of Climatology 6:661-75. Central Administration of the Unified Hydrometeorological Service of the USSR. 1935, 1936. Guide to making meteorological observations and their processing (3rd and 4th eds.). Leningrad. Central Administration of the Unified Hydrometeorological Service of the USSR. 1939. Guide to making meteorological observations and their processing (5th ed.). Moscow. Central Administration of the Unified Hydrometeorological Service of the USSR. 1940. Guide to making meteorological observations and their processing (6th ed.). Leningrad-Moscow. Council of Ministers of the USSR. 1946, 1954, 1958, 1962, 1969, 1985. Manual for hydrometeorological stations and posts, Issue 3 (meteorological observations at stations), Part 1: Main meteorological observations. Leningrad. Council of Ministers of the USSR. 1958 69. Manual for hydrometeorological stations and posts, Issue 3 (meteorological observations at stations), Part 2: Processing of the meteorological observations. Leningrad. Gidrometeoizdat, 1972. USSR climate reference book: History, physical, and geographic descriptions of meteorological stations and posts. Leningrad. Gullet, D. W., L. Vincent, and L. H. Malone. 1991. Homogeneity Testing of Monthly Temperature Series: Application of Multiple-Phase Regression Models With Mathematical Changepoints. Atmospheric Environment Service, Downsview, Ontario, Canada. Karl, T. R., and C. N. Williams, Jr. 1987. An approach to adjusting climatological time series for discontinuous inhomogeneities. Journal of Climate and Applied Meteorology 26:1744-63. Peterson, T. C. and D. R. Easterling. 1993. Creation of homogeneous composite climatological reference series. International Journal of Climatology, in press. Potter, K. W. 1981. Illustration of a new test for detecting a shift in precipitation series. Monthly Weather Review 109:2040-45. The Nicholas Main Physical Observatory. 1915. Guide to second grade meteorological stations, Issue 1. Petrograd. The Voyeikov Main Geophysical Observatory. 1928, 1931. Guide to second grade meteorological stations, Issue 1 (main meteorological observations). Leningrad. The Voyeikov Main Geophysical Observatory. 1963. Review of changes in the technique of making meteorological observations over the network of stations and posts. Leningrad. Tatusko, R. L. 1990. Cooperation in climate research: An evaluation of the activities conducted under the US-USSR agreement for environmental protection since 1974. National Oceanic and Atmospheric Administration, Washington, D.C.