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Global Analysis - October 1999

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Note: GHCN-M Data Notice

An omission in processing a correction algorithm led to some small errors on the Global Historical Climatology Network-Monthly dataset (GHCN-M v3.2.0). This led to small errors in the reported land surface temperatures in the October, November, December and Annual U.S. and global climate reports. On February 14, 2013, NCDC fixed this error in its software, included an additional improvement (described below), and implemented both changes as GHCN-M version 3.2.1. With this update to GHCN-M, the Merged Land and Ocean Surface Temperature dataset also is subsequently revised as MLOST version 3.5.3.

The net result of this new version of GHCN-M reveals very small changes in temperature and ranks. The 2012 U.S. temperature is 0.01°F higher than reported in early January, but still remains approximately 1.0°F warmer than the next warmest year, and approximately 3.25°F warmer than the 20th century average. The U.S. annual time series from version 3.2.1 is almost identical to the series from version 3.2.0 and that the 1895-2012 annual temperature trend remains 0.13°F/decade. The trend for certain calendar months changed more than others (discussed below). For the globe, ranks of individual years changed in some instances by a few positions, but global land temperature trends changed no more than 0.01°C/century for any month since 1880.

NCDC uses two correction processes to remove inhomogeneities associated with factors unrelated to climate such as changes in observer practices, instrumentation, and changes in station location and environment that have occurred through time. The first correction for time of observation changes in the United States was inadvertently disabled during late 2012. That algorithm provides for a physically based correction for observing time changes based on station history information. NCDC also routinely runs a .pairwise correction. algorithm that addresses such issues, but in an indirect manner. It successfully corrected for many of the time of observation issues, which minimized the effect of this processing omission.

The version 3.2.1 release also includes the use of updated data to improve quality control and correction processes of other U.S. stations and neighboring stations in Canada and Mexico.

Compared to analyses released in January 2013, the trend for certain calendar months has changed more than others. This effect is related to the seasonal nature of the reintroduced time-of-observation correction. Trends in U.S. winter temperature are higher while trends in summer temperatures are lower. For the globe, ranks of individual years changed in some instances by a few positions, but global temperature trends changed no more than 0.01°C/century for any month since 1880.

More complete information about this issue is available at this supplemental page.

NCDC will not update the static reports from October through December 2012 and the 2012 U.S and Global annual reports, but will use the current dataset (GHCN-M v. 3.2.1 and MLOST v. 3.5.3) for the January 2013 report and other comparisons to previous months and years.

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The above figure shows October 1999 temperature anomalies calculated from available in-situ stations using a 1961-1990 base period. Temperatures were above normal in many regions of the world during October. A dominant ridge of high pressure over central Russia produced temperatures that were more than 4C above average throughout much of the West Siberian Plain. (See the October atmospheric circulation pattern for the Northern Hemisphere.) Above average temperatures also stretched throughout Europe and the Mediteranean, where temperatures were more than 2 C above average in most areas. Much of India, China and southeast Asia recorded temperatures that were slightly above the long term mean. Western areas of the United States also experienced above average temperatures as an area of high pressure persisted throughout the month. A persistent low pressure trough over eastern Canada produced temperatures 1 to 2 C below average in northeastern sections of the United States and southeastern areas of Canada. Temperatures were also cooler than average throughout much of Alaska and parts of the Yukon and Inuvik regions of western Canada.

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Temperature

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Preliminary mean monthly temperature anomalies (using a base period 1880-1998) for October are shown in the figure to the left. Both land and ocean temperatures were above their respective long term means but below the record values recorded during the 1997/1998 El Nino episode. Ocean temperature anomalies were 0.26 C above average, but they were 0.29 C below the record value recorded in 1997. Land temperatures continued to be historically warm in October as the global temperature averaged 0.67 C above the long term mean.

Precipitation

larger image As shown on the adjacent map of precipitation anomalies calculated from reporting in-situ stations (1961-1990 base period), several regions of the world received much above average precipitation in October. Wetter than average conditions persisted across much of Spain for the third month in a row. October precipitation was as much as 100 mm above average in some areas. October was also another wetter than average month in the Sahel region of Africa as precipitation was more than 25 mm above average across a large part of the region.

Devastating flooding occurred in India as two strong typhoons brought torrential rains to eastern sections of the country. (Anomalies are not shown due to an absence of reporting stations in this region of the country.) Precipitation was also much above average in northern sections of South America. Stations in Venezuela averaged 79 mm above the 1961-1990 normal. However, southeast coastal areas of South America were extremely dry in October. Drier than average conditions were also experienced across much of North America as a ridge of high pressure was a dominate feature over central sections of the continent for much of the month. (See the U.S. national page for a complete discussion.) Drier than average conditions prevailed across the Mediteranean, parts of Northern Europe, the West Siberian Plain, and parts of Southeast Asia. For additional details on precipitation and temperatures in October see the Global Regional page .

References:

Peterson, T.C. and R.S. Vose, 1997: An Overview of the Global Historical Climatology Network Database. Bull. Amer. Meteorol. Soc., 78, 2837-2849.

Citing This Report

NOAA National Climatic Data Center, State of the Climate: Global Analysis for October 1999, published online November 1999, retrieved on June 18, 2013 from http://www.ncdc.noaa.gov/sotc/global/1999/10.