Global Analysis - August 1999
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.
The above figure shows August 1999 temperature anomalies calculated from available in-situ stations using an 1880 - 1998 base period. Temperature anomalies are absent from several areas of the globe due to a lack of reporting stations. Several areas of the globe had temperatures above the long-term mean. A good deal of central and southern Europe around the Mediterranean basin into the Middle East were covered mainly by high pressure, which promoted the warm anomalies. In contrast, northern Scandinavia and the area around the U.S. Great Lakes were dominated by upper level troughs, which promoted cooler than average temperatures.
Note: Satellite data is unavailable this month due to processing problems; blended satellite/in-situ products should be available again in the September report.
|Preliminary mean monthly temperature anomalies (using a base period 1880-1998) for August are shown in the figure to the left. August 1999 land and ocean temperatures were much lower than the record values recorded in 1998. Temperatures (for land and ocean) remained above the long-term mean for the 23rd year in a row.|
|The atmospheric circulation anomaly pattern for August 1999 is available for the Northern Hemisphere . See the U.S. Regional / Statewide Analyses pages and the Global Regional Analyses pages for more details on regional climate in the United States and throughout the world.|
There are some distinct features on the precipitation anomaly map. The largest negative anomalies occurred over portions of eastern and south central United States. A special report on the drought is available. Drier that average conditions were also observed across portions of western India - the dryness in this region is due to the lack of the southwest monsoon in that portion of India. In contrast, flooding occurred across portions of eastern India and Bangladesh for the second month in a row. Portions of Korea and Japan in Asia, and the Sahel in Africa also had above average rainfall. Flooding was responsible for a number of deaths across these regions as well.