Global Analysis - July 1999
The above figure shows July 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. To improve spatial coverage of global temperature anomalies, satellite data has been combined with in-situ station records in the spatial temperature plot below. Several areas of the globe had temperatures above the long-term mean. The British Isles to the Black Sea, the eastern half of North America, and central Asia were all covered by high pressure, which promoted the warm anomalies. In contrast, northern Scandinavia and northwestern Canada were dominated by upper level troughs, which promoted cooler than average temperatures. Southeastern China and most of Argentina were cooler than average.
|Preliminary mean monthly temperature anomalies (using a base period 1880-1998) for July are shown in the figure to the left. July 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.|
There are three areas of the globe with distinct warm surface temperature anomalies. The majority of the United States and southeastern Canada were well above average this month. High pressure dominated western Russia southward to the Mediterranean Sea, causing the surface to be much warmer than usual. The largest warm anomalies resided just north of the Black Sea. Another area of warmer than usual temperatures occurred over central Russia, and extended southward into Mongolia and northeastern China. This area was also associated with a persistent upper level ridge.
Cold temperature anomalies were most evident in the east equatorial Pacific, in association with La Niña. These cool anomalies extended eastwards into the coastal and southern areas of South America. The greatest cold anomalies were in northwestern Canada, and these corresponded with a upper level trough.
larger image There are some distinct features on the precipitation anomaly map. The largest negative anomalies occurred over most of India. This is the season of the southwest monsoon when India gets its monsoonal rain. The monsoon was weaker than usual this July and restricted to eastern India and Bangladesh where flooding occurred. In contrast, the Mediterranean area is usually very dry at this time of year, yet in July they had above average precipitation. Widespread flooding occurred along the Yangtze River in southern China and Japan received above average rainfall, while parts of northeastern China were drier than usual. The western Sahel received more rain than average, which is excellent for their growing season, while northeastern Europe was drier than usual. The majority of Argentina had above average rainfall, which is beneficial for their winter wheat crop.
In contrast, rainfall was below average across the remainder of the western and southern portions of Asia. Much of southeastern Australia was drier than usual, while the adjoining area to the southwest had above average rainfall. Rainfall in the Sahel region of Africa was above average, but some sectors experienced unusually dry conditions.
The summer monsoon rains over Mexico and the southwest U.S. were stronger than normal in July, which caused above average surface wetness. It was also wetter than average across the Plains near the U.S.-Canadian border. The snow in northern Canada was slow to melt this summer, which promoted above average surface wetness in July. This was also true for north central Russia. Heavy rains fell across eastern portions of the Indian subcontinent and brought major flooding across portions of eastern India and Bangladesh. Heavy rains also caused flooding in the Yangtze river basin in China.