Global Simultaneity of the Abrupt Seasonal Changes in Precipitation during May and June of 1979

Abstract

Global simultaneity of the abrupt seasonal changes in precipitation during May and June of 1979 has been studied by using the FGGE level II-c precipitation and snow data set. Two stages of abrupt change in 10-day precipitation are identified around the first 10-day periods of May and June.
The first stage is around the first 10-day period of May. The heavy rainfall area (above 50mm/ 10-day) shifts northwards from Indonesia to the Philippines and around the Bay of Bengal (the east coast of India and the west coast of Burma) in the second 10-day period of May. Simultaneously, non-precipitation area extends northwards in the mid-latitudes of mid- and western Eurasia, and western North America. Precipitation increases over equatorial East Africa. One 10-day period earlier (in the first 10-day period of May), it increases over equatorial West Africa, coincident with the northward shift of the non-precipitation area along the west coast of South America.
The second stage is around the first 10-day period of June. Precipitation increases between 20°N and 60°N along the east coast of Eurasia in the first 10-day period of June. Simultaneously, the main rainbelt shifts northwards from eastern South America to around the Caribbean Sea, and from the equator to 15°N over West Africa. One 10-day period later (in the second 10-day period of June), monsoon rain begins along the west coast of India. At the same time, precipitation decreases over equatorial East Africa, while it increases along the east coasts of Madagascar and South Africa.
Based on the periods of the two stages of abrupt change, we can divide the whole hemisphere into four sectors (Sector I (north-east), Sector II (north-west), Sector III (south-west) and Sector IV (south-east)) in terms of two boundary lines which roughly coincide with the meridians of 70°E and 90°E and the parallels of 20°N and 35°N, and cross at the eastern Tibetan Plateau.
In Sector I (over eastern Eurasia), abrupt change occurs in the first 10-day period of June.
In Sector II (in the mid-latitudes of mid- and western Eurasia, and western North America), abrupt changes occur in the second 10-day period of May.
In Sector IV (over Indonesia and the Philippines, and around the Bay of Bengal), abrupt changesoccur in the second 10-day period of May.
In Sector III, abrupt changes occur around the first 10-day periods of May and June. In detail, abrupt changes occur in the western Sector III (around the Atlantic Ocean) in the first 10-day periods of May and June, and in the eastern Sector III (around the western Indian Ocean) in the second 10day periods of May and June.