Summer Mean Fields Over Tropical Africa, Indian and Atlantic Oceans During El Nino and La Nina Years

El- Nino and La- Nina conditions have been reported during the years of 1997 and 1998 respectively. Different meteorological fields of NCEP/NCAR data have been investigated during summers of 96, 97, 98, and 1999 in a trial to explain the mechanism through which El Nino and La Nina conditions may affect the climate of Africa. Negative anomalies of precipitation rate dominate over tropical Africa and SE Asia during the summer of 1997, while positive anomalies dominate during 98 and 1999. In the lower troposphere both the SE trades of the southern hemispheres and the southwest monsoons over both Indian and Atlantic Oceans have been observed stronger and occupy a larger area during summers of 98, 1999 than those observed during 1997. In the upper troposphere the subtropical westerly jet stream of the southern hemisphere has been found to extend more zonally during 1997 than that during 1996,to become weaker during summers of 98 and 1999. The tropical Easterly Jet (TEJ) has been observed stronger during 98 and 1999 than that observed during summer of 1997. The results revealed that intensification of TEJ is usually associated with stronger monsoons over Indian Ocean and eastern tropical Africa during La-Nina years which may lead to above normal rainfall. Also, during 1998 the strongest easterlies in the upper troposphere can be noticed to extend from over the west Pacific Ocean to Atlantic Ocean . So, the more zonal extend of the TEJ may enhance the monsoon circulation over western tropical Africa which may lead to a rainy summer during La Nina condition. Investigation of the meteorological fields show many other significant differences between the summer seasons of 96, 97 , 98, and 1999.