Abstract
The relationship between the NAO index and ENSO and the mean surface air temperature over Egypt has been investigated. The NCEP/NCAR reanalysis data of the monthly mean surface air temperature over Egypt for the period (1948-2005) have been used in this study. The corresponding monthly mean values of NAO index, SOI, and El-Nino3 have been also used. Monte Carlo methodology as a linear correlation analysis has been used to obtain the correlation coefficient between the mean surface air temperature over Egypt and NAO, SOI, and El-Nino3 through the period (1948-2005). The results show that surface air temperature in Egypt is significantly correlated with the climatic index NAO and ENSO only for a south western part of Egypt. There is a significant negative correlation (-0.6) between surface air temperature over south west part of Egypt in winter season and NAO index. The relationship between EL-Nino3 and surface air temperature has contradicted the relationship with SOI. Whereas, a significant positive correlation (+0.6) between surface air temperature over south west part of Egypt and EL-Nino3 in autumn season. Surface air temperature correlated with SOI by a significant negative correlation (-0.5) during the same season over south west of Egypt. It is concluded that the surface air temperature is significantly correlated with NAO index and ENSO over the south west part of Egypt.
Highlights
The North Atlantic Oscillation (NAO) is one of the major modes of variability of the Northern Hemisphere atmosphere
For each grid point in the domain of Egypt, seasonal and annual averages for surface temperature have been calculated using of the NCEP/NECAR reanalysis monthly data sets and using of statistical mean average (i.e. (Dec. + Jan.+ Feb.)/3) for winter season, mean of Mar., Apr., and May months for spring and so on for summer and autumn seasons through the period of (1948-2005)
The seasonal and annual values of NAO index, SOI, and El-Nino3 have been calculated in the same manner; El NinoSouthern Oscillation (ENSO) phenomenon is the combination of SOI and El-Nino3
Summary
The North Atlantic Oscillation (NAO) is one of the major modes of variability of the Northern Hemisphere atmosphere. The NAO index is defined as the pressure gradient between Greenland and the Azores and describes the zonality of the flow in the North Atlantic region. I.e., NAO is the difference of the normalized sea level pressures between Ponta Delgada, Azores and Reykjavik, Iceland. The relative strengths and positions of these systems vary from year to year and this variation is known as the NAO. A large difference in the pressure at the two locations (a high index year, denoted NAO+) leads to increased westerlies and, cool summers and mild and wet winters in Central Europe and its Atlantic facade. If the index is low (NAO-), westerlies are suppressed, these areas suffer cold winters and storms track southerly toward the Mediterranean Sea
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