چكيده لاتين :
Introduction
The term 'teleconnection pattern' refers to the statistically significant negative
correlation of recurring and persistent circulation anomalies between two or more
geographical areas that could be or may not be adjacent. A pattern between the EM
and northeastern Atlantic was identified in the correlation matrices. This pattern was
predominantly identified in the upper troposphere,in winter with negative
correlations of -0.62 to -0.67. More specifically, at the isobaric level of 500 hPa,a
maximum negative correlation (teleconnectivity center) was found between 25 W,
52.5N in the northeastern Atlantic and 22.5 °E, 32.5°N in the EM. More specifically,
the Positive Phase indicates that the EM PI value is greater than the mean index value,
EMPI, suggesting that the difference between the geopotential heights of the two
centers is diminished, while during the negative phase this difference is increased,
taking into account that the geopotential heights of the northern pole are naturally
lower than the heights of the southern pole. It can be seen that during the negative
phase a strong negative anomaly prevails over the NW Atlantic, characterized by
increased cyclonic (counterclockwise) circulation. On the other hand, a shallow
positive anomaly forms over the EM and northern Africa, implying clockwise
circulation around it. This pattern causes an increased southwesterly anomaly flow
toward the central Mediterranean and strong westerlies across the middle Atlantic.
On the contrary, the positive phase is characterized by a strong anticyclonic anomaly
over the NW Atlantic, associated with the intensification of the Atlantic anticyclone
and warm air advection, while a cyclonic anomaly predominates over the EM.
Material and Methodology
The EMP index (EMPI) was defined as follows: EMPI = gpm {25 ow, 52.5°N}
-gpm(22.5 °E, 32.5°N) where gpm is the mean monthly geopotential height of the
grid point representing each pole. It can be clearly seen that the values of the
winterstandardized anomalies between the two poles are reversed, verifying the
existence of a seesaw pattern.ln general, an intense positive anomaly of one pole is
accompanied by a corresponding negative anomaly of the other. The index was then
calculated for each season and for each month and standardized as follows: the
difference between the index defined above and its seasonal longterm average
divided by its standard deviation:
zi = (EMPI i- EMPI)/o
where the EM PI is the index value of the year i, and EM PI is its long-term average and
a the corresponding standard deviation for the period 1981-2010. In order to
differentiate the two situations, the Negative and the Positive Phase of the EMP are
defined when zi < -0.5 and zi > 0.5, respectively.
Because the eastern mediterranean index data has been gathered in standardized
form, the normalized precipitation data (Z Scores) was used and correlation test was
fulfilled on them.
Discussion
According to this analysis, the precipitation and eastern Mediterranean oscillation in
March have the highest correlation coefficient, which Kermanshah,Khoramabad and
Saghez stations were meaningful at 0.01 level,while other stations were meaningful
at 0.05 level, so this relationship was reverse and strong. The correlation of Saghez in
January and those of Khoramabad in December were meaningful at 0.01 level.while
the of Shahre Kord, Kermanshah and Oromieh in April with the mentioned oscillation
were meaningful at 0.05 level. In winter, with the increaseing of negative values of
standardized data of EMO, increase and with positive phases the precipitation
decrease. The severity of this reduction with respect to the severity of increasing in
negative phases has a milder slope.The winter correllations with the mentioned
oscillation in positive phases for all the stations except Ahwaz and Dezful were not
meaningfui.While this corellation in negative phases only for Ahwaz,Tabriz and
Oromieh stations was not meaningfui.The rest,except the above mentioned
stations,are meaningful at 0.05 level. The decrease of precipitation the northern part
of the region has been more than its southern part. In negative phases the positive
shallow flow forms over Eastern mediterranean and north of Africa, which creates
the anticyclonic circulation and the southern flow to west in mediterranean, and the
warm weather spreads to surroundings.This increases from the minimum 0.02° in
Saghez station to maximum 0.85 with respect to average statistical periods, which
leads to emerging unusual winter warm waves. The increases from 0.01° to 1 °c as
weii.Such an increase,has had winter abundance periods in the region.Aiso,the
increasing of has been more in north than south.Therefore,it concluded that the
warm and cold periods in the under study months and seasons compeletly agree with
positive and negative phases of eastern mediterranean oscillation (EMO)
alternatively, such as the warm years of 1990 and 1994 which had negative phases
and the cold years of 1981,1992,and 2005 which were in positive phases.
Conclusion
The study results show that ther is a negative correlation between the stations
precipitation of the north of the under study region and the above mentioned
oscillation,and ther is a strong positive correlation in southern stations,that most of
them are meaningful at 0.05 level. Also, this study proves that stations precipitation
in southern half of the under study region in positive phases increases from 5 to 41
mms and in negative phases decreases from 4 to 20 mms.But, contrary to southern
half, in the northern half the rainful increases up to 8 mms in negative phases and
precipitation decreases in posetive phases.
