M. Turkes, INFLUENCE OF GEOPOTENTIAL HEIGHTS, CYCLONE FREQUENCY AND SOUTHERN OSCILLATION ON RAINFALL VARIATIONS IN TURKEY, International journal of climatology, 18(6), 1998, pp. 649-680
Normalized rainfall of Turkey tended to decrease in many annual and wi
nter series and to increase in some spring and summer series during 19
30-1993. Low-frequency fluctuation of regional winter rainfall series
was generally dominated by cycles of 3-3.2, 6-7, 7-8.4, and 14-21 year
s. Spring rainfall series depicted high-frequency oscillations with cy
cles of 2-2.2 years, and longer cycles of 4.2-4.7 years. Mean 700 and
500 hPa geopotential heights over Turkey generally experienced positiv
e anomalies from late 1970s to early 1990s, and showed an upward trend
in winter and summer. Significant negative correlations were found be
tween geopotential height and rainfall anomalies in winter over most o
f Turkey. Cycles of 2-2.2 and 3.2-3.8 years in spring rainfalls appear
ed to be associated with similar oscillations of spring geopotential h
eights. Cycles of 13 years in both winter geopotential series reflecte
d in a similar cycle of 14 years in annual and winter rainfall. The nu
mber of depressions reaching Turkey tended to decrease for about 10 ye
ars. Increased frequencies and intensities of dry conditions in the la
st ca. 20 years may have been related to increased geopotential height
s and decreased frequency of depressions over Turkey. Signs of warm mi
nus cold event winter anomalies during various stages of the Southern
Oscillation revealed the existence of some coherent regions without si
gnificant signals. Most of the selected 48 stations had a positive sig
n anomaly during year -1 warm and cold events. The cold event rainfall
means showed a coherent region of significantly increased rainfall co
nditions over the central-west and central parts of Turkey. Slightly w
etter than normal warm event conditions during year +1 were observed i
n many stations. Most of warm and cold event responses were characteri
zed by a decreased rainfall. Drier than long-term average conditions w
ere significant at some stations during year +1 cold events. Warm minu
s cold event differences had an opposite signal between year -1 and ye
ar 0 (+ 1) in many stations. Opposition of composite anomalies was evi
dent in most of stations between year -1 and year +1 cold events. (C)
1998 Royal Meteorological Society.