isabellacyclone.tau.ac.il

1

??????? ??????? ????-??????? ???????? ??????
????????? ?????? ????? ??? ??????

• ???? ????? ????? ????? ??? ?????
• ?????? ?????????
• isabella_at_cyclone.tau.ac.il
• ???? ????' ???? ?????

2
Outline

• The Eastern Mediterranean (EM) daily surface
  rain-bearing synoptic systems
• Long-term trends
• Daily statistics
• Calendaricities and multimodality
• Teleconnections

3
Eastern Mediterranean Synoptic Classes - total
19
1. Winter Lows (cool season, 7 classes) Cold
Low to the West
Cyprus Low
Deep to the North

Shallow to the North

Deep to the South

Shallow to the South

Low to the East Deep Shallow 2. Red
Sea Trough (cool season, 3 classes) with
Eastern axis
with
Central axis
with
Western axis 3. Persian Trough (summer, 3
classes) Weak, Medium, and Strong 4. Sharav
Low (spring, 2 classes) to the West,
over Israel 5. Highs (4 classes) to the East,
to the North, over Israel (cool season) to
the West (round a year) (P. Alpert,
I.Osetinsky, B. Ziv, H. Shafir, 2004, Int. J.
Climatol. 24)
4
Eastern Mediterranean Synoptic Classes -
rain-bearing

• Winter Lows (Mediterranean cyclones)
• 2. Red Sea Trough (only when coupled with an
  upper trough)

5
ExamplesWinter Lows
Cold Low to the West
Deep Cyprus Low to the North
Shallow Cyprus Low to the North
Deep Cyprus Low to the South
Shallow Cyprus Low to the South
Deep Low to the East
Shallow Low to the East
6
Examples Red Sea Trough (RST)
RST with western axis
RST with central axis
RST with eastern axis
7
(No Transcript)
8
http//www.grida.no/climate/ipcc_tar/wg1/057.htm
9
1976-2003
1948-1975
http//www.cgd.ucar.edu/cas/jhurrell/nao.stat.wint
er.html
10
1948-1975
Total Winter Lows
winter
1976-2003
11
(No Transcript)
12
Deep Low to the east and Shallow Low to the
eastdaily results
DEEP LOW TO THE EAST
SHALLOW LOW TO THE EAST
13
Deep Low to the east and Shallow Low to the
eastpentads

• Frequency of occurrence of the DEEP LOW TO THE
  EAST decreases with the years while of the
  SHALLOW - - increases. It maybe associated with
  decrease of rainfall since the deep lows are more
  favorable for rain.

DEEP LOW TO THE EAST
SHALLOW LOW TO THE EAST
Pentads
Pentads
14
late Oct floods
15
RST with an eastern axis

• Occurrences of the RST with an eastern axis
  clearly keep their late Oct early Nov maximum.

Pentads
16
RST with a central axis

• Occurrences of the RST with a central axis widen
  their season with the years, increasing in
  frequencies, from almost exclusive occurrences in
  January in 1948 until the period of October
  through May in 2004. That might be a reason for
  the increase in floods in S. Israel.

Pentads
17
Red Sea Trough
18
PDO index (Aleutian Islands California), a
leading principal component of monthly SST
anomalies in the North Pacific Ocean, poleward
of 20N. Data from http//jisao.washington.edu/pdo
/PDO.latest
Largest correlations between the RST annual
frequencies and PDO, 1948(1950) 2004. Lag ?
m (in brackets) means the EM synoptic system
frequency series shifted by m years in
positive/negative direction.
Red Sea Trough
1Note for PDO-PT correlation, the largest values
were found when PDO averaged over the EM
hydrological year (August-July), not calendar
year
19
Summary
1. The EM winter season is shown to be
multimodal. The Winter Lows' (WL) frequency of
occurrence has its main peak on the 6 February,
in midwinter, and secondary maxima on 18-19
December, 19 January, 1 March, 20 March. There is
also a pronounced spring WL maximum on 19 April.
The five maxima of the winter cyclonic activity,
centered on early February, are nearly
bell-shaped over their magnitudes. 2. The Red
Sea Trough frequency of occurrence has one
pronounced peak in late October - early November.
A small proportion of the mostly dry Red Sea
Troughs that coupled with an upper trough, turns
out to cause heavy rainfall over the southern EM
areas. This time has the highest probability for
the catastrophic floods in the southern part of
the EM. 3. The quite fixed dates for the
majority of the maxima and minima in the EM
cyclonic activity have been kept for two
climatologically representative 28-yr periods of
1948-75 and 1976-2003, in spite of the
significant differences in the global
atmospheric-oceanic activity during the two
periods. 4. The most unexpected results are the
strongly-kept calendar dates for the secondary
maxima of cyclonic activity rather than for major
ones, and during the transitional seasons rather
than in the middle of the established winter.
(I. Osetinsky and P. Alpert, 2006. NHESS, to be
published)
20
Thank you !