Temperature Variability and Trends in North Libya from 1961 to 1990

1
Temperature Variability and Trends in North
Libya from 1961 to 1990
Younis Al-Fenadi Libyan National Meteorological
Centre (LNMC) Fenadi_at_yahoo.com
2
Climate Definitions

• 1 AMS (Huschke, 1959)
• the slowly varying aspects of the
  atmosphere-hydrosphere-land surface system. It is
  typically characterized in terms of suitable
  averages of the climate system of periods of a
  month or more, taking into consideration the
  variability in these time averaged quantities
• 2 Met. Office Glossary (1991)
• the climate of a locality is the synthesis of
  the day-to-day values of the meteorological
  elements that affect the locality.

3
Climate variability
The issue of climate variability and change goes
back to the 19th century with the Swedish
professor Svante Arrhenius. (Moore, 1998)

• It is a term used to describe deviation of
  climate statistics and calculated averages over a
  given specific month, season or year from the
  long term climate statistic. And measured by
  variations in the climate statistics, and ranges
  over many time and space scales (Geer, 1996)

An important issue in the study of climate
variability is to find out whether the variations
of climate variables are natural or
anthropogenic.
4
Mediterranean Climate

• Closed sea - 21 countries Complex mountain
  features and land topography.
• The Med. basin makes a transitional zone
  westerly flow affecting northern and central
  Europe and the arid zone of the subtropical high
  over the deserts in North Africa.
• The Mediterranean climate is quite complex as it
  involves influences from various phenomena
• the Siberian high pressure system,
• the El Niño Southern Oscillation (ENSO) and,
• the North Atlantic Oscillation (NAO).

5
Mediterranean climate studies

• Many studies with different results, such as
• 1 - Metaxas et al. (1991) studied SST and AT for
  120 years. In Med. SST and AT have the same main
  characteristics as those observed over the north
  hemisphere and the whole globe.
• 2 - Larrasoana et al. (2003) studied variations
  of Saharan dust supply into the eastern
  Mediterranean Sea. The variation in dust supply
  was found to be related to changes in the climate
  variables source areas located north of the
  central Saharan watershed.

6

• 3 - Raicich et al. (2001) have studied
  precipitation and the teleconnections between sea
  level pressure and sea level elevation, and the
  Indian summer monsoon and Sahel rainfall.
• They have found significant correlations between
  Indian monsoon, Sahel rainfall and sea level
  pressure difference with differences between
  western and eastern basins of the Mediterranean.
• 4 - Moron and Ward (1998) have studied ENSO
  teleconnections with climate variability in the
  European and African sectors, including the
  Mediterranean basin. The study has shown that
  ENSO influence is noticeable in the Sahel region
  of Africa.

7
Surface Temperature and Trends
Combined annual land-surface and sea surface
temperature anomalies in C from 1861 to 2000.
(Source IPCC, 2001).
8
Geography and climate of Libya
9
Why Temperature in Libya?
http//www.wmo.int/pages/mediacentre/news_members/
documents/Libya.pdf
10
Data Description

• The data consist of
• - Monthly mean surface temperature
• - 8 Libyan stations
• - The stations are distributed along North Libya
• - The data from January 1961 to December 1990
• - Obtained from the climate directorate LNMC

11
Selected Stations
12
Data Distribution
13
Data Statistics
14
Data Seasonal Cycle
15
Trend Analysis for individual stations

• Climate variability or change is detected by
  temperature upward growth or a downward decline
  trend.
• Chatfield (2001) has described the trend as
  long-term change in the underlying mean level per
  unit time.
• According to this, the global warming or cooling
  could be referred to as a trend over a period of
  years.
• Trend analysis fits a general trend model to time
  series data, e.g. linear quadratic exponential
  growth curve and S-curve.

16
The quadratic trend equation
17
Quadratic trend calculations
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
Results

• The quadratic model analysis for the 8 stations
  in North Libya has shown different weak and
  strong temperature trends.
• The trend differs from one station to another.
  The clearest trend was found in Sirte, Shahat,
  Zwara, Tripoli, Misurata and Nalut, but it was
  found weak in Benina and Derna.
• The annual temperature variability and
  fluctuation was wide in Benina, Tripoli, and
  Derna.
• However,
• An upward temperature trend was clearly
  identified starting from the mid-1970s in most of
  the stations.

22
North Libya Temperature Index (NLTI)

• The NLTI time series is a monthly time series of
  air surface temperature from January 1961 to
  December 1990. It is obtained by spatially
  averaging the values of the 8 stations.
• We consider the averaged index to be more
  reliable than the eight individual stations
  separately since the averaging procedure helps to
  reduce error effects.
• The index also gives a summary measure of monthly
  surface temperature over North Libya.

23
NLTI Trend analysis (Annual means)
24
NLTI Trend analysis (Annual means)
25
NLTI standardized annual temperature trend
26
NLTI Trend analysis (Seasonal means) MAM
27
NLTI Trend analysis (Seasonal means) DJF
28
NLTI Trend analysis (Seasonal means) SON
29
NLTI Trend analysis (Seasonal means) JJA
30
NLTI large-scale Teleconnections

• 1 - North Atlantic Oscillation (NAO)
• 2 - El Nino Southern Oscillation (ENSO)
• 3 NCAR/NCEP fields
• 4 http//climexp.knmi.nl

31
NLTI correlation with SLP (DJF and JJA)
32
NLTI correlation with SLP (SON and MAM)
33
NAO correlation with NCAR/NCEP sea level pressure
SLP
34
NLTI correlation with 2m temperature (DJF and MAM)
35
NLTI correlation with 2m temperature (SON and JJA)
36
NAO correlation with NCAR/NCEP 2m temperature
index
37
Conclusion

• Instantaneous (lag is zero) teleconnections in
  SLP between NLTI and NAO were evident during the
  winter season (December-February).
• Instantaneous (lag is zero) teleconnections in 2m
  air surface temperature between NLTI and ENSO
  were evident during wintertime (December-February)
  .
• Instantaneous (lag is zero) teleconnections show
  that NAO has a strong effect during winter season
  (December-February).
• Evidence was found that ENSO influences NLTI at
  spring season (March May).

38

• Finally, due to the absence of previous
  statistical and climatic studies on temperature
  trend and variability over Libya, it is not
  possible to compare and contrast the results
  obtained in this work with those of others

39
Thanks