Transcript Climate, ENSO and SPCZ in Solomon Islands

Climate, ENSO and SPCZ in
Solomon Islands
24 – 26 August 2010
Apia, Samoa
By
Lloyd Tahani
Solomon Island Meteorological Service
Monday, July 20, 2015
International Workshop on the South Pacific
Convergence Zone (SPCZ)
Introduction
Solomon Islands
 Climate
 Climate Variability affecting Solomon
Islands – ENSO & SPCZ.
 Conclusion.
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Solomon Islands is located
between latitude 5S and 12S
and longitudes 155E and
170E.
Covers over 600,000 sq. km
of sea with about 29,785 sq.
km of land.
Six main islands and about
900 small islands. The main
islands are rugged and
mountainous , the highest
pick of 2,447m is on
Guadalcanal island.
Population – 500,000.
Type of Government –
Westminster unitary system
of
government,
where
Governor General is the
head of state and the
government is headed by the
Prime Minister and its
cabinet.
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Climate of Solomon Islands
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The Solomon Islands, lying within 12 degrees latitude of
the equator and more than 1500km from the nearest
continent, has a climate typical of many tropical areas,
being characterised by high and rather uniform
temperature and humidity and, in most areas, abundant
rainfall in all months
Rainfall is the least uniform of these climatic elements,
as topographical effects cause significant variations
between locations.
The Islands, because of their low latitude, are less
subject to the damaging effects of tropical cyclones than
elsewhere in the Southwest Pacific, though cyclones still
pose a serious threat each year.
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The weather and climate of the region can be explained largely by
the seasonal movement and development of the equatorial
trough; a belt of low pressure that migrates between hemispheres
following the apparent movement of the sun, and the subtropical
ridge of the southern hemisphere (a belt of high pressure typically
located at about latitude 30 to 35 degrees south).
From about January to March the equatorial trough is usually
found close to, or south of the Solomons, and this is a period of
West to North-westerly monsoonal winds. The heaviest rainfall at
most places also occurs at this time.
The equatorial trough is in the Northern hemisphere from May to
October and the Islands then lie within the region of the Southeast
trade winds; the trades being the stronger and more persistent
winds blowing out from the subtropical ridge towards the
equatorial trough.
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These winds are moisture bearing, having had a long path over the
ocean and heavy rainfall can also occur during the South-easterly
season, especially on the windward side of the Islands. The
transition months between the two seasons are marked by a greater
frequency of calm winds.
Because of the low latitude of the Solomons, atmospheric pressure
has a small variation from month to month and, unlike places in
temperate latitudes, records little change from day to day except
when a tropical cyclone is in the area.
The lowest mean monthly pressure (for Honiara for example) at 9
a.m is 1007.6 hpa in January, when the equatorial trough is in the
vicinity, and the highest 1010.9 hpa in August. The decrease of
pressure from 9 a.m to 3 p.m is part of an atmospheric tidal effect
caused largely by the alternate heating and cooling every 24 hours.
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Climate variability affecting
Solomon Islands
 Seasonal Variations (ITCZ and SPCZ)
 Inter annual (El Niño/La Nina)
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The Inter Tropical Convergence Zone
(also called the Equatorial trough)
 A zone
of convergence of the trade winds
 Moves north and south with the seasons
 Associated with a peak in rainfall and
cloud activity
Location of ITCZ
July
January
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Climate of Henderson in Solomon
Islands
Rainfall(mm)
More rainfall in Summer when the ITCZ crosses the
country.
300
35.0
250
30.0
25.0
200
20.0
150
15.0
100
10.0
50
5.0
0
0.0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Months
Rainfall(mm)
Max Temp (deg. Celsius)
Min Temp (deg.celsius)
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Rainfall Pattern
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Rainfall patterns show location of:
1. Monsoon
2. Inter-tropical convergence zone
3. South Pacific convergence zone
ITCZ
MONSOON
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SPCZ
Regional Training Workshop on Drought
Monitoring and Forecasting Validation
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The South Pacific Convergence
Zone (SPCZ)
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The largest and most persistent “drive” of the ITCZ
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Stretches from the Solomon Islands to Fiji, Samoa and
Tonga and weakens further to the south-east.
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Associated with sea surface temperature maxima,
cloudiness and precipitation.
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Is present year round but most active in the SH summer
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The El Niño – Southern
Oscillation (ENSO)
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Solomon Islands climate is positively but not
strongly, correlated to the fluctuation in the
Southern Oscillation. The positive correlation differs
from place to place in the country.
One station could be contemporary while others
reveal a lag relationship to the Southern Oscillation.
Thus, rainfall is above average in the SOI positive
phases and vice versa in the negative phases
however, by comparing the actual rainfall to the
expected rainfalls, reveal that the above is a general
comment that is not totally true for all stations.
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SPCZ position very different for El Niño
and La Niña
El Niño
year
La Niña
year
Henderson Rainfall Vs SOI
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Munda Rainfall Vs SOI
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Conclusion
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Climate in Solomon Islands varies greatly in
both time and space. Unlike, other South
Pacific tropical areas there is no marked
seasonality in rainfall e.g. marked wet
season (Oct/Nov – Mar/Apr) and dry season
(Apr/May – Sept/Oct).
Irregularities in Solomon Islands Rainfall
patterns.
ENSO impacts – decrease rainfall (El Niño) &
increase rainfall (La Nina).
SPCZ – flash flooding, etc.
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Thank you !
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