The Annual Cycle on the Southern Hemisphere

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The Annual Cycle on the Southern Hemisphere

• Its Semi-Annual Component
• Harry van Loon and George N. Kiladis

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Long-Term Mean SLP at Mid-Latitude (Top) and
Antarctic Stations (Bottom)
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Long-Term mean SLP at Mid-Latitude Mid-Ocean
Stations. Table Shows First and Second Harmonics
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The Amplitude and Phase of the First Harmonic.
The Large Dot the Long-Term Mean and Phase, the
Small Dots are Individual Years
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Left Amplitude of the Second Hamonic in the
Long-Term Mean SLP. Right Phase as Month of
First Maximum
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Percentage of the Annual Variance of the Second
Harmonic in the Long-Term Mean SLP
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The Second Harmonic in 500-mb Height
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Long-Term Mean SLP Differences between
Mid-Latitude and Antarctic Stations
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Geostrophic Wind in the Drake Passage (from
Werner Schwerdtfeger)
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Schematic Diagram of the Second Harmonic in
Pressure and the Meridional Pressure Differences
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The Second Harmonic in the Zonal Geostrophic
WindLeft Amplitude, Right Phase
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Amplitude, Phase, and Variance of the Second
Harmonic in the Geostrophic Wind in 1979
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Pressure Difference across the Drake Passage at a
Depth of 500m
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The Second Harmonic in the Drift of Buoys
(Surface Currents) in 1979
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Then Something HappensThe Semi-Annual
Oscillation Breaks Down in 1978-1980.It is
Fairly Quickly Restored in the Atlantic and
Western Half of the Indian Ocean, but it is still
out in the Rest of the Hemisphere
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Mean Decadal SLP at Amsterdam Island
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Amplitude and Variance of the Second Harmonic in
SLP at Amsterdam Island
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Mean Decadal Values of Amplitude, Phase, and
Variance at Amsterdam, Chatham, and Gough Islands
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Second harmonic in the Sea Level PressureBefore
and after the Crash Left 1958-1978. Right
1979-2001
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Second harmonic in the 500-mb HeightBefore and
after the Crash Left 1958-1978. Right 1979-2001
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Two-Year Running Means of the Amplitude of the
Second Harmonic. Top The Hemisphere. Middle The
Pacific. Bottom the Hemisphere minus the Pacific
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Two-Year Running Means of the Amplitude of the
Second Harmonic in SLP in the South Pacific Ocean
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Amplitudes of the Second Harmonic in SLP at
Chatham Islands and Dunedin
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Average SLP at Chatham Is. In Three Peak Periods
of the Second Harmonic(Top) and Three Minima in
the Harmonic (Bottom)
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SLP, October 1979-2005 minus 1954-1978
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SLP, Nov.-Jan. 1979-2007 minus 1950-1978
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Summary The annual cycle in the general
circulation at middle and high southern latitudes
contains a half-yearly component (double wave)
which varies substantially with time In some
multidecadal periods it dominates the
circulation, in others it is reduced appreciably.
The periods of weak second harmonics are due to
the collapse of the spring peak of the
harmonic.The second harmonic in the wind-driven
Antarctic Circumpolar Current presumably behaves
in the same manner.
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Annual Means of Global Sea-Surface
Temperature1948-2008
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Annual Mean Global Sea-Surface Temperature Change
1979-2008 minus 1948-1978
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Left The Zonally-Averaged Mean Vertical Motion
in October Right The Zonally-Averaged
Difference (1979-2008 minus 1957-1978) in
Vertical Motion in October
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Left Zonally-Averaged Zonal Wind in
OctoberRight Zonally-Averaged Difference
(1979-2008 minus 1957-1978) in Zonal Wind in
October
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Left SLP Difference in November (1979-2008 minus
1957-1978)Right Zonally-Averaged Zonal Wind
Difference in November (1979-2008 minus 1957-1978)
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The collapse of the latest spring peak can be
examined in three dimensions. It was associated,
in the Southern Hemisphere, with increased
vertical motion of the rising branch and
increased sinking motion in the downward branch
of the Hadley Cell. Accompanied by a weaker
subtropical jet and stronger westerlies at higher
latitudes, in spring.
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Mean Annual, Global Surface-Air Temperatures
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SLP Change in Winter1979-2005 minus 1950-1978
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Zonally-Averaged Temperature Difference,
1977-2007 minus 1950-1976
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Zonally- and Area-Averaged Temperature at the
SurfaceLeft 0 to 45N Right 45N to 90N
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Antarctic Temperature Trends
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Trends in the Surface-Air Temperature over
AntarcticaLeft January-February. Right
March-April
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Trends in the Surface-Air Temperature over
Antarctica Left June-July. Right
September-October
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The Change in Sfc.-Air Temperature, 1979-2008
minus 1950-1978 in the Antarctic. Left Summer.
Right Winter
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Vertical Sections of Temperature Change in the
Antarctic 1979-2008 minus 1950-1978. Left
Summer. Right Winter