METO 637

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METO 637

• Lesson 12

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Temperature and chlorine monoxide in the Arctic
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TOMS data 3/11/90
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Background

• Dobson (1927), first noted that sudden changes in
  total ozone coincided with the passage of upper
  level fronts.
• Shalamyanskiy and Romanshkina (1980) analyzed
  long aircraft flights that intersected both the
  polar and subtropical jets between 1974 and 1977.
  They found that the jet streams always coincided
  with regions of large gradients of total ozone.
  In regions outside the jet stream the total ozone
  gradients were small.

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Background

• Karol et al. 1980 compared total ozone
  measurements coincident with rawinsonde
  measurements.
• They used the geopotential height on the 200 mb
  surface to identify the sub-tropical jet stream,
  and on the 300 mb surface to identify the polar
  jet stream. Found that over the course of a month
  these boundaries differed by less than 80 m.
• Also found that the ozone value at the position
  of the boundary was constant to within 2.
• Shapiro et al. (1978,1987) and Uccellini (1985)
  found a strong coincidence between the sharp
  gradients in total ozone and upper level jet
  streams/frontal zone tropopause folding.

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Upper Troposphere Fronts

• Associated with waves in the upper troposphere
  Rossby waves
• Where the Jet Streams are found
• Subtropical front separates the tropical
  airmass from the midlatitude airmass
• Polar front separates the midlatitude airmass
  from the polar airmass
• Storms and weather patterns tend to follow the
  position of the fronts
• If the position of the fronts show a long-term
  trend with time this means that the weather
  patterns have moved with time a climate change

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Fronts and Weather
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Regimes

• The total ozone field can be separated into
  distinct regions.
• At the ground these are known as air masses. In
  the stratosphere a new term must be defined
  regime
• Four regimes are identified
• (a) tropical regime between the subtropical
  front and the equator
• (b) mid-latitude regime between the
  subtropical and polafr fronts.
• (c) polar regime between the polar front and
  the polar vortex.
• (d) arctic regime within the polar vortex.
  Note that this regime only exists in the winter
  months.

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Schematic of the total ozone versus latitude
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Latitudinal Average for Total OzoneMarch 11, 1990
(Hudson et al., 2003)
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Ozone profiles sorted by regime
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TOMS Image with RawinsondesN. America
March 11, 1990
Polar Front
Subtropical Front
Hudson et al. (2003)
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Rawinsonde Temperature Profiles Separated by
Regime
Hudson et al. (2003)
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Trends in total ozone

• Trends that are found in the official reports are
  zonal averages. Not broken down by regimes.
  Expressed as per cent per decade.
• Most trends are calculated for the Northern
  mid-latitudes where most politicians live?.
• Usually averages are made from 25 to 60 degrees
  latitude.
• (1) Always within a meteorological hemisphere
• (2) TOMS data does not exist above 60 degrees
  North in the winter uses backscattered solar
  ultraviolet
• The data show a strong seasonal component this
  is removed (deseasonalized) before the trend is
  determined.

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Total ozone 25 to 60 N
Red tropical Green mid-latitude Dark blue
polar Light blue arctic Black - zonal
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Total ozone with seasonal component removed
LINEAR FITS Overall (black) 3.2 decade Polar
(Blue) 2.1 per decade Mid-latitude (Green) 1.7
per decade Tropical (Red) 1.7 per decade
Linear fit from Jan 1979 to May 1991
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Contributions to the Equivalent Effective
Stratospheric Chlorine
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Total Mass of Ozone

• Between 25 and 60 degrees latitude the zonal
  trend from 1979 to May 1991 is -3.2 per decade,
  whereas the trend for the tropical regime is
  -1.7, -1.7 for the mid-latitude regime, and
  -2.1 for the polar regime.
• The difference between the zonal and regime
  trends can be explained by looking at the
  equation for the total mass of ozone
• M AO0 APOP AMOM ATOT AAOA
• A total area between 25 and 60N, and O0
  zonal mean column ozone
• AP, AM, AT, AA, regime areas, and OP, OM, OT,
  OA regime mean column ozone

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Total Mass of Ozone

• Define the relative area as the ratio of the area
  of a regime to the total area between 25 and 60
  degrees North Then
• O0 RPOP RMOM RTOT RAOA
• One can get a trend if the regime Os varies with
  time, or the regime Rs varies with time, or
  both.
• Over the period 1797 to 1991 the relative area of
  the tropical regime increased by 10, while that
  of the polar regime decreased by 15

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The relative area as a function of time for the
Northern hemisphere
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Deseasonalized Relative Areas
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Relative contributions of each regime to the
change in ozone
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Dynamics versus Chemistry