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METO 637

METO 637. Lesson 12. Temperature and chlorine monoxide in the Arctic. TOMS data 3/11/90. Background. Dobson (1927), first noted that sudden changes in total ozone coincided with the passage of upper level fronts.

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METO 637

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  1. METO 637 Lesson 12

  2. Temperature and chlorine monoxide in the Arctic

  3. TOMS data 3/11/90

  4. 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.

  5. 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.

  6. 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

  7. Fronts and Weather

  8. 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.

  9. Schematic of the total ozone versus latitude

  10. Latitudinal Average for Total OzoneMarch 11, 1990 (Hudson et al., 2003)

  11. Ozone profiles sorted by regime

  12. TOMS Image with RawinsondesN. America March 11, 1990 Polar Front Subtropical Front Hudson et al. (2003)

  13. Rawinsonde Temperature Profiles Separated by Regime Hudson et al. (2003)

  14. 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.

  15. Total ozone – 25 to 60 ˚N Red – tropical Green mid-latitude Dark blue – polar Light blue – arctic Black - zonal

  16. 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

  17. Contributions to the Equivalent Effective Stratospheric Chlorine

  18. 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 = AΩ0 = APΩP + AMΩM + ATΩT + AAΩA • A =total area between 25 and 60°N, and Ω0 = zonal mean column ozone • AP, AM, AT, AA, = regime areas, and ΩP, ΩM, ΩT, ΩA = regime mean column ozone

  19. 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 Ω0 = RPΩP + RMΩM + RTΩT + RAΩA • One can get a trend if the regime Ω’s varies with time, or the regime R’s 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%

  20. The relative area as a function of time for the Northern hemisphere

  21. Deseasonalized Relative Areas

  22. Relative contributions of each regime to the change in ozone

  23. Dynamics versus Chemistry

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