Global dimming at Bet Dagan: a paradigm for our polluted cities

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Global dimming at Bet Dagan a paradigm for our
polluted cities?

• Shabtai Cohen
• Inst. Soil Water and Env. Sciences
• ARO Volcani Center
• Bet Dagan

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Also

• Collaborators
• Gerald Stanhill, Volcani Center
• Amiran Ianitz, Israel Meteorological Service

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Objectives

• Analyze trends in the records of
• Global Radiation
• Diffuse Radiation
• Direct Radiation
• What causes are implicated by the trends?

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Global warming at Bet Dagan
Notes - DTR is sometimes taken as a proxy for
solar radiation - Why isnt Tmax increasing at
the same rate as Tmin?
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The solar radiation data set for Bet Dagan
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Global Radiation
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Diffuse radiation
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Global (and direct) declined Diffuse increased
Both declined
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What about global radiation at other sites in
Israel?
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In which season and time of day are the changes
significant?
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Global radiation converted to atmospheric
transmittance
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For the same sunshine duration we now get less
global radiation
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Summary

• Global radiation at Bet Dagan was low between
  1980 and 1990, with a second decrease occurring
  between 1995 and 2000.
• The decrease between 1980 and 1990 also occurred
  in Jerusalem.
• The 1980-1990 decrease was accompanied by
  increased diffuse radiation and diffuse/global
  ratio.
• This indicates increased cloudiness or haziness

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Summary continued

• Seasonal diurnal trends for the whole period
  indicate significant decreases during morning and
  evening hours and during mid-day in February
• This, and other evidence may implicate increasing
  haziness caused by increasing aerosol loads.
• Shorter term trends are currently being analyzed
• Is this an example of a polluted city or a
  regional phenomenon?

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Thanks for your attention
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