The Effect of Cloud on Radiation in Niamey

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The Effect of Cloud on Radiation in Niamey

• Helen White
• Supervisors Tony Slingo, N. Ali Bharmal

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My project

• Effects of cloud on radiation still uncertain
• Year long data set of cloud radiative forcing
  estimates at surface and TOA
• ARM/GERB make this possible

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2006 Radiation and Meteorology

• Large dry season variability in LW vapour
  advection
• Frequent variability from monsoon cloud
• Monsoon increased LW, decreased SW
• SW shows clear sky annual cycle in winter
• Monsoon seems shorter in SW cloud retreats
  before humid monsoon air

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• Cooler surface and LW absorption reduced OLR
• Dry season OLR variability similar to LW at
  surface vapour advection
• Largest variability again due to cloud
• Reduced summer reflected SW from lower albedo
  geometry, cloud greatly increased it

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Meteorology

• Tb dry season showed similar pattern to LW fluxes
• Big Tb change with monsoon humidity variations
  now had small effect, controlled by large scale
  advection
• RH decreased in winter, increased most with rain
  clouds
• Atmosphere warming before monsoon
• Humidity during monsoon reduced LW humidity
  sensitivity

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Divergence
Dotted Surface absorption Downwelling
Upwelling Dashed System absorption Incoming
Outgoing Solid Atmospheric absorption System
Surface Affected by cloud
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Divergence

• Surface cooled most in winter
• Monsoon reduced OLR
• Atmospheric absorption steady more absorbing in
  monsoon, but less heating from surface
• Surface albedo steady more solar received, more
  absorbed
• Earth albedo higher in summer
• Atmospheric absorption steady more insolation
  in monsoon, but more absorbed at surface and
  reflected at TOA
• Start of monsoon less compensation

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Cloud forcing

• Identify clear/cloudy data using cloud mask
• Interpolate using model or function fitting
• Build data set of clear and cloudy fluxes
• Cloudy Clear Cloud radiative forcing