The featured graph has a lot going on. The three data lines are from the NSTL Flux site near Ames for Tuesday morning. The green line is long wave radiation and simply shows the period up until 5 AM which was cloudy (clear sky values are around -100 W m**-2). The orange line is short wave (solar) radiation and its obviously near 0 until sunrise around 8 AM increasing to around 400 W m**-2 at midday. The air temperature trace in red shows three distinct regimes during this period.

• Between midnight-5AM: Cloudy skies trap heat near the surface (decreased long wave) and temperatures slowly cool.
• Between 5AM-8AM: Skies clear, long wave radiation increases, and air temperatures cool rapidly at 4 times the rate with clouds.
• 8AM - after: The sun rises and short wave radiation exceeds long wave radiation (net radiation positive) and the result is heating.

Really great stuff! You can view plots like these here.

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Tags:   radiation