Tuesday, August 21, 2012

Dew this morning

Sunlight filtering through pines/red maples

What: Ryan and I went on a Centennial Woods wander early this morning right as the sun was coming over the Greens. The grass soaked our feet, and everything under the powerlines was covered with dew; a steamy mist was rising up from the ground and the forest had a beautiful glow.

Sunlight filtering through pines in Centennial Woods powerline cut

Ecological notes: We had really warm weather yesterday (in the 80s, and an afternoon rainshower) and it was relatively warm at night, cooling significantly by about 4am. Dew forms when heat radiates off an object and moisture in the air condenses out as it cools (like when droplets form on a cool glass of lemonade). The rate of condensation has to be quicker than rate of evaporation. So you wouldn't expect to get dew when:

  • it's windy (increased rate of evaporation), 
  • dry (not enough moisture to condense out), 
  • there's little difference in temperature between the surface of an object and the air
  • when it's super sunny or when it's cloudy
This is why dew tends to form in the morning or evening under a cloudless sky without wind. Dew is a common late summer phenomenon when days are warm and nights cool. But because the ground is so warm in the late summer, things directly touching the ground don't have dew on them. On the other hand,leaves, my windshield, and other exposed surfaces do get dew.

Dew on unopened chicory flowerDew on mugwort flower buds

Where: Centennial Woods

Dew on Phragmites leavesDew on Phragmites leaves

Other notes: The jewelweed is in full bloom right now, providing some wonderful late season nourishment for bees and hummingbirds.

Dew on bumblebee and spotted jewelweedAptly named birds nest (Queen Anne's lace)

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