Past IEM Features tagged: sun
Ames webcam used for sunsets (often facing west) and Nevada webcam used for sunrises (often facing east)
Most are familiar with the old adage; "Red sky at night, sailor's delight. Red sky at morning, sailor take warning." Does this saying apply for us land-locked Iowans? IEM's webcam archive contains an image every five minutes dating back to as far as 2003. For the featured analysis, webcam images approximately 10 minutes prior to sunrise and 10 minutes after sunset were analyzed for amount of red in the sky. The algorithm attempted to differentiate red sky from the red horizon that is common with everyday sun rises and sets. Of 2300 some sunrises and sunsets, 248 red sunrises and 88 red sunsets were identified by an algorithm. For these events, hourly precipitation data from Ames was queried to see if measurable precipitation fell in the 24 hours proceeding the event. The third bar is daily climatology which shows not much of a signal with these events, but there is a slight increase for red sky at morning events. Obviously, a limited sample and computer program does not prove or disprove this adage.
Tags: webcam sun folklore
The featured graph and images are from the Ames SchoolNet Site and Webcamera. The time series is of instantaneous solar radiation sampled every minute. Notice how the curve transitions from smooth to choppy in the afternoon and then smooth again just before sunset. The shape of this curve tells the story shown in the featured 3 webcam images, a transition from clear skies to party clooudy to mostly clear at sunset. The solar radiation curve becomes choppy as the sun plays peekaboo with the clouds as opposed to being a pure function of location in the sky during optically clear situations.
Tags: sun radiation
The featured image is of the sunrise for 3 dates this year from the Madrid webcamera. Any ideas why the sun's position relative to the water tower (indicated by red arrow) changes? Is the sun moving relative to the Earth? Is the water tower moving? Of course, the answer is related to the changing of the seasons as the tilt of the Northern Hemisphere is slowly starting to point away from the Sun and thus the sun is more southerly in our sky. The effect can be illustrated by comparing webcam shots of the sunrise against a stationary object (water tower). The camera is looking east, so the sun is appearing further to the right in the image (to the south) as the days go by since late June. You can also notice the change in sunrise time as our days get shorter.
Tags: webcam sun