Shortwave radiation dip

I added a new question on the FAQ page that I thought I should put here as well:

Q: Why does the graph of incoming radiation sometimes have a dip in the readings around noon even when it seems like it is a perfectly sunny day?

In the fall of 2002 we installed a device on top of the Micrometeorology tower south of the main station to measure the incoming precipitation from different directions.

See a picture of the installation here

Unfortunately, as the tower is south of the main station and the device is rather large there are times of the year when it will cast a shadow on the incoming solar radiation gauge. That is the reason for the dip in the solar radiation readings.

This effect is seen from about January 9th to March 7th and then again from October 5th to November 21st.

At the moment we have no solution to this problem, however we are examining whether or not the device will be kept at the station.