On 26 februari 2012 I measured the solar noise on my 23cm tropo station.
Using the funcube dongel pro and the software SpectraVue I could easily measure the solar noise.
The antenna is aimed at the horizon. From about 5 degrees elevation the noise power goes up.
In the picture I put in the values of the elevation from the sun.
You can see several peaks, at 3.4 degrees, 2.5 degrees etc caused by the interference of the reflected ground wave.
The maximum solar noise is measured when the sun is calculated to be below the horizon between -0.2 and -0.4 degrees.
At -0.9 degrees the solar noise is gone.
The effect of having the maximum noise when the sun is already below horizon is probably caused by the difference in K factor for light compared to radio signals.
The maximum solar noise measured is 4.4 dB.