TWP/SKYRAD/C2 - Tracker problem

The tracker has a problem in tracking the sun continuously in the southern hemisphere and 
close to the equator. This happened between the March equinox and September equinox 
around solar noon. Affected hours are between 00:00 to 1:00 each day for the specified time 
range.

Note: This will likely occur again in 2013 between March equinox and September equinox 
around solar noon.

Note2: The tracker tracking being off only affects data when there is direct sun, i.e. 
when the sun is not blocked by cloud. Thus in the tropics much of this data are not 
inherently "bad" plus only the direct and diffuse are "bad" when there's direct sun present. The 
QCRad has a test for "tracker off" that detects the tracker not shading the diffuse 
instrument and the NIP not being aimed at the sun when the sun is not blocked by cloud. Thus 
the ARM recommended measure QCRad data set will catch most of these "bad" data and set the 
values to "-9999.9" when the sun is not blocked by cloud, and leave the data that is OK 
when the sun is blocked by cloud (unless that data fails some other testing of course).

Use twpqcrad1longC2.c1 data

• Shortwave direct normal irradiance, pyrheliometer, minima(short_direct_normal_min)
• Shortwave direct normal irradiance, pyrheliometer(short_direct_normal)
• Downwelling shortwave diffuse hemispheric irradiance, pyranometer, maxima(down_short_diffuse_hemisp_max)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Pyranometer, Standard
  Deviation(down_short_diffuse_hemisp_std)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Pyrgeometer, Minima(down_short_diffuse_hemisp_min)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer(down_short_diffuse_hemisp)
• Shortwave Direct Normal Irradiance, Pyrgeometer, Standard Deviation(short_direct_normal_std)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)

• Instantaneous uncorrected downwelling shortwave diffuse, shaded pyranometer
  thermopile voltage(inst_diffuse)
• Instantaneous direct normal shortwave irradiance, pyrheliometer thermopile
  voltage(inst_direct_normal)